Experimental Drought Reduces The Transfer Of Recently Fixed Plant Carbon To Soil Microbes And Alters The Bacterial Community Composition In A Mountain Meadow

Summary

Drought affects plants and soil microorganisms, but it is still not clear how it alters the carbon (C) transfer at the plant￢ﾀﾓmicrobial interface. Here, we tested direct and indirect effects of drought on soil microbes and microbial turnover of recent plant￢ﾀﾐderived C in a mountain meadow.

Microbial community composition was assessed using phospholipid fatty acids (PLFAs); the allocation of recent plant￢ﾀﾐderived C to microbial groups was analysed by pulse￢ﾀﾐlabelling of canopy sections with 13CO2 and the subsequent tracing of the label into microbial PLFAs.

Microbial biomass was significantly higher in plots exposed to a severe experimental drought. In addition, drought induced a shift of the microbial community composition, mainly driven by an increase of Gram￢ﾀﾐpositive bacteria. Drought reduced belowground C allocation, but not the transfer of recently plant￢ﾀﾐassimilated C to fungi, and in particular reduced tracer uptake by bacteria. This was accompanied by an increase of 13C in the extractable organic C pool during drought, which was even more pronounced after plots were mown.

We conclude that drought weakened the link between plant and bacterial, but not fungal, C turnover, and facilitated the growth of potentially slow￢ﾀﾐgrowing, drought￢ﾀﾐadapted soil microbes, such as Gram￢ﾀﾐpositive bacteria.