Effect Of Temperature And Nitrogen Fertilizer Interactions On Starch And Yield Formation And Nitrogen Use Efficiency In Dryland Potato Tubers

In order to clarify the mechanism of potato starch formation and yield response to environmental changes under the combined effect of nitrogen fertilizer management and temperature changes,to investigate the biological role of nitrogen in potato tuber starch formation and accumulation,and to propose a nitrogen fertilizer management scheme to alleviate the limitation of potato yield formation by high temperature stress.The experiment was conducted from 2020 to 2021 in the villages of Wu Plateau and Dazui in Haiyuan County,Ningxia,using the local potato cultivar "Qingye 9" as the test material.(N0:0 kg-hm-2,N1:75 kg-hm-2,N2:150 kg-hm-2,N3:225 kg-hm-2)to investigate the response of potato tuber starch and starch-forming enzymes,leaf fluorescence characteristics,nitrogen uptake and yield characteristics to environmental factors under the combined effect of nitrogen fertilizer transport and temperature changes.1.the interaction of temperature and nitrogen application levels had significant or highly significant effects on total tuber starch,straight-chain starch,branched-chain starch,ADPG pyrophosphorylase(AGPase),UDPG pyrophosphorylase(UGPase),starch branching enzyme(SBE),soluble starch synthase(SSS),bound starch synthase(GBSS)throughout the potato reproductive period.The application of nitrogen fertiliser significantly reduced the effect of high temperature on the key enzymes of potato starch synthesis and starch content,effectively increasing potato yield.The activities of branched-chain starch content,straight-chain starch content,AGP,UGP,SSS,GBSS and SBE were highest at N2(150 kg-hm-2),with two-year average yields of 36.33 t-hm-2(CK:ambient treatment)and 27.49 t-hm-2(HT:high temperature treatment),respectively.2.Under the combined effect of N fertilizer application gradient and temperature change,photosynthetic fluorescence parameters such as leaf N,chlorophyll,photosystem Ⅱ(PSⅡ)reaction centre activity parameters,PSII J-phase variable fluorescence(VJ),PSII energy partitioning rate,PI,Fv/FO and Fv/Fm all showed an increasing and then decreasing trend as the fertility period progressed,and they all obtained the maximum value under each N fertilizer gradient at N2 application rate.The maximum values were obtained at each N2 fertilizer gradient.The differences in photoynthetic fluorescence parameters between the different temperature treatments were obvious when the same amount of N was applied,and both leaf N content and photosynthetic fluorescence parameters decreased after the high temperature treatment,indicating that the high temperature stress caused a decrease in PSⅡ activity.Under the same temperature environment,the leaf SPAD,ABS/RC,ET0/RC,PI,DI0/RC,Fv/F0 and Fv/Fm of potato showed an increasing and then decreasing trend as the amount of nitrogen fertilizer was gradually increased,while VJ showed a different pattern from the rest of the indicators,decreasing and then increasing,with a maximum value at N3.This indicates that reasonable N application can alleviate the damage to the photosynthetic system under high temperature stress.The interaction between N fertilizer application and ambient temperature on nitrogen accumulation in potato leaves,leaf SPAD,ABS/RC,TRO/RC,PI,Fv/F0 and Fv/Fm all reached significant levels,and some parameters reached highly significant levels.3.The combined effect of N fertilizer application and ambient temperature had a significant effect on the total N content and N accumulation of potato plants.The N2 treatment(150 kg-hm-2)showed the best performance in terms of total nitrogen content and nitrogen accumulation.At this rate of nitrogen fertilisation,the effect of high temperature stress on the nitrogen uptake and utilisation capacity of the potato plant can be significantly reduced,while facilitating the transfer of nutrients to the tubers.4.Nitrogen fertilizer application,ambient temperature and the combined effect of the two had a significant effect on potato tuber dry matter accumulation.High temperature stress led to a decrease in the amount and rate of dry matter accumulation in potato,resulting in a lower yield and a lower number of medium-sized potatoes,which decreased gradually with increasing N fertilizer application.Among all the different N fertilizer treatments,the N2 treatment(150 kg-hm-2)significantly reduced the response of potato to high temperature stress,promoted stable dry matter accumulation and yield formation,and promoted high and stable potato yields.5.Differences in genes related to starch metabolism in potato tubers under N fertilizer and temperature interactions.Initially,five(two up-regulated and three down-regulated),four(all upregulated)and seven(one up-regulated and six down-regulated)genes were found to be involved in the regulation of starch metabolism pathway in N1,N2 and N3 treatments respectively compared to N0.This indicates that the amount of nitrogen fertilizer affects the expression of genes involved in the starch metabolism process of potato tubers,which in turn affects the synthesis of potato tuber starch.6.High temperature stress increased the membrane fatification of potato leaves and markedly reduced the activity of antioxidant enzymes in the leaves.Nitrogen fertilizer application increased the activity of antioxidant enzymes,with the N2 treatment being the best.