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The evolutionary dynamics of tree species are influenced by their specific climatic environments, and their ability to persist is determined by adaptive strategies such as broad climate tolerance, phenotypic plasticity or genetic differentiation. Biogeographical predictions indicate that populations located at the edges of their ranges are more likely to experience heightened vulnerability to climatic fluctuations due to approaching tolerance limits. However, if local phenotypic acclimation or genetic adaptation has taken place, trees near the edge of their range could demonstrate comparable sensitivity to freeze and drought as the rest of the sampled population. Nevertheless, there remains uncertainty regarding the extent of developmental and evolutionary adjustments in climate sensitivity across the entire ranges of many tree species.Here, we document the biogeography of tree growth sensitivity to freeze and soil water and vapour pressure deficits during 1950–2018 using an extensive multi‐species tree‐ring dataset of 35,784 trees at 4535 sites covering boreal, temperate conifer and temperate deciduous forests of Canada. We quantify the relationships between tree radial growth increment and seasonal climate variables and explore factors driving the observed patterns of annual growth and climate sensitivity such as species, regional climate and local site conditions, and tree age and size.Freeze and drought had widespread impacts on tree growth that were contingent on the presence of focal species in interaction with tree size. An indirect growth thermal limitation towards cold/wet edges, occurring through the site moisture conditions, was observed in seven widespread species (e.g. Picea glauca, Picea mariana and Larix laricina). Moreover, six species had negative drought impacts more strongly expressed towards their warm/dry edges (e.g. Abies balsamea, Betula papyrifera and Pseudotsuga menziesii). However, widespread Picea, Pinus and Populus species showed no indication of increased sensitivity to soil water conditions at these edges.Synthesis. Our findings support the idea of evolutionary or acclimatization adjustments in the development of populations in response to long‐term climate conditions experienced in their respective locations. This underscores the importance of incorporating phenotypic and genomic data into future analyses of climate change impacts, which would enhance our ability to predict potential ecological shifts. [ABSTRACT FROM AUTHOR]

Water stress can trigger acclimation responses and damage plants. The aim of this study was to evaluate the integrative responses of cotton hydraulic conductance, leaf photosynthesis, and carbon metabolism to short-term drought and subsequent rewatering. A water-controlled pot experiment was conducted in 2020, with soil water drying continuing for one day (D1), two days (D2), and three days (D3) after it reached 40% ± 5% of the soil water holding capacity at the blooming stage of cotton, and the soil was then rewatered to the soil water holding capacity. We investigated how the stem hydraulic conductance, gas exchange, and biochemical traits of cotton were affected by imposed drought stress and subsequent rewatering. The hydraulic characteristics of cotton in the D2 and D3 treatments evolved with damage, complete closure of stomatal conductance, and complete deterioration of photosynthesis, in addition to severe floating changes in the carbon metabolism affected by drought. The leaves' functional characteristics after rewatering cannot be completely recovered to full-irrigation levels, and the recovery extent was strongly linked to the duration. Consequently, it is considered desirable to maintain normal physiological activity during the cotton reproductive period, and the drought episode can be sustained for 1 day in a long-term perspective when the soil water content is depleted to 40% ± 5% of the soil water holding capacity. These results can provide in-depth ideas for better understanding the hydraulic and physiological responses of cotton to drought episodes and rewatering, and they can help drought-affected cotton to cope with future climate change. [ABSTRACT FROM AUTHOR]

Background and aims: The root barrier to radial O2 loss is a trait induced during soil flooding restricting oxygen loss from the roots to the anoxic soil. It can also restrict radial water loss, potentially providing tolerance towards drought during conditions of water deficit. Several root traits (aerenchyma and xylem vessels area) respond in a similar way to soil flooding and low soil water potentials. Therefore, we hypothesised that root acclimations to soil flooding prime plants to withstand conditions of water deficit. Methods: We raised plants in hydroponics mimicking contrasting soil water conditions (aerated controls for well-watered soils; stagnant, deoxygenated solutions for flooded soils, and aerated solutions with different PEG6000 concentrations to mimic conditions of water deficit). We used O2 microsensors and gravimetric measurements to characterize the formation of a barrier to radial O2 loss during conditions of water deficit, and measured key anatomical root traits using light microscopy. Results: Several root traits were induced in stagnant conditions as well as in conditions of water deficit, including the barrier to radial O2 loss. The tightness of the barrier to water loss was similar in both stagnant and PEG6000 treatments. Moreover, plants growing in stagnant conditions tolerated a following severe condition of water deficit, whereas those growing in mimicked well-watered conditions did not. Conclusions: We demonstrated that plants growing in stagnant conditions can withstand following severe conditions of water deficit. We propose that key root traits, such as the barrier to radial O2 loss, which are induced in stagnant conditions as well as mild conditions of water deficit, prime the plants for a following severe condition of water deficit. [ABSTRACT FROM AUTHOR]

Future climate will be characterized by an increase in frequency and duration of drought and warming that exacerbates atmospheric evaporative demand. How trees acclimate to long-term soil moisture changes and whether these long-term changes alter trees' sensitivity to short-term (day to months) variations of vapor pressure deficit (VPD) and soil moisture is largely unknown. Leaf gas exchange measurements were performed within a long-term (17 years) irrigation experiment in a drought-prone Scots pine-dominated forest in one of Switzerland's driest areas on trees in naturally dry (control), irrigated, and 'irrigation-stop' (after 11 years of irrigation) conditions. Seventeen years of irrigation increased photosynthesis (A) and stomatal conductance (g s) and reduced g s sensitivity to increasing VPD and soil drying. Following irrigation-stop, gas exchange decreased only after 3 years. After 5 years, maximum carboxylation (V cmax) and electron transport (J max) rates in irrigation-stop recovered to similar levels as to before the irrigation-stop. These results suggest that long-term release from soil drought reduces the sensitivity to VPD and that atmospheric constraints may play an increasingly important role in combination with soil drought. Moreover, our study indicates that structural adjustments lead to an attenuation of initially strong leaf-level acclimation to strong multiple-year drought. [ABSTRACT FROM AUTHOR]

The adaptability of plants to drought not only includes their ability to resist drought stress, but also their ability to recover after stress is relieved. In this study, a weighting method was used to control the soil water content to produce a soil water stress gradient. The effects of drought and rewatering on the changes in osmotic adjustment substance content, antioxidant enzyme activity, and photosynthetic characteristics of potted Dicranostigma henanensis seedlings were measured on Day 28 after the imposition of watering treatments and Day 7 after rewatering. During the drought stress process, the relative electrical conductivity, thiobarbituric acid, water use efficiency, and proline content displayed a continuously increasing trend. Further, the net photosynthetic rate, stomatal conductance, and transpiration rate constantly decreased, while the chlorophyll content first increased and then decreased. After rehydration, superoxide dismutase (EC 1.15.1.1) activity and photosynthetic parameters quickly recovered to the CK level (soil moisture is 75%-80% of the maximum water holding capacity in the field), indicating that D. henanensis plants have a strong ability to repair the damage caused by drought stress. In particular, the photosynthetic machinery may have sophisticated regulation and repair mechanisms, which may be associated with its stable photosystem. Collectively, our findings demonstrate that the D. henanensis plant has a strong ability to adapt to arid environments, and therefore could be an excellent ornamental flower for landscaping in arid and semiarid areas. [ABSTRACT FROM AUTHOR]

Summary: Understanding the genetic and physiological basis of abiotic stress tolerance under field conditions is key to varietal crop improvement in the face of climate variability. Here, we investigate dynamic physiological responses to water stress in silico and their relationships to genotypic variation in hydraulic traits of cotton (Gossypium hirsutum), an economically important species for renewable textile fiber production.In conjunction with an ecophysiological process‐based model, heterogeneous data (plant hydraulic traits, spatially‐distributed soil texture, soil water content and canopy temperature) were used to examine hydraulic characteristics of cotton, evaluate their consequences on whole plant performance under drought, and explore potential genotype × environment effects.Cotton was found to have R‐shaped hydraulic vulnerability curves (VCs), which were consistent under drought stress initiated at flowering. Stem VCs, expressed as percent loss of conductivity, differed across genotypes, whereas root VCs did not. Simulation results demonstrated how plant physiological stress can depend on the interaction between soil properties and irrigation management, which in turn affect genotypic rankings of transpiration in a time‐dependent manner.Our study shows how a process‐based modeling framework can be used to link genotypic variation in hydraulic traits to differential acclimating behaviors under drought. [ABSTRACT FROM AUTHOR]

Summary: Recent research has shown that plant acclimation to diverse patterns of light intensity modifies the dynamics of their stomatal response. Therefore, whether plants are grown in controlled conditions or in the field may impact their stomatal dynamics.We analysed the stomatal dynamics of two Populus euramericana and two Populus nigra genotypes grown in the field under contrasting water availability. By comparing their stomatal dynamics with that of the same genotypes grown in a glasshouse, we were able to test whether differences between these growing conditions interacted with genotypic differences in affecting stomatal dynamics and responses to soil water deficit.We found that, despite higher stomatal density and smaller size, in the field stomatal dynamics were much slower than in the glasshouse. Overall, differences among genotypes and their response to soil water deficit were much less pronounced in the field compared with the glasshouse.These results indicate that stomatal dynamics are regulated by both genotype‐specific and environmental factors. Moreover, having slower stomata may be advantageous under some conditions. While stomatal dynamics were linked with whole‐plant transpiration per leaf area in both experiments, the contribution of stomatal morphology varies dependent on the environmental conditions. [ABSTRACT FROM AUTHOR]

Black locust (Robinia pseudoacacia) is widely planted throughout semiarid and subhumid regions of the Loess Plateau of China. Determining the changes in transpiration of this species in different climatic areas is important for revealing the acclimation mechanism of black locust and developing suitable forest management practices, particularly in the context of global climate change. Here, sap flow and canopy conductance of black locust plantation trees in semiarid (Yan'an) and subhumid (Yongshou) sites were quantified using Granier-type thermal dissipation probes and concurrent environmental observations from 2012 to 2017. Several physiological parameters were measured throughout the growing season. The results showed that sap flow was correlated with phenological factors across seasons within a year. However, interannual changes in sap flow were affected mainly by the reference evapotranspiration (ET 0) at the Yongshou site, and jointly by precipitation (P), soil water content, and P / ET 0 at the Yan'an site. Sap flow response to meteorological factors showed less discrepancy between pre- and post-rainfall periods at the Yan'an site. Moreover, canopy conductance fluctuated less with a wider range of vapor pressure deficit (VPD) and the slope of canopy resistance as a function of VPD was lower, indicating relatively lower sensitivity of stomatal conductance to environmental factors in Yan'an site. Physiological parameters, except for predawn leaf water potential, were significantly different between the two sites. The results suggested that black locust tended to reduce transpiration, modify leaf morphology, and improve water use efficiency to enhance its adaptability to the dryer site. The species changes stomatal regulation characteristics and general growth rate to acclimatize to distinct water habitats. • Sap flow characteristics of black locust differ between semiarid and subhumid sites. • Dominant environmental factors controlling transpiration varied with habitats. • Adaptability and responses to long-term and short-term drought are different. • Longterm soil water shortage weakened stomatal regulation and growth. • Future intensified drought potentially threatens the plantation stability. [ABSTRACT FROM AUTHOR]

• Interannual variation in J s was controlled by PPT-induced-VWC and LAI • Long term summer drought reduce J s and stomatal conductance more than spring drought • The reduction highlights physiological adjustment in acclimation to drought • Among three species, HM was least sensitive, more resistant and resilient to drought Extreme seasonal droughts frequently occur in semiarid and arid areas of the world. They can exert a profound influence on the physiological state of desert plants. Short-term rainfall and long-term water shortages in the Mu Us Desert have differentiated the role of individual species with their distinct ability to resist and recover from drought. This study explores how the scale of rainfall events affects interannual variation in sap flow in three dominant desert-shrub species [i.e., Salix psammophila (SP), Artemisia ordosica (AO), and Hedysarum mongolicum (HM)], and whether the associated changes in soil-water dynamics helped to modify sap flow. As a result, interannual variation in sap flow (J s) was mostly driven by precipitation (PPT), Volumetric soil water content (VWC), and leaf area index (LAI), with their individual influences varying as a function of plant phenophases. The species acclimated to long-term summer drought (> 30 days, i.e., no rain over a 30-day period or longer) by reducing stomatal conductance in the three species by 66.5, 59.5, and 43.5%, respectively, suggesting a physiological adjustment in water conservation in response to drought. Average summer drought (June–July) reduced J s in the three species by 55.5 (in SP), 42 (AO), and 28.5% (HM), more than spring drought (May–June) at 28% in SP and 9.5% in AO. Among those species, HM exhibited the least sensitivity and the highest overall resistance and resilience to drought. The relationship between J s and VWC was modulated by the effect of PPT. Our findings provide compelling evidence that HM is seen to be better suited to future climatic warming, as the species may be capable of accessing deep groundwater reserves replenished by large PPT pulses (5–10 mm), in sustaining its physiological activity over longer periods. These results could help formulate a selection process in determining which shrub species to plant in the sustainable management of desert ecosystems. [ABSTRACT FROM AUTHOR]

• Sustained drought, but not repeated, promoted physiological acclimation. • More variable physiological responses occurred in repeated than sustained drought. • Sustained drought led to conservative responses and minimal growth. • Physiology during repeated drought was opportunistic, linked to water availability. Climate change is predicted to result in more variable and extreme precipitation regimes, with potentially longer periods between precipitation events. However, the effects of multiple, sequential drought events on ecosystems and potential acclimation, particularly in grasslands, is poorly understood. In this study, we tested if two simulated drought regimes, (i) sustained drought (soil moisture content reduced from 75 to 25 % field capacity over 14 days and maintained for 29 days) and (ii) repeated drought (two cycles of a reduction to 25 % field capacity, reached after 22 days and 15 days, separated by a rewatering event to 75 % field capacity for 5 days), differentially influence fourteen key physiological responses in the model grass species (Brachypodium distachyon). In addition, we aimed to determine whether plants may acclimate differently to sustained and/or repeated drought events. B. distachyon exhibited plasticity in response to drought, exhibiting two distinct drought resistance responses to the two watering regimes. Plants exposed to sustained drought exhibited early reductions in photosynthesis, stomatal conductance and water potential (43 %, 42 % and 37 %, respectively). However, plants showed physiological acclimation and recovery in these parameters after an additional 3–21 days, but had a ∼50 % lower shoot biomass than well-watered plants. These data demonstrate a conservative, albeit plastic, response to soil water deficit. In contrast, plants exposed to repeated drought responded opportunistically whereby greater fluctuations in photosynthesis, stomatal conductance and water potential (reductions of up to 62 %, 71 % and 90 %, respectively) were closely related to drought and rewatering events. Since plants exposed to repeated drought had a greater reduction in water potential and faster reductions in relative photosynthesis in the second drought event compared to the initial drought event, this may indicate a lack of acclimation under this drought regime. Our results provide evidence for differential responses of B. distachyon to drought and rewatering events, which are dependent on the drought regime (sustained or repeated) and must be carefully considered when interpreting experimental data. [ABSTRACT FROM AUTHOR]