Physiology of rice and red rice plants in competition for nitrogen
Understanding the influence of nitrogen under the physiological behavior of rice and red rice in competition is critical to success in integrated weed management. In view of this, the objective of this work was to evaluate the physiological effects of the competition of rice and red rice submitted to different nitrogen concentrations. The experiments were conducted under greenhouse conditions in the 2011/12 crop year. The experimental design was completely randomized, with six replicates. The treatments were arranged in a factorial scheme, consisting of different combinations of the rice cultivar IRGA 424 and the red rice biotype, varying the ratios between them [intraspecific competition (100:0) and interspecific competition (50:50)]; and nitrogen doses (0, 30, 60, 90, and 120 g dm-3) added to the soil as urea, divided in two periods, at 15 and 53 days after emergence. The variables evaluated were: stomatal conductance of water vapor, photosynthetic rate, hydrogen peroxide and lipid peroxidation. The results show that, in general, when compared to intraspecific competition, interspecific competition causes greater oxidative stress and negatively interferes with photosynthesis even when plants are submitted to high (90 and 120 g dm-3 N) nitrogen doses. For red rice, in turn, it is the intraspecific competition that causes higher oxidative stress and loss of photosynthesis in plants under lower (0 g dm-3 N) and higher (90 and 120 g dm-3 N) nitrogen concentrations, respectively, in relation to interspecific competition.
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