The Morphological And Physiological Response Of Three Plants To The Water Level Variation

Eco-remediation is one of the most important ways to protect water from contaminations. Applying aquatic plants (wetland plants) in situ to remediate polluted water is drawing more and more attentions due to its various advantages. However, different plant species have different tolerance to water level variations because of their different niches in the environment. If we shall take some of these plants for remediation use, we must understand their response to different water levels or water level variations to determine their morphological and physiological characters in different water levels. Once we understand the suitable water level for the plants to grow, it will also be helpful for us to choose or use the best suitable plants in eco-remediation in different circumstances.This study choses Polygonum lapathifolium L., Xanthium sibiricum Patr. and Scirpus yagara Ohwi to understand their morphological and physiological response to two different water level treatments including stable water level set at low water level(5cm), medium water level(10cm), high water level(15cm) and fluctuant water level involving low-medium-high and high-medium-low. And the relevant indexs are measured respectively at day 3, day 6, day 9. Two way ANOVA was used to analyze the main factor affecting three plants in different treatments (water level, time). One way ANOVA was used to analyze how plants react under different treatments. The differences between stable water level and fluctuant water level were compared and concluded the main results below:(1) Polygonum lapathifolium L. has a good adaptation to water level variations. Low water level has little influence while stable high water level and fluctuant water level has a significant effect to stimulate its growth(p<0.05). Meanwhile, the fluctuant water level has less physiological disadvantage in Polygonum lapathifolium L. and is good for its growth. In morphological way, shoot length growth increased shortly at day 3. Adventitious roots were substantially produced at day 6. Above ground biomass increased significantly which led to the ratio between above ground biomass and below ground biomass increased fast and significantly (p<0.05). In physiological way, chlorophyll and WSP content reduced respectively at day 6 and day 3 in stable high water level. However, it had less effect on chlorophyll (p>0.05) and increased WSP content in fluctuant water level.(2) Xanthium sibiricum Patr. has a poor adaptability to water level variations. It can resist the flooding stress through altering its morphological and physiological characters in stable low level while the medium, high stable water level and fluctuant water level are bad for its growth. In stable low water level, Xanthium sibiricum Patr. would produce adventitious roots at day 9 in stable low water levels. To cooperate with morphological response, chlorophyll a/b and WSP content increased significantly within time (p<0.05). However,20% and 40% death showed respectively in stable medium water level and stable high water level while the death rate was 60% in fluctuant water level at day 9. More details showed that there was no significant differences between treatments and the control in shoot length(p>0.05). Branch numbers decreased and below ground biomass decreased significantly at day 9(p<0.05). And the chlorophyll a/b was less than 3:1 all the time.(3) Scirpus yagara Ohwi has a good adaptation to water level variations. The stable low water level has little effect on its growth while medium and high stable water level would increase its shoot to grow significantly in a short time among which the stable high water level s influence on the shoot is greater. Meanwhile, this plant has a better adaptability to fluctuant water level. The result showed that shoot length growth increased respectively at day 9 in stable medium water level and at day3-6 in stable high water level while just the high water level in water level addition group had the auxo-action(p>0.05). In physiological way, chlorophyll had a temperate decrease at day 6 in stable high water level treatment while it remained the same(p>0.05) in fluctuant water level treatment. In addition, WSP content showed temperate increase at day 6 in both treatments.(4) To conclude, three plants had their respectively different morphological and physiological response to temprate water variations. Of which Polygonum lapathifolium L. had an obvious morphological response such as shoot length, substantial roots and biomass allocations. Scirpus yagara Ohwi also had obvious shoot growing response. Although Xanthium sibiricum Patr. was poor at adapting to water level variations, it would produce substantial root in low water level. All three plants would increase WSP content to resist flooding stress. Negative effect on chlorophyll in stable high water level treatments would be relieved in fluctuant water level treatments to stable photosynthesis. Thus fluctuant water would promote the growth of Polygonum lapathifolium L. and Scirpus yagara Ohwi while it would inhibit the growth of Xanthium sibiricum Patr. At the same time, the effects of two water level variation methods in fluctuant water level on three plants had little difference.