洱海漂浮草垫的物种组成及分布

研究通过调查洱海2017年夏季和冬季漂浮草垫的物种组成及分布模式, 探究洱海在水位上升过程中, 哪些挺水植物更易形成漂浮草垫而存活下来。夏季共调查到漂浮草垫18个, 植物分属15科, 18属, 24种, 冬季共调查到漂浮草垫22个, 植物分属13科, 17属, 22种, 形成洱海漂浮草垫的植物共15科, 19属, 26个物种。草垫下水体中总氮(TN)、总磷(TP)、溶解性总磷(TDP)都明显高于开阔水域的(P<0.05), 而开阔水域的溶氧(DO)明显高于草垫下水体的(P<0.05)。结果表明在夏季和冬季漂浮草垫面积大小与其组成草垫的物种数和漂浮草垫生物量都呈显著正相关(P<0.01), 而在夏季和冬季漂浮草垫面积大小与漂浮草垫单位面积平均生物量相关性都不显著(P>0.05), 漂浮草垫面积大小与漂浮草垫下最长根在夏季相关性显著(P<0.01), 而在冬季相关性不显著(P>0.05)。漂浮草垫主要分布在离岸距离60 m以内以及水深不超过2 m的水域, 漂浮草垫面积大部分都小于600 m2(夏季占87%, 冬季占95%), 每个漂浮草垫的物种数都小于10个, 漂浮草垫下最长根主要分布在40—120 cm。组成漂浮草垫的物种中菰(Zizania latifolia)的频度和相对生物量在夏季和冬季(频度: 夏季-73.33%, 冬季-66.67%; 生物量: 夏季-43.38%, 冬季-41.91%)都是最高的, 说明菰相比其他挺水植物更容易形成漂浮草垫从而避免洱海水位上升对其生长和繁殖的影响, 这可能是菰成为洱海单优挺水植物的主要原因。而菰比其他挺水植物更容易形成漂浮草垫的机制则需要更进一步的研究。

SPECIES COMPOSITION AND DISTRIBUTION OF FLOATING MAT IN LAKE ERHAI

The growth and propagation of aquatic plants will be greatly suppressed if the water level rises promptly. Some aquatic plants, especially for some emergent plants, can form floating mats to avoid the effects of deep flooding. We studied the species composition and distribution pattern of floating mat to find which species could form floating mats more easily and survive in the process of increasing water level in Lake Erhai in 2017. A total of 26 aquatic species (attached to 15 families and 19 genera) were recorded. The concentrations of total nitrogen (TN), total phosphorus (TP) and total dissolved phosphorus (TDP) in the water under the floating mat were greater than those in the open water, while the concentration of dissolved oxygen (DO) was vice versa. The results showed that both species richness and biomass of the floating mat were positively correlated with the area of floating mat (P<0.01), and the mean biomass of the floating mat was not significantly correlated with the area of floating mat (P>0.05). The longest root of the floating mat was significantly correlated with the area of floating mat in summer (P<0.01) but not in winter (P>0.05). Most of the floating mats distributed in the region within an offshore distance of 60 m and the water depth less than 2 m. The area of the most floating mats was less than 600 m2 (87% for summer and 95% for winter), and the number of species in the floating mats is less than 10, the longest root in the floating mats ranged from 40 to 120 cm. The frequency and relative biomass of Zizania latifolia were the greatest among all recorded species on the floating mats in two seasons (frequency: 73.33% in summer and 66.67% in winter; relative biomass: 43.38% in summer and 41.91% in winter). These results indicated that Z. latifolia was easier to form floating mats in escape of the stress of deep water than the other emergent species to explain its sino-dominance in the emergent community. The mechanism that Z. latifolia is easier to form floating mats than the other emergent plants deserves further investigations.