Effects Of Nitrogen On Leaf Senescence Of Maize (Zea Mays L.) And Carbon/Nitrogen Balance Under Drought Stress

Drought stress affects the growth and yield of crops seriously. So how to delay leaf senescence and increase the drought resistance of crops are significant. Carbon and nitrogen metabolism is the material basis of crop growth and yield, it plays an important role in regulation of leaf senescence. And nitrogen has a certain impact on crop drought resistance as an essential element for plant growth. Therefore, to investigate the influence of nitrogen on carbon/nitrogen balance and leaf senescence under drought stress, and the association with drought resistance. In this study, we select different maize varieties as the research object, set different nitrogen levels, as well as drought stress and rehydration.Which to investigate the influence of nitrogen on carbon/nitrogen balance of leaf senescence under drought stress and rehydration. The main conclusions are as follows:1. Drought stress induced the maize leaf senescence. The net photosynthetic, Fv/Fm and chlorophyll content decreased significantly under drought stress in different maize varieties. And the different varieties affected by the drought stress are different, there is a difference between maize varieties.2. Drought stress induced the imbalance of carbon and nitrogen. Under drought stress,the maize leaf accompanied with the accumulation of soluble sugar content, slightly changed of starch content, decreased of total nitrogen content, and increased of carbon/nitrogen ratio, carbon and nitrogen balance was damaged. Both the non-structural carbohydrates content and carbon/nitrogen ratio showed a significant negative correlation with chlorophyll content, and there was a significant positive correlation between totalnitrogen content and chlorophyll content. Therefore, the carbon/nitrogen balance may involve in the regulation of drought-induced leaf senescence.3. Under normal water conditions, it increased the net photosynthetic, Fv/Fm and chlorophyll content of maize leaf when increased the content of nitrogen. Which enhanced the internal physiological metabolic activity in maize leaf. Drought stress severely inhibited the net photosynthesis rate of maize leaf, Fv/Fm and chlorophyll content dropped significantly. But these indicators in maize leaves are affected severely under high nitrogen levels. By shoot dry weight calculations and we found that drought resistance and recovery capacity under high nitrogen level are significantly lower than low nitrogen level. Which indicated that nitrogen increases the drought stress sensitivity of maize under drought stress.4. After drought and rehydration, the biomass, leaf relative water content,photosynthetic parameters and other indicators of maize were recovered. However, carbon and nitrogen imbalance which induced by drought stress was not quickly recover. Soluble sugar content and carbon/nitrogen ratio continued to rise, and total nitrogen content continued to reduce. This indicated that leaf senescence sometimes may accelerated after drought and rehydration. The senescence may related to carbon/nitrogen ratio could not back to normal soon.From the above results, we can obtain that leaf senescence and carbon/nitrogen imbalance of drought stress and recovery are highly correlated. Which indicated that carbion/nitrogen imbalance may be involved in the regulation of leaf senescence.