Reinvestigating the regulatory gate hypothesis for a better understanding of microbial redundancy in soil

Abstract

● Moderate dilution of natural soil with clay mineral complexes generated oligotrophic soils with a gradient of microbial abundance but similar C availability.

● In contrast to the regulatory gate hypothesis, small changes in microbial abundance strongly influenced soil C decomposition despite similar C availability.

The regulatory gate hypothesis suggests that the mineralization of soil organic matter (SOM) is controlled by carbon accessibility due to microbial redundancy. However, this opinion is contentious because the extensively high available carbon released during the fumigation in these studies strongly stimulated microbial activity, which is unlikely to occur in real soil and would compensate for the effect of reduced microbial abundance. In this study, natural soil was moderately diluted with mineral complexes in varying proportions to obtain soils with a gradient of microbial abundance and low carbon availability. The results revealed that despite minimal changes in the dissolved organic carbon content (DOC), the CO₂ emission rate and activity of SOM hydrolysis significantly decreased with decreasing microbial abundance. Regression analysis and the random forest model highlighted microbial abundance as the primary factor influencing carbon decomposition, which was more fundamental than DOC and microbial diversity. These findings underline the crucial role of microbes in soil carbon turnover and the importance of maintaining microbial abundance to preserve the soil carbon cycling capacity.

Graphical abstract

Keywords

regulatory gate hypothesis / microbial abundance / microbial redundancy / carbon availability / carbon mineralization

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