ß-diversity in temperate grasslands is driven by stronger environmental filtering of plant species with large genomes.

Elucidating mechanisms underlying community assembly and biodiversity patterns is central to ecology and evolution. Genome size (GS) has long been hypothesized to potentially affect species' capacity to tolerate environmental stress and might therefore help drive community assembly. However, its role in driving ß-diversity (i.e., spatial variability in species composition) remains unclear. We measured GS for 161 plant species and community composition across 52 sites spanning a 3200-km transect in the temperate grasslands of China. By correlating the turnover of species composition with environmental dissimilarity, we found that resource filtering (i.e., environmental dissimilarity that includes precipitation, and soil nitrogen and phosphorus concentrations) affected ß-diversity patterns of large-GS species more than small-GS species. By contrast, geographical distance explained more variation of ß-diversity for small-GS than for large-GS species. In a 10-year experiment manipulating levels of water, nitrogen, and phosphorus, adding resources increased plant biomass in species with large GS, suggesting that large-GS species are more sensitive to the changes in resource availability. These findings highlight the role of GS in driving community assembly and predicting species responses to global change.

The impacts of nitrogen deposition on community N:P stoichiometry do not depend on phosphorus availability in a temperate meadow steppe.

Nitrogen (N) enrichment has great consequences on several fundamental ecological processes through its impacts on plant nutrition traits (i.e. nutrient concentration and stoichiometric ratios); however, the extent to which the effects of N enrichment depend on phosphorus (P) availability are less well understood. While there is mounting evidence for the species-specific responses of plant nutrition traits to nutrient enrichment, we know little about the changes at the community-level. Here, we measured community-level biomass weighted (CWM) and non-weighted (CM) plant N and P concentrations and N:P ratio in a temperate meadow steppe after four years factorial N and P addition, with biomass and nutrition traits of each species in each plot being recorded. Nitrogen addition significantly increased community-level N concentration, decreased P concentration, and enhanced community N:P ratio. Phosphorus addition had no impacts on community-level N concentration, significantly increased P concentration, and reduced community N:P ratio. The impacts of N addition on community nutrition traits were not dependent on P addition and the community-level nutrition trait responses to N and P additions were primarily driven by intraspecific trait variation (ITV) rather than by species turnover. Community-level nutrition traits in the temperate meadow steppe were sensitive to the projected N and P enrichment. While nutrient enrichment had substantially changed community composition, its impacts on community nutrition traits were driven by ITV. Nitrogen deposition would result in imbalance of N and P in plant community, as indicated by the substantial increase in community-level N:P, which was not affected by increased P availability.

Convergent responses of nitrogen and phosphorus resorption to nitrogen inputs in a semiarid grassland.

Human activities have significantly altered nitrogen (N) availability in most terrestrial ecosystems, with consequences for community composition and ecosystem functioning. Although studies of how changes in N availability affect biodiversity and community composition are relatively common, much less remains known about the effects of N inputs on the coupled biogeochemical cycling of N and phosphorus (P), and still fewer data exist regarding how increased N inputs affect the internal cycling of these two elements in plants. Nutrient resorption is an important driver of plant nutrient economies and of the quality of litter plants produce. Accordingly, resorption patterns have marked ecological implications for plant population and community fitness, as well as for ecosystem nutrient cycling. In a semiarid grassland in northern China, we studied the effects of a wide range of N inputs on foliar nutrient resorption of two dominant grasses, Leymus chinensis and Stipa grandis. After 4 years of treatments, N and P availability in soil and N and P concentrations in green and senesced grass leaves increased with increasing rates of N addition. Foliar N and P resorption significantly decreased along the N addition gradient, implying a resorption-mediated, positive plant-soil feedback induced by N inputs. Furthermore, N : P resorption ratios were negatively correlated with the rates of N addition, indicating the sensitivity of plant N and P stoichiometry to N inputs. Taken together, the results demonstrate that N additions accelerate ecosystem uptake and turnover of both N and P in the temperate steppe and that N and P cycles are coupled in dynamic ways. The convergence of N and P resorption in response to N inputs emphasizes the importance of nutrient resorption as a pathway by which plants and ecosystems adjust in the face of increasing N availability.