Tree growth rate and soil nutrient status determine the shift in nutrient-use strategy of Chinese fir plantations along a chronosequence

Nutrient resorption is a key nutrient-use strategy exhibited by perennial plants to overcome nutrient limitations and meet their nutritional demands. However, the factors that drive nutrient resorption with stand development remain largely unknown. In this study, we examined how a nutrient source (soil) and sink (trees) affected the resorption efficiency (RE) of nitrogen (N) and phosphorus (P). Fresh leaves, leaf litterfall, and soil samples were collected from a chronosequence of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook., Taxodiaceae) plantations at the ages of 3, 8–11, 16, 20, 25, 29, and 32 years. The N and P concentrations in stems, branches, leaves, coarse roots, and fine roots, stocks of N and P in soils, and the relative growth rate (RGR) of trees were measured. Fresh leaf N and P concentrations and RE decreased with stand age, while the N:P ratio in fresh leaves as well as the N and P concentrations in leaf litterfall increased. The RGR of trees declined with stand age. Soil P stocks increased but soil N stocks slightly decreased with stand age. A variation partitioning analysis revealed that the combined effect of RGR and soil P stocks on the RE of P (PRE) was stronger than the individual effect of each factor, while the RE of N (NRE) was greatly affected by the individual effect of RGR. With increasing age, Chinese fir plantations shifted from N-limiting to P-limiting conditions, and the nutrient-use strategy changed from “conservative consumption” to “resource spending”. These patterns were co-regulated by the tree growth rate and soil nutrient status. Thus, supply-demand relationships reflected the nutrient cycling status and could provide valuable information for sustainable nutrient management practices in tree plantations.