Effect Of Nitrogen×Environment Interaction On Water Productivity And Root Growth Of Maize(Zea Mays L.)

Nitrogen (N) application is an important way to regulate crop growth and increase crop yield. However, the effect of N on crop growth are affected by the weather (drought, temperature, etc.) and soil conditions, therefore N× environment interaction affects the crop yield, nutrient use efficiency and water productivity. In this study, the approaches of field experiments and data mining from literature were used to reveal the current status of water productivity of spring maize (Zea mays. L) in Northeast China, the effect of N x environments interaction on maize yield and water productivity, and the relationships among maize water productivity, yield and water consumption, so as to provide a theoretical basis for the simultaneous improvement of yield and water productivity. Meanwhile, two maize near isogenic lines (NILs) with significant differences in root size were used to further clarify the interaction effect of water and N on maize root and shoot growth during vegetative growth stage; furthermore, a field experiment with different sowing dates and N rates was conducted to understand the interaction effect of temperature and N on maize root growth; finally, the physiological mechanism underlying the effect of temperture on root growth was analyzed using the model plant Arabidopsis thaliana. The main results were as follows:1. Water productivity was positive correlated to grain yield. The effect of N application on water productivity was mainly contributed to its effect on grain yield, rather than water consumption. With the increase of N rates, grain yield and water productivity increased at first, reached the maximum value at N240 and then decreased. Correlation analysis showed that the highest yield and water productivity could be achieved simultaneously in loamy soil when the N application rate was about 215 kg ha-1. However, in sandy soil, the rate of N application for the highest yield (241 kg ha-1) was higher than that for the maximum water productivity (207 kg ha-1). Overuse of N (N312) decreased the water productivity and yield by 11% and 8%, respectively.2. Soil type affected water productivity significantly. The water productivity of maize in loamy soil was significantly higher than that in sandy soil because of the higher grain yield in loamy soil. The interaction between N and soil type was not significant. The difference of water consumption was mainly shown in silking stage, with higher water consumption in loamy soil than sandy soil, due to the larger leaf area index in loamy soil. Weather conditions significantly affected water productivity of maize, because water consumption was significantly affected by rainfall. Too much rainfall at the seedling and silking stages had no contribution to biomass accumulation and grain filling, but increased water consumption, resulting in a decrease in water productivity.3. Root growth increased with increased N rates. However, excessive N (N360) reduced root length, root weight and root surface area, as well as the distribution of the root in deep soil, which aggravated the negative effects of drought stress. Large root genotype (L67) had a better growth performance at drought condition compared to the small root genotype (L98).4. Maize aboveground dry matter, plant height and the final leaf length was not affected by sowing dates when compared at the same leaf age. Maize sown at early date had more root number and greater root weight for the first and second round nodal roots, and the root length of the first round of nodal root, compared to that sown late. However, the length of the second and the third round nodal roots were longer, and the number and weight of the third round nodal roots were greater in late-sown maize. Regardless of the sowing dates, shoot and root growth were the best at a N rate (N180), while overuse of N (N360) limited the growth of both shoot and root.5. The maximal elemental elongation rate and final cell length of root gradually increased with the increase of temperature (15℃-25℃), while the elongation zone length remained constant. Meristem length shortened with the increase of temperature, while the total cell production rate remained constant. 30℃ was a stress temperature level for Arabidopsis thaliana, at which root elongation zone shortened, and the cell division rate was restricted.In conclusion, higher grain yield, N and water productivity can be achieved simultaneously via optimization of N management, as well as improvement of soil quality. Overuse of N inhibited root growth and led to a shallow root system, reducing the potential for water-shortage resistance of maize. Low temperature (early sowing) was disadvantageous for nodal root elongation, and excessive N application aggravated this negative effect.