Responses of species diversity and aboveground biomass to nitrogen addition in fenced and grazed grassland on the Loess Plateau

doi:10.11686/cyxb2017064

Abstract

Abstract: Nitrogen addition can increase the aboveground biomass of the plant community in grasslands. However, it can also lead to a loss of species diversity, but the mechanisms involved in this process are unclear. The objective of this study was to explore the effects of nitrogen addition on aboveground biomass, species diversity, community composition, and the relationship between species richness and aboveground biomass in long-term fenced grassland and grazed grassland on the semi-arid Loess Plateau. We focused on the differences and similarities in the grassland responses under these two typical management systems, and tried to identify the the ecological mechanisms underlying these responses. We added nitrogen at different rates [0, 5, 10, 20, 40, 80 g CO(NH₂)₂/(m²·yr)] to long-term fenced grassland and grazed grassland. After 3 years of treatment, we measured aboveground biomass, calculated species diversity indexes (species richness, Shannon-Wiener index, and Pielou index) and analyzed the relationship between species diversity and productivity using regression analyses. The results showed that, in the long-term fenced grassland, nitrogen addition significantly increased the aboveground biomass and decreased species diversity, while the grazed grassland showed similar but weaker responses to nitrogen addition. The species diversity in fenced and fertilized grassland decreased as the litter biomass increased, and also increased with greater light penetration. In comparison, species diversity in grazed and fertilized grassland decreased slowly and did not change significantly with greater light penetration. The Shannon-Wiener index was significantly negatively correlated with above-ground productivity in fenced and fertilized grassland, but no such relationship existed in grazed grassland. These results indicated that grazing can relieve the negative effect of fertilization on species diversity. Therefore, grazing is a reasonable grassland management method to retain species diversity while increasing the community aboveground biomass by fertilization.

ZHAO Jie, LI Wei, JING Guang-Hua, WEI Lin, CHENG Ji-Min. Responses of species diversity and aboveground biomass to nitrogen addition in fenced and grazed grassland on the Loess Plateau[J]. Acta Prataculturae Sinica, 2017, 26(8): 54-64.

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