The response of grassland productivity to atmospheric nitrogen deposition in northern China

Abstract

Increasing atmospheric nitrogen (N) deposition is expected to increase grassland productivity on a regional or global scale. However, it is unclear whether there are regional differences. Exploring regional differences and their underlying mechanisms may help examine the impact of N deposition on terrestrial ecosystems and improve the accuracy of models. Based on the “gray box” conceptual model and a linear model between N deposition and aboveground net primary productivity (ANPP), we proposed a new intrinsic parameter, “RN-int”, defined as the increase of ANPP induced by per unit low-level N addition, as a simulation of N deposition. Based on the data of 86 N addition experiments in the northern grasslands of China, RN-int showed no regional differences, and the mean value was 5.23 ± 0.59 g C g N –1. RN-int was relatively stable mainly as an intrinsic parameter, resulting from the stoichiometric homeostasis of the C:N requirement for plant growth rather than environmental factors. Combined with the N deposition dataset, the increase of ANPP induced by N deposition (ANPPN) in these grasslands from 1996 to 2020 was 8.37 ± 0.51 Tg C yr–1. The ANPPN was significantly different among grassland types (p < 0.05), and the order was grassland, desert, and meadow (4.68 ± 0.24, 2.53 ± 0.22, and 1.15 ± 0.06 Tg C yr–1, respectively). The spatial pattern of ANPPN was influenced by that of the amount of N deposition. Our findings provide new insights into predicting the effect of N deposition on grassland productivity and help better parameterize these ecological models on a regional scale.