Compensatory Photosynthetic Mechanism Of Mulberry Under Soil Drought Stress And Rewatering

Mulberry industry has developed rapidly in high cold region of Northeast China since the project, which mulberry should move to Northwest from Southeast of China, was well carried out. Nowadays, mulberry is cultivated widely in Northeast of China, especially in arid and semi-arid region of Heilongjiang province, which helps local farmers develop sericulture, construct mulberry eco-orchard, resist drought and increase their income. Therefore, it is very important to research mulberry drought resistance. Plant responses to drought are a process from adaptation, injury and repair to compensation. In previous researches, plant injury and adaptation to drought have been paid more attention, but ess attention to repair and compensation ability. For the reason, this paper was conducted to treatments with different soil moisture and different stages drought during mulberry seedling stage and grand stage. Growth and physiochemical indics were detected. On the one hand, effects of growth and metabolic compensation were investigated; On the other hand, characteristics of reversible and repair compensation in mulberry were clarified during different stages. Hypothesis of this paper is protecting themselves by physiological changes or repairing damage by own photosynthetic metabolic process, or the two processes coexist when mulberry under drought and rewatering.The compensation effects of mulberry under soil water drought with different levels were carried using pot experiments. Mulberry compensation growth characteristics, photochemical reaction and carbon assimilation characteristics were investigated by using infrared CO2analysis and chlorophyll fluorescence technique, and changes of protective enzyme and osmoregulation substance. The results were as following:1Mulberry growth appeared to compensation effects for rewatering after drought. Compensatory ability depended on drought level, days and stage. During drought, mulberry height and leaf area index reduced, and reduced in seedling stage more than in flourishing growth stage of mulberry. After rewatering, short-term drought exceeded CK and produced super compensation. Long-term drought only produced part compensation, and compensation effect was more obvious in seedling stage.2Compensation mechanisms were analysed through photosynthesis photochemical and carbon assimilation coordination. In short-term drought, Pn, Fv/Fm and ETR decreased, NPQ and xanthophyll cycle increased, which indicated that seedling stage short-term drought was due to reversible cut of PSⅡ reaction centers. Most of excess energy, which light harvesting pigment absorbed wasn’t used in electronic transfer, dissipated by NPQ or lutein circulation. SOD, AsA, soluble protein and proline content increased during short-term drought, which was useful to eliminate active oxygen and protect photosynthetic institutions. When the drought removed, ETR increased, which indicated that short-term drought during seedling stage induced photosynthetic reaction center vitality, light energy from photosynthetic pigments was used more for the formation of NADPH and ATP and production of photosynthesis was enhanced. Therefore, rewatering made mulberry produced super compensation in seedling stage after short-term drought. Seedling stage that short-term drought the reaction centers of photosynthesis induction vigor, make the light energy used to capture photosynthetic pigment NADPH and the increase of the proportion of the formation of the ATP, so as to increase the photosynthetic capability. Therefore, mulberry in seedling stage after short-term drought complex water appeared over the compensation.Severe drought and grand stage long-term drought processing made Pn, Fv/Fm and ETR decrease obviously. Photosynthetic agencies accumulated too much excitation energy, PSⅡ response center lost the ability to separate charge, D1protein degradated and PS II response center was inactivation, which indicated that severe drought and grand stage long-term drought made PSⅡ response center injuryed. SOD, POD, soluble protein and proline content decreased under severe drought, cell osmotic regulation capacity reduced, which indicated that ROS damaged PSⅡ response center. After rewatering, index did not return to original state. So, severe drought or grand stage long-term drought made mulberry compensation ability decline or even did not make mulberry produce compensation growth.In conclusion, seedling stage short-term drought made mulberry intracellular protection mechanism protect photosynthetic institutions. After rewatering, physiological function returned to normal and photosynthetic metabolic ability improved. Super compensation effect was produced. However, severe drought and grand stage long-term drought destroyed photosynthetic institutions. After rewatering. self-photosynthetic metabolic process repair didn’t return to original state. There was no obvious compensation under severe drought and grand stage long-term drought.