Soil organic carbon formation in grassland ecosystems: Higher efficiency of roots than shoots and rhizodeposition

Abstract

The formation and stability of soil organic carbon (SOC) are crucial for ecosystem carbon sequestration. Plant shoot litter, root litter, and rhizodeposition are the primary plant-derived carbon sources for SOC, and their quantities and proportions are susceptible to global change. However, their relative contributions to the formation and pool size of SOC and its fractions remain uncertain. In this study, we conducted a pot experiment followed by two incubation experiments, using natural ¹³C abundance isotope tracing to disentangle the effects of plant rhizodeposition, shoot litter, and root litter on SOC. The results showed that rhizodeposition during plant growth increased SOC stability by enhancing mineral-associated organic carbon and reducing particulate organic carbon, without affecting total SOC in the short term. Neither shoot litter nor root litter impacted SOC during short-term decomposition. Over the entire plant life cycle, the efficiency of plant carbon incorporation into SOC from root litter was 10 and 12 folds of that from shoot litter and rhizodeposition, respectively. Our findings indicate that, although root litter is less abundant than shoot litter, it plays a pivotal role in driving new SOC formation. This should be taken into account when predicting SOC sequestration, particularly given the turnover of roots under global change.