Short-term Responses to Supplementary Nitrogen in Young Apple Trees as Related to Carbohydrate Nutrition

Abstract

Young MM·104 apple rootstocks were grown in containers with soil of moderate nitrogen status. Doses of supplementary ammonium nitrate were supplied to the soil, and comparable treated and watered control plants were harvested shortly (40 h) afterwards. Their parts were analysed for extractable carbohydrates (and nitrogen) to test whether interdependence between carbohydrate status and nitrogen assimilation could be demonstrated. Results showed that extractable carbohydrate content did not change significantly in response to treatment, although results to be presented in another paper have shown appreciable nitrogen assimilation over the same period. On the basis that carbon skeletons required for amino-nitrogen incorporation are derived from hexose, it has been calculated that the amounts involved would be sufficient to allow detection of localized changes in root carbohydrates. The absence of an observed effect on roots is interpreted as being due to rapid responses by other parts of the tree—probably involving increases in rates of formation and translocation of resources. This is regarded as part of a mechanism for maintaining a steady composition in terms of carbohydrates and other metabolites.