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Harvard Forest REU Symposium Abstract 2012

• Title: Seasonality of Fine Root Growth, Mortality, and Carbon Allocation in Temperate Forest Trees: Underground Observations with a Minirhizotron Camera
• Author: Samuel P Knapp (University of Wisconsin - Stevens Point)
• Abstract:

  Above ground phenology has been extensively studied in temperate forests; however, due to the difficulties of studying below ground systems, seasonal changes in root growth and death are relatively unknown. Many climate models incorrectly assume that above and below ground processes are in sync and use things like air temperature or remote sensing data to infer root production. Studies have shown, however, that root phenologies vary widely relative to aboveground in woody and herbaceous species. To understand carbon flux in temperate forests, it is therefore necessary to study root phenologies at the species level. This study investigated fine root production and mortality in two prevalent temperate tree species, Quercus rubra and Tsuga candadensis. Using a minirhizotron camera, fine root systems were photographed in situ weekly to determine seasonal growth and death patterns. In both species, leaf flushes were not in synchrony with root flushes. Differences between the species mirrored known aboveground physiologies—Q. rubra roots were observed growing in pulses, while T. canadensis roots were observed to grow at relatively stable rates. Heterogeneity of soils, moisture, and individual organisms likely accounted for observed differences in root growth and death within species. This study also investigated an alternative method of scaling to forest level carbon flux. Allometric relationships between diameter and linear mass density were determined for fine roots of five temperate tree species: Q. rubra, T. canadensis, Fagus grandifolia, Acer saccharum, and Fraxinus americana. All species displayed quadratic relationships between root diameter and linear mass density, and there appeared to be little species level variation in the densities of roots under ~ 0.5 mm. Rather than assuming percentage length production and percentage mass production were equal in fine roots, the density relationships were used to calculate actual percentage mass production and, using data from soil cores and known carbon percentages in fine roots, carbon allocation rates. This method of scaling from 2-dimensional minirhizotron photographs to 3-dimensional ecosystems may be superior to those making questionable assumptions regarding viewing depth into soil and equality between length and mass production percentages. Data from this study will be incorporated in the Ph D. thesis of Rose Abramoff, of Finzi Lab at Boston University, investigating the biotic and abiotic drivers of root phenology, as well as a cooperative paper by Sam and Rose on fine root morphology.
  
  

• Research Category: Physiological Ecology, Population Dynamics, and Species Interactions


• Figures:
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