Abstract: The variations in tuber distribution in a dishshaped sublake of Poyang Lake and the consumption by tuberfeeding waterbirds were investigated in two years with different water level conditions. Our aims were to explore impacts of wintering waterbird foraging and water level fluctuation on tuber distribution of submerged macrophytes. Four investigations on species, density and biomass of tubers of submerged plants were conducted in Shahu Lake in October 2012, April 2013, October 2013 and April 2014, respectively, using quadrat method. The results showed that there were two different kinds of tubers occurring in the same distribution area in Shahu Lake, which derived from Vallisneria spinulosa and Hydrilla verticillata var. rosburghii, respectively. Both their density and biomass were significantly lower in October 2013 than in October 2012. This is mainly due to the dramatic interannual changes in water level of Poyang Lake during flood seasons and resultant significant impact on water quality. It was found that both the duration in which Shahu Lake was connected to the main region of Poyang Lake and the average daily water depth during April to September (flood season) in 2013 were significantly lower than in 2012, while the water turbidity during that period in 2013 was much higher. This condition was not advantageous to the growth and development of submerged plants. The density and biomass of the two kinds of tubers declined significantly at the end of wintering period of 2012-2013, while both of them remained unchanged before and after the wintering period of 2013-2014. The foraging activities of tuberfeeding waterbirds and the negative effects of high water level on food
availability could probably account for these differences. In short, the dramatic hydrological fluctuation in Poyang Lake would result in interannual fluctuation in food resources of waterbirds, while the food availability would be influenced by both tuber abundance and its accessibility by tuber feeders during the wintering period. This study is of important guiding significance to submerged macrophytes revegetation, waterbird conservation, as well as ecosystem function estimation for Poyang Lake and even for regions along the middle and lower reaches of the Yangtze River.

Key words: apple, fruit quality, partial least squares regression, soil nutrient