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1. Passive water ascent in a tall, scalable synthetic tree

   https://doi.org/10.1038/s41598-019-57109-z  

   Shi, Weiwei; Dalrymple, Richard M.; McKenny, Collin J.; Morrow, David S.; Rashed, Ziad T.; Surinach, Daniel A.; Boreyko, Jonathan B. (January 2020, Scientific Reports)

   Abstract The transpiration cycle in trees is powered by a negative water potential generated within the leaves, which pumps water up a dense array of xylem conduits. Synthetic trees can mimic this transpiration cycle, but have been confined to pumping water across a single microcapillary or microfluidic channels. Here, we fabricated tall synthetic trees where water ascends up an array of large diameter conduits, to enable transpiration at the same macroscopic scale as natural trees. An array of 19 tubes of millimetric diameter were embedded inside of a nanoporous ceramic disk on one end, while their free end was submerged in a water reservoir. After saturating the synthetic tree by boiling it underwater, water can flow continuously up the tubes even when the ceramic disk was elevated over 3 m above the reservoir. A theory is developed to reveal two distinct modes of transpiration: an evaporation-limited regime and a flow-limited regime. 

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2. Evapotranspiration Partitioning Across US Ecoregions: A Multi‐Site Study Using Field Stable‐Isotope Observations

   https://doi.org/10.1029/2025GL115367  

   Matos, Katarena_A; Bowen, Gabriel_J; Good, Stephen_P; Allen, Scott_T (July 2025, Geophysical Research Letters)

   Abstract Quantifying relative contributions of plant transpiration (T) and soil evaporation to evapotranspiration (ET) is crucial to better understand how vegetation influences and controlsET, the largest efflux of the terrestrial water balance. Here, we derive estimates of transpiration fraction (T/ET) using consistent isotope‐basedETpartitioning methods for 13 sites spanning five ecosystem types of the continental US, capturing 56 snapshots ofT/ETduring the growing season. We found transpiration dominated theETflux across all sites with a meanT/ETof 0.81 ± 0.08 (±standard error). Sites and dates with higher vegetation indices exhibited higherT/ETand transpiration rates, with the latter increasing 0.30 mm/day per unit Leaf Area Index and 2.9 mm/day per unit Normalized Difference Vegetation Index. Counter to expectations, antecedent precipitation had no effect onT/ET. Despite the breadth of ecosystems and conditions represented, evaporation exceeded transpiration only once, suggesting that evaporation rarely dominatesETin the growing season. 

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3. Asymmetric response of Amazon forest water and energy fluxes to wet and dry hydrological extremes reveals onset of a local drought‐induced tipping point

   https://doi.org/10.1111/gcb.16933  

   Restrepo‐Coupe, Natalia; O’Donnell Christoffersen, Bradley; Longo, Marcos; Alves, Luciana F.; Campos, Kleber Silva; da Araujo, Alessandro C.; de Oliveira, Jr, Raimundo C.; Prohaska, Neill; da Silva, Rodrigo; Tapajos, Raphael; et al (September 2023, Global Change Biology)

   Abstract Understanding the effects of intensification of Amazon basin hydrological cycling—manifest as increasingly frequent floods and droughts—on water and energy cycles of tropical forests is essential to meeting the challenge of predicting ecosystem responses to climate change, including forest “tipping points”. Here, we investigated the impacts of hydrological extremes on forest function using 12+ years of observations (between 2001–2020) of water and energy fluxes from eddy covariance, along with associated ecological dynamics from biometry, at the Tapajós National Forest. Measurements encompass the strong 2015–2016 El Niño drought and La Niña 2008–2009 wet events. We found that the forest responded strongly to El Niño‐Southern Oscillation (ENSO): Drought reduced water availability for evapotranspiration (ET) leading to large increases in sensible heat fluxes (H). PartitioningETby an approach that assumes transpiration (T) is proportional to photosynthesis, we found that water stress‐induced reductions in canopy conductance (G_s) droveTdeclines partly compensated by higher evaporation (E). By contrast, the abnormally wet La Niña period gave higherTand lowerE, with little change in seasonalET. Both El Niño‐Southern Oscillation (ENSO) events resulted in changes in forest structure, manifested as lower wet‐season leaf area index. However, only during El Niño 2015–2016, we observed a breakdown in the strong meteorological control of transpiration fluxes (via energy availability and atmospheric demand) because of slowing vegetation functions (via shutdown ofG_sand significant leaf shedding). Drought‐reducedTandG_s, higherHandE, amplified by feedbacks with higher temperatures and vapor pressure deficits, signaled that forest function had crossed a threshold, from which it recovered slowly, with delay, post‐drought. Identifying such tipping point onsets (beyond which future irreversible processes may occur) at local scale is crucial for predicting basin‐scale threshold‐crossing changes in forest energy and water cycling, leading to slow‐down in forest function, potentially resulting in Amazon forests shifting into alternate degraded states. 

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4. Differential transpiration occurs in soybean under a wide range of water deficit and heat stress combination conditions

   https://doi.org/10.1111/ppl.70251  

   Sinha, Ranjita; Peláez‐Vico, María Ángeles; Fritschi, Felix B; Mittler, Ron (May 2025, Physiologia Plantarum)

   Differential transpiration is a newly discovered acclimation strategy of annual plants that mitigates the negative impacts of combined water deficit (WD) and heat stress (HS) on plant reproduction. Under conditions of WD + HS, transpiration of vegetative tissues is suppressed in plants such as soybean and tomato, while transpiration of reproductive tissues is not (termed ‘Differential Transpiration’; DT). This newly identified acclimation process enables the cooling of reproductive organs under conditions of WD + HS, limiting HS‐induced damage to plant reproduction. However, the thresholds at which DT remains active and effectively cools reproductive tissues, as well as the developmental stages at which it is activated in soybean, remain unknown. Here, we report that DT occurs at most nodes (leaf developmental stages) of soybean plants subjected to WD + HS, and that it can function under extreme conditions of WD + HS (i.e.,18% of field water capacity and 42°C combined). Our findings reveal that DT is an effective acclimation strategy that protects reproductive processes from extreme conditions of WD + HS at almost all developmental stages. In addition, our findings suggest that, under field conditions, DT could also be active in plants subjected to low or mild levels of WD during a heat wave. 

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5. Enhanced Water Evaporation with Floating Synthetic Leaves

   Shi, Weiwei; Vieitez, Joshua R.; Berrier, Austin S.; Roseveare, Matthew W.; Boreyko, Jonathan B. (August 2018, International Heat Transfer Conference)

   The evaporation of water exposed to a subsaturated environment is relevant for a variety of water harvesting and energy harvesting applications. Here, we show that the diffusive evaporation rate of water can be greatly modulated by floating a nanoporous synthetic leaf at the water’s free interface. The floating leaf was able to evaporate at least as much water as a free interface under equivalent conditions, which is remarkable considering that only about a third of the leaf’s interface is open to the ambient.We attribute the enhanced evaporation of the water menisci to their sharp curvature and three-dimensional surface area. At low humidities the water menisci cannot achieve a local equilibrium, due to the mismatch in water activity across the interface outcompeting the negative Laplace pressure. As a result, the mensici retreat partway into the leaf, which increases the local humidity directly above the menisci until equilibrium is reached. Using a ceramic disk with pore diameters of 160 nm, we find the surprising result that leaves exposed to an ambient relative humidity of 95% can evaporate water at the same rate as leaves exposed to only 50% humidity, due to the long and tortuous vapor pathway in the latter case. 

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