Climate change is expected to exacerbate drought for many plants, making drought tolerance a key driver of species and ecosystem responses. Plant drought tolerance is determined by multiple traits, ...but the relationships among traits, either within individual plants or across species, have not been evaluated for general patterns across plant diversity. We synthesized the published data for stomatal closure, wilting, declines in hydraulic conductivity in the leaves, stems, and roots, and plant mortality for 262 woody angiosperm and 48 gymnosperm species. We evaluated the correlations among the drought tolerance traits across species, and the general sequence of water potential thresholds for these traits within individual plants. The trait correlations across species provide a framework for predicting plant responses to a wide range of water stress from one or two sampled traits, increasing the ability to rapidly characterize drought tolerance across diverse species. Analyzing these correlations also identified correlations among the leaf and stem hydraulic traits and the wilting point, or turgor loss point, beyond those expected from shared ancestry or independent associations with water stress alone. Further, on average, the angiosperm species generally exhibited a sequence of drought tolerance traits that is expected to limit severe tissue damage during drought, such as wilting and substantial stem embolism. This synthesis of the relationships among the drought tolerance traits provides crucial, empirically supported insight into representing variation in multiple traits in models of plant and ecosystem responses to drought.
Ecology Letters (2012) 15: 393–405
Increasing drought is one of the most critical challenges facing species and ecosystems worldwide, and improved theory and practices are needed for quantification ...of species tolerances. Leaf water potential at turgor loss, or wilting (πtlp), is classically recognised as a major physiological determinant of plant water stress response. However, the cellular basis of πtlp and its importance for predicting ecological drought tolerance have been controversial. A meta‐analysis of 317 species from 72 studies showed that πtlp was strongly correlated with water availability within and across biomes, indicating power for anticipating drought responses. We derived new equations giving both πtlp and relative water content at turgor loss point (RWCtlp) as explicit functions of osmotic potential at full turgor (πo) and bulk modulus of elasticity (ε). Sensitivity analyses and meta‐analyses showed that πo is the major driver of πtlp. In contrast, ε plays no direct role in driving drought tolerance within or across species, but sclerophylly and elastic adjustments act to maintain RWCtlp, preventing cell dehydration, and additionally protect against nutrient, mechanical and herbivory stresses independent of drought tolerance. These findings clarify biogeographic trends and the underlying basis of drought tolerance parameters with applications in comparative assessments of species and ecosystems worldwide.
Many species face increasing drought under climate change. Plasticity has been predicted to strongly influence species' drought responses, but broad patterns in plasticity have not been examined for ...key drought tolerance traits, including turgor loss or ‘wilting’ point (πtlp). As soil dries, plants shift πtlp by accumulating solutes (i.e. ‘osmotic adjustment’). We conducted the first global analysis of plasticity in Δπtlp and related traits for 283 wild and crop species in ecosystems worldwide. Δπtlp was widely prevalent but moderate (−0.44 MPa), accounting for 16% of post‐drought πtlp. Thus, pre‐drought πtlp was a considerably stronger predictor of post‐drought πtlp across species of wild plants. For cultivars of certain crops Δπtlp accounted for major differences in post‐drought πtlp. Climate was correlated with pre‐ and post‐drought πtlp, but not Δπtlp. Thus, despite the wide prevalence of plasticity, πtlp measured in one season can reliably characterise most species' constitutive drought tolerances and distributions relative to water supply.
The mechanisms governing tree drought mortality and recovery remain a subject of inquiry and active debate given their role in the terrestrial carbon cycle and their concomitant impact on climate ...change. Counter‐intuitively, many trees do not die during the drought itself. Indeed, observations globally have documented that trees often grow for several years after drought before mortality. A combination of meta‐analysis and tree physiological models demonstrate that optimal carbon allocation after drought explains observed patterns of delayed tree mortality and provides a predictive recovery framework. Specifically, post‐drought, trees attempt to repair water transport tissue and achieve positive carbon balance through regrowing drought‐damaged xylem. Furthermore, the number of years of xylem regrowth required to recover function increases with tree size, explaining why drought mortality increases with size. These results indicate that tree resilience to drought‐kill may increase in the future, provided that CO2 fertilisation facilitates more rapid xylem regrowth.
Stomata, the microvalves on leaf surfaces, exert major influences across scales, from plant growth and productivity to global carbon and water cycling. Stomatal opening enables leaf photosynthesis, ...and plant growth and water use, whereas plant survival of drought depends on stomatal closure. Here we report that stomatal function is constrained by a safety-efficiency trade-off, such that species with greater stomatal conductance under high water availability (g
) show greater sensitivity to closure during leaf dehydration, i.e., a higher leaf water potential at which stomatal conductance is reduced by 50% (Ψ
). The g
- Ψ
trade-off and its mechanistic basis is supported by experiments on leaves of California woody species, and in analyses of previous studies of the responses of diverse flowering plant species around the world. Linking the two fundamental key roles of stomata-the enabling of gas exchange, and the first defense against drought-this trade-off constrains the rates of water use and the drought sensitivity of leaves, with potential impacts on ecosystems.
Summary
Amazonian droughts are predicted to become increasingly frequent and intense, and the vulnerability of Amazonian trees has become increasingly documented. However, little is known about the ...physiological mechanisms and the diversity of drought tolerance of tropical trees due to the lack of quantitative measurements.
Leaf water potential at wilting or turgor loss point (πtlp) is a determinant of the tolerance of leaves to drought stress and contributes to plant‐level physiological drought tolerance. Recently, it has been demonstrated that leaf osmotic water potential at full hydration (πo) is tightly correlated with πtlp. Estimating πtlp from osmometer measurements of πo is much faster than the standard pressure–volume curve approach of πtlp determination. We used this technique to estimate πtlp for 165 trees of 71 species, at three sites within forests in French Guiana. Our data set represents a significant increase in available data for this trait for tropical tree species.
Tropical trees showed a wider range of drought tolerance than previously found in the literature, πtlp ranging from −1·4 to −3·2 MPa. This range likely corresponds in part to adaptation and acclimation to occasionally extreme droughts during the dry season.
Leaf‐level drought tolerance varied across species, in agreement with the available published observations of species variation in drought‐induced mortality. On average, species with a more negative πtlp (i.e. with greater leaf‐level drought tolerance) occurred less frequently across the region than drought‐sensitive species.
Across individuals, πtlp correlated positively but weakly with leaf toughness (R2 = 0·22, P = 0·04) and leaf thickness (R2 = 0·03, P = 0·03). No correlation was detected with other functional traits (leaf mass per area, leaf area, nitrogen or carbon concentrations, carbon isotope ratio, sapwood density or bark thickness).
The variability in πtlp among species indicates a potential for highly diverse species responses to drought within given forest communities. Given the weak correlations between πtlp and traditionally measured plant functional traits, vegetation models seeking to predict forest response to drought should integrate improved quantification of comparative drought tolerance among tree species.
Lay Summary
Forest leaf area has enormous leverage on the carbon cycle because it mediates both forest productivity and resilience to climate extremes. Despite widespread evidence that trees are capable of ...adjusting to changes in environment across both space and time through modifying carbon allocation to leaves, many vegetation models use fixed carbon allocation schemes independent of environment, which introduces large uncertainties into predictions of future forest responses to atmospheric CO2 fertilization and anthropogenic climate change. Here, we develop an optimization‐based model, whereby tree carbon allocation to leaves is an emergent property of environment and plant hydraulic traits. Using a combination of meta‐analysis, observational datasets, and model predictions, we find strong evidence that optimal hydraulic–carbon coupling explains observed patterns in leaf allocation across large environmental and CO2 concentration gradients. Furthermore, testing the sensitivity of leaf allocation strategy to a diversity in hydraulic and economic spectrum physiological traits, we show that plant hydraulic traits in particular have an enormous impact on the global change response of forest leaf area. Our results provide a rigorous theoretical underpinning for improving carbon cycle predictions through advancing model predictions of leaf area, and underscore that tree‐level carbon allocation to leaves should be derived from first principles using mechanistic plant hydraulic processes in the next generation of vegetation models.
Forest leaf area mediates both forest productivity and tree resilience to climate extremes. Here, we develop an optimization‐based model, whereby tree carbon allocation to leaves is an emergent property of environment and plant hydraulic traits. Using a combination of meta‐analysis, observational datasets, and model predictions, we find strong evidence that optimal hydraulic–carbon coupling explains observed patterns in leaf allocation across large environmental gradients. Our results provide a theoretical underpinning for improving terrestrial productivity predictions through advancing model predictions of leaf area, and underscore that tree‐level carbon allocation to leaves should be derived from first principles using mechanistic plant hydraulic processes.
Purpose
The purpose of this study is to explore factors that help to determine employee trust in and affective commitment toward the organization.
Design/methodology/approach
Data for this study were ...collected using surveys administered to employees of a company located in the southeastern United States. The final sample included 391 matched supervisor–subordinate dyads.
Findings
We found organizational signals of trustworthiness led to affective commitment through increased levels of employee trust. Employees and supervisors who perceived HR professionals to be competent, who felt organizational information distributions were of high quality and who felt the organization disclosed relevant information exhibited higher levels of trust in the organization. Employees showed higher affective commitment when they trusted the organization. We found that supervisor trust directly impacted subordinate affective commitment as well.
Originality/value
These findings help extend signaling theory from the attraction of employees to their retention and help researchers and practitioners alike to understand the organizational trust- and commitment-building process.
Background Frequent perioperative morbidity and mortality have been observed in randomized surgical studies for gastric cancer, but specific patient factors associated with morbidity and mortality ...after total gastrectomy have not been well characterized. Methods We queried the American College of Surgeons National Surgical Quality Improvement Program database (2005–2011) for all patients with a gastric neoplasm undergoing total gastrectomy. Univariate and multivariate logistic regression analyses were performed to identify factors associated with an increased risk of morbidity or mortality. Results In 1,165 patients undergoing total gastrectomy, 416 patients (36%) experienced a complication, and 55 died (4.7%) within 30 days of operation. In a reduced multivariate model, age >70 years, preoperative weight loss, splenectomy, and pancreatectomy were associated with morbidity, whereas age >70 years, weight loss, albumin <3 g/dL, and pancreatectomy were associated with mortality ( P < .05 each). The number of present preoperative risk factors stratified morbidity from 26 to 46%, with an adjacent organ resection (splenectomy, pancreatectomy) associated with 56% morbidity. Similarly, mortality rates ranged from 0.4% in those without risk factors to 5 of 9 patients with all three preoperative factors present. Patients undergoing pancreatectomy had a 13% mortality rate. Conclusion Total gastrectomy for malignancy is associated with substantial morbidity and mortality. Identification of high-risk factors may allow more rational patient selection or sequencing of therapy.
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