Nitrogen cycling responses to simulated emerald ash borer infestation in Fraxinus nigra-dominated wetlands

• Published in: Biogeochemistry 2019-10, Vol.145 (3), p.275-294
• Main Authors: Davis, Joshua C., Shannon, Joseph P., Van Grinsven, Matthew J., Bolton, Nicholas W., Wagenbrenner, Joseph W., Kolka, Randall K., Pypker, Thomas G.
• Format: Article
• Language: English
• Subjects: Acer rubrum; Availability; Betula alleghaniensis; Biogeochemical cycle; Biogeochemical cycles; Biogeochemistry; Biogeosciences; Birch trees; Black ash; Cycles; Earth and Environmental Science; Earth Sciences; Ecological monitoring; Ecosystems; Environmental Chemistry; Fertility; Forests; Fraxinus nigra; Girdling; Immobilization; Infestation; Invasive insects; Leaf litter; Leaves; Life Sciences; Litter fall; Long-term changes; Microorganisms; Nitrogen; Nitrogen cycle; Nutrient cycles; ORIGINAL PAPERS; Plant cover; Soil; Soil microorganisms; Soils; Swamps; Trees; Uptake; Wetlands; Woody plants
• ISSN: 0168-2563; 1573-515X
• DOI: 10.1007/s10533-019-00604-2

Understanding short- and long-term responses of forest nutrient cycling to disturbance is vital to predicting future forest function. Mortality of ash trees (Fraxinus spp.) due to emerald ash borer [EAB, Agrilus planipennis (Coleoptera: Buprestidae)] invasion is likely to alter ecosystem processes within infested stands throughout North America. In particular, the loss of Fraxinus nigra (black ash) from F. nigra-dominated swamps may significantly impact the biogeochemical cycles within these ecologically important wetlands. A multiyear manipulative study of nine F. nigra-dominated wetlands in Michigan, USA was undertaken to investigate the potential response of above- and belowground biogeochemical processes to EAB. Short- and long-term changes to site conditions following infestation were emulated by respectively girdling or felling F. nigra saplings and overstory trees. Following disturbance, a short-term reduction in demand for soil nitrogen (N) by dominant canopy species was hypothesized to result in increased soil N availability and a subsequent increase in N uptake by retained species. Though reduced total N return via litterfall indicated decreased demand, this resulted in minimal impacts to soil N availability following treatment. Additionally, increased N uptake by co-dominant Acer rubrum (red maple) and Betula alleghaniensis (yellow birch) was not observed; these combined responses may be attributable to increased immobilization of N by soil microbes. In the 3 years following treatment, the response of foliar characteristics of residual stems—including decreased N concentrations and increased leaf mass per area—appeared to be driven primarily by aboveground conditions and a change from shade- to sun-acclimated leaves. While increased microbial immobilization of N may reduce long-term changes in site fertility, these responses may also limit the potential for short-term positive growth responses of extant woody vegetation. In the longer term, replacing N-rich F. nigra leaf litter with that of A. rubrum and B. alleghaniensis, which have lower N content, is likely to have important feedback effects on soil processes.