Last week, I attended the Green Life Sciences Symposium organized by the Green Life Sciences Initiative at the University of Michigan. The two-day symposium brought together plant scientists from all over the US and a few international places. I gave a talk on my recent paper looking at the effects of dew deposition on leaf transpiration using stable isotopes. For me, it was especially great to connect with plant scientists at the University of Michigan that I had not had a chance to interact with yet. The organizers also worked really hard to ensure that women and POC were represented, and we got to see multiple talks by inspiring women in the field, including Johanna Schmitt, Beronda Montgomery, and Deborah Goldberg.
Our new article “Dew‑induced transpiration suppression impacts the water and isotope balances of Colocasia leaves“ was just published in a special issue of Oecologia honoring the career of Jim Ehleringer. In collaboration with Paul Gauthier and my PhD advisor Kelly Caylor, this paper looks at the effects of dew deposition on the isotope composition of Colocasia esculenta leaf water. See the abstract below for a quick overview of the study and results or head over to Oecologia’s website to read the full paper.Abstract
Foliar uptake of water from the surface of leaves is common when rainfall is scarce and non-meteoric water such as dew or fog is more abundant. However, many species in more mesic environments have hydrophobic leaves that do not allow the plant to uptake water. Unlike foliar uptake, all species can benefit from dew- or fog-induced transpiration suppression, but despite its ubiquity, transpiration suppression has so far never been quantified. Here, we investigate the effect of dew-induced transpiration suppression on the water balance and the isotope composition of leaves via a series of experiments. Characteristically, hydrophobic leaves of a tropical plant, Colocasia esculenta, are misted with isotopically enriched water to reproduce dew deposition. This species does not uptake water from the surface of its leaves. We measure leaf water isotopes and water potential and find that misted leaves exhibit a higher water potential and a more depleted water isotope composition than dry leaves, suggesting a ∼30% decrease in transpiration rate compared to control leaves. We propose three possible mechanisms governing the interaction of water droplets with leaf energy balance: increase in albedo from the presence of dew droplets, decrease in leaf temperature from the evaporation of dew, and local decrease in vapor pressure deficit. Comparing previous studies on foliar uptake to our results, we conclude that transpiration suppression has an effect of similar amplitude, yet opposite sign to foliar uptake on leaf water isotopes.
Our new article, “Dew deposition suppresses transpiration and carbon uptake in leaves” was just published in Agricultural and Forest Meteorology. The work was a collaboration with Kelly Caylor, Sally Thompson’s lab at UC Berkeley, and Tony Rockwell at Harvard University. For this work, we built a leaf energy balance model to test the effects of dew and fog on the leaf water, carbon, and energy balances. We compared our model to data from UC Berkeley’s Blue Oak Ranch Reserve in CA. See the abstract below for a quick overview of the study and results or head to the A&FM website to read the full paper.
Dew deposition occurs in ecosystems worldwide, even in the driest deserts and in times of drought. Although some species absorb dew water directly via foliar uptake, a ubiquitous effect of dew on plant water balance is the interference of dew droplets with the leaf energy balance, which increases leaf albedo and emissivity and decreases leaf temperature through dew evaporation. Dew deposition frequency and amount are expected to be affected by changing environmental conditions, with unknown consequences for plant water stress and ecosystem carbon, water and energy fluxes. Here we present a simple leaf energy balance that characterizes the effect of deposition and the evaporation of dew on leaf energy balance, transpiration, and carbon uptake. The model is driven by five common meteorological variables and shows very good agreement with leaf wetness sensor data from the Blue Oak Ranch Reserve in California. We explore the tradeoffs between energy, water, and carbon balances for leaves of different sizes across a range of relative humidity, wind speed, and air temperature conditions. Our results show significant water savings from transpiration suppression up to 25% for leaf characteristic lengths of 50 cm. CO2 assimilation is decreased by up to 12% by the presence of dew, except for bigger leaves in windspeed conditions below 1 m s−1 when an increase in assimilation is expected.
After thinking a lot about pre-print and how they fit in the world of plant research, I have decided to give it a try! My first pre-print entitled “Dew-induced transpiration suppression impacts the water and isotope balances of Colocasia leaves“ is now available on the bioRxiv: see the article!
The paper examines the effects of dew on transpiration suppression in Colocasia esculenta leaves using stable isotopes of water to track changes in the water status of the leaves. The article has been submitted to a peer-reviewed journal.
Abstract: Foliar uptake of water from the surface of leaves is common when rainfall is scarce and non-meteoric water such as dew or fog is more abundant. However, many species in more mesic environments have hydrophobic leaves that do not allow the plant to uptake water. Unlike foliar uptake, all species can benefit from dew- or fog-induced transpiration suppression, but despite its ubiquity, transpiration suppression has so far never been quantified. Here, we investigate the effect of dew-induced transpiration suppression on the water balance and the isotopic composition of leaves via a series of experiments. Characteristically hydrophobic leaves of a tropical plant, Colocasia esculenta, are misted with isotopically enriched water to reproduce dew deposition. We measure leaf water isotopes and water potential and find that misted leaves exhibit a higher water potential (p < 0.05) and a more depleted water isotopic composition than misted leaves (p < 0.001), suggesting a ∼30% decrease in transpiration rate (p < 0.001) compared to control leaves. We propose three possible mechanisms governing the interaction of water droplets with leaf energy balance. Comparing previous studies on foliar uptake to our results, we conclude that transpiration suppression has an effect of similar amplitude, yet opposite sign to foliar uptake on leaf water isotopes.
My new paper is finally available online on Plant, Cell & Environment. For this paper, entitled “Leaf water 18O and 2H maps show directional enrichment discrepancy in Colocasia esculenta“, we looked at spatial patterns of water isotopes in Colocasia esculenta leaves. See the abstract below for a quick overview of the study and results or head to the PCE website to read the full paper.
Spatial patterns of leaf water isotopes are challenging to predict because of the intricate link between vein and lamina water. Many models have attempted to predict these patterns, but to date most have focused on monocots with parallel veins. These provide a simple system to study, but do not represent the majority of plant species. Here, a new protocol is developed using a Picarro induction module coupled to a cavity ringdown spectrometer to obtain maps of the leaf water isotopes (18O and 2H). The technique is applied to Colocasia esculenta leaves. The results are compared to isotope ratio mass spectrometry. In C. esculenta, a large enrichment in the radial direction is observed, but not in the longitudinal direction. The string-of-lakes model fails to predict the observed patterns, while the Farquhar-Gan model is more successful, especially when enrichment is accounted for along the radial direction. Our results show that reticulate veined leaves experience a larger enrichment along the axis of the secondary veins than along the midrib. We hypothesize that this is due to the lower major/minor vein ratio that leads to longer pathways between major veins and sites of evaporation.
I just receive the great news that I have been awarded one of the Mary and Randall Hack ‘69 Graduate Awards by the Princeton Environmental Institute! The Mary and Randall Hack ’69 Award provides research funding to support Princeton University graduate students pursuing innovative research on water and water-related topics with implications for the environment.
I am planning on using the award to focus my summer research on my project using QuikSCAT data to map dew formation over tropical forests.
You can read more about my project in the official announcement HERE.
Elliot Chang, a senior at Princeton University who has been working in the Caylor Lab since his freshman year, just published his senior thesis in the journal Rapid Communications in Mass Spectrometry. The article focuses on the innovative use of solid-phase extraction (SPE) to remove organic compounds such as ethanol and methanol from water samples extracted from plants. Those organic compounds are known for causing interferences when using isotope ratio infrared spectroscopy to determine the isotopic composition of the extracted water. The article is co-authored by Kelly Caylor, Adam Wolf and myself.
Today, I officially started my visit at Harvard University. For the next year, I will be sitting in Pr. N. Michele Holbrook’s lab in the department of Organismic and Evolutionary Biology. I am excited to improve my plant physiology knowledge, and to get more lab experience. I will still be a full time student in the EcoHydrology Lab at Princeton University and will go to Princeton regularly throughout the year.
I gave the EEWR (Environmental Engineering and Water Resources) departmental seminar on Friday, March 27th 2015. My talk focused on the latest results from the lab experiments I conducted last summer and fall, looking at the impact of dew deposition on Colocasia esculenta‘s energy balance. Please contact me if you would like to hear more on the topic!
This summer I finally started my own research project. I spent the summer working in the Caylor Lab in Princeton, helped by Craig Sinkler, a student from Rider University who did an internship in our lab this summer. We planted six large bulbs of Colocasia esculenta that we watered until the plants reached maturity. After about 4 weeks of growth, we stopped watering the plants. Every two days, we sprayed the leaves of half of the plants with isotopically spiked water, while the other half of the plants did not get any water. We collected leaves from each treatment and looked at the spatial distribution of water isotopes in the leaf using the Picarro Induction Module. I then built maps of the leaf isotopes for leaves collected at different times within a 4 week long treatment.
In order to help us interpret the evolution of the spatial patterns of the leaf isotopes, I also started running a water potential experiment in which I leave a leaf dry out under a heat lamp over a period of 10 hours and collect samples every half hour that I run on the WP4C to measure leaf water potential. I have been running the same experiment but spraying the leaf with ultra pure water every hour to look at whether foliar uptake is actually happening in Colocasia esculenta and how it improves water potential. Preliminary results show that foliar uptake is indeed happening!