Monday, August 4, 2008

PS 3-53: Dynamics and partitioning of whole ecosystem respiration in a controlled grassland ecosystem

Dafeng Hui, Tennessee State University, Paul S.J. Verburg, Desert Research Institute, Jay Arnone, Desert Research Institute,, and Yiqi Luo, University of Oklahoma.


Ecosystem respiration is an important component in global carbon cycling in terrestrial ecosystems. However, partitioning whole ecosystem respiration into its components is still a challenge, mainly due to the difficulty in direct measurements of ecosystem respiration and its components. We grew annual cheatgrass (Bromus tectorum L.) over one year in a unique facility EcoCELLS (Ecologically Controlled Enclosed Lysimeter Laboratory). Whole ecosystem carbon exchanges were continuously measured during this period including three stages: without plants seeded, with plants growing, and after plants harvested. Soil CO2 effluxes (RS) were also monitored continuously using an automated open-flow gas exchange system. Based on these data, we partitioned the whole ecosystem respiration (RE) into above-ground plant respiration (RA), soil organic matter-derived respiration (RH), and root-derived (or rhizosphere) respiration (RR).


We found that net ecosystem carbon exchange in this grassland over one year was -215 g C m-2, a carbon loss to the atmosphere. Total ecosystem photosynthesis was 563 g C m-2, but whole ecosystem respiration was 778 g C m-2. About 12%, 53%, and 35% of RE were contributed by RA, RH, and RR, respectively. Both RA and RR varied seasonally. Ecosystem respiration after plants harvested followed a decay function with RE=0.85+2.04 exp(-0.023t), where t is the number of days after harvest. About 90% of root-derived soil respiration disappeared in three months after plants were harvested.