Abstract
Soil microorganisms are key drivers of soil biochemical processes, but the resilience of microbial communities and their metabolic activity after an extreme environmental change is still largely unknown. We studied structural (bacterial and fungal communities) and functional responses (soil respiration, adenosine triphosphate (ATP) content, hydrolase activities involved in the mineralization of organic C, N, P and S, and microbial community-level physiological profiles (CLPPs)) during the microbial recolonization of three heat-sterilized forest soils followed by cross- or self-reinoculation and incubation for 1, 7 and 30 days. Soil ATP content, biochemical activities and CLPP were annihilated by autoclaving, whereas most of the hydrolase activities were reduced to varying extents depending on the soil and enzyme activity considered. During the incubation period, the combination of self- and cross-reinoculation of different sterilized soils produced rapid dynamic changes in enzymatic activity as well as in microbial structure and catabolic activity. Physicochemical properties of the original soils exerted a major influence in shaping soil functional diversity, while reinoculation of sterilized soils promoted faster and greater changes in bacterial community structure than in fungal communities, varying with incubation period and soil type. Our results also confirmed the importance of microbial richness in determining soil resilience under severe disturbances. In particular, the new microbial communities detected in the treated soils revealed the occurrence of taxa which were not detected in the original soils. This result confirmed that rare microbial taxa rather than the dominant ones may be the major drivers of soil functionality and resilience.
Highlights
Soil microbial communities display high metabolic diversity and functional redundancy, two features that make them major drivers of nutrient biogeochemical cycles and globally a key factor of soil resilience [1,2,3,4]
Heat-sterilization drastically reduced soil respiration; it recovered after reinoculation and incubation with trends similar in all treatments but different in values depending on the recipient soil and the inoculum source (Figure 1A)
At the end of the incubation period, the Romola soil (Rom) soil showed the lowest cumulative respiration values compared to Vicarello soil (Vic) and Vallombrosa soil (Val) soils
Summary
Soil microbial communities display high metabolic diversity and functional redundancy, two features that make them major drivers of nutrient biogeochemical cycles and globally a key factor of soil resilience [1,2,3,4]. Despite the fast proliferation rates and high colonization capacities of microbial species, the long-held historical view that “everything is everywhere, but the environment selects” [5] is no longer accepted in soil microbial ecology to explain the complex interactions occurring among environmental characteristics, microbial community structure and microbial functional activity. Experiments with soil sterilization and soil mixing have been considered a suitable approach to understand the recovery of microbial diversity and soil functions after extreme impacts and variations induced by the coalescence of soil communities. Previous studies on soil microbial recolonization after sterilization by fumigation, autoclaving or γ-irradiation [13,14,15,16] have shown that microbial metabolic activities are primarily involved in the colonization capacity of microbial communities of the same and/or different sterilized soils. Latour et al [19] reported that the composition of a mixed Pseudomonas community developed differently when inoculated into sterile soils with different characteristics
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