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Forests 2018, 9(6), 301; https://doi.org/10.3390/f9060301

Biotic and Abiotic Drivers of Sap Flux in Mature Green Ash Trees (Fraxinus pennsylvanica) Experiencing Varying Levels of Emerald Ash Borer (Agrilus planipennis) Infestation

1
USDA Forest Service, Northern Research Station, 359 Main Rd., Delaware, OH 43015, USA
2
Department of Biological Sciences, University of Illinois at Chicago, 845 W. Taylor St., Chicago, IL 43015, USA
3
LI-COR Biosciences, 4421 Superior Street, Lincoln, NE 68504, USA
*
Author to whom correspondence should be addressed.
Received: 16 April 2018 / Revised: 16 May 2018 / Accepted: 24 May 2018 / Published: 28 May 2018
(This article belongs to the Special Issue Understanding and Managing Emerald Ash Borer Impacts on Ash Forests)
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Abstract

While the relationship between abiotic drivers of sap flux are well established, the role of biotic disturbances on sap flux remain understudied. The invasion of the emerald ash borer (Agrilus planipennis Fairmaire, EAB) into North America in the 1990s represents a significant threat to ash trees (Fraxinus spp.), which are a substantial component of temperate forests. Serpentine feeding galleries excavated by EAB larvae in the cambial and phloem tissue are linked to rapid tree mortality. To assess how varying levels of EAB infestation impact the plant water status and stress levels of mature green ash (Fraxinus pennsylvanica Marshall) trees, we combined tree-level sap flux measurements with leaf-level gas exchange, isotopes, morphology and labile carbohydrate measurements. Results show sap flux and whole tree water use are reduced by as much as 80% as EAB damage increases. Heavily EAB impacted trees exhibited reduced leaf area and leaf mass, but maintained constant levels of specific leaf area relative to lightly EAB-impacted trees. Altered foliar gas exchange (reduced light saturated assimilation, internal CO2 concentrations) paired with depleted foliar δ13C values of heavily EAB impacted trees point to chronic water stress at the canopy level, indicative of xylem damage. Reduced photosynthetic rates in trees more impacted by EAB likely contributed to the lack of nonstructural carbohydrate (soluble sugars and starch) accumulation in leaf tissue, further supporting the notion that EAB damages not only phloem, but xylem tissue as well, resulting in reduced water availability. These findings can be incorporated into modeling efforts to untangle post disturbance shifts in ecosystem hydrology. View Full-Text
Keywords: emerald ash borer (Agrilus planipennis); invasive species; Fraxinus; forest disturbance; sap flux; tree water use; thermal dissipation probe emerald ash borer (Agrilus planipennis); invasive species; Fraxinus; forest disturbance; sap flux; tree water use; thermal dissipation probe
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Flower, C.E.; Lynch, D.J.; Knight, K.S.; Gonzalez-Meler, M.A. Biotic and Abiotic Drivers of Sap Flux in Mature Green Ash Trees (Fraxinus pennsylvanica) Experiencing Varying Levels of Emerald Ash Borer (Agrilus planipennis) Infestation. Forests 2018, 9, 301.

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