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The interaction between plant diversity and soil physicochemical factors has been predicted to influence the variation in soil microbial diversity across space and time; however, only limited robust evidence has been found to support this prediction at broad scale. We examined the relationships between plant community functional attributes (i.e., community-weighted mean (CWM) and functional trait diversity (FD)) and soil microbial diversity in Tibetan alpine meadows under different environmental regimes. Soil bacterial diversity was weakly associated with plant species diversity but was significantly associated with both CWM and FD of five key functional traits, explaining nearly half of the variation in soil bacterial diversity. Soil bacterial diversity was positively associated with CWM and FD of plant height, leaf specific area, and leaf phosphorus but was negatively associated with CWM of leaf dry matter content. These results provide robust evidence supporting the theoretical prediction that the plant community functional attributes can explain variation in soil bacterial diversity. In addition, these results provide novel insights that could facilitate the understanding of the mechanisms of assembly of soil microbial diversity.

With rapid changes in climate conditions and grazing regimes, a decline in soil quality has become a main challenge for sustainability of Tibetan rangeland. Increasing evidence highlights the significance of plant biomass, but few studies test the role of realistic loss of plant diversity in impacting soil quality. We hypothesized that loss of species diversity will decrease soil quality, not only through lost standing biomass (i.e., “mass effect”) but also directly via the loss of the “diversity effect”. Considering the realistic loss of species diversity following overgrazing, grazing exclusion and climate change, we experimentally removed grass, sedge and various forb species from a Tibetan alpine meadow to test this hypothesis. After target plant species had been removed for five years, we examined the effect of the species removal on the plant community and soil quality with Bayesian linear mixed effect models and inferred potentially causal linkages between plants and soil with a Bayesian network. Results showed (i) overall, plant species removal not only significantly decreased plant diversity and standing biomass but also decreased soil organic matter and nutrients; (ii) the standing biomass decreased more pronouncedly in response to the removal of sedge and grass species, but plant diversity and soil nutrients decreased more pronouncedly in response to the removal of various forb species; and (iii) the loss of species diversity rather than standing biomass was directly associated with the decline in the soil quality, especially a decrease in soil available P. In short, our results indicate that realistic loss of plant species diversity can decrease soil quality in a Tibetan alpine meadow through lost the “diversity effect”. The functional significance of plant species diversity in maintaining soil quality supports the expectation of local pastoralists that diverse plants, promoted by traditionally rotational grazing, can ensure the sustainability of alpine soil and Tibetan rangeland.

Climate warming has substantially advanced spring leaf flushing, but winter chilling and photoperiod co-determine the leaf flushing process in ways that vary among species. As a result, the interspecific differences in spring phenology (IDSP) are expected to change with climate warming, which may, in turn, induce negative or positive ecological consequences. However, the temporal change of IDSP at large spatiotemporal scales remains unclear. In this study, we analyzed long-term in-situ observations (1951-2016) of six, coexisting temperate tree species from 305 sites across Central Europe and found that phenological ranking did not change when comparing the rapidly warming period 1984-2016 to the marginally warming period 1951-1983. However, the advance of leaf flushing was significantly larger in early-flushing species EFS (6.7 +/- 0.3 days) than in late-flushing species LFS (5.9 +/- 0.2 days) between the two periods, indicating extended IDSP. This IDSP extension could not be explained by differences in temperature sensitivity between EFS and LFS; however, climatic warming-induced heat accumulation effects on leaf flushing, which were linked to a greater heat requirement and higher photoperiod sensitivity in LFS, drove the shifts in IDSP. Continued climate warming is expected to further extend IDSP across temperate trees, with associated implications for ecosystem function.

Grazing is the primary land‐use activity on the Tibetan Plateau and can affect soil microbes and their function through aboveground vegetation removal, animal trampling, and manure deposition. Two distinct grazing systems (i.e., winter grazing [WG] and annual grazing [AG]) dominate on the Tibetan Plateau, but their effects on soil microbes have rarely been assessed. Taking advantage of a 5‐year field experiment that controlled timing and density of grazers via fence exclosures, we examined impacts of different grazing practices on the biomass, diversity, and composition of the soil microbial community in a Tibetan alpine meadow. On the basis of high‐throughput sequencing, we found that grazing had no significant effects on bacterial and fungal α‐diversities but altered their community compositions. Although total soil carbon (TC), total soil nitrogen (TN), and carbon/nitrogen (C/N) were related to both bacterial and fungal community compositions, plant shoot biomass only correlated with bacteria, and soil pH and moisture significantly influenced fungi under grazing. Also, grazing altered plant community composition but did not lead to corresponding changes in bacterial or fungal community composition. Moreover, grazing practices affected the relative abundance of specific bacterial and fungal taxa, reducing Actinobacteria but increasing Basidiomycete fungi in WG. Soil TC and TN were higher, and the soil microbial community was more stable in AG than WG, likely due to more stable litter inputs in AG. Together, these results showed that AG was less disruptive to soil microbes, suggesting that AG may provide a viable option for sustainable utilization and conservation of these fragile alpine systems.

Increasing effort has been devoted to restoring coastal ecosystems to counteract their degradation globally. Restoration success of coastal ecosystems often relies on harnessing biotic interactions that shape the performance of foundation plant species. Crabs acting as essential ecosystem engineers and consumers are commonly present in coastal saltmarshes. Previous work has focused on the grazing effect of crabs on plants. In line with the idea of top-down control, plant performance (in terms of biomass or height) is often used as indicators of plant-animal interactions. However, crabs could also produce facilitative effects through non-consumptive behavior. It remains unclear if and to what extent the net effect of crabs on coastal plants is dependent on environmental context. Therefore, systematic assessments are needed to test if the reliability of plant performance as an indicator of plant-crab interactions is context-dependent. Here, we conducted field survey in two similar intertidal saltmarsh ecosystems along the Yellow Sea coast, eastern China, and examined the effects of crab burrowing, soil properties, and nutrient availability on plant (Suaeda salsa) performance using multiple regression and structural equation models. We found that crab burrow density was significantly correlated with plant height, which signals strong plant-crab interactions. Surprisingly, we observed opposite signs (positive vs. negative) of plant-crab relationships between the two study sites that have highly similar composition and structure of plant communities. A possible explanation is that soil compactness can mediate crab burrowing behavior, resulting in differential facilitative effects on the plants. Thus, the usefulness of plant height serving as an indicator of plant-crab interactions depends on environmental context to a substantial degree. More comprehensive indicators taking into account soil compactness may facilitate robust inference of plant-crab interactions. Our results highlight landscape-scale spatial heterogeneity and context-dependency of plant-animal interactions in coastal saltmarshes, and provide a useful implication to inferring nuanced biotic interactions using compressive biotic and abiotic indicators in coastal ecosystems.

The effects of grazing-induced dung deposition on plant growth and soil attributes are well established, but little is known about dung effects on litter decomposition. Here, we tested effects of yak dung on litter decomposition and nutrient content in a Tibetan alpine meadow. We incubated litter of four common alpine meadow species using litter bags in the field. Two low-quality species (Kobresia capillifolia and Elymus nutans) with low nitrogen (N), high C/N and Lignin/N, and two high-quality species, (Saussurea nigrescens and Thermopsis lanceolata) were incubated in monoculture with and without dung addition. Mass loss of leaf litter, fibre fraction (cellulose, hemi-cellulose and lignin), N and phosphorus (P) were measured after 6, 12 and 18 months of incubation in the field. Dung addition significantly increased decomposition constants for low-quality litter species, but not for high-quality litter species. Dung addition promoted cellulose and hemi-cellulose loss, but lignin loss was not affected by dung addition, except after 12 months for high-quality litter species. Dung reduced N immobilization after 6 months and did not affect subsequent release in low-quality litter species, and promoted N release after 6 and 12 months in high-quality litter species. Regardless of litter quality, dung increased P release after 6 and 12 months. Our results suggest grazing-induced dung deposition may accelerate C and nutrient turnover, primarily through increasing the mass loss of low-quality litter, P release from litter and N release from high-quality litter. The mechanisms underlying the effects of dung deposition need to be clarified in future studies.

UV-B radiation is known to affect plant physiology and growth rate in ways that can influence community species composition and structure. Nevertheless, comparatively little is known about how UV-B radiation induced changes in the performance of individual species cascades to affect overall community properties. Because foliage leaves are primarily responsible for photosynthesis and carbon gain and are the major organ that senses and responds to UV-B radiation, we hypothesized that, under reduced UV-B radiation, species with larger leaf areas per plant would manifest higher growth rates and hence tend to improve their community status compared to species with smaller leaf areas per plant in herbaceous plant communities. We tested this hypothesis by examining plant traits (leaf area per plant and plant height), plant growth rate (aboveground biomass per plant and plant biomass per area) and community status (species within-community relative biomass) for 19 common species in a two-year field experiment in an alpine meadow on Tibetan Plateau. Aboveground biomass per plant, as well as per area, progressively increased in a 39% reduced (relative to ambient) UV-B treatment during the experimental period. At the second year, 11 out of 19 species significantly or marginally significantly increased their plant height, leaf area per plant and aboveground biomass per plant. No species was negatively affected by reducing UV-B. As hypothesized, the increase in aboveground biomass per plant increased with increasing leaf area per plant, as indicated by cross-species regression analysis. Moreover, the change in species within-community status increased with increasing leaf area per plant. Our study demonstrates that UV-B radiation has differential effects on plant growth rate across species and hence significantly affects species composition and plant community structure. We suggest that UV-B radiation is an ecological factor structuring plant communities particularly in alpine and polar areas.

Traits that favor rapid plant growth are expected to have an important influence on species relative abundance (SRA) in semi-natural grasslands where competitive exclusion is reduced by grazing. However, which traits are more strongly associated with variation in SRA remains largely unknown, especially in P-limited but species-rich grasslands. We assessed the relative importance of traits predicting SRA in P-limited Tibetan alpine meadows subject to long term grazing. We assessed abundance in terms of both aboveground biomass and ramet numbers in relation to seven traits (specific leaf area, LDMC: leaf dry matter content, leaf carbon concentration, leaf nitrogen concentration, LPC: leaf phosphorus concentration, mature height, and seed size) for all component species in grazed and ungrazed plots in each of three contrasting sites on the Tibetan Plateau. We used CATS regression (i.e. regression for Community Assembly through Trait Selection) to quantify the relative importance of different traits in predicting SRA, and tested dependence of trait importance values on both environmental context and alternative measures of abundance. Species were primarily differentiated along a trade-off axis involving traits promoting nutrient acquisition for fast growth vs resource conservation and competitive ability. A higher LPC consistently was the most important trait predicting species abundance in grazed plots, while species with low LPC but higher LDMC held an advantage in ungrazed plots. This suggests that in competition-released communities, species with a high ability to uptake soil available P tend to become abundant, while in competition-dominated communities, species using fixed P efficiently do better. The relative importance of traits in ungrazed plots did not change across sites, but in grazed plots species that have traits associated with nutrient conservation were favored in colder and drier conditions. The results highlight the importance of traits affecting acquisition of soil available P in these Tibetan alpine meadow communities. Species tradeoffs in nutrient acquisition versus conservation are a primary determinant of SRA, but the relative importance of traits depended on both environmental context and whether SRA was estimated as above-ground biomass or as number of ramets.

Pastoralists claim that traditional management practices involving light to moderate grazing ensure sustainable yield and promote the multifunctional services provided by rangeland ecosystems. Nectar production is a key ecosystem function crucial to successful apiculture and to the sustainability of services provided by pollinators in the Tibetan alpine rangeland. Here, we evaluated whether traditional (light to moderate) grazing promotes plant biodiversity and nectar production at the level of individual plants and at the level of an entire community. We compared plant species diversity and nectar production of the dominant nectariferous species ( Saussurea nigrescens ) at the individual plant level and at the community level in ungrazed, lightly grazed, moderately grazed, and heavily grazed plots in each of three Tibetan alpine meadow sites. Individual nectar production was quantified as nectar volume × floret number per capitulum × capitulum per plant. Community nectar production was calculated as individual nectar production × the number of flowering plants per 1.0 m 2 plot. We found that nectar production at the floret, individual, and community levels was significantly higher in lightly and moderately grazed plots compared to heavily grazed or ungrazed plots. This somewhat counterintuitive observation (particularly with regard to ungrazed plots) resulted from the fact that light and moderate grazing increased floret and capitulum number, and the number of flowering individuals per plot as a result of lowered competition for light. Moreover, species richness was significantly correlated with nectar production (as a result of light to moderate grazing) both at the individual level and at the community level. These results support the traditional view that light to moderate grazing not only promotes plant biodiversity but also ensures a sustainable yield in nectar production (and forage). Thus, traditional grazing management practices are more “eco-friendly” compared to recent and widespread practices involving either grazing exclusion or overgrazing in the Tibetan rangelands examined in this study.

Pastoralists on Eurasian rangeland often believe that traditional management practices involving moderate rotational grazing ensure sustainable yield, increase plant digestibility and promote biodiversity. To assess the generality of these suppositions we compared biomass production, community leaf C, N and P stoichiometry, leaf trait diversity and carbon and nutrient pools in root and soil for moderately grazed vs. ungrazed plots in Tibetan alpine meadows. We used five leaf traits (leaf C, leaf N and leaf P concentrations; SLA: specific leaf area, and LDMC: leaf dry matter content) as indicators of plant digestibility and rangeland quality. We measured these foliar traits and the ramet numbers for component species in moderately grazed plots as well as in exclosures (3–11 years) at five sites across the Qinghai-Tibetan plateau. Community weighted mean (CWM) trait values and functional dispersion (FDis) were used to quantify the mean and the variance in the distribution of trait values, respectively. Both the leaf P CWM and leaf P FDis generally increased under grazing and the LDMC CWM decreased, leading to improved plant digestibility and rangeland quality (e.g. high, community-wide leaf nutrients). The leaf C CWM , leaf N CWM and SLA CWM increased under grazing but the FDis of these traits tended to decrease. Grazing generally increased species diversity but decreased aboveground biomass, organic carbon, and nutrient concentrations in soil and root, especially decreasing root nitrogen and soil available phosphorus. Both root biomass and the leaf C:N CWM decreased in grazed plots at wet sites, but increased at dry sites. The community-wide increase and greater interspecific diversity in leaf nutrient concentrations coupled with decreasing LDMC CWM show that grazing induced an increase in plant digestibility, nutrient concentrations, and nutrient diversity in these alpine meadows. However, this increase in forage quality comes at the cost of losses in both carbon stock and nutrient availability that depress biomass production. Our findings and a review of related literature suggest that traditional grazing practices involve a trade-off between short-term yield and sustainability, a management challenge that must be addressed on rangelands with low soil fertility.

Plant community diversity and ecosystem function are conditioned by competition among co-occurring species for multiple resources. Previous studies suggest that removal of standing biomass by grazing decreases competition for light, but coincident grazing effects on competition for soil nutrients remain largely unknown in Tibetan rangelands where grazing tends to deplete soil phosphorus availability. We measured five functional traits indicative of plant productivity and stoichiometry leaf carbon concentration (LCC), leaf nitrogen concentration (LNC), leaf phosphorus concentration (LPC), specific leaf area (SLA), leaf dry matter content (LDMC) for component species of plant communities in grazed and ungrazed plots in five Tibetan alpine meadows. We examined the diversity of traits singly Rao index of functional diversity (FDrao) and in aggregate functional richness (FRic), functional divergence (FDiv), and functional evenness (FEve) in response to grazing. We tested whether foliar trait diversity increases with nutrient competition but decreases with light competition when competitive exclusion is reduced by grazing. The FDrao of LPC significantly increased under grazing, but FDrao for LCC, LNC and SLA tended to decrease. The FDrao of LDMC increased at the drier site but decreased at the wettest site. There was a strong negative association between increase in FDrao of LPC and decrease in soil nutrients, especially soil phosphorus availability. The FRic for all five traits together increased with species diversity following grazing, but neither FDiv nor FEve differed significantly between grazed and ungrazed plots at most sites. Grazing in Tibetan alpine meadows tends to increase competition for soil phosphorus while decreasing competition for light, resulting in an increase in the functional richness in grazed plant communities without any significant changes in the overall functional diversity of foliar traits. Our study highlights the potential importance of grazing mediated competition for multiple resources in alpine meadow ecosystems.

In competition‐dominated communities, traits promoting resource conservation and competitive ability are expected to have an important influence on species relative abundance (SRA). Yet, few studies have tested the trait‐abundance relations in the line of species trade‐off in resource conservation versus acquisition, indicating by multiple traits coordination. We measured SRA and key functional traits involving leaf economic spectrum (SLA, specific leaf area; LDMC, leaf dry matter content; LCC, leaf carbon concentration; LNC, leaf nitrogen concentration; LPC, leaf phosphorus concentration; Hs, mature height) for ten common species in all plots subjected to addition of nitrogen fertilizer (N), phosphorus fertilizer (P), or both of them (NP) in a Tibetan alpine meadow. We test whether SRA is positively related with traits promoting plant resource conservation, while negatively correlated with traits promoting plant growth and resource acquisition. We found that species were primarily differentiated along a trade‐off axis involving traits promoting nutrient acquisition and fast growth (e.g., LPC and SLA) versus traits promoting resource conservation and competition ability (e.g., large LDMC). We further found that SRA was positively correlated with plant height, LDMC, and LCC, but negatively associated with SLA and leaf nutrient concentration irrespective of fertilization. A stronger positive height‐SRA was found in NP‐fertilized plots than in other plots, while negative correlations between SRA and SLA and LPC were found in N or P fertilized plots. The results indicate that species trade‐off in nutrient acquisition and resource conservation was a key driver of SRA in competition‐dominated communities following fertilization, with the linkage between SRA and traits depending on plant competition for specific soil nutrient and/or light availability. The results highlight the importance of competitive exclusion in plant community assembly following fertilization and suggest that abundant species in local communities become dominated at expense of growth while infrequent species hold an advantage in fast growth and dispersals to neighbor meta‐communities.

The link between biodiversity and grassland productivity remains a central puzzle for both theoretical and applied ecologists. Little is known about the response of functional diversity (FD, i.e. the extent of trait differences between organisms in a given community) to increased grassland productivity following fertilization. Species diversity is often used as a surrogate for FD but evidence shows that FD is often independent from species diversity. We conducted a three-year (2004–2006) experiment in a Tibetan alpine grassland to examine the effect of fertilization on FD and SD, and its relationship with productivity. We measured specific leaf area, plant height and seed size for 32 species in control, low- and high-fertilization treatments over three years, and quantified three components of FD: functional richness (FRic), functional evenness (FEve) and functional divergence using Rao's index (FDrao). While SD decreased rapidly, as expected, both FRic and FDrao increased significantly with fertilization. Neither species evenness nor FEve was affected by fertilization. Aboveground biomass was not significantly correlated with SD, but it was significantly positively correlated with both FRic and FDrao, with the strongest correlations found in 2006 for FRic and in 2005 for FDrao. The results showed that FD and SD have opposite responses to short-term fertilization. The increased FD suggests enhanced niche differentiation between species remaining after fertilization, which caused species loss. This study highlights the importance of examining FD in assessing fertilization-induced biodiversity loss and its impacts on ecosystem functioning in grasslands.

Frequent outbreaks of plateau pika (Ochotona curzoniae) have become a major challenge for the sustainability of Tibetan rangeland, although top-down control has been widely employed since the 1960s over the plateau. Based on studies on plant trait-mediated soil-plant-herbivore relations, we hypothesized that impoverished soil was a consequence of rangeland degradation as well as a cause of increasing pika numbers through lowered functional trait diversity (FD) of the plant community that provides advantages for pika fitness. At three sites of alpine meadows on the eastern Tibetan Plateau, we counted active burrows of pika in 27 plots (i.e., 9 plots per site) distributed along a gradient of soil fertility. For every plant species within each plot, we measured five functional traits (e.g., mature height, SLA: specific leaf area, LDMC: leaf dry matter content, and leaf N and P: leaf nitrogen and phosphorus concentrations), indicating plant performance in response to changing soil fertility and impacting the fitness of pika. We employed Bayesian regression, structural equation modeling and network analyses to assess causal relations from soil fertility to FD and burrow density. The results show i) there was no significant difference in burrow density between three sites; spatial variation among plots in terms of soil fertility, plant species diversity and FD accounted for 57%–72%, 26%–41% and 59%–73%, respectively, of the variation in burrow density; ii) the burrow density was associated positively with soil moisture and organic matter, plant coverage, forb abundance and FD of leaf P, but negatively with soil nutrients, plant species diversity and FD for SLA, height and leaf N; and iii) deficiency of soil P potentially resulted in an increase in pika density, likely through lowered FD of SLA and height, with other soil factors and FD of leaf nutrients indirectly associated with burrow density. Our study suggested that under the joint effect of intensive grazing by livestock and output of livestock products from region, deficiency of soil P potentially increased pika density, likely by supporting more and diverse food resources while decreasing the risk of being preyed upon. Control of pika outbreak should pay more attention to bottom-up restoration of degraded soil and vegetation via traditional rotational grazing and promotion of recycling and compensation of lost soil P and plant trait diversity.

The “energetic equivalence rule” predicts that abundance should always scale as the −3/4 power of body size within a trophic group, but if the body size–abundance allometry (BSA) of soil fauna in fact is labile then the relationship could potentially be used as a standard descriptor for shifts in community functional structure in response to environmental change. To assess the possibility that the BSA could serve as an index of community functional structure, we measured the effect of fertilization on the slope and intercept of the BSA in nematode communities in a rice–wheat crop rotation over three years. Fertilization increased the BSA intercept but did not affect the slope in either rice or wheat phases, which highlights the stable scaling of BSA.

Background: The adaptation, evolution and function of flower colour diversity in response to changing environments are one of the oldest puzzles in plant ecology. It is logical that comparative studies on fitness of flower colour would be the most meaningful if they were conducted on the same genotype. Aims: We used Gentiana leucomelaena, which produces both white and blue flowers on different tillers of the same individual, as a model species to test adaption and fitness differences of contrasting flowers in contrasting environments. Methods: We examined seed production by white and blue flowers in response to increased temperatures (28 °C/2 °C vs. 12 °C/2 °C; 12 h light/12 h dark) in a climate chamber study and to watering in the field (+1.5 l m−2 d−1 vs. control with no supplementary irrigation). Results: For white and blue flowers warming decreased but watering increased seed number. Increased temperature and watering increased the size of seeds from white flowers, but neither warming nor watering sig...

Due to the role leaf phenolics in defending against ultraviolet B (UVB) under previously controlled conditions, we hypothesize that ultraviolet radiation (UVR) could be a primary factor driving the variation in leaf phenolics in plants over a large geographic scale. We measured leaf total phenolics, ultraviolet-absorbing compounds (UVAC), and corresponding leaf N, P, and specific leaf area (SLA) in 151 common species. These species were from 84 sites across the Tibetan Plateau and Inner Mongolian grasslands of China with contrasting UVR (354 vs. 161 mW/cm(2) on average). Overall, leaf phenolics and UVAC were all significantly higher on the Tibetan Plateau than in the Inner Mongolian grasslands, independent of phylogenetic relationships between species. Regression analyses showed that the variation in leaf phenolics was strongly affected by climatic factors, particularly UVR, and soil attributes across all sites. Structural equation modeling (SEM) identified the primary role of UVR in determining leaf phenolic concentrations, after accounting for colinearities with altitude, climatic, and edaphic factors. In addition, phenolics correlated positively with UVAC and SLA, and negatively with leaf N and N: P. These relationships were steeper in the lower-elevation Inner Mongolian than on the Tibetan Plateau grasslands. Our data support that the variation in leaf phenolics is controlled mainly by UV radiation, implying high leaf phenolics facilitates the adaptation of plants to strong irradiation via its UV-screening and/or antioxidation functions, particularly on the Tibetan Plateau. Importantly, our results also suggest that leaf phenolics may influence on vegetation attributes and indirectly affect ecosystem processes by covarying with leaf functional traits.

Aims Plants can change in phenology and biomass allocation in response to environmental change. It has been demonstrated that nitrogen is the most limiting resource for plants in many terrestrial ecosystems. Previous studies have usually focused on either flowering phenology or biomass allocation of plants in response to nitrogen addition; how ever, attempts to link flowering phenology and biomass allocation are still rare. In this study, we tested the effects of nitrogen addition on both flowering phenology and reproductive allocation in 34 common species. We also examined the potential linkage between flowering time and reproductive allocation in response to nitrogen addition. Methods We conducted a 3-year nitrogen addition experiment in Tibetan alpine meadow. We measured first flowering date and the repro ductive allocation for 34 common plant species in control, low and high nitrogen added plots, respectively. One-way analysis of variance was used to examine differences of first flowering date and reproductive allocation among treatments. The relationships between the change in species first flowering date and change in reproductive allocation in response to nitrogen addition were exam ined by calculating Pearson correlation coefficients. Important Findings For most species, both first flowering date and reproductive alloca tion significantly responded to nitrogen addition. Nitrogen addition significantly delayed the first flowering date and reduced the reproductive allocation for all graminoid species, but accelerated flower ing and increased reproductive allocation for most forb species. We found that changes in first flowering date significantly negatively correlated with the changes in reproductive allocation over spe cies in response to nitrogen, which indicated a positive relationship between flowering response and plant performance in reproductive allocation. Species that advanced their flowering time with nitrogen addition increased their reproductive allocation, whereas those that delayed flowering time tended to decline in reproductive alloca tion with nitrogen addition. Our results suggest that species-specific switch from vegetative growth to reproductive growth could influ ence species performance.

Productivity of artificial grassland communities was investigated in a 6-year field experiment on the Qinghai-Tibetan Plateau. In the experiment, assemblages varying in seven species compositions and four density gradients were grown in fertilized and non-fertilized subplots. We measured biomass of sown species as an indicator of community productivity. In general, 6-years of experiments indicated that: (i) species composition had a significant influence on community productivity. During the initial phase of the experiment, sown density significantly affected community productivity, but the effects disappear with the increase of grown years. This productivity increased with biodiversity increase and fertilization, while the biodiversity effects disappeared when the influence of composition was removed. (ii) The increase of community productivity with biodiversity was resulted from joint effects of selection and complementarity. (iii) With an increase of growth time, the selection effects become weaker while complementarities become enhanced. Influence of density on both effects was significantly different in early stages, but ultimately this all became insignificant. Fertilization dramatically increased the complementarity effects in all experiment processes, but had different influences on selection effects during different experimental period.

Allelopathy is an important process in plant communities, but the role of seed allelopathy in natural ecosystems remains poorly understood. In the present study, we examined the potential allelopathic effects of Ligularia virgaurea (a dominant species in degraded Tibetan grasslands) seeds on the germination of four native grass species (Festuca sinensis, Agrostis gigantean, Bromus inermis, and Elymus nutans). The results showed that L. virgaurea seeds can have potential allelopathic effects on seed germination, mean time to germination and root growth rates of native grass species. We further demonstrate that these effects are driven by a water-soluble seed leachate. Species with smaller seeds were generally more sensitive than larger seeded species. The results suggest that seed-to-seed allelopathic potential may be an important mechanism driving the dominance of L. virgaurea in degraded alpine grasslands on the Tibetan Plateau. Further studies are required to demonstrate effects of seed-to-seed potential allelopathy in a field setting.

Above- and belowground biomass allocation not only influences growth of individual plants, but also influences vegetation structures and functions, and consequently impacts soil carbon input as well as terrestrial ecosystem carbon cycling. However, due to sampling difficulties, a considerable amount of uncertainty remains about the root: shoot ratio (R/S), a key parameter for models of terrestrial ecosystem carbon cycling. We investigated biomass allocation patterns across a broad spatial scale. We collected data on individual plant biomass and systematically sampled along a transect across the temperate grasslands in Inner Mongolia as well as in the alpine grasslands on the Tibetan Plateau. Our results indicated that the median of R/S for herbaceous species was 0.78 in China's grasslands as a whole. R/S was significantly higher in temperate grasslands than in alpine grasslands (0.84 vs. 0.65). The slope of the allometric relationship between above- and belowground biomass was steeper for temperate grasslands than for alpine. Our results did not support the hypothesis that aboveground biomass scales isometrically with belowground biomass. The R/S in China's grasslands was not significantly correlated with mean annual temperature (MAT) or mean annual precipitation (MAP). Moreover, comparisons of our results with previous findings indicated a large difference between R/S data from individual plants and communities. This might be mainly caused by the underestimation of R/S at the individual level as a result of an inevitable loss of fine roots and the overestimation of R/S in community-level surveys due to grazing and difficulties in identifying dead roots. Our findings suggest that root biomass in grasslands tended to have been overestimated in previous reports of R/S.

Whether grazing response of species abundance can be predicted by plant functional trait remains a challenge untested in a specific ecosystem. We measured species abundance and relevant functional traits for 30 common component species in a moderately grazed and a control community over 3 years (2005, 2006 and 2007) in a Kobresia capillifolia dominated alpine meadow on the Tibetan Plateau. Our objective was to examine species response to grazing and to test the relationship between the response of species abundance and functional traits in grazed and control habitats. Our results showed: i) in terms of species relative abundance and saturated height (the maximum height of an adult individual), most component species significantly decrease in response to moderate grazing and the effect differed among species and between functional groups. ii) The response of species abundance was significantly negatively correlated with saturated height, but not correlated with specific leaf area or seed size. We concluded that the response direction of species abundance to grazing can be predicted by functional traits, whereas it is a weak predictor of the extent of grazing response in species abundance.

International audience; 1. Reproductive biomass (RB) is a key component of plant life history. Because RB is allometric, it remains unclear whether the observed variations of RB in response to land use are driven only by a size dependency effect or if the partitioning of plant biomass may also shift independently of plant size. This question has not been addressed for all the main component species of a given plant community. 2. Here, we report the results of a 3-year experimental study conducted in Tibetan alpine grass-lands. The above- ground vegetative biomass (VB) and the RB of 32 species were measured during 2 years in control, grazed and fertilized plots. We estimated the allometric slope and intercept for 301 VB-RB bivariates, using type II regression analyses in order to disentangle size-dependent and size-independent effects of treatment on RB. 3. Our results indicate significant changes in the VB-RB allometric slope for 26 out of 102 cases in grazed plots, and 16 out of 88 cases in fertilized plots. Moreover, in cases where slopes were not affected by treatment, a significant change in the allometric intercept was found in 50% of the models. For these cases, intercepts which are indicative of the biomass invested in reproductive parts for a given VB - generally increased in grazed plots and decreased in fertilized plots. 4. Grazing and fertilization triggered a significant decreases or increases in the plant size for species, especially graminoids. However, we found no relationship between changes in allometric coefficients and magnitude of the biomass response. 5. At the interspecific level, the intercept, but not the slope, of the allometric VB-RB relationships was significantly affected by land use. Graminoids and forbs responded similarly to treatment. 6. Synthesis. We conclude that (i) size-dependent effects did not explain all the changes observed in RB following grazing and fertilization in alpine grasslands, and that (ii) changes in allometric intercept explained most of the size-independent variations both at the intra- and interspecific level. We discuss why size-independent changes in RB could be important for plant performance in changing environments.

International audience; Proposed mechanisms for explaining biodiversity loss due to fertilization include interspecific competition and assemblage-level thinning. The interspecific competition hypothesis (ICH) assumes a link between population changes and species competitive ability, which is related to functional traits such as biomass allocation patterns. Based on a 2-year fertilization experiment in an alpine meadow on the Tibetan Plateau, we attempted to explore the relationships between individual and population responses. Individual response was Measured by changes In plant biomass and biomass allocation, and population response was estimated by changes in species abundance. The results Suggested that following fertilization (1) changes in individual biomass differ among species and functional groups, (2) reproductive allocation tends to decrease for all species whereas leaf allocation generally increases for grasses but decreases for forbs, (3) a strong positive correlation exists between species relative abundance change and individual biomass response, and (4) species relative abundance change has a positive correlation with leaf allocation response, a negative correlation with stern allocation response, and no significant correlation with reproductive allocation response. We Conclude that the individual biomass responses and biomass allocation strategy can partly explain diversity loss due to fertilization, a result consistent with the ICH. (C) 2007 Gesellschaft fur Okologie. Published by Elsevier GmbH. All rights reserved.

Niche differentiation arising in functional trait diversity is expected to increase the potential for species coexistence, but empirical evidence for these relationships is sparse. We test whether grazing increases the functional diversity of leaf traits and niche differentiation in phosphorus limited Tibetan alpine meadows. We measured five traits in the leaf economic spectrum (LES; LC, leaf carbon concentration; LN, leaf nitrogen concentration; LP, leaf phosphorus concentration; SLA, specific leaf area; and LDMC, leaf dry matter content) for all species occurring in grazed and ungrazed plots at each of five sites. By comparing indicators of the fundamental and realized niches of co-occurring plants in both grazed and ungrazed plots, we quantified a grazing-mediated competitive effect on trait divergence and convergence. This trait response reflects the relative importance of niche differentiation and competitive exclusion in response to grazing. We found that while grazing induced LP divergence, both LC...

BackgroundUnderstanding the relationship between species traits and species abundance is an important goal in ecology and biodiversity science. Although theoretical studies predict that traits related to performance (e.g. reproductive allocation) are most directly linked to species abundance within a community, empirical investigations have rarely been done. It also remains unclear how environmental factors such as grazing or fertilizer application affect the predicted relationship.MethodologyWe conducted a 3-year field experiment in a Tibetan alpine meadow to assess the relationship between plant reproductive allocation (RA) and species relative abundance (SRA) on control, grazed and fertilized plots. Overall, the studied plant community contained 32 common species.Principal findingsAt the treatment level, (i) RA was negatively correlated with SRA on control plots and during the first year on fertilized plots. (ii) No negative RA-SRA correlations were observed on grazed plots and during the second and third year on fertilized plots. (iii) Seed size was positively correlated with SRA on control plots. At the plot level, the correlation between SRA and RA were not affected by treatment, year or species composition.Conclusions/significanceOur study shows that the performance-related trait RA can negatively affect SRA within communities, which is possibly due to the tradeoffs between clonal growth (for space occupancy) and sexual reproduction. We propose that if different species occupy different positions along these tradeoffs it will contribute to biodiversity maintenance in local communities or even at lager scale.