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

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 CO 2 concentrations) paired with depleted foliar δ 13 C 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.

Release and suppression: forest layer responses to emerald ash borer (Agrilus planipennis)-caused ash death

“…The role of other limiting resources may be particularly important for non-ash canopy trees which likely already have access to full sun. Previous ash mortality studies have shown water table rise (Slesak et al 2014), a decrease in sap flux during early of EAB infestation (Flower et al 2018), and significant increases in maple tree radial growth without greater sun exposure each support belowground resource availability increasing with ash mortality. Furthermore, changes in belowground resources were attributed to higher fine root densities within red spruce, Picea rubens, declinecaused gaps (Battles and Fahey 2000).…”

Thirst or Malnutrition: The Impacts of Invasive Insect Agrilus mali on the Physiological Status of Wild Apple Trees

“…The latest research indicated that A. mali could lead to a significant seasonal decrease in chlorophyll fluorescence parameter Fv/Fm (Dr. Zhang Jing, Xinjiang institute of Ecology and Geography, unpublished), which may determine photosynthetic carbon gain, causing the decline in long-term WUE under seasonal droughts. According to the finding of Flower et al [11], ash tree mortality was related to chronic water stress due to the damage of vascular tissues caused by A. planipennis, and an enriched leaf δ 13 C indicated high stomatal resistance and low photosynthetic rate under water stress. Similarly, δ 13 C enrichment in leaf tissues observed in our study indicated the reduction in water availability due to the damage by A. mali.…”

“…Understanding the causality between insect infestation and tree mortality is critical to successful pest management and enhancement of forest ecosystem resilience. The health status of individual trees, as well as of the forest ecosystem, was associated with physical stresses caused by pests, including water stress and nutrition deficiency [10][11][12][13][14][15]. Due to restricted water and nutrient use efficiency, as well as altered metabolic dynamics after pest infestation, trees can become more susceptible to subsequent, secondary biotic and abiotic stresses [16,17].…”

Effects of grafting on host plant resistance in ash (Fraxinusspp.) to emerald ash borer (Agrilus planipennisFairmaire)

“…Females lay their eggs in crevices of ash bark and, upon hatching, larvae bore into the phloem to feed, creating serpentine galleries in the phloem and outer sapwood. These galleries slow the movement of nutrients and water throughout a tree, girdling the branches and trunk (Flower et al ., ). Girdled branches are nutrient‐starved and do not produce leaves.…”