Authors:
Dr. Khatab Abdalla | Agroecology, Bayreuth Center of Ecology and Environmental Research (BayCEER), University of Bayreuth, Bayreuth, Germany | Germany
Prof. Dr. Johanna Pausch | Agroecology, Bayreuth Center of Ecology and Environmental Research (BayCEER), University of Bayreuth, Bayreuth, Germany | Germany
Projected risks of global warming due to high greenhouse gas emissions increase the need for agricultural practices with high carbon (C) sink capacity and low water demand without compromising 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 may accelerate soil organic matter mineralization via priming effects. We hypothesized that higher root-derived C input triggers higher losses due to the enhanced mineralization via priming. Our main objective was to compile C budgets, allowing to conclude on C stock changes in well-watered and drought-stressed maize systems. To achieve this objective, soil CO2 efflux and its 13C, in conjunction with plant and soil parameters were measured over three years from well-watered, drought-stressed maize and unplanted control. Well-watered maize increased annual average CO2 efflux (by 24.5%), root biomass and root C stocks in the first three years compared to drought-stressed maize. Despite the higher input of newly allocated C (C4-derived) to soil, no significant changes in soil C stocks were observed. This is explained by priming-induced mineralization of soil organic matter as shown by higher replacement of old C3 by new C4-derived C in well-watered maize compared to drought-stressed maize. Accordingly, a lower input of new C4-C along with lower decomposition preserves C stocks in drought-stressed maize. Overall, these findings suggested that a higher input of C to soil is offset by elevated decomposition through priming effects. As a result, soil C stocks remain unchanged. This highlights the importance of accounting for priming effects in soil carbon management.