Episode 24: Building a National Water Potential Network

Episode 24: Building a national water potential network

Champions of water potential, Drs. Kim Novick and Jessica Guo, team up to discuss the vital role water potential measurement plays in both plant and soil sciences and the work they are doing to establish the first-of-its-kind nationwide water potential network. Join their discussion to understand how a communal knowledge of these measurements could impact what we know about climate change and ecology as a whole.


Dr. Kim Novick is a professor, Paul H. O’Neill Chair, Fischer Faculty Fellow, and director of the Ph.D. Program in Environmental Sciences at Indiana University.  She earned her bachelor’s and Ph.D. in environmental science at Duke University’s Nicholas School of the Environment. Her research areas span ecology and conservation, hydrology and water resources, and sustainability and sustainable development, with specific interests in land-atmosphere interactions, terrestrial carbon cycling, plant ecophysiology, and nature-based climate solutions.

Dr. Jessica Guo is a plant ecophysiologist and data scientist who studies plant-environment interactions under extreme climate conditions. She earned her bachelor’s in environmental biology from Columbia University and her Ph.D. in biological sciences from Northern Arizona University.  She is currently at the University of Arizona, where she blends her passion for reproducible workflows, interactive visualizations, and hierarchical Bayesian models with her expertise in plant water relations.

Links to learn more about Dr. Kim Novick
Links to learn more about Dr. Jessica Guo
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Hello everybody, and welcome to We Measure the World, a podcast produced by scientists, for scientists.

That’s not something I’ve all had been thinking about. But just thinking, yeah, there’s, you know, we think about models that have these inputs, outputs, and then these parameters. Well what if the parameters themselves are dynamic? Does that mean we have to measure everything everywhere all at once to get them to work? In which case if we already measured everything everywhere all at once, then we would need these models now, would we? So, yeah, thinking about how to incorporate the biology and the expected relationship to have that next layer of like, how do the parameters involved in something like that?

That’s a small taste of what we have in store for you today. We Measure the World explores interesting environmental research trends, how scientists are solving research issues, and what tools are helping them better understand measurements across the entire soil plant atmospheric continuum. Today’s guests are doctors Kim Novick and Jessica Guo. Dr. Kim Novick is a Professor Paul H. O Neill, chair, Fisher Faculty Fellow and Director of the Ph. D program in environmental sciences at Indiana University. She earned her bachelor’s and PhD in Environmental Science at Duke University’s Nikolas School of the Environment. Her research areas and specific interests are in land atmosphere interactions, terrestrial carbon cycling, plant eco physiology and nature based climate solutions. And Dr. Jessica Guo, is a plant eco physiologist and data scientist who studies plant environment interactions under extreme climate conditions. She earned her Bachelor’s in environmental biology from Columbia University, and her PhD in biological sciences from Northern Arizona University. She is currently at the University of Arizona where she blends her passion for data science, with her expertise in plant water relations. And today, Kim and Jessica are both here to talk about their many research projects. So thank you so much for being with us today.

I’m happy to be here.

Thanks for having us.

All right. So definitely today we wanted to talk about and get into your projects and research interests. But first, can you just tell us a little bit about your background. So we’d like to know how you got into the sciences in general and how you worked your way into the fields and specialties of environmental and climate studies. So I don’t know, Kim, if you if you want to go first with that.

Sure yeah, I’d be happy to. You know, my path started as an undergrad. I elected to major in Civil and Environmental Engineering has born out of just sort of a general affinity for math and physics and of the engineering majors that were available at the university I attended. Civil and Environmental Engineering seemed like it offered the most potential to sort of do good in the world. And it was, I think, my junior year, I participated in a field trip out to a set of ameriflux towers in the forest run at at the time, and for the duration of their existence by Professor Gabby, a tool. And we got to climb the towers, which was really fun and exciting. And I thought, well, that might be an interesting way to spend a summer. So I emailed Gabby to see if he was accepting undergraduate research assistants. And he sent me a very short reply, send me your transcripts. And I did, I guess it passed muster. Because that turned into a really excellent summer research experience that turned into a senior’s honors thesis, that after a few years out, working in the NGO sector, eventually turned into my PhD. And so you know, most of what I’ve been doing since is working to apply what I learned about measuring land atmosphere, fluxes of carbon, water and energy, to understand eco physiological processes and a range of skills, but also to apply that knowledge to solve practical problems, as I like to think of it, for example, concerning questions surrounding nature based climate solutions, and drought monitoring, in this sort of applications.

Great. And Jessica, how about you?

Yeah, so I’m, I’m from Arizona from Phoenix and I couldn’t wait to get out of the state Nevada and back here now but at the time, it was like New York City that’s about as different from Phoenix is like, I my mind at the time, imagine? And I got in with the E three B department ecology, evolution, and environmental biology. And yeah, I took took all the courses they had did a summer research internship in forest ecology and Wisconsin Madison. There’s a lot of pretty classical and community ecology driven questions. But my one of my mentors Shahid Naemm wasn’t interested in biodiversity and ecosystem functioning and that really got me thinking about the functioning and kind of functional trait side which is still you know, still a very popular field now. And when I went to Northern Arizona University I, you know, wanted wanted to dig deeper into mechanism. And so that leads me to plant eco physiology. My master’s project was on a trying to do plant eco physiology at the community scale. It involved a lot of fieldwork, a lot of lab work and yield the data that were not easily analyzable. So that’s when I kind of took another turn towards more quantitative approaches. Data Science wasn’t actually a very popular term, at least not in my not in my world back then. So I didn’t call it data science. But I went on in search of a more quantitative, more quantitative tools, because ecology data just is messy, it is not going to fit neatly and to the criteria that are required for some of these tests. So I sought my advisor Kuna Ogle, and the rest is history, as they say, because I took to Bayesian modeling, is I found it very useful. And so I can still work on the questions. And I’m very driven by you know, how do plants cope with changing climate? At which timescales are they’re responding? And then I have this tool that has served me and, and yeah, so it turns on, I’m back in Arizona, I do love Arizona. It’s a great state in many way, many ways. But it turns out, it took leaving to figure that out for me.

That’s often the case, isn’t it? Right. So we’ve had podcast episodes, where we’ve had multiple guests on the same time. But this is the first episode, where we’ve had collaborators together to discuss their projects. And so could you tell us a little bit about how you first came to become collaborators and begin to work together on research projects.

I would love to tell that story. I met just at the AGU conference. And I think we disagree on the year in my mind, it was 2019. But it might have been 2018. I walked by her poster, and I saw something on her poster I had never seen before, which was a continuous record of plant water content data. So she had been measuring. It was really stem water potential using psychometry that our field research sites Outlast. And I didn’t know at the time that this was possible. And I was just amazed by these beautiful figures, I saw just this poster. Because what it showed for me is that it would be possible to measure the water potential of plants at timescales over which things like temperature and humidity very, which could really allow us, you know, the opportunity to answer questions about how plants stalemates respond to drought stress that that really have not historically been possible to answer using more discrete datasets. So that’s certainly how we met. And from there, we’ve just been thinking over the years about ways to enable those observations to be collected and more sites and also to create Pentwater potential databases that are that are more accessible and open for the broader community. But we can definitely trace it back to that poster, where we also bonded over the fact that we had both received a AGU biogeosciences travel grant for parents of young children at the time. So I think that my my daughter is about a year older, or maybe about the same age as justice. So that was obvious from her poster. So we had a chat about that as well.

Is that how you remember it, Jessica?

I do. I remember it because I think that year was I mean, that was my year I had I had a baby. I had a poster I was ready to go. That was really my first real AGU. And I remember I they were giving out these pins that said job seeker. It was kind of like, Oh, Kim Novick. I mean, I’ve read her work. This is amazing. She’s at my poster. She thinks my poster I figures are cool. Kind of like hey, like I have this job seeker. And she’s like, well, I they need to make one for me. That’s called grant seeker. I remember her saying that. And so I think that also, it was like, okay, grant so good. That’s what we need then to make this work. How can we work together of course, things take time, I stuck it out long enough in academia to for some of those things to come to fruition. But I also want to give a shout out to George Koch, who really, you know, it was it was his instruments he had gotten a grant and was kind enough to lend them to me for the duration of my dissertation research and taught me showed me the ropes taught me how to use these instruments. And later on I figured out that not not not everyone most people don’t have a George Koch in their lives. And so, this technology is not really accessible even I mean even if you did get a grant and purchase these instruments, just the know how and how to install them and keep them functional and like and then what how to deal with you go from you know spot measurements of plant water potential to time series of the half hourly scale like then you have to deal with the data side of side of things. Yeah, so it takes a lot to get there. And I think that’s one of the things that motivated us is like, okay, so how can we feel this up? You know, not just me and Kim and maybe a handful of other people who are really, really invested. But how can this, you know, there’s so many, there’s so many questions. There’s so many species, so many and a great sense of urgency, I think, to our work as well. So how do we put that make that available to others?

Right? I know that those that know us here at METER Group know that we are water potential super fans, and feel that it is a measurement that should be included in any kind of research dealing with questions surrounding soil moisture, or exploring the behavior movement of water all throughout the soil plant atmosphere continuum. Can you give us a little background? For those in our audience who might not be super familiar with water potential? Can you give a little background into into what it is and how you use it in applications in your specific research interest?

Yeah, I’ll be happy to take a try at answering that question and then maybe Jess can follow up, I’ll start by focusing on the soils. Where it’s, you know, soil water potential is long been a core hydrologic variable. You know, if you take a college level hydrology course, you’re going to be introduced to the concept, it’s usually negative in soil. So you can think of it as a measure of the tension under which water is bound to the soil. And it is gradients in water potential that move water from one soil layer to another, or from one place in the soil to another, that also gradients in water potential between soils and plants, the move water through plants, and then eventually to the atmosphere. You know, it’s a variable that shows up in Darcy’s Law and it shows up in Richards Hydrology Equation. But at least in my world, it’s not a variable that we routinely measure in the field. I think that we certainly should do that more often. And I applaud NIDA for providing us with some instruments to make that possible. But historically, in ecological research or ecosystem science research, we measure soil moisture content, which is a little bit different. It’s the volume of water in the soil, not so much the pressure under which it is bound. And there are some some things you can do some tricks, you can try to convert between soil moisture, and soil water potential. But depending on which tools you are using, these can end up being very uncertain conversions. But the truth is for many of the questions that we seek to ask such as, you know, what determines us to model results, responses to decline soil water, or what determines the water potentials within the plant that can ultimately drive drought driven plant mortality, we really need to know water potential. And so we are very enthusiastic about on the one hand, motivating the community to either make more instrument measurements of soil water potential in situ, or to do some of those lab derived water retention curves, that can allow us to make this site specific comparisons. But also just to recognize that, you know, when we want to understand how plants are responding to the environment, it is water potential that is ultimately the more relevant driver most of the time than soil moisture content. And then I maybe I’ll punted to Jess who might be able to tell us a few things about about the water potential in plants.

Well, that’s just like as as, as was alluded to, to it’s just a key measurement that should be measured with a lot of other when you’re measuring a lot of other things about how a plant is functioning, say photosynthesis or other fluxes, it’s nice to get a sense of what’s the water status of the plant. And so I think that in that regard, measuring plant water potential is, is key to understanding right and so, in planning your physiology, we don’t have the same kind of functional tray where you can take one measurement, and that represents a certain characteristic of a plant, we often look at how it changes along gradient, so kind of like you know, ACI curves, where you change the level of co2 inside your chamber and measure the photosynthesis, how photosynthesis react so that in plant water relations, we often look at as the leaf or the branch dries down and the water potential becomes even more negative. How does that affect the hydraulic properties of the tissue of the conductive tissue in that stem or in that leaf and so that can give us parameters such as, so vulnerability curves can give us something like p 50, or the water potential at which 50% of the maximum conductivity is lost. And as if you’re doing this on leaves you can get at things like trigger loss point at what point to the leaves lose their trigger and collapse and generally is considered not not reversible from there. So those are important factors that we you know, in a lot of traditional ecology work we want to know like which species are more vulnerable, which species are less vulnerable? under climate change? What can we expect from species A versus species B? And so, yeah, the water potential is quite critical to all of those. And those are more kind of snapshot maybe parameters, but with the, with some technologies that are monitoring both soil water potential continuously, and are also possible to measure plant water potential continuously, can get at some of those other timescales of question, like what happens when, you know a rain of event happens? Or what happens during a heatwave? That wasn’t previously possible with the manual measurement?

Right, right. Can you speak to, I guess, go into a little bit more detail on some of the successes that you’ve had in making water potential measurements in soil or plants.

I’d love to hear Jess tell us a little bit more about her work on the creosote and the other charismatic species we find in the in the southwest, because she’s, again, I think, really pushing the envelope in terms of what’s possible for for measurements and plants out there.

Oh, sure. Thanks, Kim. Um, yeah, so the creosote bush Larrea tridentata, is this very drought tolerant shrub, and it’s, it’s just known in the literature for going down to pretty negative, pretty extreme water potentials. And so, because of an, you know, desert shrub, not very fast growing, it’s, it’s unusual, in many ways, and it’s, surprisingly, really has really taken to being sent monitor for the stem water potential. And so the way these these products work is that you expose the surface of the xylem, and you attach a sensor to it, you seal it really well. But that can be affected by things like the wounding response of the plant or plant tissue growing into the sensor, you do have to rotate them. And so I, you know, and I look back on it, I think all of us can have, you know, down moments where we’re like, oh, man, that was just bad luck, I missed out on this opportunity or that opportunity. But I really have to say that I had just the incredible luck of being able to learn about the sensors from George Koch, and working in a system when I was at ASU, temporarily at ASU to work with a tree, a shrub of plant species that just really worked very well with the sensors. And so yeah, the time series produce there, because of the variability in the Sonoran Desert, you know, really dry periods, followed by really wet dynamic periods, experiencing all those different environmental conditions, you can also see that variability so clearly in the water potential time series. And it’s led me to think differently about, you know, kind of classifying entire species, as, you know, very drought tolerant or very drought avoided, because, you know, plants are living organisms, and they, especially, I think, if they’re in environments where the conditions are known to be evolved for these conditions that are, you know, go from extremes, they have can have different strategies for those different times.

You’re talking about extreme areas, and I think a lot of our audience might be familiar with permanent wilting point. What are the plants that you’re studying out in the extreme, you know, Sonoran deserts and other places? What is their tolerance level?

I’m sure the creosote has a permanent wilting point, because if you push the envelope far enough, you know, plants aren’t not going to be able to handle that. But I’ve recorded water potentials of predawn water potentials increase out of down to negative nine,

mega Pascal’s mega Pascal’s sorry, okay. Yeah,

negative nine megapascals. How does that 90 bar and so and I think this particular plant, it is on the extreme, right, so it has properties that lead it. So even after the leaves lose turgor, they’re able to after rainfall, recover and keep growing is not typical, I think of plants. And so yeah. There is a species in Australia that I’ve read of having more negative water potentials than that, but I think that’s about that’s about it. That’s why Yeah, I don’t know what the permanent wilting

point. haven’t got there yet. That’s super interesting. What are some of the other difficulties you have encountered in measuring water potential?

Well, um, so when you’re working with something as water potentials as negative as Korea, so running out of gas is like the number one fear that I have. For my dissertation study, and enough for some current work, my plan is just whole hog deliver a whole giant tank of pressure, pressurized air to the site, and to avoid that problem, the small portable tanks just never know when you’re going to run out. And then it takes it also takes a lot longer. So some people you know, are like, oh, yeah, you can go out and measure like 30 plants, and I’m like well the amount of time that you it takes to get down to like a negative six or negative nine. It just you can you can do fewer samples, and then you have to let the air out slowly sometimes as well. So that’s one thing that in my favor are that the creases are short. So I don’t have to do any kind of pull pruning. I just heard from a I have done the like a blooming and pole pruning before and some Aspen’s, that was really tough and physical. I just heard from someone at NAU, the other week about carbon fiber window washing poles. I don’t know if Kim if this is something that you guys could explore. Apparently, they’re pricey, but it might be worth it. He’s like, Yeah, you can just lift it with one hand. Oh!

There you go.

Well have to look into it, I have to say, you know, I’m joking, but I only only 50% Joking, when I say 50% of sort of the work that Jess and I are doing right now. It’s just to allow my lab group to avoid future pre Dawn measures. Because while I have many, many, you know, very dedicated postdocs and students that I’m lucky enough to work with, personally, I hate them. And I hate having to ask people to do them. It’s, it’s hard. And we work in tall forests. So our trees are 30 plus meters tall. And it’s hard enough to access the leaves when the sun is shining. And it’s really hard to get to them in the pitch black darkness. You know, the the benefit of this predawn measurements is that it gives you a proxy for what the soil water potential is over the you know, integrated root zone. So we’re always sort of scratching our heads to think of there might be other ways that we can get it that that don’t involve driving an an, 80 foot, boom, lift around in the dark, at 4:30 in the morning. But it’s hard when you work in big forest, accessing at the top of the canopy is a real challenge for us. We tried everything we do we have the slingshots, we get the boom lift out, it’s really a cherry picker track and we go up that way. But then we’re sort of limited to trees that grow by the little road. Some some groups are able to access leaves from their Eddy covariance towers, but ours isn’t quite close enough to any of the trees. So that doesn’t work for us. We are prohibited from firing a shotgun in our research area. So that’s off the table. But it is it is one of the biggest headaches of our work is just getting to the leaves of these of these tall trees.

How about measuring water potential in soils? What are some of the difficulties there?

Interesting question, because I think we’re still not at the point where we have, you know, perfect sensors for the task. But we have sensors that are better than they were historically. And so when I tried to think about why is it the case that most of the time and field research settings, typically in the Eco logical and ecosystem science community, we measure soil moisture instead of soil water potential. I think it’s because simply the measurements historically been easier for soil moisture content. You know, we’re just starting to get to the point where we’re installing Institute of soil water potential sensors. TEROS 21? I think I got it right. And we can quite pleased with those so far. You know, but we work in in fairly music environments, we would never see plant water potentials of negative nine MPa, you know, in our worst droughts, you know, maybe the soil gets down to negative two or three MPa. So we’re working within a much more limited range. But you know, we’re, if I can just take a second to mention to sort of broader efforts to increase the collection of these sorts of measurements through the ameriflux networks to your water. There’s sort of two things going on, on the one hand ameriflux, which is a network of Eddy covariance Fox towers for North and South America. It has has purchased and sent out to individual sites, a wide array of in situ so the water potential sensors, I think we just started to see them installed this summer. And it’d be really exciting to get those data back and see how they can help us interpret the fluxes. Another major initiative is being led by my lab together with rich Phillips, who’s at IU down in the biology department and ameriflux, where we are doing generating site level water retention curves, using equipment provided by meter, which is just a few doors down from where I’m sitting right now. And the idea is that we are asking ameriflux PI’s to send us their soils, we send out a sampling kits and they are to collect somewhere in the ballpark of fall soil course, from three different depths, maybe four different profiles, send it back to us. And we’re analyzing those samples for saturated hydraulic conductivity and the water retention curve, flow texture and find rate density, which is data that will again return to the network. And so the hope is that, you know, we’re beginning to generate the information necessary Sorry to transform those historic observations of soil moisture content into estimates of soil water potential, which I am really excited to see how this plays out, because it’s so common in our field to relate some sort of ecosystem process, maybe it’s GPP, which is canopy scale photosynthesis, or evapotranspiration, or, or model or surface conductance, the soil moisture content. And so frequently, we see that those relationships appear to be threshold driven, right, there’s some range of soil moisture, where we don’t see much of a change in photosynthesis or conductance, and then we reach what appears to be a critical threshold. And then And then things start to decline rapidly. And the hypothesis that we’re looking forward to testing is that a lot of the nature of that apparent threshold relationship is really driven by by the soil and water retention characteristics of the soil so that if we switched out the x axis from soil moisture content to soil water potential, we might see much, far more linear relationships, and reduce a lot of the heterogeneity from one site to the next. Stay tuned. We will be making an announcement soon to collect more soils as part of that project. And I want to particularly acknowledge Daniel Beverley, who’s a postdoc that’s been really driving that project forward together with Alexander Crookshanks, who’s a postback research assistant, who I’m pretty sure at some point in the near future will be pursuing graduate school applications. Awesome. Keep your eye out for her. That’s awesome.

Kim you talk about seeing Jessica’s poster for the first time and one of the things that really piqued your interest was her continuous data? Why was that of interest to you at that time,

we’ve been historically my group and many others have been interested in understanding how plants respond to drought stress of course, but specifically how they respond to both drying soil and also trying air right. So dry soil we can measure as a function of soil moisture content or more ideally swing water potential and the air and you know, the best proxy is the vapor pressure deficit. So, the difference between the amount of air the atmosphere can actually hold and then and then the actual water vapor content. And so you know, as a as a drought unfolds, usually soil water declines, but often the vapor pressure deficit also goes up. And these things tend to happen together. So through land atmosphere feedbacks, a soil moisture, dret VPD goes up, the plants can respond independently to each rests. So if you can grow a plant in an environment where PPD rises, the soil moisture stays the same, you will still see declines in some model conductance and photosynthesis driven by plants actively closing their stomates to avoid excessive water loss to this drier first year atmosphere. But because these things tend to go together, using you know, data collected at weekly or monthly timescales, it’s very hard to disentangle the two, all right, however, it is very straightforward. To do it when you have continuous data, because over the course of a day, or even a couple of days, usually soil water tends to be relatively stationary, whereas VPD can vary quite a bit. And so you can leverage this, these different timescales of variation, together with continuous measurements of whatever response variable you’re interested in looking at, and be able to disentangle the vapor pressure deficit from soil moisture impacts on plant function. And we’ve been able to do this quite well. There’s no no shortage of studies that are doing this looking using data from Eddy covariance flux towers, which come in and a half hourly, or hourly timescale, and also from set flux measurements of tree water use, which are also made continuously. But the potential table to do the same thing. And perform complimentary analyses on continuous measurements of plant water potential, would really allow us to connect the dots in a way that we haven’t been able to do so before.

Anything to add to that, Jessica.

I think I just want to reflect that like the it’s, it was amazing that Kim saw that was immediately like honed in on Oh, wow, that is a game changer. Because I had tried to pitch this same idea was like, Oh, we’re gonna go from these manual measurements, Spot measurements, continuous measurements to various other you know, as a grad student, small grants to support and they generally just came back as review it as like, not very, you know, there’s sensors for everything. You know, like what’s so exciting about you using a sensor that doesn’t sound all that novel, but it really is novel in the sphere because of what what’s never, it’s never been able to measure before. And because of all the difficulties you were you just spent some time describing to get pre dogs. And I think pairing that with other sensors like at the same time scale. I think that’s really where a lot of my interest also lies like sap flow, and I haven’t used these myself but other people use the drop stem dramaturgs and But maybe there could be people measure wood water content. And so pairing these together looking to just like, it’s still a wide open question, I think like, what are some of the good proxies, maybe there’s some good relationships between these, I personally think that being able to instrument, a plant with water potential, maybe soil water potential, the sap flow in the stem, and then a branch of STEM water potential looking at that gradient, we can calculate hydraulic conductivity in situ, and see how that changes, you know that versus you know, harvesting a stem and doing those dry down measurements I mentioned before in a lab setting like doing that on living tree, or shrub as the, as the environment is changing as the VPD, or the soil moisture content might be changing. I think that just gets us closer to like, closer to the mechanism of what the plants are actually doing. Right? Instead of extrapolating from snapshots.

And extrapolating from snapshots, how then can we work with these more powerful modeling systems to work with the data that we have, or maybe kind of overcome, I don’t wanna say overcome the limitations of the sensors, because, you know, garbage in garbage out when you’re dealing with with the data. But in your practice, and in your experience, how have you been able to better model these complex processes within soil? Plant water interaction, sir?

Yeah, thanks for that question. I think about a lot like how the plant itself is responding. So the biology is really interesting to me. And the, but the biology is still, you know, there’s still inputs right there. So the plants are sensing the external environment and then responding in a particular way, depending on those conditions. And so one way I’ve been, like taking this snapshot approach, but like having these longer time series, using the same kind of theoretical framework is being able to see, okay, well, how did these parameters themselves change over time? And can we expect a especially something you know, it’s pretty obvious that a creosote because they’re an evergreen species, and in June, they look just mostly dead. They don’t look all that they keep their leaves. Leaves are brown at that point. But they’re still living. And they’re still photosynthesizing. And so like, it’s just natural to Okay, well, clearly, creosote at this point isn’t behaving the same way or responding to the environment in the same way as it does in a wetter, more, more suitable a time period. And so yeah, I think that matters a lot for these flexes, right, like, you know, creases are really dominant. And across these deserts are some places where it’s pretty much creases, the only major woody plant out there, they might not be highly productive. They’re not as productive as other ecosystems, but that variability, they account for a lot of the variability in the carbon cycle. And so yeah, and then, if we, if we try to then put a snapshot parameter into a into one of these biophysical models that you know, have lots of equate lots of systems of equations that explain our best, or that represent our best understanding of how Photosynthesis Photosynthesis works, what’s going to underestimate or maybe overestimate, but mostly underestimate what’s going to happen, because you’re like, it’s a drought tolerant plant, its parameters are really low. That’s not something I’ve alone had been thinking about. But just thinking, yeah, there’s, you know, we think about models that having these inputs, outputs, and then these parameters, but what if the parameters themselves? are dynamic? Do does that mean we have to measure everything everywhere all at once to get them to work? In which case if we already measured everything everywhere, all at once that we would need these models now? Would we? So? Yeah, thinking about how to incorporate the biology in the expected relationship to have that next layer of like, how do the parameters evolve? That’s something that that I’ve been thinking about.

Alright. We have been hearing about your efforts towards standardizing a national meteorological network that would include water potential measurements, and you’ve published and presented on this topic, can you tell us a little bit more about this idea and the goals surrounding this potential network?

We’d be thrilled to do that. So the network is called tsinet. Because we often abbreviate water potential with the Greek letter tsi, T-S-I-N-E-T, tsinet. And I think just a little bit of background, that’s an idea that’s been in you know, we’ve been kicking the the idea around for a few years now and it involves a much broader team of collaborators than just Jess and I. But, you know, the original idea sort of, was born out of two things. The first is sort of the recognition that in many fields of ecosystem ecology, or you know, eco physiological research, we have developed these really accessible and open databases, whereby, you know, individual site PIs will collect data and then you Frequently voluntarily share the data to networks like ameriflux, or flux net or set flux net in a way that they are, they’re accessible and open to the global community. Now, just to take a step back, I mentioned earlier in our discussion how I started my PhD work on on some ameriflux towers in the do force. And I really didn’t know much about the scientific enterprise at the time. But what I knew I learned from from my advisor and the lab group, but Jessica we collect these measurements, and we use them to answer questions we’re interested in, but we also give the data to the network. Simple, that makes sense. That must be how science is done. And it took me a long time to realize that that the flux community in America community and SR networks across the world were really kind of on the leading edge of sort of this transition to open, accessible data sharing. And so I’m very lucky, I think, to have been sort of brought up in a community that places such a high value on that service. You know, the other observation is when we when I think about plant hydraulics, research, and eco physiological research more generally, specifically, when it concerns the function of things like plant stalemates, I get the impression that we’re a very theory rich, but data poor fields, which might be a bit of a surprising statement to some. So to say exactly what I mean, I think, you know, there’s the the functioning of plants domains, which on the one hand is relatively quite straightforward, they’re either relatively more open a relatively more closed, it’s, on the other hand, so complex, right, especially when we want to connect those dynamics to what’s happening with water flows through the stem, and what’s happening through the soils and what’s happening in terms of plant risk of, of mortality. And so we see these very beautiful papers being written all the time, they’re largely modeling papers, the present different ways to model that dynamic system model function, which is a really noble goal, I mean, some other the pathway by which co2 enters plants through photosynthesis. And that’s the pathway by which most of the energy just to support most life on Earth is created. So that’s an important thing to study, we’ve got all these models is very nice mathematical models. But as soon as that we lack the data necessary to evaluate and cross compare them, because particularly when we’re thinking about water potential, but also I would argue some of the other traits that are really important pieces of the puzzle, we do not yet have these open, accessible databases of the time series of water potential, that are necessary to link environmental drivers to sort of ecosystem scale responses, like photosynthesis, and evapotranspiration, so we’re hoping to fill that gap by creating a database that would aggregate pre existing and new observations of plant and soil water potential. And we will happily accept observations made with pressure chambers. So discrete plant water potential observations, as well as, you know, increasingly frequent attempts to measure those data continuously. And so we’re really excited to kick the project off, we’re gonna pair it with a lot of you know, in addition to building, let’s say, a network of data, we’re also excited about building a network of people. So there will be a lot of programming associated with a network webinars and early career training opportunities. And a graduate distributed graduate seminar down the line workshops, conference sessions, that sort of thing. But yeah, it’s been it’s been years in the works. And so we’re really, really excited to get it kicked off this year.

That’s awesome. Along with that, as well. And you talked about Yeah, building this kind of community of researchers as well. Are you interested then and also improving or creating kind of best practices when it comes to observations and measurements within and interpretations of water potential data?

Definitely, I think that’s part, a large part of where the network of people comes in. I think, you know, people are trained in their labs and their advisors were taught by their advisors. And there’s these different lineages sometimes of how we do things, even though it’s, you know, especially with the pressure chamber, it seems like it’s a fairly standard thing, but it turns out it’s not. And there was a really nice paper that came out recently by Celia Rodriguez Dominguez on on this that reflected some of these experiments, they took, oh, it doesn’t matter if you do it this one particular way versus this other way. And so we want to collect some of that, like, how do we like first of all, even just like for too big a database at all, like what is the standard data reporting format? Can we agree on that as you know, as kind of a field and we want as many people’s thoughts and opinions on this as we can get? I only know the way that I was trained, really. And so it’s been eye opening in some of these conversations. We’ve had to build dinette across the globe, really international team of researchers that we have different takes on this and I think it’s also because is very plant specific. And that’s a lot of the problem with some of these instruments that are plant instruments is like, what works for you what one species is just plainly not going to work for someone else depends on if there’s resin? Or if you know, for pressure chamber methods, it’s like, how big are your leaves? How big are your petioles? Like, will fit like I, you know, all kinds of things, are you trying to get a snapshot of lots of lots of different species are you focused on like the variation within a species or within even different branches of the same individual. And so those are all things we’re going to have to consider. We do want to develop some kind of data reporting formats, and also best practices for the stem psychrometer. I think that’s something that folks are interested in learning. But again, if they don’t have a personal connection, or like, have this lineage of learning of passing on the knowledge from someone who knows, it can be really tricky. And I have had the opportunity to work with some folks who have these instruments have had trouble with them. And just went, you know, there’s something you know, there’s a lot we can do over the internet, and with these webinars, and we’re gonna have a lot of them. But the the training, one of the one of which will be fist fest, really gives us an opportunity to provide some hands on some of these things. It’s hard to describe or say what it is we’re doing, but it’s really, really necessary to show rather than tell. Because there’s a lot of things I’m excited about.

Right now, what is the timeline looking at for where it’s off the ground, and you know, you got the ball rolling, and things are looking good?

Sure. So I in fact, it hasn’t officially started yet. But we hope to move quickly. Once it does, you know, sort of our early goals will be supporting some of these early career training workshops. As I just mentioned, fist fest, we also have connections to Flux corpse just sort of emerged from the attic, various community, but we’re excited to, to bring water potential to Flux course, at least a little bit next year. We are very, you know, I hope we hope that within the first few months of the project, we’ll be opening the call for submission of pressure chamber water potential measurements and associated meter logical observations. And in that regard, we will owe a pretty big debt to the folks that run SAP flux net, who have already begun to do some of this work for the sites to learn that work. So they can sort of piggyback off of what they’ve learned from that experience. The project I mentioned, collecting the water retention curves, and the mere flux sites will be an important, I think, early way to populate. So a lot of potential information into the database. But you can look for us to be having webinars and organizing cockpit sessions, and beaten on your door asking for your data. But as we do, and we recognize that these data are hard fought, you know, we discussed some of the difficulties associated with feet on measurements and working in tall forests already. So we’re also thinking through the right incentives, to motivate people to want to share their data with the network. And also ways to properly reward and attribute What are frequently the early career scientists that collected the data.

Oh, and just just be on the lookout, we, one of the first things we’re going to do is put out a call for membership on our working groups. And so and one of the first working groups will be the data working group where we’re going to Yeah, see people’s input on these data reporting formats and awesome. And yeah, survey them about how, what would they be incentivized by? What would work for them? What would incentivize them to share their data and, and make it easier? Or, you know, it’s always a little bit of a leap to like, take the data from a format that you’re used to working with to make it a format that someone else can also find it useful, right? What would what would make that process a bit more streamlined?

Yeah. What do you see as the future of this research either within your, your own particular specialty, or within this, this idea of of a network of interconnected researchers who are looking at Eco physiology or solar or plants water potentials?

Yeah, I can take your first stab at that, you know, we already mentioned sort of the challenge of, of getting these processes, right and models and so I’m hopeful that the database that will build can enable progress on that front, where it’s currently been hindered by just a lack of systematic representative open data, you know, from from a wide range of sites. Another really, I think, exciting friends here concerns our ability to measure really important features of not only canopy water use, but also canopy water content remotely. So we have it’s just amazing to me how rapidly the satellite platforms are developing. We have eco stress and orbit on the on the spaceship station that can provide a proxy of VT at the scale of it. Individual farm fields, which is really amazing. We also have a growing interest in the use of vegetation, optical depth measurements, or VOD as a proxy for water contents. And here, I really want to credit Alex koenings Visit Stanford and is part of signups for kind of really helping to develop those approaches and spread them throughout the community. And so what’s really exciting is, I think the opportunity to pair a much more representative dataset of ground observations of water potential. And, and ideally, oftentimes co located with with measurements of the fluxes themselves, whether it’s from fluxs towers or soft flux, as ground truthing, and reality check data on what we’re seeing from space, because that could really open the door to new ways to characterize not only plant water stress, or, or vegetation, water stress or drought stress. But also I mean, thinking about you know, we you don’t have to connect too many dots to see that this presents the possibility for whole new ways to conceive water retention curves, ecosystem water retention curve or to, to think about how to understand the relationships between water content and water potential are really core skills. So I’m really excited to see, you know, where how far we can get in that direction over the coming years.

Jessica, your thoughts on the future? In this regard?

Yeah, well, Kim covered a very nicely, there’s a lot of there’s a lot of things, we don’t even know that it could it could be, it could be useful for validation datasets for these newer data, newer data platforms. But, you know, I think it can also be really useful for kind of really standard questions in plant eco physiology, you know, this assumption that predawn water potential is a proxy for the soil water potential in the root zone, that Kim mentioned earlier. You know, that’s not always going to be the case. And there’s, there’s individual papers that have gone out there and done fine scale measurements to show that that’s not always the case. But we don’t have a good idea across the board, like under what conditions can we does assumption hold or species. There’s this assumption hold, and under what conditions do we have to, you know, revisit this assumption. And so, you know, the power of the database of people working at different in different places with different interest species is that it will really allow us to, I think, have I anticipate lots of synthesis coming out of this, including some really standard kind of, you know, I was also thinking to like, early on driven, like, my questions maybe don’t seem very sophisticated, because some of the things were literally like, how does water potential affected by soil moisture content and VPD? Like the dryness of the atmosphere? And it’s like, shouldn’t we know that already? Like, that’s a pretty stale as a plant environment interaction question. That’s you people have been asking, we have had the tools to answer for a long time. But to answer those questions more systematically in a synthetic way that accounts for what we know are different about different species in an environment. That’s been really hard to do because of the paucity of data.

Well, thank you both for taking your time. I just wanted to ask if there’s any place that our listeners can go if they want to learn more about your various research projects?

Yeah, we’re a little too early to throw out a signup web address or email address but um folks are welcome to email me. At early Google gold name, not too hard to find the username so feel free to find me and record Indiana University and shoot me an email.

Alright and Jessica?

Same you can find me just google whoa.github.io

Stay safe, and we’ll see you next time on We Measure the World!

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