Subtropic evergreen and deciduous broadleaved mixed forest forms the transitions from deciduous broadleaved forest to evergreen broadleaved forest. This forest type has an extensive distribution in subtropical mountainous regions of China. This paper focuses on the caloric value, ash content and their dynamics in various layer mature leaves of the dominant plant species in the community. The sampling site was located in the broadleaved forest community at Bei Mountain of Zhejiang Province (29°13′N, 119°38′E), and the caloric value was measured by GR3500 type oxygen bomb calorimeter.
The ash content of the community species ranged from 4.49% (Rosa wichuriana) to 12.19% (Sasamorpha sinica), and varied with plant species and sampling seasons. Among 18 plant species in our study, only two species’ ash contents (S. sinica and Glochidion puberum) exceeded 10%. The rank order of the average ash contents in the leaves was the following: tree layer (7.49%±2.59%) > shrub layer (7.20% ±3.22%) > herbaceous layer (6.68% ±1.02%) > liana layer ( 6.28% ±1.31%), and the differences among those layers were found not to be significant by nonparametric tests (p>0.05). Compared with other plants in tropical and subtropical zones, our study plants had relatively high ash contents (7.33%±2.15%) in leaves, similar only to some mangrove woods in Dongzhai Harbor Mangrove Forest Reserve of Hainan Province. The ash contents were related with amounts of nutrient elements absorbed in the plant body, which could indicate the role of element enrichment of plants. Levels of these element enrichment in plant components depended on their respective need for elements, and were related with element contents in soils. Ash-free caloric values of community species ranged from 16.28% (Pueraria edulis) to 23.55% (Camellia fraterne), which varied among plant species and sampling seasons. Among the 18 plant species, 6 species had high ash-free caloric values (>20.00 kJ/g), and 4 species had low ash-free caloric values (<18.00 kJ/g). In the same community layer, evergreen species commonly had higher ash-free caloric value than deciduous species. The rank order of average ash-free caloric values in the leaves was the following: shrub layer (20.33±2.29） kJ/g > tree layer (19.92±1.05） kJ/g > liana layer (19.71±3.26） kJ/g> herbaceous layer (18.14±0.74） kJ/g, and the difference between tree layer and liana layer was found to be significant by nonparametric test (p<0.05). Caloric values of leaves varied with phenological phase, and changes were related to biological characteristics of species. In our plant community, annual fluctuation of the caloric values was different among the species, and most species had higher ash-free caloric values in spring and autumn than in summer. To some extent, the variation of caloric values within a species reflected the difference of developmental status. To reflect the effect of habitat fragmentation on the caloric values, the caloric values of three tree species in different habitats were compared. Gross and ash-free caloric values of three species outside the forest were highest, and the difference between outside and inside the forest was significant according to t test (p<0.05), indicating that habitat fragmentation had obvious influences on the caloric values. Our analysis showed that some environment factors vary. For instance increase of light intensity and water content of soil, and caloric values of the sampling species outside the forest all were significant higher (p<0.05) than inside the forest. However, dynamic changes of ash content in different habitat showed no regular trend