Quantifying stoichiometry of crop N and P acquisition (i.e. removal from farmland) under different agronomic practices is essential for understanding nutrient budgets and optimizing N and P fertilizer application in agroecosystems. It is not clear how plant N and P uptake and N:P stoichiometry vary between monoculture and intercropping throughout an entire growing season under different N fertilization and mulching practices. Here, we addressed how plant interspecific competition for nutrients have affected the temporal dynamics of crop N and P uptake (and N:P ratios) in five cropping systems (wheat, maize and barley monocultures, and wheat/maize and barley/maize intercropping), under two N levels (0 and 225 kg N ha−1) and two maize mulching treatments (with and without). Wheat and barley had greater N and P competitive ability than maize, leading to an increase in N and P uptake of wheat and barley and a decrease in N and P uptake of maize during co-growth stages in intercropping. N:P ratios of three crop species decreased with plant growth. Crop-level N:P ratios were either not affected by intercropping or did not change consistently with N fertilization while film mulching decreased maize N:P ratios. Community-level N:P ratios of the two intercrops were different from those of the corresponding monoculture at maturity. Because (i) the proportion of N and P removal from intercropping differs from monocultures, and (ii) N and P uptake by crops is decoupled under N fertilization and mulching, these findings may have practical implications for the nutrient budget of intercropping systems.
The effects of contemporary climate, habitat heterogeneity and long-term climate change on species richness are well studied for woody plants in forest ecosystems, but poorly understood for herbaceous plants, especially in alpine–arctic ecosystems. Here, we aim to test if the previously proposed hypothesis based on the richness–environment relationship could explain the variation in richness patterns of the typical alpine–arctic herbaceous genus Saxifraga.
Using a newly compiled distribution database of 437 Saxifraga species, we estimated the species richness patterns for all species, narrow- and wide-ranged species. We used generalized linear models and simultaneous autoregressive models to evaluate the effects of contemporary climate, habitat heterogeneity and historical climate on species richness patterns. Partial regressions were used to determine the independent and shared effects of different variables. Four widely used models were tested to identify their predictive power in explaining patterns of species richness.
We found that temperature was negatively correlated with the richness patterns of all and wide-ranged species, and that was the most important environmental factor, indicating a strong conservatism of its ancestral temperate niche. Habitat heterogeneity and long-term climate change were the best predictors of the spatial variation of narrow-ranged species richness. Overall, the combined model containing five predictors can explain ca. 40%–50% of the variation in species richness. We further argued that additional evolutionary and biogeographical processes might have also played an essential role in shaping the Saxifraga diversity patterns and should be considered in future studies.
Acid grasslands are threatened both by agricultural intensification with nutrient addition and increased livestock densities as well as by land abandonment. In order to understand and quantify the effect of selected environmental and land-use factors on the observed variation and changes in the vegetation of acid grasslands, large-scale spatial and temporal pin-point plant cover monitoring data are fitted in a structural equation model. The important sources of measurement and sampling uncertainties have been included using a hierarchical model structure. Furthermore, uncertainties associated with the measurement and sampling are separated from the process uncertainty, which is important when generating ecological predictions that may feed into local conservation management decisions. Generally, increasing atmospheric nitrogen deposition led to more grass-dominated acid grassland habitats at the expense of the cover of forbs. Sandy soils were relatively more acidic, and the effects of soil type on the vegetation include both direct effects of soil type and indirect effects mediated by the effect of soil type on soil pH. Both soil type and soil pH affected the vegetation of acid grasslands. Even though only a relatively small proportion of the temporal variation in cover was explained by the model, it would still be useful to quantify the uncertainties when using the model for generating local ecological predictions and adaptive management plans.
Moso bamboo expansions into Japanese cedar forests are common. The expansion effects on soil nitrous oxide (N2O) emissions have not been thoroughly understood, and the underlying microbial mechanisms remain unclear. We studied bacterial and fungal contribution to soil N2O emissions under moso bamboo or Japanese cedar by applying bacterial or fungal inhibitors using streptomycin and iprodione, respectively. Soil N2O emissions were measured and the relative contribution of bacteria and fungi to soil N2O emissions was calculated. N2O emission from soil with moso bamboo was significantly higher than under Japanese cedar. Compared with control, bacterial or fungal inhibitor or their combination decreased N2O emissions, indicating substantial contribution of microbial activities to N2O emissions. However, the relative contribution of bacteria and fungi to N2O emissions was not affected by plants. Soil organic carbon, total and ammonium nitrogen were lower in soil under moso bamboo than Japanese cedar, suggesting faster microbial decomposition under moso bamboo. Fungal inhibitor and plants interactively affected soil pH, total phosphorus and ammonium nitrogen, while bacterial inhibitor and plants interactively affected total nitrogen, indicating substantial dependence of effects by microbial communities on plant species. Moso bamboo and Japanese cedar differed in their effects on soil N2O emissions with higher emissions under moso bamboo. Stimulation of N2O emission under moso bamboo might occur due to higher nitrogen mineralization and subsequent denitrification induced by high root exudation. These results highlight the need to consider the effect of species shifts on N2O emissions in forests.
Calcium (Ca) is an essential nutrient for plant growth and Ca concentrations in forage have important implications for ruminant diet and health. It remains an open question whether forage Ca concentration would be decreased by increasing nitrogen (N) deposition. We manipulated the increasing rates of N addition (2008–2015) in a semiarid grassland, northern China. Plant Ca concentrations for all species were examined in each plot under N treatment. The Ca concentrations at functional group and community levels were calculated based on the concentration of each species presented and their relative biomass in each plot. We found that community-level Ca concentration remained stable across a gradient of wide-ranged N addition rates, although Ca concentration at both species and functional group levels showed negative responses to N enrichment. Given that forbs had higher Ca concentration than grasses, the increasing relative biomass of forbs canceled out the negative responses of species-level and functional group-level Ca concentration. Our results further showed that community Ca pool showed a positive but saturating response to N addition, with a threshold at the rate of 10 g N m−2 yr−1. Our findings highlight the role of changes in plant relative biomass in controlling the responses of forage Ca concentration and stock to N enrichment.
Host-mediated effects on hemiparasitic mistletoes were hypothesized to contribute to mistletoes reproductive phenological asynchrony, thus providing a longer period of food supply to its mutualistic pollinators and dispersers. However, studies with empirical data interrogating this hypothesis are lacking. Weekly monitoring of flowering and fruiting patterns on a generalist mistletoe Dendrophthoe pentandra (Loranthaceae) was conducted for two consecutive years in tropical Xishuangbanna, Southwest China. We examined whether flowering and fruiting patterns were seasonal, quantified the degree of stagger within D. pentandra populations and determined the factors influencing the first flowering date (FFD) of D. pentandra. Furthermore, the effect of change in the number of host species on reproductive phenological asynchrony of mistletoe was examined. We found that (i) both flowering and fruiting exhibited unimodal peaks in the two consecutive years of the study; (ii) the FFD was significantly influenced by crown area of mistletoe and light, such that clump with larger crown and more light exposure had an earlier FFD and longer flowering and fruiting durations; (iii) different host species had a significant impact on the phenology of mistletoes. However, contrary to our hypothesis, the number of host species did not significantly change the asynchrony of reproductive phenology of mistletoe. Therefore, these results suggest that alternative hypotheses are needed to interpret the ecological significance of the number of host species and phenological asynchrony of generalist mistletoes.
While recent studies have shown the importance of intraspecific trait variation in the processes of community assembly, we still know little about the contributions of intraspecific trait variability to ecosystem functions. Here, we conducted a functional group removal experiment in an alpine meadow in Qinghai-Tibetan Plateau over 4 years to investigate the relative importance of inter- and intraspecific variability in plant height for productivity. We split total variability in plant height within each of 75 manipulated communities into interspecific variability (TVinter) and intraspecific variability within a community (ITVwithin). Community-weighted mean height among communities was decomposed into fixed community-weighted mean (CWMfixed) and intraspecific variability among communities (ITVamong). We constructed a series of generalized additive mixed models and piecewise structural equation modeling to determine how trait variability (i.e. TVinter, ITVwithin, CWMfixed and ITVamong) indirectly mediated the changes in productivity in response to functional group removal. Community productivity was not only affected directly by treatment manipulations, but also increased with both inter- and intraspecific variability (i.e. CWMfixed and ITVamong) in plant height indirectly. This suggests that both the ‘selection effect’ and a ‘shade-avoidance syndrome’ can incur higher CWMfixed and ITVamong, and may simultaneously operate to regulate productivity. Our findings provide new evidence that, besides interspecific variability, intraspecific trait variability in plant height also plays a role in maintaining net primary productivity.
Tropical and subtropical evergreen broad-leaved forests (EBFs) and needle-leaved forests (ENFs) in China exhibit complex leaf shedding strategies in responses to soil water availability, vapor pressure deficits (VPDs) and sunlight availability. However, the seasonal variations and triggers of litterfall differ significantly in tropical/subtropical forests, and there are still many uncertainties. Herein, we aim to explore the distinct climatic factors of seasonal litterfall in a climate–phenology correlation framework. We collected seasonal litterfall data from 85 sites across tropical/subtropical China and used linear correlation coefficients between sunlight and rainfall to partition synchronous/asynchronous climates. Additional phase analysis and structural equation model analysis were conducted to model the climatic triggers of tropical phenology. Results indicated two types of tropical litterfall phenology under two types of climates. In synchronous climates, where seasonal sunlight and rainfall are positively correlated, the litterfall peak of the unimodal phenology and the first litterfall peak of the bimodal phenology both happen at the end of dry season. The second litterfall peak of the bimodal phenology occurs at the end of rainy season due to water stress. In asynchronous climates, where seasonal sunlight and rainfall are negatively correlated, VPD shows consistent seasonal variations with incoming sunlight. The leaf senescence is accelerated at the end of dry season by higher VPD; while soil water deficit is in anti-phase with sunlight and mainly controls the second litterfall peak of the bimodal phenology in EBF. Our findings provide an important reference for modeling tropical phenology in Earth system models.
植物通过凋落叶、根系凋落物和根系分泌物向土壤输入有机碳，显著影响土壤碳储量。然而，高寒灌丛生态系统这3种植物碳输入途径对气候变暖的响应仍不清楚。本文通过为期3年的野外增温实验， 研究了青藏高原东部高寒灌丛优势种窄叶鲜卑花(Sibiraea angustata)凋落叶、根系凋落物和根系分泌物对 土壤碳输入的相对贡献及其对增温的响应。研究结果表明，窄叶鲜卑花通过凋落叶、根系凋落物和根系分泌物向土壤输入有机碳的数量分别为77.45、90.58和26.94 g C m-2。增温分别使凋落叶和根系凋落物有机碳输入轻微增加8.04和11.13 g C m-2，同时使根系分泌物有机碳输入显著增加15.40 g C m-2。增温使根系分泌物有机碳输入途径相对贡献显著增加4.6%，分别使凋落叶和根系凋落物有机碳输入途径相对贡献轻微降低了2.5%和2.1%。这些结果表明，在青藏高原高寒灌丛生态系统中，气候变暖主要通过促进根系分泌物输入途径而不是凋落物输入途径来增加植物源土壤有机碳的输入。
Wildfire is crucial in the regulation of nutrient allocation during the succession of boreal forests. However, the allocation strategies of carbon (C), nitrogen (N) and phosphorus (P) between leaves and fine roots in response to wildfire severities remain poorly studied. We aimed to explore the allocation strategies of C, N and P between leaves and fine roots among different fire severities. We selected four wildfire severities (unburned, low, moderate and high severity) after 10 years recovery in the Great Xing’an Mountains, northeast China, and compared C, N and P concentrations in leaves and fine roots of all species among fire severities using stoichiometry theory and allometric growth equations. Compared with unburned treatment, C concentrations in leaves and fine roots increased at low severity, and leaf N concentration was the greatest at high severity, but the lowest fine root N concentration occurred at high severity. Plant nutrient utilization tended to be P-limited at high fire severity according to the mean value of N:P ratio > 16. More importantly, C, N and P allocation strategies between fine roots and leaves changed from allometry to isometry with increasing fire severities, which showed more elements allocated to leaves than to fine roots with increasing fire severities. These changes in patterns suggest that the allocation strategies of elements between leaves and fine roots are of imbalance with the wildfire severity. This study deepens our understanding of nutrient dynamics between plant and soil in ecosystem succession.
Grassland reconstruction is a major approach to alleviate the ‘black beach’ in Sanjiangyuan of the Qinghai-Tibetan Plateau. It is vital to understand how to manage the planting grassland after reconstruction. And which artificial grassland management pattern is more likely to restore the degraded grassland of ‘black beach?’ To provide the scientific basis for the restoration of ‘black beach’, we investigated the changes in vegetation characteristics, soil physicochemical properties and soil microbial community structure of planting grassland under different management patterns, and explored the effect of the management patterns on community succession of planting grassland. In this study, vegetation characteristics and soil physicochemical properties were measured by field investigation and laboratory analyses, respectively. Soil microbial community composition was determined by high-throughput sequencing techniques. The results showed that there were significant differences in vegetation characteristics, soil physicochemical properties and soil microbial community structure of the planting grassland under different management patterns. Actinobacteria and Basidiomycota were mainly controlled by vegetation plant species diversity, aboveground biomass (AGB) and soil organic carbon (SOC). Shannon-Wiener index, AGB and SOC peaked and the relative abundance of amplicon sequence variants annotated by Actinobacteria and Basidiomycota were significantly enriched under the management pattern of the planting once treatment. Additionally, the soil had the highest bacterial diversity and the lowest fungal diversity under the planting once treatment, becoming a ‘bacterial’ soil. These vegetation characteristics and soil environment were more conducive to overall positive community succession, indicating that the planting once treatment is the most reasonable management pattern for restoring the ‘black beach’.
The role of biophysical variables in constructing community structure changes with the time since fire. The major objective of this study is to verify the transition stage and its underlying variables for the postfire forest and soil microbial function in the boreal forested area of China. A 50-year fire chronosequence was presented, and biomass of forbs, shrubs and woody plants was separately weighted to assess their contribution to the whole community with the year since fire (YSF). Simultaneously, soil biophysical properties were measured for stands in different time periods after fire. Soil microbial functions, i.e. growth efficiency (GE) and carbon use efficiency (CUE), were calculated based on ecoenzymatic and soil nutrient stoichiometry. In terms of vegetative structure, forbs’ proportion decreased from 75% to 1.5%, but the proportion of woody plants increased from 0.04% to 70% across this fire chronosequence. GE and CUE of soil microorganisms averaged 0.242 and 0.236 and were significantly higher in 9, 15 and 31 YSF than in 2 and 3 YSF. Soil metal content was significantly increased at the late stage of this fire chronosequence, and soil calcium content showed a positive correlation with woody plant biomass and a negative correlation with soil microbial function. Overall, the present work highlights that the time period of 15 and 31 YSF is a hallmark stage for aboveground vegetative structure and soil microbial function to change in different trends and that the calcium content may partly account for these two divergent trajectories.
Biodiversity is found to have a significant promotion effect on ecosystem functions in manipulation experiments on grassland communities. However, its relative role compared with stand factors or functional identity is still controversial in natural forests. Here, we examined their relative effects on biomass and productivity during forest restoration. We investigated stand biomass and productivity for 24 plots (600 m2) across restoration stages in the subtropical forests of Mt. Shennongjia, Central China. We measured five key functional traits and calculated functional diversity (functional richness, evenness and dispersion) and community-weighted mean of traits. We used general linear models, variation partitioning methods to test the relative importance of stand factors (density, stand age, maximum height, etc.), functional identity, species and functional diversity on biomass and productivity. Our results illustrated that stand biomass and productivity increased significantly as forest restoration, and that community species richness increased, while functional dispersion decreased significantly. Variation partitioning analyses showed that diversity had no significant pure effects on biomass and productivity. However, diversity may affect biomass and productivity through the joint effect with stand factors and functional identity. Overall, we found that stand factors had the strongest effect on biomass and productivity, while functional identity significantly affects productivity but not biomass, suggesting that modulating stand structure and species identity are effective ways to enhance forest carbon storage and sequestrations potential in forest management.
Litter is the crucial carrier of soil nutrition transformation. The influence of arbuscular mycorrhizal (AM) fungi on nutrient acquisition in plants has been widely recognized. However, in nutrient-deficient karst habitat, how competitive plants utilize nutrients regulated by AM fungi via litter remain largely unknown. The experimental treatments included the inoculation with or without Glomus etunicatum, the litter addition by the mixed leaves of Broussonetia papyrifera and Carpinus pubescens or no addition, and the competition through the intraspecific competition of B. papyrifera and C. pubescens, respectively, and the interspecific competition mixed both plants. AM fungi differently affected plant on nutrient acquisition, increasing nutrients acquisitions of B. papyrifera in intra- and interspecific competitions while decreasing for C. pubescens. Litter presented opposite influences on N acquisitions of both plants in interspecific competition with AM fungi, being positive for C. pubescens and negative for B. papyrifera, respectively. Under the interaction of AM fungi and litter, nitrogen (N), phosphorus (P) and potassium (K) acquisitions by B. papyrifera and N acquisition by C. pubescens in interspecific competition were all greater than intraspecific competition. In the interspecific competition, the competitive ability of plants on nutrient absorption presented significant species difference, which of B. papyrifera on P and K was significantly increased, while was converse for C. pubescens on K. In conclusion, these results suggest that the interspecific competition presents greater nutrient facilitation compared with intraspecific competition through AM fungi interacting with litter for plants in karst soil.
Forest edges have been well studied in temperate and tropical forests, but less so in open canopy forests. We investigated edge influence on plant species diversity and soil properties in sparse oak forest fragments. Data were collected along three transects from the edge to the interior of three small (under 10 ha) and three large (over 10 ha) oak forest fragments in Kermanshah Province, Iran. We measured herbaceous plants (<0.5 m in height) and soil attributes at 0 (forest edge), 25, 50, 100 and 150 m. We quantified species diversity using the Shannon index, used rarefaction to compare species richness between two different sizes of fragments and applied non-metric multidimensional scaling ordination to investigate the variation in species composition. We estimated the distance of edge influence using randomization tests. Generalized linear mixed models with post-hoc Tukey’s HSD tests were used to assess the effects of distance from edge and fragment size on diversity and soil properties. We found greater species richness, diversity and evenness at the edge of both small and large fragments and lower nitrogen and organic carbon at the edge compared to the interior of large fragments, with most changes within 50 m of the edge. Species composition, organic carbon and total nitrogen were significantly different between small and large fragments. Our findings of significant edge influence on herbaceous plants and soil properties in these sparse forests provide a significant contribution to the literature on edges, especially in relation to herbaceous plants.