Phenology, morphology and physiology of eastern deciduous seedlings under increased temperature and precipitation treatments

Open Access
Wagner, Rebekah
Graduate Program:
Doctor of Philosophy
Document Type:
Date of Defense:
October 13, 2011
Committee Members:
  • Margot Wilkinson Kaye, Dissertation Advisor
  • Margot Wilkinson Kaye, Committee Chair
  • Jason Philip Kaye, Committee Member
  • Marc David Abrams, Committee Member
  • David A Mortensen, Committee Member
  • climate change
  • deciduous
  • physiology
I examined phenology, morphology and physiology of 11 early successional eastern deciduous tree species grown under increased temperature and irrigation treatments over three years in Central Pennsylvania. The relationship between climate manipulation and the phenology, growth rate and biomass allocation was explored for species predicted to experience changes in habitat suitability over the next century as climate changes. Seedling physiology was used to test the biological responses to manipulated climate conditions through gas exchange and plant-water relations during the final year of the experimental study. Climate manipulation treatments were established in a four-hectare area that was clear-cut and fenced in August 2007. Sixteen plots were established in a 2x2 factorial design with four treatments; ambient (control), irrigated (20% increase), warmed (2°C increase), and warmed+irrigated (20% + 2°C increase). Seeds of 9 northeastern and 2 southeastern species were planted in the fall of 2007-2009 and were allowed to germinate and grow under treatment conditions until August 2010. Both germination and leaf out advanced under warmed treatment conditions (10-20 days and 7-11 days respectively). Increasing temperature stimulates biomass production and growth of young, deciduous seedlings, with the greatest proportional increase found in above ground woody tissue. Seedlings in warmed treatments displayed lower leaf area ratios and altered leaf morphology. Climate treatments did not appear to alter leaf-level measures of foliar carbon and nitrogen. Warming also resulted in strong positive correlations between relative growth rate and photosynthetic capacity, suggesting that the increase in temperature facilitated an increase in assimilation and growth for the study species. Warming decreased seedling water potentials, however these decreases did not correspond to declines in biomass allocation (root:shoot), photosynthetic rates or stomatal conductance responses. Instead, early seedling growth was not limited by changes in plant water potential and the increased rates of photosynthesis are a potential cause for the decreases in predawn water potentials observed over the course of the 2010 growing season. My results highlight the importance of examining both observable morphological responses, as well as the mechanistic physiological responses that young trees exhibit in response to changing climate. Increasing the temperature and precipitation experienced by developing seedlings in this study showed that the responses of individuals and species may be limited by the developmental constraints of small tree morphology and physiology. The implications of the results suggest that temperate forests systems experiencing moderate climate change may have a greater resilience at the seedling stage.