The contribution of wetland plant litter to soil carbon pool: Decomposition rates and priming effects

Plant litter input is an important driver of soil/sediment organic carbon (SOC) turnover. A large number of studies have targeted litter-derived C input tracing at a global level. However, little is known about how litter carbon (C) input via various plant tissues affects SOC accumulation and mineralization. Here, we conducted laboratory incubation to investigate the effects of leaf litter and stem litter input on SOC dynamics using the natural 13C isotope technique. A 122-day laboratory incubation period showed that litter input facilitated SOC accumulation. Leaf and stem litter inputs increased soil total organic carbon content by 37.6% and 15.5%, respectively. Leaf litter input had a higher contribution to SOC accumulation than stem litter input. Throughout the incubation period, the delta 13C values of stem litter and leaf litter increased by 1.5%0 and 3.3%0, respectively, while delta 13CO2 derived from stem litter and delta 13CO2 derived from leaf litter decreased by 4.2%0 and 6.1%0, respectively, suggesting that the magnitude of delta 13C in litter and delta 13CO2 shifts varied, depending on litter tissues. The cumulative CO2-C emissions of leaf litter input treatments were 27.56%-42.47% higher than those of the stem litter input treatments, and thus leaf litter input promoted SOC mineralization more than stem litter input. Moreover, the proportion of increased CO2-C emissions to cumulative CO2-C emissions (57.18%-92.12%) was greater than the proportion of litter C input to total C (18.7%-36.8%), indicating that litter input could stimulate native SOC mineralization, which offsets litter-derived C in the soil. Overall, litter input caused a net increase in SOC accumulation, but it also accelerated the loss of native SOC. These findings provide a reliable basis for assessing SOC stability and net C sink capacity in wetlands.

Automated summary

Plant litter input is a crucial factor in the turnover of soil/sediment organic carbon (SOC). This study investigated the effects of leaf litter and stem litter input on SOC dynamics using the 13C isotope technique. It was found that both leaf and stem litter input facilitated SOC accumulation, with leaf litter having a higher contribution. However, leaf litter input also promoted SOC mineralization more than stem litter input. Overall, litter input led to a net increase in SOC accumulation but accelerated the loss of native SOC.