Shifts in soil microbial biological and functional diversity under long-term carbon depletion. Soil microbial and functional diversity under long-term fallow

Soil organisms are crucial to the support and maintenance of ecosystems through the provision of ecosystem services. Nutrient cycling and decomposition are important processes by which soil organisms support aboveground plant communities. Anthropogenic disturbances can disrupt these processes. However, some organisms respond positively to disturbance and could mitigate the effects of disturbance. We assessed soil community composition and functional processes during a long-term carbon deprivation field experiment. Two sets of paired samples were deprived of carbon inputs for 10 years and 1 year, respectively. Soil DNA was extracted for metabarcoding and Geochip microarray analyses. Richness of bacteria, fungi, protists, and viruses fell under carbon depravation after 10 years, but not after 1 year. Log-fold change in gene expression of carbon cycling genes generally fell as well, though it increased for some genes involved in decomposing recalcitrant carbon. Similarly, log-fold change of several methanogenesis genes increased under carbon starvation. Several taxa were identified as indicators of both normal and deprived soils. Our results highlight the dynamic nature of soil communities. Bioindicators of carbon depravation may utilise alternative gene pathways to take advantage of opened niche space. The impact of carbon depletion requires long timescales and may be prevented with timely interventions.