Stoichiometric flexibility and soil bacterial communities respond to nitrogen fertilization and neighbor competition at the early stage of primary succession

Abstract

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.