Photosynthesis in Sitka Spruce (Picea sitchensis (Bong.) Carr.). VII. Measurements of stomatal conductance and 14CO2 uptake in a forest canopy.
[Cf. FA 37, 4389, 4390] Reports studies in situ on diurnal and seasonal variation in the rates of photosynthesis (Fc) and stomatal conductance (Ks) of needles of different ages and position in order to define the location of the main sources of H2O vapour and sinks of CO2 in a 25-year old P. sitchensis stand SE of Aberdeen, Scotland. Diurnal variation in Fc was chiefly dependent upon the incident photon flux density and was apparently unrelated to vapour pressure deficit or shoot water potential; Fc was more dependent on temperature in spring than in summer and was largely independent of Ks (at values above 0.2 cm./sec.) at all light intensities. Relations are discussed between Ks and light intensity, shoot water potential and vapour pressure deficit. Seasonal variation in both Fc and Ks during summer and autumn was dependent upon the conditions of the current-year shoots and the environmental conditions (particularly photon flux density for Fc and vapour pressure deficit for Ks).