PARENT SESSION
Poster Session #26: Soil Ecology I.
Tuesday, August 6. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Nitrogen and water limitations on soil microbial activity and function in northern Arizona ponderosa pine forests.

BOYLE, SARAH^*,1, HART, STEPHEN¹, ¹ NORTHERN ARIZONA UNIVERSITY, FLAGSTAFF, ARIZONA

ABSTRACT- We added water (doubling annual precipitation), and water plus nitrogen (N) (doubling annual precipitation and adding 45 g Nm-2 y-1) every two weeks to subplots within a restored (i.e., thinned to pre-Euro American stand structure followed by a prescribed burn) and unrestored ponderosa pine forest stands in northern Arizona. After over a year of amendments, we assessed enzyme activity (-glucosidase, -glucosidase, galactase, -xylosidase, cellobiohydrolase, N-acetyl-glucosaminadase, alkaline phosphatase, and sulfatase), soil respiration, and substrate utilization patterns of soil bacteria and fungi (Biolog ECO and SFN microtiter plates) before and after the onset of summer rains (dry and wet periods). Enzyme activity was negatively affected by N additions, but generally unchanged by water additions alone. Enzymes responded more to the amendments in the restored stand, indicating that the microbial communities in these soils may be more sensitive to changes in water and N availabilities. Soil respiration was elevated in water and N amended subplots for both stands during the dry period only. Non-metric multi dimensional scaling ordination and analysis of similarity of overall plate utilization patterns showed that N subplots in both stands were functionally distinct from un-amended subplots during the dry period. The advent of rains in mid-summer negated differences in function and soil respiration caused by our amendments, but differences in enzyme activity among treatments increased. Enzyme activity, Biolog utilization, and soil respiration increased from dry to wet periods, with enzyme activity increasing by almost 300%. In general, water amendments had little effect on enzyme activity and substrate utilization patterns of the soil microflora in the unrestored stand, suggesting water availability is not the primary factor regulating microbial communities in these semi-arid forests.

KEY WORDS: Forest restoration, Micrtobial ecology