三峡水库消落区植物群落结构及其季节性变化规律

为揭示三峡水库消落区出露期间植物群落结构特征的季节性变化规律，于2017年4、6和98月，设置了15个调查样地，并根据高程将消落区分为145~155 m、156~165 m和166~175 m等3个区域，并设置未水淹区域（高程176~-185 m）为对照。结果表明，消落区出露时间显著影响着植物群落的组成，随着出露时间的延长，消落区植物群落优势种及其优势度变化规律因植物的生活型不同呈现出相反的变化规律。从4月至8月，优势植物狗牙根、牛鞭草、喜旱莲子草等多年生草本植物优势度下降，鬼针草、苍耳、醴肠、水蓼、野胡萝卜、狗尾草等一年生草本植物优势度增加。而未水淹区植物优势种及其优势度变化规律不会因生活型不同而表现出不同的规律，不同地点的植物群落优势种差异较大，相对来说艾蒿较为优势，其次为小飞蓬。高程也是影响植物群落特征的主要因子，消落区植物群落Shannon-Wiener指数、Margalef指数、Simpson指数、植物高度均值显著低于未水淹区域，随着高程的增加，Shannon-Wiener指数、Margalef指数、Simpson指数生物多样性指数及、植物高度均值呈增加趋势。三峡水库消落区之所以呈现出目前的植物群落分布特征，植物内在的适应机制包括植物本身的冬季耐水淹能力、夏季抗旱能力、抗病虫害能力以及植物的及其繁殖对策、种源扩散对策等是主因，而外界环境条件，包括消落区土层厚度、地形坡度、土壤基质氮磷等营养盐，以及受水淹持续时间、水淹深度、高程、消落区出露时间等是其主要驱动因子。

Plant Community Structure and Seasonal Variation in the Water Level Fluctuation Zone of Three Gorges Reservoir

The aim of this study was try to answer the seasonal variation of plant community characteristics during the period of exposure in the Three Gorges reservoir. In April, June and AugustSeptember 2017, a total of 174 plots were sampled belong to 58 sampling belts and 15 sampling sites. According to the elevation, the subsidence was divided into three areas of 145~-155 m, 156~-165 m and 166~-175 m. The un-flooded area at the altitude of 176~-185 m was set as the control. The results showed that the dominant species and their dominance showed the opposite variation rules due to the different life forms of plants with an increase of exposed time. From April to August, the dominance of perennial herbs decreased such as Cynodon dactylon, Hemarthria altissima and Alternanthera philoxeroides. However, the dominance of annual herbs increased such as Bidens pilosa, Xanthium sibiricum, Eclipta prostrata, Polygonum hydropiper, Daucus carota and Setaria viridis. The variation rule of dominant species and dominant of plants in the un-flooded area did not show different rules due to different life forms. In the un-flooded area, difference in the dominant species of plant community was obvious in the different sampling sites. Artemisia argyi was relatively dominant, followed by Comnyza canadensis. Elevation was also a major factor affecting the characteristics of plant communities. The mean value of Shannon Wiener index, Margalef index, Simpson index and plant height of plant community in the water level fluctuation zone (WLFZ) were significantly lower than those in the un-flooded area. With an increase of elevation, the mean value of Shannon Wiener index, Margalef index, Simpson index and plant height increased. Why did the plant community present the current distribution pattern in the Three Gorges Reservoir area? The internal adaptation mechanism of plants was the main reason, including the flood tolerance ability in winter, drought resistance ability in summer, disease and insect resistance ability, plant propagation strategy, provenance diffusion strategy and so on. While, the external environmental conditions were the main driving factors including the thickness of soil layer, terrain slope, nitrogen and phosphorus and other nutrients in the soil, the duration and depth of flooding, elevation and the exposure time in the WLFZ.