Experimental warming increases respiration and affects microbial communities of soil wetlands at different elevations of the Argentinean Puna

Abstract

● Under warming soil respiration was higher, but soil microbial biomass was lower. ● Warming effect on soil respiration was higher in soil from the highest elevation. ● Soil respiration was higher in soil with higher soil carbon content. ● Warming increased biomass-specific respiration and enzyme activity. ● The Q10 did not differ among soils from different elevations. Global warming is expected to increase the rate of soil carbon (C) efflux through enhanced soil microbial processes, mainly in systems, such as high elevation wetlands, storing large quantities of soil organic C. Here, we assessed the impact of experimental warming on respiration and microbial communities of high Andean wetland soils of the Puna region located at three different elevations (3793, 3862, 4206 m a.s.l.). We incubated soils at 10°C and 25°C for 68 days and measured the soil respiration rate and its temperature sensitivity (Q10). Furthermore, we measured biomass and composition and enzymatic activity of soil microbial communities, and initial and final soil C content. Although warming increased soil respiration rates, with more pronounced effect in soils sampled from 4206 m a.s.l., Q10 did not differ between elevations. Soil C content was higher at the highest elevation. Soil microbial biomass, but not enzymatic activity, was lower for warmed soil samples. However, the biomass-specific respiration and biomass-specific enzymatic activity were higher under warming, and in soil from the highest elevation wetland. These results suggest that, in the short-term, warming could stimulate resource allocation to respiration rather than microbial growth, probably related to a reduction in the microbial carbon use efficiency. Simultaneously, soils with higher soil C concentrations could release more CO2 , despite the similar Q10 in the different wetlands. Overall, the soil of these high Andean wetlands could become C sources instead of C sinks, in view of forecasted increasing temperatures, with C-losses at regional scale.