Phosphorus limitation of Pinus massoniana reforestation increases with stand development: evidence from plant, leaf litter, and soil

Soil phosphorus (P) can often regulate plant productivity. However, the medium- to long-term effects of reforestation on P cycle within the continuum of plant, litter, and soil (including deep soil layers), and the subsequent regulation of soil P storage and its fractions, remain unclear. We determined soil (0–100 cm) P fractions, acid phosphatase, stoichiometric ratios, root and leaf N/P ratios, leaf P resorption efficiency (PRE), and leaf-litter P concentration of 32-, 45-, and 60-year-old Pinus massoniana reforestation in southwest China. The storage of soil labile, moderately labile, and occluded P decreased with the increase of stand age. The concentration of NaHCO3-Pi, NaHCO3-Po, and total labile P in top-soil layers decreased with the increase of stand age. The concentration of NaOH-Po and total moderately labile P in the entire soil profile declined over time. The concentration of C.HCl-Pi and total occluded P in the 0–100 cm soil layer were lower in the 60-year-old stand than in the 32-year-old stand. The PRE, leaf N/P ratio, top-soil C/P ratio and acid phosphatase activity increased, and the leaf-litter P concentration decreased with the increase of stand age. P. massoniana trees secreted more acid phosphatase and increased PRE to compensate for the decrease in soil P availability with stand development, which in turn decreased leaf-litter P concentration and thus resulted in a depletion of soil P. Overall, our results highlighted that P limitation of P. massoniana reforestation increased with stand development.