Short-term changes in plant dissolved organic carbon inputs are fundamental in mediating soil organic carbon dynamics

Climate change and management may alter plant dissolved organic carbon (DOC) inputs to forest soils, thereby altering soil organic carbon (SOC) storage. However, mechanisms underlying the effects of aboveground and belowground DOC inputs across forest stands and soil profiles on SOC dynamics and their microbial and faunal mediators remain poorly understood. Here, we performed a field manipulation experiment comparing relative roles of aboveground (leaf litter leachates) and belowground (root exudates) DOC inputs in SOC dynamics in mineral topsoil (0-10 cm) and subsoil (50-60 cm) of broadleaf (European beech) and coniferous (Norway spruce) forest stands. We also focused on understanding the relationships between SOC dynamics, DOC input quantity and quality and microbial and faunal communities. Within the 2-year-span of the experiment, we show that changes in both leaf litter leachates and root exudates inputs are fundamental in mediating SOC dynamics, with specific effects depending on the SOC stability and DOC input chemistry. On the other hand, forest stand did not exert a large effect over SOC dynamics through DOC inputs. Further, we found evident DOC inputs effects on soil and microbial, but not faunal properties only in the subsoil, indicating that subsoil rather than topsoil properties are generally more sensitive to changes in DOC inputs. However, SOC dynamics in the subsoil were generally not as sensitive to DOC inputs as in the topsoil. This implies that topsoil rather than subsoil is more vulnerable to significant SOC loss. Collectively, our findings suggest that changes in plant DOC inputs are fundamental in mediating SOC dynamics already in the short term, which can help better predict SOC dynamics under altered plant DOC inputs to soil.