The P limitation of Pinus massoniana reforestation increases with stand maturity: Evidence from plants, leaf litter, and soil

Abstract

Background and Aims : Soil phosphorus (P) regulates plant productivity. However, the medium to long-term time-scale effects of reforestation on the P recycle of plants, litter, and soil continuum, thus regulating soil P storage, especially deep-soil P fractions dynamics, are unclear. Methods We determined soil (0 ~ 100 cm) P fractions, root and leaf N/P ratio, leaf-litter P concentration, and biogeochemical drivers in 32-, 45-, and 60-year-old Pinus massoniana reforestations in southwest China. Results The storages of soil labile, moderately labile, and occluded P in the 45- and 60-year stands were lower than the 32-year stand. The concentrations of NaHCO3-Pi, NaHCO3-Po, and total labile P in top-soil were lower while those in sub- and bottom-soil were not significantly in the 45- and 60-year stands compared to the 32-year stand. The concentrations of all soil layer NaOH-Po and total moderately labile P were lower in the 45- and 60-year stands than the 32-year stand. The concentrations of all soil layers C.HCl-Pi and total occluded P were lower in the 60-year stand than the 32-year stand. The leaf N/P ratio and top-soil C/P ratio and acid phosphatase were higher and the leaf-litter P concentration was lower in the older stands. Conclusions P. massoniana secreted more acid phosphatase and increased leaf P resorption to compensate for the drop in soil P-availability with stand age, which in turn decreased leaf-litter P input and thus resulted in a depletion of soil P. Overall, our results highlighted that P limitation increased with stand maturity in P. massoniana reforestations.