Climate extremes like drought are threatening forests worldwide. Record breaking forest mortality has been observed in central Europe in the past five years. Meanwhile, more and more experiments are being set up that enable measurements of the hydraulic states of dying trees under extreme drought stress. These experimental data can be exploited by mechanistic vegetation models, offering the possibility to disentangle environmental drought stressors, e.g. atmospheric and soil moisture dryness, and their effects on a plant’s hydraulic system, such as stomatal closure and loss of hydraulic conductivity. Here, we show how a next generation plant hydraulic modelling is able to accurately reproduce the water potential dynamics of dying trees. We apply this plant hydraulic model to European drought experimental sites, including the canopy crane experiment II in Basel, Switzerland, and the KROOF experiment in Freising, Germany. We find that soil heterogeneity, rooting depth and stem hydraulic capacity are critical in determining whether a tree survives or succumbs to drought. Furthermore, good knowledge of four parameters is crucial to accurately capture the magnitude and temporal development of observed leaf and stem water potential: (1) stem hydraulic capacitance, (2) P50 (the water potential at which 50% of a plant’s hydraulic conductivity is lost), (3) saturated xylem hydraulic conductivity, and (4) the reference leaf water potential associated with full stomatal closure. Finally, when implemented into the terrestrial biosphere model QUINCY, our hydraulic scheme produces a clear mortality signal associated with recent drought events, giving confidence in our capacity to project the impact of future droughts on European forests

The balance between terrestrial carbon assimilation and water loss is optimized by stomatal control in leaves. The response of stomatal conductance to increasing vapor pressure deficit (VPD) is critical in the context of climatic change and highly variable between tree species and environments. Why this variability in VPD sensitivity exists is still largely unknown. Yet, as the regulatory cues initiating closure remain unclear, current simulations of forest water use face significant uncertainty. To address this knowledge gap for most of the common European tree species, we present data measured regularly in the crowns of mature trees growing in a natural forest at the Swiss Canopy Crane II (SCCII) site (Basel, Switzerland). We used three years of repeated stomatal conductance measurements across the growing season performed at the leaf level (over 1000 measurements), in combination with concurrent diel leaf water potential measurements and VPD monitoring of over 80 individuals. We show that pre-dawn, rather than the expected midday, tree water status is more critical in adjusting the stomatal closure responses to increasing VPD. A striking reduction can be found in this VPD sensitivity when pre-dawn leaf water potential approaches -1.2 MPa, independent of the species. Only above this threshold, i.e., when trees were well-hydrated, did the species show variance in midday stomatal sensitivity to VPD. This aligns with the commonly adopted hydraulic safety-efficiency theorem for explaining species-specific variance. We argue that daytime canopy conductance does not solely optimize assimilation against the risk of cavitation, which commonly happens during high midday VPD. Rather, our novel finding suggests that mature trees might adjust their water-use strategy to sustain high nighttime turgor pressure (as required for sugar transport and growth), although the regulating mechanisms are yet unknown. The discovery of this uniform pre-dawn threshold across species is particularly critical for reducing uncertainty when modeling forest water use responses to VPD.

Water loss and carbon gain are balanced by stomatal control1, a trade-off that has allowed trees to survive and thrive under fluctuating environmental conditions2-4. During periods of lower water availability, stomatal closure prevents excess water loss5. Various strategies of stomatal control have been found among tree species6,7, but the trigger for this behaviour remains elusive. We found a uniform pre-dawn water potential threshold (-1.2 MPa) for stomatal closure across species, which coincided with stem-growth cessation. Meanwhile, midday water potentials at stomatal closure were more variable across species and stomatal control did not follow species-specific thresholds of hydraulic failure, a commonly adopted theory in plant biology8-10, and often used in predictive water-use modelling11,12. This indicates that nocturnal rehydration, rather than daytime hydraulic safety is an optimization priority for stomatal closure in trees13. We suggest that these processes are critical for forecasting the global carbon cycle dynamics.

Summary The link between above‐ and belowground communities is a key uncertainty in drought and rewetting effects on forest carbon (C) cycle. In young beech model ecosystems and mature naturally dry pine forest exposed to 15‐yr‐long irrigation, we performed 13 C pulse labeling experiments, one during drought and one 2 wk after rewetting, tracing tree assimilates into rhizosphere communities. The 13 C pulses applied in tree crowns reached soil microbial communities of the young and mature forests one and 4 d later, respectively. Drought decreased the transfer of labeled assimilates relative to the irrigation treatment. The 13 C label in phospholipid fatty acids (PLFAs) indicated greater drought reduction of assimilate incorporation by fungi (−85%) than by gram‐positive (−43%) and gram‐negative bacteria (−58%). 13 C label incorporation was more strongly reduced for PLFAs (cell membrane) than for microbial cytoplasm extracted by chloroform. This suggests that fresh rhizodeposits are predominantly used for osmoregulation or storage under drought, at the expense of new cell formation. Two weeks after rewetting, 13 C enrichment in PLFAs was greater in previously dry than in continuously moist soils. Drought and rewetting effects were greater in beech systems than in pine forest. Belowground C allocation and rhizosphere communities are highly resilient to drought.

Canopy phenology is a widely used proxy for deciduous forest growth with various applications in terrestrial ecosystem modeling. Its use relies on common assumptions that canopy greening and stem growth are tightly coordinated processes, enabling predictions on the timing and the quantity of annual tree growth. Here, we present parallel observations of canopy and stem growth phenology and annual stem increment in around 90 deciduous forest trees with diffuse-porous (Fagus sylvatica, Acer pseudoplatanus, Carpinus betulus) or ring-porous (Quercus robur x petraea) wood anatomy. These data were collected in a mixed temperate forest at the Swiss-Canopy-Crane II site, in 4 years with strongly contrasting weather conditions. We found that stem growth resumption lagged several weeks behind spring canopy greening in diffuse-porous but not in ring-porous trees. Canopy greening and stem growth resumption showed no or only weak signs of temporal coordination across the observation years. Within the assessed species, the seasonal timing of stem growth varied strongly among individuals, as trees with high annual increments resumed growth earlier and also completed their main growth earlier. The length of main growth activity had no influence on annual increments. Our findings not only challenge tight temporal coordination of canopy and stem growth phenology but also demonstrate that longer main growth activity does not translate into higher annual increments. This may compromise approaches modeling tree growth and forest productivity with canopy phenology and growth length.

Understanding the within-tree variability of non-structural carbohydrates (NSC) is crucial for interpreting point measurements and calculating whole-tree carbon balances. Yet, little is known about how the vertical light gradient within tree crowns influences branch NSC concentrations and dynamics. We measured NSC concentrations, irradiance and key leaf traits in uppermost, sun-exposed and lowest, shaded branches in the crowns of mature, temperate trees from nine species with high temporal resolution throughout one growing season. Measurements from two additional years allowed us to test the generality of our findings amongst climatically contrasting years. Despite the vertical light gradient, we found very similar seasonal NSC dynamics and concentrations between sun and shade branches in most species. This can at least partially be explained by acclimations in specific leaf area and photosynthetic leaf traits compensating the different light availability between the top and bottom canopy. Only in the ring-porous species Quercus petraea x robur and Fraxinus  excelsior was starch refilling after budbreak slower in lower branches. End-of-season NSC concentrations were similar between canopy positions and amongst observation years. Only Fagus sylvatica had 40 and 29% lower starch concentrations by the end of the extremely dry year 2020, relative to the other 2 years. We show that NSC measured anywhere in a tree crown is often representative of the whole crown. Overall, our results suggest that carbon reserve dynamics in trees are largely insensitive to both microclimatic gradients and inter-annual climatic variation, and only deviate under severe carbon deficits, as was presumably the case with Fagus in our study.

On December 5, 2022, an indirect drive fusion implosion on the National Ignition Facility (NIF) achieved a target gain G_{target} of 1.5. This is the first laboratory demonstration of exceeding "scientific breakeven" (or G_{target}>1) where 2.05 MJ of 351 nm laser light produced 3.1 MJ of total fusion yield, a result which significantly exceeds the Lawson criterion for fusion ignition as reported in a previous NIF implosion [H. Abu-Shawareb et al. (Indirect Drive ICF Collaboration), Phys. Rev. Lett. 129, 075001 (2022)PRLTAO0031-900710.1103/PhysRevLett.129.075001]. This achievement is the culmination of more than five decades of research and gives proof that laboratory fusion, based on fundamental physics principles, is possible. This Letter reports on the target, laser, design, and experimental advancements that led to this result.

Older adults (OA) increasingly use smartphones, which provide visual, auditory, and haptic signals. However, it remains unclear if multimodality's positive effects on performance during controlled experiments and driving scenarios apply to OA smartphone interaction. Multilevel models showed that reaction times (RT) of 18 younger adults (YA) and 15 OA to unimodal stimuli (M = 1,178 ms) are significantly higher [F(2, 5,308.7) = 69.17, p <.001] than to bimodal (M = 1,110 ms; do = 0.26) or trimodal stimuli (M = 1,071; do = 0.42). The difference between unimodal (M = 1,307) and bimodal stimuli (M = 1,216; do = 0.35) and between unimodal and trimodal stimuli (M = 1,188; do = 0.46), was greater for OY than YA [F(2, 5,308.7) = 3.77; p =.023]. Results thus confirm findings from aging and multimodal information processing literature and suggest using more than one feedback modality to improve OAs smartphone interaction.

The files contain the NSC data (NSC.xlsx), the measurements used for fitting the light response curves (LRC.xlsx) and the specific leaf area values (SLA.xlsx) as reported in:Zahnd C, Zehnder M, Arend M, Kahmen A, Hoch G 2024. Uniform carbon reserve dynamics along the vertical light gradient in mature tree crowns. Tree Physiology, tpae005. https://doi.org/10.1093/treephys/tpae005Please refer to the metadata sheets within each file, and to the original publication (https://doi.org/10.1093/treephys/tpae005) for details on the data collection.

Tree crowns experience strong vertical microclimatic gradients, particularly in light availability. Surprisingly, little is known about whether these gradients cause within-crown variation in leaf phenology and whether such variations represent different light-use strategies of sun-and shade leaves.In a temperate mixed forest at the Swiss Canopy Crane II site in Switzerland, we measured over three years the annual leaf phenology in the upper and lower crowns of mature trees from six broadleaved and three conifer species. We further recorded the microclimate (temperature, humidity, light) continuously in various positions within the canopy.We found microclimatic canopy gradients to be strongest during summer, but negligible in winter and spring, indicating that any phenological gradients in autumn, but not in spring, might be driven by microclimatic dif-ferences. Budbreak timing did not differ within the crowns of any of the broadleaved trees. However, in the three species with deeper crowns, leaf unfolding was up to 10 days faster in the lower crown but showed no difference in the more shallow-crowned species. Surprisingly, only the evergreen conifers Abies alba and Picea abies showed earlier bud break in the lower crowns. In autumn, senescence in all broadleaved species progressed from the upper crown downwards, resulting in up to two weeks longer vegetation seasons in the lower crown.With this first broad assessment of within-tree phenology, we show how microclimatic gradients and different light-use strategies lead to a considerable variability of within-crown phenological gradients. We interpret the faster leaf unfolding in the lower crown of three broadleaved species as a shade avoidance strategy, allowing shade branches to improve their C balance early in the season. In contrast, longer retention of lower leaves in autumn is unlikely to significantly improve the C balance, and more likely caused by higher summer temperature and irradiance in the upper leaves.

While fitness tracker users consent to the processing of their sensitive data based on privacy policies, previous research has demonstrated that legal texts often remain unread or incomprehensible. This questions whether the given consent is indeed informed. While past research concentrated on improving privacy comprehension, our research aims to better understand user requirements for interactive and transparent privacy information and control systems. We mainly focus on users’ assessment of contextual and functional aspects. Findings from an online survey with fitness tracker users and non-users (N = 204) reveal that such systems need to support users and potential users throughout the usage life cycle, illustrating a dynamic change in requirements and their prioritization of information transparency and privacy control. Design recommendations derived from our results support the development of interactive and comprehensible privacy systems that enable more knowledgeable decisions on sharing and processing fitness tracker data.

&lt;p&gt;Temperate trees are facing an increasing challenge from limited water supply and increased atmospheric demand due to an extreme trend in drought events. Particularly, structural-morphological traits such as root-water uptake depth (RWUD) are key for determining the performance of a species during drought. In addition to RWUD, ultimately understanding the temporal origin of the soil water used by trees could provide important insights into a species drought vulnerability.&lt;/p&gt; &lt;p&gt;The goal of this study is to determine the ability of species to adjust RWUD during drought. For this purpose, we analyzed &amp;#8706;&lt;sup&gt;2&lt;/sup&gt;H and &amp;#8706;&lt;sup&gt;18&lt;/sup&gt;O isotope data from xylem water samples collected from mature trees of nine co-occurring temperate tree species growing at the Swiss Canopy Crane II site in Switzerland, over three growing seasons (2020 &amp;#173;&amp;#8211; 2022). Additionally, we analyzed bi-weekly water samples from precipitation, throughfall, and soil water at different depths. Both 2020 and 2022 were relatively dry (compared to the reference of 1991-2021), while 2021 had a wet summer, allowing us to identify RWUD dynamics within a wide range of soil water supply. We applied the LWFBrook90.jl hydrological model to assess RWUD dynamics as response to variability in soil moisture and soil water potential in high temporal resolution.&lt;/p&gt; &lt;p&gt;Initial results revealed distinct species-specific differences in the summer &amp;#8706;&lt;sup&gt;2&lt;/sup&gt;H and &amp;#8706;&lt;sup&gt;18&lt;/sup&gt;O isotopic signals. Xylem-water &amp;#8706;&lt;sup&gt;2&lt;/sup&gt;H and &amp;#8706;&lt;sup&gt;18&lt;/sup&gt;O values of &lt;em&gt;Quercus sp&lt;/em&gt;., &lt;em&gt;Fraxinus excelsior&lt;/em&gt; and &lt;em&gt;Sorbus torminalis&lt;/em&gt; were the lowest and coincided with soil water values in deeper soil. These patterns were contrasted by &lt;em&gt;Carpinus betulus&lt;/em&gt;, &lt;em&gt;Picea abies&lt;/em&gt; and &lt;em&gt;Abies alba&lt;/em&gt; showing highest &amp;#8706;&lt;sup&gt;2&lt;/sup&gt;H and &amp;#8706;&lt;sup&gt;18&lt;/sup&gt;O values and a suggested predominant RWU in the top soil. &lt;em&gt;Fagus sylvatica&lt;/em&gt; and &lt;em&gt;Pinus sylvestris &lt;/em&gt;showed variability within their values suggesting RWUD adjustment.&lt;/p&gt; &lt;p&gt;The initial findings already indicate different rooting strategies as well as a certain level of resource partitioning within the rhizosphere. We expect the final results of this study to have significant implications for understanding the mechanisms behind drought vulnerability of temperate trees and for improving the prediction of tree species&#039; responses to an altered hydrological regime.&lt;/p&gt;

Summary European beech (Fagus sylvatica) was among the most affected tree species during the severe 2018 European drought. It not only suffered from instant physiological stress but also showed severe symptoms of defoliation and canopy decline in the following year. To explore the underlying mechanisms, we used the Swiss‐Canopy‐Crane II site and studied in branches of healthy and symptomatic trees the repair of hydraulic function and concentration of carbohydrates during the 2018 drought and in 2019. We found loss of hydraulic conductance in 2018, which did not recover in 2019 in trees that developed defoliation symptoms in the year after drought. Reduced branch foliation in symptomatic trees was associated with a gradual decline in wood starch concentration throughout summer 2019. Visualization of water transport in healthy and symptomatic branches in the year after the drought confirmed the close relationship between xylem functionality and supported branch leaf area. Our findings showed that embolized xylem does not regain function in the season following a drought and that sustained branch hydraulic dysfunction is counterbalanced by the reduction in supported leaf area. It suggests acclimation of leaf development after drought to mitigate disturbances in canopy hydraulic function.

with previously published lower strain data (101–107 s-1), we observe a change in rate dependence, suggesting a transition from thermally activated to defect-limited (phonon drag) dislocation motion occurring at a strain rate of about 105 s-1.

Drought-associated woody-plant mortality has been increasing in most regions with multi-decadal records and is projected to increase in the future, impacting terrestrial climate forcing, biodiversity and resource availability. The mechanisms underlying such mortality, however, are debated, owing to complex interactions between the drivers and the processes. In this Review, we synthesize knowledge of drought-related tree mortality under a warming and drying atmosphere with rising atmospheric CO2. Drought-associated mortality results from water and carbon depletion and declines in their fluxes relative to demand by living tissues. These pools and fluxes are interdependent and underlay plant defences against biotic agents. Death via failure to maintain a positive water balance is particularly dependent on soil-to-root conductance, capacitance, vulnerability to hydraulic failure, cuticular water losses and dehydration tolerance, all of which could be exacerbated by reduced carbon supply rates to support cellular survival or the carbon starvation process. The depletion of plant water and carbon pools is accelerated under rising vapour pressure deficit, but increasing CO2 can mitigate these impacts. Advancing knowledge and reducing predictive uncertainties requires the integration of carbon, water and defensive processes, and the use of a range of experimental and modelling approaches. Enhanced drought frequency and magnitude have impacted tree mortality, leading to multiple examples of regional-scale dieback. This Review outlines the mechanisms leading to mortality, including carbon starvation and hydraulic failure.

We took advantage of the European 2018 drought and assessed the mechanisms causing differences in drought vulnerability among mature individuals of nine co-occurring tree species at the Swiss Canopy Crane II site in Switzerland. Throughout the drought we monitored leaf water status and determined native embolism formation in the canopy of the trees as indicators of drought vulnerability. We also determined hydraulic vulnerability thresholds (Ψ12 -, Ψ50 - and Ψ88 -values), corresponding hydraulic safety margins (HSMs) and carbohydrate reserves for all species as well as total average leaf area per tree, and used stable isotopes to assess differences in root water uptake depth among the nine species as variables predicting differences in drought vulnerability among species. Marked differences in drought vulnerability were observed among the nine tree species. Six species maintained their water potentials above hydraulic thresholds, while three species, Fagus sylvatica, Carpinus betulus and Picea abies, were pushed beyond their hydraulic thresholds and showed loss of hydraulic conductivity in their canopies at the end of the drought. Embolism resistance thresholds and associated HSMs did not explain why the co-existing species differed in their drought vulnerability, neither did their degree of isohydry, nor their regulation of carbohydrate reserves. Instead, differences in structural-morphological traits, in particular root water uptake depth, were associated with the risk of reaching hydraulic vulnerability thresholds and embolism formation among the nine species. Our study shows that structural-morphological traits, such as root water uptake depth, determine how quickly different species approach hydraulic vulnerability thresholds during a drought event and can thus explain species differences in drought vulnerability among mature field-grown trees.

For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. As recently reported, a burning plasma state, where the alpha-heating in the plasma is the primary source of heating, was achieved in laboratory experiments. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin ``burn propagation'' into surrounding cold fuel, enabling the possibility of high energy gain. While ``scientific breakeven'' (i.e. unity target gain) has not yet been achieved, this talk reports the first controlled fusion experiment on the National Ignition Facility to produce capsule gain greater than unity (here 5.8) and reach ignition by many different formulations of the Lawson criterion. In the talk, we will discuss some key basic physics inertial confinement fusion (ICF) principles behind the burning plasma and ignition results as well as discuss future challenges.

In search and rescue missions, teleoperated rovers equipped with sensor technology are deployed into harsh environments to search for targets. To support the search task, unimodal/multimodal cues can be presented via visual, acoustic and/or haptic channels. However, human operators often perform the search task in parallel with the driving task, which can cause interference of attentional resources based on multiple resource theory. Navigating corners can be a particularly challenging aspect of remote driving, as described with the Cornering Law. Therefore, search cues should not interfere with cornering. The present research explores how unimodal/multimodal search cues affect cornering performance, with typical communication delays of 50 ms and 500 ms. One-hundred thirty-one participants, distributed into two delay groups, performed a target search task with unimodal/multimodal search cues. Search cues did not interfere with cornering performance with 50 ms delays. For 500 ms delays, search cues presented via the haptic channel significantly interfered with the driving task. Practitioner summary: Teleoperated rovers can support search and rescue missions. Search cues may assist the human operator, but they may also interfere with the task of driving. The study examined interference of unimodal and multimodal search cues. Haptic cues should not be implemented for systems with a delay of 500 ms or more.

Understanding the vulnerability of trees to drought-induced mortality is key to predicting the fate of forests in a future climate with more frequent and intense droughts, although the underlying mechanisms are difficult to study in adult trees. Here, we explored the dynamic changes of water relations and limits of hydraulic function in dying adults of Norway spruce (Picea abies L.) during the progression of the record-breaking 2018 Central European drought. In trees on the trajectory to drought-induced mortality, we observed rapid, nonlinear declines of xylem pressure that commenced at the early onset of xylem cavitation and caused a complete loss of xylem hydraulic conductance within a very short time. We also observed severe depletions of nonstructural carbohydrates, though carbon starvation could be ruled out as the cause of the observed tree death, as both dying and surviving trees showed these metabolic limitations. Our observations provide striking field-based evidence for fast dehydration and hydraulic collapse as the cause of drought-induced mortality in adult Norway spruce. The nonlinear decline of tree water relations suggests that considering the temporal dynamics of dehydration is critical for predicting tree death. The collapse of the hydraulic system within a short time demonstrates that trees can rapidly be pushed out of the zone of hydraulic safety during the progression of a severe drought. In summary, our findings point toward a higher mortality risk for Norway spruce than previously assumed, which is in line with current reports of unprecedented levels of drought-induced mortality in this major European tree species.