悬浮泥沙与斜生栅藻(Scenedesmus obliquus)对亚洲苦草(Valisneria natans)光合放氧速率的影响

Effect of suspended sediment and Scenedesmus obliquus on the photosynthesis oxygen evolution rate of the Vallisneria natans

光照强度是沉水植物生长的主要限制因子。采用Clark型氧电极研究了悬浮泥沙与斜生栅藻(Scenedesmus obliquus)共同作用对亚洲苦草(Vallisneria natans)光合放氧速率的影响。将亚洲苦草种植于添加不同浓度悬浮泥沙(0.1、0.2、0.5、1.0 g·L–1)和斜生栅藻(105、106、107、108 cell·L–1)水体中,定期测定水体中斜生栅藻叶绿素a、光照强度及亚洲苦草光合放氧速率。结果表明:(1)各实验组斜生栅藻呈"S"型增长,且到达稳定期时间与悬浮泥沙浓度正相关,与藻细胞添加浓度负相关;(2)除对照组外,各实验组水体中光照强度曲线均呈先上升后下降变化趋势,第3天各实验组的光照强度均出现了高峰值,而第3天以后,光照强度均开始下降,其中下降最快的是0.1g·L–1悬浮泥沙含量实验组,15 d后该组平均下降了57.8%,与空白对照组相比,差异显著(P<0.05);(3)随着时间推移,各实验组亚洲苦草光合放氧速率均呈下降的趋势,其中悬浮泥沙浓度1.0 g·L–1、藻细胞浓度为108 cell·L–1实验组下降最明显,15 d后降到了10.88μmol·g–1(FW)·h–1;(4)由可重复双因子方差分析可知悬浮泥沙和斜生栅藻对苦草光合放氧速率的影响均极显著(P<0.01),且添加不同藻细胞密度造成的组间差异明显大于悬浮泥沙含量造成的组间差异,这说明亚洲苦草光合放氧速率变化对藻细胞密度变化比悬浮泥沙含量变化更为敏感。研究结果进一步揭示了富营养化泥沙水体苦草群落衰退原因,且为沉水植被恢复工程提供了科学依据。

Light intensity is the main limiting factor of submerged plant growth. We studied the effect of suspended sediment（SS） and Scenedesmus obliquus on the photosynthesis oxygen evolution rate of the Vallisneria natans with Clark-type Oxygen Electrode. The V. Natans were primarily planted in different concentrations of suspended sediment（0.1, 0.2, 0.5, 1.0 g·L^-1） and S. obliquus（105, 106, 107, 108 cell·L^-1） in water, and then we periodically measured S. obliquus chlorophyll a, light intensity and photosynthetic oxygen evolution rate. The results can be divided into four parts. Firstly, all the experimental groups of S.obliquus were growing in ＂S＂-type. The time of reaching the stable phase was positively correlated with the concentration of SS but negatively correlated with the concentration of added algal cells. Secondly, the light intensity curves of all the experimental groups showed a falling trend after the first rising except the control group, and the peak values of the light intensity in the third day. However, the light intensity began to decline gradually after the third day. After 15 days＇ experiment, the fastest decline ratio belonged to the SS concentration 0.1g·L^-1 group, decreased by 57.8% on average. Thirdly, as time went on, the V. natans photosynthetic oxygen evolution rate of all the experimental groups showed a downward trend. The photosynthetic oxygen evolution rate of SS concentration 1.0 g·L^-1, algae cell concentration of 108 cell·L^-1 group in the experiment fell to the lowest 10.88 μmol·g^-1（FW）·h^-1 after 15 days. Fourthly, the repeatable two-factors variance analysis illustrated that the impacts of SS and S. oblique on the photosynthesis oxygen evolution rate of Vallisneria natans were highly significant（P〈0.01）. While compared with the SS concentration, adding different algal cell density caused more obvious differences among those groups. It indicated that the change of the photosynthesis oxygen evolution rate was more sensitive to algal cell density change than the SS concentration change. This study not only could reveal the causes of V. natans communities recession in eutrophication and sediment waters further, but also provided scientific basis for submerged vegetation restoration project.