ECOLOGICAL CONTROLS OVER MONOTERPENE EMISSIONS FROM DOUGLAS-FIR (PSEUDOTSUGA-MENZIESII)

The roles of nitrogen availability and seasonality in controlling mono terpene concentration in and emission from Douglas-fir (Pseudotsuga me nziesii) were examined in a greenhouse study. Plants were maintained a t three nitrogen levels, and foliar nitrogen concentration, photosynth etic rate, monoterpene concentration, and monoterpene emission rate we re measured over an entire phenological cycle, from before bud break i n the spring through winter dormancy. Both nitrogen fertilization leve l and phenological stage affected the concentration of monoterpenes in the foliage. There was also a consistent linear relationship between monoterpene concentration and monoterpene emission. Out of the nitroge n-phenology-concentration and the concentration-emission relationships comes a predictable relationship between nitrogen, phenology and mono terpene emission, This relationship allows linkage between atmospheric chemical processes, such as ozone production, and ecological ones, su ch as leaf expansion. The results also demonstrate that theories on al location to defense need to consider the phenological stage of the pla nt as well as the availability of resources.