Ecological Controls over Monoterpene Emissions from Douglas‐Fir (Pseudotsuga Menziesii)

The roles of nitrogen availability and seasonality in controlling monoterpene concentration in and emission from Douglas—fir (Pseudotsuga menziesii) were examined in a greenhouse study. Plants were maintained at three nitrogen levels, and foliar nitrogen concentration, photosynthetic rate, monoterpene concentration, and monoterpene emission rate were measured over an entire phenological cycle, from before bud break in the spring through winter dormancy. Both nitrogen fertilization level 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 nitrogen—phenology—concentration and the concentration—emission relationships comes a predictable relationship between nitrogen, phenology and monoterpene emission. This relationship allows linkage between atmospheric chemical processes, such as ozone production, and ecological ones, such as leaf expansion. The results also demonstrate that theories on allocation to defense need to consider the phenological stage of the plant as well as the availability of resources.