Studies On The Characteristics Of Rice Allelopathy On Barnyardgrass(Echinochloa Crusgalli L.) Exposed To Low Phosphorus Condition

The study on the physioecological process and its mechanism of allelopathy has now become main issue in the world.For this purpose, two cultivars i.e. allelopathic rice PI312777 and non-allelopathic rice Lemont introduced from U.S.A were used as donor plants, and barnyardgrass was employed as receiver plants.The two rice cultivars were respectively co-cultured with barnyardgrass exposed to the stress of low phosphorus condition(0.5mgP/L) in the hydroponic culture for study on the physiological and biochemistry mechanism of allelopathic and non-allelopathic rice cultivars under the nutrient stress .The results were summarized as follows:It was showed that the SOD activity of strong allelopathic rice PI312777 exposed to the nutrient stress was significantly enhanced compared to the control.But the activity of POD and CAT were increased then reduced gradually.The reverse was true in non-allelopathic rice, Lemont.This led to increased content of MDA compared to that in PI312777.The result also indicated that the contents of flavonoid , carotenoid, putrescine and spermidine in the allelopathic rice were higher.This implied that the allelopathic rice had the stronger ability resistant to the nutrient stress.It was also indicated that the allelopathicrice absorbed more amounts of N , P , K elements, in turn accumulated more dry matter compared with non-allelopathy rice Lemont exposed to low phosphorus condition, which was attributed to its higher root activity.It therefore suggested that the allelopathic rice was much stronger in resources competition under the nutrient stress condition compared with the countpart.It was also found that the activity of PAL could be induced by the nutrient stress, resulting in the increased content of phenolic compounds, then the higher allelopathic effect on barnyardgrass was the result, consequently leading to decreased dry matter weight and reduced root activity of the target grass.Further study suggested that it was caused by the higher contents of allelochemicals, resulting from the nutrient stress in rice and weed co-culture system, which led to decreased protective enzyme acitivities such as SOD and CAT, coupling with the increase of free radical contents and serious membrane lipid peroxidation.lt therefore could be concluded that the higher allelopathic potential of rice in the suppression on target weed , resulted from enhanced survival interference including the abilities of resistence to the stress, resource competition and amensalism.