不同林分类型叶片氮磷含量、氮磷比及其内吸收率

以福建东山沿海防护林中木麻黄、厚荚相思、刚果桉和湿地松4种主要树种为研究对象，探讨了纯林和混交林成熟叶与衰老叶中的养分状况、氮磷比、养分内吸收率以及它们之间的关系。结果表明:叶片中的养分浓度和内吸收率一般表现为纯林高于混交林、固氮树种高于非固氮树种。这是由于混交林和固氮树种改善了立地条件，林木能够从土壤中吸收较多的养分，从而降低了二者叶片中的养分内吸收率。各林分类型成熟叶片中的氮磷比都大于14，表明这些立地条件都存在不同程度的磷限制，导致大部分林分叶片磷内吸收率(REP)大于氮内吸收率(REN)，因而衰老叶中的氮磷比大于成熟叶，但成熟叶和衰老叶氮磷比之间依然存在显著的正相关关系。不同林分类型成熟叶和衰老叶养分浓度、内吸收率和氮磷比在固氮树种和非固氮树种中存在互补性，表明固氮树种和非固氮树种在养分利用方面存在差异。不同树种的营养利用策略不同，在选择造林树种时，应优先考虑叶片养分含量低而内吸收率高的“营养保存型”树种。 

Nitrogen and phosphorus concentrations, N: P ratio and resorption efficiency of leaves in different forest types

Nitrogen and phosphorus concentrations, N∶P ratio, nutrient resorption efficiency and their relationship in mature and senescent leaves in pure and mixed protection forest of Casuarina equisetifolia, Acacia crassicarpa, Eucalyptus ABL 12 W5 and Pinus elliottii were discussed in this paper. The results showed that nutrient concentration and resorption efficiency of leaves were higher in pure forest and N fixing species than in mixed forest and non N fixing species, respectively. This indicated that soil nutrient availability increased in mixed forest and N fixing species, so the trees could absorb more nutrients from soil and depended less on nutrient resorption from senescent leaves. The N∶P ratios of mature leaves were all above 14, nitrogen was less limiting than phosphorus, and accordingly phosphorus resorption efficiency (REP) was higher than nitrogen resorption efficiency (REN).N∶P ratio was increased with leaf senescence. There was significant positive relationship between N∶P ratio in mature and in senescent leaves. Inter and intraspecific correlations among nutrient concentrations, nutrient resorption and N∶P ratio of mature and senescent leaves in various forest types were different in N fixing and non N fixing species. Due to the difference of nutrient use strategy for various life forms, there was a significant correlation in N fixing species, but no correlation in non N fixing species, and vice versa. “Nutrient conservation” species, such as P. elliottii, with low leaf nutrient and high nutrient resorption efficiency should be prior selected for afforestation.