亚热带常绿阔叶林和暖温带落叶阔叶林叶片热值比较研究

植物干重热值(GCV)是衡量植物生命活动及组成成分的重要指标之一,反映了植物光合作用中固定太阳辐射的能力。利用氧弹量热仪测定了亚热带和暖温带两个典型森林生态系统常见的276种常见植物叶片的干重热值,探讨了亚热带和暖温带植物热值分布特征,以及不同生活型、乔木类型间植物热值的变化规律。实验结果发现:亚热带常绿阔叶林和暖温带落叶阔叶林叶片热值的平均值分别为17.83 k J/g(n=191)和17.21k J/g(n=85),整体表现为亚热带植物暖温带植物。不同地带性植被的植物叶片热值在不同生活型间表现出相似的规律,其中亚热带常绿阔叶林表现为:乔木(19.09 k J/g)灌木(17.87 k J/g)草本(16.65 k J/g);暖温带落叶阔叶林表现为:乔木(18.41 k J/g)灌木(17.94 k J/g)草本(16.53 k J/g);不同乔木类型间均呈现常绿乔木落叶乔木、针叶乔木阔叶乔木的趋势。落叶阔叶乔木表现为亚热带暖温带,而常绿针叶乔木则呈现亚热带暖温带的趋势。此外,我们对于两个分布区域内的4种针叶树种叶片热值进行了比较,发现华北落叶松(19.32 k J/g,暖温带)杉木(19.40 k J/g,亚热带)马尾松(19.82 k J/g,亚热带)油松(20.95 k J/g,暖温带)。亚热带常绿阔叶林和暖温带落叶阔叶林植物热值的特征及其变化规律,为森林生态系统的能量流动提供了理论基础。

Comparison of leaf calorific values in subtropical evergreen broad-leaved and warm temperate deciduous broad-leaved forests in China

Gross calorific value (GCV) has been introduced to biological research and applied to reflect the capability of plant species to fix solar radiation. Calorific value has also been considered as a coefficient characteristic to evaluate the adaptation strategies of plant species to the external environment. Therefore, understanding the variation in GCV among different ecosystems may provide a basis for assessing energy fixation, transformation, and utilization efficiency. A number of studies have indicated that GCV varies among different geographical locations and ecological categories. Some studies have suggested that the energy contents of alpine plants should be higher than those of tropical plants, and have also shown that energy content differs among different plant life forms, decreasing in the sequence tree > shrub > herb. However, little has been reported on the patterns of GCV in different typical ecosystems (at the levels of species, life form, and community) across multiple zones. In this study, we compared the leaf calorific values of plant species in two forest ecosystem-subtropical evergreen broad-leaved and warm temperate deciduous broad-leaved forests in China. Field sampling was carried out in early August 2013 at Jiulian Mountain (Jiangxi Province) and Dongling Mountain (Beijing Province), China. Leaf samples of 276 plant species were collected from subtropical evergreen broad-leaved and warm temperate deciduous broad-leaved forests, and the calorific values of these leaves were measured using a PARR 1281 oxygen bomb calorimeter. To explore the variability in GCV, we analyzed the data at the levels of species, life form (trees, shrubs, and herbs), and community in the two forest types. Furthermore, trees were subdivided into evergreen and deciduous, and coniferous and broad-leaved. The results showed that the GCV of the subtropical evergreen broad-leaved forest was 17.83 kJ/g (n=191), whereas that of the warm temperate deciduous broad-leaved forest was 17.21 kJ/g (n=85). The changing trends in GCV among the different life forms were similar in both forests. The sequence of GCV in the subtropical evergreen broad-leaved forest was tree (19.09 kJ/g) > shrub (17.87 kJ/g) > herb (16.65 kJ/g), while the sequence in the warm temperate deciduous broad-leaved forest was tree (18.41 kJ/g) > shrub (17.94 kJ/g) > herb (16.53 kJ/g). Moreover, in both forest types, we found that the GCV values decreased in the following order: evergreen trees > deciduous trees and coniferous trees > broad-leaved trees in the both forests. The average GCV for deciduous broad-leaved trees was larger in the subtropical forests than in the warm temperate forests, whereas the GCV values of evergreen coniferous trees showed the opposite trend. In addition, the leaf calorific values of four coniferous trees in both forests were: Larix principis-rupprechtii (19.32 kJ/g, warm temperate deciduous broad-leaved forest) < Cunninghamia lanceolata (19.40 kJ/g, subtropical evergreen broad-leaved forest) < Pinus massoniana (19.82 kJ/g, subtropical evergreen broad-leaved forest) < P. tabuliformis (20.95 kJ/g, warm temperate deciduous broad-leaved forest). The findings of this study demonstrate the preliminary characteristics of GCV in subtropical evergreen broad-leaved and warm temperate deciduous broad-leaved forests, and also provide new insights about the energy cycles of forest ecosystems and the adaption strategies of plant species to environmental changes.