Responses of plant diversity and primary productivity to nutrient addition in a Stipa baicalensis grassland, China

Nutrient addition can affect the structure and diversity of grassland plant communities, thus alter the grassland productivity. Studies on grassland plant community composition, structure and diversity in response to nutrient addition have an important theoretical and practical significance for the scientific management of grassland, protection of plant diversity and the recovery of degraded grassland. A randomized block design experiment was conducted with six blocks of eight treatments each: control (no nutrient addition) and K, P, N, PK, NK, NP, and NPK addition. We evaluated plant composition, height, coverage, density, and aboveground biomass to estimate, primary productivity and plant diversity. Results showed that all treatments increased primary productivity significantly (P<0.05) with the exception of the K and the NPK treatments had the greatest effect, increasing aboveground biomass 2.46 times compared with the control (P<0.05). One-way ANOVA and factorial analysis were used for the species richness, Shannon-Wiener index, Pielou index and aboveground biomass, and the relationships between the diversity indices and aboveground biomass were determined through linear regression. We found that fertilization altered the community structure; N (but not P or K) addition increased the proportion of perennial rhizome grasses and significantly reduced that of perennial forbs (P<0.05), thus it presented a trend of decrease in species richness, Shannon-Wiener and Pielou indexex, respectively. Only the main effects of N had significant impacts on both the diversity indices and the aboveground biomass (P<0.05), and the interactions between N-P, N-K, P-K and N-P-K could be neglected. With fertilization, plant diversity (correlation coefficient, -0.61), species richness (-0.49), and species evenness (-0.51) were all negatively linearly correlated with primary productivity. The correlations were all significant (P<0.01). Scientific nutrient management is an effective way to improve grassland productivity, protect the plant diversity as well as recover the degraded grassland.