Temperature Dictates if Roots Can Supply Carbohydrates to the Canopy

The environment of the roots is unique as they are embedded in a thermally buffered soil. Generally, temperature in the rhizosphere vary seasonally, with minimal diurnal fluctuations, and lags behind the average temperature of the canopy. It creates a temperature gradient in plants that is synchronized with numerous critical phenology changes. Specifically to orchards, in spring soil is cold and non-structural carbohydrate (NSC) move towards the emerging buds while in fall soil is warm and the newly assimilated photosynthates transport towards the roots. We hypothesized that if this annual cycle is compromised, as in recent warm winters, roots cannot effectively support spring growth. To study this we set to identify the effects of roots temperature on NSC assimilation by the canopy, starch degradation in the roots, and the attributes of flow between them in deciduous apple trees. We found that cold soil (10°C) inhibited transpiration, independent of water status, and obstructed roots from utilizing their NSC resources. These roots were high on starch and low on sugar, and they didn’t change their NSC status throughout the day. Warm soil (21°C) on the other hand promoted photosynthesis and flow of NSC to the roots. Yet these warm roots depleted their resources during the night and needed a new supply by morning. We concluded that to effectively support canopy, roots have to be colder than shoots, and we continue our study to identify the enzymatic processes involved and illustrate how recent climate shifts disturb them.