[Distribution characteristics of microbial necromass carbon along soil profiles in different restoration periods of Caragana korshinskii in mountainous areas of Southern Ningxia, China].

Microbial necromass, an important and stable source of soil organic carbon (SOC), is an important index to evaluate the contribution of microorganisms to SOC transformation and accumulation. It is not clear about the accumulation of microbial necromass in deep soil layer and its contribution to SOC during the restoration process of Caragana korshinskii forests. Combined with the biomarker method, we investigated the carbon contents of bacte-rial, fungal, and microbial necromass in the soil profiles (0-100 cm) of C. korshinskii forests in 16, 28, and 38 years of restoration, with natural grassland as control. We further examined the contribution of microbial necromass to soil organic carbon. The results showed that: 1) Along the soil profile (0-100 cm), the contents of fungal necromass carbon (FNC), bacterial necromass carbon (BNC), and microbial necromass carbon (MNC) significantly decreased with increasing soil depth in natural grassland and C. korshinskii forests. Except for the significant decrease in FNC/SOC, BNC/SOC, and MNC/SOC in the soil of C. korshinskii forests in 38 years of restoration, FNC/SOC and MNC/SOC generally showed an increasing trend followed by a decreasing trend in other plots, while BNC/SOC gradually decreased. 2) With the increases of restoration years, the contents of FNC, BNC, and MNC significantly decreased in C. korshinskii forests. FNC/SOC and MNC/SOC showed an overall increasing trend followed by a decreasing trend, while BNC/SOC gradually decreased. 3) The average contribution of microbial necromass carbon to SOC was highest in C. korshinskii forests in 28 years of restoration (35.0%), followed by C. korshinskii forests in 16 years of restoration (33.5%), natural grassland (31.0%), and C. korshinskii forests in 38 years of restoration (28.6%). In conclusion, when the restoration years of C. korshinskii forests are 16, the contents of microbial necromass carbon and their contributions to SOC are higher compared to natural grassland, which are beneficial for SOC sequestration.微生物残体是土壤有机碳(SOC)重要且稳定的来源,已成为评价微生物对SOC转化和积累贡献的重要指标。目前尚不清楚柠条林恢复过程中深层土壤微生物残体的积累及其对SOC的贡献特征。本研究采用生物标志物方法,以宁南山区天然草地为对照,研究了恢复16年、28年和38年的柠条林地沿0～100 cm剖面土壤细菌、真菌、微生物残体碳含量及其对有机碳的贡献特征。结果表明: 1) 沿0～100 cm土壤剖面,随着土层深度的增加,天然草地和柠条林地土壤中真菌残体碳(FNC)、细菌残体碳(BNC)和微生物残体碳(MNC)含量均显著降低;除恢复38年的柠条林土壤FNC/SOC、BNC/SOC和MNC/SOC显著降低外,其余样地FNC/SOC、MNC/SOC总体上呈现先增加后降低的趋势,BNC/SOC则逐渐降低。2) 随着恢复年限增加,柠条林地土壤中FNC、BNC和MNC含量均显著降低;FNC/SOC和MNC/SOC总体上先增后减,BNC/SOC逐渐降低。3) MNC对SOC的平均贡献表现为恢复28年的柠条(35.0%)>恢复16年的柠条(33.5%)>天然草地(31.0%)>恢复38年的柠条(28.6%)。综上,与天然草地相比,当柠条林恢复年限为16年时,土壤微生物残体碳含量及其对SOC的贡献均较高,有利于SOC的固存。.