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