Patterns and determinants of the response of plant biomass to addition of nitrogen in semi-arid and alpine grasslands of China

Abstract

Although the effects of adding nitrogen (N) to grasslands have been studied worldwide, little is known about how those effects are, in turn, influenced by climate, soil, and vegetation. Data from such experiments conducted in two main types of grassland in China, alpine and semi-arid, which differed widely in terms of climate, soil, and vegetation, were compiled and analysed to examine the response of above-ground biomass to N. Adding N increased the above-ground biomass by 51% on average. Although the response of biomass showed no obvious trend with the dose of N in the alpine grasslands, the response in the semi-arid grassland peaked at 15–20 g m−2 of N applied annually. Nitrogen addition efficiency in the alpine grasslands was higher than that in the semi-arid grasslands. The difference was mainly due to the differences in total soil N and its interactions with the above-ground biomass, which were particularly influenced by the soil's capacity to provide available N. These results suggest that soil N and features of local vegetation should be taken into account in arriving at the appropriate dose of N for a given site.