The importance of nutrient inputs via aeolian processes is well known for highly weathered, nutrient-poor ecosystems of the wet tropics. However, recent research has suggested that even on geologically young land surfaces of temperate regions, aeolian inputs (dust) can substantially impact the structure and function of ecosystems. Dust contributions to soils and the ecosystems that they support include addition of organism-limiting nutrients (i.e., P), and potentially novel microorganisms that may further impact recipient ecosystems. Here, we describe some recent research conducted at multiple sites across the western United States evaluating the significance of these exogenous inputs to temperate ecosystems. Dust inputs were captured and quantified using passive traps and as particulate matter collected on snow. Dust samples (and in some cases surficial soil) were analyzed for major elements to assess the magnitude of nutrient inputs from this pathway, and radiogenic isotopes were used to track dust sources. The bioavailability of P inputs from dust was evaluated using X-ray absorption near edge structure (XANES) and 31-P NMR. In addition, for the Sierra Nevada sites, microbial communities associated with the dust particles were also assessed (16S rDNA) and compared to extant surficial soil microbial communities.
Results/Conclusions
Dust inputs to the Sierra Nevada and Rocky Mountains originated from both regional and transpacific (e.g., Asia) sources, the latter contributing from 10-50% of the total influx. At these same sites, P-XANES indicated a mixture of several P species dominated by organic forms, especially in samples from higher elevations. In contrast, at the southern Colorado Plateau sites, dust inputs were dominated by Ca-bound inorganic P (54 - 80%), with 11-23% Fe/Al-bound P, and only 0-25% organic P. Surface soils from the Sierran and Colorado Plateau sites generally had a greater proportion of the total P associated with Fe/Al clay minerals compared to dust inputs. Microbial communities associated with dust inputs along an altitudinal gradient in the Sierra were distinct from each other and from the surficial soil communities at each site. In addition, species (OTU) richness of dust communities was less than half that of surficial soil communities. Taken together, our results suggest that exogenous inputs of dust have profound impacts on temperate ecosystems, and these effects are likely to increase globally as agricultural activities intensify and as our planet continues to warm.