Effects of Stand Density on Soil Respiration and Soil Labile Organic Carbon and Their Influence Mechanism in Larix Principis-Rupprechtii Plantations

Abstract

BackgroundForest soil carbon pool plays a vital role in the global carbon sequestration and carbon emission. Forest management can regulate the sequestration and output of forest soil carbon pool to a certain extent, but mechanism of forest density effects on soil carbon pool still needs to be further researched. MethodsWe established sample plots with density gradients in three-age stands of Larix principis-rupprechtii plantation and measured soil respiration (RS), soil organic carbon (SOC), soil dissolved organic carbon (DOC), and microbial biomass carbon (MBC), light fraction organic carbon (LFOC), and easily oxidizeable organic carbon (ROC). Results and ConclusionsThe results showed that, among the forest stands of three ages, RS, heterotrophic respiration (RH), MBC, LFOC, ROC of different stand density levels were significantly different. Moderate density promotes RS rate and RH rate and the sequestration of MBC and LFOC and inhibits ROC sequestration. With the increase of forest stand density, RS, RH, LFOC, and MBC first increased and then decreased, and ROC first decreased and then increased, the quadratic function could fit these changing trends. The RS, RH, and autotrophic respiration (RA) rates of older forest stands were relatively fast, and contents of SOC, MBC, LFOC, DOC, and ROC were higher, and they were more sensitive to changes in stand density. SOC, LFOC, MBC, DOC, and ROC explained 56.05% variations of RS, Rh, and RA. MBC, LFOC, and ROC in soil labile organic carbon were closely related to RS and Rh, but not SOC. Among them, LFOC and MBC played the role of "warehouse" and "tool" and significantly correlated with RS and Rh. ROC, as "raw material," had a significant negative correlation with RS and RH. When the RS and RH rate were fast, ROC maintained a dynamic and stable state of low soil content. Stand density could regulate RH by affecting soil labile organic carbon, an essential path for stand density to regulate soil respiration. Given soil carbon pool significance in forest ecosystems, Continuous research on soil respiration and stand density is suggested to bridge the gaps in our comprehension of the Regulation of Forest Management on forest soil carbon pool.