Atmospheric nitrogen (N) deposition is a matter of serious concern for the structure and functioning of global ecosystems, but the effect of N application of species diversity (D), primary productivity (P), and stability (S) of tropical grassland ecosystems is not known. The present study reports the effects of different levels of N application on species composition, and the D, P, S, and their relationships in a tropical grassland. Within the experimental grassland, 72 1 × 1 m plots with 6 N-input levels and with 12 replicates, were established in 2013. For 3 yr, different doses of urea as a source of N were applied to the plots. Data on individuals and biomass of each species were recorded and statistically analyzed. The study revealed that the N applied caused variations in species composition, D, P, and S. Below the 90 kg N dose, D was positively related to P and S while, above this level, the relations were negative due to N-induced responses of species and functional group composition as well as biomass distribution among them. The optimum applied N levels for maximum D (50-60 kg N), P (120 kg N), and a positive relationship of S with D (up to 90 kg N treatment) suggested that the 90-kg N dose could be the maximum dose of N that the grassland can tolerate. Hence, N application should not exceed the 90-kg level for sustainability of the structure and functioning of tropical grassland ecosystems.

中文翻译：

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热带草原中多样性，生产力和稳定性对氮输入的响应。

大气氮（N）的沉积是全球生态系统的结构和功能的一个严重问题，但是氮对热带草原生态系统物种多样性（D），初级生产力（P）和稳定性（S）的影响是未知。本研究报告了在热带草原上不同水平的施氮对物种组成，D，P，S及其关系的影响。在实验草原上，于2013年建立了72个1×1 m样地，含6个氮输入水平，重复12次。三年中，对样地应用了不同剂量的尿素作为氮源。记录每个物种的个体和生物量数据并进行统计分析。研究表明，施用的氮导致物种组成，D，P和S的变化。在90 kg以下的氮剂量下，D与P和S呈正相关，而在此水平之上，由于N诱导的物种和功能基团组成以及其中生物量的分布，这种关系呈负相关。最大D（50-60 kg N），P（120 kg N）和S与D的正相关关系（最高达90 kg N处理）的最佳施用氮水平表明，90 kg N剂量可能是最大剂量。草地可以忍受的最大氮素剂量。因此，为使热带草原生态系统的结构和功能可持续，氮的施用量不应超过90千克。S与D的正相关关系（氮素处理量最大为90 kg）表明90 kg的氮素剂量可能是草地可以忍受的最大N剂量。因此，为使热带草原生态系统的结构和功能可持续，氮的施用量不应超过90千克。S与D的正相关关系（氮素处理量最大为90 kg）表明90 kg的氮素剂量可能是草地可以忍受的最大N剂量。因此，为使热带草原生态系统的结构和功能可持续，氮的施用量不应超过90千克。