Effects of climate warming on canopy water dynamics of a boreal black spruce plantation

The purpose of this study was to quantify the effects of climate change (in the form of elevated air and soil temperatures) on transpiration and sap flux rates of black spruce (Picea mariana (Mill.) BSP). Five treatments were established in northern Manitoba, Canada, with the experimental design consisting of heated and control blocks. Air and soil temperatures were maintained approximately 5 degrees C above control temperatures using greenhouse chambers. Two of the chambers also included controls to maintain ambient vapor pressure difference (VPD). Sap flux (J(S)), was not significantly different among treatments in the May or July time periods. However, J(S) was significantly greater for heated VPD controlled trees than for trees in all other treatments when averaged over the entire study period. JS was positively correlated to photosynthetic photon flux density for all trees. Lower photosynthetic photon flux density in chamber treatments resulted in the creation of models used to estimate J(S) and canopy transpiration (EC()) values that were used in the analysis. Average daily and cumulative growing season E(C) values were significantly greater for the heated VPD controlled treatments than for other treatments. The results from this study suggest that E(C) of boreal black spruce will increase if VPD remains unchanged while air temperatures increase.