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2005 Harvard Forest REU Student Symposium Abstracts

Brian Warshay - Cornell University

Physiological Girdling of Forest Trees: Developments of a New Method to Understand Soil Respiration


The global carbon cycle has become an important part of ecological study since it was discovered that the burning of fossil fuels contributes to global warming. It is understood that the largest terrestrial pool of carbon is stored in the soil and that a portion of that pool is respired yearly from the soil. Little is understood about how much of that carbon dioxide flux is from heterotrophic microbial respiration or root respiration. Studies on root respiration have been done, but most are highly invasive and likely disturb the soil-root-mycorhizzal continuum. Our method can be done both in situ and is noninvasive. Physiological girdling, or cold blocking, temporarily chills the cambium of trees by wrapping them with tubes of cold circulating water. In this way it is possible to slow the rate of photosynthate flowing from the leaves to the roots thereby significantly decreasing root respiration. Soil CO2 flux is measured before, during and after treatment to establish a percent change and is compared to a nearby control plot of similar forest composition. This method will allow us to calculate the percent of soil respiration that results from root respiration and will further allow us to quantify root respiration versus soil microbe respiration. When this method is put into use in soil warming experiments it will be possible to discern how soil microbe respiration reacts to heated conditions without root respiration. This information will enhance our ability to predict future feedback mechanisms in forests resulting from global warming.

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