If you ever looked at a classical ecohydrological description of how plants use water you might have noticed something a bit odd. These descriptions go into detail about atmospheric conditions, using them to assign a potential evaporation or evaporative demand. They go into detail about water in the soil running water balances and computing water potentials. And they have (almost**) no detail in them about actual plant properties: the plant sits in between the soil and the atmosphere and just down-regulates the rate of water extraction from the soil (like the left hand side of the picture below). But in the plant, over the same range of water availability, a whole suite of changes are taking place which impact drought recovery, carbon exchange, and plant health (the right hand side of the picture below). And this contrast might lead you to ask, legitimately - Where, actually, is the eco in the ecohydrology?
Putting plant physiology into ecohydrological thinking, and putting some hydrology into plant ecophysiological thinking has been a persistent theme of work in our lab for the past 15 years or so, and it's been a total pleasure to collaborate with awesome physiologists like Todd Dawson and Rob Skelton to do this. Jeannie Wilkening positioned her PhD work squarely across these disciplines, and when she came to writing the introduction to her PhD, what she produced was a beautiful, if initial, exploration of ecohydrology and ecophysiology and why the disciplines have been so separate from each other when they are so intimately connected with the same suite of phenomena and processes.
This lovely publication "Different Roads, Same Destination" is the maturation and development of those ideas from Jeannie's PhD introduction, with invaluable input from Todd Dawson and Xue Feng. It provides the first history (er, that I'm aware of) of the development of ecohydrology as a discipline, and which compares and contrasts it with how plant ecophysiology developed. This illuminates some of the gaps in conceptual understanding and toolkits between the disciplines, which helps understand why it can be hard to work across the disciplines. One of the neat aspects of this paper is the thought Jeannie put into outlining methods to help the disciplines better engage with each other. We used case studies to show how things can go wrong if we don't engage - and also what can go very right when we do.
I have personally loved working with plant ecophysiologists who have helped me appreciate the richness and complexity of what it is plants are doing in the water cycle. I hope the feeling is mutual - and I hope that this paper helps researchers in both disciplines identify new and fruitful opportunities to work together on our common problems.
** Ok, computing PET might involve some conductances if you use a full Penman Monteith Equation, root depth shows up to some extent, and soil parameters can be adjusted to reflect plant sensitivity. But these models don't actually model the plant - they model the effect of the plant on soil moisture thresholds and evaporative demand, letting hydrologists continue to model the non-living things we are most comfortable with.
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