This is a very nice paper which provides a summary of the current state of the science on this topic. I have received 3 reviews, all positive, and all with suggestions that will improve the paper. Please revise as you have said you will in your responses to the referees.

Please also add some discussion along the lines of the last paragraph of the discussion in Bowling et al. (2017), which was focused on the question "How can plants use tightly bound soil water when more mobile water is available to their roots?" This issue concerns all the plant physiologists I have talked to who are familiar with the two water worlds hypothesis (some in the list of authors of your paper). I don't care if you cite my paper, but please bring up the issue in a meaningful way so that people will consider it (and investigate it) as the community moves ahead.

Nice work!