水深梯度对苦草生长和生物量的影响

将采用沙壤土培育的苦草幼苗（Vallisneria natans）放置于60-170 cm的水深范围内，每10 cm一个处理，使用光照计测定不同水深的光照强度并用 Skalar 水质流动分析仪测定试验水体的理化指标，观测苦草在不同的水深梯度下形态及叶片、叶绿素含量的变化，以研究水深梯度对沉水植物的个体生长发育及生物量的影响。试验结果表明：（1）试验30 d后，在60-130 cm的水深范围内，苦草株高随水深的增加而增高，在130-170 cm的水深范围内，随水深增加而降低，130 cm处苦草的平均高度最大，达67.9 cm；试验60 d，苦草的叶片长度、宽度、面积都随着水深的增加而减小，且在150-170 cm水深范围内叶片长度明显变小，苦草的生长速率随水深的增加显著下降；（2）不同试验组苦草的叶片长度、宽度、面积以及生长速率与水深呈明显的负相关（P＜0.01），而叶绿素含量与水深呈明显的正相关（P＜0.01），叶片面积在140-150 cm水深范围内减小最明显，且在140-160 cm水深范围内苦草各叶绿素指标较高，尤其是chl a＋b在水深160 cm处高达1.876 mg·g^-1；（3）苦草叶片叶绿素含量随着水深的增加（光强降低）而升高，其变化幅度为0.369-1.876 mg·g^-1，其中叶片叶绿素a随着水深的增加呈波动递增的趋势，且在水深80 cm处较低（0.268 mg·g^-1），而叶绿素b在60-170 cm水深范围内总体较平稳，在水深160 cm处达到最高（0.505 mg·g^-1），chl a/b变化幅度较小，仅在2.49-2.84 mg·g^-1之间；（4）试验60 d后，各试验组总生物量的较大值主要集中在100-140 cm水深范围内，其中地上部分生物量平均占全株生物量的89.5%，地下部分生物量只占10.5%，生物量的分配随水深梯度变化不明显。说明水深梯度的变化对苦草的叶片生长及叶绿素含量有影响，但对生物量的分配作用不明显。研究表明在100-140 cm的水深范围内?

Effects of Water Gradient on Seedlings Growth and Biomass of Vallisneria natans

In order to study the influence of water depths on seedlings growth and biomass of Vallisneria natans,seedlings of V.natans were studied by the way of culturing experiment under submersed condition in the depths range from 60 cm to 170 cm, each 10 cm a treatment, then the variation of chlorophyll content and leaves’s morphological feature were observed, the light intensity of various depths and the physical chemistry indexes were investigated using pulse-amplitude modulated fluorometer （PAM） and Water flow analyzer Skalar. The results showed that：（1） 30 days later, the height of the V. natans increased gradually with the water depth within 60-130 cm, however, within the 130-170 cm, the height decreased with the depth.The maximal average height was at the depth of 130 cm which peaked at 67.9 cm;60 days later, the blade length, width, area and growth rate were decreased toward the water depth, otherwise, a significant decrease of blade length was shown within 150-170 cm; （2） There is a negative correlation between water depth and blade length,blade width,blade area,growth rate respectively. But a positive correlation with chlorophyll content （P〈0.01）; the blade area decreased significantly within 140-150 cm,while each index of chlorophyll was high within 140-160 cm,especially the chla＋b peaked to 1.876 mg·g^-1 at the depth of 160cm;（3）The chlorophyll content of V. natans leaves has an increasing tendency with the light intensity decreasing, and the change range is 0.369-1.876 mg·g^-1;the chl-a fluctuate increased with the water depth and reduced to 0.268 mg·g^-1 at the depth of 80cm, but the chl-b had no significant change within 60-170 cm and peaked at 0.505 mg·g^-1 at the depth of 160 cm while the chl a/b had a little change within 2.49-2.84 mg·g^-1;（4）60 days later, the maximum value of biomass focused on the depth of 100-140 cm and the underground biomass of per treatment is 89.5%and 10.5%, furthermore, the distribution of the biomass has no obvious change with water depth.