中文摘要：

以现有11年生马尾松（Pinus massoniana）人工林为基础，通过均匀间伐、抚育修枝，结合冠层分析仪（CI-110）测定郁闭度，形成林冠郁闭度约为0.9、0.8、0.7、0.6、0.5的5个梯度系列样地，研究马尾松叶片碳（C）、氮（N）、磷（P）养分含量、养分再吸收率及化学计量特征. 结果显示：1）随林冠郁闭度减小，叶片N含量、C：N、N：P皆存在显著差异，叶片C含量、P含量、C：P都没有显著差异；C含量、N含量、C：N、N：P皆呈抛物线趋势；C含量在0.6郁闭度时最大，N含量、N：P在0.7郁闭度时最大，C：N在0.7郁闭度时最小. N：P在11.15-16.38之间，说明该研究区的马尾松生长同时受N、P限制. 2）随林冠郁闭度减小，N养分再吸收率、N与P养分再吸收率之比都存在显著差异，P养分再吸收率没有显著差异；N、P养分再吸收率皆呈抛物线趋势，且都在0.7郁闭度时最大. 3）不同林冠郁闭度马尾松叶片C：N：P化学计量比与N养分再吸收率、P养分再吸收率、N与P养分再吸收率之比都存在极强的相关性关系. 4）随林冠郁闭度处理时间的延长，土壤pH值都有所升高，土壤含水量和土壤全N累积量有所下降，土壤有机碳累积量在3个中等林冠郁闭度下有所降低，土壤全P累积量在低林冠郁闭度时有所升高，而在0.7中等林冠郁闭度下有所降低. 5）不同年份间马尾松叶片C：N：P及其N与P养分再吸收率之比皆在林冠郁闭度0.7时较为稳定. 本研究表明林冠郁闭度为0.7的马尾松人工林林内微环境为马尾松的快速生长、良好发育提供了最为适宜的环境，具有较高的化学计量比内稳性.

英文摘要：

In order to study organic carbon （C）, nitrogen （N）, and phosphorus （P） content, N and P absorption efficiency, and the C：N：P stoichiometric ratio in leaves of Pinus massoniana, in the present study, five canopy densities of P. massoniana plantations, i.e., 0.9, 0.8, 0.7, 0.6, and 0.5, were formed by thinning and pruning, assisted by a canopy analysis system （CI-110 Plant Canopy Imager）. The main results are as follows： 1） with the decrease of crown density, there were significant differences in N content, C：N, and N：P, but no significant differences in C content, P content, and C：P in leaves of P. massoniana. The organic C, N content, C：N, and N：P in leaves of P. massoniana showed a trend similar to a parabolic curve. The highest organic C content was for 0.6 canopy density; the highest N content and N：P, and the minimum C：N, in the leaves of P. massoniana were for 0.7 canopy density. In all canopy densities of P. massoniana, the range of N：P was 11.15–16.38, which indicated that growth of P. massoniana was limited by both N and P nutrients. 2） With decreasing crown density, there were significant differences in N nutrient absorption and the ratio of N and P nutrient absorption rates, but no significant differences in P nutrient absorption. Both N and P nutrient absorption showed trends similar to parabolic curves and was the maximum for 0.7 canopy density. 3） There was a strong correlation between the C：N：P stoichiometric ratio and N nutrient absorption, P nutrient absorption, and the ratio of N and P nutrient absorption rates. 4） With the extension of forming of crown densities, soil pH value increased, soil water content and soil total N accumulation decreased, and soil organic carbon accumulation decreased for 0.8, 0.7, and 0.6 crown density. Total P accumulation in soil increased for 0.5 canopy density, but decreased for 0.7 canopy density. 5） Between different years, the C：N：P stoichiometric ratio and N and P nutrient absorption rates in leaves of P.