seasonal changes in gas exchange and foliar nitrogen of three conifer species growing on an ontario boreal mixedwood site
abstract
jack pine, black spruce and white spruce are three vital species of the
ontario boreal mixedwood forest. the purpose of this study is to compare and
contrast the ecophysiological characteristics of each species and to examine
changes that occur in these characteristics over a growing season.
ecophysiological measurements (photosynthesis, stomatal conductance and
transpiration) were taken on six trees each of jack pine, black spruce and white
spruce from three blocks, at three times during the growing season (july, august
and september). foliar n concentration was also determined for each
measured seedling in july and september. for all three species, photosynthetic
rates were highest in september and lowest in july. overall, rates were
consistently highest for jack pine, even in partially shaded conditions. white
spruce had its best performance in the lower light conditions, likely due to its
shade tolerance. black spruce performed in between the jack pine and white
spruce. jack pine had the lowest specific leaf areas, nitrogen use efficiencies
and the highest water use efficiencies. for all three species, water use
efficiency was lowest in july. foliar nitrogen concentration and photosynthesis
were only weakly correlated in this study.
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