At the early stage of primary succession, there are deficient nutrient resources as well as competition stress among neighboring plants. Our aims were to elucidate the flexibility of tree seedlings’ stoichiometric relationships and their effects on soil microbial communities, and to determine the driving forces of species turnover during primary succession through the evaluation of carbon (C) : nitrogen (N) : phosphorus (P) stoichiometric relationships. We conducted an experiment testing N addition effect on two species from the early stage of primary succession, under intra- and interspecific competition conditions. Our results showed that higher values of δ15N-NO3− and δ13C were observed in Populus purdomii individuals than in Salix rehderiana after N application, which indicated a more efficient N uptake and water-use efficiency in P. purdomii plants. Furthermore, under N addition, the intraspecific competition of P. purdomii presented a higher urease activity, microbial biomass C (MBC), microbial N:P ratio (MBN:MBP), and phylogenetic diversity compared to the intraspecific competition of S. rehderiana. The results showed that P. purdomii seedlings influenced soil properties in a way that led to a positive feedback on their performance with an increasing N availability. In contrast, S. rehderiana seedlings influenced soil properties in a way that caused a negative feedback on their performance with increasing N. Such events can promote species turnover from Salix to Populus during succession. Additionally, DNA sequencing of soil bacterial communities showed differences in the composition of microbial communities in response to N fertilization and different competition patterns. Altogether, our results showed that plant, soil, and microbial community responses to N fertilization in a subalpine glacier forefield differed among tree species and competition patterns. This study brings new insight into mechanisms that drive species replacement and biogeochemical cycling during primary succession.

中文翻译：

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化学计量的灵活性和土壤细菌群落对初级演替早期施氮和邻居竞争的反应

初代演替初期，养分资源不足，相邻植物之间存在竞争压力。我们的目的是阐明树木幼苗化学计量关系的灵活性及其对土壤微生物群落的影响，并通过评估碳（C）：氮（N）：磷（P）来确定初级演替过程中物种周转的驱动力) 化学计量关系。我们在种内和种间竞争条件下进行了一项实验，测试了初级演替早期对两个物种的氮添加效应。我们的结果表明，施氮后，在杨树个体中观察到的 δ15N-NO3− 和 δ13C 值高于红柳，这表明在杨树中氮吸收和水分利用效率更高。purdomii 植物。此外，在氮添加下，与 S. rehderiana 的种内竞争相比，P. purdomii 的种内竞争表现出更高的脲酶活性、微生物生物量 C (MBC)、微生物 N:P 比 (MBN:MBP) 和系统发育多样性。结果表明，P. purdomii 幼苗影响土壤特性的方式导致对其性能的积极反馈，并增加 N 可用性。相比之下，S. rehderiana 幼苗影响土壤特性的方式是随着 N 的增加对其性能产生负反馈。此类事件可以促进物种在演替过程中从柳树到杨树的转换。此外，土壤细菌群落的 DNA 测序显示，微生物群落组成因施氮和不同竞争模式而异。总之，我们的结果表明，在亚高山冰川前场，植物、土壤和微生物群落对施氮的反应因树种和竞争模式而异。这项研究为原始演替过程中驱动物种更替和生物地球化学循环的机制带来了新的见解。