Is CO2 produced when KHCO3 reacts with H2O?
Compiling the comments by Max and orthocresol: 


  What is the reaction taking place to produce CO2?


$$\ce{HCO3− (aq) + H2O (l) 
&lt;=&gt; H2CO3 (aq) + OH− (aq) 
&lt;=&gt; H2O (l) + CO2 (aq) + OH−(aq)}$$

or
\begin{align}
\ce{HCO3− (aq) + H2O (l) &amp;&lt;=&gt; H2CO3 (aq) + OH−}\\
\ce{H2CO3 (aq) &amp;&lt;=&gt; H2O (l) + CO2 (aq)}
\end{align}


  $\ce{KHCO3}$ does not readily decompose into $\ce{CO2}$ when dissolved in water. 
  It is just that the plant is using the $\ce{CO2}$, so that pulls the equilibrium over, Le Chatelier's principle.