Effect Of Different Drying-wetting Cycles On Mulberry Seedling Growth And Physiology

Mulberry(Morus alba L.) 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. Mulberry seedlings’ plant height, leaf area growth index, physiological&biochemical indexes, protective enzymes and osmotic regulation substances on water environment changes in response were determined. 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. Test results are as follows:1. Drying-wetting cycles times different, mulberry seedlings by different processing period, plant height, leaf area and the change rule were different. Mulberry seedlings’growth gradually reduced with the increase of number of dry ing-wetting cycles during seedling stage and grand stage. From the water stress indexes, once wet treatment after water stress index was larger. Through wet processing, water stress index decreased,2times3times after alternating drying-wetting cycles processing, water stress index rose again, reflects the mulberry seedlings from the reaction to the alternating drying-wetting cycle environment, not to adapt to the process. From the point of processing time, mulberry seedlings in grand stage under the influence of water stress were greater than the seedling stage. After water, mulberry seedlings had different degrees of recovery, but didn’t restore to control levels. Plant height and leaf area recovery degree because of alternating drying-wetting cycles processed times and processed times. Recovery of growth period of performance was T2>T1>T3. The reason was that not after drought resistance exercise of T1treatment after water recovery speed was slow, and had experienced two times of drought circulation T2processing had certain adaptability, about the drought water recovered faster. However, mulberry seedlings more than about the drought adaptation limit, complex water did not make it a good recovery. Experiment three times after the drying-wetting cycles circulation, mulberry seedling damage by the stress. Therefore, T3treatment seedlings recovery capacity was less than T2. Seen from the degree of recovery, mulberry seedlings grand stage compared with seedling stage, after exposure to the water stress can not recover very well. So we should avoid vigorous mulberry seedlings under drought stress. 2. Mulberry seedling in seedling stage suffered drying-wetting cycles alternate, the main net photosynthetic rate, maximum photosynthetic indexes of photochemical efficiency (Fv/Fm) and electron transport rate (ETR) tended to decline, rather than the law of photochemical quenching showed up, this was because the light system Ⅱ reversible cut caused the mulberry seedling drought stress, excess light energy through non photochemical quenching or xanthophyll cycle dissipation, at the same time, the activities of antioxidant enzymes, osmoregulation substance content increased, in order to clear the internal institutions of photosynthetic production of harmful reactive oxygen species. Enhanced recovery after water, ETR, light system Ⅱ activity center number increased, that seedling dry ing-wetting cycles alternate treatment increase photosynthetic reaction center activity, photosynthetic productivity rise.Prosperous long-term alternating drying-wetting cycles processing of mulberry seedlings found that:net photosynthetic rate decreased, maximum photochemical efficiency and electron transfer also declined significantly, from the perspective of the change of chlorophyll fluorescence parameters of D1protein degradation, PS Ⅱ deactivation reaction center, show that the period of frequent alternating drying-wetting cycles processing make the mulberry seedling damage by the stress. The damage make the mulberry seedling body used for removal of harmful reactive oxygen free radicals of the activity of antioxidant enzymes such as SOD and POD decreased, osmotic regulation substances such as soluble protein and free proline content of Pr will decline, after water also can’t make the mulberry seedlings a good recovery. Therefore, vigorous should avoid frequent alternating drying-wetting cycles processing.To sum up, after the mulberry seedling under drying-wetting cycles alternate processing, through the heat dissipation, leaf protective enzymes and osmotic regulation to protect the photosynthetic mechanism under stress from stress damage,1drying-wetting cycles circulation will enhance mulberry seedling resistance to drought stress, but frequent alternating drying-wetting cycles processing destroys the mulberry seedling photosynthetic system, at the same time, the moisture is flourishing, restricting the mulberry seedling growth over a long period of time of the main factors of the growth period should not be affected by frequent alternating drying-wetting cycles processing.