Skip to main content
Dryad logo

Community functional structure modulates the responses of net primary productivity to application of various N compounds in a meadow steppe

Citation

Cai, Jiangping et al. (2020), Community functional structure modulates the responses of net primary productivity to application of various N compounds in a meadow steppe, Dryad, Dataset, https://doi.org/10.5061/dryad.02v6wwq1t

Abstract

1. Increasing atmospheric nitrogen (N) deposition influences grassland productivity. The deposited N contains various N forms with different ecological effects on community functions. However, how grassland primary productivity responds to community functional structure in relation to different N compounds remains largely unclear.

2. In this study, we examined the responses of aboveground primary productivity (ANPP) and community function composition to addition of three different N compounds (NH4NO3, (NH4)2SO4, and CO(NH2)2) at the rates of 0, 5, 10, 20 g N m-2 yr-1. We distinguished the functional responses into intraspecific variation (ITV) and species turnover. We used structural equation modeling (SEM) to evaluate how functional structure affects the responses of community productivity to various N compounds used.

3. We found that N addition increased community-level leaf chlorophylls contents but decreased leaf dry matter content and phosphorus content, irrespective of N forms. These changes were attributed to the intra-specific trait variation but not to species turnover. Functional dispersion (FDis) of all traits was reduced with N enrichment by species turnover. SEM analysis revealed that fertilizer effects rather than soil acidification played a more important role in mediating the responses of ANPP under CO(NH2)2 addition. CO(NH2)2 addition enhanced community productivity via decreasing FDis. By contrast, (NH4)2SO4 and NH4NO3 addition showed stronger soil acidification effect and influenced community productivity via its effects on CWM of functional traits.

4. Our results suggest that community’s responses to N deposition transfer from dominant species’ trait-aggregation to synergistic resistance of each individuals along with increasingly severe acidification. Our study further emphasizes the necessity of in situ experiments with various N compounds to accurately understand the ecological effects of future atmospheric nitrogen deposition on plant ecosystems.

Methods

We assessed the total aboveground biomass (g/m2) and the relative aboveground biomass of each species in a 1 m × 1 m randomly established quadrat in each plot in August 2017. All aboveground parts of vascular plants were harvested and sorted into species and then dried at 65℃ for 48h before weighing for dry biomass. After recording all species occurred in the studied quadrat of each plot, we collected fresh leaves for all those species within each plot, to measure their specific leaf area (SLA, the ratio of leaf area to leaf dry mass, cm2/g), leaf dry matter content (LDMC, the ratio of leaf dry mass to water saturated fresh mass, mg/g), leaf chlorophyll content (Chls, mg/g), and leaf phosphorus concentration based on mass (LPC, mg/kg) of all the emerging species.

In each plot, topsoil samples (0–10 cm) were taken from five random soil cores after removing litter and mixed to form one composite sample. Soil pH was determined in a 1:2.5 soil-to-water suspension with a pH electrode (S210 SevenCompact™, Mettler, Gießen, Germany).

Usage Notes

Community weighted mean (CWM) for each functional trait was weighted by the relative biomass of each species (Garnier et al., 2004). Community functional dispersion (FDis) was calculated based on the four functional traits and every single trait. FDis was calculated as the average distance of each individual species to the centroid of all species in the community trait space, and FDis of multi-trait is multi-dimensional index based on multi-trait space.

Funding

National Natural Science Foundation of China, Award: 31800398

China Postdoctoral Science Foundation, Award: 2018M640263