| In Southwest China, the intercrop of maize-sweet potato is the most common mode in sweet potato cultivation, which not only promotes the crop diversity, but also, to some extent,improves the efficiency of land use and cropping index, and eventually improves crop yield.Sweet potato is highly drought-resistant in its life cycles except a certain sensitive period to soil moisture. When soil water is less than 50% of the water that demanded by sweet potato in this period, the formation of root and growth of seedlings will be negatively affected, which finally leads to the reduction of yield. Symbiotic period of sweet potato and maize is between June and July, which is the most critical developmental stage of sweet potato and during which temperature and drought stress are more likely to occur in Chongqing. Under these stresses, the growth and development of sweet potato will be heavily stunted, followed by a series of physiological responses and an ultimate reduction in crop output. However, with the existence of the higher intercrop—Maize, the growth of sweet potato benefits from the shade of maize and lower transpiration of soil water. This theory provides a foundation for drought resistance of intercropping. In order to ensure the high yield of sweet potato under drought through improving the drought resistance by agronomic measures, it’s of great importance to study on the effects of drought stress on the growth of sweet potato in its early developmental stages and explore its agronomic and physiological changes..To research the yields and variations of photosynthesis, osmotic adjustment substances,ROS scavengers and usage of water and fertilizer of sweet potato in maize-sweet potato intercropping systems under drought and normal water supply, two cultivars of sweet potato(Yu Shu33 and Nan Shu88) were intercropped with one maize cultivar(San Xia Yu No.6). The results showed that:a. Soil water of intercropping system was shifted to the surface layer from deeper layer of soil under drought stress, due to the hydraulic lift of maize, soil environment was relatively improved than control. Thus, normal growth of sweet potato was insured and improved to some extent.b. Under the treatment of drought, vine length of intercropped sweet potato is shorter and stem diameter is smaller than that of control, but the difference was smaller than in control. The cultivation mode of intercrop had an advantage to the growth of stems and leaves under drought, comparing with monoculture.c. Due to comprehensive impacts of intercropping and soil water stress, intercropped sweet potato under drought was in a more disadvantageous light and soil water condition,which resulted in the closure of stomatal and the decrease in Tr and Ci. The lowest Pn,Gs, Tr and Ci were detected in this treatment. Correlations among Gs, Pn and Ci were remarkably positive. In Yushu33, total content of Chl was negatively related with Gs, Pn and Ci, but Chl and Ci, Tr were positively correlated with each other in Nanshu88, while a negtive correlation was found between Chl and Pn. Stomatal factor was the main limitation of photosynthsis in Yushu33, but there were some other non-stomatal factors resulting in the photosynthetic reduction in Nanshu88.d. Content of proline in sweet potato leaves were much higher under drought and accumulated due to prolonged soil water stress, but increase rate varied among different cultivars. Content of proline in intercropped sweet potato were lower than sole-planted under drought, which indicated a lighter stress in the intercropped group. Conternt of soluble saccharide incresed, followed by a decrease in the extension of water control.e. In this study, drought did not increase the contents of molondialdehyde and activate catalase, but it significantly improve the activation of peroxidase and superoxide dismutase. The removal mechanism of ROS in the condition of this research was relevant to approaches of peroxidase and superoxide, not molondialdehyde and catalase.f. Under drought, intercropping could improve nutrient uptake to a certain extent.g. Compared with normal soil water, yields of both maize and sweet potato wereslightly lower under drought. Yields of maize and sweet potato were prominent higher when sole-planted than co-planted. The reduction rate of sweet potato yield was lower in intercropped group under drought, compared to control. Under drought, yield of the intercropped crops was more stable than control. LER and aboveground biomass under every treatments in intercropping were higher than control, indicating the advantages of intercropping. When intercropped with Nanshu88, yield of maize was remarkably lower, which suggested Nanshu88 had a great impact to maize..h. Yield of sweet potato and tubers per plant were positively correlated;aboveground biomass of sweet potato and soil moisture also showed a significantly positive correlation. The correlations between soil moisture vs peroxidase and superoxide vs proline were significantly negative, but correlations among peroxidase, superoxide and proline were positive.i. Intercropping of maize and sweet potato increases surface soil moisture at the root of sweet potato,which allievates the effects of water stress. Beside, sweet potato in this system grows vigorously and shows stability of physiological and biochemical process due to the rational use of water and fertilizer. Additionally,the total production of those two crops under drought is at an approximate level as in intercropping system with nomal water. Therefore,the effectiveness of intercropping on increasing yield is with great potential. |
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