| 摘 要： |
Plant-microbial interaction for nitrogen (N) is important in plant growth, soil fertility, and function of grasslands. However, it remains unclear how plant-microbial competition for N changes after the restoration of degraded alpine grasslands. This study aimed to explore the dynamics of plant-microbial competition for N in restoration chronosequences (i.e., short-, medium-, and long-term) in an alpine meadow and an alpine steppe on the Qinghai-Tibetan Plateau. Two inorganic forms of N (ammonium (NH4+ ) and nitrate (NO3-)) and one organic N (glycine) were used for the in situ N-15 labeling experiments. The competition between microorganisms and plants (i.e., ratios) for N increased by 4.8 times after medium- than short-term restoration in the alpine meadow and remained stable after each restoration. Compared to short-term restoration, medium-term restoration increased the N uptake of microorganisms by 2.4 times in alpine meadow and 4.3 times in alpine steppe. Microorganisms and plants showed chemical niche differentiation between NH4+ and NO3- uptake in both alpine ecosystems after medium-term restoration, with microorganisms taking up more NH4+ but plants taking up more NO3-. Competition between microorganisms and plants decreased after long-term compared with medium-term restoration, maintaining the microbial to plant N uptake ratio > 1. Long-term restoration increased plant N uptake in the alpine meadow, while decreased the microbial N uptake in the alpine steppe. Neither microorganisms nor plants showed a preference for glycine, but glycine uptake by microorganisms was higher than plants after medium- and long-term restorations. These findings provide valuable insights into the restoration of degraded alpine grasslands from the perspective of plant-microbial competition for available N in soil, which may be useful for developing sustainable grassland management practices. |
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