Heavy Thinning Shifts the Plant–Soil Coupling From Nutrients to pH in Cunninghamia lanceolata and Pinus massoniana Plantations
摘要
This study examined the leaf and soil stoichiometry, as well as the nutrient coupling dynamics, of Cunninghamia lanceolata and Pinus massoniana plantations subjected to heavy thinning. Experiments were conducted in approximately 30-year-old plantations in Zhejiang Province, China, comparing heavily thinned stands (six years post-thinning) with control stands (no thinning). Thinning reduced stand density by approximately 53%–65% and 44%–57%, respectively. For both species, heavy thinning markedly reduced soil moisture and total carbon (C), nitrogen (N), and phosphorus (P) concentrations, but increased pH and bulk density. Stand biomass did not change significantly, but soil N stock and N supply per unit biomass of retained trees decreased. Thinning significantly lowered the leaf N and P concentrations in C. lanceolata and the leaf P concentration in P. massoniana (p < 0.001). Consequently, the corresponding C: P and N: P ratios increased. In the control stands, leaf N and P of C. lanceolata were significantly correlated with soil available nitrogen (AN) and available phosphorus (AP), while leaf N of P. massoniana was correlated with soil AN (p < 0.05). After thinning, these correlations disappeared, replaced by strong correlations between leaf nutrients and soil pH, indicating a shift from leaf nutrient–soil nutrient coupling to leaf nutrient–soil pH coupling. Heavy thinning altered the dominant environmental driver regulating plant–soil nutrient interactions, shifting the primary coupling from soil nutrient availability to soil pH. This finding suggests that intensive thinning restructures plant–soil interactions through ecosystem-level changes in the soil environment rather than solely through reductions in soil nutrient pools.
Graphical Abstract