Effect Of Water Turbidity On The Growth And Development Of Vallisneria Asiatic And Hydrilla Verticillata

In turbid water rich in sands, various suspended components of water turbidity can affect the productivity of submerged macrophytes. Suspended sands in water can physically block the penetration of irradiance through the water column, and greatly lower light availability to submerged plants and inhibit their growth. Further, suspended sands may be harmful to submerged macrophytes when deposited on leaf surfaces by reducing light transmission to photosynthetically active leaf surfaces and possibly altering gas and nutrient exchange, which finally would lead to the decrease of photosynthetic capability and the damage to photosynthetic apparatus. Therefore, it is necessary to study the effect of water turbidity on the growth of submerged macrophytes and the mechanism of submerged macrophytes to the stress of wate turbidity.Two kinds of submerged macrophytes (Vallisneria Asiatic and Hydrilla verticillata) were planted in ponds with different turbidities. The turbidity was caused by suspended sands (lower than 100μm). Some growing parameters and some chlorophyll fluorescence measurements (via Diving-PAM) were determined. The results show that:(i) In shallow turbid water (depth lower than 60 cm), the sprouts of Vallisneria Asiatic could grow well in water whose turbidity lower than 60NTU, and grow better in water whose turbidity lower than 30NTU (including 30NTU) . The minimum relative light intensity (I/I₀) for the growth of Vallisneria Asiatic's sprouts was 3.6%. In the water whose turbidity higher than 60NTU (including 60NTU), the growth of Vallisneria Asiatic's sprouts were significantly inhibited with the increase of water turbidity.(ii) In shallow turbid water (depth lower than 60cm), water turbidity had no obvious effect on the growth of Hydrilla verticillata's sprouts, therefore Hydrilla verticillata's sprouts could grow well in water whose turbidity lower than 90NTU (including 90NTU). The minimal relative light intensity (I/I₀) for the growth of Hydrilla verticillata's sprouts was 0.12%.(iii) In water whose turbidity lower than 30NTU (including 30NTU), some extent of deposit sands can protect the leaves of Vallisneria Asiatic from the higer irradiance in autumn. Compared with control, more light energy was used in the photochemistry action in leaves with deposit sands. However, things were different for Hydrilla verticillata. These deposit sands could not only obviously decreased the photosynthetic capacity of Hydrilla verticillata's leaves, that is more light energy was dissipated as heat and less energy was engaged in photochemistry reaction, but also activate more oxide radicals which could threaten the survival of Hydrilla verticillata.