3.4 Relationship between root traits and soil properties
The rooting depth of the four species was negatively correlated with SWC and nutrient content along the RFC gradient (P < 0.05, Fig. 6). Reductions in soil water, TC, TN and TP were the main factors influencing the depth of the fine root profiles under high RFC conditions (Fig. 6). Variations in SWC along the RFC gradient was the main explanatory factor for changes in fine root traits across soil profiles (Fig. 7 and Table S2). Fine root biomass, length density, and specific root length all showed an increasing trend with the increase in RFC and were significantly correlated with the decrease in both SWC and available phosphorus (Fig. 7).