天然次生林植物叶片生态化学计量特征及光合特性对长期N沉降的响应

2006年5月于吉林省抚松县露水河林业局实验林场布设了人工模拟氮沉降控制试验，共设置3个氮（N）添加梯度，分别为对照（CK 0 g·N·m^-2·a^-1）、低N（LN 2.5 g·N·m^-2·a^-1）和高N（HN 5.0 g·N·m^-2·a^-1），旨在探讨N沉降对天然次生林先锋树种白桦（Betula platyphylla）和山杨（Populus davidiana）鲜叶、凋落叶化学计量特征、养分重吸收的影响，以及鲜叶光合特性的变化和各性状之间的相互关系。结果表明：（1）模拟N沉降处理下白桦、山杨鲜叶的C含量较对照均无显著影响，LN处理显著降低了山杨鲜叶N、P含量（P<0.05），显著增加了C：N、C：P和N：P（P<0.05）；HN处理显著增加了白桦鲜叶N含量和N：P，显著降低了C：N（P<0.05）。（2）白桦、山杨鲜叶N、P重吸收率在两个梯度N添加下均显著下降（P<0.05），且均为负值。山杨鲜叶N重吸收率与P重吸收率呈显著正相关关系（P<0.05），与鲜叶C：N呈显著负相关关系（P<0.05）。（3）N添加可以提高2种树木叶片氮素光合利用效率（PNUE）（P<0.05）、净光合速率（P_n）（P<0.05）。白桦鲜叶N含量与P_n、PNUE呈显著正相关（P<0.05）；白桦、山杨鲜叶比叶重（LMA）与N含量呈显著负相关（P<0.05）；P_n与PNUE呈显著正相关（P<0.05）。本试验研究表明：在生长季，白桦、山杨鲜叶中N、P均表现为富集状态，土壤养分及外源N可供林木较快吸收并促进其生长，无需从凋落叶中吸收养分。N添加可以增强白桦、山杨鲜叶的光合性能，进而促进植物养分吸收和叶片发育。HN对长白山天然次生林的生长有促进作用。

Response of Ecological Stoichiometric Characteristics and Photosynthetic Characteristics of Plant Leaves to Long-term N Deposition in Natural Secondary Forest

Three nitrogen(N) concentration gradients were set up in Experimental Forest Farm of Lushuihe Forestry Bureau in Fusong County, Jilin Province, including control(CK 0 g·N·m^-2·a^-1), low nitrogen(LN 2.5 g·N·m^-2·a^-1) and high nitrogen(HN 5.0 g·N·m^-2·a^-1), to study the effects of N deposition on the stoichiometric characteristics, nutrient reuptake and changes of photosynthetic characteristics of leaves of birch(Betula platyphylla) and poplar(Populus davidiana), a pioneer tree in natural secondary forest, and the relationship between the characters. The results showed that:(1)Under the simulated N deposition, the C content of the fresh leaves of birch and poplar showed no significant influence compared with that of the control group, and the N and P contents of the fresh leaves of poplar were significantly reduced by LN treatment(P<0.05), and C:N, C:P and N:P were significantly increased(P<0.05). HN treatment significantly increased N content and N:P in birch leaf and significantly decreased C:N(P<0.05). (2)The resorption efficiency of leaves N and P of birch and poplar decreased significantly in the treatment of LN(P<0.05) and were all negative. There was a significant positive correlation between N and P resorption efficiency(P<0.05), and a significant negative correlation between C:N and N resorption efficiency(P<0.05). (3)N addition can improve the nitrogen photosynthetic efficiency(PNUE) and net photosynthetic rate(P_n) of two kinds of trees(P<0.05), leaf dry matter to leaf area(LMA) of birch and poplar showed a significant negative correlation with N content(P<0.05), and there was significant positive correlation between P_n and PNUE(P<0.05). The N content of birch leaf was significantly positively correlated with P_n and PNUE(P<0.05). The results showed that N and P in birch and poplar leaves were enriched in the growing season, and soil nutrient and exogenous N could be used to absorb and promote the growth of trees quickly, without the need to absorb nutrients from litters leaves. N addition can enhance the photosynthetic performance of the leaves of birch and poplar, thus promoting the plant nutrient absorption and leaf development. HN deposition can promote the growth of natural secondary forest in Changbai Mountains.