Plant functional groups shift their nitrogen uptake during restoration of degraded alpine grasslands

Abstract

AbstractAlpine grasslands are undergoing severe degradation and are mainly restored through fencing. Numerous studies have explored the patterns, processes, and mechanisms of plant and soil during degradation, but few have been conducted on nitrogen (N) uptake by plant functional groups during restoration. An alpine meadow and an alpine steppe on the Tibetan Plateau were chosen to carry out in situ 15N labelling experiments in the forms of NH4+, NO3−, and glycine during restoration. Short‐, moderate‐, and long‐term restoration periods were explored, and plants were classified by functional groups into grasses, sedges, and forbs. Our results found biomass of grasses increased and that of sedges decreased with restoration in alpine meadow. In alpine steppe, forbs gradually became dominant in the community biomass by 58% during restoration. Long‐term restoration increased NH4+ uptake by grasses in alpine meadow. The total N uptake rates by grasses increased, but by forbs decreased during restoration in alpine meadow. Restoration decreased the total N uptake rates of grasses and forbs in alpine steppe. Chemical niche in N uptake was discovered during long‐term restoration in alpine meadow and during moderate‐term restoration in alpine steppe. We conclude that restoration alters the biomass composition of grasses, sedges, and forbs in alpine grasslands and shifts N uptake partitions. Chemical niche in N uptake by different functional groups in grasslands during restoration can decrease the fierce competition for N. Our results provide a synthesis for plant N utilization from soil during restoration of degraded grasslands from the perspective of shifting N uptake strategies.