UC Davis

Trees in seasonal climates gauge winter progression to assure vital and productive blooming. However, how dormant plants asses environmental conditions remains obscure. We postulated that it involves the energetic reserves required for bloom, and therefore studied winter carbohydrate metabolism in deciduous trees. We quantified non-structural carbohydrates throughout winter in almond, peach, and pistachio trees in California and Israel and characterized winter metabolism. We constructed a carbohydrate-temperature (C–T) model that projects changes in starch and soluble carbohydrate concentrations by temperature mediated kinetics. Then, we tested the C–T model projections of bloom times by 20 years of temperature and phenology records from California. The C–T model attributes winter carbohydrate regulation in dormant trees to continuous updates of metabolic pathways. The model projects a surge in starch synthesis at the end of winter, and critically low concentrations of soluble carbohydrates, that trigger bloom. This is supported by field measurements of starch accumulation at the end of winter (˜50 mg g−1 DW in almonds) that preceded bloom by ˜10 days. The C–T model provides a physiological framework for bloom forecasts in deciduous orchards. It integrates contrasting notions of chill and heat and elucidates why abnormal winter temperatures may compromise bloom in deciduous orchards.