Anthropogenic sources have increasingly contributed to deposition of elevated levels of nitrogen and other pollutants such as metals.  One such source is vehicular traffic, for example along interstate highways.  Roadside deposition may influence the growth of plants along roadways, but those same plants may accumulate pollutants and thus help safeguard freshwaters.   Our objective was to determine short- and long-term effects of roadside deposition on the growth of Salix miyabaena, and in turn the ability of this willow to accumulate nitrogen and metals.  To examine the short-term effects of atmospheric deposition on growth in a way that removed the variable of previous soil accumulation of pollutants, we planted willows in imported, homogenized, uncontaminated soil at distances of 0, 10, 30, and 100 m from a designated baseline a few meters from I-81 in Binghamton, NY.  Six replicates provided a total of 24 willows.  To examine the long-term effects of pollutant accumulation in the soil, we planted willows in the greenhouse in soil collected from each of the same 24 points in the field.  Willows were harvested following 10-11 weeks to determine relative growth rate (RGR) and accumulation of nitrogen and metals.

Results/Conclusions

In the field on uncontaminated soil, the RGR showed a 31% decrease (.0208 to .0143 day^-1; P<0.05) as distance increased from 0 to 100 m.  In contrast, greenhouse willows grew nearly 150% faster on soil collected at the greatest distance from the roadway (RGR: 0.0118 day^-1 on 100 m soil versus 0.0048 day^-1 on 0 m soil; P<0.05).  Correlates  for these contrasting RGR trends include:  greater amounts of sunlight and soil moisture for the field willows closest to the highway (0 m and 10 m), and higher levels of extractable inorganic nitrogen in the soil of the greenhouse willows corresponding to greater distances from the roadway (30 m and 100 m).  Roadside deposition appears to have a negative effect on plant growth in the long-term, but not the short-term.