Needle microepiphytes in a Douglas fir canopy: biomass and distribution patterns

Distribution patterns and total cell-volume estimates for needle microepiphytes are presentedfor three strata in the canopy of a single old-growth Douglas fir tree. Microbial cell volume wasestimated by photographing transverse sections of needles, tracing microbial profiles on Mylarfilm, cutting out the tracings, and determining the pooled trace weights from various zones of eachneedle section. Microbial cells are concentrated in the midrib groove and over the stomatal zonesof individual needles. Microbial cell volume on the upper needle surfaces increases during the 1styear and declines in subsequent years. Cell volumes on the lower needle surfaces increase fromthe 1st to the 3rd year and decrease from the 3rd to the 4th year. An increase in microbial cellvolume occurs on both upper and lower surfaces from year 7 to year 8. Total microbial cellvolume in relation to available needle surface area is greatest in the lower canopy and decreaseswith increasing height in the canopy. The total volume of microbial cells on needles was estimatedto be 1093 cm3 for the entire tree.