Atmospheric Vapor Research Articles

Glycerol Vapor Assisted Cu Direct Bonding: Implications for 3D Semiconductor Packaging

AbstractAs the scaling down of semiconductor devices reaches its physical limits, 3D stacking packaging technology is emerging as a new miniaturization solution. Among the various 3D packaging technologies, Cu direct bonding is widely adopted due to copper's excellent electrical conductivity and the absence of intermetallic compounds for solder bumps. Since copper readily undergoes oxidation, technologies that prevent Cu surface oxidation during Cu direct bonding are essential. However, current research suggests that the methods require additional pretreatment processes, which demand high costs. In this study, a Cu direct bonding method utilizing glycerol vapor is developed to effectively streamline the pretreatment steps. The potential of glycerol as a reducing agent and antioxidant for Cu is demonstrated using a silicon die sample with a size of 10 × 10 mm2, verified through the X‐ray photoelectron spectroscopy. The Cu direct bonding for 3D semiconductor packaging is successfully performed under glycerol vapor atmosphere, without any plasma pretreatment. The cross‐section of the bonded specimens is examined by scanning electron microscopy, and mechanical reliability is assessed by die shear testing.

The impact of non-isothermal adsorption of dissolved gas on drying of acoustically levitated slurry droplet

In this study, we developed a transient convective heat and mass transfer model of an acoustically levitated slurry droplet evaporating in an atmosphere of air, water vapor, and soluble gas. The advanced model considers the effects of acoustic streaming, forced convection, non-isothermal gas absorption, and adsorption of dissolved gas on the evaporation rate of a liquid droplet containing small active solid particles. Adsorption of dissolved in a droplet soluble gas by solid particles leads to decreased dissolved gas concentration in a liquid droplet. A reduction in dissolved gas concentration in a liquid droplet causes an increase in the mass flux of active soluble gas from a gaseous phase to a slurry droplet, which causes a rise in the heating effect of absorption and an increase in evaporation rate of a droplet. The heat effect of adsorption also intensifies the evaporation rate. It is shown that the time of porous shell formation is essentially shorter when solid particles in slurry droplets are active compared to inert particles.

Irrigation rates and turfgrass evapotranspiration in cities with contrasting water availability

AbstractAs water scarcity is worsened by drought and climate change, there is more interest in efficient management of urban irrigation, requiring understanding of the drivers of evapotranspiration (ET) and the role of irrigation inputs. We developed and validated a method to accurately measure ET of turfgrass lawns in contrasting climates using portable static chambers. We made in situ measurements of ET and irrigation inputs in lawns across three metropolitan areas in the United States with varying climatic conditions, water availability, and water conservation policies: Salt Lake Valley, Utah; San Fernando Valley, California; and Tallahassee, Florida. In full sun, mean daily ET estimates (ETsun) were 0.7 ± 0.4 mm day−1 in Tallahassee, 1.6 ± 0.8 mm day−1 in Los Angeles, and 3.3 ± 1.1 mm day−1 in Salt Lake Valley. In the shade, daily ET estimates (ETshade) were two to three times lower. In all three regions, ET was primarily driven by solar radiation (I0) and atmospheric vapor pressure deficit (D). Across the cities, irrigation rates were a key driver of ET, along with I0 and D. Daily irrigation ranged from 0 mm day−1 in Tallahassee (most were unirrigated) to 1.9 ± 1.2 mm day−1 in Los Angeles and 5.1 ± 2.9 mm day−1 in Salt Lake Valley. ET increased linearly with irrigation up to ~3 mm day−1, after which ET remained relatively constant despite irrigation increases. Our results highlight the importance of accounting for nonlinear responses and shading effects on ET in developing accurate irrigation recommendations.

Enhancement of removing OH bonds from low-temperature deposited silicon oxide films by adding water vapor into NH3 gas annealing at 130 oC

Abstract It was found that annealing with water-vapor-added NH3 gas (water-added NH3) is more effective than with dry NH3 at removing residual OH bonds in silicon oxide (SiOx) films deposited by atmospheric chemical vapor deposition with an organic silicon source. Fourier transform infrared spectra showed that reduction amount of OH bonds using the water-added NH3 was ~4 or ~1.3 times larger than using the conventional dry N2 or dry NH3 mixed with N2 gas without water, respectively. This result is something strange because water can be a potential candidate of OH sources. The effect of water vapor on OH-bond removal can be explained by considering following three factors. One is that low-temperature SiOx films are constrained somewhat, the second is that strained Si-O-Si bonds are in higher or more unstable energy state than strain-free ones, and the third is that highly strained bonds are easily hydroxylated to form Si-OH bonds.

Water vapor oxidation of SiC layer of tristructural isotropic particles

AbstractTristructural isotropic (TRISO) fuel particles, developed for use in high‐temperature gas‐cooled nuclear reactors, can be subjected to oxidizing environments in off‐normal accident scenarios. In this study, surrogate TRISO fuel particles were oxidized at 1000–1350°C for 4 h in 20 kPa water vapor atmosphere balanced with ultrahigh‐purity helium gas. The oxide scale morphology and thickness were studied via scanning electron microscopy, focused ion beam, and transmission electron microscopy. The oxide thickness increased as the oxidation temperature was increased. Although the oxide scale at 1000°C was completely amorphous, pockets of crystalline oxide were observed on particles oxidized at 1200 and 1300°C. Kinetic analysis was performed to deduce the oxidation mechanism by determining the apparent activation energy using linear regression analysis. The oxidation mechanism was consistent for temperatures from 1000 to 1200°C with an activation energy of 412.4 ± 8.8 kJ/mol. The activation energy then dropped to approximately 201 ± 7.1 kJ/mol for temperatures 1200–1350°C. Therefore, there is a change in oxidation mechanism at ∼1200°C. This change is attributed to the existence of a network of significant bubbles in the oxide layer at higher temperatures, which serve as rapid diffusion pathways for the transport of oxidants from the surface to the SiC/SiO2 interface, instead of relying on the bulk diffusion through the SiO2 layer at lower temperatures where only small bubbles are present along the SiC/SiO2 interface.

CONTROL SYSTEM OF CATENARY CONTINOUS VULCANIZATION LINE FOR RUBBER CABLES

The paper presents the control system of a continuous vulcanization line for the production of cables and conductors with rubber insulation, where the vulcanization process takes place in water and steam (vapour) atmosphere. The control, monitoring and recording of relevant parameters of the whole technological process was carried out with help of PLC (Programmable Logic Controller) and HMI (Human Machine Interface) and KepwareEx server. The control system is used to generate control signals for the regulation of speed, tension force, extruder temperature, water level and steam pressure in the vulcanization tube according to the technological parameters of the line. The monitoring system enables visualization of all technological units of the line via the HMI screens. The parts and entirety of the line are represented by conveniently drawn symbols that change colour depending on the current state and display the variables relevant to the operation of this object. Through the use of the KepwareEx server and database, the values of the variables important for the operation of the plant are recorded in real time. The developed supervisory and control system allows easy operation and monitoring of all important parameters of the plant.

Fog Harvesting Via Multistage Edge‐Effect Condensation

AbstractThe escalating global population and rapid industrialization have precipitated a severe freshwater scarcity crisis. To address this challenge, innovative strategies are essential to exploit unconventional water sources such as atmospheric vapor. This study proposes a novel approach integrating 3D printing technology with surface chemistry principles for atmospheric fog harvesting. The approach entails leveraging 3D printing technology, chosen for its cost‐effectiveness, unparalleled design flexibility to design intricate geometries, and time efficiency to fabricate cylindrical millimeter‐scale size vertical pillars. Harnessing the intricate interplay of surface phenomena, condensation preferentially occurs on the pillar tops due to surface phenomena. The pillars are imbued with nonadecane, a hydrocarbon renowned for its low surface energy characteristics ensures the uninterrupted progression of water droplet formation, coalescence, and seamless transportation, unveiling a symphony of molecular interactions at the microscale. The design demonstrates promising results, yielding an impressive yield of ≈3.956 g of water per hour from 1 cm2 area. Geometric discontinuities associated with parahydrophobic pillars amplify water harvesting via an edge effect. This study represents a significant step toward a more sustainable and technologically advanced solution for the global water crisis.

Economic Effects Assessment of Forest City Construction: Empirical Evidence from the County-Level Areas in China

Forests are both an irreplaceable natural resource and a vital economic asset for all humankind. Based on the data of counties in mainland China from 2007 to 2020, the article explores the direct impact and spatial spillover effects of the policy implementation on the economic growth of counties with the help of the forest city pilot policy and the policy evaluation model. The results reveal that policy implementation can have a positive economic growth effect on the pilot counties, which, in turn, can significantly increase the size of the county′s GDP, the level of GDP per capita, and the total amount of nighttime lighting brightness. The implementation of forest city construction can bring about 2.74% of total GDP size, about 2.63% of per capita GDP development level, and about 7.25% of nighttime light brightness to the county on average. Cost–benefit analysis also indicates that forest city construction can bring about a comprehensive economic benefit of approximately CNY 686.453 million (approximately USD 96.82 million) to the counties. The rapid improvement in labor productivity, significant influx of high-end factors, and continuous expansion of market potential are important mechanisms through which policy implementation promotes economic growth in pilot counties. While promoting economic growth in the pilot counties, forest city construction can also have positive spatial spillover effects on neighboring areas in the pilot counties. Furthermore, when the deficits in atmospheric vapor pressure and annual evapotranspiration are used as instrumental variables for forest city construction, the empirical estimates are not significantly altered. In the process of building forest cities, county governments should be wary of issues such as the high cost of forest maintenance. This study provides a Chinese model and policy reference for other countries and regions in the world to deal with the relationship between forest city construction and county economic growth.

Oxygen Isotope Exchange between Dust Aggregates and Ambient Nebular Gas

Meteorites and their components exhibit a diverse range of oxygen isotope compositions, and the isotopic exchange timescale between dust grains and ambient gas is a key parameter for understanding the spatiotemporal evolution of the solar nebula. As dust grains existed as macroscopic aggregates in the solar nebula, it is necessary to consider the isotopic exchange timescales for these aggregates. Here, we theoretically estimate the isotope exchange timescales between dust aggregates and ambient vapor. The isotope exchange process between aggregates and ambient vapor is divided into four processes: (i) supply of gas molecules to the aggregate surface, (ii) diffusion of molecules within the aggregate, (iii) isotope exchange on the surface of constituent particles, and (iv) isotope diffusion within the particles. We evaluate these timescales and assess which one becomes the rate-determining step. We reveal that the isotope exchange timescale is approximately the same as that of the constituent particles when the aggregate radius is smaller than the critical value, which is a few centimeters when considering the exchange reaction between amorphous forsterite aggregates and water vapor.

JWST reveals the rapid and strong day-side variability of 55 Cancri e

Context. The nature of the close-in rocky planet 55 Cnce is puzzling, despite it having been observed extensively. Its optical and infrared occultation depths show temporal variability, in addition to a phase curve variability observed in the optical. Aims. We wish to explore the possibility that the variability originates from the planet being in a 3:2 spin–orbit resonance, and thus showing different sides during occultations. We proposed and were awarded Cycle 1 time at the James Webb Space Telescope (JWST) to test this hypothesis. Methods. JWST/NIRCam (Near Infrared Camera) observed five occultations (secondary eclipses) of the planet – of which four were observed within a week – simultaneously at 2.1 and 4.5 µm. While the former gives band-integrated photometry, the latter provides a spectrum between 3.9–5.0 µm. Results. We find that the occultation depths in both bandpasses are highly variable and change between a non-detection (−5 ± 6 ppm and 7 ± 9 ppm) to 96 ± 8 ppm and 119−19+34 ppm at 2.1 µm and 4.5 µm, respectively. Interestingly, the variations in both bandpasses are not correlated and do not support the 3:2 spin-orbit resonance explanation. The measured brightness temperature at 4.5 µm varies between 873–2256 K and is lower than the expected day-side temperature of bare rock with no heat redistribution (2500 K), which is indicative of an atmosphere. Our atmospheric retrieval analysis of occultation depth spectra at 4.5 µm finds that different visits statistically favour various atmospheric scenarios including a thin outgassed CO/CO2 atmosphere and a silicate rock vapour atmosphere. Some visits even support a flat line model. Conclusions. The observed variability could be explained by stochastic outgassing of CO/CO2, which is also hinted at by retrievals. Alternatively, the variability observed at both 2.1 and 4.5 µm could be the result of a circumstellar patchy dust torus generated by volcanism on the planet.

Characteristics of liquid sugar from old oil palm trunk sap as affected by processing methods

The sap of old oil palm trunks contains appreciable sugar, but it has not been considered a potential sugar source. This study aimed to find the best method for producing oil palm liquid sugar that complies with the Indonesian National Standard (SNI) The non-factorial experiment was arranged in a Completely Randomized Block Design (CRBD) with 6 replications. The treatments were a combination of lime-rotary vacuum evaporation (P1), without lime-vacuum rotary evaporation (P2), lime-atmospheric evaporation (P3); without lime-atmospheric evaporation (P4). The parameters observed were pH, °brix, reducing sugar, color, aroma, and overall acceptance. The data were subjected to ANOVA to determine the effects of the treatments and then, continued testing using HSD at α 0,05 for means separation. The best treatment was found on liquid sugar processed using lime, and atmospheric evaporation with brix of 68.75%, pH of 5.4, moisture content of 17.74, ash content of 0.86%, reducing sugar of 44.31%, sensory score of color, aroma, and overall acceptance were f 3.42 (brownies yellow), 4.4 (like), and 4.04 (like).Keywords: lime, liquid sugar, old oil palm trunk, sensory, vacuum rotary evaporator

Climate change impacts on the hydrological behaviour of watershed in northeastern Tunisia (Oued El Abid watershed)

Climate change significantly impacts watershed hydrology, altering water supplies, natural disasters, and eco-hydrologic processes. These effects vary geographically, with some regions facing severe droughts while others experience increased precipitation and flooding. Climate change influences atmospheric evaporation demand, precipitation patterns, vegetation composition, streamflow characteristics, and groundwater dynamics. The temperature increases and rainfall changes in some watersheds can lead to increased potential evapotranspiration and decreased streamflow and soil water. Flood frequency analyses indicate an overall increasing trend in the latter half of the 21st century. The Oued El Abid catchment area, as like all catchments in northern Tunisia, is likely to be subject to major climatic and hydrological variations as a result of climate change. Advanced hydrological modelling using the HBV-Light model was set up to simulate current conditions and future scenarios based on Afric-Cordex climate models. The model demonstrates robust performance, achieving Nash-Sutcliffe Efficiency (NSE) values of 0.71 in calibration (1972-1992), and 0.66 in validation from 1993-2001. This climate change has a direct effect on the hydrological projections, which reveal significant changes, with annual flow reductions ranging from 35% to 43%, with more severe impacts under the RCP8.5 scenario for 2069-2099. Spring and summer seasons are particularly vulnerable, showing flow decreases of up to 68% and over 40%, respectively, extreme monthly variability is projected, reaching 88% reduction in July under RCP8.5. This research provides important results for water resource managers, highlighting the necessity of long-term planning and sustainable water management practices in the face of climate change.

What caused the lag between oxygen-18 and deuterium excess in atmospheric vapor and precipitation during the earlier summer season in southwest China?

A combined interpretation of oxygen-18 (δ18O) and deuterium excess (d-excess) in various archives in the Indian monsoon-dominated region may add value to the isotopic climate significance. Yet, coupling water δ18O and d-excess together is rarely discussed. Here, we present measurements for both δ18O and δ2H in water vapor and precipitation samples collected in the Nujiang River valley, an important moisture corridor for the Indian monsoon in southwestern China, aiming for an improved understanding of the hydrological cycle on seasonal scales. The observation found a significant drop occurred in the earlier summer season for δ18O and d-excess in vapor and precipitation. However, an approximately one-month lag between vapor δ18O and vapor d-excess is observed in seasonal variations, revealing different drivers for the seasonal patterns of vapor d-excess and δ18O. Spatial correlation analysis found that d-excess is mainly modulated by the relative humidity over the core moisture source over the Bay of Bengal (BOB), while the sharp decrease of vapor δ18O corresponds to the onset of the Indian summer monsoon associated with large-scale convective activities, which significantly depleted the vapor heavy isotopes. The finding of the phase difference in the seasonal isotope signals and the underlying mechanism will benefit the study in particularly using both δ18O and d-excess for an improved understanding of the hydrological processes in the Indian monsoon-dominated region, and will provide new insight into studies of paleoclimate rebuilding by using isotope-based proxy as well.

Magnetization processes features in the tapes of cobalt-based amorphous alloy

Studies of the amorphous cobalt-based soft magnetic alloy AMAG-172 (Co–Ni–Fe–Cr–Mn–Si–B) from different manufacturers have shown that in the as-quenched state there is nonuniformity of the magnetic characteristics, and therefore the level of internal stresses across the width of the tape produced by MSTATOR (Borovichi) significantly lower. However, similar to the tape produced by NIIMET (Kaluga), there is nonuniformity of the tape in thickness, which contributes to the formation of a bimodal field dependence of magnetic permeability.This may be a consequence of the non-uniform concentration along the width of the tape of hydrogen and oxygen atoms embedded in its surface during interaction with atmospheric vapor and the presence of temperature gradients during the manufacturing process. A stepwise shape of the initial sections of the magnetization curves in the region of the first maximum of magnetic permeability was discovered. The abrupt nature of the magnetization processes in the region of weak fields allows us to conclude that in the samples of tape produced by MSTATOR, the formation of the first maximum of the field dependence is associated with an independent magnetization reversal of the surface layer, while the main layer of the tape participates in the formation of the second maximum. The smoothed shape of the stepped initial section of the magnetization curve of samples produced by NIIMET corresponds to the gradual involvement of the main layer of the tape in the processes of magnetization and remagnetization. A comparison of the hysteresis loops of both parts of the tape, measured in the same magnetic field region, shows that the field shift of the hysteresis loops is associated with the interlayer interaction of the surface and volume of the tape, and the formation of asymmetric hysteresis loops occurs with the participation of the second layer with its gradual involvement in the processes of magnetization and magnetization reversal.

Understanding tropical cyclone persistence over land: A case study of Cyclone Gulab

Abstract Tropical Cyclone (TC) Gulab originated in the Bay of Bengal during the post-monsoon season of 2021. Following an unusual westward trajectory, TC Gulab made landfall on the east coast of India, traversed central India, and reintensified over the Arabian Sea into TC Shaheen. This study employed an online Eulerian water vapor tracer (WVT) tool embedded within the Weather Research and Forecasting (WRF) model to investigate the role of land in terms of soil moisture and Land Use Land Cover (LULC) in persistance of TC Gulab over central India. We quantified the contributions of sub-regions and dominant LULC types within the Indian subcontinent to the precipitation associated with TC Gulab. Our findings indicate that evapotranspiration across the entire Indian subcontinent contributed approximately 30% to the post-landfall precipitation associated with TC Gulab. The highest contribution originated from the northwestern region, followed by the northeast. Croplands, the dominant LULC type, were the primary contributors, followed by forests. Despite changing the dominant land cover from cropland to forest, the low-pressure system persisted over land while altering the spatial patterns of precipitation. Sensitivity experiments demonstrated a linear decrease in precipitation originating from land with decreasing soil moisture (SM). Notably, there is a disproportionate decline in total precipitation with decreasing SM. Further analysis separating atmospheric vapor sources into land and ocean contributions using WVT revealed a compensatory mechanism. The contribution of oceanic vapor to atmospheric vapor over land increased when SM decreased due to increase in the latent heat over ocean. However, the total atmospheric vapor remained low, ultimately leading to a lower total precipitation. Although SM plays a role, our results highlight the importance of oceanic and atmospheric processes in determining TC persistence over land. This study offers valuable insights into the dynamics of land-atmosphere interactions during low-pressure systems of TCs.

Controllable growth of large 1T-NbTe2 nanosheets on mica by chemical vapor deposition and its magnetic properties

Two-dimensional (2D) magnetic materials have recently attracted broad attention for their potential technological applications. Here, we report controllable growth of NbTe2 nanosheets on mica substrate by atmospheric chemical vapor deposition. Different from the SiO2/Si substrates, dangling bonds on the surface of the mica are absent, which induces low nucleation density and higher lateral growth rate. As a result, the lateral size of NbTe2 nanosheets on mica substrates can be significantly larger than those on SiO2/Si substrates. Large single crystal NbTe2 nanosheets with a lateral size of up to 151 µm were fabricated on a mica. High-resolution transmission electron microscope image, XRD patterns and Raman spectra reveal the NbTe2 nanosheets adopt the single crystal with 1T phase. Furthermore, the NbTe2 nanosheets on mica demonstrate ferromagnetic properties with a Curie temperature of up to 162 K. Our work paves the way for the atmospheric chemical vapor deposition growth and applications of many more 2D magnets.

Species-Specific Root Distribution and Leaf Iso/Anisohydric Tendencies Shape Transpiration Patterns Across Heterogeneous Karst Habitats.

The driving forces of transpiration are not only atmospheric evaporation but also root zone water supply and stomatal regulation among species. However, the biophysiological drivers of transpiration remain incompletely understood in heterogeneous karst habitats. This study investigated the commonly coexisting tree species Mallotus philippensis and Celtis biondii in two typical karst habitats: rock-dominated (RD) habitat and control soil-dominated (SD) habitat. Over 2 years, soil moisture, transpiration, root distribution, and leaf water potential were measured. The results showed that soil moisture in the RD habitat was significantly lower than in the SD habitat. Transpiration patterns also differed between habitats, with species-specific distinctions driven by biophysiological traits. M. philippensis showed small hydroscape areas and its root system mainly distributed in the soil zone in both habitats. The isohydric behaviour and lower root density in the RD habitat drove M. philippensis to reduce transpiration in response to soil water deficiency. Conversely, C. biondii had large hydroscape areas and roots capable of penetrating bedrock. It transpired higher relying on ample accessible water through anisohydric behaviour and having a more robust root system both in soil and bedrock zones in the RD habitat. Our study highlights the critical role of root water accessibility and leaf iso/anisohydric tendencies in driving transpiration.

Improved surface morphology and reduced V-pits density of lattice-matched AlInN films grown by atmospheric pressure metalorganic chemical vapor deposition

AlInN has emerged as a promising material for advanced optoelectronic and electronic devices due to its unique properties. However, achieving AlInN layers with excellent surface morphology remains challenging. Here, Al0.83In0.17N layers lattice-matched to GaN/sapphire were grown by atmospheric-pressure metalorganic chemical vapor deposition at 875 °C. The lowest surface roughness measured by atomic force microscopy was 0.37 nm after optimizing the growth temperature and flux of precursors. The roughness value was constant in the range of 15–72 nm film thickness. Introducing a TMI pre-flow period before AlInN growth, further reduced roughness to 0.28 nm, although a graded inclusion of Ga into the AlInN near the GaN/AlInN interface was observed. This improved surface morphology was interpreted by the In-surfactant effect enriched by the pre-flow in the early stage of AlInN. Additionally, the V-pits density was as low as 2×105 cm−2, primarily due to high growth pressure and also influenced by relatively high growth temperature. Analysis of Al incorporation using second-order reaction model suggests that the severe parasitic reactions between TMA and NH3 at atmospheric pressure can be effectively eliminated by a high total gas flow rate of 72 slm, ensuring in-plane uniformity in surface morphology and relatively good crystalline quality.

Local neighborhood affects stem rehydration under drought: evidence from mixtures of European beech with two different conifers.

Mixed-species forests are, for multiple reasons, promising options for forest management in Central Europe. However, the extent to which interspecific competition affects tree hydrological processes is not clear. High-resolution dendrometers capture sub-daily variations in stem diameter; they can simultaneously monitor stem growth (irreversible changes in diameter) and water status (reversible changes) of individual trees. Using the information on water status, we aimed to assess potential effects of tree species mixture, expressed as local neighborhood identity, on night-time rehydration and water stress. We deployed 112 sensors in pure and mixed forest stands of European beech, Norway spruce, and Douglas fir on four sites in north-western Germany, measuring stem diameter in 10-minute intervals for a period of four years (2019-2022). In a mixture distribution model, we used environmental variables, namely soil matric potential, atmospheric vapor pressure deficit, temperature, precipitation, and neighborhood identity to explain night-time rehydration, measured as the daily minimum tree water deficit (TWDmin). TWDmin was used as a daily indicator of water stress and the daily occurrence of sufficient water supply, allowing for stem growth (potential growth). We found that species and neighborhood identity affected night-time rehydration, but the impacts varied depending on soil water availability. While there was no effect at high water availability, increasing drought revealed species-specific patterns. Beech improved night-time rehydration in mixture with Douglas fir, but not in mixture with spruce. Douglas fir however, only improved rehydration at a smaller share of beech in the neighborhood, while beech dominance tended to reverse this effect. Spruce was adversely affected when mixed with beech. At species level and under dry conditions, we found that night-time rehydration was reduced in all species, but beech had a greater capacity to rehydrate under high to moderate soil water availability than the conifers, even under high atmospheric water demand. Our study gives new insights into neighborhood effects on tree water status and highlights the importance of species-specific characteristics for tree-water relations in mixed-species forests. It shows that drought stress of European beech can be reduced by admixing Douglas fir, which may point towards a strategy to adapt beech stands to climate change.

Divergent Responses of Fir and Pine Trees to Increasing CO2 Levels in the Face of Climate Change

AbstractUnderstanding the response of forests to the increases in atmospheric CO2 (ca) is fundamental to implementing innovative management strategies and for assessing impacts on the global carbon and water cycles. Here, we explored correlations between ecophysiological traits and climate variability that influence changes in stable isotope carbon and oxygen (δ13C and δ18O) of tree‐rings. We present these relationships between species of the contrasting genera Abies and Pinus, along a latitudinal transect encompassing different biogeographical regions in North America. We also tested if the rate of intrinsic water‐use efficiency per unit of ca (dW/dca) during two periods (1890–1965 vs. 1966–2016), for fir and pine were different and indicated acclimation to ca increases. We hypothesize that, spatially and temporally, the divergent responses among species to carbon and oxygen isotopes and dW/dca are influenced by the site conditions and the historical increases in ca. From our results, we show that fir and pine species will behave physiologically different as global warming progresses. Firs are more responsive to atmosphere vapor pressure deficit along different geographical zones. The survival of forests species under climate change will rely on the response to water stress and species' traits that influence the regulation of dW. Finally, we want to highlight the concept of “progressive resource limitation” of soil water and nutrients, previously proposed by other authors, that likely indicate fir species that inhabit moister sites will benefit more from increased ca than pine, but this positive effect is likely transitory as global warming increases.