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.