부산대학교 도서관

Increased availability of monomeric aluminum (Al.sup.3+) in forest soils is an important adverse effect of acidic deposition that reduces root growth and inhibits nutrient uptake. There is evidence that Al.sup.3+ exposure interferes with NO.sub.3.sup.- uptake. If true for overstory trees, the reduction in stand demand for NO.sub.3.sup.- could increase NO.sub.3.sup.- discharge in stream water. These effects may also differ between species that tolerate different levels of soil acidity. To examine these ideas, we measured changes in relative uptake of NO.sub.3.sup.- and NH.sub.4.sup.+ by six tree species in situ under increased soil Al.sup.3+ using a .sup.15N-labeling technique, and measured soluble soil Al levels in a separate whole-watershed acidification experiment in the Fernow Experimental Forest (WV). When exposed to added Al.sup.3+, the proportion of inorganic N acquired as NO.sub.3.sup.- dropped 14% across species, but we did not detect a reduction in overall N uptake, nor did tree species differ in this response. In the long-term acidification experiment, we found that soluble soil Al was mostly in the free Al.sup.3+ form, and the concentration of Al.sup.3+ was ~65 [mu]M higher (~250%) in the mineral soil of the acidified watershed vs. an untreated watershed. Thus, increased levels of soil Al.sup.3+ under acidic deposition cause a reduction in uptake of NO.sub.3.sup.- by mature trees. When our .sup.15N uptake results were applied to the watershed acidification experiment, they suggest that increased Al.sup.3+ exposure could reduce tree uptake of NO.sub.3.sup.- by 7.73 kg N ha.sup.-1 year.sup.-1, and thus increase watershed NO.sub.3.sup.- discharge.
Author(s): Mark B. Burnham [sup.1] , Jonathan R. Cumming [sup.1] , Mary Beth Adams [sup.2] , William T. Peterjohn [sup.1] Author Affiliations: (1) Department of Biology, West Virginia University, 0000 [...]