Influence of Elevated CO2 on
Heterotrophic Ecosystem Processes

Table 3. Summary of the influence of elevated CO 2 on microbial processes and related belowground activity in C 3 and C 4 plant communities.

 

Community

 

C3

C4

Winter soil respiration C 4 microbial respiration

+

0

Microbial respiration

+

0

*Sulfate reduction

+

0

*Methane production

+

0

Methane emissions

+

0

Dissolved inorganic C

+

0

Dissolved organic C

+

0

*Reported first here.

We previously reported considerable evidence that some of the excess carbon produced in response to elevated CO2 was feeding heterotrophic processes such as nitrogen fixation (Dakora and Drake, 2000), CH 4 production (Dacey and Drake, 1994) and microbial respiration (Ball, 1996). By extension this means some of the excess carbon is in belowground pools where it is subjected to decomposition and respiration by microbes. In salt marshes, the single most important process that converts organic C to CO2 is sulfate reduction (Megonigal et al., 2004). The influence of elevated CO2 on sulfate reduction activity has implications for the production of the important major greenhouse gas methane (CH 4 ). Yet, the effects of elevated CO2 on the process have never been quantified. Here we report the first data on elevated CO2 effects on SO 4 reduction. Enhanced SO 4 reduction is one explanation for higher concentrations of dissolved inorganic carbon in pore-water (see next section). We also report the preliminary results of a study to determine if elevated CO2 stimulates the decomposition of old (i.e. pre-treatment) organic carbon through a so-called 'priming' effect.


Research Questions