The occurrence and distribution characteristics of microbial necromass carbon in lake sediments

As a critical component of SOC, microbial necromass carbon (MNC) has been well studied in forest, farmland, and grassland ecosystems. However, the distribution, forms, and storage of MNC, which bound to the sediments in lakes, remain unclear. Herein, the lake sediments in the West Dongting Lake have been collected to investigate the distributions of MNC in sediments, particulated organic matter (POM), and mineral-associated organic matter (MAOM). The contribution of MNC to the sedimentary organic carbon was 20–30 %, which was lower than the average value of 50 % in other ecosystems. The reasons might be related to the selective migration of soil particles with uneven distribution of MNC and the accelerated mineralization of MNC prior to sedimentation. The results revealed that MNC_maom was the predominant form of MNC, accounting for 61–73 % of the total MNC. In addition, the MNC content in the sediments ranged from 2.03 g kg⁻¹ to 4.33 g kg⁻¹, showing an increasing trend along the direction of the water flow from the lake shore to the center. The redundancy analyses and the partial least square path model analyses indicated that sediment organic carbon, total nitrogen, silt and MAOM had a substantial impact on the MNC. Silt played an essential role in regulating the distributions of MNC in lake sediments by promoting MNC sedimentation and providing protection from degradation. These findings revealed that the accumulation of MNC in lake sediment was mainly affected by sediment particles, which differed from other non-lake ecosystems. The presented findings provided essential insights into the accumulation of MNC in lake sediments, highlighting the importance of the MNC in lake sediments and a more profound understanding of the role of MNC in lake carbon cycling.