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INTERACTION OF GRASS COMPETITION AND OZONE STRESS ON C/N RATIO IN PONDEROSA PINE
Citation:
Andersen, C P., W E. Hogsett, M. Plocher, K. Rodecap, AND E H. Lee. INTERACTION OF GRASS COMPETITION AND OZONE STRESS ON C/N RATIO IN PONDEROSA PINE. Presented at International Meeting for Specialists in Air Pollution Effects on Forest Ecosystems, Houghton, MI, May 28-31, 2000.
Description:
Individual ponderosa pine (Pinus ponderosa Dougl. ex Laws.) seedlings were grown with three levels of blue wild-rye grass (Elymus glaucus Buckl.) (0,32, or 88 plants m-2) to determine if the presence of a natural competitor altered ponderosa pine seedling response to ozone. Grass presence significantly reduced total pine mass by nearly 50% after three years of ozone exposure, while ozone alone had no significant main effect on pine growth. Ozone and grass together resulted in an interaction such that needle, stem and branch dry weights were significantly reduced compared to treatments where only grass competition was present. In the absence of grass, ozone-treated seedlings tended to have higher tissue N concentrations than controls. In the presence of grass, N concentration increased without ozone and decreased with ozone, resulting in a significant interaction between these two stresses in one and two year old foliage. C/N ratios in foliage decreased in response to grass due to increased N concentration (no change in C). An opposite response was observed in ozone treated plots, where C/N ratios increased with grass competition due to decreased N concentrations. Ozone-exposed seedlings were unable to take up or retain as much nitrogen when growing in the presence of grass. It appeared that competition for soil N, soil moisture, and light were the primary factors driving the response to grass treatment. The results suggest that ponderosa pine seedlings are more susceptible to ozone when growing with other plant species.