Global climate change and land use change underlie a need to develop new crop breeding strategies, and crop wild relatives (CWR) have become an important potential source of new genetic material to improve breeding efforts. Many recent approaches assume adaptive trait variation increases towards the relative environmental extremes of a species range, potentially missing valuable trait variation in more moderate or typical climates. Here, we leveraged distinct genotypes of wild chickpea (Cicer reticulatum) that differ in their relative climates from moderate to more extreme and perform targeted assessments of drought and heat tolerance. We found significance variation in ecophysiological function and stress tolerance between genotypes but contrary to expectations and current paradigms, it was individuals from more moderate climates that exhibited greater capacity for stress tolerance than individuals from warmer and drier climates. These results indicate that wild germplasm collection efforts to identify adaptive variation should include the full range of environmental conditions and habitats instead of only environmental extremes, and that doing so may significantly enhance the success of breeding programs broadly.

Tradeoffs between the energetic benefits and costs of traits can shape species and trait distributions along environmental gradients. Here we test predictions based on such tradeoffs using survival, growth, and 50 photosynthetic, hydraulic, and allocational traits of ten Eucalyptus species grown in four common gardens along an 8-fold gradient in precipitation/pan evaporation (P/Ep) in Victoria, Australia. Phylogenetically structured tests show that most trait-environment relationships accord qualitatively with theory. Most traits appear adaptive across species within gardens (indicating fixed genetic differences) and within species across gardens (indicating plasticity). However, species from moister climates have lower stomatal conductance than others grown under the same conditions. Responses in stomatal conductance and five related traits appear to reflect greater mesophyll photosynthetic sensitivity of mesic species to lower leaf water potential. Our data support adaptive cross-over, with realized height growth of most species exceeding that of others in climates they dominate. Our findings show that pervasive physiological, hydraulic, and allocational adaptations shape the distributions of dominant Eucalyptus species along a subcontinental climatic moisture gradient, driven by rapid divergence in species P/Ep and associated adaptations.

Abstract Conifers inhabit some of the most challenging landscapes where multiple abiotic stressors (e.g., aridity, freezing temperatures) often co-occur. Physiological tolerance to multiple stressors (‘poly-tolerance’) is thought to be rare because exposure to one stress generally limits responses to another through functional trade-offs. However, the capacity to exhibit poly-tolerance may be greater when combined abiotic stressors have similar physiological impacts, such as the disruption of hydraulic function imposed by drought or freezing. Here, we reviewed empirical data in light of theoretical expectations for conifer adaptations to drought and freeze–thaw cycles with particular attention to hydraulic traits of the stem and leaf. Additionally, we examined the commonality and spatial distribution of poly-stress along indices of these combined stressors. We found that locations with the highest values of our poly-stress index (PSi) are characterized by moderate drought and moderate freeze–thaw, and most of the global conifer distribution occupies areas of moderate poly-stress. Among traits examined, we found diverse responses to the stressors. Turgor loss point did not correlate with freeze–thaw or drought stress individually, but did with the PSi, albeit inverse to what was hypothesized. Leaf mass per area was more strongly linked with drought stress than the poly-stress and not at all with freeze–thaw stress. In stems, the water potential causing 50% loss of hydraulic conductivity became more negative with increasing drought stress and poly-stress but did not correlate with freeze–thaw stress. For these traits, we identified a striking lack of coverage for substantial portions of species ranges, particularly at the upper boundaries of their respective PSis, demonstrating a critical gap in our understanding of trait prevalence and plasticity along these stress gradients. Future research should investigate traits that confer tolerance to both freeze–thaw and drought stress in a wide range of species across broad geographic scales.

Background Despite the recognized importance of hydraulic capacitance as a mechanism used by plants to maintain hydraulic functioning during high transpiration, characterizing the dynamics of capacitance remains a challenge. Methods We used a novel 'two-balance method' to investigate relationships between stem rehydration kinetics and other hydraulic traits in multiple tree species, and we developed a model to explore stem rehydration kinetics further. Key Results We found that: (1) rehydration time constants and the amount of water uptake occurring during rehydration differed significantly across species; (2) time constants did not change with declining water potential (psi), while water uptake increased at lower psi in some species; (3) longer time constants were associated with lower wood density, higher capacitance and less negative stem pressures causing 50 % loss of hydraulic conductivity (P-50); (4) greater water uptake occurred in stems with lower wood density and less negative P-50 values; and (5) the model could estimate the total hydraulic resistance of the rehydration path, which cannot be measured directly. Conclusions Overall, the two-balance method can be used to examine rehydration dynamics quickly and thoroughly in detached woody stems. This method has the potential to improve our understanding of how capacitance functions across tree species, which is an often-overlooked component of whole-plant hydraulics.

The isohydric-anisohydric continuum describes the relative stringency of stomatal control of leaf water potential ( ψ ) during drought. Hydroscape area ( HA ) – the water potential landscape over which stomata regulate ψ – has emerged as a useful metric of the iso/anisohydric continuum because it is strongly linked to several hydraulic, photosynthetic, and structural traits. Previous research on HA focused on broad ecological patterns involving several plant clades. Here we investigate relationships of HA to climatic conditions and functional traits across ecologically diverse but closely related species while accounting for phylogeny. Across a macroclimatic moisture gradient, defined by the ratio of mean annual precipitation to mean annual pan evaporation ( P/E ), HA decreased with P/E for ten Eucalyptus species. Greater anisohydry reflects lower turgor loss points and greater hydraulic safety, mirroring global patterns. More isohydric species have mesophyll photosynthetic capacity that is more sensitive to ψ , consistent with an earlier model for optimal stomatal behavior. Hydroscapes exhibit little plasticity in response to variation in water supply, and the extent of plasticity does not vary with P/E of native habitats. These findings strengthen the case that HA is a useful metric for characterizing drought tolerance and water-status regulation.

BACKGROUND AND AIMS:An individual plant consists of different-sized shoots, each of which consists of different-sized leaves. To predict plant-level physiological responses from the responses of individual leaves, modelling this within-shoot leaf size variation is necessary. Within-plant leaf trait variation has been well investigated in canopy photosynthesis models but less so in plant allometry. Therefore, integration of these two different approaches is needed. METHODS:We focused on an established leaf-level relationship that the area of an individual leaf lamina is proportional to the product of its length and width. The geometric interpretation of this equation is that different-sized leaf laminas from a single species share the same basic form. Based on this shared basic form, we synthesized a new length-times-width equation predicting total shoot leaf area from the collective dimensions of leaves that comprise a shoot. Furthermore, we showed that several previously established empirical relationships, including the allometric relationships between total shoot leaf area, maximum individual leaf length within the shoot and total leaf number of the shoot, can be unified under the same geometric argument. We tested the model predictions using five species, all of which have simple leaves, selected from diverse taxa (Magnoliids, monocots and eudicots) and from different growth forms (trees, erect herbs and rosette herbs). KEY RESULTS:For all five species, the length-times-width equation explained within-species variation of total leaf area of a shoot with high accuracy (R2 > 0.994). These strong relationships existed despite leaf dimensions scaling very differently between species. We also found good support for all derived predictions from the model (R2 > 0.85). CONCLUSIONS:Our model can be incorporated to improve previous models of allometry that do not consider within-shoot size variation of individual leaves, providing a cross-scale linkage between individual leaf-size variation and shoot-size variation.

Trade-offs between photosynthesis and the costs of resource capture inform economic strategies of plants across environmental gradients and result in predictable variation in leaf traits. However, understudied functional groups like hemiparasites that involve dramatically different strategies for resource capture may have traits that deviate from expectations. We measured leaf traits related to gas exchange in mistletoes and their eucalypt hosts along a climatic gradient in relative moisture supply, measured as the ratio of precipitation to pan evaporation ( P / E p ), in Victoria, Australia. We compared traits for mistletoes vs. hosts as functions of relative moisture supply and examined trait–trait correlations in both groups. Eucalypt leaf traits responded strongly to decreasing P / E p , consistent with economic theory. Leaf area and specific leaf area (SLA) decreased along the P / E p gradient, while C:N ratio, leaf thickness, N per area, and δ 13 C all increased. Mistletoes responded overall less strongly to P / E p based on multivariate analyses; individual traits sometimes shifted in parallel with those of hosts, but SLA, leaf thickness, and N per area showed no significant change across the gradient. For mistletoes, leaf thickness was inversely related to leaf dry matter content (LDMC), with no relationship between SLA and mass-based N. In mistletoes, reduced costs of transpiration (reflecting their lack of roots) and abundant succulent leaf tissue help account for observed differences from their eucalypt hosts. Trait-based analysis of atypical functional types such as mistletoes help refine hypotheses based on plant economics and specialized adaptations to resource limitation.

Background: ERCP has become widely available for the diagnosis and treatment of benign and malignant pancreaticobiliary diseases. In this prospective study, the overall complication rate and risk factors for diagnostic and therapeutic ERCP were identified.Methods: Data were collected prospectively on patient characteristics and endoscopic techniques from 1223 ERCPs performed at a single referral center and entered into a database. Univariate and multivariate analyses were used to identify risk factors for ERCP-associated complications.Results: Of 1223 ERCPs performed, 554 (45.3%) were diagnostic and 667 (54.7%) therapeutic. The overall complication rate was 11.2%. Post-ERCP pancreatitis was the most common (7.2%) and in 93% of cases was self-limiting, requiring only conservative treatment. Bleeding occurred in 10 patients (0.8%) and was related to a therapeutic procedure in all cases. Nine patients had cholangitis develop, most cases being secondary to incomplete drainage. There was one perforation (0.08%). All other complications totaled 1.5%. Variables derived from cannulation technique associated with an increased risk for post-ERCP pancreatitis were precut access papillotomy (20%), multiple cannulation attempts (14.9%), sphincterotome use to achieve cannulation (13.1%), pancreatic duct manipulation (13%), multiple pancreatic injections (12.3%), guidewire use to achieve cannulation (10.2%), and the extent of pancreatic duct opacification (10%). Patient characteristics associated with an increased risk of pancreatitis were sphincter of Oddi dysfunction (21.7%) documented by manometry, previous ERCP-related pancreatitis (19%), and recurrent pancreatitis (16.2%). Pain during the procedure was an important indicator of an increased risk of post-ERCP pancreatitis (27%). Independent risk factors for post-ERCP pancreatitis were identified as a history of recurrent pancreatitis, previous ERCP-related pancreatitis, multiple cannulation attempts, pancreatic brush cytology, and pain during the procedure.Conclusions: The most frequent ERCP-related complication was pancreatitis, which was mild in the majority of patients. The frequency of post-ERCP pancreatitis was similar for both diagnostic and therapeutic procedures. Bleeding was rare and mostly associated with sphincterotomy. Other complications such as cholangitis and perforation were rare. Specific patient- and technique-related characteristics that can increase the risk of post-ERCP complications were identified.

Wild-type KRAS ( KRAS WT ) amplification has been shown to be a secondary means of KRAS activation in cancer and associated with poor survival. Nevertheless, the precise role of KRAS WT overexpression in lung cancer progression is largely unexplored. Here, we identify and characterize a KRAS-responsive lncRNA, KIMAT1 (ENSG00000228709) and show that it correlates with KRAS levels both in cell lines and in lung cancer specimens. Mechanistically, KIMAT1 is a MYC target and drives lung tumorigenesis by promoting the processing of oncogenic microRNAs (miRNAs) through DHX9 and NPM1 stabilization while halting the biogenesis of miRNAs with tumor suppressor function via MYC-dependent silencing of p21, a component of the Microprocessor Complex. KIMAT1 knockdown suppresses not only KRAS expression but also KRAS downstream signaling, thereby arresting lung cancer growth in vitro and in vivo. Taken together, this study uncovers a role for KIMAT1 in maintaining a positive feedback loop that sustains KRAS signaling during lung cancer progression and provides a proof of principle that interfering with KIMAT1 could be a strategy to hamper KRAS-induced tumorigenesis.

The intensity of extreme heat and drought events has drastically risen in recent decades and will likely continue throughout the century. Northern forests have already seen increases in tree mortality and a lack of new recruitment, which is partially attributed to these extreme events. Boreal species, such as paper birch (Betula papyrifera) and white spruce (Picea glauca), appear to be more sensitive to these changes than lower-latitude species. Our objectives were to investigate the effects of repeated heatwaves and drought on young paper birch and white spruce trees by examining (i) responses in leaf gas exchange and plant growth and (ii) thermal acclimation of photosynthetic and respiratory traits to compare ecophysiological responses of two co-occurring, yet functionally dissimilar species. To address these objectives, we subjected greenhouse-grown seedlings to two consecutive summers of three 8-day long, +10 degrees C heatwaves in elevated atmospheric CO2 conditions with and without water restriction. The data show that heatwave stress reduced net photosynthesis, stomatal conductance and growth-more severely so when combined with drought. Acclimation of both photosynthesis and respiration did not occur in either species. The combination of heat and drought stress had a similar total effect on both species, but each species adjusted traits differently to the combined stress. Birch experienced greater declines in gas exchange across both years and showed moderate respiratory but not photosynthetic acclimation to heatwaves. In spruce, heatwave stress reduced the increase in basal area in both experimental years and had a minor effect on photosynthetic acclimation. The data suggest these species lack the ability to physiologically adjust to extreme heat events, which may limit their future distributions, thereby altering the composition of boreal forests.

This article comments on: Alex Fajardo, Juan P. Mora and Etienne Robert, Corner’s rules pass the test of time: little effect of phenology on leaf–shoot and other scaling relationships, Annals of Botany, Volume 126, Issue 7, 25 November 2020, Pages 1129–1139, https://doi.org/10.1093/aob/mcaa124

The vast majority of measurements in the field of plant hydraulics have been on small-diameter branches from woody species. These measurements have provided considerable insight into plant functioning, but our understanding of plant physiology and ecology would benefit from a broader view, because branch hydraulic properties are influenced by many factors. Here, we discuss the influence that other components of the hydraulic network have on branch vulnerability to embolism propagation. We also modelled the impact of changes in the ratio of root-to-leaf areas and soil texture on vulnerability to hydraulic failure along the soil-to-leaf continuum and showed that hydraulic function is better maintained through changes in root vulnerability and root-to-leaf area ratio than in branch vulnerability. Differences among species in the stringency with which they regulate leaf water potential and in reliance on stored water to buffer changes in water potential also affect the need to construct embolism resistant branches. Many approaches, such as measurements on fine roots, small individuals, combining sap flow and psychrometry techniques, and modelling efforts, could vastly improve our understanding of whole-plant hydraulic functioning. A better understanding of how traits are coordinated across the whole plant will improve predictions for plant function under future climate conditions.

The degree of plant iso/anisohydry, a widely used framework for classifying species-specific hydraulic strategies, integrates multiple components of the whole-plant hydraulic pathway. However, little is known about how it associates with coordination of functional and structural traits within and across different organs. We examined stem and leaf hydraulic capacitance and conductivity/conductance, stem xylem anatomical features, stomatal regulation of daily minimum leaf and stem water potential (Ψ), and the kinetics of stomatal responses to vapour pressure deficit (VPD) in six diverse woody species differing markedly in their degree of iso/anisohydry. At the stem level, more anisohydric species had higher wood density and lower native capacitance and conductivity. Like stems, leaves of more anisohydric species had lower hydraulic conductance; however, unlike stems, their leaves had higher native capacitance at their daily minimum values of leaf Ψ. Moreover, rates of VPD-induced stomatal closure were related to intrinsic rather than native leaf capacitance and were not associated with species' degree of iso/anisohydry. Our results suggest a trade-off between hydraulic storage and efficiency in the leaf, but a coordination between hydraulic storage and efficiency in the stem along a spectrum of plant iso/anisohydry.

Many plant species experience large differences in soil moisture availability within a season, potentially leading to a wide range of leaf water potentials (ΨLEAF). In order to decrease the risk of leaf dehydration, among species, there is a continuum ranging from strict control (isohydry) to little control (anisohydry) of minimum ΨLEAF. In central Texas USA, species are exposed to a range of soil moisture from wet springs to hot, dry summers. There are diverging water management strategies among the four dominant woody species in this system; two of these species are more isohydric (Prosopis glandulosa, Quercus fusiformis) while two others are more anisohydric (Diospyros texana, Juniperus asheii). To maintain leaf turgor and photosynthesis during periods of limited soil moisture, anisohydric species may adjust leaf hydraulic parameters more than isohydric species. To test this hypothesis, we quantified iso/anisohydry from 3 years of ΨLEAF predawn and midday measurements, and we measured the changes in turgor loss points (ΨTLP), osmotic potential at full hydration (Ψπ₁₀₀), and resistance to leaf hydraulic dysfunction (leaf P₅₀) throughout the spring and summer of 2016. Diospyros and Juniperus experienced more negative ΨLEAF and adjusted ΨTLP and Ψπ₁₀₀ in response to both drying soils during the summer also in response to rainfall events during September. In contrast, the more isohydric species (Quercus and Prosopis) did not appear to adjust ΨTLP or Ψπ₁₀₀ in response to soil moisture. The more anisohydric species also adjusted leaf P₅₀ during periods of reduced soil moisture. Our results suggest that species that experience wider ranges of ΨLEAF have a greater ability to alter leaf hydraulic properties. This provides insight on how species with different strategies for water potential regulation may modify properties to mitigate drought effects in the future. A plain language summary is available for this article.

Vulnerability-to-cavitation curves (VCs) can vary within a tree crown in relation to position or branch age. We tested the hypothesis that VC variation can arise from differential susceptibility to the number of diurnal sap pressure cycles experienced. We designed a method to distinguish between effects of cycling vs exposure time to negative pressure, and tested the influence of sap pressure cycles on cavitation vulnerability between upper and lower branches in Acer negundo L. trees using static and flow centrifuge, and air-injection methods. Branches from the upper crown had greater hydraulic conductivity and were more resistant to cavitation than branches from the lower crown. Upper branches also showed little change after exposure to 10 or 20 pressure cycles between -0.5 MPa and -2.0 MPa. Lower branches, however, showed a marked increase in vulnerability to cavitation after pressure-cycling. This result suggests that 'cavitation fatigue' can occur without the actual induction (and reversal) of cavitation as documented previously, but simply from the cycling of pressures in the sub-cavitation range. This 'pressure fatigue' may explain age-related shifts in VCs that could eventually induce dieback in suppressed branches or trees. Pressure fatigue may help explain developmental variation in hydraulic capacity of branches within individuals.

Background and Aims Corner’s rule states that thicker twigs bear larger leaves. The exact nature of this relationship and why it should occur has been the subject of numerous studies. It is obvious that thicker twigs should support greater total leaf area (Atwig) for hydraulical and mechanical reasons. But it is not obvious why mean leaf size (A-) should scale positively with Atwig. We asked what this scaling relationship is within species and how variable it is across species. We then developed a model to explain why these relationships exist. Methods To minimize potential sources of variability, we compared twig properties from six co-occurring and functionally similar species: Acer grandidentatum, Amelanchier alnifolia, Betula occidentalis, Cornus sericea, Populus fremontii and Symphoricarpos oreophilus. We modelled the economics of leaf display, weighing the benefit from light absorption against the cost of leaf tissue, to predict the optimal A- :Atwig combinations under different canopy openings. Key Results We observed a common A- by Atwig exponent of 0.6, meaning that A -and leaf number on twigs increased in a specific coordination. Common scaling exponents were not supported for relationships between any other measured twig properties. The model consistently predicted positive A- by Atwig scaling when twigs optimally filled canopy openings. The observed 0·6 exponent was predicted when self-shading decreased with larger canopy opening. Conclusions Our results suggest Corner’s rule may be better understood when recast as positive A- by Atwig scaling. Our model provides a tentative explanation of observed A- by Atwig scaling and suggests different scaling may exist in different environments.

Here, we summarize studies on the effects of elevated [CO2 ] (CO2e ) on the structure and function of plant hydraulic architecture and explore the implications of those changes using a model. Changes in conduit diameter and hydraulic conductance due to CO2e vary among species. Ring-porous species tend towards an increase in conduit size and consequently conductivity. The effect in diffuse-porous species is much more limited. In conifers, the results are mixed, some species show minor changes in xylem structure, while other studies found increases in tracheid density and diameter. Non-woody plants generally exhibited the reverse pattern with narrower conduits and lower hydraulic conductivity under CO2e . Further, changes in drought-resistance traits suggest that non-woody plants were the most affected by CO2e , which may permit them to better resist drought-induced embolism under future conditions. Due to their complexity, acclimation in hydraulic traits in response to CO2e is difficult to interpret when relying solely on measurements. When we examined how the observed tissues-specific trends might alter plant function, our modelling results suggest that these hydraulic changes would lead to reduced conductance and more frequent drought stress in trees that develop under CO2e with a more pronounced effect in isohydric than in anisohydric species.

Species' differences in the stringency of stomatal control of plant water potential represent a continuum of isohydric to anisohydric behaviours. However, little is known about how quasi-steady-state stomatal regulation of water potential may relate to dynamic behaviour of stomata and photosynthetic gas exchange in species operating at different positions along this continuum. Here, we evaluated kinetics of light-induced stomatal opening, activation of photosynthesis and features of quasi-steady-state photosynthetic gas exchange in 10 woody species selected to represent different degrees of anisohydry. Based on a previously developed proxy for the degree of anisohydry, species' leaf water potentials at turgor loss, we found consistent trends in photosynthetic gas exchange traits across a spectrum of isohydry to anisohydry. More anisohydric species had faster kinetics of stomatal opening and activation of photosynthesis, and these kinetics were closely coordinated within species. Quasi-steady-state stomatal conductance and measures of photosynthetic capacity and performance were also greater in more anisohydric species. Intrinsic water-use efficiency estimated from leaf gas exchange and stable carbon isotope ratios was lowest in the most anisohydric species. In comparisons between gas exchange traits, species rankings were highly consistent, leading to species-independent scaling relationships over the range of isohydry to anisohydry observed.