Abstract
The effect of nitrogen (N) deposition on N limitation, phosphorus (P) limitation and the related soil and microbial stoichiometries remains unclear. A simulated nitrogen deposition (SND) experiment (control, ambient, medium and high) and molecular techniques (high-throughput sequencing of 16S and ITS) were conducted to examine the variations in abiotic and biotic properties and to describe the responses of microbial (bacteria and fungi) adaptation strategies in a moso bamboo (Phyllostachys edulis J. Houzeau) forest following SND. Soil water content (SWC) was positively correlated with the microbial community composition. Observed increases in total N and nitrate N contents and decreased ammonia N suggested that SND influenced nitrification. Chao1 and F:B showed that bacteria were more sensitive to SND than fungi. PCoA and linear discriminant analysis (LDA), coupled with effect size measurements (LefSe), confirmed that microbial community composition, including the subgroups (below class level), responded to SND by employing different adaptation strategies. Soil C:N indicated that the soil of the moso bamboo forest was under N limitation prior to SND. The increase in total P (TP), available P (AP) and microbial biomass P (MBP) suggested the acceleration of soil P cycling. Microbial biomass C (MBC) and microbial biomass N (MBN) were not affected by SND, which led to a significant shift in MBC:MBP and MBN:MBP, suggesting that P utilization per unit of C or N was promoted. There was a negative gradient correlation between the fungal community composition and MBC:MBP, while bacteria were positively correlated with MBN:MBP. The results illustrated that the response of fungi to MBC was more sensitive than that of bacteria in the process of accelerated P cycling, while bacteria were sensitive to MBN. Prior to P limitation, SND eliminated the soil N limitation and stimulated soil microorganisms to absorb more P, resulting in an increase in MBP, but did not alter MBC or MBN. This study contributes to our understanding of the adaptation strategies of fungi and bacteria and their responses to soil and microbial stoichiometries.
Highlights
N deposition has become an important global change factor [1]
soil organic carbon (SOC) decreased at N90, and water dissolved organic carbon (WSOC) decreased at N30, N60 and N90
Our results showed that the N60 and N90 levels had an impact on soil pH, but pH had no gradient correlation with the microbial community composition, while soil water content (SWC) did have a gradient correlation, which may be related to the short implementation of simulated nitrogen deposition (SND), which had not yet affected the overall microorganism community [43]
Summary
N deposition has become an important global change factor [1]. During the last century, the amount of reactive nitrogen (N) has doubled globally, and the biodiversity of soil microorganisms has responded sensitively [2]. Active N produced by human activities enters the atmosphere and settles in terrestrial ecosystems, which interferes with the natural cycling of N, changes the availability of N, and has a wide impact on the fixing capacity of forest N, and accelerates soil N leaching, causes changes in soil N use efficiency and soil C:N and C:P stoichiometric ratios, and results in soil acidification. The soil stoichiometric regulation of the microbial community assembly and its impact on microbial ecological adaptability in the soil of wetland forests remains unclear. The change in soil pH and stoichiometry under the continuous increase in N deposition makes the study of the soil microbial feedback mechanism an important topic in global change research [1] N and P availability plays a crucial role in C cycling in terrestrial ecosystems [3,4,5,6,7].
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