Recovery succession drives the convergence, and grazing versus fencing drives the divergence of plant and soil N/P stoichiometry in a semiarid steppe of Inner Mongolia

Abstract

Understanding the plant and soil elemental stoichiometry during grassland dynamics is important for developing measures to enhance the restoration of degraded grassland. A number of restoration practices have been applied in the degraded typical steppe grassland in Inner Mongolia, either for research purpose or as actual restoration projects. However, the effects of different restoration measures on soil and plant N/P stoichiometry remain unclear. Here we explored the effects of three restoration measures (i.e., natural recovery, NR; shallow ploughing, SP; and harrowing HA) on the N, P stoichiometry of plant and soil in a typical steppe of Inner Mongolia, by comparing plant and soil N, P content and N/P ratio among the grasslands restored through NA, SP and HA, and that under sustained animal grazing (GR). Long-term restoration increased aboveground plant biomass, litter accumulation and changed soil and plant N/P ratio. Soil N and P contents in restored grassland (NR, SP or HA) were higher than those under grazing (GR); the restored grasslands shared a common slope of N-P linear regression, which was significantly greater than that of grazing grassland. Plant N content and N/P ratio decreased firstly and then increased during the restoration of degraded grassland. Soil N limitation is greater than soil P limitation in typical steppe of Inner Mongolia. Soil N limitation is smaller in naturally recovered grassland and grazing grassland than in the restored grassland following shallow ploughing and harrowing. The restoration succession over 26-years after the exclusion of animal grazing have changed the N-P coupling relation in grassland soil, with a common N-P relation converged under grassland that are treated with different restoration measures.