Soil and Tree Nutrient Status of High Elevation Mixed Red Spruce (Picea rubens Sarg.) and Broadleaf Deciduous Forests

Abstract

Anthropogenic and industrial emissions have resulted in historically high levels of acidic deposition into central Appalachian forests. Despite the reduction in acidic inputs due to legislation curbing industrial emissions in the United States, continued N deposition may impact forest ecosystems. Soil and foliar samples were collected from four high elevation red spruce sites along a modeled gradient of historic N deposition. The three most abundant tree species at all sites, Acer rubrum L., Betula alleghaniensis Britt., and Picea rubens Sarg., were sampled. Bulk soil beneath the canopies of individual trees were collected from the top 15-cm and separated into organic and mineral fractions for analysis. Mehlich-III soil extracts of soil fractions and foliar digests from these trees were subjected to elemental analysis. Soil N concentrations supported the presence of a N deposition gradient: in organic horizon soil fractions, N concentrations were driven by precipitation volume and elevation; whereas in mineral soil fractions, N concentration was explained by modeled N deposition rate and elevation. In organic fractions, significant reductions in Ca, K, and P were evident as N deposition increased, whereas the Ca:Sr ratio increased. Foliar Ca, K, and Sr declined in foliage with increasing N deposition, with concomitant increases in foliar Ca:Sr ratios. Although the three species were sympatric in mixed stands at all four sites, the foliar-soil nutrient associations differed among them across the gradient, indicating differential uptake and cycling of nutrients/metals by these forest tree species.

Extracellular Soil Enzyme Activities in High-Elevation Mixed Red Spruce Forests in Central Appalachia, U.S.A.

“…In contrast, P declined in the organic fraction, but increased substantially in the mineral layers, which suggests an acid-induced redistribution of P from the organic to mineral horizons. We also noted substantial redistribution of cations and metals in these soils [15]. Such changes are typical of N-deposition impacted soils [29][30][31][32] and have the potential to alter microbial communities and their activity directly or indirectly though changes in tree rhizodeposition.…”

“…With the implementation of the Clean Air Act, N and S inputs have declined into these systems, although N deposition is still substantial. Increases in soil N, concomitant reductions in cations, and inputs of metals in these soils [15] have the potential to alter microbial community structure and function. In this study, we evaluated the activity of a suite of microbially-produced soil enzymes involved in SOM and nutrient cycling in soils along a modeled N-deposition gradient in the central Appalachian Mountains.…”

“…ESE activities as a whole were not influenced by the mycorrhizal functional status (ECM vs. AM) of the tree of collection, but rather were more responsive to plot-level characteristics, such as broadleaf RIV and ECM RIV (Tables 2 and 3), which may influence plot litter quality. We previously reported [15] that, while foliar nutrient concentrations varied extensively among the tree species on these sites, soil nutrient pools were relatively homogeneous. This suggests that plot-level redistribution plays an important factor in establishing soil characteristics and the activity of the microbial community [45,46].…”

“…Four high-elevation red spruce stands were selected based on site elevation (>1100 m), tree species composition (mixed hardwood-red spruce), and position along a gradient of modeled acid deposition, which ranged from 326 to 400 kg N ha −1 over the past 27 years in central Appalachia, as outlined by Crim et al (2019) [15]. Site selection for modeled acid deposition relied upon data from the National Atmospheric Deposition Program (NADP) from 1985 to 2012.…”

Long-Term Projection of Species-Specific Responses to Chronic Additions of Nitrogen, Sulfur, and Lime

“…These soils are normally low in base cations such as calcium (Ca 2+ ) and magnesium (Mg 2+ ), which also limits their buffering capacity [8]. As H 2 SO 4 and HNO 3 deposition increases, hydrogen ions (H + ) disassociate in soil solution, which increases the rates of mineral weathering and displaces cations from cation exchange sites [9,10]. Additionally, H + ions associate with aluminum (Al 3+ ) bearing compounds, increasing the amount of aluminum ions in soil solution, which negatively affects root growth [11,12].…”