Survival Strategy Of Emergent Plants Along Water Depth Gradient

Based on the present emergent macrophytes in Erhai lake, four typical emergent macrophytes(Scirpus validus,Acorus calamus,Typha orientalis,Zizania caduciflora) were selected, and the relationship between emergent macrophytes and different gradient water level was studied, by measuring some relative index finding the rules of emergent macrophytes responsive to water gradient levels. We also collected some field emergent macrophytes and measured the relative index to find the rule of the field emergent macrophytes responsive to water gradient levels. Then we compared the rules in this two growth condition to seem the uniformity. The rules of the four emergent macrophytes responsive to water gradient levels are as following:As the water level from Ocm to 100cm, inhibiting effect on S. validus are gradually increased. The rhizome, tiller number and biomass are significantly decreased due to the increasing water level. In deep water, S. validus put the large proportion biomass to the above ground and less to the below ground, thus, the biomass proportion of above ground to below ground (BPAGBG) are increased compared to sallow water. In addition, the diameters of leaves are bigger in deep water than in sallow water, and the ratio of dry weight and fresh weight of leaves are decreased as the increasing water level, which may because S. validus developed much aeration tissue to enhance the exchange of gases.The inhibiting effect on the growth of the A. calamus increased as the increasing water level. To adapt to the adverse condition A. calamus adjust its strategy of energy allocation, decreasing the length of roots and rhizomes and increasing the BPAGBG in deep water. Effected by the water, the largest content of chlorophyll of A. calamus was in 30cm water depth.The most advantageous water level to the growth of T. orientalis was not in Ocm water depth, but 35cm water depth, under which water depth T. orientalis has the longest length of rhizome and the largest biomass, and the length and biomass are significantly big than the other three water level (0cm,70cm,120cm). However, the tiller number of the Ocm and 35cm water level were not significant. As the increasing water depth, the BPAGBG also increased as S. validus and A. calamus. The mean largest and least diameter of the T. orientalis increased as the water depth increasing.The suitable depth for the growth of Z. caduciflora is from 0cm to 30cm, and the too deep water level would inhibit the growth severely or would lead to death. Based on the length of the rhizome, tiller number and biomass, the best depth of water for growth is 30cm. The height and BPAGBG of Z. caduciflora increased as the increasing water depth. The transverse section of Z. caduciflora changed from ellipse to round probably due to the leaves falling off as the increasing water depth and the time extending.Comprehensive analysis of the four emergent macrophytes, A. calamus has the longest living time in drowned condition, but its rhizome length is shorter, till number less and reproducing and spreading slower than the other three emergent macrophytes. The rhizome of S. validus, T. orientalis and Z. caduciflora extending very fast, they can reach large areas in very short time. The best suitable depth for T. orientali growth is about 35cm water depth, and the suitable depth for S. validus, A. calamus, Z. caduciflora is from 0cm to 30cm water depth.