Soil ecoenzymatic stoichiometry and microbial resource limitation driven by thinning practices and season types in Larix principis-rupprechtii plantations in North China

Abstract

The extracellular ecoenzymatic stoichiometry (EES) of the soil are key indicators of the nutritional status and relative resource limitations of microbes that play important roles in biogeochemical cycling and ecosystem functions. However, our knowledge of the effects of forest thinning and the seasons on the variability of extracellular ecoenzymatic activities (EEA) and EES in the soil is limited. We examined the soils from Larix principis-rupprechtii plantations after nine years of treatments with four different thinning intensities (i.e., control (CK), low thinning (LT), moderate thinning (MT), and high thinning (HT)) in four different seasons. We measured the activities of one carbon (C) acquiring enzyme (β-1,4-glucosidase (BG)), two nitrogen (N) acquiring enzymes (β-1,4-N-acetylglucosaminidase (NAG), leucine aminopeptidase (LAP)), and one phosphorus (P) acquiring enzyme (acid phosphatase (AP)), and examined potential factors (soil environment, nutrients, and microbial biomass) that may influence the activities of these enzymes. Our results showed that thinning significantly (p < 0.05) enhanced the activities of the BG, NAG + LAP, and AP. The EEA were higher in summer and autumn than those in spring and winter. Further, MT and HT stands exhibited lower BG:(NAG + LAP) and higher (NAG + LAP):AP ratios than the CK and LT stands, demonstrating that MT and HT caused a greater N limitation for soil microbes. The higher (NAG + LAP):AP ratio during winter indicated that the microbial N limitation was increased in this season. The variations in the EEA, EES, environment, nutrients, and microbial biomass in the soil among different thinning treatments demonstrated that thinning could markedly promote microbial activities and metabolism and improve nutrient cycling. Based on analyses of the BG:(NAG + LAP) ratio, (NAG + LAP):AP ratio, and the threshold element ratio, we found that the metabolism of soil microbes was limited by N in L. principis-rupprechtii plantations in North China. A redundancy analysis and a variation partitioning analysis revealed that variations in the EEA and EES of soils could attributed to the alterations in soil properties, especially soil nutrient and microbial biomass. Overall, the ecoenzymatic C:N:P stoichiometry was dependent on the resource availability in the soils rather than on homeostatic mechanisms. Our research highlights the importance of the effects of thinning practices and season types on ecoenzymes and microbial metabolism, and provides insights into the microbial resource limitation, nutrient cycling, and ecological processes in plantation forests after thinning.