Soil biochemical properties and bacteria community in a repeatedly fumigated-incubated soil

The regulatory gate hypothesis considers that soil organic C mineralization is a two-step process, where stable C is firstly transformed abiotically and is only then a microbially available substrate. The mechanisms involved in the abiotic conversion of non-microbially available to available soil organic C remain largely unknown. We conducted a perfusion experiment using a repeated fumigated-incubated soil and the corresponding fresh soil. We found that repeated fumigation-incubation significantly decreased soil microbial ATP to 0.22 nmol g(-1) soil, 10% of that in the fresh soil, and significantly destroyed microbial composition and diversity. However, it had little influence on the soil CO2-C evolution rate after the flush of fumigant-killed dead biomass (8 mu g CO2-C g(-1) soil day(-1)) or dissolved organic C (DOC) concentration (about 7 mu g C g(-1) soil) and composition during long-term perfusion. We conclude that soil CO2 evolution rate and DOC generation were not regulated by the size or composition of the soil microbial communities. This is in support of the regulatory gate hypothesis. We suggest that abiotic processes in soil organic C mineralization need to be considered more and studied further. Graphical abstract