Decoupled responses of above- and below-ground beta-diversity to nitrogen enrichment in a typical steppe

Increased atmospheric nitrogen (N) deposition affects biodiversity in terrestrial ecosystems. However, we do not know whether the effects of N on above-ground plant β-diversity are coupled with changes occurring in the soil seed bank. We conducted a long-term N-addition experiment in a typical steppe and found that above-ground β-diversity increased and then decreased with increasing N addition, whereas below-ground β-diversity decreased linearly. This suggests decoupled dynamics of plant communities and their soil seed bank under N enrichment. Species substitution determined above- and below-ground β-diversity change via an increasing role of deterministic processes with N addition. These effects were mostly driven by differential responses of the above-ground vegetation and the soil seed bank β-diversities to N-induced changes in environmental heterogeneity, increased soil inorganic N concentrations and soil acidification. Our findings highlight the importance of considering above- an...

大气氮（N，nitrogen）沉降增加会影响陆地生态系统的生物多样性。然而，目前尚不清楚氮对地上植物β多样性(β-diversity)的影响是否与土壤种子库(soil seed bank)的变化相耦合。本研究在典型草原开展了长期氮添加试验，结果发现：随着氮添加水平升高，地上植物β多样性呈先升后降的变化趋势，而地下β多样性则呈线性下降趋势。这表明在氮富集条件下，植物群落与其土壤种子库的动态存在解耦现象。随着氮添加水平升高，确定性过程(deterministic processes)的作用不断增强，物种替代通过该途径调控了地上与地下β多样性的变化。这些效应主要源于地上植被与土壤种子库β多样性对氮诱导的环境异质性(environmental heterogeneity)变化、土壤无机氮浓度升高以及土壤酸化的响应差异。本研究结果凸显了考虑地上与