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Lawren Sack - One of the best experts on this subject based on the ideXlab platform.
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evolution of leaf structure and Drought Tolerance in species of californian ceanothus
American Journal of Botany, 2018Co-Authors: Leila R Fletcher, Dylan O Burge, Hongxia Cui, Hilary S Callahan, Christine Scoffoni, Grace P John, Megan K Bartlett, Lawren SackAbstract:PREMISE OF THE STUDY Studies across diverse species have established theory for the contribution of leaf traits to plant Drought Tolerance. For example, species in more arid climates tend to have smaller leaves of higher vein density, higher leaf mass per area, and more negative osmotic potential at turgor loss point (πTLP ). However, few studies have tested these associations for species within a given lineage that have diversified across an aridity gradient. METHODS We analyzed the anatomy and physiology of 10 Ceanothus (Rhamnaceae) species grown in a common garden for variation between and within "wet" and "dry" subgenera (Ceanothus and Cerastes, respectively) and analyzed a database for 35 species for leaf size and leaf mass per area (LMA). We used a phylogenetic generalized least squares approach to test hypothesized relationships among traits, and of traits with climatic aridity in the native range. We also tested for allometric relationships among anatomical traits. KEY RESULTS Leaf form, anatomy, and Drought Tolerance varied strongly among species within and between subgenera. Cerastes species had specialized anatomy including hypodermis and encrypted stomata that may confer superior water storage and retention. The osmotic potentials at turgor loss point (πTLP ) and full turgor (πo ) showed evolutionary correlations with the aridity index (AI) and precipitation of the 10 species' native distributions, and LMA with potential evapotranspiration for the 35 species in the larger database. We found an allometric correlation between upper and lower epidermal cell wall thicknesses, but other anatomical traits diversified independently. CONCLUSIONS Leaf traits and Drought Tolerance evolved within and across lineages of Ceanothus consistently with climatic distributions. The πTLP has signal to indicate the evolution of Drought Tolerance within small clades.
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Drought Tolerance as a driver of tropical forest assembly resolving spatial signatures for multiple processes
Ecology, 2016Co-Authors: Megan K Bartlett, Ya Zhang, Jie Yang, Nissa Kreidler, Yuehua Hu, Lawren SackAbstract:Spatial patterns in trait variation reflect underlying community assembly processes, allowing us to test hypotheses about their trait and environmental drivers by identifying the strongest correlates of characteristic spatial patterns. For 43 evergreen tree species (g 1 cm dbh) in a 20-ha seasonal tropical rainforest plot in Xishuangbanna, China, we compared the ability of Drought-Tolerance traits, other physiological traits, and commonly measured functional traits to predict the spatial patterns expected from the assembly processes of habitat associations, niche-overlap-based competition, and hierarchical competition. We distinguished the neighborhood--scale (0-20 m) patterns expected from competition from larger-scale habitat associations with a wavelet method. Species' Drought Tolerance and habitat variables related to soil water supply were strong drivers of habitat associations, and Drought Tolerance showed a significant spatial signal for influencing competition. Overall, the traits most strongly associated with habitat, as quantified using multivariate models, were leaf density, leaf turgor loss point (pi(tlp); also known as the leaf wilting point), and stem hydraulic conductivity (r(2) range for the best fit models = 0.27-0.36). At neighborhood scales, species spatial associations were positively correlated with similarity in pi(tlp), consistent with predictions for hierarchical competition. Although the correlation between pi(tlp) and interspecific spatial associations was weak (r(2) l 0.01), this showed a persistent influence of Drought Tolerance on neighborhood interactions and community assembly. Quantifying the full impact of traits on competitive interactions in forests may require incorporating plasticity among individuals within species, especially among specific life stages, and moving beyond individual traits to integrate the impact of multiple traits on whole-plant performance and resource demand.
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Drought Tolerance as predicted by leaf water potential at turgor loss point varies strongly across species within an amazonian forest
Functional Ecology, 2015Co-Authors: Megan K Bartlett, Lawren Sack, Isabelle Marechaux, Christopher Baraloto, Julien Engel, Emilie Joetzjer, Jerome ChaveAbstract: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.
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rapid determination of comparative Drought Tolerance traits using an osmometer to predict turgor loss point
Methods in Ecology and Evolution, 2012Co-Authors: Megan K Bartlett, Christine Scoffoni, Rico Chandra Ardy, Ya Zhang, Shanwen Sun, Kunfang Cao, Lawren SackAbstract:1. Across plant species, Drought Tolerance and distributions with respect to water availability are strongly correlated with two physiological traits, the leaf water potential at wilting, that is, turgor loss point (ptlp), and the cell solute potential at full hydration, that is, osmotic potential (po). We present methods to determine these parameters 30 times more rapidly than the standard pressurevolume (pv) curve approach, making feasible community-scale studies of plant Drought Tolerance. 2. We optimized existing methods for measurements of pi o using vapour-pressure osmometry of freeze-thawed leaf discs from 30 species growing in two precipitation regimes, and developed the first regression relationships to accurately estimate pressurevolume curve values of both pi o and pi tlp from osmometer values. 3. The pi o determined with the osmometer (pi osm) was an excellent predictor of the pi o determined from the pv curve (pi pv,r2 = 0.80). Although the correlation of pi osm and pi pv enabled prediction, the relationship departed from the 1 : 1 line. The discrepancy between the methods could be quantitatively accounted for by known sources of error in osmometer measurements, that is, dilution by the apoplastic water, and solute dissolution from destroyed cell walls. An even stronger prediction of pi pv could be made using pi osm, leaf density (rho), and their interaction (r2 = 0.85, all P l 2 x 10-10). 4. The pi osm could also be used to predict pi tlp (r2 = 0.86). Indeed, pi osm was a better predictor of pi tlp than leaf mass per unit area (LMA; r2 = 0.54), leaf thickness (T; r2 = 0.12), rho (r2 = 0.63), and leaf dry matter content (LDMC; r2 = 0.60), which have been previously proposed as Drought Tolerance indicators. Models combining posm with LMA, T, rho, or LDMC or other pv curve parameters (i.e. elasticity and apoplastic fraction) did not significantly improve prediction of pi tlp. 5. This osmometer method enables accurate measurements of Drought Tolerance traits across a wide range of leaf types and for plants with diverse habitat preferences, with a fraction of effort of previous methods. We expect it to have wide application for predicting species responses to climate variability and for assessing ecological and evolutionary variation in Drought Tolerance in natural populations and agricultural cultivars.
Jonathan P. Lynch - One of the best experts on this subject based on the ideXlab platform.
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Reduced Lateral Root Branching Density Improves Drought Tolerance in Maize
Plant physiology, 2015Co-Authors: Ai Zhan, Hannah M. Schneider, Jonathan P. LynchAbstract:An emerging paradigm is that root traits that reduce the metabolic costs of soil exploration improve the acquisition of limiting soil resources. Here, we test the hypothesis that reduced lateral root branching density will improve Drought Tolerance in maize (Zea mays) by reducing the metabolic costs of soil exploration, permitting greater axial root elongation, greater rooting depth, and thereby greater water acquisition from drying soil. Maize recombinant inbred lines with contrasting lateral root number and length (few but long [FL] and many but short [MS]) were grown under water stress in greenhouse mesocosms, in field rainout shelters, and in a second field environment with natural Drought. Under water stress in mesocosms, lines with the FL phenotype had substantially less lateral root respiration per unit of axial root length, deeper rooting, greater leaf relative water content, greater stomatal conductance, and 50% greater shoot biomass than lines with the MS phenotype. Under water stress in the two field sites, lines with the FL phenotype had deeper rooting, much lighter stem water isotopic signature, signifying deeper water capture, 51% to 67% greater shoot biomass at flowering, and 144% greater yield than lines with the MS phenotype. These results entirely support the hypothesis that reduced lateral root branching density improves Drought Tolerance. The FL lateral root phenotype merits consideration as a selection target to improve the Drought Tolerance of maize and possibly other cereal crops.
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reduced root cortical cell file number improves Drought Tolerance in maize
Plant Physiology, 2014Co-Authors: Joseph G Chimungu, Kathleen M Brown, Jonathan P. LynchAbstract:We tested the hypothesis that reduced root cortical cell file number (CCFN) would improve Drought Tolerance in maize (Zea mays) by reducing the metabolic costs of soil exploration. Maize genotypes with contrasting CCFN were grown under well-watered and water-stressed conditions in greenhouse mesocosms and in the field in the United States and Malawi. CCFN ranged from six to 19 among maize genotypes. In mesocosms, reduced CCFN was correlated with 57% reduction of root respiration per unit of root length. Under water stress in the mesocosms, genotypes with reduced CCFN had between 15% and 60% deeper rooting, 78% greater stomatal conductance, 36% greater leaf CO2 assimilation, and between 52% to 139% greater shoot biomass than genotypes with many cell files. Under water stress in the field, genotypes with reduced CCFN had between 33% and 40% deeper rooting, 28% lighter stem water oxygen isotope enrichment (δ18O) signature signifying deeper water capture, between 10% and 35% greater leaf relative water content, between 35% and 70% greater shoot biomass at flowering, and between 33% and 114% greater yield than genotypes with many cell files. These results support the hypothesis that reduced CCFN improves Drought Tolerance by reducing the metabolic costs of soil exploration, enabling deeper soil exploration, greater water acquisition, and improved growth and yield under water stress. The large genetic variation for CCFN in maize germplasm suggests that CCFN merits attention as a breeding target to improve the Drought Tolerance of maize and possibly other cereal crops.
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large root cortical cell size improves Drought Tolerance in maize
Plant Physiology, 2014Co-Authors: Joseph G Chimungu, Kathleen M Brown, Jonathan P. LynchAbstract:The objective of this study was to test the hypothesis that large cortical cell size (CCS) would improve Drought Tolerance by reducing root metabolic costs. Maize (Zea mays) lines contrasting in root CCS measured as cross-sectional area were grown under well-watered and water-stressed conditions in greenhouse mesocosms and in the field in the United States and Malawi. CCS varied among genotypes, ranging from 101 to 533 µm2. In mesocosms, large CCS reduced respiration per unit of root length by 59%. Under water stress in mesocosms, lines with large CCS had between 21% and 27% deeper rooting (depth above which 95% of total root length is located in the soil profile), 50% greater stomatal conductance, 59% greater leaf CO2 assimilation, and between 34% and 44% greater shoot biomass than lines with small CCS. Under water stress in the field, lines with large CCS had between 32% and 41% deeper rooting (depth above which 95% of total root length is located in the soil profile), 32% lighter stem water isotopic ratio of 18O to 16O signature, signifying deeper water capture, between 22% and 30% greater leaf relative water content, between 51% and 100% greater shoot biomass at flowering, and between 99% and 145% greater yield than lines with small cells. Our results are consistent with the hypothesis that large CCS improves Drought Tolerance by reducing the metabolic cost of soil exploration, enabling deeper soil exploration, greater water acquisition, and improved growth and yield under water stress. These results, coupled with the substantial genetic variation for CCS in diverse maize germplasm, suggest that CCS merits attention as a potential breeding target to improve the Drought Tolerance of maize and possibly other cereal crops.
Jessica M Koczan - One of the best experts on this subject based on the ideXlab platform.
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identification of Drought Tolerance determinants by genetic analysis of root response to Drought stress and abscisic acid
Plant Physiology, 2006Co-Authors: Liming Xiong, Ruigang Wang, Guohong Mao, Jessica M KoczanAbstract:Drought stress is a common adverse environmental condition that seriously affects crop productivity worldwide. Due to the complexity of Drought as a stress signal, deciphering Drought Tolerance mechanisms has remained a major challenge to plant biologists. To develop new approaches to study plant Drought Tolerance, we searched for phenotypes conferred by Drought stress and identified the inhibition of lateral root development by Drought stress as an adaptive response to the stress. This Drought response is partly mediated by the phytohormone abscisic acid. Genetic screens using Arabidopsis (Arabidopsis thaliana) were devised, and Drought inhibition of lateral root growth (dig) mutants with altered responses to Drought or abscisic acid in lateral root development were isolated. Characterization of these dig mutants revealed that they also exhibit altered Drought stress Tolerance, indicating that this root response to Drought stress is intimately linked to Drought adaptation of the entire plant and can be used as a trait to access the elusive Drought Tolerance machinery. Our study also revealed that multiple mechanisms coexist and together contribute to whole-plant Drought Tolerance.
Jahnavi Koppolu - One of the best experts on this subject based on the ideXlab platform.
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genetic dissection of Drought Tolerance in chickpea cicer arietinum l
Theoretical and Applied Genetics, 2014Co-Authors: Rajeev K Varshney, Mahendar Thudi, Spurthi N Nayak, P M Gaur, J Kashiwagi, Lakshmanan Krishnamurthy, Deepa Jaganathan, Jahnavi KoppoluAbstract:Key message Analysis of phenotypic data for 20 Drought Tolerance traits in 1–7 seasons at 1–5 locations together with genetic mapping data for two mapping populations provided 9 QTL clusters of which one present on CaLG04 has a high potential to enhance Drought Tolerance in chickpea improvement.
Megan K Bartlett - One of the best experts on this subject based on the ideXlab platform.
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evolution of leaf structure and Drought Tolerance in species of californian ceanothus
American Journal of Botany, 2018Co-Authors: Leila R Fletcher, Dylan O Burge, Hongxia Cui, Hilary S Callahan, Christine Scoffoni, Grace P John, Megan K Bartlett, Lawren SackAbstract:PREMISE OF THE STUDY Studies across diverse species have established theory for the contribution of leaf traits to plant Drought Tolerance. For example, species in more arid climates tend to have smaller leaves of higher vein density, higher leaf mass per area, and more negative osmotic potential at turgor loss point (πTLP ). However, few studies have tested these associations for species within a given lineage that have diversified across an aridity gradient. METHODS We analyzed the anatomy and physiology of 10 Ceanothus (Rhamnaceae) species grown in a common garden for variation between and within "wet" and "dry" subgenera (Ceanothus and Cerastes, respectively) and analyzed a database for 35 species for leaf size and leaf mass per area (LMA). We used a phylogenetic generalized least squares approach to test hypothesized relationships among traits, and of traits with climatic aridity in the native range. We also tested for allometric relationships among anatomical traits. KEY RESULTS Leaf form, anatomy, and Drought Tolerance varied strongly among species within and between subgenera. Cerastes species had specialized anatomy including hypodermis and encrypted stomata that may confer superior water storage and retention. The osmotic potentials at turgor loss point (πTLP ) and full turgor (πo ) showed evolutionary correlations with the aridity index (AI) and precipitation of the 10 species' native distributions, and LMA with potential evapotranspiration for the 35 species in the larger database. We found an allometric correlation between upper and lower epidermal cell wall thicknesses, but other anatomical traits diversified independently. CONCLUSIONS Leaf traits and Drought Tolerance evolved within and across lineages of Ceanothus consistently with climatic distributions. The πTLP has signal to indicate the evolution of Drought Tolerance within small clades.
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Drought Tolerance as a driver of tropical forest assembly resolving spatial signatures for multiple processes
Ecology, 2016Co-Authors: Megan K Bartlett, Ya Zhang, Jie Yang, Nissa Kreidler, Yuehua Hu, Lawren SackAbstract:Spatial patterns in trait variation reflect underlying community assembly processes, allowing us to test hypotheses about their trait and environmental drivers by identifying the strongest correlates of characteristic spatial patterns. For 43 evergreen tree species (g 1 cm dbh) in a 20-ha seasonal tropical rainforest plot in Xishuangbanna, China, we compared the ability of Drought-Tolerance traits, other physiological traits, and commonly measured functional traits to predict the spatial patterns expected from the assembly processes of habitat associations, niche-overlap-based competition, and hierarchical competition. We distinguished the neighborhood--scale (0-20 m) patterns expected from competition from larger-scale habitat associations with a wavelet method. Species' Drought Tolerance and habitat variables related to soil water supply were strong drivers of habitat associations, and Drought Tolerance showed a significant spatial signal for influencing competition. Overall, the traits most strongly associated with habitat, as quantified using multivariate models, were leaf density, leaf turgor loss point (pi(tlp); also known as the leaf wilting point), and stem hydraulic conductivity (r(2) range for the best fit models = 0.27-0.36). At neighborhood scales, species spatial associations were positively correlated with similarity in pi(tlp), consistent with predictions for hierarchical competition. Although the correlation between pi(tlp) and interspecific spatial associations was weak (r(2) l 0.01), this showed a persistent influence of Drought Tolerance on neighborhood interactions and community assembly. Quantifying the full impact of traits on competitive interactions in forests may require incorporating plasticity among individuals within species, especially among specific life stages, and moving beyond individual traits to integrate the impact of multiple traits on whole-plant performance and resource demand.
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Drought Tolerance as predicted by leaf water potential at turgor loss point varies strongly across species within an amazonian forest
Functional Ecology, 2015Co-Authors: Megan K Bartlett, Lawren Sack, Isabelle Marechaux, Christopher Baraloto, Julien Engel, Emilie Joetzjer, Jerome ChaveAbstract: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.
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rapid determination of comparative Drought Tolerance traits using an osmometer to predict turgor loss point
Methods in Ecology and Evolution, 2012Co-Authors: Megan K Bartlett, Christine Scoffoni, Rico Chandra Ardy, Ya Zhang, Shanwen Sun, Kunfang Cao, Lawren SackAbstract:1. Across plant species, Drought Tolerance and distributions with respect to water availability are strongly correlated with two physiological traits, the leaf water potential at wilting, that is, turgor loss point (ptlp), and the cell solute potential at full hydration, that is, osmotic potential (po). We present methods to determine these parameters 30 times more rapidly than the standard pressurevolume (pv) curve approach, making feasible community-scale studies of plant Drought Tolerance. 2. We optimized existing methods for measurements of pi o using vapour-pressure osmometry of freeze-thawed leaf discs from 30 species growing in two precipitation regimes, and developed the first regression relationships to accurately estimate pressurevolume curve values of both pi o and pi tlp from osmometer values. 3. The pi o determined with the osmometer (pi osm) was an excellent predictor of the pi o determined from the pv curve (pi pv,r2 = 0.80). Although the correlation of pi osm and pi pv enabled prediction, the relationship departed from the 1 : 1 line. The discrepancy between the methods could be quantitatively accounted for by known sources of error in osmometer measurements, that is, dilution by the apoplastic water, and solute dissolution from destroyed cell walls. An even stronger prediction of pi pv could be made using pi osm, leaf density (rho), and their interaction (r2 = 0.85, all P l 2 x 10-10). 4. The pi osm could also be used to predict pi tlp (r2 = 0.86). Indeed, pi osm was a better predictor of pi tlp than leaf mass per unit area (LMA; r2 = 0.54), leaf thickness (T; r2 = 0.12), rho (r2 = 0.63), and leaf dry matter content (LDMC; r2 = 0.60), which have been previously proposed as Drought Tolerance indicators. Models combining posm with LMA, T, rho, or LDMC or other pv curve parameters (i.e. elasticity and apoplastic fraction) did not significantly improve prediction of pi tlp. 5. This osmometer method enables accurate measurements of Drought Tolerance traits across a wide range of leaf types and for plants with diverse habitat preferences, with a fraction of effort of previous methods. We expect it to have wide application for predicting species responses to climate variability and for assessing ecological and evolutionary variation in Drought Tolerance in natural populations and agricultural cultivars.
