Abstract: Under the context of increasing nitrogen (N) deposition, studies on the effects of N addition on leaf N resorption of plantations with different ages could improve our understanding of the response of forest ecosystems to climate changes. In this study, we explored the effects of different N addition levels (no N added as control, CK; 20 kg N·hm^-2·a^-1 as low N addition, N20; 50 kg N·hm^-2·a^-1 as high N addition, N50) on leaf dry mass, leaf volume, leaf N concentration and N resorption efficiency (NRE) of Larix principisrupprechtii with different ages (i.e. S11, S20 and S45 represented 11-, 20- and 45-year-old stand, respectively). The results showed that the dry mass of both green and senescent leaves decreased with increasing stand ages (P<0.05). During the leaf senescence, the loss of leaf dry mass in S20 was significantly greater than those of S11 and S45 (P<0.01). The loss of leaf volume in S45 was significantly lower than those in S20 and S11. N addition significantly decreased the volume of green leaf in S11 before senescence (P<0.05). Leaf N resorption efficiency of S11 was significantly lower than those of S20 and S45 (P<0.001). Furthermore, the reduction of NRE caused by N addition in S11 was significantly larger than the corresponding values in S20 and S45 (P<0.01). Our results areimportant for accurate assessment of N cycle in forest ecosystem and better understanding of growth strategies of forest ecosystems.

Key words: stomatal conductivity optimization model, abscisic acid, hydraulic regulation, water-regulation strategy