SEASONAL NUTRIENT DYNAMICS IN WHITE-PINE AND WHITE SPRUCE IN RESPONSETO ENVIRONMENTAL MANIPULATION

Seasonal retranslocation in white pine (Pinus strobus L.) and white sp ruce (Picea glauca(Moench) Voss) was examined in response to silvicult ural treatments (scarification, annual fertilizer application, and ann ual control of competing vegetation with herbicide) that changed both environmental conditions and the growth rate of the trees. Four years after plantation establishment and initial treatment, nutrient accumul ation in current-year needles of white pine and retranslocation from 1 -year-old needles were increased following the vegetation control trea tment, which increased resource availability (nutrients, water and lig ht) and, hence, growth rate. Nutrient accumulation also increased in c urrent-year white spruce needles following the same treatment, whereas retranslocation decreased in 1-year-old white spruce needles. Correla tions of retranslocation (N, P and K) with growth rate (shoot biomass increment) showed a strong positive relationship for white pine and a negative relationship for white spruce. Retranslocation of K was corre lated with foliar and soil K concentrations; the availability of this nutrient was also significantly reduced by vegetation control. A gener al theory for the control of nutrient retranslocation in conifers, whi ch is not based exclusively on either sink strength or soil nutrient a vail ability, is proposed. We conclude that retranslocation response i s species specific and related to the potential phenotypic growth resp onse to changing environmental conditions and to short-term imbalance in the supply versus the demand for nutrients.