PS 2 Q3

Kara, I suspect that you are referring to pneumatic (gas pressure) potential, mentioned in lecture on Jan 20 (ie lecture no.8) as one of the components of the total water potential. We often assume that this pneumatic potential is equal to zero, which corresponds to water under normal atmospheric pressure. This pressure increases with increasing gas pressure on the soil water and becomes negative if gas pressure is less than atmospheric pressure.

Ahhh yes, there it is. I didn't have it written in my notes. Must've missed it the first time around. Thank you!