Nutrient amendment promotes vegetation restoration and improves ecosystem carbon uptake capacity in a degraded grassland

Abstract

Approximately 49 % of global grasslands are degraded due to overgrazing and other forms of mismanagement, resulting in great reduction in vegetation productivity and carbon uptake capacity. Degradation-induced losses of soil nutrients, particularly nitrogen (N) and phosphorus (P), severely hinder the restoration of degraded grasslands in China. However, whether and how amendments of N and/or P promote vegetation recovery and improve carbon uptake capacity in degraded grasslands remain poorly understood. Here we present the results of a nutrient amendment experiment conducted in a degraded grassland in Inner Mongolia, where we evaluated the individual and joint effects of N and P amendments. We found that N amendment increased the aboveground net primary productivity (ANPP), belowground net primary productivity (BNPP), gross ecosystem carbon production (GEP), ecosystem respiration (ER), and net ecosystem exchange (NEE) by 66.9 %, 61.6 %, 27.3 %, 18.8 %, and 32.3 %, respectively, while NP co-amendment stimulated these variables by 104.7 %, 171.4 %, 48.7 %, 36.7 % and 56.8 %, respectively. In contrast, P amendment alone had little effect on these variables except for BNPP. We observed a distinct shift in the dominance of plant species, with short-stature, unproductive grasses being replaced by the originally-dominant, tall-stature, productive grasses. This shift significantly contributed to the improvement of ecosystem carbon uptake capacity. Moreover, we identified a synergistic interaction between N and P on GEP, ER, and NEE. Our results suggest that effective restoration strategies, such as the proper amendment of limiting nutrients, can help restore the large-scale, degraded grasslands and enhance their carbon uptake capacity in China.