Physiological Responses Of Zea. Mays. L. To Soil Water Regime During Seedling Stage

Improving water use efficiency of natural rainfall and irrigation is the core issue of water-saving agriculture, and it has great potential. It is essential to understand the sensitivity of every physiological process to water deficit and the threshold of crops to soil water deficit in order to establish a high efficiency water-saving system. Seedling stage is the crucial stage in maize to improve water use efficiency. So, studying the relationship between every physiological process and soil water content is of important practical significance in order to carry out water-saving irrigation. The author conducted the experiments with following three treatment groups: progressive drying; constant soil water continuum; drought with rewatering, to study the physiological responses of maize (Zea mays L.) to soil water content and to confirm proper water-providing amount and time in seedling stage of maize.The dynamic of photosynthetic parameters of Z. mays.L during seedling stage were studied in response to progressive drought The results showed that photosynthetic rate (Pn) and transpiration rate (Tr) increased a little with the declining of soil water content during the early drought days. When soil relative water content (SRWC) was 90% Field Water Capacity (FWC), bom Pn and Tr reached the maximum. Then they began to decrease with unceasing drought .The rate of decreasing was slow when soil water was higher than 70% FWC, but decreased linearly with decreasing soil water when soil water was lower than 70% FWC. It was indicated that the changes were caused synthetically or alternately by stomatal and non-stomatal factors. The curve of water use efficiency of single leaf (WUE) to SRWC was a parabola, its maximum occured under soil water content of 65% FWC. By analysing the curve of leaf relative water content (LRWC) to SRWC, the author found that when SRWC was above 60%, the change of LRWC was mild, nearly keeping on the same level, which was suggested to be the result of adjustment of leaf metabolic reaction. The adjustment also made Pn to become insensitive to stomatal closure, while Tr was always keeping sensitive to stoma, which resulted in single leaf WUE of enhancing. When SRWC was about 65%, WUE reachedthe maximum. With more drought and SRWC was less than 60%, Pn became sensitive to stomatal closure since the adjustment of leaf metabolic reaction was limited, which resulted in single leaf WUE of decreasing. It was concluded from the above results that SRWC 60% was the key to water-saving irrigation at seedling stage of maize. Under this soil water content, LRWC decreased rapidly and the growth was restrained. By analysing with leaf water potential , it can be found that stoma was the most sensitive to with leaf water potential when at -0.8Mpa, and it was also a crucial point to Pn and Tr.In constant soil water treatment, the effects of soil relative water on different physiological parameters of maize seedling were studied. It was found that Pn and Tr decreased when SRWC was 40%-70%, while WUE was little affected. At the same time, light use efficiency, carboxylated efficiency and the growth of maize were hardly affected when SRWC was 70%. Based on above results, it was infered that SRWC 70% was the upper threshold for proper water-providing and it was of little benefit to water-saving beyond this range.By rewatering for different invariable soil relative water to 100% FWC, the author found that Pn and WUE restored to normal level, and even exceeded the normal level. The intensity and occurring time of compensatory effects was changed with soil water level and days after rewatering. Especially, light use efficiency of maize showed compensatory reponse, and carboxylated efficiency was increased a lot when rewatering from 50%-70% to 100% FWC. So, 50% FWC can be considered to be the minimum value of water-saving during seedling stage of maize.The present studies provided theoretical basic for water-saving irrigation and were helpful to ascertain the proper water-providing range for seedling of...