Several Ecological Problems In Manipulating Submersed Macrophytes By Harvest

This dissertation investigated several ecological problems in manipulating submersed macrophytes by harvest, which included growth of plants after cut, effects of harvest at moderate intensity on interspecific competition, sinking and settlement of shoot fragments, ability of nutrient absorption by leaves, effects of acetic acid on germination and bud growth of plants, restoring and manipulating submersed macrophytes in Lake Small Lotus and Lake Yuehu.1. Cultured in outdoor buckets filled with sediment and water from Lake Donghu, Myriophyllum spicatum L. and Hydrilla verticillata (L.f.) Royle was able to recover after cutting apexes, although their relative growth rates were reduced. New shoots mainly germinated from the cut points and turions for M. spicatum, and most new shoots from turions for H. verticillata. The diameters of new shoots were reduced after M. spicatum recovered from the cut, but those of H. verticillata were not significantly affected. Stolon development of H. verticillata was accelerated by each single cut, but was inhibited by continuously intensive cuts. M. spicatum was able to live through winter after the cut treatments in autumn, and the production of lateral shoots was not apparently reduced by 6 cm cut and 12 cm cut.2. In mixed-species cultures, there was no significant difference in dry weight between Potamogeton crispus L. and Elodea nuttallii (Planch.) St. John while surface cover of the former was greater than that of the latter before harvest. However, both surface cover and dry weight of E. nuttallii was higher than P. Crispus after harvest at moderate intensity. In mixed-species cultures, H. verticillata dominated E. nuttallii, both before and after the harvest.