Inferring Adaptation at Community Composition Level From the Relationship Between Succession Rate and Global Change Intensity.

In response to anthropogenic environmental changes, biological communities often undergo compositional changes, which are traditionally thought to represent adaptation. However, this hypothesis and its mechanism remain surprisingly underexplored. In this study, we conducted a 10-year nitrogen deposition experiment in the Eurasian steppe, manipulating nine intensities under two management strategies (fencing or mowing). As the intensity increased from 0-20 to 50 g N m-2 yr-1, the succession rates of both plant and soil microbial communities first increased but then decreased, implying that high intensities of N deposition exceed the capacity of community adaptation. In addition, both the succession rate of the deterministic component of community compositional variation and the succession rate of soil physicochemical characteristics increased and then decreased with increasing N intensity. They were positively correlated, demonstrating that adaptation is primarily driven by deterministic ecological processes. Meanwhile, mowing promoted the plant community's adaptation, while fencing promoted adaptation of the microbial community, both by restraining stochastic processes. Overall, to enable biological communities to adapt compositionally to environmental changes, we should aim to limit the intensity of changes below certain thresholds, and implement reasonable strategies, whether deterministic (e.g., restoring soil physicochemical conditions) or stochastic (e.g., adding seeds of adaptive species).