Abstract Diazotrophs have a vital role in nitrogen (N) supply to ecosystems. Yet, response of diazotroph community profiles and N2-fixation to N deposition and phosphorus (P) addition remains poorly understood. Two-year nutrient addition experiments (control, N, P, and a combination of N plus P) were conducted in a karst grassland. The relative abundances of diazotroph orders Rhizobiales and Rhodospirillales were higher in July, while those of Nostocales and Burkholderiales were higher in December. Diazotroph abundances and N2-fixation activity in July were significantly higher compared with December under control, while an opposite pattern was observed for diazotroph richness and Shannon diversity index. N, P, and N plus P plots showed no significant changes between July and December in terms of diazotroph abundance and diversity. Diazotroph abundances and N2-fixation activity in N and NP plots were significantly reduced compared with control plots in July. P addition plots in July showed a significant increase in diazotroph diversity and stronger interaction patterns among diazotroph taxa compared with control plots. Diazotroph diversity and community compositions were primarily affected by P availability. Overall, our findings suggested diazotroph diversity and community compositions were more sensitive to P addition than to N addition, and P availability played an important role in regulating N2 fixation by increasing diazotroph diversity in karst ecosystems. N and P addition may alter the dry-cold and wet-hot seasonal dynamics of diazotroph communities, while sampling months also affect diazotroph community changes among treatments (no difference between treatments in December).

中文翻译：

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添加磷而非氮显着改变典型喀斯特草地土壤固氮菌多样性和群落组成

摘要 固氮菌在向生态系统提供氮 (N) 方面起着至关重要的作用。然而，固氮菌群落概况和 N2 固定对 N 沉积和磷 (P) 添加的响应仍然知之甚少。在喀斯特草原进行了为期两年的养分添加实验（对照、N、P 和 N 加 P 的组合）。固氮菌目根瘤菌目和红螺菌目的相对丰度在 7 月份较高，而乡土目和伯克霍尔德菌目在 12 月份的相对丰度较高。与控制下的 12 月相比，7 月份的固氮丰度和固氮活性显着更高，而固氮丰富度和香农多样性指数则观察到相反的模式。N、P 和 N 加 P 地块在固氮菌丰度和多样性方面在 7 月和 12 月之间没有显着变化。与对照地块相比，7 月份 N 和 NP 地块中固氮菌丰度和 N2 固定活性显着降低。与对照样地相比，7 月的磷添加地块显示固氮菌多样性显着增加，固氮菌类群之间的相互作用模式更强。固氮菌多样性和群落组成主要受磷可用性的影响。总体而言，我们的研究结果表明固氮菌多样性和群落组成对磷的添加比对氮的添加更敏感，并且磷的可用性通过增加喀斯特生态系统中的固氮菌多样性在调节 N2 固定方面发挥了重要作用。N和P的添加可能会改变固氮菌群落的干冷和湿热季节动态，