ROAD DUST ALTERS EXTRACELLULAR ENZYME-ACTIVITIES IN TUSSOCK TUNDRA SOILS, ALASKA, USA

Dust from gravel roads affects soil physical-chemical characteristics, microclimate, and plant communities of tussock tundra ecosystems in n orthern Alaska, U.S.A. We found that activities of extracellular enzym es associated with cellulose decay and phosphorus mineralization in so ils were inversely proportional to dust loading along the Dalton Highw ay, Alaska. Overall, endocellulase, exocellulase, and phosphatase acti vities within 5 m of this gravel road were reduced by 88, 74, and 45%, respectively, of activity levels at 500 m. Detailed examinations of s oil components showed that phosphatase enzyme activities were displace d from organic matter complexes by dust inputs and became adsorbed ont o mineral materials. This decreased the rate of enzyme-mediated reacti ons. Mathematical models incorporating these reduced levels of enzyme activities projected substantial reductions in carbon (from cellulose) and phosphorus mineralization. Moreover, reduced carbon utilization b y decomposer microbiota, resulting from slower cellulose decay, also d ecreased microbial immobilization of nitrogen, thus increasing simulat ed net nitrogen mineralization. Such changes in soil nutrient dynamics would be expected to affect the structure of plant communities, as ha s been reported for vegetation adjacent to the Dalton Highway. However , concurrent changes in other environmental characteristics of the soi l environment near this road (e.g., drainage) limit our ability to est ablish causal relationships.