Effects Of Water Levels On The Growth And Reproductive Characteristics Of Dominant Plants In The Dongting Lake Wetlands, China

In freshwater wetland ecosystems, water level is the key factor controlling the growth and reproduction of macrophytes, and consequently influencing the species composition, community succession and vegetation distribution. At present, many researches focus on studying the effects of water levels on the growth and reproduction of the same plants or different species in one habitat, but the studies of the same species which grow in different habitats in flood and water levels in Daratt are relatively weak. As most plants affected by water levels for long period have the capacity of clonal reproduction, they have formed a unique characteristic to adapt to the changes in water and sediment environment. Therefore, a systematic research on how wetland plant species through growth and reproductive allocation strategy in response to the water and sediment environment is of great significance to investigate the cause of changes in Dongting lake wetland vegetation zone and provide scientific basis for revegetation. This paper takes the typical plants in Dongting lake as the research object and uses the methods of field investigation and indoor experiments to examine the effects of water level on plant growth and reproduction. The results are presented as follows:(1) There was a significant seasonal and elevation dynamics in the growth and reproductive characteristics of Carex brevicuspis. In general, total biomass was higher at high elevations than that at low and middle elevations, and the proportion of ground biomass was higher at the low elevations than that t the middle and high elevations in January and March. These results indicated that Carex brevicuspis increased the ground biomass to store more energy through photosynthesis in the area of higher soil moisture content, and decreased sexual reproduction ratio and increased asexual reproduction ratio along the elevation gradient.(2) The principal component analysis (PCA) of soil environmental factors in Carex brevicuspis community showed that the soil environmental changes induced by soil moisture content were the key factors that affect plants growth and reproductive characteristics. Asexual reproduction as the main source of Carex brevicuspis regeneration, was sensitive to environment changes. In November, it was negatively correlated with the third principal component of soil, while it was also negatively correlated with the second principal component of soil in January the next year, and with flowering period (March) coming, it was not only negatively correlated with the first principal component of soil, but also positively correlated with the density of plants. In conclusion, Carex brevicuspis is inclined to choose sexual reproduction when resources are abundant, while it chooses asexual reproduction in scarce resource environment.(3) Water levels had a significant effect on the growth and reproductive characteristics of Carex brevicuspis, while the ecotype did not. The two study species exhibited very different growth and vegetative reproduction responses as the water level increased from -30 cm to 30 cm. The height and total biomass of Carex brevicuspis from low elevation decreased significantly when under flooding conditions (15 cm and 30 cm water levels), but they did not change much under drought conditions (-30 cm -15 cm water levels). The height and total biomass of Carex brevicuspis from high elevation did not change much under drought conditions, but they decreased when under flooding conditions, what’s more, they all died at the water level of 30 cm. This indicated that the Carex brevicuspis from high elevation area was less tolerant to flood than that from the low elevation area. Flooding treatment reduced the asexual reproduction ratio of both ecotype species, whereas each species responded differently to the drought treatment. The asexual reproduction ratio of Carex brevicuspis from low elevation area reduced significantly, while it increased when it is from high elevation. So, it is clear that mild drought was beneficial to reproductive production of Carex brevicuspis from the high elevation area but it was a threat to the survival of Carex brevicuspis from the low elevation area.(4) Both water levels and ecotype had significant effects on the growth and reproductive characteristics of Polygonum hydropiper. The growth characteristics of Polygonum hydropiper from low elevation did not change significantly under drought conditions, but they decreased under flooding conditions, while the growth characteristics of Polygonum hydropiper from high elevation did not change significantly whether under drought conditions or flooding conditions. This indicated that the Polygonum hydropiper from high elevation area was more tolerant to water than that from low elevation area. Compared to 0 cm water level, the asexual reproduction ratio of Polygonum hydropiper from low elevation area increased significantly under drought conditions and it showed a strategy to reduce the length of rhizome buds and the asexual reproduction ratio under flooding conditions. While the asexual reproduction ratio of Polygonum hydropiper from high elevation area increased significantly under drought conditions and it showed a strategy to reduce the number and length of rhizome buds to adapt to flooding treatments. So, we can see the two studied species had the strategy to adapt to drought stress by increasing the growth and the asexual reproduction ratio. These results indicated that Polygonum hydropiper was more tolerant to high levels of drought.(5)Compared to 0 cm water level, the soluble sugar content and the starch content of the two dominant species decreased under flooding conditions, while the four ecotype plants showed appropriate strategies to adapt drought stress. Overall, Carex brevicuspis from low elevation area was sensitive to flooding, while that from the high elevation area was more sensitive to drought stress. Polygonum hydropiper from high elevation area had low energy consumptions under drought conditions, and it used carbohydrates economically, and high starch content could also meet the needs of survival, so it showed strong ability to tolerate drought and recover growth. While Polygonum hydropiper from low elevation area was more sensitive to environmental stress, it stored little energy in the body so it was not good to recovery growth later. In all, the adaptation ability of typical wetland plants of Dongting Lake to a changeable environment is based on the capacity of energy storage and energy consumption.