Since the advent of large-scale power generation in the Ohio Valley, acidic deposition has had profound effects on forest ecosystems in Central Appalachia. With the enactment of the Clean Air Act beginning in the 1970s, the quantity of air pollutants responsible for the formation of acidic precipitation declined sharply. Before mitigation efforts were implemented, acidic precipitation resulted in both aboveground and belowground impacts on tree species, as foliage was exposed to low-pH precipitation and root systems were subjected to substrate acidification. Concentrations of plant-available metals, especially aluminum, began to exceed phytotoxic levels even as essential nutrients became scarce. The depositional history of Central Appalachian forests— having experienced historically high but currently low rates of acidic deposition— provides a unique window into the recovery process of these ecosystems. Four high-elevation red spruce stands were selected in this region based on historical NADP data for total nitrogen deposition from 1985-2012. Foliar samples were collected in July 2014 from mid-canopy of four of the most common species at these sites: Acer rubrum L., Betula alleghaniensis Britton, Picea rubens Sarg., and Tsuga canadensis(L.) Carr. Foliar samples were taken from three replicates of each species at each site, ground, and subjected to microwave-assisted digestion. Analysis of foliar elements was completed using ICP-OES, while carbon and nitrogen were measured with a ThermoQuest elemental analyzer.
Results/Conclusions
Although red spruce stands were selected to represent a range of total nitrogen deposition values typical of Central Appalachia, site was not a significant factor in determining foliar elemental content. However, there were trends towards significance by site for calcium and magnesium, important plant macronutrients sensitive to changes in pH resulting from acid deposition. These trends were strongest at sites with the highest total N deposition. The full suite of elements analyzed includes Al, B, Ca, Co, Cu, Fe, K, Mg, Mn, P, S, Sr, Ni, Mo, and Zn. Differences in foliar elemental content were significant for most elements analyzed, with especially strong relationships between species and concentration for Al, Ca, K, Fe, Mg, Mn, Zn, and P. Across sites, the mean aluminum/calcium ratio was much higher in A. rubrum (838) than B. allegheniensis (243), P. rubens (73.7), or T. canadensis (21.6). Broadly, these results indicate that species-specific differences are the current drivers of the accumulation of elements in plant biomass rather than landscape or regional-scale processes such as acid deposition and associated legacy effects.