In situ short-term carbon and nitrogen dynamics in relation to microbial dynamics after a simulated rainfall in croplands of different soil texture in Thailand

Abstract

The wetting—drying cycles of soil primarily drive carbon (C) and nitrogen (N) dynamics in tropical monsoon climates. We evaluated the in situ short-term C and N dynamics and the effect of soil texture during a wetting—drying cycle in relation to hourly microbial dynamics. Two croplands of differing soil textures (clay [THc] and sand [THs]) in Thailand were used for the experiment. Hourly measurements of soil CO2 efflux and inorganic nitrogen (Inorg-N) were conducted and we determined fluctuations in the in situ microbial biomass (In-situ-MB) and in situ microbial activity (In-situ-qCO2) after the application of a simulated rainfall (W plot) and a rainfall/glucose (WG plot) treatment. The rewetting of dry soil led to a C flush, which finished within 50–120 h because of rapid soil drying at both sites. Comparing the microbial dynamics in the THc-W and THs-W plots, it is clear that the rainfall treatment predominantly increased In-situ-qCO2 in the THc-W plot, whereas it increased In-situ-MB in the THs-W plot. These different microbial dynamics resulted in different C and N dynamics; that is, the cumulative soil CO2 efflux for the first 100 h after the treatment was effectively greater in the THs-W plot (3.4 g Cm−2) than in the THc-W plot (2.8 g Cm−2). In addition, distinct N-mineralization associated with a decreasing In-situ- MB was observed only in the THs-Wplot, although this was not the case in the THc-W plot. Hence, we concluded that rainfall events should play a more important role in the C and N dynamics in sandy soils compared with clayey soils because of different microbial dynamics after rewetting of a dry soil.