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Abstract: Pathogens can cause chronic premature needle abscission in coniferous species.
To assess the potential impacts on tree productivity, stomatal regulation was investigated in
Douglas fir with chronic stomatal occlusion and defoliation from varying levels of the Swiss
needle cast (SNC) fungus, Phaeocryptopus gaeumannii. Levels of SNC disease and subsequent
defoliation were manipulated by choosing six sites with varying levels of disease and by foliar
applications of fungicides on six trees per site. Diurnal measurements of leaf water potential ( Psi
leaf), stomatal conductance (gs) and vapor pressure deficit (D) were made on six fungicide
treated and six control trees per site. In addition, leaf specific hydraulic conductance was
calculated on a single branch (KL_B) from three trees per treatment per site. Stomatal
conductance at D=1 kPa (gsref) was negatively correlated with fungal colonization (number of
fruiting bodies present in needle stomata) and positively correlated with KL_B. Despite reduced
needle retention in diseased trees, KL declined due to a reduction in sapwood area and
permeability (i.e., increasing presence of latewood in functional sapwood). In general, stomatal
sensitivity to D for all foliage was consistent with stomatal regulation based on a simple hydraulic
model [gs=KL( Psi soil- Psi leaf)/D], which assumes strict stomatal regulation of Psi leaf.
However, when fungal presence reduced maximum gs below the potential maximum supported
by hydraulic architecture, stomatal sensitivity was lower than expected based on the theoretical
relationship: d gs/dln D=0.6.gsref. The results indicate that losses in productivity associated with
physical blockage of stomata and defoliation are compounded by additional losses in KL and a
reduction in gs in remaining functional stomata.
364. Margolis, H.A. and R.H. Waring. 1986a. Carbon and nitrogen allocation patterns of Douglas-fir
seedlings fertilized with nitrogen in autumn. I. Overwinter metabolism. Canadian-Journal-of-
Forest-Research 16(5): 897-902.
Keywords: nursery operations
nursery fertilization
tree physiology
Abstract: Dormant Douglas fir seedlings (2+0) in a western Oregon nursery were fertilized
with ammonium nitrate in Oct. 1983 and harvested for biochemical analyses before fertilization
and in Nov. 1983 and Feb. and Mar. 1984. Free amino acid (FAA) concn. and total N in the
needles of fertilized seedlings showed a large increase 1 month after fertilization. FAA concn. of
fertilized seedlings decreased in needles during winter, but remained stable in stems and fine
roots. Just before budbreak in mid-Mar., FAA concn. increased significantly in needles and
stems. Total N increased 1 month after fertilization, remained stable during winter and tended to
decrease just before budbreak. Starch and total nonstructural carbohydrate concn. of needles and
stems were lower in fertilized than in unfertilized seedlings just before budbreak. When data from
all harvests were combined, sugar concn. of fine roots were lower in fertilized seedlings. The
depletion of carbohydrate reserves following N fertilization probably reflected increased
maintenance respiration which required synthesis of additional enzymes.
365. Margolis, H.A. and R.H. Waring. 1986b. Carbon and nitrogen allocation patterns of Douglas-fir
seedlings fertilized with nitrogen in autumn. II. Field performance. Canadian-Journal-of-Forest-
Research 16(5): 903-909.
Keywords: nursery operations
nursery fertilization
tree phenology
growth