Measuring and modeling fine root dynamics in temperate forests

Open Access
Mccormack, Michael Luke
Graduate Program:
Doctor of Philosophy
Document Type:
Date of Defense:
October 16, 2012
Committee Members:
  • David Eissenstat, Dissertation Advisor
  • David Eissenstat, Committee Chair
  • Erica A H Smithwick, Committee Member
  • Roger Tai Koide, Committee Member
  • Kenneth James Davis, Committee Member
  • root turnover lifespan
  • minirhizotron
  • ecosystem model
  • functional traits
  • scaling
  • carbon cycle
  • MC1
  • ED2
Temperate forests represent a major ecological and economic resource across much of the globe. As in many ecosystems, belowground ecology in temperate forests is poorly understood and quantification of many biogeochemical fluxes belowground may be weakly constrained. Fine roots control plant uptake of soil resources such as water and nutrients as well as a major flux of carbon from plants into soil through production and turnover. However, basic patterns of fine root dynamics across species remain elusive and model incorporation of these processes may be inadequate. We address these limitations through both field observations and modeling activities. In Chapter 2 we identified relationships between fine root lifespan with plant growth rate, stem wood density, root diameter, and root nitrogen to carbon ratios across 12 temperate species grown in a common garden in central Pennsylvania, USA. We then further explored the relationships between timing and interannual variation in the amount of root production with different measures of fine root turnover in Chapter 3. Here, results indicated that despite relatively little attention previously given to patterns of root phenology and production, both may have strong effects on root turnover rates in temperate forests and potentially across most perennial plant ecosystems. We then conducted a sensitivity test of four different models of terrestrial biogeochemistry to adjustments in fine root turnover rates and discovered that reasonable adjustments of root turnover rate resulted in substantial changes in total systems carbon (i.e. all live and dead plant carbon plus all soil carbon) that were greater than 30% in some cases (Chapter 4). Finally, given the uncertainty in model parameterizations of fine root dynamics, in Chapter 5 we developed a method to describe fine root lifespan and turnover at broad spatial scales using known distributions of temperate tree species combined with species-specific estimates of root dynamics estimated using direct observations and patterns discovered in Chapters 2 and 3. Future efforts should expand to better appreciate how climate and edaphic factors drive variation in fine root dynamics within species and broadly across sites.