氮素形态对'妃子笑'荔枝光合及果实糖代谢的影响OA

[Objective]This study aimed to investigate the responses of leaf photosynthetic characteristics,fruit sugar composition and key enzyme activities of sucrose metabolism in'Feizixiao'litchi(Litchi chinensis Sonn.cv.Feizixiao)to dif-ferent ammonium-nitrate ratios,clarify the physiological basis of nitrogen forms affecting litchi fruit quality formation,and provide a theoretical basis for formulating nitrogen fertilizer management strategies for high-quality litchi cultivation.[Meth-ods]A field experiment was conducted using 12-year-old'Feizixiao'litchi trees.Five treatments with different ammonium-nitrate ratios(NH4+-N∶NO3--N=100∶0,75∶25,50∶50,25∶75,0∶100)were set up,with equal amounts applied in two splits(after flowering and during fruit expansion period),and the total nitrogen application rate was kept consistent.Leaf photosynthetic parameters,fruit quality traits,sugar content,and key enzyme activities involved in sucrose metabolism were measured.A principal component analysis(PCA)was used for a comprehensive evaluation.[Results]The nitrogen form ratio significantly affected photosynthesis and sugar metabolism.When the ammonium-nitrate ratio was 50:50(T3 treat-ment),the leaf net photosynthetic rate(Pn)was the highest,reaching 16.88 μmol·m-2·s-1.Fruits from the T3 treatment also exhibited the best quality,with the highest single fruit weight(25.76 g),soluble solids content(19.63 °Brix),and total sugar content(193.34 mg·g-1 FW),along with the greatest sucrose accumulation.Physiologically,the T3 treatment signifi-cantly increased the activities of sucrose phosphate synthase(SPS)and sucrose synthase(SS),while inhibiting the activities of acid invertase(AI)and neutral invertase(NI).Correlation analysis revealed a significant positive correlation between Pn and sucrose content,as well as SPS and SS activities.PCA comprehensive scoring ranked the T3 treatment first.[Conclusion]A 1∶1 ammonium-to-nitrate ratio optimally coordinated the source(photosynthesis)and sink(sugar metabolism)relationship in'Feizixiao'litchi by enhancing photosynthetic capacity and regulating the activity direction of key sucrose-metabolizing enzymes(promoting synthesis and inhibiting decomposition),thereby effectively improving fruit sugar accumulation,predominantly su-crose,and overall fruit quality.