Differences And Mechanism Of Nutrient Absorption And Utilization Of Apple On Different Rootstocks Under Drought Conditions

China is the origin and evolution center of Malus in the world and has abundant germplasm resources.The yield and quality are influenced by water supply in loess plateau.Rootstocks play an important role in improving stress resistance of apples.Different kinds of rootstocks have different effects on sicons resistance.Drought-resistant rootstocks can improve the drought resistance of scions,which involves in many factors,each of which has a certain relationship with drought resistance.In this experiment,potted grafted seedlings of different apple rootstocks were used to carry out drought treatment,and the rootstocks with high utilization of mineral nutrients under drought conditions were screened out,and the mechanism of high efficiency absorption of nitrogen was discussed,which provided theoretical and technical basis for stress resistance and rootstock selection of apple.The main results are as follows:1.One-year old ‘Honeycrisp' seedlings grafted on G11,G30,Gx,G935,Pajam2,Pajam1,T337,M9,M26 and G41 were used to investigate effects of rootstocks on biomass accumulation,leaf nutrients(N,K,P,Ca and Mg)contents,nutrient absorption and utilization under two kinds water conditions(normal water supply and moderate drought).The results showed that the response degree of different rootstocks to drought stress was different.After drought stress treatment,the plant biomass and relative growth rate of plants grafted on T337 and G30 were higher,while those on Pajam2 and M9 were lower.After drought stress treatment,the net photosynthetic rate and instantaneous water use efficiency of plants grafted on G11,M26 and other rootstocks were higher.The net photosynthetic rate and instantaneous water use efficiency of plants grafted on Pajam2 and M9 was lower.The increase of relative membrane permeability of plants grafted on M26 was the smallest(3.51%),while that grafted on Gx was the largest(36.97%).The reduction of water content and water retention in leaves of plants grafted on G11 was the smallest,while that grafted on G935 was the largest.2.Drought reduced the content of a large number of elements in most plant leaves.Under drought stress,plants with the highest content of N,P,K,Ca and Mg in plant leaves were grafted on M26,M26,Gx,M9 and G11,and the lowest were grafted on G30,M9,G41,T337 and T337,respectively.Compared with the control group,the N,P,K,Ca and Mg absorption fluxes of the plants grafted on Pajam2 all decreased the most after drought stress.However,the nutrient uptake fluxes of the plants grafted on M26 and T337 decreased slightly.Drought reduced the utilization efficiency of N,Ca and Mg in most plants,and the rootstocks with the largest decreases were Pajam1,M9 and M9,respectively.While the rootstocks with the largest increases were Gx and G41,respectively.Under drought conditions,Seedlings grafted on M26,Gx and T337 had high ability of absorption and utilization of mineral nutrients,while those of G935,Pajam1,Pajam2 and G30 were medium,and those of G41,G11 and M9 were low.3.The one-year ‘Honeycrisp' apple seedlings grafted on four rootstocks(M26,T337,M9 and Pajam2)with significant difference in nutrient absorption and utilization were used to analyze the different nitrogen absorption and utilization mechanisms of plants on different rootstocks under drought condition.The results showed that,compared with M9 and Pajam2 rootstocks M26 and T337 increased the nitrogen transfer and distribution in the aboveground of plants,and then increased the relative growth rate of the aboveground under drought conditions.Rootstocks M26 and T337 promoted the expression of genes related to nitrogen absorption and metabolism in plants,increased the activity of nitrogen metabolic enzymes,and enhanced the efficiency of nitrogen absorption and utilization in plants.M26 and T337 increased the ABA content in plants,and then regulated the opening and closing of stomata to increase the drought resistance of plants.Plants grafted on M26 efficiently recycled nitrogen in the plant in the late growth stage and increased the drought resistance of plants.