Aims

Forest gaps disturb soil available nutrients and microbial biomass unparallelly along precipitation gradients, leading to stoichiometric mismatches that limit the growth of microbial communities. However, adaptions of microbial physiological and metabolic processes to the stoichiometric limitations and the resulting effects on soil carbon (C) dynamics are still poorly understood. The main aims here were to understand how microbial metabolic limitation is affected by interactions of forest gaps and mean annual precipitation in relation to plant and soil physiochemical properties, and how the metabolisms impact rates of key soil processes such as soil microbial respiration.

Methods

We compared microbial physiological adaptive traits (metabolic limitation, C use efficiency (CUE) and extracellular enzyme activities) and respiration rate between harvested gaps and unharvested stands within Robinia pseudoacacia plantations along the mean annual precipitation gradient in northern Shaanxi, China.

Results

Forest gaps strengthened metabolic limitation for soil microbes, as well as their dependence on mean annual precipitation. Plant biomass (58.9%) predominantly accounted for variations in microbial relative C limitation, while soil water content (29.1%), dissolved nutrient availability and stoichiometry (52.0%) were primary predictors for microbial P limitation. In this context, soil microbial communities adapted by altering their ecoenzymatic production, CUE, and biomass composition simultaneously. The PiecewiseSEM analysis revealed that the elevated microbial respiration after forest gap formation was directly associated with a reduction in microbial biomass and indirectly related to lower microbial CUE and higher enzymatic activity. These findings indicate that the synchronized regulation of lower CUE and higher enzymatic production results in a greater expenditure of energy on the maintenance of microorganisms than on the formation of cells.

Conclusion

This study presents novel insights into microbial-driven C dynamics response to interactive effects of forest gaps and precipitation variabilities, having implications for evaluating sustainability of forest management strategies in the anticipated climate-change scenario.