油松天然林针叶功能性状及其与土壤养分的关系

Needle leaf functional traits and their soil nutrient relationships in natural Pinus tabulaeformis forests of different ages

为研究油松针叶功能性状随林龄的变化及其对土壤养分的响应,揭示油松天然林对土壤养分供应的适应策略。通过对山西中条山林区3个龄级15块油松天然林样地进行调查,对土壤和林分优势木当年生针叶进行取样测定,分析针叶功能性状变化的规律和对土壤养分的响应机制。研究结果表明:7个针叶功能性状中,针叶含磷量变异程度最大,为28.6%,其他6个针叶功能性状变异程度弱。随林龄增长,比叶面积和叶干物质含量在林龄间无显著差异,Ⅱ龄级(31~40 a)叶长宽比、投影面积、叶含氮量与含磷量均显著增大,Ⅲ龄级(41~50 a)则转而下降,且Ⅲ龄级叶含磷量较Ⅰ龄级显著降低,含碳量呈减小趋势,最小值为540.6 g·kg^(-1)。针叶长宽比与投影面积、含氮量、含磷量,以及投影面积与含氮量均呈显著相关。当油松林处于幼龄林I龄级时,叶功能性状指标快速增长,树体发育较快,应注意营养的添加;而土壤含碳量是影响不同龄级油松天然林针叶功能性状的主要土壤养分因子,但是也与其他养分结合共同影响油松天然林针叶。不同龄级油松天然林针叶的功能性状差异表明油松针叶有着较强的适应性,在Ⅱ、Ⅲ龄级叶功能性状趋于稳定。

In this study, we aimed to investigate the changes in Pinus tabulaeformis needle leaf functional traits with age and in response to soil nutrients, and to determine the adaptive strategies of P. tabulaeformis natural forest to soil nutrient supply. We investigated 15 natural P. tabulaeformis forest plots of 3 ages on Zhongtiao Mountain, Shanxi Province. The soil and the dominant tree needles of the year were sampled in each plot to analyze the needle leaf functional trait change rules and response mechanisms to soil nutrients.The results showed that among 7 needle leaf functional traits, the degree of variation in phosphorus content in the needles was high(28.6%), whereas the degree of variation among the other 6 functional traits was weak. With an increase in forest age, there were no significant differences in the specific leaf area and leaf dry matter content. The leaf length-to-width ratio, projected area, and leaf nitrogen content increased significantly in forest age class Ⅱ(31-40 a), and age class Ⅲ(41-50 a);however, the leaf phosphorus content increased in age class Ⅱ, but decreased in age class Ⅲ to a value lower than that in age class Ⅰ. The carbon content showed a decreasing trend with forest age, with a minimum value of 540.6 g·kg^(-1). The needle leaf length to width ratio was significantly correlated with the projected area, and nitrogen and phosphorus content, and the projected area was significantly correlated with nitrogen content. Our findings show that in young P. tabulaeformis forests(i.e., in age class Ⅰ), the leaf functional traits change rapidly and the trees grow fast;therefore, attention should be paid to the addition of nutrients. Furthermore, soil carbon content, the main soil nutrient factor affecting the function of needles in different aged natural P. tabulaeformis forests, also affects needle leaves in these forests in combination with other nutrients. The functional trait differences among needle leaves in P. tabulaeformis natural forests of different ages indicated that the needles have strong adaptability, and the leaf functional traits tend to be stable in trees 31 years and older(age classes Ⅱ and Ⅲ).