Microbial traits are shaped by soil type with potential implications for microbial necromass carbon cycling

Microbial necromass carbon (MNC) is 15-80% of SOC and is controlled by necromass production (microbial growth and death), stabilisation (minerals and aggregates), and consumption (recycling and destabilisation). Microbial traits (i.e., quantitative measures that capture differences in life strategies or niche segregation among taxa) provide a step-change in understanding the interactions between microbes and soil organic carbon (SOC) cycling, particularly regarding the contribution of MNC. However, it remains unclear which traits consistently inform MNC and its relationship with SOC in cropland soils. Here, we address this gap by collecting soil samples from 22 farm fields spanning 4 soil types in Luxembourg, then we inferred genomic bacterial traits using representative genomes available in the Genome Taxonomy Database (GTDB) and the Bacterial Diversity Metadatabase (BacDive) and correlated them with SOC and MNC stocks.

Our preliminary results suggest that soil-type selects traits linked to resource acquisition and high-yield microbial strategies, including genome size, GC content, 16S rRNA copy number, and motility. We also observed positive or negative correlations between the traits themselves, suggesting possible trade-offs in community-level life history strategies, with potential implications for carbon derived from microbes. However, these traits or trade-offs had no direct links with bulk SOC stocks. Our ongoing analysis will instead link these traits and trade-offs directly to MNC stocks, to assess whether genome-derived traits can be useful for informing the necromass cycle. If this microbial trait relationship with MNC stocks holds true, the results and method will be useful for better understanding the MNC cycle in cropland soils and for improving next-generation SOC models.