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Harvard Forest Research

Linking aboveground and belowground responses to chronic soil warming

Principal Investigator: Jerry Melillo
Marine Biological Laboratories: Mar 01 2007 - Sep 01 2009:

Abstract:
Cold girdling project:
Large-scale root respiration measurements were recently taken via the girdling of trees such that photosynthate translocation from the shoots to roots was permanently blocked due to phloem breakage. This non-reversible method demonstrates that recently synthesized photosynthate drives the majority of trees’ root respiration. The factors that determine the relative contribution of the roots and rhizosphere to total soil respiration are not well understood and may change over time if warming affects vegetative sink fine-root growth and photosynthate source-sink dynamics. We recently adapted a tree cold-girdling method by which delicate rhizosphere autotrophic -heterotrophic interactions are not physically disturbed while phloem photosynthate transport is inhibited by rapidly chilling a portion of selected trees’ trunks. We have implemented a test of this method near the large scale Barre Woods soil warming experiment that will be completed in October, 2007. Based on these results, we may move the cold girdling apparatus into the soil warming experiment. This method for separating the components of soil respiration is appealing because of its non-invasive and reversible nature, allowing the ability to capture differences in the contribution of recently synthesized C to total soil respiration throughout the growing season and over multiple years of warming. This project will be complemented by work on fine root response to soil warming.

Photosynthetic response to soil warming: In order to better characterize changing canopy C capture potential at the species level in response to warming, I will test a set of related hypotheses, under the overarching premise that differences in tree species’ growth response to soil warming may be partly due to variation in species’ leaf traits that influence C gain. Photosynthetic response to soil warming will be tested in canopy and juvenile hardwoods in the Barre Woods soil warming experiment. :