Mycelium, root exudation and root litter promote soil organic carbon sequestration under N addition by influencing different soil carbon fractions

Abstract

Aims

Belowground plant carbon (C) inputs constitute a significant source of soil organic carbon (SOC). However, the relative contributions of different C input pathways to SOC accumulation under nitrogen (N) addition remain unclear.

Methods

Using ingrowth-core technique, we assessed the contributions of mycelium, fine roots, fine roots & litter to SOC under N addition, where N0, N3, N6, and N9 correspond to N addition rates of 0, 3, 6, and 9 g N m⁻² y⁻¹, respectively. Mycorrhizal colonisation, root exudation and litter C inputs, and their effects on SOC were evaluated.

Results

(1) N addition increased the contribution of mycelium C input to occluded particulate organic carbon (o-POC), leading to a significant SOC increase of 2.99 g/kg under N9. (2) N3 enhanced the contribution of fine root C input to SOC by 2.62 g/kg relative to N0, primarily because fine roots exerted weaker negative effects on mineral-associated organic carbon (MAOC) under N3 than under N0. (3) Fine root & litter C input substantially enhanced free-POC concentrations relative to mycelium and fine roots, contributing the most to SOC accumulation (6.27–10.86 g/kg). (4) Root exudation C input had a greater positive effect on MAOC and o-POC accumulation than root litter; extensive root extension and exudation C inputs in bulk soil may reduce free-POC, while root litter input can continue to increase free-POC.

Conclusion

Mycelium and root C input contributed to SOC accumulation by influencing different C fractions, with their relative contributions under N addition being closely associated with quantities of belowground C input.