Effects of nitrogen forms and ratios on plant growth, seed antioxidant enzyme activities and reactive oxygen metabolism of vegetable soybean

Using the vermiculite culture, the effects of ratios of NO-3-N and NH+4-N on plant growth, seed antioxidant enzyme activities and reactive oxygen metabolism of vegetable soybean ［Glycine max (L.) Merr. cv. Li-xiang 95-1］ were studied. The results show that the appropriate ratio of NO-3-N and NH+4-N is about 75∶25 which is beneficial to the growth and development of the soybean, and produces the maximum plant biomass. Under the treatment of excessive NO-3 (100%) or NH+4 (75%), both biomass production and yields are decreased obviously, especially for the NH+4 (75%) treatment. In the NO-3∶NH+4 treatments of 75∶25 and 50∶50, the activities of antioxidant enzymes are low, and the O2 producing rate, hydrogen peroxide (H2O2) and malondiadehyde (MDA) contents are also low, therefore the degree of oxidative stress is comparatively low. However, under the NO-3∶NH+4 treatment of 25∶75, the antioxidant enzyme activities, the O2 producing rate, H2O2 and MDA contents reach to their highest values. These results indicate that excessive NH+4 is harmful to cell membrane integrity, resulting in severe degree of oxidative damage in the seeds of vegetable soybean.