Root-derived carbon explains the pattern of soil carbon dynamics in well-watered and drought-stressed maize.

The projected global warming risks due to high greenhouse gas emissions, increase the need for an agricultural practice with high carbon (C) sink capacity and low water requirements without compromising on crop productivity. On the one hand, it’s well accepted that soil moisture directly affects microbial activity, whereas, on the other hand, drought stress was recently postulated to increase root exudates, which in turn will accelerate soil organic matter mineralization via priming effects. Thus, this study aimed to investigate the interplay between soil moisture (well-watered and drought-stressed) and maize (Zea mays L.) C allocation on soil C dynamics. The experiment consisted of three treatments: well-watered, drought-stressed maize plus an unplanted control. Soil CO₂ efflux and its ¹³C were measured over three years in conjunction with soil temperature and moisture content. Under well-watered conditions, the annual average of CO₂ efflux was 0.12 g CO₂-C m^-2 hr^-1, which was 24.5 and 20% significantly higher than under drought-stressed and the control, respectively. Moreover, well-watered maize had significantly greater primed carbon than drought-stressed maize. Overall, these results suggested that the root exudates decreased under drought conditions, thus explaining the lower soil respiration under drought-stressed than well-watered maize.