Effects of the length of inundation periods on investment in tuber biomass and sexual reproduction by

Modification and reductions in flows are reducing inundation times in some Yangtze River wetlands, potentially affecting the growth of submerged macrophytes. The effects of shortening the inundation period from April to October (control) to April to September (treatment) were tested on the production of surface and below-ground tubers and fruits in individual Vallisneria spinulosa ramets in microcosm experiments. Mean numbers of below-ground tubers produced did not differ significantly between treatments, but individual tuber dry mass was significantly greater when harvested in October compared with plants harvested in September. Significantly more surface tubers were initiated by the ramets in the later harvest, but these did not differ in dry mass. Fewer ramets had initiated sexual reproduction by the September harvest compared with the October harvest. Almost all October fruits were mature, while the ratio of mature to unripe fruits was significantly greater than in September. There was no support for the hypothesis that more tubers were initiated deeper in the substrate with a longer inundation period to avoid predation by fish or birds. Based on these results, shortening of the inundation periods experienced by Vallisneria spinulosa plants in Yangtze River ephemeral wetlands may reduce the dry biomass of below-ground tubers and the production of surface tubers in this keystone macrophyte.