Microbial biomass was believed to be labile and the contribution of its residues (called necromass) to stable organic matter has been underrated in the past. Only until recently, it is suggested that the contribution of soil microbial necromass to soil organic matter may be high. However, until now, there is still no direct evidence of the turnover rate or the residence time of soil microbial necromass nitrogen (N) in soils. We used the isotope labelling technique to study the residence time of necromass N of three groups of soil microbes (bacteria, fungi, and actinobacteria) in a temperate forest soil.
Results/Conclusions
We found that 25-34% of the initial necromass 15N still remained in the soil after 490 days of in situ incubation. Fungal-derived necromass N decomposed more slowly than bacterial-derived and actinobacterial derived necromass N, although the three groups showed similar decomposition curves. Their decomposition curves can be divided into three phases: very fast, fast and slow, with the decomposition rate during the slow phase similar to that of plant litter mass. Using the first order decay model and the Monte Carlo simulation, we estimated that microbial necromass N accounted for 29.2 ± 22.6 % of soil total N in our studied soil at the steady state. Our findings highlight the importance of microbial necromass to stable soil organic matter. We suggest that necromass carbon and N may have different residence time in soil, and the fates of microbial-derived N-containing compounds in soil should be studied more to better understand soil organic matter.