[Variations of water use efficiency and foliar nutrient concentrations in Cunninghamia lanceolata plantations at different ages].

We studied water use efficiency (WUE), nitrogen (N) and phosphorus (P) status of leaves at different leaf ages (current year, 1-, 2-, and 3-year-old foliage) as well as their relationships in a subtropical chronosequence of Chinese fir (Cunninghamia lanceolata) forests (3-, 8-, 14-, 21- and 46-year-old). The results showed that foliar WUE varied significantly with foliar age in the order of current year foliage > 1-year-old foliage > 2-year-old foliage > 3-year-old foliage, while stand age had no significant impact on foliar WUE. Foliar N/P ranged from 11.4 to 19.6 and was higher in younger and older stands than in stands at the fast-growing stage. The foliar N and P concentrations tended to display similar trends with foliar ages in the order of current year foliage>1-year-old foliage>2-year-old foliage>3-year-old foliage. WUE did not change significantly with stand ages, probably because the photosynthetic rates and stomatal conductance decreased simultaneously with stand age. There was no relationship between WUE and foliar N. WUE had significant positive correlation with foliar P and significant negative correlation with foliar N/P. It is indicated that foliar P concentration would be a key factor affecting WUE with increasing atmospheric N deposition in subtropical forests.