Abstract:

Sugar-acid balance is a key parameter in the quality evaluation system of apple (Malus × domestica Borkh.) fruit, as it comprehensively indicates the metabolic equilibrium between sugars and organic acids and directly determines fruit flavor characteristics and market value. The formation of sugar and acid in apple fruit is jointly regulated by genetic background and environmental factors, and the underlying metabolic and regulatory mechanisms have become a major focus in fruit quality research. Currently, environmental factors such as light, temperature, water, and soil nutrients not only independently affect the metabolism and transport of sugars and organic acids, but also shape the overall metabolic landscape of the fruit through complex regulatory networks. This review summarizes the molecular mechanisms governing sugar-acid metabolism and transport in apples, and systematically analyzes how the dynamic interplay of environmental factors modulates carbon flux partitioning and acid accumulation via signal transduction pathways. These multidimensional environmental interactions constitute the core ecological network regulating sugar-acid metabolism. Furthermore, this review discusses the potential and challenges of agricultural management practices in balancing sugar-acid ratios and improving fruit flavor. Future studies should integrate multi-omics, single-cell, and spatial transcriptomic approaches to elucidate the sugar-acid metabolic networks under genotype-environment-management interactions, and uncover the molecular basis of environmental signal integration and epigenetic memory. A deeper understanding of these mechanisms will facilitate environment-adaptive apple breeding and provide theoretical and practical support for maintaining fruit quality stability and superior flavor under changing climatic condition.

Key words: apple, sugar-acid quality, environmental factors, interaction, adaptive breeding