How microbes cope with short-term N addition in a Pinus tabuliformis forest-ecological stoichiometry

Abstract

Global nitrogen (N) deposition can change the contents and stoichiometry of soil resources and thus of microbial communities, which can drive the flow of carbon (C) and nutrients in food webs in forest ecosystems. It is critical to understand the status of soil elements required for microbial growth, the elements of microbial growth, and how soil microorganisms would reallocate resources and release extracellular enzymes for adjusting the imbalance between resources and microorganisms due to N deposition. We chose a plantation of Pinus tabuliformis where N had been added across a gradient (0–9 g N m−2 y−1) for two years to reveal how matters flow and soil resources were reallocated by microbes to cope N addition. Our results showed that although two years of N inputs only significantly affect the ratio between the activities of β-1,4-N‑acetylglucosaminidase and alkaline phosphatase in the 0–20 cm soil layer, activities for both organic N and organic phosphorus (P) acquisition enzymes scale with C acquisition with slope of about 1, following the global ecoenzymatic patterns. Contents and elemental ratios of soil organic carbon (SOC), total N (TN) and total phosphorus (TP) were changed after this short-term N addition. Ratios of SMBC, SMBN and SMBP were concentrated from soil and lower than ratios of soil resources. Soil microbial communities under N addition were limited by N and co-limited by P at 3 and 6 g N m−2 y−1. Although imbalance between soil and microbes caused by N addition, in the 0–20 and 20–40 cm layers, C: N relationship between soil and the microbial community indicated microbial community maintained homeostasis. However, C:P relationship between soil and the microbial community indicated no microbial community homeostasis. In addition, both soil resources elemental stoichiometry and contents can affect soil microbial communities. Further study of the structure of soil microbial communities, identifying the microbes that are more adaptive to high N concentrations and N deposition, is needed for a better understanding of the mechanisms of nutrient flow in the food web and how to maintain microbial homeostasis in response to N deposition in forest ecosystems.