不同水深条件下沉水植物苦草（Vallisneria natans）的形态响应和生长策略

苦草(Vallisneria natans)为我国常见的沉水植物之一,目前对水生态修复工程后苦草种群生长策略尚缺乏深入了解.以水生态修复工程1年后的苦草种群为研究对象,探讨水深对苦草叶片、匍匐茎、块茎等形态特征和苦草株数、匍匐茎数以及生物量等种群参数的影响,并分析水深胁迫下苦草的生长策略.结果表明,随着水深增加,尽管苦草单位面积株数和单位面积匍匐茎数均显著降低,但叶片长度、叶片宽度、叶片厚度、叶面积、匍匐茎长度、匍匐茎粗和块茎粗随水深显著增加,因而,苦草地上生物量也显著增加.其中,叶片长度和叶面积变异较大,对水深变化敏感,而叶片宽度、叶片厚度、匍匐茎长度、匍匐茎粗和块茎粗变异不大,对水深变化敏感程度低.在低光照胁迫下,苦草在亲株生长和子株输出之间存在权衡,一方面通过增加叶片投资保障亲株的资源利用效率,一方面通过降低亲株密度保障子株生长发育,从而实现种群空间生态位扩展和持续更新.在水生态修复工程中,考虑苦草的种群更新能力和施工的可操作性,在透明度为1.0~1.5m的条件下,苦草的适宜种植水深为0.5~1.0 m.

Morphological response and growth strategy of the submerged macrophyte Vallisneria natans under different water depths

Vallisneria natans is one of the most common submerged macrophytes in lakes of China. In present, the growth strategies of V. natans population in the water ecological restoration project remain unclear. In this paper, the responses of V. natans morphological traits such as leaf, stolon and tuber and population parameters such as plant number, stolon number and biomass to water depth were discussed on basis of one year effects after the implementation of water ecological restoration project. The growth strategies of V. natans were also analyzed. The results showed that the plant number per area and stolon number per area significantly decreased with the increasing of water depth, whereas the above-ground biomass increased significantly. The leaf length, leaf width, leaf thickness, leaf area, stolon length, stolon diameter and tuber diameter also increased significantly with the water depth increasing. Among them, the leaf length and leaf area varied dramatically because they were sensitive to water depth, whereas leaf width, leaf thickness, stolon length and diameter, and tuber diameter varied lightly and were insensitive to water depth. A trade-off between parent shoot growth and daughter shoot output was found under stress of less light. V. natans guarantees the resource utilization efficiency of parent shoots by increasing investments to leaf. On the other hand, V. natans improves the growth of daughter shoots by decreasing the parent shoot density, and thus the plant realizes the spatial niche expansion and population regeneration. In water ecological restoration project, considering the regeneration ability of V. natans population and construction maneuverability, water depth at appropriate 0.5 m to 1.0 m is suggested.