• McIntire, Cameron D.
  USDA Forest Service
  
• Huggett, Brett A.
  University of New Hampshire
  
• Dunn, Emma
  Bates College
  
• Munck, Isabel A.
  USDA Forest Service
  
• Vadeboncoeur, Matthew A.
  University of New Hampshire
  
• Asbjornsen, Heidi
  University of New Hampshire
  

Pathogen-induced defoliation resulted in a reduction in transpiration, an upregulation of photosynthesis in the early growing season, and no change in NSC reserves across stem, root, and foliar tissues. Abstract The defoliation of eastern white pine (Pinus strobus L.) by native fungi associated with white pine needle damage (WPND) can substantially reduce foliar area for much of the growing season in the northeastern United States. Chronic defoliations in the region are known to have slowed growth rates in symptomatic stands, but the physiological impacts of WPND as it relates to tree water use and carbon assimilation are largely unresolved. We investigated how the severity of WPND defoliation infuences transpiration throughout the course of a growing season. We also assessed leaf-level gas exchange between defoliation severity classes and needle age over time. Finally, we compared concentrations of non-structural carbohydrates (NSC) between defoliation severity classes in fve diferent tissue types over time. We found that trees experiencing a high-severity defoliation had 20% lower sap fux density compared to low-severity individuals. We found that rates of photosynthesis were signifcantly infuenced by the needle age class and time of year, while instantaneous water use efciency was higher across all needle age classes late in the growing season. Our fndings suggest that the residual current-year foliage of high-severity defoliated trees compensated for the loss of mature second- and third-year foliage in the early portion of the growing season. This study found that soluble sugars and starch varied signifcantly over time and by tissue type, but defoliation severity had little efect on NSC concentrations. Together with reduced basal area increment in high-severity trees relative to low-severity trees, this indicates that WPND-afected trees are prioritizing NSC storage over secondary growth.