Non-structural carbohydrates (NSCs) are plant storage compounds used for metabolism, transport, osmoregulation and regrowth following the loss of plant tissue. Even in conditions suitable for optimal growth, plants continue to store NSCs. This storage may be due to passive accumulation from sink-inhibited growth or active reserves that come at the expense of growth. The former pathway implies that NSCs may be a by-product of sink limitation, while the latter suggests a functional role of NSCs for use during poor conditions.

Using 13C pulse labelling, we traced the source of soluble sugars in stem and root organs during drought and everwet conditions for seedlings of two tropical tree species that differ in drought tolerance to estimate the relative allocation of NSCs stored prior to drought versus NSCs assimilated during drought. We monitored growth, stomatal conductance, stem water potential and NSC storage to assess a broad carbon response to drought.

We found that the drought-sensitive species had reduced growth, conserved NSC concentrations in leaf, stem and root organs and had a larger proportion of soluble sugars in stem and root organs that originated from pre-drought storage relative to seedlings in control conditions. In contrast, the drought-tolerant species maintained growth and stem and root NSC concentrations but had reduced leaf NSCs concentrations with a larger proportion of stem and root soluble sugars originated from freshly assimilated photosynthates relative to control seedlings. These results suggest the drought-sensitive species passively accumulated NSCs during water deficit due to growth inhibition, while the drought-tolerant species actively responded to water deficit by allocating NSCs to stem and root organs. These strategies seem correlated with baseline maximum growth rates, which supports previous research suggesting a trade-off between growth and drought tolerance while providing new evidence for the importance of plasticity in NSC allocation during drought.

With the increase of land-use change, habitat fragmentation has become a major factor affecting plant diversity. Generally, when the adult density is high, the survival rate of conspecific saplings may decline and provide more resources and space for other species to maintain a high local species diversity. Therefore, the spatial relationship of conspecific saplings and adults (SRCSA) can regulate plant diversity. However, very few studies have assessed SRCSA within fragmented forests, and we still largely unknown the relationship between SRCSA and species diversity in fragmented landscapes.

We calculated the mean strength of SRCSA using the spatial distribution data of saplings and adults with a log-transformed hierarchical offset-power model on 27 islands in a land-bridge island system. The higher strength of SRCSA reflects a more negative relationship between the density of conspecific saplings and adults on an island (i.e. the looser pattern of SRCSA). We tested the relationships among island attributes (i.e. island area, the distance to the mainland—MD, and the distance to the nearest island—ND), SRCSA and species diversity.

The strength of SRCSA increased with ND. Meanwhile, the species diversity significantly increased with the strength of SRCSA, and island area and the strength of SRCSA independently explained 26% and 6% of variation of species diversity, respectively, and their interactions explained 8%. Shade-intolerant and low-abundant species showed looser patterns of SRCSA. Our study suggests that SRCSA may have the effect of excluding species with a relatively low abundance in isolated island forests, which illustrates the importance of biotic interactions in maintaining plant diversity in fragmented forests. Our results also emphasize that we should consider forest connectivity when testing the conspecific negative density dependence.

Plant invasions have the potential to affect the community structure of soil nematodes, but little is known about whether such effects are mediated by aboveground herbivores since invasive plants are not completely released from herbivores in the introduced range. In this study, we explored how aboveground insect herbivores mediated the effect of invasive plant Alternanthera philoxeroides on soil nematodes and examined the temporal variations of such an herbivory-elicited effect.

We conducted a greenhouse experiment by applying different herbivory treatments (no insect herbivores, specialist Agasicles hygrophila and generalist Cassida piperata) to potted A. philoxeroides, and then measured the community compositions of soil nematodes in corresponding pots on the 1st, 10th and 20th day after removal of all herbivores. In addition, the carbon content of roots and root exudate of A. philoxeroides were also measured.

Our results showed that aboveground herbivory significantly increased the abundance of soil nematodes of A. philoxeroides, likely plant feeder nematodes, after insect herbivores were removed immediately (1st day). However, such impacts waned with time and there was no significant difference at later stages (10th and 20th days). Furthermore, the effects of specialist A. hygrophila and generalist C. piperata herbivory were consistent on the abundance of soil nematodes. Overall, our results suggest that aboveground insect herbivores have the potential to alter the effects of plant invasions on soil nematodes, but such impacts are transient. Furthermore, our study highlighted the importance of integrating the effects of above- and belowground organisms when evaluating the impacts of plant invasions.

In a contact zone between related taxa, phenotypic variation can result from genetic and/or environmental gradients. This study aimed to clarify the cause of phenotypic variation in leaf morphology of two Quercus crispula varieties—crispula (QCC) and mongolicoides (QCM)—in their contact zone along an altitudinal gradient.

We measured 6 morphological traits of leaves and recorded genotypes of 13 nuclear microsatellite loci for 48 individuals in the contact zone and 24 individuals in each of the reference populations of QCC and QCM. We constructed a model explaining the phenotypic variation (leaf morphology) in relation to environmental (altitude) and genetic (ancestry from the reference population) gradients.

Both morphological and genetic markers distinguished the two varieties in the reference populations well. We were able to confirm the power of both morphological and genetic markers. Individuals within the contact zone population had intermediate ancestry that was slightly biased to QCM ancestry, and the distribution of their morphologies overlapped with those of the two varieties in the reference populations. The effect of altitude on leaf morphological traits was significant, while that of ancestry was not. Distributions of ancestry and interclass heterozygosity in the contact zone population resembled those in F₂ or later generation hybrids. These results indicate that in the contact zone between QCC and QCM, there is no ongoing hybridization, but environmental pressure has created an altitudinal gradient in morphological traits through phenotypic plasticity and/or variation in functional genes.

Plants have limited resources for defenses and species that invest in biotic defenses might exhibit leaves that invest less in other types of defenses. We have investigated whether plants that have few mechanical defenses, but have extrafloral nectaries (EFNs) patrolled by ants, are less prone to herbivory, compared with plants without EFNs that have tougher leaves.

Data from the literature were extracted to examine the reported levels of herbivory in plants with or without EFNs. In a savanna vegetation in southern Brazil, field data were collected in leaves from six tropical species and herbivory and specific leaf area (SLA) levels were measured. We further evaluated differences in herbivory and SLA among species and between plants with or without EFNs. In order to test the relationship between herbivory and leaf toughness we regressed average herbivory and average SLA per plant.

Plants exhibited variable levels of leaf damage, but plants without ant defenses experienced the highest levels of leaf area loss to herbivory. Levels of mechanical defenses were also variable among the plant species. Plants without EFNs were tougher, exhibiting lower values of SLA. Although plants without EFNs had more sclerophyllous leaves, this mechanical defense was not sufficient to impair and/or reduce herbivore feeding, suggesting that the biotic defenses performed by patrolling ants might be more effective than investment in mechanical defenses associated with leaf palatability.

Biodiversity is often positively related to the capacity of an ecosystem to provide multiple functions simultaneously (i.e. multifunctionality). However, there is some controversy over whether biodiversity–multifunctionality relationships depend on the number of functions considered. Particularly, investigators have documented contrasting findings that the effects of biodiversity on ecosystem multifunctionality do not change or increase with the number of ecosystem functions. Here, we provide some clarity on this issue by examining the statistical underpinnings of different multifunctionality metrics.

We used simulations and data from a variety of empirical studies conducted across spatial scales (from local to global) and biomes (temperate and alpine grasslands, forests and drylands). We revisited three methods to quantify multifunctionality including the averaging approach, summing approach and threshold-based approach.

Biodiversity–multifunctionality relationships either did not change or increased as more functions were considered. These results were best explained by the statistical underpinnings of the averaging and summing multifunctionality metrics. Specifically, by averaging the individual ecosystem functions, the biodiversity–multifunctionality relationships equal the population mean of biodiversity-single function relationships, and thus will not change with the number of functions. Likewise, by summing the individual ecosystem functions, the strength of biodiversity–multifunctionality relationships increases as the number of functions increased. We proposed a scaling standardization method by converting the averaging or summing metrics into a scaling metric, which would make comparisons among different biodiversity studies. In addition, we showed that the range-relevant standardization can be applied to the threshold-based approach by solving for the mathematical artefact of the approach (i.e. the effects of biodiversity may artificially increase with the number of functions considered). Our study highlights different approaches yield different results and that it is essential to develop an understanding of the statistical underpinnings of different approaches. The standardization methods provide a prospective way of comparing biodiversity–multifunctionality relationships across studies.

Global change may cause unparalleled supplies of soil nutrients and further lead to stoichiometric imbalance of nitrogen (N) and phosphorus (P) in terrestrial plants. While previous studies had reported the effects of global change factors on plant N, P contents and their ratios, few had examined whether or how these factors may influence the scaling of these two elements.

Taking advantage of a manipulative experiment with altered precipitation, warming and N addition, and using the general scaling function N = βPα, we examined how the scaling of plant N to P may respond to global change factors in a Loess grassland in northwestern China.

We found that precipitation reduction (PR) and warming decreased plant P concentrations, while N addition increased plant N concentrations, resulting in increased N:P ratios. The slopes of the linear regressions between plant N and P (i.e. log-transformed N versus P) did not change significantly, whereas the intercepts increased significantly under PR, warming and N addition. These results indicate that global change factors may not affect the synergistic variation of plant N and P, showing a closely coupled relationship between them. Our findings may help to better understand plant nutrient dynamics and element balance in a changing world.

As one of the most important agents driving floral evolution, pollinators shape the diversity of flowers in angiosperms. However, most previous studies have only quantified pollinators driving the evolution of a single floral trait, and experimental estimates of the potential role of pollinators in shaping the evolution of floral trait associations are relatively rare.

We experimentally identified and estimated the pollinator-mediated directional and correlational selection on single floral traits and trait combinations across 2 years in an orchid species, Spiranthes sinensis.

Pollinators mediated directional selection for an earlier flowering start date and larger corolla size. Pollinators mediated positive correlational selection on the combinations of floral display traits and negative correlational selection on the combinations of flowering phenology and floral display traits. In addition, the strength of selection differed over time. Our results highlight the potential role of pollinators in driving the evolution of floral trait combinations and suggest that it is necessary to consider floral character functional associations when seeking to understand and predict the evolutionary trajectory of flowers in angiosperms.

Subalpine coniferous species are distributed over a wide range of elevations in which they must contend with stressful conditions, such as high elevations and extended periods of darkness. Two evergreen coniferous species, Abies veitchii and Abies mariesii, dominate at low and high elevations, respectively, in the subalpine zone, central Japan. The aim of this study is to examine the effects of leaf age, elevation and light conditions on photosynthetic rates through changes in morphological and physiological leaf traits in the two species.

We here examined effects of leaf age, elevation and light conditions on photosynthesis, and leaf traits in A. veitchii and A. mariesii. Saplings of the two conifers were sampled in the understory and canopy gaps at their lower (1600 m) and upper (2300 m) distribution limits.

The two species showed similar responses to leaf age and different responses to elevation and light conditions in photosynthesis and leaf traits. The maximum photosynthetic rate of A. veitchii is correlated negatively with leaf mass per area (LMA) and non-structural carbohydrate (NSC) concentration. LMA increased at high elevations in the two species, whereas NSC concentrations increased only in A. veitchii. Therefore, the maximum photosynthetic rate of A. veitchiidecreased at high elevations. Furthermore, maximum photosynthetic rates correlate positively with nitrogen concentration in both species. In the understory, leaf nitrogen concentrations decreased and increased in A. veitchii and A. mariesii, respectively. LMA decreased and the chlorophyll-to-nitrogen ratio increased in understory conditions only for A. mariesii, suggesting it has a higher light-capture efficiency in dark conditions than does A. veitchii. This study concluded that A. mariesiihas more shade-tolerant photosynthetic and leaf traits and its photosynthetic rate is less affected by elevation compared with A. veitchii, allowing A. mariesii to survive in the understory and to dominate at high elevations.

Climate change in the eastern Mediterranean region will have a strong impact on ecosystem functioning and plant community dynamics due to a reduction in annual rainfall and increased variability. We aim to understand the role of seed banks as potential buffers against climatic uncertainty determined by climate change.

We examined germination strategies of 18 common species present along an aridity gradient. Data were obtained from soil seed banks germinated during nine consecutive years from arid, semi-arid, Mediterranean and mesic Mediterranean ecosystems. At the semi-arid and Mediterranean sites, rainfall manipulations simulating 30% drought and 30% rainfall increase were applied. Germination strategies were tested under optimal irrigation conditions during three consecutive germination seasons to determine overall seed germinability in each soil sample. Changes in germination strategy were examined using a novel statistical approach that considers the climatic and biotic factors that may affect seed germinability.

The results showed that dominant species controlled their germination fractions by producing seeds with a different yearly germination fraction probability. The amount of rainfall under which the seeds were produced led to two major seed types with respect to germinability: high germinability, seeds leading to transient seed banks, and low germinability, seeds leading to persistent seed banks. We conclude that differential seed production among wet and dry years of both seed types creates a stable balance along the aridity gradient, enabling the soil seed bank to serve as a stabilizing mechanism buffering against rainfall unpredictability. Additionally, we present a general model of germination strategies of dominant annual species in Mediterranean and arid ecosystems that strengthens the notion of soil seed banks as buffers against climatic uncertainty induced by climate change in the region.

Intensive land management practices can compromise soil biodiversity, thus jeopardizing long-term soil productivity. Arbuscular mycorrhizal fungi (AMF) play a pivotal role in promoting soil productivity through obligate symbiotic associations with plants. However, it is not clear how properties of plant communities, especially species richness and composition influence the viability of AMF populations in soils.

Here we test whether monocultures of eight plant species from different plant functional groups, or a diverse mixture of plant species, maintain more viable AMF propagules. To address this question, we extracted AMF spores from 12-year old plant monocultures and mixtures and paired single AMF spores with single plants in a factorial design crossing AMF spore origin with plant species identity.

AMF spores from diverse plant mixtures were more successful at colonizing multiple plant species and plant individuals than AMF spores from plant monocultures. Furthermore, we found evidence that AMF spores originating from diverse mixtures more strongly increased biomass than AMF from monocultures in the legume Trifolium repens L. AMF viability and ability to interact with many plant species were greater when AMF spores originated from 12-year old mixtures than monocultures. Our results show for the first time that diverse plant communities can sustain AMF viability in soils and demonstrate the potential of diverse plant communities to maintain viable AMF propagules that are a key component to soil health and productivity.

Ecological strategies related to the adaptation of plants to environmental stress have long been studied by ecologists, but few studies have systematically revealed the ecological process of plant adaptation to herbivores as a whole.

In this study, Stipa breviflora, the dominant species in the desert steppe of Inner Mongolia, was used to analyse its reproductive individual characteristics and seed traits as well as the soil seed bank and spatial patterns under heavy-grazing and no-grazing treatments.

The results showed that the number of reproductive branches positively affected the number of vegetative branches. The analysis of the soil seed bank showed that the density of S. breviflora seeds beneath reproductive S. breviflora individuals was significantly higher than that in bare land. The seed density was also significantly negatively correlated with the seed characteristics and the soil seed bank in bare land. The spatial distribution of S. breviflora was aggregated under heavy grazing. Our results suggest that under heavy grazing, reproductive activity plays a key role in resource allocation. Stipa breviflora evolved the ecological strategy of nearby diffusion by regulating the morphological characteristics of the seeds, which promotes a positive spatial correlation between the juvenile and adult populations at a small scale, thus leading to the formation of ‘safe islands’.

Bacteria and fungi are two primary groups of soil microbes, and their stability determines the persistence of microbial functions in response to a changing environment. Recent studies reported higher fungal than bacterial stability under precipitation alteration, the underlying mechanisms, however, remain elusive.

A 3-year precipitation manipulation experiment in a semi-arid grassland was used to compare the bacterial and fungal diversities, including alpha diversity, beta diversity and microbial community composition turnover, in response to precipitation manipulations. A framework is proposed to understand the stability properties of bacteria and fungi under precipitation alteration. We conceived a diagrammatic valley to illustrate microbial stability with the depth representing resistance and the width ecological resilience.

We found that ±60% in precipitation significantly reduced the richness and increased the evenness of bacteria but had trivial impacts on fungi. Precipitation alteration yielded stronger impacts on the variation in alpha diversity of bacteria than fungi, suggesting that the bacterial community is more sensitive to water stress than the fungal community. Moreover, fungi had wider composition turnover than that of bacteria, indicating higher composition variation of fungi than bacteria. The population turnover of fungi, reflected by composition variation, coefficient variation of diversity index and composition turnover, was larger than that of bacteria at both temporal and spatial scales, indicating the population turnover promotes fungal stability. The higher stability of fungal community in tolerating water stress is analogous to a ball in a wide valley that swing substantially but remain close to its steady state; while the lower stability of bacteria community is analogous to a ball that swings slightly but stay far away from its steady state. Our finding that the fungal community had higher stability than bacterial community in a semi-arid grassland might be applicable to other biomes.