Diel metabolic plasticity of CAM photosynthesis in MD-2 pineapple (Ananas comosus) under contrasting tropical environments: biochemical patterns and agronomic implications.

Abstract The current understanding of Crassulacean Acid Metabolism (CAM), including semi-controlled studies in pineapple, does not fully explain outcomes observed under commercial field conditions. Although empirical agronomy confirms a strong climatic influence on growth and development, mechanistic explanations at the metabolic level particularly for photosynthate allocation remain scarce. This study evaluated how environmental variation affects diel CAM outputs and how such effects can be agronomically interpreted. MD-2 pineapple plants were cultivated in contrasting natural environments across Costa Rica. Leaf samples were collected at defined phenological stages and at the end of CAM Phases I and IV. Field data revealed distinct metabolic balances between soluble sugar accumulation and nocturnal malic acid content. Under high radiation and temperature, sucrose concentrations increased markedly, reflecting shifts toward leaf growth over stem reserve storage. These shifts were associated with differences in harvest index, highlighting the role of sucrose dynamics in phenotypic plasticity. From a seed selection perspective, integrating CAM diel profiling into research protocols together with physiological age (thermal units) could provide a stronger basis for classifying planting material beyond current fresh-weight standards. Such integration would improve the prediction of photosynthetic performance, early establishment success, and ultimately, crop uniformity at harvest. Approximately 38% of diel metabolic patterns deviated from the classical CAM model, indicating dynamic regulatory mechanisms under field conditions. Understanding these patterns could improve the interpretation of yield variability, natural flowering incidence, and harvest index across agroecosystems. Recognizing these CAM particularities offers a path to bridge the gap between fundamental CAM biochemistry and agronomic application, enabling the development of precise management strategies that respond to metabolic plasticity under real-world conditions. Closing this gap is essential to enhance productivity, uniformity, and sustainability in pineapple agroecosystems. Keywords: photosynthate, sugar, malic-acid, metabolites, plasticity, hexose, partitioning.