Document: JUL-3-60-1

Contrasting and comparing the species effects of a nitrogen fixing species, Ceanothus velutinus, and a non-nitrogen-fixing species, Psuedotsuga meziesii, Douglas-fir, on soil phosphorus and nitrogen properties in the Oregon Cascades .

SPEARS, J.D.H.*, K.LAJTHA, S.B.PENNINGTON, B.A.CALDWELL and K.VANDERBILT

Oregon State University, Corvallis, OR 97331-2902 USA 1

Abstract:
Many authors have hypothesized that nitrogen-fixing species, as a functional group, would express different controls on soil properties and ecosystem development than non-nitrogen-fixing species. Although nitrogen (N) accretion under nitrogen-fixing tree species has been well studied, the effect of nitrogen-fixing species on other soil nutrients, such as phosphorus (P), have received less attention. We studied differences in soil phosphorus and nitrogen properties beneath Ceanothus velutinus (Ceanothus), a nitrogen-fixing species, and Psuedotsuga menziesii (Douglas-fir), a non-fixing species, in a high elevation successional watershed in the H.J. Andrews Experimental Forest, Oregon. Total P was 20 % greater in Douglas-fir soils than Ceanothus soils in surface horizons, but there was no significant difference in deeper soil horizons. Surface soils (5 and 15 cm) under Douglas-fir generally had higher concentrations of specific P fractions than surface soils under Ceanothus, but this difference either disappeared or was not as apparent at greater soil depths (30 and 60cm). Total nitrogen, and extractable ammonium and nitrate were greater in surface soils under Ceanothus than under Douglas-fir. delta15N values of leaves and litter differed between Ceanothus and Douglas-fir (p-value= 0.0001, 0.03 respectively), but the delta15N of bulk soil and KCl extracted nitrate and ammonium did not differ. Soil enzyme activities suggested greater mineralization of organic P (phosphatase activity) under Ceanothus in summer, but not in fall, while no significant differences in general decomposition (b-glucosidase activity) were found in soils between the two species.

Keywords: Phosphorus fractionation, nitrogen-fixation, soil enzymes, d15N natural abundance, Ceanothus, Douglas-fir

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This abstract is being presented at: 3:30 PM in session:
Poster Session #15: Nutrient Cycling.