Document: KEL-3-58-3

Potential effects of elevated CO₂ and O₃ on soil microbiota in ponderosa pine mesocosms.

DONEGAN, K.K.* ¹, L.L.WATRUD ², S.MAGGARD ¹, T.SHIROYAMA ², L.A.PORTEOUS ² and R.J.SEIDLER ²

Dynamac Corporation, NHEERL-WED, Corvallis, OR, 97333 ¹
U.S. EPA, NHEERL-WED, Corvallis, OR 97333 ²

Abstract:
Outdoor, sunlit mesocosms containing reconstructed litter and soil horizons from a central Oregon ponderosa pine site were used to expose ponderosa pine seedlings to elevated levels of CO₂ and O₃. Each of 4 treatments, ambient or elevated (ambient + 300 ppm) CO₂ combined with low (SUM 06 = 0) or elevated (SUM 06 = 10 ppm hours) O₃ was replicated in 3 mesocosms. Mid-way through a planned 4 year experiment, no significant treatment effects have been observed on the size or diversity of nematode and microarthropod populations. In the ambient CO₂ + elevated O₃ treatment, counts of culturable saprophytic fungi in the AC soil horizon (5-24 cm) were significantly lower on one sampling date (7/99). Counts of total culturable bacteria and spore-forming bacteria in the A and AC soil horizons (0-5 cm and 5-24 cm, respectively) were also significantly lower with ambient CO₂ + elevated O₃ treatment (4/99, 7/99). Microbial community substrate utilization patterns on Biolog ECO plates differed significantly across all soil horizons on one sampling date (10/98) with the elevated CO₂ + low O₃ treatment. Microbial community fingerprints produced by PCR amplification of Pseudomonas 16S DNA suggested decreased diversity in the A horizon in the elevated CO₂ + low O₃ treatment (7/99). These preliminary results at soil depths greater than those expected for diffusion of atmospheric O₃ and CO₂ suggest potential plant-mediated effects of O₃ and CO₂ on soil microorganisms.

Keywords: soil ecology, microbial ecology, ozone, carbon dioxide, DNA, ponderosa pine

This abstract is being presented at: 3:30 PM in session:
MICROBIAL ECOLOGY