The Effect Of Weedy Rice On Cultivated Rice Photosynthetic Characteristic And Their Competitive Relationship Under Different N Levels

In recent years, due to the popularity of cultivated rice direct sowing, the weedy rice happened in the fields seriously interfered with the growth, yield and quality of cultivated rice. Cultivated rice yield losses affected by weedy rice are different due to the weedy rice density, duration of interference and cultivated rice varieties vary. Therefore, it is very valuable to study the mechanism of weedy rice affecting cultivated rice production. In addition, the different ability to compete light, water, nutrition between weedy rice and cultivated rice may change their competitive relationship because weedy rice has more tillers, leaf area, plant height and other excellent features, especially competitive ability of uptaking and using nitrogen.In this study, the effect of weedy rice(Oryza sativa L. f. spontanea, JS-Y1) with different density on photosynthetic characteristics and yield of cultivated rice(Oryza sativa L., Nanjing44) was investigateed. The results showed that there was no significant effect on other morphological characteristics of cultivated rice at tillering stage except for the number of tillers. Weedy rice had little effect on the chlorophyll content of the cultivated rice, but the net photosynthetic rate was significantly reduced with the increase in the density of weedy rice, especially at late grain filling stage. Weedy rice also had impact on net assimilation rate, grain filling rate and the ratio of source to sink increment at grain filling stage. Moreover, the yield components analysis showed that weedy rice had a most significant effect on the percent of filled grain and number of rice panicles with the increasing density. Hence, our results suggested that the yield loss of cultivated rice by weedy rice was mainly based on three main reasons. First, increasesing Weedy rice density reduced the effective panicles by affecting the number of tillers of cultivated rice; Secondly, weedy rice had impact on net photosynthetic rate of cultivated rice eapecially late grain filling stage, which reduced the seed setting rate; Finally, the effect of weedy rice on whole plant assimilative capacity, grain filling process of cultivated rice also had certain influence on seed setting rate. The combined action of three reasons eventually led to cultivated rice production severe cuts.There was obvious effect on tiller numbers, leaf area and yield of cultivated rice by weedy rice occurred in different time except for photosynthetic characteristics. The sooner weedy rice occurred, the greater impact on cultivated rice. In addition, compared to the growth prophase, the late growth stage was affected greater by weedy rice. Therefore, early preventation and promptly removing should be the priority in control measures to avoid weedy rice affecting the growth and yield of cultivated rice through its long and wide leaves, greater leaf area index and advantage of growth earlier and faster than the cultivated rice, it would occupy a favourable position competition nutrients, water and light with cultivated rice, thereby affected the growth and reduced the yield.Further research of different nitrogen levels impact on the competitive relationship between weedy rice and cultivated rice showed that the weedy rice and cultivated rice growth and development as well as photosynthetic characteristics was not only affected by the nitrogen concentration but also cultivation methods. Under hydroponic culture, different nitrogen concentrations had a significant effect on the weedy rice and cultivated rice morphological characteristics and photosynthetic characteristics.Under low nitrogen level root length, leaf area, tiller numbers, chlorophyll content and gas exchange parameters were significant different under middle nitrogen and high nitrogen levels, except for plant height and chlorophyll fluorescence parameters. In addition, the weedy rice plant height, leaf area, tiller numbers was significantly higher than cultivated rice, degrees of difference of net photosynthetic rate and chlorophyll fluorescence parameters were varying between weedy rice and cultivated rice at different nitrogen levels.Under potted culture, nitrogen had significant impact on leaf number, tiller numbers, leaf area, chlorophyll content, net photosynthetic rate and so on; It significantly increased the second and the third leaf chlorophyll content, net photosynthetic rate, and weedy rice increased more than cultivated rice in middle and high nitrogen levels. Thus, with the increasing nitrogen, the growth ability of whole plant improved by the growth of the lower leaves. Pot and field experimental datas also indicated that the increase of nitrogen had lager effect on the plant growth prophase than the late. Totally, we would find that the competitive relationship between weedy rice and cultivated rice under different nitrogen levels were different when cultivation methods were changed.