西双版纳不同海拔热带雨林凋落量变化研究

LITTERFALL OF TROPICAL RAIN FORESTS AT DIFFERENT ALTITUDES,XISHUANGBANNA, SOUTHWEST CHINA

在3个海拔梯度(600、1 100和1 600 m)选取8块热带雨林样地,研究了印度季风环境下西双版纳热带季节雨林和山地雨林的凋落动态随海拔的变化及其与气候的关系.在3个梯度上,年平均温度分别为22.1、20.1和16.6℃,年平均温度递减率为-0.005 3℃·m-1.随海拔增加,年平均降雨量增加(分别为1 532、1 659和2 011 mm),但旱季的降雨量基本相同(282～295 mm);年蒸发量变化较小(分别为1 369、1 374和1 330mm);年平均空气相对湿度降低(分别为86%、81%和84%),旱季后期湿度降低更明显;样地土壤含水显著增加.热带季节雨林凋落量(1 072～1 285 g·m-2·a-1)显著高于热带山地雨林凋落量(718～1 014 g·m-2·a-1).凋落量和凋落进程变异系数与海拔之间存在线性显著负相关,凋落量与温度线性显著正相关而与降雨量显著负相关.旱季凋落高峰受到空气相对湿度和土壤含水量影响,随海拔增加空气相对湿度降低使得海拔1 105～1 720 m的凋落高峰提前,但土壤含水量继续增加又会使凋落高峰推后.研究结果得出:1)热带季节雨林凋落量与东南亚热带潮湿雨林相近;2)旱季水分限制随海拔增加而变化,影响凋落高峰出现时间;3)随海拔增加,热带山地雨林凋落年进程由季节性向平稳过渡.

To assess the effects of the Indo monsoon on litterfall dynamics and changes of litterfall along altitudinal gradients in the tropical rain forests of southwestern China, eight plots were chosen along three elevational gradients of 600, 1 100 and 1600 m in Xishuangbanna, China. We examined the relationship between litterfall dynamics and climate, and their changes with increasing altitude. On three gradients, average annual temperature was 22.1, 20.1 and 16.6℃ respectively, with a mean lapse rate of -0.005 3 ℃ m^-1. With increasing altitude, annual average rainfall increased （1 532, 1 659 and 2 011 mm, respectively）, while in the dry season they were similar （282 - 295 mm） ; evaporation changed slightly （ 1 369, 1 374 and 1 330 mm, respectively） ; annual average relative humidity decreased （86%, 81% and 84%, respectively） and was much more pronounced in the late dry season; and soil water content increased significantly. Litterfall production of tropical seasonal rain forest （1 072 to 1 285g·m^-2·a^-1） was higher than in the tropical montane rain forest （718 to 1 014g·m^-2·a^-1）. Both litterfall production and CV of annual litterfall processes had a significant and negative linear relationship with altitude. Litterfall production had a significant and positive linear relationship with temperature and was inversely related to rainfall. Peak litterfall during the dry season was influenced by relative air humidity and soil water content. Peak litterfall occurred earlier in the dry season at altitudes of 1 100 to 1 720 m due to decreasing humidity with altitude whereas at higher sites （1 820 m）, increasing soil moisture levels delayed the litterfall peak. Our results suggested that 1 ） litterfall production of the tropical seasonal rain forest coincided with those of moist tropical rain forests in Southeast Asia; 2） water stress in the dry season changed with altitude and determined the timing of peak litteffall; and 3） with increasing altitude, there was a transition from seasonality to stability in annual litterfall process.