Abstract

Forest succession fundamentally alters soil carbon–moisture coupling through progressive changes in organic matter accumulation, soil structure development, and hydrological processes. This comprehensive study examines carbon–moisture interactions across a 125-year forest succession chronosequence in temperate deciduous forests, monitoring 89 forest stands representing early (5-15 years), mid (20-40 years), late (50-80 years), and mature (>100 years) successional stages. We employed continuous soil moisture monitoring, carbon stock measurements, and hydraulic property analysis to quantify coupling dynamics. Results demonstrate that soil organic carbon (SOC) content increases from 42.3 ± 8.7 Mg ha⁻¹ in early succession to 156.8 ± 23.4 Mg ha⁻¹ in mature forests, with concurrent improvements in water retention capacity from 18.2 ± 4.1% to 32.7 ± 6.8% volumetric water content at field capacity. Carbon–moisture coupling strength, quantified through correlation analysis, increases progressively from r = 0.43 in early stages to r = 0.89 in mature forests, indicating increasingly integrated biogeochemical–hydrological systems. Water retention efficiency improves 2.8-fold during succession, with organic matter contributing 67% of total water holding capacity in mature soils compared to 23% in early succession. Temporal analysis reveals that carbon–moisture coupling strengthens exponentially, reaching 80% of maximum coupling by 45-55 years post-disturbance. Depth profile analysis shows coupling intensification throughout the soil profile, with surface layers (0-15 cm) showing strongest relationships (r = 0.94) but significant coupling extending to 60 cm depth (r = 0.71). Seasonal dynamics demonstrate that coupling strength varies temporally, with strongest relationships during summer drought periods (r = 0.91) and weakest during spring saturation (r = 0.58). Mechanistic analysis reveals that soil aggregation mediated by fungal hyphae and root exudates drives coupling enhancement, with aggregate stability increasing 3.4-fold during succession. Economic valuation indicates that enhanced water regulation services provide benefits worth $234-567 ha⁻¹ year⁻¹ in mature forests through flood control, drought mitigation, and groundwater recharge. However, climate change scenarios suggest 15-23% reductions in coupling strength under projected warming, emphasizing the vulnerability of these integrated systems to environmental change.