The Exogenous Calcium Regulation Of Photosynthetic Disorder For Arachis Hypogaea L. Under Low Phosphorus Stress

Phosphorus?P?deficiency in arable land as a prevalent issue in worldwide has been severely restricting agriculture production.Phosphorus is a non-renewable resource and also non-substitutable.With the decrease of P resources,agricultural production costs will increase.Peanut?Arachis hypogaea L.?is a sort of crop with high demand for P and calcium?Ca?.Phosphorus avails its direct responsibility for photosynthetic apparatus building-up and photosynthetic carbon assimilation process of peanuts,so it is essential to peanut yield and quality formation.Changes from exogenous P exert their influence on P demanding crops in extensive ways.To be specific,photosynthesis has been sensitive to changes from the nutrient environment.The nutrient stress caused excessive light energy absorbed by the leaves,and then this led to photoinhibition.Reasonable measures can improve the photoprotection ability of the leaves,which will reduce the photoinhibition damage.Therefore,we expected to pinpoint the response characteristics of photochemical activity to P deficiency for peanut leaves,so that we guide production practice and develop new fertilizer.The experimental cultivar was“Fenghua 1”and“Fenghua 2”.“Fenghua 1”is a large fruit type peanut cultivar and“Fenghua 2”is a small fruit type cultivar.Peanuts were grown in artificial climate chamber and cultivated in nutrient solution.We studied the peanuts growing development and photosynthetic characteristics of P and Ca in different concentrations.Then we screened out suitable concentrations of P and Ca for peanuts.Based on previous work,we studied the regularity of photosynthesis in peanuts under suboptimal low P stress.And we use the suitable exogenous Ca and Ca inhibitor?EGTA?,which is selected by the research group in the early stage,to regulate it.We investigated the mechanism of exogenous Ca in alleviating photosynthetic disorders in peanut under suboptimal low phosphorus stress.The main findings are as follows:1.Response characteristics of growing development and photochemical activity of peanut leaves to different concentrations of exogenous P have been clarified.Phosphorus concentration near 28 mg·L^-1 is the most suitable for peanuts growth.Phosphorus concentration between 11-28 mg·L^-11 and 28-54 mg·L^-11 can be recognized as the suboptimal low P and suboptimal high P.Photoinhibition occurs in PSII.The other is the extremely unsuitable P concentration?beyond suboptimal P?,and the photoinhibition occurred in both PSII and PSI and photoinhibition injury is difficult to reverse and recover.There are two reasons for the decrease of photosynthetic products accumulation under unsuitable P.One reason is the decrease of leaf area,the other is the decrease of photosynthetic ability.The decrease of photosynthetic ability of peanut was mainly caused by non-stomatal restriction.The decline in PSII photosynthetic quantum production is mainly caused by the increase of closed PSII reaction center.The main reason for the decrease of photosynthetic quantum yield of PSI is the increase of Y?ND?.2.Response characteristics of photochemical activity of peanut leaves to different concentrations of exogenous Ca have been clarified.Calcium concentration near 120 mg·L^-1 is the most suitable for peanuts growth.Unsuitable Ca concentration could decrease the dry weight,fresh weight photosynthetic rate?Pn?,transpiration rate?Tr?,stomatal conductance?g_s?,water use efficiency?WUE?.The decrease of photosynthetic ability of peanut was mainly caused by non-stomatal restriction.The main reason for the decrease of PSII photosynthetic quantum yield is the increase of Y?NO?.The main reason for the decrease of photosynthetic quantum yield of PSI is the increase of Y?ND?.3.It is clear that exogenous Ca can significantly alleviate the photosynthetic disturbance induced by suboptimal P stress.Exogenous Ca increased the fresh weight and dry weight of peanut plants and root length,root surface area,root volume and number of tips in the diameter range of 0.5-1 mm.It increased the photosynthetic ability,chlorophyll content,PPUE and PNUE.The main photoinhibition of PSII under low P stress are as follow:a.Closed PSII is increase.Oxygen release complex is damaged.Electron transfer from Q_A^-to Q_B is blocked.b.The main reason for the decrease of photosynthetic quantum yield of PSI is the increase of Y?ND?.c.The strong light tolerance ability of peanut leaves is decreased.The decrease of photosynthetic electron transfer rate and PQ pool resulted in the decrease of quantum yield of PSII and PSI.The main effects of exogenous Ca on photoprotection are as follows:a.Exogenous Ca increased flavonoid content and antioxidant capacity,then alleviated the injury of reactive oxygen.b.Exogenous Ca accelerates the cyclic electron transfer flow.Photoprotection capability of leaves is promoted by exogenous Ca,and the photoinhibition of PSII and PSI been alleviated.c.Exogenous Ca increased the accumulation of zeaxanthin?Z?.It increase the integrity of thylakoid membrane and the ATPase activity.Then it increase the excessive acidification of membrane.