Winding up the bloom clock—do sugar levels at senescence determine how trees respond to winter temperature?

Abstract

Abstract Variable winter temperatures cause a year-to-year discrepancy in the phenology of deciduous trees. This implies that an intrinsic ‘winter clock’ synchronizes bloom with the progression of winter to spring. The carbohydrate–temperature (C–T) model established a mechanistic association between carbohydrate metabolism in dormant trees and hourly winter temperatures. Using historical winter temperature and bloom times of Prunus dulcis (Mill.) D. A. Webb (almond), Malus domestica L. (apple), Pistachia vera L. (pistachio) and Juglans regia L. (walnut) in California and Washington states, we parametrized species-specific metabolic parameters to the C–T model. There was a sound fit between actual and projected bloom dates with a deviation (root mean square error) of 4–7 days in all species. The parameterized model enabled us to study how the observed variability in soluble carbohydrate concentrations at senescence (SC0) could affect bloom time. The C–T model projected that low SC0 could advance, while high SC0 possibly delays, the bloom of the early blooming almond trees. In contrast, high SC0 would advance the bloom of apple, pistachio and walnut trees. These novel projections suggest that after experimental validation, SC0 could guide post-harvest farming applications that affect fall carbohydrate accumulation to mediate the effects of climate shifts.