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.
This week, I attended the Michigan University-wide Sustainability and Environment (MUSE) conference. Since arriving at the University of Michigan, I have been attending the MUSE bi-weekly workshops during which PhD students and postdocs give presentations or discuss articles on a range of topics related to sustainability and the environment.
The MUSE conference is a large-scale version of these workshops, bringing people from across the University of Michigan to present their research during a two-day event. I chaired the session on Land Use and Land Cover Change on Thursday morning and presented my own results from using solar-induced fluorescence to map reforestation in China.
It was a fun occasion to meet students, postdocs, and faculty from a range of departments, from English to Psychology, and Mechanical Engineering to the School of Public Health, and I hope that some of the contacts made at the conference will eventually turn into long-term collaborations.
This year, the AGU Fall Meeting moved from its traditional location in San Francisco to New Orleans. As usual, the meeting was a wonderful occasion to catch up with former classmates and colleagues, and hear about all the new science!
This year, I was the co-chair for the CYGNSS session A11F, Early On-Orbit Results of the Cyclone Global Navigation Satellite System, together with Chris Ruf. The poster session was a great way for all the people using and working on CYGNSS to chat about their respective results.
In addition, I gave an oral presentation entitled Effects of dew deposition on transpiration and carbon uptake in leaves that presented the results of a collaboration with Sally Thompson‘s lab at UC Berkeley.
Finally, I had the opportunity to attend the Ecohydrology Technical Committee and to help out with the Hydrology Business Meeting. Both events were great opportunities to meet new people in my field, and I’m hoping to get more and more involved with the hydrology community at AGU in the future.
A new paper entitled ‘Advancing ecohydrology in the changing tropics: Perspectives from early career scientists‘ just appeared in Ecohydrology today. The article is a student-lead paper focusing on current and future threats faced by tropical ecosystems, and what the potential research gaps that would help the scientific community better understand and mitigate some of these threats.
The article stemmed out of the AGU Chapman conference on tropical ecohydrology that I attended in June 2016. All the co-authors of the article are graduate students and early-career scientists from institutions around the world, and it was both a lot a fun and a great learning experience to write this together! You can see the article on the Ecohydrology website HERE.
Tropical ecosystems offer a unique setting for understanding ecohydrological processes, but to date, such investigations have been limited. The purpose of this paper is to highlight the importance of studying these processes—specifically, how they are being affected by the transformative changes taking place in the tropics—and to offer an agenda for future research. At present, the ongoing loss of native ecosystems is largely due to agricultural expansion, but parallel processes of afforestation are also taking place, leading to shifts in ecohydrological fluxes. Similarly, shifts in water availability due to climate change will affect both water and carbon fluxes in tropical ecosystems. A number of methods exist that can help us better understand how changes in land use and climate affect ecohydrological processes; these include stable isotopes, remote sensing, and process-based models. Still, our knowledge of the underlying physical mechanisms, especially those that determine the effects of scale on ecosystem processes, remains incomplete. We assert that development of a knowledge base concerning the effects of transformative change on ecological, hydrological, and biogeochemical processes at different spatio-temporal scales is an urgent need for tropical regions and should serve as a compass for emerging ecohydrologists. To reach this goal, we advocate a research agenda that expands the number and diversity of ecosystems targeted for ecohydrological investigations and connects researchers across the tropics. We believe that the use of big data and open source software—already an important integrative tool/skill for the young ecohydrologist — will be key in expanding research capabilities.
Photo credits: James Aldred