First And Second Sets Of Shoots In Evergreen Woody Species From Tiantong National Forest Park Of Zhejiang, China

Evergreen broad-leaved forest is the regional vegetation in the subtropical area of eastern China. Based on the field investigation data, some woody species of subtropical evergreen broad-leaved forests in Eastern China form a second set of shoots in late summer or autumn after a first set in spring. However, little is known about the second set of shoots so far, and therefore resource utilization strategies remain poorly understood for such species. Our objective is to elucidate the features of this second set of shoots, including their adaptive significance.In order to understand the difference between the first and second sets of shoots for evergreen woody species, seven woody species (including Eurya rubiginosa var. attenuata, Loropetalum chinense, Symplocos lancifolia, Castanopsis fargesii, Lithocarpus glaber, Myrica rubra, Schima superb) were chosen as the study objects from an evergreen broad-leaved forest in Tiantong National Forest Park of Zhejiang, China. Herbivore damage of leaves was estimated, leaf emergence rate, leaf expansion rate and duration were calculated, and twig investment (leaf number and individual leaf area within twigs, twig stem length and diameter) was measured for both sets of shoots. In this paper, the habitat, life form and size of species (basal diameter, diameter at breast height, height of tree) in evergreen broad-leaved forests were investigated and researched in the proportion of the second sets of shoots at Tiantong forest region. The results were as follows:(1) The result of leaf damage between the first and second sets of shoots for those seven species (E. rubiginosa var. attenuata, L. chinense, S. lancifolia, C. fargesii, L. glaber, M. rubra, S. superb) showed:S. superb, M. rubra, L. glaber, C. fargesii suffered greater herbivore damage to the second shoots compared with the first, and no significant difference was found in damage between the two sets of shoots for S. lancfolia, L. chinense, E. rubiginosa var. attenuata. The difference of leaf damage between the first and second sets of shoots may be ascribed to genetic traits, climate factors (such as temperature, moisture and other factors), multiple strategies against insect herbivores and so on.(2) The result of leaf emergence rate between the first and second sets of shoots for five woody species (E. rubiginosa var. attenuata, L. chinense, S. lancfolia, C. fargesii, M. rubra) showed:the first and second sets of shoots shared the same leaf emergence pattern. S. lancifolia, L. chinense, E. rubiginosa var. attenuata, and M. rubra showed a succeeding type of leaf emergence, and C. fargesii showed a flushing type of leaf emergence. However, the duration of leaf emergence was much shorter in the second set of shoots for S. lancifolia, E. rubiginosa var. attenuata and M. rubra than in the first but not for the other two species. The difference of leaf emergence rate between the first and second sets of shoots could be adaptation of plants to seasonal climate, or adaptation of herbivores to selective force.(3) The result of leaf expansion rate between the first and second sets of shoots for five woody species(E. rubiginosa var. attenuata, L. chinense, S. lancifolia, C. fargesii, M. rubra) showed:the leaf expansion was similar to the leaf emergence. For S. lancifolia, L. chinense and E. rubiginosa var. attenuata that leafed out early in spring, their leaf expansion rate was significantly higher for the second set of shoots than for the first set, and their duration of leaf area expansion was much shorter for the second set than for the first set. For M. rubra, C. fargesii that leafed out late in the first set of shoots, there was no difference in leaf expansion rate. Meanwhile both sets showed high leaf expansion rate and short duration of leaf area expansion. The difference of leaf expansion rate between the first and second sets of shoots could be adaptation of plants to temperature, or adaptation of herbivores to selective force.(4) The result of leaf mass per area (LMA) between the first and second sets of shoots for three woody species (L. chinense, S. lancifolia, M. rubra) showed:although the second set of shoots leafed out a little later, the LMA increased more quickly compared with the first set of shoots. Finally the LMA of the second set of shoots was larger than that of the first set. The second set of shoots could resist the insect herbivory by quickly increasing LMA, or probably combined with leaf thickness and toughness.(5) The result of twig investment between the first and second sets of shoots for those seven woody species (E. rubiginosa var. attenuata, L. chinense, S. lancifolia, C. fargesii, L. glaber, M. rubra, S. superb) showed:leaf number (except for L. chinense), individual leaf area, twig stem length (except for L. chinense) and diameter were significantly smaller in the second set of shoots than in the first set of shoots for six species, indicating lower twig investment during the second set of shoots for all the sampled species. To cut down the investment of the second set of shoots might reduce unnecessary losses in the coming winter, also might have something to nutrient limitation. The lesser investment of the second set of shoots may be related with nutrient limitation; additionally it could reduce losses in the coming winter.(6) The result of proportion of the second set of shoots at Tiantong National Forest Park of Zhejiang showed:based on the field survey, for each species the average proportion of the second set of shoots was18.2%at the twig level among43sampled woody species.18of them had no second set of shoots. The second-shooting-proportion of seven species was less than1.0%while the proportion of19species was more than5.0%.In general, leaf herbivory damage, rates of leaf emergence and expansion, leaf mass per area were not smaller (sometimes significantly greater), but the total investment on twigs was significantly lower in the second shoots compared to the first. We speculate that these differences might result from the selective force of heavy herbivory pressure and adverse climate conditions of coming winter for the leaves produced during the second set of shoots. The second set of shoots is an important life history strategy of plants during their evolution. It is beneficial to improve the adaptive capacity of broad-leaved evergreen forests and plays a significant role for protecting their biodiversity and maintaining community stability.