The influences of atmospheric nitrates and annual climactic variables in predisposition to winter desiccation injury in Fraser fir and red spruce

The occurrence of winter injury in red spruce (Picea rubens) L. sarg. and Fraser fir (Abies fraseri) pursh. poir. in relation to the level of atmospheric nitrates and climatic parameters of precipitation and temperatures was investigated. Data and foliage samples were collected from established field plots at 5500, 6000, and 6500 feet in the Black Mountains of North Carolina and from seedlings under 4 treatments of artificial rainfall. varying by N03 concentration. Samples were collected 4 times over the 1987 growing season.

Responses were similar in shadehouse and field samples. Wax content differed between collections but not between treatment levels. except for shadehouse spruce. and wax content decreased after collection 2. Between treatment levels. differences were found in the amount of water lost over 14 hours, but not in the average initial fresh weight dry weight ratio (RWT). Differences were found in both RWT and transpiration rate over the growing season with field trees decreasing or remaining stable with each collection. and shadehouse seedlings increasing. No relationship between climatic parameters and annual leader growth was modeled because understory field trees were immature and exhibiting height growth. masking the effects of climate to understory trees. Winter injury ratings decreased from summer of 1987 to spring of 1988 and no significant differences in ratings were found between elevations. Classic winter injury symptoms were observed on one plot at 6500 feet, but most ratings greater than 0 were given because of the effects of shading from the overstory.