PAR ABSORPTION AND ITS RELATION TO ABOVEGROUND DRY-MATTER PRODUCTION OF SITKA SPRUCE

(1) The annual amounts of PAR absorbed were measured for six Sitka spruce (Picea sitchensis) plots with different thinning and fertilizer treatments in Central Scotland, and related to the annual above-ground biomass production estimated for four consecutive years. It was found that the above-ground dry matter production was proportional to the amount of PAR absorbed, irrespective of treatments. (2) Based on the radiation data collected from these six plots, amounts of PAR absorbed were estimated for the other twenty-four experimental plots in the same stand. The quotients of above-ground dry matter produced and PAR absorbed were 0.43 g mol-1 for nitrogen-fertilized plots and 0.33 g mol-1 for the other plots. (3) The annual photosynthetic efficiency of Sitka spruce was estimated to be c. 3% using a physiological processes-based model, MAESTRO, and the upper limit of biomass production of a Sitka spruce stand in Scotland was estimated to be 36 t ha-1 year-1.