Mineral nutrition, resin flow and phloem phytochemistry in loblolly pine

Southern pine beetles and associated pathogenic fungi represent the largest biotic threat to pine forests in the southeastern USA. The two primary def ensive mechanisms of the tree to the beetle-fungal complex are the primary oleoresin flow and the concentrations of preformed and induced secondary co mpounds. We compared oleoresin flow and concentrations of phloem nutrients, soluble sugars, starch, total phenolics and proanthocyanidins in Pinus tae da L. trees in fertilized and control plots in the Sandhills region of Nort h Carolina. Four blocks of 10 trees per treatment were sampled on five date s from May to November 1995. Phloem nitrogen and potassium concentrations w ere elevated in trees on fertilized plots, whereas phloem calcium concentra tions were decreased. Fertilization significantly enhanced (10-20%) concent rations of phloem phenolics and proanthocyanidins. In contrast, phloem solu ble sugars and starch concentrations were up to 30% lower in fertilized tre es than in control trees. Increased phenolic concentrations and lower nonst ructural carbohydrates should correlate with reduced tissue palatability an d decreased pathogen susceptibility in fertilized toes; however, resin flow s were significantly lower (30-100%) in fertilized trees compared with cont rol trees, which may facilitate pine bark beetle establishment. Furthermore , fertilization-induced increases in phloem nitrogen concentration may be m ore important than tissue carbohydrate or phenolic content in determining t issue palatability.