Although understanding mutualism stability has advanced over the last few decades, two fundamental problems still remain in explaining how mutualisms maintain stable. (i) How does resolve conflict between mutualists over resources? (ii) In the presence of less cooperative and/or uncooperative symbionts, how does prevent symbiont populations from becoming dominated by uncooperative individuals? Many past explanations of mutualism stability have assumed that interactions between mutualists are symmetrical. However, in most mutualisms, interactions between hosts and symbionts show varying degrees of asymmetry at different levels. Here, we review three major types of asymmetric interactions within obligate mutualisms: (i) asymmetric payoffs, which is also defined as individual power differences, (ii) asymmetric potential rates of evolutionary change, and (iii) asymmetric information states between hosts and symbionts. We suggest that these asymmetries between mutualists help explain why cooperation and conflict are inherent in the evolution of mutualisms, and why both hosts and symbionts present diversified phenotypes while cooperation predominates.

In angiosperms, diverse floral traits are adaptations to various selective pressures and ecological functions. So far, studies on floral traits in orchids have focused primarily on the labellum but never on bracts. A bumblebee-pollinated and rewarding terrestrial or epiphytic herb, Thunia alba (Lindley) H. G. Reichenbach (Orchidaceae), has conspicuously large and curly bracts that enclose the spur and pedicel of flowers. We hypothesized that these large bracts could protect spurs against nectar robbers. To confirm this hypothesis, we experimentally removed the bracts to record the changes in visiting behavior of mutualistic pollinators and antagonistic nectar robbers and evaluated their effects on reproduction success. Our result revealed that Bombus breviceps, the only pollinator of T. alba, shifted to nectar robbery when the bracts were removed, and the proportion of robbed flowers also significantly increased. Thunia alba was found to be pollinator limited regardless of whether in intact treatment or removed bract treatment. Removal of bracts had no effect on the visiting frequency of B. breviceps, but it reduced male and female reproductive success. These findings indicate that, under complex environmental pressures with limited pollination, large bracts can protect against nectar robbers and enhance the fitness of T. alba.

Energy partitioning and evapotranspiration (ET) of alpine meadows in permafrost areas are crucial for water cycle on the Qinghai-Tibet Plateau. However, seasonal (freeze-thaw cycle) variations in energy partitioning and ET and their driving factors must be clarified. Therefore, 4-year energy fluxes [i.e. latent heat (LE) and sensible heat (H)] were observed, and bulk parameters [i.e. surface conductance, decoupling coefficient (Ω), and Priestley-Taylor coefficient (α)] were estimated in an alpine meadow in the Qinghai-Tibet Plateau. Mean daily LE (27.45 ± 23.89 W/m²) and H (32.51 ± 16.72 W/m²) accounted for 31.71% and 50.14% of available energy, respectively. More available energy was allocated to LE during the rainfall period, while 67.54 ± 28.44% was allocated to H during the frozen period. H was half the LE during rainfall period and seven times the LE during frozen period due to low soil water content and vegetation coverage during the frozen season. Mean annual ET was 347.34 ± 8.39 mm/year, close to mean annual precipitation. Low mean daily Ω (0.45 ± 0.23) and α (0.60 ± 0.29) throughout the year suggested that ET in the alpine meadow was limited by water availability. However, ET was constrained by available energy because of sufficient water supply from precipitation during rainfall season. In contrast, large differences between ET and precipitation indicated that soil water was supplied via lateral flow from melting upstream glaciers and snow during the transition season. The results suggest that seasonal variations in bulk parameters should be considered when simulating water and energy fluxes in permafrost regions.

Managing invasions in the context of globalization is a challenge in part because of the difficulty of inferring invader impacts from their invasiveness (i.e. ability to invade ecosystems). Specifically, the relationship between invasiveness and impact may be context-dependent and it has not been explored in such a unique ecosystem as the Tibetan Plateau. Here, we investigated 32 invasive plant species on the Tibetan Plateau in terms of their distribution, abundance, per capita effects on natives and traits across a large geographic transect to test the relationship between invasiveness and impacts on native communities. We decomposed the components (range, R; local abundance, A; per capita effect, E) that drive the impacts, and investigated the relative contributions of plant traits to these components. The results showed that there was no correlation between invasiveness (R × A) and impacts (R × A × E) of invasive species on the Tibetan Plateau. Specifically, plant invasiveness per se did not indicate a serious threat of harmful impact. In this ecosystem, R and A together drove invasiveness, while R alone drove impacts. Fruit type significantly influenced E, and species bearing berry fruits had the most negative per capita effects. However, plant traits did not drive invasiveness or impact through R, A or E. Our results suggest that the mismatch between components driving invasiveness vs. impact prevent the prediction of impacts of invasive species from their invasiveness. Therefore, management actions directed against invasive plants should prioritize broadly distributed species or those with demonstrated high impacts on native species.

According to the original optimal reproductive allocation theory, plants should shift from vegetative growth to reproductive allocation abruptly and completely. Some plants do this, and it is also considered a good strategy for crop plants to maximize yield, but most plants shift gradually. Modified versions of the theory predict such a gradual transition from growth to reproduction. We hypothesize that kin selection can also alter the predictions of optimal allocation theory. We investigated the theoretical implications of both positive and negative kin selection on the timing of plant reproductive development using mathematical models. Under reasonable assumptions of costs and benefits, plants under kin selection are more likely to shift from growth to reproduction in an abrupt way when the initial value of the ratio between reproductive and vegetative biomass is high. Supported by empirical observations, our theoretical predictions have important implications in linking life history and energy allocation as well as for improving yields in agriculture.

Although flower temperature plays an important role in plant reproduction, how it varies spatially on the flower surface is unclear, especially in alpine plants. To characterize spatial variation in flower surface temperature, we examined thermal images of flowers of 18 species along an altitudinal transect from 3200 to 4000 m on Lenglong Mountain on the north-eastern Qinghai-Tibetan Plateau. The surface temperature varied considerably within a flower or floral unit in all plants under sunlight, and was about 1 °C with a maximum of 11 °C higher in the center than at the edges. Solar radiation and flower shape significantly affected the temperature range and standard deviation and the ratio of flower center to edge temperature. The spatial variability of temperature increased with flower size. Flowers in the Asteraceae had higher surface temperatures, greater spatial variability of temperature, and consistently higher and more stable temperatures in the center than at the edge. The ratio of flower center to edge temperature increased with altitude in most species. Heat buildup at the flower center is likely to be widespread in alpine plants; further studies are needed to explore its ecological and evolutional roles.

Rhizosheaths can form on the surface of rice (Oryza sativa L.) roots and improve the water-use efficiency of rice under drought stress. The microbes in rhizosheaths can also offer the potential to increase the resilience of rice to future drought. However, little is known about the microbial community in rhizosheath of rice under drought stress. In this study, we compared the root traits, rhizosheath formation and microbial community in the rhizosheath under three irrigation regimes, including well-watered and drought treatments I and II. The irrigation plays important roles in influencing the microbial composition and co-occurrence networks. Drought can promote the accumulation of beneficial microorganisms in rhizosheaths, such as bacteria that are members of the phylum Patescibacteria and the Massilia, Nocardioides, Frateuria and Angustibacter genera and fungi in the genus Talaromyces. However, drought can also induce risk factors for harmful fungi in rice rhizosheaths. Our results suggest that both the rhizosheath and microbes in rhizosheath can offer the potential to improve the resistance of rice to drought. In the future, the isolation and application of beneficial microorganisms in rhizosheaths and scientific planting methods should be studied for the green cultivation of rice.

One central challenge for humanity is to mitigate and adapt to an ongoing climate and biodiversity crisis while providing resources to a growing human population. Ecological intensification (EI) aims to maximize crop productivity while minimizing impacts on the environment, especially by using biodiversity to improve ecosystem functions and services. Many EI measures are based on trophic interactions between organisms (e.g. pollination, biocontrol). Here, we investigate how research on multitrophic effects of biodiversity on ecosystem functioning could advance the application of EI measures in agriculture and forestry. We review previous studies and use qualitative analyses of the literature to test how important variables such as landuse parameters or habitat complexity affect multitrophic diversity, ecosystem functions and multitrophic biodiversity-ecosystem functioning relationships. We found that positive effects of biodiversity on ecosystem functions are prevalent in production systems, largely across ecosystem function dimensions, trophic levels, study methodologies and different ecosystem functions, however, with certain context dependencies. We also found strong impacts of land use and management on multitrophic biodiversity and ecosystem functions. We detected knowledge gaps in terms of data from underrepresented geographical areas, production systems, organism groups and functional diversity measurements. Additionally, we identified several aspects that require more attention in the future, such as trade-offs between multiple functions, temporal dynamics, effects of climate change, the spatial scale of the measures and their implementation. This information will be vital to ensure that agricultural and forest landscapes produce resources for humanity sustainably within the environmental limits of the planet.

Expansion of global trade and acceleration of climate change dramatically promote plant invasions. As a result, a large number of habitats harbor multiple invasive plant species. However, patterns of invasive interactions and the drivers mediating their interactions remain unclear. In this greenhouse, potted plant study, we tested the impacts of 18 invasive plant species on the growth of target invader Erigeron canadensis which is dominant in central China. Neighboring invasive species belong to three functional groups (grass, forb and legume) and have different levels of relatedness to E. canadensis. Growth of E. canadensis’ strongly depended on the identity of neighboring invaders. Some neighboring invasive species suppressed growth of E. canadensis, others had no effect, while some promoted growth of E. canadensis. Through analyses of functional and phylogenetic similarities between the target species and neighboring invaders, we showed that two factors probably play roles in determining the relative responses of E. canadensis. Generally, E. canadensis responded negatively to invasive grasses and forbs, while it responded positively to invasive legumes. Furthermore, the negative responses to neighboring invasive grasses and forbs increased with increasing phylogenetic distance between the neighbors and E. canadensis. In contrast, the positive responses to invasive legumes did not depend on phylogenetic distance from E. canadensis. Our results suggest that successful invasion of E. canadensis probably depends on the identity of co-occurring invasive plant species. Interactions between E. canadensis and other invasive species should help managers select management priorities.

树种菌根类型通过细根生物量和凋落物动态影响土壤呼吸和土壤碳储存
热带森林是高生产力但同时也是脆弱的生态系统之一。一些全球范围的造林项目计划未来十年在热带地区种植数百万棵树。树种菌根类型影响森林土壤碳储存已成为共识，但在热带地区，树种菌根类型如何影响土壤呼吸(Rs)和碳储存，目前仍知之甚少。为研究树种菌根类型对Rs和土壤碳储存的影响，本实验在一个近30年热带同质园的3种丛枝菌根(AM)树种和3种外生菌根(EM)树种的单种林中，测量了其Rs和表层20 cm的碳含量，以及有关的生物因子(如根生物量、凋落物动态、土壤微生物)和非生物因子(如微气候)。研究结果表明，AM单种林的Rs、土壤碳含量，以及凋落物周转速率和细根生物量显著高于EM单种林。分析表明，与其他生物和非生物因子比较，树种菌根类型对Rs和土壤碳含量的影响最大。进一步分析表明，菌根类型是通过细根生物量和凋落物动态(凋落物产量、凋落物现存量、凋落物周转速率)直接和间接影响Rs和土壤碳含量。本研究结果强调了树种菌根类型对森林碳循环的影响，表明在热带地区种植AM树种可能比种植EM树种更能促进土壤固碳。

While the relationship between genetic diversity and plant productivity has been established for many species, it is unclear whether environmental conditions and biotic associations alter the nature of the relationship. To address this, we investigated the interactive effects of genotypic diversity, drought and mycorrhizal association on plant productivity and plant traits. Our mesocosm study was set up at the Konza Prairie Biological Research Station, located in the south of Manhattan, Kansas. Andropogon gerardii, the focal species for our study, was planted in two levels of genotypic richness treatment: monoculture or three-genotype polyculture. A rainout shelter was constructed over half of the experimental area to impose a drought and Thiophanate-methyl fungicide was used to suppress arbuscular mycorrhizal fungi in selected pots within each genotypic richness and drought treatment. Genotypic richness and mycorrhizal association did not affect above-ground biomass of A. gerardii. Drought differentially affected the above-ground biomass, the number of flowers and bolts of A. gerardii genotypes, and the biomass and the functional traits also differed for monoculture versus polyculture. Our results suggest that drought and genotypic richness can have variable outcomes for different genotypes of a plant species.

Accelerated global warming in the late 20th century led to frequent forest-decline events in the Northern Hemisphere and increased the complexity of the relationships between tree growth and climate factors. However, few studies have explored the heterogeneity of responses of tree growth to climate factors in different regions of the Northern Hemisphere before and after accelerated warming. In this study, a total of 229 temperature-sensitive tree-ring width chronologies from nine regions on three continents in the Northern Hemisphere were used in the data analysis performed herein. A bootstrapped correlation analysis method was used to investigate whether the tree growth-climate response changed significantly in different regions between the periods before and after rapid warming. Probability density functions and piecewise linear fitting were used to study the fluctuation characteristics of the tree-ring width indices before and after rapid warming. At the end of the 20th century (from 1977 to 2000), rapid warming significantly promoted the radial growth of trees in different regions of the Northern Hemisphere, but tree radial growth was heterogeneous among the different regions from 1950 to 2000. After 1976, except in central North America and northern Europe, the correlation between tree growth and temperature increased significantly in the Northern Hemisphere, especially in Asia. From 1977 to 2000, tree-ring index and temperature divergences were observed in nine regions with a divergence of 2–5 years. From 1950 to 2000, tree growth tracked better average temperature variability in the Northern Hemisphere than regional temperature.

Leaf is the main organ of photosynthesis. Leaf phenotypic plasticity largely determines the adaptation of plants to enriched nitrogen (N) environments. However, it remains unclear whether the optimal number (proportion) of leaves representing the leaf traits of the whole plant is similar between ambient and N-enriched conditions. Moreover, whether alteration in ammonium (NH₄⁺-N) to nitrate (NO₃^--N) ratios in atmospheric N deposition will alter the optimal leaf number is unexplored. By adding three NH₄⁺-N/NO₃^--N ratios in a temperate grassland of northern China since 2014, three traits (leaf area, thickness and chlorophyll content) of two dominant clonal grasses, Leymus chinensis and Agropyron cristatum, were measured in August 2020. Results showed that under ambient conditions, the mean leaf area, thickness and chlorophyll content values of two fully expanded leaves were similar to these of all leaves at the plant level, except for the leaf area of L. chinensis, which needed five leaves (78.82% of leaves in the plant). The ratios of NH₄⁺-N/NO₃^--N increased the number of required sampled leaves and significantly changed the mean value of leaf traits and the maximum value along leaf order. Moreover, the ratios of NH₄⁺-N/NO₃^--N altered the trade-off among the three leaf traits, which is dependent on leaf order, by increasing leaf area and decreasing leaf thickness. Therefore, our study suggests that to better indicate the leaf traits’ value of the whole plant under N-enriched conditions, measuring all fully expanded leaves or providing a suitable scaling-up parameter is needed.

Despite a large number of studies examining the effects of abiotic stress factors on plants, the mechanistic explanations of drought-induced tree mortality remain inconclusive and even less is known about how multiple stressors interact. The role of non-structural carbohydrates (NSCs) in preventing or postponing drought mortality is gaining attention. Here, we tested the role of NSCs in mitigating the effects of drought and salinity in New Zealand mangroves, Avicennia marina subsp. australasica. We experimentally manipulated plant NSC levels, prior to subjecting them to combinations of drought and salinity. Plant growth and survival rates were 2- and 3-fold higher in the high-NSC (H-NSC) group than in the low-NSC (L-NSC) group under high salinity and drought conditions, respectively. After 12 weeks under high salinity–high drought conditions, the H-NSC group showed higher stem hydraulic conductivity (281 ± 50 mmol cm⁻¹ s⁻¹ MPa⁻¹) compared with the L-NSC group (134 ± 40 mmol cm⁻¹ s⁻¹ MPa⁻¹). Although starch levels remained relatively constant, we found a 20% increase in soluble sugars in the stems of H-NSC group under high drought and high salinity in week 8 compared with week 12. Our results suggest (i) an important role of NSCs in mitigating the effects of low soil water potential caused by drought and salinity, and (ii) sink-limited growth under conditions of combined salinity and drought.

Tropical forests are characterized by vast biomass, complex structures and mega-biodiversity. However, the adaptation processes of these forests to seasonal water availability are less understood, especially those located in the monsoonal and mountainous regions of tropical Southeast Asia. This study used four representative tropical forests spanning from 2° N to 22° N in continental Southeast Asia to address dry-condition photosynthesis at the seasonal scale. We first provided novel and reliable estimations of ecosystem photosynthesis (gross primary production; GPP) seasonality at all four sites. As expected, both evergreen and deciduous seasonal forests exhibited higher GPPs during the rainy season than during the dry season. A bimodal pattern corresponding to solar radiation occurred in the GPP of the perhumid forest. The surface conductance (G_s) was consistently lower both in the dry season and during dry spells (DSPs) than during the wet season and non-dry spells. However, this did not prevent GPP from increasing alongside increasing irradiance in the perhumid forest, suggesting that other ecosystem physiological properties, for example, the light-saturated photosynthetic rate, must have increased, thus surpassing the effect of G_s reduction. Thus, perhumid forests could be defined as light-demanding ecosystems with regard to their seasonal dynamics. Seasonal forests are water-stressed ecosystems in the dry season, as shown by the reductions in GPP, G_s and related ecosystem physiological properties. At all four forest sites, we observed a lack of consistent adaptive strategy to fit the water seasonality due to the diversity in leaf phenology, soil nutrient availability, root depth and other potential factors.

Plant density and nitrogen (N) availability influence plant survival and nutrient use strategies, but the interaction between these two factors for plant growth and the balance of elements remains poorly addressed. Here, we conducted experimental manipulations using Arabidopsis thaliana, with the combination of four levels of plant density and four levels of N addition, and then examined the corresponding changes in plant biomass production (indicated by total plant biomass and biomass partitioning) and nutrient use strategies (indicated by leaf N and phosphorus (P) stoichiometry). The biomass-density relationship was regulated by N availability, with a negative pattern in low N availability but an asymptotic constant final yield pattern at high N availability. Excessive N addition reduced plant growth at low plant density, but this effect was alleviated by increasing plant density. The root to shoot biomass ratio increased with plant density at low N availability, but decreased at high N availability. N availability was more important than plant density in regulating leaf N and P stoichiometry, with the increasing leaf N concentration and decreasing leaf P concentration under increasing N addition, resulting in a negative scaling relationship between these two elemental concentrations. Our results show that N availability and plant density interactively regulate plant biomass production and leaf stoichiometry of A. thaliana, and highlight that the interactive effects of these two factors should be considered when predicting plant growth behaviour under intraspecific competitive environments in the context of nutrient changes.

Understanding large-scale patterns of biodiversity and their drivers remains central in ecology. Many hypotheses have been proposed, including hydrothermal dynamic hypothesis, tropical niche conservatism hypothesis, Janzen’s hypothesis and a combination model containing energy, water, seasonality and habitat heterogeneity. Yet, their relative contributions to groups with different lifeforms and range sizes remain controversial, which have limited our ability to understand the general mechanisms underlying species richness patterns. Here we evaluated how lifeforms and species range sizes influenced the relative contributions of these three hypotheses to species richness patterns of a tropical family Moraceae. The distribution data of Moraceae species at a spatial resolution of 50 km × 50 km and their lifeforms (i.e. shrubs, small trees and large trees) were compiled. The species richness patterns were estimated for the entire family, different life forms and species with different range sizes separately. The effects of environmental variables on species richness were analyzed, and relative contributions of different hypotheses were evaluated across life forms and species range size groups. The species richness patterns were consistent across different species groups and the species richness was the highest in Sichuan, Guangzhou and Hainan provinces, making these provinces the hotspots of this family. Climate seasonality is the primary factor in determining richness variation of Moraceae. The best combination model gave the largest explanatory power for Moraceae species richness across each group of range size and life forms followed by the hydrothermal dynamic hypothesis, Janzen’s hypothesis and tropical niche conservatism hypothesis. All these models has a large shared effects but a low independent effect (< 5%), except rare species. These findings suggest unique patterns and mechanisms underlying rare species richness and provide a theoretical basis for protection of the Moraceae species in China.

When the shoot apical meristem of plants is damaged or removed, fecundity and/or plant growth may suffer (under-compensation), remain unaffected (compensation) or increase (overcompensation). The latter signifies a potential ‘cost’ of apical dominance. Using natural populations of 19 herbaceous angiosperm species with a conspicuously vertical, apically dominant growth form, we removed (clipped) the shoot apical meristem for replicate plants early in the growing season to test for a potential cost of apical dominance. Clipped and unclipped (control) plants had their near neighbours removed, and were harvested after flowering production had finished but before seed dispersal. Dry mass was measured separately for aboveground body size (shoots), leaves, seeds and fruits; and number of leaves, fruits and seeds per plant were counted. We predicted that: (i) our study species (because of their strong apically dominant growth form) would respond to shoot apical meristem removal with greater branching intensity, and thus overcompensation in terms of fecundity and/or biomass; and (ii) overcompensation is particularly enabled for species that produce smaller but more leaves, and hence with a larger bud bank of axillary meristems available for deployment in branching and/or fruit production. Widely variable compensatory capacities were recorded, and with no significant between-species relationship with leaf size or leafing intensity—thus indicating no generalized potential cost of apical dominance. Overall, the results point to species-specific treatment effects on meristem allocation patterns, and suggest importance for effects involving local variation in resource availability, and between-species variation in phenology, life history traits and susceptibility to herbivory.

Fine-root decomposition is a critical process regulating ecosystem carbon cycles and affecting nutrient cycling and soil fertility. However, whether interaction between warming and grazing affects fine-root decomposition is still under-researched in natural grasslands. A two-factorial experiment with asymmetric warming (i.e. daytime vs. nighttime and growing season vs. nongrowing season) and moderate grazing (i.e. about average 50% forage utilization rate) was conducted to explore whether warming and grazing affect fine-root decomposition and loss of nutrients during a 2-year decomposition period in an alpine meadow on the Tibetan Plateau. Both warming and grazing facilitated carbon cycling through increase in fine-root decomposition, and influenced element cycling which varies among elements. The effects of warming and grazing on fine-root decomposition and loss of nutrients were additive. Both warming and grazing significantly increased cumulative percentage mass loss and total organic carbon loss of fine roots during the 2-year experiment. Only warming with grazing treatment reduced percentage nitrogen loss, whereas warming, regardless of grazing, decreased percentage phosphorus loss. Warming and grazing alone increased percentage loss of potassium, sodium, calcium and magnesium compared with control. There were no interactions between warming and grazing on fine-root decomposition and loss of nutrients. There was greater temperature sensitivity of decreased phosphorus loss than that of decreased nitrogen loss. Different temperature sensitivities of percentage loss of nutrients from fine-root decomposition would alter ratios of the available nutrients in soils, and may further affect ecosystem structure and functions in future warming.

Land use and nutrient enrichment can substantially affect biodiversity and ecosystem functioning. However, whether and how the responses of community temporal stability to land use and nutrient enrichment change with time remain poorly understood. As part of a 15-year (2005-2019) field experiment, this study was conducted to explore the effects of mowing, nitrogen (N) and phosphorus (P) additions on community temporal stability in a temperate steppe on the Mongolian Plateau. Over the 15 years, N and P additions decreased community temporal stability by reducing the population stability, especially the shrub and semi-shrub stability. However, mowing increased community temporal stability in the early stage (2005-2009) only. Nitrogen addition suppressed community temporal stability in the early and late (2015-2019) stages, whereas enhanced it in the intermediate stage (2010-2014). Phosphorus addition decreased community temporal stability marginally in the early stage and significantly in the late stage. The fluctuations of N-induced changes in community temporal stability are mainly explained by its diverse effects on species asynchrony and population stability over time. Our findings highlight the important role of plant functional groups and species asynchrony in regulating community temporal stability, suggesting that more long-term studies are needed to accurately forecast ecosystem response patterns in the context of global change.

The pollution of freshwater ecosystems is threatening freshwater plant species diversity worldwide. Freshwater plants, such as the common duckweed (Lemna minor), are potentially sensitive to novel stressful environments. To test if ecotype diversity could increase resistance to stressful environments, I used seven L. minor populations and measured their growth rates with and without moderate salt stress across an ecotype diversity gradient. The L. minor populations were grown over 5 months in 92 experimental mesocosms, either in ecotype monocultures or in polyculture with either one or three conspecific ecotypes (23 unique compositions). After growing the duckweed in unperturbed conditions (phase 1), the cultures were subjected to moderate salt stress (50 mmol/L NaCl) for several weeks (phase 2). The experiment was conducted in the presence of the natural epimicrobial community associated with the different ecotypes. In phase 2, a subset of these algae added an unintentional second stressor to the experiment. The ecotypes differed in their growth rates, the fastest growing at twice the rate of others. The diversity context further shaped the ecotype growth rates. Ecotype polycultures showed higher abundances towards the end of the experiment, thus over time, as the environment deteriorated, ecotype diversity gained in importance. These findings show that within-species variation in growth rates can translate to a positive effect of ecotype diversity on population abundance. Exposure of L. minor to moderate salt levels did not significantly impact growth rates, although the effect may have been masked by reduced algal stress in the saline environments.

Acid rain (AR), which occurs frequently in southern China, negatively affects the growth of subtropical tree species. Arbuscular mycorrhizal fungi (AMF) mitigate the detrimental effects induced by AR. However, the mechanisms by which AMF protect Zelkova serrata, an economically important tree species in southern China, from AR stress remain unclear. We conducted a greenhouse experiment in which Z. serrata plants were inoculated with AMF species Rhizophagus intraradices and Diversispora versiformis, either alone or as a mixed culture, or with a sterilized inoculum (negative control). The plants were subjected to three levels of simulated sulfuric AR and nitric AR (pH 2.5, 4.0 and 5.6) to examine any interactive effects on growth, photosynthetic capabilities, antioxidant enzymes, osmotic adjustment and soil enzymes. AR significantly decreased dry weight, chlorophyll content, net photosynthetic rate and soluble protein (SP) of non-mycorrhizal plants. Mycorrhizal inoculation, especially a combination of R. intraradices and D. versiformis, notably improved dry weight, photosynthetic capabilities, catalase, peroxidase, superoxide dismutase, SP and root acid phosphatase activity of Z. serrata under harsh AR stress. Moreover, the benefits from AMF symbionts depended on the identity of AM fungal species and the gradient of AR stress. Our results indicate that AM fungi protect Z. serrata against AR stress by synchronously activating photosynthetic ability, antioxidant enzymes and osmolyte accumulation. These findings suggest that a combination of R. intraradices and D. versiformis may be a preferable choice for culturing Z. serrata in southern China.

Evergreen and deciduous species coexist in the subtropical forests in southeastern China. It has been suggested that phosphorus (P) is the main limiting nutrient in subtropical forests, and that evergreen and deciduous species adopt different carbon capture strategies to deal with this limitation. However, these hypotheses have not been examined empirically to a sufficient degree. In order to fill this knowledge gap, we measured leaf photosynthetic and respiration rates, and nutrient traits related to P-, nitrogen (N)- and carbon (C)-use efficiencies and resorption using 75 woody species (44 evergreen and 31 deciduous species) sampled in a subtropical forest. The photosynthetic N-use efficiency (PNUE), respiration rate per unit N and P (R_d,N and R_d,P, respectively) of the deciduous species were all significantly higher than those of evergreen species, but not in the case of photosynthetic P-use efficiency. These results indicate that, for any given leaf P, evergreen species manifest higher carbon-use efficiency (CUE) than deciduous species, a speculation that is empirically confirmed. In addition, no significant differences were observed between deciduous and evergreen species for nitrogen resorption efficiency, phosphorus resorption efficiency or N:P ratios. These results indicate that evergreen species coexist with deciduous species and maintain dominance in P-limited subtropical forests by maintaining CUE. Our results also indicate that it is important to compare the PNUE of deciduous species with evergreen species in other biomes. These observations provide insights into modeling community dynamics in subtropical forests, particularly in light of future climate change.

The ecosystem apparent quantum yield (α), maximum rate of gross CO₂ assimilation (P_max) and daytime ecosystem respiration rate (R_d), reflecting the physiological functioning of ecosystem, are vital photosynthetic parameters for the estimation of ecosystem carbon budget. Climatic drivers may affect photosynthetic parameters both directly and indirectly by altering the response of vegetation. However, the relative contribution and regulation pathway of environmental and physiological controls remain unclear, especially in semi-arid grasslands. We analyzed seasonal and interannual variations of photosynthetic parameters derived from eddy-covariance observation in a typical semi-arid grassland in Inner Mongolia, Northern China, over 12 years from 2006 to 2017. Regression analyses and a structural equation model (SEM) were adopted to separate the contributions of environmental and physiological effects. The photosynthetic parameters showed unimodal seasonal patterns and significantly interannual variations. Variations of air temperature (T_a) and soil water content (SWC) drove the seasonal patterns of photosynthetic parameters, while SWC predominated their interannual variations. Moreover, contrasting with the predominant roles of T_a on α and R_d, SWC explained more variance of P_max than T_a. Results of SEM revealed that environmental factors impacted photosynthetic parameters both directly and indirectly through regulating physiological responses reflected by stomatal conductance at the canopy level. Moreover, leaf area index (LAI) directly affected α, P_max and R_d and dominated the variation of P_max. On the other hand, SWC influenced photosynthetic parameters indirectly through LAI and canopy surface conductance (gc). Our findings highlight the importance of physiological regulation on the photosynthetic parameters and carbon assimilation capacity, especially in water-limited grassland ecosystems.

To compare current methods of pretreatment/determination for plant foliar pH, we proposed a method for long-period sample preservation with little interference with the stability of foliar pH. Four hundred leaf samples from 20 species were collected and four methods of pH determination were used: refrigerated (stored at 4 °C for 4 days), frozen (stored at −16 °C for 4 days), oven-dried and fresh green-leaf pH (control). To explore the effects of different leaf:water mixing ratio on the pH determination results, we measured oven-dried green-leaf pH by leaf:water volume ratio of 1:8 and mass ratio of 1:10, and measured frozen senesced-leaf pH by mass ratio of 1:10 and 1:15. The standard major axis regression was used to analyze the relationship and the conversion equation between the measured pH with different methods. Foliar pH of refrigerated and frozen green leaves did not significantly differ from that of fresh green-leaf, but drying always overrated fresh green-leaf pH. During the field sampling, cryopreservation with a portable refrigerator was an advisable choice to get a precise pH. For long-duration field sampling, freezing was the optimal choice, and refrigeration is the best choice for the short-time preservation. The different leaf:water mixing ratio significantly influenced the measured foliar pH. High dilution reduced the proton concentration and increased the measured pH. Our findings provide the conversion relationships between the existing pretreatment and measurement methods, and establish a connection among pH determined by different methods. Our study can facilitate foliar pH measurement, thus contributing to understanding of this interesting plant functional trait.

Senesced-leaf nutrient concentrations vary significantly among coexisting plant species reflecting different leaf nutrient use strategies. However, interspecific variation in senesced-leaf nutrients and its driving factors are not well understood. Here, we aimed to determine interspecific variation and its driving factors in senesced-leaf nutrients. We explored interspecific variation in carbon (C), nitrogen (N) and phosphorus (P) concentrations in newly fallen leaves of 46 coexisting temperate deciduous woody species across the Maoershan Forest Ecosystem Research Station, Northeast China. The relative importance of 10 biotic factors (i.e. mycorrhiza type, N-fixing type, growth form, shade tolerance, laminar texture, coloring degree, coloring type, peak leaf-coloration date, peak leaf-fall date and end leaf-fall date) was quantified with the random forest model. N and P concentrations varied 4- and 9-fold among species, respectively. The high mean N (15.38 mg g⁻¹) and P (1.24 mg g⁻¹) concentrations suggested a weak N and P limitation in the studied forest. Functional groups had only significant effects on specific nutrients and their ratios. P concentration and N:P were negatively correlated with peak and end leaf-fall dates for the ectomycorrhiza species group. Brighter-colored leaves (red > brown > yellow > yellow-green > green) tended to have lower N and P concentrations and higher C:N and C:P than darker-colored leaves. The random forest model showed that autumn coloration and leaf-fall phenology contributed 80% to the total explanation of nutrient variability among species. The results increase our understanding of the variability in senesced-leaf nutrients as a strategy of woody plant nutrition in temperate forests.

Precipitation (PPT) is the primary climatic determinant of plant growth and aboveground net primary productivity (ANPP) for many of the world’s major terrestrial ecosystems. Thus, relationships between PPT and productivity can provide insight into how changes in climate may alter ecosystem functions globally. Spatial PPT–ANPP relationships for grasslands are found remarkably similar around the world, but whether and how they change during periods of extended climatic anomalies remain unknown. Here, we quantified how regional-scale PPT-ANPP relationships vary between an extended wet and a dry period by taking advantage of a 35-year record of PPT and NDVI (as a surrogate for ANPP) at 1700 sites in the temperate grasslands of northern China. We found a sharp decrease in the strength of the spatial PPT–ANPP relationship during an 11-year period of below average PPT. We attributed the collapse of this relationship to asynchrony in the responses of different grassland types to this decadal period of increased aridity. Our results challenge the robustness of regional PPT–productivity if aridity in grasslands is increased globally by climate change.

Only targeted and sustainable management will preserve extensively managed grasslands, one of Europe's most species-rich habitats. Traditionally, largely abandoned irrigation might prove a sustainable management strategy, but the understanding of the interactions among irrigation, soil properties and plant species are low for a generally humid ecoregion. We aimed at advancing our understanding of plant ecology by disentangling plant community responses to traditional lowland meadow irrigation from traditionally low fertilization rates. We studied plant composition and diversity jointly with the underlying links to soil properties (Corg, total N, water holding capacity and mesofaunal activity) and soil nutrients (Nmin, P, K, Mg and B). In a field study, we compared 13 long-term traditionally irrigated and 13 non-irrigated (17 fertilized and 9 non-fertilized) meadows. We surveyed plant diversity, composition and soil nutrients as well as soil properties for 1 year assuming low annual variation. Irrigation and fertilization led to differences in soil properties and soil nutrients without impact on sheer plant species diversity but on plant species composition. Finer grain sizes due to siltation increased water holding capacity and nutrient storage. Hence, resource-acquisitive graminoid species had advantages in irrigated meadows. Thus, irrigation is not only a mean to preserve biodiversity of extensively used meadows of Central Europe but may prove a tool to differentiate between plant functional traits.

The four alien farmland weeds of genus Veronica (i.e. V. arvensis, V. didyma, V. hederifolia and V. persica) have successfully colonized in China, but caused different ecological consequences in the colonized habitats. However, the key biological traits conferring bioinvasion differences under different light conditions among the four alien species of Veronica remain unknown. A comprehensive contrastive analysis experiment was conducted to assess the contribution of the intensity of photosynthetic and sexual and asexual reproductive traits of the four alien Veronica weeds to their invasion level in both field trial and laboratory. The field survey showed that V. persica had the highest invasion level, followed by V. didyma, V. hederifolia and V. arvensis. Their invasiveness was mainly attributed to photosynthetic-related parameters (LMA) and asexual reproduction traits (the ratio of adventitious roots) out of all the 22 tested indexes. The photosynthetic-related and some asexual reproduction indexes from separate determinations under both sun and shade conditions showed that V. persica was able to adapt to strong illumination but was more tolerant of shade than the other species. This adaptive differentiation to illumination conferred different competitiveness over crops on the four alien Veronica weeds by allocating resources to the biomass of each organ in farmland. It may be concluded that the adaptability to illumination conditions and the asexual reproduction traits may endow their successful invasion and become different important farmland weeds.

Recent warmer and wetter climate in northern China remains a hot topic in recent years, yet its effect on vegetation growth has not been fully understood. This study investigated the temporal change of vegetation cover and its correlations with climatic variables from 1982 to 2018 for grasslands in northern China. Our aim is to clarify whether the warmer and wetter climate in recent years drives the greening of the vegetation in this region.

We investigated the temporal dynamic of vegetation normalized difference vegetation index (NDVI) and its driving forces based on long time-series data. Piecewise regression was used to examine whether there was a turning point of the trend of NDVI and climatic variables. Pearson correlation analyses were conducted to quantify the relationship between NDVI and climatic factors. Stepwise multivariable regression was used to quantify the contributions of climate variables to the temporal variations in NDVI.

We found a turning point of NDVI trend in 2008, with GIMMS NDVI indicating a slight increase of 0.00022 yr⁻¹ during 1982–2008 to an increase of 0.002 yr⁻¹ for GIMMS NDVI during 2008–2015 and 0.0018 yr⁻¹ for MODIS NDVI during 2008–2018. Precipitation was the predominant driver, and air temperature and vapor pressure deficit exerted a minor impact on the temporal dynamics of NDVI. Overall, our results suggest a turning point of NDVI trend, and that recent warmer and wetter climate has caused vegetation greening, which provides insights for better predicting the vegetation cover in this region under changing climate.

The limitations of classical Lotka–Volterra models for analyzing and interpreting competitive interactions among plant species have become increasingly clear in recent years. Three of the problems that have been identified are (i) the absence of frequency-dependence, which is important for long-term coexistence of species, (ii) the need to take unmeasured (often unmeasurable) variables influencing individual performance into account (e.g. spatial variation in soil nutrients or pathogens) and (iii) the need to separate measurement error from biological variation.

We modified the classical Lotka–Volterra competition models to address these limitations. We fitted eight alternative models to pin-point cover data on Festuca ovina and Agrostis capillaris over 3 years in an herbaceous plant community in Denmark. A Bayesian modeling framework was used to ascertain whether the model amendments improve the performance of the models and increase their ability to predict community dynamics and to test hypotheses.

Inclusion of frequency-dependence and measurement error, but not unmeasured variables, improved model performance greatly. Our results emphasize the importance of comparing alternative models in quantitative studies of plant community dynamics. Only by considering possible alternative models can we identify the forces driving community assembly and change, and improve our ability to predict the behavior of plant communities.

Interactions between plants and their soil biota, arbuscular mycorrhizal fungi (AMF) in particular, may play a vital role in the establishment and the range expansion of exotic plants in new environments. However, whether there are post-introduction shifts in dependence on AMF and how dependency interacts with competition remains poorly understood.

We conducted a common garden greenhouse experiment to examine how native (USA) and invasive (China) populations of the plant species Plantago virginica, respond to soil biota, and whether these responses change in the presence of a competitor.

We found that while native populations consistently had a higher AMF colonization rate and benefited from AMF in both biomass and seed production, invasive populations received less benefit from AMF, and even showed reduced biomass with AMF in the presence of a competitor. This low mycorrhizal dependency in invasive populations correlated with greater suppression by an indigenous competitor for the invader. The different responses of the invasive and native populations to AMF suggest that alteration of mycorrhizal dependency has occurred during the invasion of P. virginica into China. Our findings suggest that this reduced dependency incurs a cost during interspecific competition.

Understanding the patterns and drivers of carbon isotope discrimination (13Δ) in C₃ and C₄ functional groups is critical for predicting C₃/C₄ vegetation ratio from the isotopic composition of soil organic matter. In this study, we aimed to evaluate how intraspecific variation will modify functional group-level 13Δ values and the associated prediction of C₃/C₄ vegetation ratio.

We investigated 13Δ of 726 individual plants (96 species; C₃ and C₄ functional groups) and topsoil organic matter in 26 grassland communities along an aridity gradient in northern China. The fraction of C₄ contribution was calculated with mixing models that considered: (i) both intra- and interspecific effects on the 13Δ values of C₃ and C₄ functional groups; (ii) only interspecific effects; or (iii) none of these effects.

We found divergent responses of plant 13Δ at the intraspecific level to the changes of aridity across the gradient. The 13Δ of both C₃ and C₄ functional groups was negatively correlated with an aridity index, with higher sensitivity for C₃ than for C₄ functional groups. Intraspecific 13Δ variation played a key role in driving the total 13Δ variations of C₃ plants. Overlooking such intraspecific effect in mixing models led to a greatly increased fraction of C₄ contribution to soil organic carbon. A correction for the effects of intraspecific variation is therefore essential for correctly inferring C₃/C₄ vegetation ratio in the past. Our findings provide basic information for the reconstruction of past vegetation change from bulk materials in arid and semiarid biomes.

The scaling relationship between nitrogen (N) and phosphorus (P) concentrations ([N] and [P], respectively) in leaves manifests plants’ relative investment between the two nutrients. However, the variation in this relationship among taxa as well as its causes was seldom described.

The analysis was based on a dataset including 2483 leaf samples from 46 genera of angiosperm woody plants from 1733 sites across China. We calculated the leaf N–P scaling exponent (β_L) with an allometric equation ([N] = α[P]β), for each genus, respectively. We then performed phylogenetic path analyses to test how the climate and soil niche conditions of these genera contributed to the inter-genus variation in β_L.

The genera living with lower soil P availability presented a more favoured P uptake relative to N, as shown by the higher β_L, suggesting a resistant trend to P limitation. Additionally, genus-wise β_L was positively correlated with soil N–P scaling exponents (β_S), implying that the variation in leaf nutrients is constrained by the variability in their sources from soil. Finally, climatic factors including temperature and moisture did not affect β_L directly, but could have an indirect influence by mediating soil nutrients. Phylogeny did not affect the inter-genus variation in β_L along environmental gradients. These results reveal that the trade-off between N and P uptake is remarkably shaped by genus niches, especially soil nutrient conditions, suggesting that the β_L could be considered as a functional trait reflecting characteristics of nutrient utilization of plant taxa in response to niche differentiation.

The evolution and expression of dispersal-related traits are intertwined with those of other life-history functions and are manifested within various physiological constraints. Such a relationship is predicted between inbreeding levels and dispersability, which may be anatomically and ontogenetically linked so that the selection pressures on one may affect the other. While both the effect of inbreeding on reproductive success and on dispersal strategies received much attention, only a few studies considered both simultaneously. Furthermore, such studies often rely on two dichotomic representations of breeding and dispersal: using selfing versus outcrossing as a representation of breeding level, and dispersal ratio as the sole representation of dispersal strategy.

Here, we used pollination experiments in the heterocarpic Crepis sancta (Asteraceae) to expand in two different manners on the common practice of using dichotomic representations of breeding and dispersal. First, we used pollination treatments that represent a continuum from selfing through pollination by kin to pollination by a distant neighbor. Second, we measured a whole set of continuous morphological and dispersal-related traits, in addition to measurements of reproductive success and dispersal ratio.

The proportion of developed capitula and the number of both dispersed and non-dispersed achenes were significantly lower in the self-pollination treatment in comparison to the outcrossed treatments. The effect of pollen sources on dispersal ratio was not statistically significant, though self-pollinated plants rarely produced non-dispersing seeds. Achene’s biomass increased with distance between parent plants, but pappus width did not, leading to a nonsignificant effect of pollination on falling velocity. Overall, pollen source affected mainly traits that were associated with reproductive output, but it had no clear effect on predominately dispersal-related traits. Such differences in the response of reproduction and dispersal traits to variation in pollen source suggest that dispersal-related selection is probably weak and/or masked by other forces.

Germination is the earliest life-history transition of a plant species. It determines the ecological breadth and geographic ranges of a species and has major effects on its invasion potential. The largest spread of the invasive salt-marsh cordgrass Spartina alterniflora in China, where it extends to latitudes lower than its native range in North America, provides an opportunity to examine germination trait variation across latitudes within and among its invasive and native ranges.

We studied seed germination traits of S. alterniflora using seeds collected from 10 locations across latitudes in its invasive range (China, 20°–40° N) and 16 locations across latitudes in its native range (USA, 27°–43° N) in growth chambers with 0 PSU sterilized distilled water. We further evaluated how climate and tide range in the original locations influenced germination traits.

Native populations showed higher (~10%) germination percentage and significantly higher (~20%) germination index than invasive populations did, but invasive populations germinated significantly earlier (~3 days) than native populations. Germination percentage and germination index increased with latitude in the invasive range but decreased with latitude in the native range. The mean germination time decreased with latitude in the invasive range and paralleled that in the native range. Germination percentage and germination index were negatively correlated with mean daily temperature (Tmean), mean daily maximum temperature (Tmax) and mean daily minimum temperature (Tmin), and inversely correlated with Tmean, Tmax and Tmin in the native range. However, the mean germination time was positively correlated with Tmean, Tmax and Tmean in both ranges. Our results demonstrate that invasive and native populations have evolved different latitudinal clines in germination percentage and index, but the mean germination time of the invasive population mirrored the latitudinal cline observed in the native range, suggesting that germination strategy across latitudes may change during invasion process.

Biomass allocation to different organs is a fundamental plant ecophysiological process to better respond to changing environments; yet, it remains poorly understood how patterns of biomass allocation respond to nitrogen (N) additions across terrestrial ecosystems worldwide.

We conducted a meta-analysis using 5474 pairwise observations from 333 articles to assess how N addition affected plant biomass and biomass allocation among different organs. We also tested the ‘ratio-based optimal partitioning’ vs. the ‘isometric allocation’ hypotheses to explain potential N addition effects on biomass allocation.

We found that (i) N addition significantly increased whole plant biomass and the biomass of different organs, but decreased root:shoot ratio (RS) and root mass fraction (RMF) while no effects of N addition on leaf mass fraction and stem mass fraction at the global scale; (ii) the effects of N addition on ratio-based biomass allocation were mediated by individual or interactive effects of moderator variables such as experimental conditions, plant functional types, latitudes and rates of N addition and (iii) N addition did not affect allometric relationships among different organs, suggesting that decreases in RS and RMF may result from isometric allocation patterns following increases in whole plant biomass. Despite alteration of ratio-based biomass allocation between root and shoot by N addition, the unaffected allometric scaling relationships among different organs (including root vs. shoot) suggest that plant biomass allocation patterns are more appropriately explained by the isometric allocation hypothesis rather than the optimal partitioning hypothesis. Our findings contribute to better understand N-induced effects on allometric relationships of terrestrial plants, and suggest that these ecophysiological responses should be incorporated into models that aim to predict how terrestrial ecosystems may respond to enhanced N deposition under future global change scenarios.

The effects of fertilization on fungal plant pathogens in agricultural soils have been studied extensively. However, we know little about how fertilization affects the relative abundance and richness of soil fungal plant pathogens in natural ecosystems, either through altering the soil properties or plant community composition.

Here, we used data from a 7-year nitrogen (N) addition experiment in an alpine meadow on the Qinghai-Tibetan Plateau to test how N addition affects the relative abundance and richness of soil fungal plant pathogens, as determined using Miseq sequencing of ITS1 gene biomarkers. We also evaluated the relative importance of changes in soil properties versus plant species diversity under N addition.

Using general linear model selection and a piecewise structural equation model, we found that N addition increased the relative abundance of soil fungal plant pathogens by significantly altering soil properties. However, higher host plant species richness led to higher soil fungal plant pathogen richness, even after excluding the effects of N addition. We conclude that the relative abundance and richness of soil fungal plant pathogens are regulated by different mechanisms in the alpine meadow. Continuous worldwide N inputs (through both fertilizer use and nitrogen deposition) not only cause species losses via altered plant species interactions, but also produce changes in soil properties that result in more abundant soil fungal plant pathogens. This increase in pathogen relative abundance may seriously threaten ecosystem health, thus interrupting important ecosystem functions and services.

Phylogenetic diversity metrics can discern the relative contributions of ecological and evolutionary processes associated with the assembly of plant communities. However, the magnitude of the potential variation associated with phylogenetic methodologies, and its effect on estimates of phylogenetic diversity, remains poorly understood. Here, we assess how sources of variation associated with estimates of phylogenetic diversity can potentially affect our understanding of plant community structure for a series of temperate forest plots in China.

In total, 20 forest plots, comprising of 274 woody species and 581 herbaceous species, were surveyed and sampled along an elevational gradient of 2800 m on Taibai Mountain, China. We used multi-model inference to search for the most parsimonious relationship between estimates of phylogenetic diversity and each of four predictors (i.e. type of phylogenetic reconstruction method, phylogenetic diversity metric, woody or herbaceous growth form and elevation), and their pairwise interactions.

There was no significant difference in patterns of phylogenetic diversity when using synthesis-based vs. molecular-based phylogenetic methods. Results showed that elevation, the type of phylogenetic diversity metric, growth form and their interactions, accounted for >44% of the variance in our estimates of phylogenetic diversity. In general, phylogenetic diversity decreased with increasing elevation; however, the trend was weaker for herbaceous plants than for woody plants. Moreover, the three phylogenetic diversity metrics showed consistent patterns (i.e. clustered) across the elevational gradient for woody plants. For herbaceous plants, the mean pairwise distance showed a random distribution over the gradient. These results suggest that a better understanding of temperate forest community structure can be obtained when estimates of phylogenetic diversity include methodological and environmental sources of variation.

Linkages formed through aquatic–terrestrial subsidies can play an important role in structuring communities and mediating ecosystem functions. Aquatic–terrestrial subsidies may be especially important in nutrient-poor ecosystems, such as the freshwater sand dunes surrounding Lake Michigan. Adult midges emerge from Lake Michigan in the spring, swarm to mate and die. Their carcasses form mounds at the base of plants, where they may increase plant productivity through their nutrient inputs. However, the effect of aquatic–terrestrial subsidies on plant productivity could depend on other biotic interactions. In particular, soil microbes might play a key role in facilitating the conversion of nutrients to plant-available forms or competing for the nutrients with plants.

In a greenhouse experiment, we tested how carcasses from lake emergent midges (Chironomidae) and soil microbes independently and interactively influenced the performance of a common dune grass, Calamovilfa longifolia. To determine whether midges influenced abiotic soil properties, we measured how midge additions influenced soil nutrients and soil moisture.

Midges greatly increased plant biomass, while soil microbes influenced the magnitude of this effect. In the absence of soil microbes plant biomass was seven times greater with midges than without midges. However, in the presence of soil microbes, plant biomass was only three times greater. The effect of midges might be driven by their nutrient inputs into the soil, as midges contained 100 times more N, 10 times more P and 150 times more K than dune soils did. Our results suggest that soil microbes may be competing with plants for these nutrients. In sum, we found that midges can be an important aquatic–terrestrial subsidy that produces strong, positive effects on plant productivity along the shorelines of Lake Michigan, but that the impact of aquatic–terrestrial subsidies must be considered within the context of the complex interactions that take place within ecological communities.