重庆石灰岩地区主要木本植物叶片性状及养分再吸收特征

Leaf traits and nutrient resorption of major woody species in the karst limestone area of Chongqing

以重庆石灰岩地区15种常绿木本植物和14种落叶木本植物为研究对象,对两种生活型植物叶片衰老前后叶干物质含量(LDMC)、比叶面积(SLA)和叶片厚度(LT)进行了比较,并采用不同的计算方法(单位质量叶片养分含量、单位面积叶片养分含量)分析了两类植物叶片衰老前后养分含量及再吸收特征,最后对养分再吸收效率与其他叶性状因子之间的关系进行了相关分析。结果表明:常绿植物成熟叶LDMC、LT及衰老叶LT显著低于落叶植物,落叶植物成熟叶和衰老叶SLA均显著高于常绿植物(P<0.05);基于单位质量叶片计算的养分含量,常绿植物成熟和衰老叶N、P量均低于落叶植物,而基于单位面积叶片计算的N、P含量则表现出相反的趋势;基于不同方法计算的N、P再吸收效率差异不明显,其中常绿植物基于单位质量叶片养分含量计算的N、P平均再吸收效率为39.42%、43.79%,落叶植物的为24.08%、33.59%;常绿和落叶植物N、P再吸收效率与LDMC、SLA、LT和成熟叶N、P含量之间没有显著相关性,但与衰老叶养分含量存在显著负相关(P<0.05)。研究发现,无论是常绿植物还是落叶植物,衰老叶N、P含量均较低,表明石灰岩地区植物具有较高的养分再吸收程度。

Nutrient resorption is a key component of nutrient conservation strategies and productivity and element cycling in ecosystems. It influences many, if not most, ecosystem processes, including carbon cycling and resource-use efficiency, plant litter decomposition through changes in litter quality, and plant competition. We studied 15 species of evergreen woody plants and 14 species of deciduous woody plants in a limestone area in Chongqing; compared leaf dry matter content （LDMC）, specific leaf area （SLA）, and leaf thickness （LT） of two different types of plants before and after leaf senescence; and analysed leaf nutrients and resorption characteristics before and after senescence by using different calculation methods （nutrient content per unit mass and leaf nutrient content per unit area）. Finally, we analysed the correlation between nutrient resorption efficiency and other leaf traits. The results showed that LDMC and LT were significantly higher in the mature leaves of evergreen species than in those of deciduous species in the Chongqing karst area. SLA and SLA in senesced leaves were significantly lower in evergreen plants than in deciduous plants; LT was significantly higher in evergreen plants than in deciduous plants; and LDMC showed no significant difference. Nutrient content per unit mass of leaves, leaf nitrogen concentration （LNC）, and leaf phosphorus concentration （LPC） were higher in the mature leaves of evergreen species, and LNC in senesced leaves was significantly lower in evergreen plants. Nutrient content per unit area of the leaves showed the opposite trend： LNC and LPC were lower in the mature and senesced leaves of evergreen species. There was no significant difference in the N to P ratio （greater than 16） in both mature and senesced leaves of the two types of plants. There was no significant difference in N and P resorption efficiency calculated using different methods, and both evergreen and deciduous species showed lower resorption efficiency. When nutrient resorption efficiency was calculated on the basis of unit mass of leaves, mean N and P resorption efficiency for evergreen species was 39.42% and 43.79%, respectively, and that for deciduous species was 24.08% and 33.59%, respectively. When nutrient resorption efficiency was calculated on the basis of per unit area of leaves, mean N and P resorption efficiency for evergreen species was 39.32% and 45.19%, respectively, and that for deciduous species was 29.59% and 38.45%, respectively. There was no significant correlation between N and P resorption efficiency and LDMC, SLA, LT, and N and P contents in the mature leaves of the two types of plants. However, N and P resorption efficiency was negatively correlated with nutrient content in senesced leaves. This indicated that lower the nutrient content in senesced leaves, higher the nutrient resorption efficiency, that is, higher the degree of resorption of nutrients, higher the nutrient resorption efficiency. In this study, we found that N and P contents were both low in evergreen and deciduous plants, indicating that plants in a limestone area have higher nutrient resorption efficiency.