Harvard Forest Research

Study physiological and environmental controls on soil CO2 production & transport, and root respiration & microbial decomposition at Harvard Forest

Principal Investigator: Jim Tang
Marine Biological Laboratory: May 01 2008 - Oct 01 2010:

Abstract:
Partitioning soil respiration into root and microbial components and understanding physiological and environmental controls on root respiration and microbial decomposition are important to advance our knowledge in ecosystem processes, carbon dynamics and ability to assess the impacts of climate change and human disturbances on forest ecosystems. The relevant ongoing projects at Harvard Forest include 1) three eddy covariance towers for long-term measurements of carbon and water fluxes, 2) three automated chamber systems to measure soil respiration, and 3) three soil warming experiments to explore climate warming impacts on forest ecosystems. However, continuous, automated measurement of soil CO2 production & transport, root respiration & microbial decomposition, and their linkage to soil warming manipulative experiments have not been conducted. This knowledge is critical for us to 1) interpret the variability of eddy covariance measurements, 2) explain the mechanism of long-term dynamics of soil respiration, and 3) understand the long-term pattern of soil respiration under the warming environment.

My objectives of my project are to 1) understand the mechanism controlling soil respiration processes through separating soil CO2 production and transport and separating root respiration and microbial respiration, 2) develop a process-based model to simulate above processes and components, and 3) use the warming experiment to validate the above knowledge and model.

In summer 2008 I propose to install a soil CO2 profile measurement system (Tang et al. 2003) in Little Prospect Hill at Harvard Forest. The CO2 profile approach will be compared with the automated chamber approach. I will collaborate with Eric Davidson at Woods Hole Research Center, and Julian Hadley and Steven C. Wofsy at Harvard University.

In summer 2008 I will measure soil respiration in three warming plots with a LiCor 6400 portable chamber, collaborating with Jerry Melillo at MBL and Serita Frey at University of New Hampshire. The purpose is to compare soil respiration under different age of warming experiments, which comprise a time chronosequence. The portable chamber will also be compared with the current measurement with the gas syringe approach.

In October 2008 I plan to conduct three 3-m-by-3-m trenchings in Little Prospect Hill. Soil respiration in the trenched plots will be primarily from microbial respiration, so that we can derive root respiration based on comparison of soil respiration between the trenched plots and control plots. The soil CO2 profile measurement system will be installed in the trenched plots with companion automated measurement, collaborated with Davidson’s group.

In year 2009 and 2010 I will install small pine trenchings (10 cm in diameter) in three warming plots to study different patterns of root respiration and microbial decomposition with different warming duration.

In year 2009 and 2010, I will measure leaf photosynthesis and stem respiration near the soil CO2 profile measurement system in the trenched and control plots. The purpose is to understand the physiological controls on root respiration.

Note: Tang, J., D. D. Baldocchi, Y. Qi, and L. Xu. 2003. Assessing soil CO2 efflux using continuous measurements of CO2 profiles in soils with small solid-state sensors. Agricultural and Forest Meteorology 118:207-220.
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