干旱对湖北省长湖水生植物多样性的影响

将断面法和地理信息系统（GIS）与全球定位系统（GPS）技术相结合，通过比较湖北省长湖2000年（干旱年）与1999年（非干旱年）的水生植物多样性，探讨了干旱对淡水湖泊水生植物多样性的影响，主要结论如下：（1）干旱对长湖淡水湖泊水生植物物种多样性无影响，但可增加优势种数目（从12个至14个）。（2）干旱使长湖水生植物群丛数目从14个增加至18个，且能显著提高各群丛的Simpson与Shannon-Wiener物种多样性指数。（3）干旱显著提高了长湖水生植被覆盖率与各群丛的盖度，并使全湖水生植被平均单位面积生物量与各群从单位面积生物量显著升高。（4）在干旱年（2000年），长湖挺水植被消失，但浮水植被面积与沉水植被面积显著扩大：分别从1999年的3.71％与41.32%上升至2000年的12.63%与53.84%（占湖泊总面积的百分比）。（5）干旱条件下淡水湖泊水生植物的生长发育明显加快：2000年7月菹草石芽萌发率、菹草幼株长度和野菱黄叶率显著高于1999年同期值。

EFFECTS OF A DROUGHT ON AQUATIC PLANT DIVERSITY IN LAKE CHANGHU OF HUBEI PROVINCE IN CHINA

Many Studies have been carried out to deal with effects of floods on aquatic plant diversity of fresh water lakes. But no attention has been paid to understanding the effects of droughts on the diversity up to now. Changhu is the third largest lake (fresh water) in Hubei Province of China. It has many kinds of functions, such as store of flood water, irrigation, aquaculture, water transportation, and so on. Combinating Transect Sampling Method with Geographical Information System Technique (GIS) and Global Position System Technique (GPS), the authors studied the effects of a drought on aquatic plant diversity of the lake by comparing the aquatic plant diversity of the lake in 2000 (a drought year) with that in 1999 (a usual year). The function mechanisms of the drought on the aquatic plant diversity were also discussed by the authors. The main results are given as follows: (1) The drought had almost no effects on species diversity of aquatic plant, but increased the number of dominant species of the aquatic vegetation in the lake from 12 to 14. (2) The number of aquatic plant associations increased from 14 in 1999 to 18 in 2000. Species diversity indices of the associations by Shannon-Wiener Index and Simpson Index also remarkably increased under the drought condition. (3) The drought significantly enhanced the vegetation coverage from 45.15% in 1999 to 66.48% in 2000 and mean biomass per square meter in the whole lake from 1039.1g/m2 in 1999 to 1904.8g/m2 in 2000. (4) Under the drought condition in 2000, the emergent vegetation disappeared from the lake, but both the floating-leaved vegetation and submerged vegetation expanded greatly, from 3.71% and 41.32% in 1999 to 12.63% and 53.84% in 2000, respectively (the percentage here means the ratio of the floating-leaved vegetation area or submerged vegetation area to the whole lake area). (5) Both the growth and development of aquatic plants in the lake were accelerated by the drought. It was found that all the turion germination percentage of Potamogeton crispus, the shoot length of young plants of the species, and the ratio of yellow leaves of Trapa incisa to its total leaves in July 2000 were much greater than those during the same period in 1999. (6) It was concluded that the improvement of aquatic plant diversity in the drought year was mainly due to increasing of the light intensity which aquatic plants could get and increasing of the temperature in water body.