Increasing stand age increases N deficiency but alleviates relative P limitations in Castanopsis hystrix plantations in southern China

Aims: Forest productivity may decrease with increasing stand age, which may be related to a shift in the nitrogen (N) and phosphorus (P) nutrient balance. However, it is unclear how the plantation nutrient balance changes with stand age and how it affects plantation productivity. Methods: We experimented with increasing stand ages (6-, 10-, 15-, 25-, 30-, and 34-year-old stands) in Castanopsis hystrix plantations in southern China. Plant growth and the carbon (C), N, and P dynamics were assessed at the ecosystem level (leaf–litter–soil–microorganism). Results: Increasing stand ages reduced plantation productivity and leaf N:P ratios (lower leaf N concentrations and stable leaf P concentrations). The reduced productivity may be related to increased N consumption rather than possible P limitations. Increasing stand ages increased N consumption mainly through decreasing soil NO 3 − -N concentrations and microbial biomass without altering plant N resorption, although enhanced N-acetylglucosaminidase, cellobiohydrolase, and polyphenol oxidase activity might accelerate N mineralization. Increased soil total P concentrations and microbial biomass P rather than plant P resorption would support a larger P supply for plants with increasing stand ages. Conclusions: These results suggest that increasing stand ages can contribute to N consumption rather than elevate possible P limitations. Therefore, N fertilizer management should receive attention to maintain the productivity of C. hystrix plantations with increasing stand age.