The Effect Of Flooding On Growth And Physiological Characteristics In 5 Legume Forages

The legume forages usually can not grow well in South China, because of the large amount of annual precipitation, the higher under-ground water levels and the sticky soil textures. It is important to screen and apply some waterlogging -tolerant legume forages for the rapid development of stockbreeding in South China. Few studies were made to flooding tolerance of legume plants, especially the legume forages. The further study of growth and physiological responses of legume plants to flooding condition is necessary to introduced waterlogging -tolerant legume forages in the South China.The object of this research was to determine the performance of 5 legume forages when flooding on different growth period and different flooding duration.The results indicated that the effect on growth in 5 legume forages was different. The growth rate of mung bean, annual wild soybean and red clover under flooding condition were significantly lower than the control at later growth period; the growth rate of white clove increased at early growth period, but decreased at later period. However the growth rate of alfalfa was lower than the control significantly at early growth period and 8^th week.Under flooding condition, root/shoot radio of mung bean was lower than the control at the 4^th, 5^th and 6^th weeks, but increased at the 8^th week while dry weight of above-ground parts quickly decreased. Compared to the control, root/shoot radio of annual wild soybean at early growth period and to alfalfa at the whole growth period decreased significantly. But the root/shoot radio of red clover and white clover changed unsignificantly under flooding condition.This study also indicated that the effect on physiological characteristics in five legume forages was different. Compared to the control, the chlorophyll content of mung bean at later growth period and annual wild soybean and alfalfa at early growth period decreased significantly. After flooding, Root porosity of mung bean and annual wild soybean were higher than the control. The root porosity of alfalfa was higher than the control at 4^th, 5^th and 8^th week. The root porosity of red clover decreased at early growth period, and increased at later period. In contrast the root porosity of white clover increased at early growth period, and decreased at later period. The cortex cell in the hypocotyl formed primary aerenchyma after the flooding treatment at early growth period. And the flooding treatment can enhance the annual wild soybean, alfalfa, red clover and white clover formed aerenchyma.The effects of different flooding duration are various. The long flooding duration has a great effect on the dry weight of mung bean and white clover. The dry weight of annual wild soybean, alfalfa and red clover after flooding were lower than the control. After flooding treatments, the number of lateral roots of mung bean after increased significantly. For on the case of alfalfa and red clover, the results are reverse.To sum up, the responses of 5 legume forages to flooding stress were different. Mung bean, annual wild soybean red clover and white clover could survive during 25 flooding days. But mung bean and red clover displayed considerable waterlogging tolerant. There were a little alfalfa death during 5 flooding days, and all plants death during 20 flooding days. Mung bean and red clover were the most tolerant to flooding, annual wild soybean and white clover were the next, and alfalfa was the lest tolerant to flooding. Mung bean acclimated to waterlogging by forming a large amount of lateral roots and primary aerenchyma. The reason of waterlogging tolerant of red clover, annual wild soybean and white clover was the formation of aerenchyma. The waterlogging-tolerant of 5 legume forage was different at different growth period. The waterlogging-tolerant of mung bean at early growth period was better than later. The waterlogging-tolerant of annual wild soybean at later growth period was better than early. The waterlogging-tolerant of alfalfa, red clover and white clover had little changed at the whole growth period.