Unexpected similar stability of soil microbial CO2 respiration in 20-year manured and in unmanured tropical soils

Soil respiration is one of the main CO₂ sources from terrestrial ecosystems. Soil respiration is therefore a major source of greenhouse gas. Knowledge of the impact of agronomic practices such as manuring on the stability, for example resistance and resilience, of heterotrophic C–CO₂ respiration to disturbance is scarce. Here, we studied the stability of soil microbial heterotrophic respiration of two tropical soils from plots annually enriched or not with manure applications during more than 20 years. Stability was quantified after heating soils artificially. We hypothesized that field manuring would change the stability of the microbial community. Additionally, the impact of both manured and unmanured soils to addition of an organic cocktail was assessed under controlled conditions in order to discriminate the metabolic capacity of the microbial community, and to link the metabolic capacity up with the microbial heterotrophic soil respiration. Our results show that total respiration was not significantly different in manured and unmanured pots. Moreover, contrary to our hypothesis, manure amendment did not affect the stability (resistance, resilience) of the microbial abundance or the basal metabolism, in our experimental conditions. By contrast, the diversity of the bacterial community in heated soils was different from that in unheated soils. After heating, surviving microorganisms showed different carbon utilization efficiency, manuring stimulating the growth of different resistant communities, that is, r-strategist or K-strategist. Microbial community of manured soils developed in the presence of the organic cocktail was less resistant to heating than microbial community of unmanured plots.