Abstract
Soil and plant stable nitrogen isotope ratios (
15 N) are influenced by atmospheric nitrogen (N) inputs and processes that regulate organic matter (OM) transformation and N cycling. The resulting
15N patterns may be useful for discerning ecosystem differences in N cycling. We studied two ecosystems; longleaf pine wiregrass (LLP) and Appalachian hardwood (AHW) forests in SE USA under different management regimes. In LLP burning removes OM. In AHW, clearcutting creates large OM pulses of logging residue. Although burning removes OM and clearcutting creates a pulse-addition of OM both management regimes increase soil N availability and N
2-fixing plants (N
2-fixers). LLP treatments included burning every 2 years with N
2-fixers and reference fire exclusion sites without N
2-fixers. AHW included 25 year-old clearcut plots with and without N
2-fixers, and uncut reference without N
2-fixers. We hypothesized that: 1) compared to the reference, OM removal (LLP) would enrich
15N values while OM addition (AHW) would deplete
15 N in soil and vegetation pools; 2) N
2-fixers will mitigate
15N enrichment in LLP response and exacerbate
15N depletion in AHW. We examined total
15N in soil profiles, tree increment cores, and foliage. LLP soil and vegetation
15 N values showed no treatment effect. In AHW
15 N values in clearcut subsurface soils (20–60 cm) were lower than the reference but N
2-fixers had no effect. Wood
15N differed with treatment; N
2-fixers had no effect. Our data suggest that AHW soil profile
15 N patterns may indicate pastdisturbance however, wood and foliar
15 N response is species specific. Additionally, N
2-fixing plants respond to ecosystem disturbance, but data suggests they play little role in soil or plant
15 N values.
Citation
Knoepp, Jennifer D.; Taylor, Scott R.; Boring, Lindsay R.; Miniat, Chelcy F. 2015. Influence of forest disturbance on stable nitrogen isotope ratios in soil and vegetation profiles. Soil Science Society of America Journal: n/a-n/a. (accepted manuscript) 43p. DOI: 10.2136/sssaj2015.03.0101