Effect of intermediate disturbance on soil microbial functional diversity depends on the amount of effective resources.

Many anthropogenic environmental changes are leading to a rapid decline in soil microbial functional diversity. However, ecological mechanisms that can serve to counteract/resist the diversity loss remain largely underexplored. In particular, although intermediate disturbance and increased amount of effective resources can promote the diversity of higher organisms, the potential role of these factors, and their combination, in maintaining microbial functional diversity is poorly studied. We conducted a 5-year experiment in a Eurasian steppe, manipulating mowing, nitrogen addition, phosphorus addition and their combinations. Nitrogen addition decreased soil pH by ~0.6 and bacterial abundance by ~19.5%, causing a disturbance effect. Phosphorus addition significantly decreased the effective amount of soil carbon-, nitrogen-, phosphorus- and water-relevant resources. Across all nitrogen-addition treatments subject to intermediate disturbance, there was a significant positive correlation between soil effective resource amount and microbial gene richness (r > 0.6, p < 0.01), which was elevated, in part, due to the increased fungal abundance. In contrast, significant correlations between gene richness and resource amount were not found under low-disturbance conditions. Overall, gene richness was greatest under conditions of both intermediate disturbance and ample effective resources, suggesting that the two factors could be manipulated in combination for the maintenance of microbial functional diversity.