Response Of Photosynthesis To Phosphorus Supply In Rhizosphere Of Chinese Cabbage And Its Calcium Regulation

Chinese cabbage is the most widely planted vegetable with the highest yield in China.As a large agricultural country,Chinese cabbage breeding has always been one of the research focuses in this field.Phosphorus is one of the essential elements for the normal growth of plants.Phosphorus is involved in a series of processes of photosynthesis,including carbon assimilation process,photosynthetic phosphorylation,light energy transport,Calvin cycle and so on.Both low and high P stress can affect the photosynthesis of plants,resulting in a series of parameters(such as photosynthetic physiological parameters and plant internal fluorescence parameters)that can significantly change to produce photoinhibition,thus affecting plant growth.At the same time,Chinese cabbage is a kind of calcium loving crop.Therefore,it is theoretical significance to find out the photosynthetic response and calcium regulation of Chinese Cabbage under different phosphorus and calcium concentrations,and finally put forward the rational fertilization technology system of Chinese cabbage and guide the research and development of new fertilizer for Chinese cabbage.In this experiment,shuishiying 91-92 Chinese cabbage was used as the experimental material to simulate the actual situation of the lack of exogenous phosphorus and calcium supply in the field by sand culture in the artificial climate chamber,to study the growth and development of Chinese cabbage and the response law of leaf photosynthesis,and to select the appropriate phosphorus and calcium concentrations for the growth of Chinese cabbage.On this basis,we studied the response rule of photosynthetic disorders under the sub suitable low and high phosphorus stress of Chinese cabbage,and with the selected suitable exogenous calcium and calcium inhibitor(EGTA)to regulate,to explore the mechanism of exogenous calcium to alleviate the occurrence of photosynthetic disorders under the sub suitable high and low phosphorus stress.The main results are as follows:1.The response of photosynthesis to P supply in rhizosphere of Chinese cabbage was clarified.The optimum phosphorus concentration in the nutrient solution for the growth of Chinese cabbage is 33 mg · L-1.The suitable range of low phosphorus concentration for Chinese cabbage growth is 14-33 mg · L-1;the suitable range of high phosphorus concentration for Chinese cabbage growth is 33-51 mg · L-1.When the phosphorus concentration is very low and very high(i.e.beyond the range of subappropriate concentration),it belongs to the growth phosphorus toxicity concentration of Chinese cabbage.Photoinhibition occurs in PSI and PSII,and the damage caused to Chinese cabbage is hard to reverse and recover.Under unsuitable phosphorus concentration,non stomatal factors were the main reason for the decrease of photosynthetic capacity of Chinese cabbage.The decrease of quantum yield of PSII is mainly due to the increase of closed state PSII and the decrease of quantum yield of PSI due to the increase of donor side restriction.2.The response of photosynthesis to rhizosphere calcium supply in Chinese cabbage was clarified..The optimum concentration of calcium for the growth of Chinese cabbage is 136.5mg · L-1.Under the unsuitable calcium concentration(too low or too high),the photosynthesis of Chinese cabbage is limited,the dry matter accumulation is decreased,the chlorophyll content is decreased,the photosynthetic site is decreased,the net photosynthetic rate is decreased,and the carbon assimilation capacity per unit area is decreased.Non stomatal factors are the main limiting factors for the decline of photosynthetic rate under the unsuitable calcium concentration.Self regulated dissipation is the main reason for the decrease of quantum yield of PSII.Thus,the increase of donor side restriction is the main reason for the decrease of quantum yield of PSI I.3.1)Exogenous calcium increased the fresh and dry weight of Chinese Cabbage under low and high phosphorus stress.Non stomatal factors are the main reason for the limitation of photosynthesis in Chinese cabbage leaves under low phosphorus stress.Exogenous calcium improves chlorophyll content and photosynthetic capacity of Chinese cabbage leaves2)However,donor side restriction is the main reason for the decrease of quantum yield of PSI.Under low and high phosphorus stress,PQ pool decreased photosynthetic electron transfer rate,which led to the decrease of PSII and PSI quantum yield.3)Exogenous calcium increased the content of flavonoids in Chinese cabbage leaves under low and high phosphorus stress,accelerated the rate of ring electron transfer,reduced the damage caused by photoinhibition and enhanced the ability of photoprotection;the accumulation of zeaxanthin(z)wereincreased,aswellas the Δ p H of thylakoid membrane decreased,Δψ increased,the over acidification of thylakoid membrane was reduced,and the higher integrity and ATPase activity of thylakoid membrane were maintained,.4)The effect of exogenous calcium on Chinese Cabbage under the stress of low phosphorus was not obvious.