Influence Of Water Stress And Rewatering On Maize WUE And Compensation Effects

Improving water use efficiency (WUE) is an important measure for water-saving and crop yield increasing under the condition of water shortage. The influences of water stress and rewatering on crop yield and WUE are the urgent problems to be resolved. To reveal the influence mechanism of water stress and rewatering on crop WUE becomes an international research frontier in the field of biological water-saving. Nowadays, with the rapid development of economy, the global agricultural water resource scarcity becomes more and more serious, and water scarcity has become the limiting factor for grain yield increasing and economic development. Drought has caused a series of eco-environmental problems and threatened the sustainable development of agriculture. To solve these problems, the inevitable choice is to improve the WUE. Therefore, studying the response of crop yield to the water stress and rewatering, and the effect of water stress and rewatering on the WUE are very important for improving water use efficiency and increasing crop yield as well, especially in dryland farming areas. The research results will provide guidelines for the efficient utilization of water in agriculture and improves water-saving irrigation technologies. To examine the response of crop yield formation and WUE to water stress and rewatering in different growth periods and to different duration of stress, water control experiments in rainshelter were conducted from2009to2010, and maize was chosen as the study material. In this study, we confirmed the main influence factors of WUE, systematically analyzed the water consumption law under the drought and rewatering condition, and the responses of maize growth and development, yield formation, photosynthesis, transpiration, nitrogen absorption, and dry matter accumulation and distribution to water stress and rewatering. We synthetically analysed the physiological and metabolic compensation effect of rewatering after drought, and revealed the effect of drought and rewatering on WUE at the critical water requirement period of maize. The main results are as follows:(1) This study found that different influences showed on drought and rewatering on maize growth and development, yield and WUE in difference growth stages. As for the influence of drought and rewatering on maize growth and development in different growth stages, a descending rank order was found which was tasseling to early filling stage> jointing to tasseling stage> early filling to milk stage> mature stage and jointing stage. Changes of plant height, leaf area and total biomass were the main reasons for the differences. As for the influence of drought and rewatering on maize yield, a descending rank order was found which was tasseling to early filling stage> early filling to milk stage> jointing to tasseling stage> mature stage. Changes of ear kernel number, kernel weight and ear length were the main factors which resultted the differences. Under the water stress, the ear kernel, kernel weight, ear length and ear diameter decreased significantly that resulted in the decrease of maize yield. The influence of drought and rewater on WUE in difference growth stages were different with a descending rank order of tasseling to milk stage> jointing to tasseling stage> mature stage and jointing stage, and no significant difference was found between mature stage and jointing stage. During the jointing stage, the water stress significantly affect maize growth and yield, but the influences on WUE were not significantly different. So the water regulation carried out during the jointing stage helped to improve the WUE. During the growth periods of tasseling to early filling stage and early filling to milk stage, the water stress significantly affected maize growth, yield and WUE, and these two stages were the critical period of water requirement and should avoid drought.(2) Based on the analysis of water stress effects on maize growth, yield and its components, the transfer rate of dry matter and water consumption, we comprehensively studied the responses of WUE to the water stress and rewatering. We found that water stressed and rewatering at the key water requirement period significantly decreased WUE. The WUE of water stress treatments during tasseling stage to early grain-filling stage, and early filling stage to milk stage were decreased8.4%-12.6%and6.5%-12.9%compared with CK respectively, and the decreasing degree of WUE varied among different maize hybrids and different length of stress time. The main reason for the decreased WUE of maize during the key water requirement period was maize growth. The physiology process were influenced under the condition of water stresses and the compensation effect after rewatering was inadequate. The contribution of maize yield for the decrease of WUE was the highest, and the second was the change of growth index, and then the changes of water consumption characteristics. Physiological processes indirectly affected the WUE through affecting these processes. In the condition of water stress, the effects of the main related characteristics on the WUE were different, with a descending rank order of ear length> ear kernels> yield> above-ground biomass> leaf area> water consumption> plant height>100-kerenl weight> the transfer rate of dry matter of steam and sheath to kermel.(3) We revealed the rule of maize water consumption under the condition of water stress and rewatering in different key water requirement periods. We found that water stress during maize critical growing stage decreased water consumption intensity during this growth period significantly, and changed the highest water consumption intensity and total water consumption, but no change was found in the trend of maize water consumption. The effects of water stress and rewatering in different growth periods on the total water consumption were tasseling to early filling stage> early filling stage to milk stage. Water stress and rewatering during the growth period from tasseling to early filling stage not only significantly decreased the water consumption of this period but also significantly affect the water consumption of the growth periods after this stage. This induced the total maize water consumption of entire growth period by water stress during tasseling stage to early filling stage<that by water stress during early filling stage to milk stage.(4) By analyzing the effect of different length of water stress on the soil water distribution and the process of water consumption, we found that water stress led water decreasing in the deep soil layer. With increasing length of water stress, the soil water in the crop root and water storage area exchanged significantly and the water active soil layer deepened. Short time water stress could increase the utilization of deep soil storage water mainly because the soil water content was timely supplemented after rewatering and the invalid evaporation and luxury transpiration decreased, which resulted in the increased WUE. After long time water stress, the deep soil water content significantly decreased, the soil water content could not recovery after rewatering and this resulted in the excessive consumption of deep soil water and the dry deep soil.(5) We systematically studied the physiological response of maize to the water stress in the critical period of water requirement and revealed the maize physiological compensation effects after rewatering. The results showed that during tasseling to early filling stage and early filling to milk stage, water stress led to photosynthesis and transpiration rate decreasing, and this trend strengthened with the stress time increasing. Long-term water stress (14d) caused the photosynthesis rate decreased by22.4%-42.2%and the recovery content of photosynthesis rate was lower, which was only62%-89.6%of that of sufficient irrigation treatment and was significantly lower than that of short-term water stress (7d) treatment recovery content of which was83.2%-96.5%. The higher physiological compensation of short-term water stress (7d) treatment resulted in the higher maize yield and WUE than long-term water stress (14d) treatment. During the growth period of early filling stage to milk stage, the water stress led to the photosynthesis and transpiration rate decreasing by38.8%-45.7%and45.6-55.9%respectively, which were higher than11.2-36.2%and29.7%-52.1%of the tasseling to early filling stage treatment and chlorophyll content7.15-10.27%. Water stress during the early filling to milk stage caused the photosynthesis and transpiration rate decreasing more significantly than the sufficient irrigation treatment, and the recovery content of photosynthesis and transpiration rate of water stress treatment were62%-80%and78.1%-84.2%of the sufficient irrigation treatment which were significantly lower than75.6%-89.6%and82.1%-92.1%of water stress treatment during tasseling to early filling stage. Early filling to milk stage was the period for the building and expanding of maize storage capacity. Water stress in this period led to the decreasing of photosynthesis and short supplying of the photosynthetic assimilation products and then resulted in the decreasing of maize yield and WUE. During the growth period of tasseling to early filling stage, water stress significantly affected the leaf water potential and this trend strengthened with the length increased of stress time. After rewatering, the canopy temperature decreased and leaf water potential recovered from the water stress. As for the short time water stress treatment, rewatering resulted in over compensatory effect of the leaf water potential of maize.(6) This study systematically revealed the effects of water stress and rewatering on the growth, production and physical characteristics of two different types of maize hybrids which provided the base for revealing internal mechanism of increasing WUE. We found that during the growth period of early filling to milk stage, the Ky value of Hudan4was higher than Zhengdang958. During the tasseling stage to the early filling stage, no significant differences were found between Ky values of these two maize hybrids and this indicated that Hudan4was more sensitive to the water stress than Zhegndan958in the critical period of water requirement. As for the physical characteristics, the canopy temperature and leaf water potential of Hudan4were more vulnerable to water stress than Zhengdan958and the photosynthetic rate of Hudan4was significantly lower than Zhengdan958. As for the maize growth and production, the total biomass, ear length and ear kernel number of Hudan4were significantly lower than those of Zhengdan958which induced the significant difference in maize yield between Hudan4and Zhegndan958, and resulted in the lower WUE of Huand4. (7) From the point of compensatory effect, the compensatory effect of drought and rewatering in different maize growth stages was analyzed comprehensively, it showed that period and degree of drought was the key factor in compensatory effect of drought and rewatering. The results showed that maize was very sensitive to the drought in tasseling to early filling stage, in this stage the compensatory effect of drought and rewater did not work well, and drought treatment (17、T14) had an remarkable influence on plant height、leafarea、rate of photosynthesis、dry matter accumulation and distribution. Except that some short-term drought and rewatering treatment resulted in positive effect, the compensatory effect of drought and rewatering was not satisfactory, and yield and WUE decreased significantly in other treatments. Relatively speaking, the influence of drought on maize growth and physiology in early filling to milk stage was weaker than that in tasseling to early filling stage. The difference of compensatory effect was obvious in critical and non-critical period of water requirement. In jointing stage, though drought had significant effect on plant height、leaf area and dry matter accumulation, after rewatering the compensatory effect of photosynthesis and yield led to WUE improved ultimately in middle and latter growth stages. Therefore, the influence of drought and rewatering period on compensatory effect was the important mechanism to improve WUE, and this threw light on deficit irrigation and controlling the opportunity of agricultural water regulation in practical production...