Effects Of Shading And Soil Water Content On Physiology Characters Of Fruit And Leaf Of Pepper During Fruiting Stage

Most of the Northwest regions in the arid and semi-arid zones, where precipitation is scarce while evaporation capacity is 4 to 10 times more than that of the precipitation. Therefore, water shortage is significant, which has become a key factor in Northwest agricultural development. Light is the most important energy source for photosynthesis of plants, which directly affects the activities of photosynthetic enzymes in the carbon cycle and also affects plant growth environment, such as: Temperature, humidity which indirectly influences the plant's physiological and biochemical processes. Pepper is a weak light-resistant fruit and vegetable and light saturation point is only 30klx, so solar radiation can easily lead to the phenomenon of photoinhabition in sunny summer afternoon. In addition pepper is shallow roots plants, which has weak regenerative capacity and a high degree of cork, the growing season is high water-consumption in high-temperature season. Therefore, shade and water supply will become critical factors in pepper's normal growth fruit ripening period.Pepper was studied in this paper in Institute of Soil and Water Conservation District conducted test sites, Northwest A & F University, Yangling, Shaanxi. In 2008, four soil moisture levels (soil water holding capacity, respectively) were designed as 40% to 55%, 55% to 70%, 70% to 85% and 85% to 100%, respectively signed W1, W2, W3, W4 ) in randomized block experiment. The influences of soil water content on the growth of pepper, fruit quality, dry matter distribution, water use efficiency, leaf photosynthetic characteristics and protective enzyme system were studied; In 2009, group tests were designed as three light levels (open field full of natural light, exposed to natural illumination 70% and 30%, respectively signed S0%, S30% and S70% ) and four soil moisture levels (water with the 2008 design) with 12 treatment combinations. The affects of the shading and soil moisture on growth and pepper quality and physiological characteristics of leaves were analysed.The best combination of shade and soil moisture for the field was confirmed through the tests, which provided a theoretical reference to improve the production of solar energy and water use efficiency of pepper. The major results are as follows:The highest output was 6.05 kg·m2 and the assimilations of distribution on the ground and the underground sections was more reasonable.in the field capacity of soil moisture content 70 %—85 % conditions. When soil water was account for 55 %—70 % of the field capacity, quality indicators reached to the maximum .Vc was 1.16 mg/g, free amino acids was 363.6 ug·g, soluble sugar was 19.4 mg·g and soluble protein was 19.7 mg·g respectively. While water utility efficiency in the conditions was also the largest (28.66 kg/m3), respectively increased 19.5 %, 30.3 % and 51.3 % to compare with W1, W3, W4.The production of pepper had some decline because of soil moisture decline from field capacity of 70% ~85% to 55% ~ 70%, but the difference was not significant. Meanwhile pepper quality was better and WUE was higher so as to save water.with the reduction of soil moisture, SPAD readings, Pn, Gs, Ci and Tr depressed accordingly showing a clear positive correlation, howover, free proline and MDA content were on the rise,the decrease of net photosynthetic rate was considered as a result of stomatal restriction;Under W1,W2 and W4 treatment the activity of SOD,CAT and POD increased respectively to a certain extent compared with the W3 treatment indicated that: leaf damage by adversity resulted in stress response and CAT and POD activity were almost presented opposite trends by comparison with the change of soil moisture; The WUE was highest in 55-70% of field capacity.In the condition of 70% -85% field capacity, pepper chlorophyll content was higher and photosynthetic capacity was more effective .Meanwhile leaves were little injured and were not easy to premature senility.With the increase of soil water content, leaf relative water content, leaf dry mass and stem mass increased, while root dry mass was a declining trend, pepper fruit length, fruit diameter and fruit weight increased in natural light and shade 30%, but pepper fruit growth showed a downward trend in soil moisture content exceeding field maximum moisture holding capacity of 70-85%;Moderate shade and reduce soil moisture content are benefit for increasing fruit quality, which vitamin C, soluble sugar, free amino acids and soluble protein content in S30%W2 are higher than in other treatments; With the increase in soil moisture content, water consumption increased, the output was first increased and then falling trend in the same light conditions, and the appropriate reduction in soil moisture is conducive to the improvement of water use efficiency; the same soil moisture and moderate shade are conducive to enhance productivity and reduce invalid water consumption. Deep shade and extreme drought stress are not the use of pepper plant vegetative growth and fruit morphogenesis.Through comprehensive analysis, pepper fruit quality was significantly improved and WUE was increased in the condition of 30% shade and 55-70% relative soil water content.With the increased of shade and soil moisture levels, leaf RWC, chlorophyll content were on the rise. The increased of soil moisture was mainly beneficial to the increase of chlorophyll a, Shade was good to the increase of chlorophyll b; Carotenoids declined with the increase of shade and the decline of soil moisture; MDA content increased under drought stress, and it declined then increased with the increase of shade. In the same light, protective enzymes activity and proline content showed degrees of increase. In the same moisture conditions, protective enzyme activities and proline content were decreased with the increased of the shade, and the protective enzyme sensitivity to light intensity is:SOD> CAT> POD. Physiological correlation analysis showed that praline, protection of enzymes and MDA have reached a very significant positive correlation. Chlorophyll content and membrane protective enzyme reached a highly significant negative correlation. In the condition of shading 30% and 70%-85% relative soil water content, pepper leaves RWC was suitable and plants were robust; chlorophyll and carotenoid contents and leaves photosynthetic capacity were higher; MDA and proline content were less which was favorable to maintain the activities of SOD, CAT and POD, so the membrane lipid peroxidation was little injuried.The results indicated that pepper plants underwent photochemical damage due to decrease in Pn and in the ratio of variable to maximal fluorescence (Fv/Fm and Fv′/Fm′) in full sun-light (0% of shade degree) condition, especially under 40-55% and 55-70% of field moisture capacity. In contrast, appropriate shading can decrease photochemical damage and structural damage to the PSII reaction center complex so that profit the carbon accumulation of fruit. 30% shade-induced plants displayed high relative chlorophyll content, photosynthesis capacity and chlorophyll fluorescence during the reproductive stages, especially under 70-85% of field capacity, however, 70% shade-induce plant presented lowest photosynthesis capacity, qP and NQP indicating there was low photosynthetic photon flux density although Fv/Fm and Fv′/Fm′increased slightly. Furthermore, shade degree×water interactions were significant in Pn, Fo and Fv/Fm, but no significant in other parameters.Conclusively, in the condition of shading 30% and 70%-85% relative soil water content chlorophyll content was higher and PSⅡreaction center was suffered less damage, leaves photosynthetic capacity was superior.