西双版纳热带季节雨林林窗内幼树叶生长与虫食动态

LEAF GROWTH AND HERBIVORY DYNAMICS OF SAPLINGS IN TROPICAL SEASONAL RAINFOREST GAPS IN XISHUANGBANNA

研究了西双版纳热带季节雨林 6种乔木幼树在林窗中的叶生长与叶虫食动态。 6种幼树叶生长主要在雨季 (5～ 10月 ) ,在旱季雾凉期 (11～ 2月 )叶停止生长。阳性树种旱季干热期 (3～ 4月 )开始叶生长 ,顶极树种至 5月雨季初才开始叶生长。表明雾凉期低温抑制两类树种叶生长 ,干热期水分不足抑制顶极树种叶生长。叶生长同步性(每两个月的叶生长量变异系数 C.V.)顺序为 :望天树 (Shorea chinensis,1.4 2 ) >金钩花 (Pseuduvariaindochinensis,1.4 1) >八宝树 (Duabanga grandiflora,1.0 2 ) >云南石梓 (Gmelina arborea,0 .98) >团花树(Anthocephalus chinensis,0 .84 )和铁刀木 (Cassia siamea,0 .84 )。旱季造成一些种类幼树出现落叶高峰 ,严重叶虫食也导致云南石梓在 7～ 8月出现落叶高峰。叶虫食主要出现在雨季 ,团花树和云南石梓在干热期叶生长能减少昆虫取食 ,但此时铁刀木叶同步生长却不能降低食叶昆虫危害。6种幼树叶生长量年进程与叶虫食量年进程间存在正相关 ,其中望天树、金钩花、八宝树和团花树分别达到显著 (p<0 .0 5 )或极显著 (p<0 .0 1)水平。望天树和金钩花在雨季初叶同步生长能减轻叶虫食。食叶昆虫偏爱取食幼叶 ,6种幼树平均幼叶的虫食量占总虫食量的 72 .9% ,幼叶虫食速率平均为成熟叶?

Leaf growth and herbivory dynamics of six tree species saplings were measured in tropical seasonal rainforest gaps in Xishuangbanna, SW China. Leaf growth in all six species mostly occurred in the rainy season (from May to Oct.) and ceased in the foggy cool period (from Nov. to Feb.) of the dry season. Saplings of the heliophilous species studied began to sprout in the dry hot period (from March to April) of the dry season, but saplings of the climax species began to sprout at the beginning of rainy season in May. These results indicate that low temperature during the foggy cool period restrained leaf sprouting in both groups while water deficiency during the dry hot period restrained leaf sprouting for climax species. Leafing synchrony, measured as the coefficients of variation (C.V. ) of leaf production in per two months,the 6 species were ranked as follows: Shorea chinensis (1.42), Pseuduvaria indochinensis (1.41), Duabanga grandiflora (1.02), Gmelina arborea (0.98), Anthocephalus chinensis (0.84), Cassia siamea (0.84). Peaks of leaf fall for some of the tree species saplings coincided with the dry season while serious herbivory of G. arborea leaves resulted in intensive defoliation of that species during July and August also. Leaf herbivory was strongest in the rainy season. While the leafing of A. chinensis and G. arborea in the dry hot periods may act to reduce herbivory, but for C. siamea, the synchronization of leafing during the time did not appear to affect the rate of leaf damage by herbivores. For these six species saplings, the annual leaf production processes were positively correlated with annual leaf herbivory processes. These correlations reached significance ( p <0.05 or p <0.01) for S. chinensis, P. indochinensis, D. grandiflora and A. chinensis. For S. chinensis, P. indochinensis, the synchronization of leafing at the beginning of the rainy season may also act to lighten herbivory impacts.Leaf eating insects preferred young leaves to mature leaves. On an average, young leaf area eaten accounted for 72.9% of the total leaf herbivory, and the grazing rates (Percentage of leaf area eaten per month) of young leaves was 4.3 times higher than that of mature leaves.