Effects Of Applying Mg Fertilization Based On Optimal Source-sink Ratio On Photosynthesis And Fruit Quality Of Jinggang Honey Pomelo

At current,the poor nutrient management level of Jinggang honey pomelo production,low yield,uneven quality,has seriously hindered the sustainable development of the Jinggang honey pomelo industry.By scientifically diagnosing fertilization and maintaining a balance between source and sink,it is possible to ensure that the tree is well-nourished,balanced,and reasonably distributed,and to obtain high-quality and high-yield fruit trees.The scientific application of fertilizer should be integrated soil nutrients and tree nutrients to comprehensive consideration,the literature has shown that the main production areas of Jinggang honey pomelo widespread soil Mg deficiency,but about the Jinggang honey pomelo tree nutrient status is not clear.In the modern production process of fruit trees,leaf nutrient diagnosis is an effective method for judging the nutritional status of fruit trees,which can guide scientific fertilization,improve nutrient utilization efficiency and fruit quality.Regulation of source-sink relationship is an important guarantee for the rational distribution of assimilates in fruit tree leaves.A reasonable source-sink relationship can effectively improve the quality of fruit and alleviate the phenomenon of alternate bearing in fruit trees.There are no studies on the source-sink relationship of Jinggang honey pomelo.This study focuses on the Jinggang Pomelo as the research object.In the main production area of Jinggang honey pomelo,leaves were collected and the nutrient content of 7 mineral elements such as N,P,K,Ca,Mg,Cu and Zn were measured.Using the DRIS comprehensive nutrition diagnosis method,the nutrient status of the tree body and the urgency of fertilization were clarified.At the same time,taking Jinlan pomelo as the research object,by setting different source-sink ratios（20,40,60leaves/fruit three source-sink ratios）,measuring leaf photosynthetic parameters,nitrogen content,sugar content and its key enzyme activity,quality indicators,etc.,to explore the impact of source-sink relationship on the photosynthetic characteristics and quality of honey pomelo leaves,and determine the optimal source-sink ratio of Jinggang honey pomelo.Based on the optimal source-sink ratio,and Mg is an urgent nutrient supplement,By using both soil and spray applications of Mg explore the effects of different magnesium fertilization methods on the photosynthesis of Jinggang honey Pomelo leaves and fruit quality,aiming to provide valuable references for improving the quality and efficiency of Jinggang honey Pomelo.The main research conclusions are as follows:（1）According to the DRIS diagnosis of leaves,there is a serious problem of magnesium deficiency in Jinggang honey pomelo trees.The results showed that the overall leaf nutrient content in Jinggang honey pomelo orchards needs to be fertilized in the order of Mg>Ca>N>K>P>Cu>Zn.The zinc nutrition supply in Jinggang honey pomelo is relatively sufficient,while there is a general phenomenon of tree magnesium deficiency,which is an important factor limiting the further improvement of fruit quality.（2）During the maturity period of honey pomelo,the Rubisco enzyme activity and photosynthetic rate of leaves treated with 40 leaves/fruit were the highest,11.7%and7.3%higher than those treated with 60 and 20 leaves/fruit,respectively.By increasing the Rubisco enzyme activity and thus increasing the photosynthetic rate,the transport of assimilates from source to sink is increased,thereby improving fruit quality.In this study,the membership function method was used to further clarify that the comprehensive fruit quality score of the 40 leaves/fruit treatment was the highest and the quality was the best.In summary,40 leaves can provide for the normal development of a Jinlan pomelo.To ensure high-quality and stable production of Jinlan pomelo year after year,it is more appropriate to control the source-sink ratio at around 40 leaves/fruit under ring peeling conditions.In actual production,in addition to supplying fruit,some leaves also supply the roots and leaves of non-fruiting branches of honey pomelo.Therefore,in actual production process,pruning should ensure more than 40-60 leaves to supply a Jinlan pomelo for growth and development.（3）Both soil application and foliar spray of Mg can significantly increase the photosynthetic rate of Jinggang honey pomelo leaves and improve fruit quality,and the effect of foliar spray of magnesium is higher than that of soil application of Mg.Taking Jinlan pomelo as the research object,under the conditions of the best source-sink ratio,four treatments were set up:conventional farming（CK）,optimized fertilization（OPT）,optimized fertilization+foliar spray of Mg(OPT+Mg _Leaf),and optimized fertilization+soil application of Mg(OPT+Mg _Soil)to explore the effect of increasing Mg fertilizer on improving the fruit quality of Jinlan pomelo.Compared with other treatments,the Mg content,SPAD value and photosynthetic rate of leaves in the OPT+Mg _Leaftreatment were significantly increased,increasing by 17.9%,19.5%,and 11.8%compared with the CK treatment.The yield and quality of fruit have also been improved.Compared with the CK treatment,the single fruit weight,peel thickness,soluble solids,and Vc content of the OPT+Mg _Leaf treatment increased significantly,while the fruit shape index and titratable acid of honey pomelo decreased.The foliar spray of Mg fertilizer treatment has a good effect on the photosynthesis and fruit quality of Jinlan leaves.When there is a phenomenon of tree body Mg deficiency,foliar spray is a more effective way to supplement Mg.