Competition between Potamogeton malaianus and Hydrilla verticillata in response to different water level conditions.

To explore the effects of different water levels on competition of submerged plants, we selected the canopy submerged plant Potamogeton malaianus Miq. and the erect submerged plant Hydrilla verticillata (L. f.) Royle as study materials. Four water level gradients (25, 50, 75, 100 cm) were chosen to simulate the hydrological environment of shallow depressions in the main distribution area of submerged plants in the field. The competition between P. malaianus and H. verticillata under different water levels was investigated by measuring plant height, root length, stem thickness, number of leaves, nodal thrift, nodal spacing, above—ground biomass, below—ground biomass, and canopy whole—plant biomass. The results show that P. malaianus and H. verticillata increased in height as the water level rose. In most treatments, above—ground parts grew better than below ground parts. In the 25 cm water level, relative yields (RYs) of the above—and below—ground parts, and whole plant of P. malaianus displayed different patterns. At the water level of 25 cm, the RY values of the above—ground part, below—ground part, and whole plant of P. malaianus were greater than 1. At the low water level of 25 cm, all treatments had relative yield total (RYT) values greater than 1, and at 50 cm water level, the RYT value of P4H8 was greater than 1. RYT was less than 1 at both 75 and 100 cm at 75 and 100 cm water levels, the growth of each species was limited by the other species. In low water level environments, submerged plants switch from a competitive relationship to a facilitative relationship as the water level decreases (stress increases). [ABSTRACT FROM AUTHOR]