The context dependency of nitrogen deposition impacts on the compositional coupling between aboveground vegetation and soil seed bank.

Abstract

The compositional coupling between aboveground vegetation and soil seed bank is critical for community stability and successional trajectories, but such relationships are highly sensitive to environmental changes. Although nitrogen (N) deposition has been reported to decouple the associations between aboveground vegetation and the soil seed bank in grasslands, it remains unclear whether and how grassland management practices, such as mowing, mediate N deposition effects. We evaluated the impacts of N input and mowing on the diversity and composition of the aboveground vegetation and soil seed bank, as well as their compositional coupling in a decadal grassland experiment. N addition increased the compositional dissimilarity between the soil seed bank and aboveground vegetation by increasing abundance gradient, but only in unmown plots. N addition did not affect the compositional dissimilarity between aboveground vegetation and the soil seed bank in mown plots. Mowing increased the graminoid abundance in the aboveground vegetation, but increased the forb abundance in the soil seed bank, and thus increased the compositional dissimilarity between aboveground vegetation and the soil seed bank by promoting balanced variation in abundance. Our results reveal the importance of context dependence in the consequences of N inputs on the compositional coupling between aboveground vegetation and the soil seed bank in grasslands. The land-use context should be fully considered when evaluating the impacts of global change drivers on grassland community dynamics and succession.