Leaf Turgor Research Articles

Physiological mechanisms preventing plant wilting under heat stress: a case study on a wheat (Triticum durum Desf.) bound water-mutant

Wilting is the main symptom of plants suffering the dehydration stresses, but the mechanisms governing this phenomenon are yet to be completely understood. In this work, a holistic analysis of physiological traits potentially involved in leaf wilting was performed, comparing a wheat wild type (WT), Trinakria and its water-mutant (WM) with a “high affinity for bound water (BW)”. In addition to the tendency to wilt, significant differences between genotypes were observed for leaf temperature achieved under heat stress, leaf turgor loss with decreasing water potential, cuticular transpiration, and Q10 of leaf water uptake velocity. We hypothesize that mutant plants prevent the increase in leaf temperature thanks to the rapid and low energetic cost of water diffusion from the vessels to the outside, driven by the BW. Under strong thermal-induced dehydration stress, BW delays leaf wilting through its positive effects on cell wall elasticity and passive osmoregulation.

Intraspecific variations of leaf hydraulic, economic, and anatomical traits in Cinnamomum camphora along an urban-rural gradient

Urbanization brings numerous benefits to residents, but it also introduces complex, variable, and heterogeneous habitat conditions to urban plants, resulting in an arid and hot urban environment that decreases tree growth and the ecological service capacity of trees. In this study, we evaluated leaf hydraulic, economic, and anatomical traits and their covariations of Cinnamomum camphora along an urban-rural gradient in Hefei, Eastern China. We found that Cinnamomum camphora in urban adopted a conservative hydraulic strategy with low leaf turgor loss point (Tlp), leaf hydraulic conductance (Kleaf), and leaf water potential resulting in 50 % loss of hydraulic conductance (P50), as well as a quick investment-return economic strategy with low unit leaf dry matter content (LMA) and high leaf nitrogen content (Leaf N). P50, Kleaf and LMA were significantly positively correlated with the urban-rural gradient (PC1urban-rural gradient), while Leaf N exhibited a negative correlation with it. The results showed a trade-off between intraspecific safety and efficiency in leaf hydraulic traits along the urban-rural gradient and an intraspecific coordinated variation in leaf hydraulic and economic traits. In addition, based on the analysis of a trait coordination network, it was revealed that leaf mesophyll and stomata were key structures for trait adjustment and coordination. Furthermore, our findings offer a significant theoretical underpinning for the effective management of landscape trees and the strategic planning of urban tree species.

Assessment of drought resistance in plants of the genus Aristolochia L.

The examination of plant resistance to drought is becoming increasingly relevant due to global warming. All species of the genus Aristolochia L. possess high decorative qualities and play an important role in natural ecosystems. However, under conditions of temperature imbalance, their ornamental value may decrease due to leaf turgor loss and even leaf shedding. The purpose of the paper is to highlight the results of studies on the drought resistance assessment of Aristolochia L. plant species to identify the most promising taxa suitable for cultivation in the city of Kyiv. The study was conducted in 2022 on three species of vines: Aristolochia macrophylla Lam., A. tomentosa Sims., A. manshuriensis Kom., which grow in the M.M. Gryshko National Botanical Garden (Kyiv). The study presented results on leaf hydration parameters, water deficit, water-holding capacity of leaves, electrical conductivity, and specific leaf area conducted in the Plant Physiology and Microbiology Laboratory of the Institute of Horticulture, National Academy of Agrarian Sciences of Ukraine. Field assessment of Aristolochia L. plant drought resistance was also conducted. It was established that Aristolochia macrophylla Lam. is the most drought-resistant species, exhibiting low transpiration rates and high water-holding capacity. Aristolochia tomentosa Sims. it is the least drought-resistant species, which therefore needs additional care. In field conditions, significant signs of wilting were not observed, indicating that leaves reduce turgor during the day and recover at night. It is also important to preserve the environment in which these plants grow, as its changes affect the drought tolerance and life cycle of lianas. The results of the drought resistance research on Aristolochia L. plants point to the potential of these species. They can be used for selecting plant assortments for creating various types of plantations in urban environments

Large leaf hydraulic safety margins limit the risk of drought‐induced leaf hydraulic dysfunction in Neotropical rainforest canopy tree species

Abstract The sequence of key water potential thresholds from the onset of water stress to mortality, and the timing of stomatal closure with regard to leaf xylem embolism formation are essential to characterizing plant adaptive strategies to drought. This constitutes a critical knowledge gap for tropical rainforest species, which may be less vulnerable to drought than previously thought. We recorded key leaf and stem water potential thresholds, leaf hydraulic safety margins (HSMleaf), leaf stomatal safety margins (SSMleaf) and estimated native embolism levels during a normal‐intensity dry season across 18 neotropical rainforest tree species. We also solved a sequence of key water potential thresholds. Additionally, we provide a cross‐biome analysis of SSMleaf encompassing 97 species from four major biomes based on a literature survey. In the studied rainforest species, leaf turgor loss point, used as a surrogate for stomatal closure, typically occurred before the onset of leaf xylem embolism. Most species exhibited positive HSMleaf and SSMleaf, with contrasting values across species and nearly absent embolism levels during the dry season irrespective of the experienced midday leaf water potentials. Our results point out that leaf xylem embolism is not routine for Neotropical rainforest tree species. Based on our proposal of the water potential sequence for tropical rainforest trees, we argue that leaf xylem embolism is a rare event for these species. This was supported by the literature survey, indicating that across biomes, most woody species have rather large SSMleaf and that leaves of tropical rainforest trees are not necessarily more vulnerable than in other biomes. However, we found evidence that some tropical rainforest species may be more vulnerable than others to ongoing climate change. Our data provide an opportunity to parametrize tree‐based or land‐surface models for tropical rainforests. Read the free Plain Language Summary for this article on the Journal blog.

Coordination of hydraulic and morphological traits across dominant grasses in eastern Australia

Abstract Leaf hydraulic traits characterize plant drought tolerance and responses to climate change. Yet, plant hydraulics are biased towards northern hemisphere woody species. We collected rhizomes of several perennial grass species along a precipitation gradient in eastern Australia and grew them in an experimental pot study to investigate potential trade‐offs between drought tolerance and plant morphology. We measured the following leaf hydraulic traits: the leaf water potential (Ψleaf) at 50% and 88% loss of leaf hydraulic conductance (P50Kleaf and P88Kleaf), the Ψleaf at 50% loss of stomatal conductance (P50gs), leaf turgor loss point (TLP), leaf dry matter content (LDMC), leaf modulus of elasticity (ε), and the slope of the relationship between predawn and midday Ψleaf. We also measured basal area, tiller density, seed head density, root collar diameter, plant height, and aboveground biomass of each individual. As expected, grass species varied widely in leaf‐level drought tolerance, with loss of 88% hydraulic conductance occurring at a Ψleaf ranging from −1.52 to −4.01 MPa. However, all but one species lost leaf turgor, and most reached P50gs before this critical threshold. Taller more productive grass species tended to have drought vulnerable leaves characterized by low LDMC and less negative P88Kleaf. Species with greater tiller production experienced stomatal closure and lost turgor at more negative Ψleaf. Although our sample size was limited, we found no relationships between these species' traits and their climate of origin. Overall, we identified important hydraulic and morphological trade‐offs in Australian grasses that were surprisingly similar to those observed for woody plants: (1) xylem of taller species was less drought tolerant and (2) turgor loss occurs and stomatal closure begins before significant loss of Kleaf. These data build upon a small yet growing field of grass hydraulics and may be informative of species responses to further drought intensification in Australia. Read the free Plain Language Summary for this article on the Journal blog.

Traits that distinguish dominant species across aridity gradients differ from those that respond to soil moisture.

Many plant traits respond to changes in water availability and might be useful for understanding ecosystem properties such as net primary production (NPP). This is especially evident in grasslands where NPP is water-limited and primarily determined by the traits of dominant species. We measured root and shoot morphology, leaf hydraulic traits, and NPP of four dominant North American prairie grasses in response to four levels of soil moisture in a greenhouse experiment. We expected that traits of species from drier regions would be more responsive to reduced water availability and that this would make these species more resistant to low soil moisture than species from wetter regions. All four species grew taller, produced more biomass, and increased total root length in wetter treatments. Each species reduced its leaf turgor loss point (TLP) in drier conditions, but only two species (one xeric, one mesic) maintained leaf water potential above TLP. We identified a suite of traits that clearly distinguished species from one another, but, surprisingly, these traits were relatively unresponsive to reduced soil moisture. Specifically, more xeric species produced thinner roots with higher specific root length and had a lower root mass fraction. This suggest that root traits are critical for distinguishing species from one another but might not respond strongly to changing water availability, though this warrants further investigation in the field. Overall, we found that NPP of these dominant grass species responded similarly to varying levels of soil moisture despite differences in species morphology, physiology, and habitat of origin.

Leaf thermal tolerance and sensitivity of temperate tree species are correlated with leaf physiological and functional drought resistance traits

Climate change is causing more frequent and severe climatic events, such as extreme heat and co-occurring drought, potentially accelerating tree mortality. Which tree species will cope better with those extreme events is still being researched. This study focuses on heat as a physiological stress factor and interspecific variation of thermal tolerance and sensitivity traits in 15 temperate coniferous and broad-leaved tree species. We investigate (1) whether thermal tolerance and sensitivity traits correlate with a drought-related physiological trait, particularly the leaf turgor loss point (πtlp, wilting point), and (2) how thermal tolerance and sensitivity traits co-vary within different tree-functional types classified by morphological and physiological traits of the leaf, i.e., leaf mass per area (LMA) and percentage loss of area (PLA). The study was carried out in the Traunstein Forest Dynamics Plot of the ForestGEO network in Germany. The temperature response of the maximum quantum yield of photosystem II (Fv/Fm) on leaf discs was determined, from which various physiological leaf traits were estimated, one of which is the breaking point temperature (T5), the temperature at which Fv/Fm declines by 5%. Additionally, the temperature of 50% (T50) and 95% (T95) decline in Fv/Fm was evaluated. The decline width between T50 and T5 (DWT50−T5) was taken as an indicator of the species’ thermal sensitivity. The breaking point temperature ranged from 35.4 ± 3.0 to 47.9 ± 3.9 °C among the investigated tree species and T50 ranged between 46.1 ± 0.4 and 53.6 ± 0.7 °C. A large interspecific variation of thermal tolerance and sensitivity was found. European ash (Fraxinus excelsior L.) was the most heat-sensitive species, while Wild cherry (Prunus avium L.) was the least heat-sensitive species. Species with a more negative πtlp tended to have a higher breaking point temperature than species with a less negative πtlp. A lower thermal sensitivity characterized species with a higher LMA, and high PLA was found in species with low thermal sensitivity. Accordingly, species with thicker and tougher leaves have lower thermal sensitivity which coincides with a lower wilting point. We conclude that species that develop drought-adapted foliage can cope better with heat stress. Further, they might be able to maintain transpirational cooling during combined heat and drought stress, which could lessen their mortality risk during climatic extremes.

인삼 재배 시 양분수준이 침수피해에 미치는 영향

Background: Nutrient conditions during plant growth may affect tolerance to abiotic stresses. This study investigated whether the waterlogging stress of ginseng (Panax ginseng C. A. Meyer) is affected by nutrient supply.BRMethods and Results: Two-year-old ginseng was cultured under nutrient-deficient (ND), -moderate (NM), and -excessive (NE) conditions, and waterlogging treatment was implemented for 3 days in August. Waterlogging caused the loss of chlorophyll, a decrease in leaf turgor, and withering of the shoots. Waterlogging-induced damage to the shoots was highest under the ND condition, and it was minimal under the NE condition. Photosynthesis and stomatal conductance were decreased by waterlogging under all nutrient conditions, and the maximum quantum yield (Fv/Fm) was highest for the NE condition. Waterlogging resulted in root rot and the loss of fine roots. Root rot after waterlogging was minimal under the NM condition. After waterlogging, root length and root weight were highest under the NM condition. The amino acid and sucrose content were also highest under the NM condition, before and after waterlogging. The saponin content was dependent on the nutrient levels, but was barely affected by waterlogging.BRConclusions: The findings of this study suggest that soil nutrient management as a standard condition during standard ginseng cultivation contributes to minimizing waterlogging stress.

Biochemical Effects of Drought Stress in Some Strawberry Cultivars

This research was 2016-2017 years of the Selcuk University Faculty of Agriculture Department of Horticulture Research and practice was carried out in the greenhouse. Study the Yalova Atatürk Central Horticultural Research Institute, Ata-77, Bolverim-77, Doruk-77, Dorukhan-77, Eren-77, Erenoğlu-77, and Hilal-77 strawberry varieties. After the planted strawberry seedlings reached the 5-6 leaf stage, after irrigation at field capacity, drought application was made until the plants lost their leaf turgor. After implementation of the varieties of drought with healing and drought period of watering again losses to determine. In strawberry cultivars, significant decreases occurred in the amount of protein with the application of drought. In the recovery period after the drought, the protein amounts increased again. Drought treatment significantly increased proline content in all cultivars compared to control. Catalase enzyme activity in all strawberry cultivars increased significantly as a result of drought application in both years. There was a slight decrease in the recovery period. In both years of the study, drought application increased the peroxidase enzyme activity in all strawberry cultivars compared to the control, and a slight decrease occurred in the recovery period compared to the drought application. Drought application in cultivars increased the superoxide dismutase enzyme activity a little compared to the control, while the activity decreased to the control level during the recovery period.

Strigolactone (GR24) Application Positively Regulates Photosynthetic Attributes, Stress-Related Metabolites and Antioxidant Enzymatic Activities of Ornamental Sunflower (Helianthus annuus cv. Vincent’s Choice) under Salinity Stress

Strigolactones, a new group of phytohormones, are reported to improve plant tolerance to multiple abiotic stresses. A pot experiment was conducted to investigate the impact of synthetic strigolactone (GR24 at 0.001, 0.01 and 0.1 mg L−1) application on ornamental sunflowers (Helianthus annuus cv. Vincent’s Choice) grown under salt stress (150 mM NaCl). Salt stress was applied after 14 days, and SL was applied 25 days seed sowing. The results showed that amongst various GR24 concentrations, 0.01 mg L−1 proved to be superior, as it enhanced the photosynthetic rate (9.29%), transpiration rate (0.76%), stomatal conductance (77.5%), total soluble protein (0.55%) and K+ (14.63% in roots; 14.87% in shoots) and Ca2+ (12.63% in roots; 11.48% in shoots) contents under control conditions. Similarly, the leaf turgor potential (Ψp), osmotic potential (Ψs) and free proline, glycinebetaine (GB), superoxide dismutase (SOD), catalase (CAT) and peroxide (POD) contents increased by 58.17, 89.95, 159.04, 101.54, 74.42, 175.68 and 53.62%, respectively, under salt stress conditions. The leaf water potential (Ψw) decreased (−0.14%) and the malondialdehyde (MDA) content increased (16.65%) when treated with the 0.001 mg L−1 GR24 level. Meanwhile, hydrogen peroxide (H2O2) and Na+ concentrations in roots and shoots increased by 62.53%, 74.66% and 38.55% under saline conditions with a GR24 level of 0 mg L−1. Regarding the plant biomass, a GR24 level of 0.01 mg L−1 with salt stress greatly decreased the root (−47.27% and −50.45%) and shoot (−44.79% and −59.42%) fresh and dry weights, respectively, compared to control conditions. These results reveal that exogenously applied GR24 might be an effective way to mitigate the perilous impacts of salt stress in ornamental sunflower production. It is suggested that the use of molecular techniques to study different processes in which GR24 could play a vital part in various commercial floricultural crops is extremely imperative and can open novel horizons for future investigations in this exhilarating field of plant hormones.

Carya Species for Use in the Managed Landscape: Predicted Drought Tolerance

Impressive ornamental features including exfoliating bark and golden fall color are among the reasons why hickories [Carya (Nutt.)] are sought after by horticulturists. Their potential for application in the green industry continues to grow as producers and consumers in the United States become more interested in adopting native plants; however, an absence of knowledge that defines which species are tolerant of abiotic stresses in the landscape limits their use. If production of stress-tolerant hickories increases, they could be used to diversify urban forests and may bolster the resiliency of managed landscapes. We examined the predicted leaf water potential at the turgor loss point to estimate drought tolerance among several species of hickories and pecans adapted to growing in northern climates in the United States. Our hypotheses were that because some bottomland habitats experience seasonal drought in addition to flooding, taxa adapted to these sites may be more drought tolerant than previously assumed, and that the degree of drought tolerance would be variable within species and populations. Predicted mean leaf turgor loss measured in summer across species was −3.38 MPa. Kingnut hickory [Carya laciniosa (F. Michx.) Loud.] exhibited the lowest mean summer leaf turgor loss point −3.64 MPa), whereas pignut hickory [Carya glabra (Mill.) Sweet.] exhibited the highest (−3.20 MPa). Provenance of trees studied influenced estimated drought tolerance of C. laciniosa. Variability between individual trees within each species was observed, suggesting clonal selections of each taxon can be made for drought-prone landscapes. The results of this work imply that all the species studied are at least moderately drought tolerant and should be considered for planting in managed landscapes. Further, species often associated with riparian habitats may exhibit substantial tolerance to drought and should not be excluded from use on drought-prone sites.

Dual effect of the presence of fruits on leaf gas exchange and water relations of olive trees.

The presence of fruits provokes significant modifications in plant water relations and leaf gas exchange. The underlying processes driving these modifications are still uncertain and likely depend on the water deficit level. Our objective was to explain and track the modification of leaf-water relations by the presence of fruits and water deficit. With this aim, net photosynthesis rate (AN), stomatal conductance (gs), leaf osmotic potential (Ψπ), leaf soluble sugars and daily changes in a variable related to leaf turgor (leaf patch pressure) were measured in olive trees with and without fruits at the same time, under well-watered (WW) and water stress (WS) conditions. Leaf gas exchange was increased by the presence of fruits, this effect being observed mainly in WW trees, likely because under severe water stress, the dominant process is the response of the plant to the water stress and the presence of fruits has less impact on the leaf gas exchange. Ψπ was also higher for WW trees with fruits than for WW trees without fruits. Moreover, leaves from trees without fruits presented higher concentrations of soluble sugars and starch than leaves from trees with fruits for both WW and WS, these differences matching those found in Ψπ. Thus, the sugar accumulation would have had a dual effect because on one hand, it decreased Ψπ, and on the other hand, it would have downregulated AN, and finally gs in WW trees. Interestingly, the modification of Ψπ by the presence of fruits affected turgor in WW trees, the change in which can be identified with leaf turgor sensors. We conclude that plant water relationships and leaf gas exchange are modified by the presence of fruits through their effect on the export of sugars from leaves to fruits. The possibility of automatically identifying the onset of sugar demand by the fruit through the use of sensors, in addition to the water stress produced by soil water deficit and atmosphere drought, could be of great help for fruit orchard management in the future.

How do functional traits influence tree demographic properties in a subtropical monsoon forest?

Abstract Functional traits are good predictors of plant responses and adaptations to ever‐changing environments. However, forecasting forest community dynamics is challenging because the relationships among different tree demographic properties (growth, mortality and recruitment) and how functional traits are associated with tree demography remain largely unknown. Here, in a 20‐ha subtropical forest permanent plot, we quantified the rates of tree growth, mortality and recruitment across 53 dominant tree species (diameter at breast height; DBH ≥ 1 cm) from 2005 to 2020. Functional traits that are closely related to plant photosynthesis, nutrients, hydraulics and drought tolerance were measured. We found that tree growth rate (GR) varied independently from rates of tree mortality and recruitment. Hydraulic conductivity was positively correlated with GR (explaining 27% variation—the strongest relationship observed) whereas wood density was negatively correlated with GR. Leaf life span was negatively related to tree mortality. Species with high carbon assimilation rate, nutrient concentration and hydraulic conductivity had high recruitment rates. Leaf turgor loss point was unrelated to plant demography. Principal component analysis revealed that species with quick resource acquisition rates had high rates of growth and recruitment. Our results illustrate that the correlations among tree demographic properties were weak in this subtropical forest with monsoonal climate. Most notably, against expectations, there was no observed trade‐off between growth and mortality. Individual functional traits explained up to 27% of each demographic rate. Variation in recruitment rate was aligned with traits indexing the leaf economic spectrum and also plant hydraulic variation. A better understanding of the role of disturbances on trait–demography relationships would help build a deeper and more nuanced understanding of the ecology of subtropical monsoon forests. Read the free Plain Language Summary for this article on the Journal blog.

Lack of Tradeoff between Leaf Hydraulic Efficiency and Safety across Six Contrasting Water-Stress Tolerant Fruit Tree Species

Water deficits affect the capacity of leaves to transport water, a process that is related to the obstruction of air in the xylem (embolism). The tolerance to this process has been negatively associated with water-transport efficiency at the xylem level across species, suggesting a tradeoff between hydraulic efficiency and safety. But there is a lack of observation at higher integration levels, i.e., organs. This study aimed to evaluate this tradeoff across six fruit tree species with a wide range of water-stress tolerance: pomegranate, olive, fig tree, mandarin, avocado, and vine. Efficiency was represented by the maximum foliar hydraulic conductance (Kmax) and stomatal conductance, whereas hydraulic security by water potential in which the leaf loses 50% of its water-transport capacity (P50), and at the point of loss of leaf turgor (Ψtlp). Results suggest that the compensation is weak or null at the foliar level. We observed that species with higher hydraulic efficiency tend to be more tolerant to leaf dehydration (higher hydraulic safety), except mandarin, which had lower Kmax and relatively higher P50. Morphological traits associated with carbon investment dynamic (leaf mass per area and petiole density) were highly correlated to water-stress tolerance across fruit tree species.

Projections of leaf turgor loss point shifts under future climate change scenarios.

Predicting the consequences of climate change is of utmost importance to mitigate impacts on vulnerable ecosystems; plant hydraulic traits are particularly useful proxies for predicting functional disruptions potentially occurring in the near future. This study assessed the current and future regional patterns of leaf water potential at turgor loss point (Ψtlp ) by measuring and projecting the Ψtlp of 166 vascular plant species (159 angiosperms and 7 gymnosperms) across a large climatic range spanning from alpine to Mediterranean areas in NE Italy. For angiosperms, random forest models predicted a consistent shift toward more negative values in low-elevation areas, whereas for gymnosperms the pattern was more variable, particularly in the alpine sector (i.e., Alps and Prealps). Simulations were also developed to evaluate the number of threatened species under two Ψtlp plasticity scenarios (low vs. high plasticity), and it was found that in the worst-case scenario approximately 72% of the angiosperm species and 68% of gymnosperms within a location were at risk to exceed their physiological plasticity. The different responses to climate change by specific clades might produce reassembly in natural communities, undermining the resilience of natural ecosystems to climate change.

Leaf turgor loss point is one of the best predictors of drought-induced tree mortality in tropical forest

Accurately predicting global drought-induced tree mortality remains a major challenge facing plant science and ecology. Stem hydraulic safety margin (HSM, the difference between water potential at the minimum value and the value that causes xylem vulnerability to embolism) performs as one of the best hydraulic traits in predicting global drought-induced tree mortality, however, HSM is time-consuming and very difficult to measure. We proposed to use leaf turgor loss point (TLP, the water potential at which leaves start to wilt) as a proxy for HSM because HSM may be highly correlated to TLP, as both of them are tightly linked with water potential changes after stomatal closure. Since TLP is more easy and rapid to measure than HSM, if we find strong HSM-TLP relationships at the global scale, TLP can be used in predicting global drought-induced tree mortality. However, no study has quantified the relationships between HSM and TLP at the global scale. Here we draw together published data on HSM and TLP for 1,773 species from 370 sites worldwide to check whether HSM and TLP are highly associated. We found that HSMs and TLPs are merely highly related in tropical forests, thus TLP can be a reliable surrogate of HSM to predict drought-induced tree mortality in tropical forest. Here we are certainly not advocating for the use of TLP instead of HSM to predict drought-induced tree mortality in tropical forests, but simply for predicting drought-induced tree mortality in tropical forests in supplementary of HSM in the future.

Selection strategies to introgress water deficit tolerance derived from Solanum galapagense accession LA1141 into cultivated tomato.

Crop wild relatives have been used as a source of genetic diversity for over one hundred years. The wild tomato relative Solanum galapagense accession LA1141 demonstrates the ability to tolerate deficit irrigation, making it a potential resource for crop improvement. Accessing traits from LA1141 through introgression may improve the response of cultivated tomatoes grown in water-limited environments. Canopy temperature is a proxy for physiological traits which are challenging to measure efficiently and may be related to water deficit tolerance. We optimized phenotypic evaluation based on variance partitioning and further show that objective phenotyping methods coupled with genomic prediction lead to gain under selection for water deficit tolerance. The objectives of this work were to improve phenotyping workflows for measuring canopy temperature, mapping quantitative trait loci (QTLs) from LA1141 that contribute to water deficit tolerance and comparing selection strategies. The phenotypic variance attributed to genetic causes for canopy temperature was higher when estimated from thermal images relative to estimates based on an infrared thermometer. Composite interval mapping using BC2S3 families, genotyped with single nucleotide polymorphisms, suggested that accession LA1141 contributed alleles that lower canopy temperature and increase plant turgor under water deficit. QTLs for lower canopy temperature were mapped to chromosomes 1 and 6 and explained between 6.6 and 9.5% of the total phenotypic variance. QTLs for higher leaf turgor were detected on chromosomes 5 and 7 and explained between 6.8 and 9.1% of the variance. We advanced tolerant BC2S3 families to the BC2S5 generation using selection indices based on phenotypic values and genomic estimated breeding values (GEBVs). Phenotypic, genomic, and combined selection strategies demonstrated gain under selection and improved performance compared to randomly advanced BC2S5 progenies. Leaf turgor, canopy temperature, stomatal conductance, and vapor pressure deficit (VPD) were evaluated and compared in BC2S5 progenies grown under deficit irrigation. Progenies co-selected for phenotypic values and GEBVs wilted less, had significantly lower canopy temperature, higher stomatal conductance, and lower VPD than randomly advanced lines. The fruit size of water deficit tolerant selections was small compared to the recurrent parent. However, lines with acceptable yield, canopy width, and quality parameters were recovered. These results suggest that we can create selection indices to improve water deficit tolerance in a recurrent parent background, and additional crossing and evaluation are warranted.

Water availability dictates how plant traits predict demographic rates.

A major goal in ecology is to make generalizable predictions of organism responses to environmental variation based on their traits. However, straightforward relationships between traits and fitness are rare and likely to vary with environmental context. Characterizing how traits mediate demographic responses to the environment may enhance the predictions of organism responses to global change. We synthesized 15 years of demographic data and species-level traits in a shortgrass steppe to determine whether the effects of leaf and root traits on growth and survival depended on seasonal water availability. We predicted that (1) species with drought-tolerant traits, such as lower leaf turgor loss point (TLP) and higher leaf and root dry matter content (LDMC and RDMC), would be more likely to survive and grow in drier years due to higher wilting resistance, (2) these traits would not predict fitness in wetter years, and (3) traits that more directly measure physiological mechanisms of water use such as TLP would best predict demographic responses. We found that graminoids with more negative TLP and higher LDMC and RDMC had higher survival rates in drier years. Forbs demonstrated similar yet more variable responses. Graminoids grew larger in wetter years, regardless of traits. However, in both wet and dry years, graminoids with more negative TLP and higher LDMC and RDMC grew larger than less negative TLP and low LDMC and RDMC species. Traits significantly mediated the impact of drought on survival, but not growth, suggesting that survival could be a stronger driver of species' drought response in this system. TLP predicted survival in drier years, but easier to measure LDMC and RDMC were equal or better predictors. These results advance our understanding of the mechanisms by which drought drives population dynamics, and show that abiotic context determines how traits drive fitness.

Coordination of leaf hydraulic and economic traits in Cinnamomum camphora under impervious pavement

BackgroundPaved urban environments can pose great threats to the physiological functioning and ecological services of street trees. In this context, assessment of leaf phenotypic plasticity is crucial for understanding the ecological strategy of tree species under impervious pavements.ResultsIn this study, we measured a set of leaf economic traits, hydraulic traits of Cinnamomum camphora, and surrounding environmental factors in a street site (the soil was covered by the impervious pavement) and a park site (the soil was covered by grass) in Hefei, eastern China. Compared with the park site, trees in the street site had higher stomatal length (SL), leaf thickness (LT), maximum photochemical quantum yield of photosystem II (Y(II)), and lower stomatal density (SD), specific leaf area (SLA), the leaf water potential at 50% loss of hydraulic conductance (P50), and leaf turgor loss point (TLP). Redundancy analysis showed that air relative humidity and volumetric soil water content caused these traits to be altered.ConclusionsOur results showed that C. camphora adapted to the street pavement environment through the coordination of leaf economic and leaf hydraulic traits, and adopted the slow investment return type in the leaf economic spectrum and high drought resistance to meet its actual physiological needs. This finding provides a new perspective for understanding the physiological strategies of street trees to adapt to urban pavement environments.

Physiological and Structural Responses to Prolonged Water Deficit in Young Trees of Two Olive Cultivars.

This study aimed to characterize the physiological and structural responses of potted one-year-old olive trees belonging to two olive cultivars—‘Nocellara del Belice’ and ‘Cerasuola’—exposed to prolonged drought under greenhouse conditions. Two irrigation treatments based on evapotranspiration (ET) were imposed for 69 days, i.e., well-watered (WW, 100% ET) and drought-stressed (DS, 10–30% ET). Leaf stomatal conductance (gs), stem water potential (Ψstem), transpiration (E), photosynthetic capacity (Amax), water use efficiency (WUE), stem (Kstem) and root (Kroot) hydraulic conductance, trunk diameter variations (TDV), and leaf patch attenuated pressure fluctuations (pp, a proxy of the inverse of leaf turgor pressure) were measured in WW and DS trees at different stages of the experiment. Leaf gs did not significantly differ between cultivars under DS, whereas differences in Ψstem only became significant at the end of prolonged drought, when ‘Nocellara del Belice’ experienced Ψstem < −4 MPa. ‘Cerasuola’ trees expressed the best WUE under drought, although they were more susceptible to photoinhibition under optimal plant water status. Both cultivars tended to increase their Kstem at the end of the drought period. A marked reduction in Kroot occurred in ‘Cerasuola’ plants after prolonged drought; however, a similar mechanism was not observed in ‘Nocellara del Belice’. The ratio between Kstem and Kroot exponentially increased towards the end of the prolonged drought period in both cultivars, but more markedly in ‘Cerasuola’. TDV and pp trends suggested that ‘Cerasuola’ plants keep better plant water status under severe drought compared to ‘Nocellara del Belice’ by maintaining high leaf turgor and reduced trunk diameter fluctuations. These responses may be related to reduced cell wall elasticity and xylem vessel size and/or wall thickness—drought avoidance mechanisms. The Kstem/Kroot ratio can serve as an indicator of drought stress avoidance mechanisms to compare genotype-specific responses to drought stress.