01:00 PM - 02:00 PM
Heidi Renninger, Boston University, Boston, MA Environmental Sciences Division
Email: Tim McKnightPhone:
The accurate assessment of carbon uptake and allocation to aboveground and belowground pools is imperative to our understanding of forest processes, how these processes may be altered with climate change and the carbon sequestration capacity of forests. Specifically, it is difficult to estimate belowground carbon at a fine temporal scale in a relatively non-invasive, non-destructive manner. However, all photosynthetic products that are transported belowground from leaves travel through the phloem, and if transport rates and capacity through these tissues can be estimated temporally, it would lead to a more refined picture of carbon allocation processes both diurnally and throughout the growing season. Therefore, this proposal seeks to develop an automated system to track phloem transport in forest trees on a fine temporal scale. The transport capacity of phloem sieve tube cells would be ascertained with anatomy and microscopy techniques. Various in situ heat tracer techniques would be investigated to monitor phloem solute flow rates temporally. Changes in electrical resistivity would be used to track changes in water content, and in turn solute concentrations, within phloem tissues. Once a satisfactory technique for monitoring phloem flow is developed, it would be validated against estimates of modeled canopy carbon assimilation and measurements of changes in soil carbon pools and fluxes in terms of soil respiration rates and root growth. Finally, phloem solute flow rates would be compared with environmental variables to determine the drivers of carbon transport belowground and to model phloem function. Likewise, accurate estimates of how much carbon is added to belowground pools, its temporal variation, and the environmental drivers of belowground carbon transport would increase the predictive power of terrestrial biogeochemical models. In total, this research will increase understanding of carbon allocation patterns in trees and forest ecosystems, particularly carbon transported belowground which remains a difficult pool to quantify.
Liane Russell Candidate