Midday Leaf Research Articles

Grafting cv. Grechetto Gentile Vines to New M4 Rootstock Improves Leaf Gas Exchange and Water Status as Compared to Commercial 1103P Rootstock

M4 is a relatively new rootstock that was selected for increased resilience of vineyards across hot regions where meteorological drought is often coupled to water scarcity. However, M4 has thus far been tested only against water-stress sensitive rootstocks. Against this backdrop, the aim of the present work is to examine the water status and gas exchange performances of vines grafted to M4 in comparison to those of vines grafted to a commercial stock that is drought-tolerant, 1103 Paulsen (1103P), under a progressive water deficit followed by re-watering. This study was undertaken on Grechetto Gentile, a cultivar that is renowned for its rather conservative water use (near-isohydric behavior). While fifty percent of both grafts were fully irrigated (WW), the remaining underwent progressive water stress by means of suspending irrigation (WS). Soil and leaf water status, as well as leaf gas exchanges, along with chlorophyll fluorescence, were followed daily from 1 day pre-stress (DOY 176) until re-watering (DOY 184). Final leaf area per vine, divided in main and lateral contribution, was also assessed. While 1103P grafted vines manifested higher water use under WW conditions, progressive stress evidenced a faster water depletion by 1103P, which also maintained slightly more negative midday leaf water potential (Ψleaf) as compared to M4 grafted plants. Daily gas exchange readings, as well as diurnal assessment performed at the peak of stress (DOY 183), also showed increased leaf assimilation rates (A) and water use efficiency (WUE) in vines grafted on M4, which were also less susceptible to photosynthetic downregulation. Dynamic of stomatal closure targeted at 90% reduction of leaf stomatal conductance showed a similar behavior among rootstocks since the above threshold was reached by both at Ψleaf of about −1.11 MPa. The same fractional reduction in leaf A was reached by vines grafted on M4 at a Ψleaf of −1.28 MPa vs. −1.10 MPa measured in 1103P, meaning that using M4 as a rootstock will postpone full stomatal closure. While mechanisms involved in improved CO2 uptake in M4-grafted vines under moderate-to-severe stress are still unclear, our data support the hypothesis that M4 might outscore the performance of a commercial drought-tolerant genotype (1103P) and can be profitably used as a tool to improve the resilience of vines to summer drought.

Photosynthetic traits and plant–water relations of two apple cultivars grown as bi-leader trees under long-term waterlogging conditions

Waterlogging has been one of the major problems in plant cultivation worldwide. As its frequency and severity are increasing in the era of climate change, waterlogging tolerance of fruit cultivars is an important factor that should be considered before plantation. In this study, we investigated leaf morphological traits, photosynthetic responses, and plant–water relations of the two most popular apple cultivars in Korea, Hongro (medium maturing) and Fuji (late maturing), under long-term waterlogging conditions. Experimental bi-leader trees grafted on a single M.9 rootstock were subjected to two irrigation regimes (well-irrigated and waterlogged) for 75 days. Waterlogging stress adversely affected most of the morphological, physiological, and anatomical characteristics as well as the plant–water relations in both cultivars; the negative effects of waterlogging were more pronounced in Hongro than in Fuji. Both cultivars experienced a significant decrease in leaf size, whereas leaf length was reduced significantly in Hongro and leaf width in Fuji. Predawn leaf water potential (ΨPD) decreased with waterlogging, but midday leaf water potential (ΨMD) was more significantly decreased in Hongro than in Fuji under waterlogging. Net photosynthetic rate (Pn) and stomatal conductance (gs) were significantly reduced in both cultivars; the reduction was greater in Hongro than in Fuji. A more pronounced reduction in vessel density, vessel diameter, and stomatal density (Sd) was observed in Hongro than in Fuji, resulting in greater reduction in daily sap flow and hydraulic conductivity in Hongro than in Fuji. These results indicate that Fuji was better adapted to waterlogging, as indicated by fewer changes in morphological, physiological, and anatomical responses when compared with those of Hongro. Our data suggest that the lower reduction in vessel density, vessel area, and vessel diameter in the Fuji cultivar under waterlogging are major factors that improve plant–water relations and photosynthetic performance, which in turn determine the leaf morphological characteristics and vegetative growth under prolonged waterlogging.

Responses to drought stress in Prunus sargentii and Larix kaempferi seedlings using morphological and physiological parameters

The frequency and severity of drought are expected to increase due to climate change; therefore, drought tolerance of tree species should be considered before planting for maximal survival in the field. In this study, we examined the response of drought stress in two of the most popular plantation species: Sargent cherry (Prunus sargentii) and Japanese larch (Larix kaempferi) based on the morphological and physiological characteristics. These plantation species are widely planted in central and northern Asia, especially in Japan and Korea, and also widely used for plantation purpose in northern Europe. Three different irrigation regimes of control (CT; 100% precipitation (P)), light drought (LD; 40% reduction of P), and heavy drought (HD; 80% reduction of P) were applied at the experimental site of Mt. Jiri, the Republic of Korea. For morphological responses, both species experienced a significant decrease in leaf size in drought conditions; however, Sargent cherry and Japanese larch experienced reduced leaf width and length, respectively. On the other hand, leaf mass area (LMA, g cm−2) increased and branch growth decreased in both species under drought conditions. As physiological responses, drought stress significantly decreased maximum photosynthesis rate (Amax) and electron transfer rate (Jmax) for both species, while stomatal conductance (Gs) at Amax significantly decreased only in Sargent cherry. Drought significantly reduced predawn (ΨPD), midday leaf water potential (ΨMD), and transpiration in Sargent cherry but not in Japanese larch. In mid-summer, carbon isotopic composition (δ13C) significantly decreased in Sargent cherry but only showed a reduction tendency in Japanese larch. However, the changes of δ13C were not significant in early summer or mid-fall. In the present study, both species showed isohydric and anisohydric characteristics, but Sargent cherry showed greater anisohydric behavior with a steeper slope (Y = 2.132X) and Japanese larch showed more isohydric behavior with a shallower slope (Y = 1.722X). Our results highlight that both species altered their morphological and physiological responses under drought stress; however, the Japanese larch showed greater resistance and resilience in morphological and physiological responses, and in plant-water relations. Therefore, Japanese larch would be more beneficial for plantations in water deficit regions than Sargent cherry.

Interactions between nurse-plants and an exotic invader along a tropical alpine elevation gradient: growth-form matters

Conceptual models of how interactions with native species influence invasions emphasize competition, but recent evidence suggests facilitation can promote invasion in stressful environments. However, how nurse-plants with contrasting growth-forms and distribution interact with invaders remains unexplored, although it could offer insights on nurse/exotic interaction mechanisms. We asked whether shrub and cushion nurses differed in their effects on the exotic Rumex acetosella in sites at four elevations in the high tropical Andes (4100–4400 m), shrubs dominating the lowest sites and cushions the highest sites. During the dry season, we measured soil organic matter (SOM) and water content (SWC) under the shrub Hypericum laricifolium, the cushion Azorella julianii, and adjacent areas outside. We compared Rumex’s performance under each situation, measuring midday leaf temperatures (Tleaf), vapor pressure deficit (VPD), minimum water potentials (Ψmin) and leaf nitrogen (Nleaf) and compared the number, size and proportion of fruiting ramets within sampling rings in each situation. SOM and SWC were higher at all elevations under cushions, then under shrubs and lower outside. Rumex’s density was generally reduced under shrubs but increased on cushions. However, both nurses had positive effects along the gradient on Rumex’s size, reproduction, water balance and Nleaf, shrubs having stronger effects on Tleaf and VPD and cushions on Nleaf. Our results indicate that alternating nurses influenced an invader’s physiological performance to different extents via contrasting effects on shading and soil resources, leading to mixed competitive/facilitative effects of shrubs on the exotic’s demography, while cushions had more consistent facilitative effects across elevations.

The seasonal regulation of gas exchange and water relations of field grown macadamia

Macadamia F. Muell is a recently domesticated nut crop characterized by a certain amount of drought tolerance. Whilst stomatal regulation of gas exchange and water relations has been documented in macadamia, there are no reports on non-stomatal limitations to photosynthesis and if changes occur over a season in relation to different phenological stages. It was hypothesised that in order for macadamias to be adapted to a seasonally dry native environment the trees would be characterised by strong stomatal control over gas exchange, indicating an isohydric water use strategy that is related to a hydraulic limtation within the tree. However, due to high assimilate demand during nut filling, the level of stomatal control would vary between fruiting and non-fruiting phenological stages. Gas exchange and water relations measurements were made for 18 months on irrigated mature macadamia trees (cv. HAES 695, ‘Beaumont’) in a subtropical region of South Africa. Results confirmed that macadamias had relatively low light-saturated net CO2 assimilation rates (Amax) (8.34 ± 1.21 μmol CO2 m−2 s-1). The low Amax values resulted from relatively high stomatal and non-stomatal limitations and decreasing stomatal conductance (gs) in response to increasing leaf-to-air vapour pressure deficit (VPDleaf) above ca. 2 kPa. Strict stomatal control and nearly constant midday leaf water potential (ψleaf = -1.16 ± 0.43 MPa) confirmed the predominantly isohydric nature of the crop, which seemed to be a result of low hydraulic conductance in the stem to leaf pathway. Significant differences in leaf gas exchange capacity were, however, observed between the fruiting and non-fruiting phenological stages. The presence of fruit resulted in significantly higher Amax (10.27 ± 2.23 μmol CO2 m−2 s−1) compared to non-fruiting periods (Amax = 6.58 ± 2.00 μmol CO2 m−2 s−1). Increases in Amax were mediated by increased rates of electron transport (Jmax) and triose phosphate use (TPU). Fruiting stages were also characterized by variable responses of gs to increases in VPDleaf, which indicated varying degrees of isohydricity. This study reaffirms that macadamias are inherently adapted to seasonally dry environments, characterized by strict stomatal control, yet under humid conditions or in the presence of developing fruit, macadamias are proposed to deviate from a purely isohydric water management strategy.

Drought survival is positively associated with high turgor loss points in temperate perennial grassland species

Abstract Turgor loss point (πtlp) has been suggested to be a key trait for drought resistance in woody species. In herbaceous grassland species, the role of πtlp for species drought survival has not yet been tested, although grasslands are projected to experience more frequent and intense droughts with climate change. To gain insights into the role of πtlp for drought resistance of temperate perennial grassland species, we assessed πtlp of 41 species common in Germany (20 forbs, 21 grasses). We directly related them to the species’ comparative whole‐plant drought survival and midday leaf water potentials under drought (ΨMD) assessed in a common garden drought experiment, and to species moisture association. Species drought survival increased with increasing πtlp across all species as well as within forbs or grasses separately. ΨMD was positively related to πtlp and drought survival. Our results imply that high πtlp promotes drought survival of common perennial European temperate mesic grassland species by enabling them to maintain high leaf water potentials under drought, that is, a desiccation avoidance strategy. However, πtlp was not related to species moisture association. The positive relationship between πtlp and drought survival in herbaceous grassland species was opposite to the negative relationship previously established in woody plants, implying that mechanisms of drought resistance differ between woody and herbaceous species. Our results highlight the necessity of directly testing the relationship of functional traits to whole‐plant drought survival in different plant life forms, before using trait assessments for predicting plant responses to drought. A free plain language summary can be found within the Supporting Information of this article.

Responses of leaf water potential and gas exchange to the precipitation manipulation in two shrubs on the Chinese Loess Plateau

Regulation of leaf gas exchange plays an important role in the survival of trees and shrubs under future climate change. However, the responses of leaf water potential and gas exchange of shrubs in semi-arid areas to the precipitation alteration are not clear. Here, we conducted a manipulated experiment with three levels of precipitation, i.e., a control with ambient precipitation, 50% above ambient precipitation (irrigation treatment), and 50% below ambient precipitation (drought treatment), with two common shrubs, Salix psammophila C. Wang & C. Y. Yang (isohydric plant, maintaining a constant leaf water potential by stomatal regulation) and Caragana korshinskii Kom. (anisohydric plant, having more variable leaf water potential), on the Chinese Loess Plateau in 2014 and 2015. We measured the seasonal variations of predawn and midday leaf water potential (Ωpd and Ωmd), two parameters of gas exchange, i.e., light-saturated assimilation (An) and stomatal conductance (gs), and other foliar and canopy traits. The isohydric S. psammophila had a similar An and a higher gs than the anisohydric C. korshinskii under drought treatment in 2015, inconsistent with the view that photosynthetic capacity of anisohydric plants is higher than isohydric plants under severe drought. The two shrubs differently responded to precipitation manipulation. Ωpd, An and gs were higher under irrigation treatment than control for S. psammophila, and these three variables and Ωmd were significantly higher under irrigation treatment and lower under drought treatment than control for C. korshinskii. Leaf water potential and gas exchange responded to manipulated precipitation more strongly for C. korshinskii than for S. psammophila. However, precipitation manipulation did not alter the sensitivity of leaf gas exchange to vapor-pressure deficit and soil moisture in these two shrubs. Acclimation to long-term changes in soil moisture in these two shrubs was primarily attributed to the changes in leaf or canopy structure rather than leaf gas exchange. These findings will be useful for modeling canopy water-carbon exchange and elucidating the adaptive strategies of these two shrubs to future changes in precipitation.

The importance of cuticular permeance in assessing plant water–use strategies

Accurate understanding of plant responses to water stress is increasingly important for quantification of ecosystem carbon and water cycling under future climates. Plant water use strategies can be characterized across a spectrum of water stress responses, from tight stomatal control (isohydric) to distinctly less stomatal control (anisohydric). A recent and popular classification method of plant water use strategies utilizes the regression slope of predawn and midday leaf water potentials, σ, to reflect the coupling of soil water availability (predawn leaf water potential) and stomatal dynamics (daily decline in leaf water potential). This type of classification is important in predicting ecosystem drought response and resiliency. However, it fails to explain the relative stomatal responses to drought of Acer sacharrum and Quercus alba, improperly ranking them on the spectrum of isohydricity. We argue this inconsistency may be in part due to the cuticular conductance of different species. We used empirical and modeling evidence to show that plants with more permeable cuticles are more often classified as anisohydric; the σ values of those species were very well correlated with measured cuticular permeance. Furthermore, we found that midday leaf water potential in species with more permeable cuticles would continue to decrease as soils become drier, but not in those with less permeable cuticles. We devised a diagnostic parameter, Γ, to identify circumstances where the impact of cuticular conductance could cause species misclassification. The results suggest that cuticular conductance needs to be considered to better understand plant water use strategies and to accurately predict forest responses to water stress under future climate scenarios.

Eco-physiological evaluation of Stele Transversal Area 1 for rice root anatomy and shoot growth

ABSTRACTLarger stele size with greater xylem area or endodermis thickness in rice roots may lead to higher plant water status and maintain yield. Sta1-NIL, a near-isogenic line of IR64 introgressed with Stele Transversal Area 1 (Sta1), a quantitative trait locus controlling stele transversal area (STA) was investigated together with IR64 for their root anatomy and physiological parameters, at seedling, heading and maturity stages in greenhouse and fields of water deficit and well-watered conditions in 2017 and 2018. Combined analysis of STA from nine observations of overall four experiments showed that STA was increased by 7% (35,400 to 37,800 μm2) by the introduction of Sta1 into IR64. Total late metaxylem area also increased by 6% (5,840 to 6,180 μm2), which came mainly from its single area rather than its number, whereas small increase in endodermis thickness was also noted. Genotype x observation for STA was marginal, but Sta1-NIL had larger STA under water deficit environments. Sta1-NIL also maintained higher mid-day leaf water potential (−2.34 ± 0.3 MPa) than IR64 (−2.57 ± 0.3 MPa). Meta-analysis of seven experiments under 14 environments showed tendency of the positive effect of Sta1 on grain yield increment (579 to 604 g m−2), which came from the increment of harvest index. This study indicated the importance of wider stele size for maintenance of higher plant water status and yield across different water regimes.

A Simple Method for Simulating Drought Effects on Plants.

Drought is expected to increase in frequency and severity in many regions in the future, so it is important to improve our understanding of how drought affects plant functional traits and ecological interactions. Imposing experimental water deficits is key to gaining this understanding, but has been hindered by logistic difficulties in maintaining consistently low water availability for plants. Here, we describe a simple method for applying soil water deficits to potted plants in glasshouse experiments. We modified an existing method (the “Snow and Tingey system”) in order to apply a gradual, moderate water deficit to 50 plant species of different life forms (grasses, vines, shrubs, trees). The method requires less maintenance and manual handling compared to other water deficit methods, so it can be used for extended periods of time and is relatively inexpensive to implement. With only a few modifications, it is possible to easily establish and maintain soil water deficits of differing intensity and duration, as well as to incorporate interacting stress factors. We tested this method by measuring physiological responses to an applied water deficit in a subset of 11 tree/shrub species with a wide range of drought tolerances and water-use strategies. For this subgroup of species, stomatal conductance was 2–17 times lower in droughted plants than controls, although only half of the species (5 out of 11) experienced midday leaf water potentials that exceeded their turgor loss (i.e., wilting) point. Leaf temperatures were up to 8°C higher in droughted plants than controls, indicating that droughted plants are at greater risk of thermal damage, relative to unstressed plants. The largest leaf temperature differences (between droughted and well-watered plants) were in species with high rates of water loss. Rapid osmotic adjustment was observed in leaves of five species when drought stress was combined with an experimental heatwave. These results highlight the potential value of further ecological and physiological experiments utilizing this simple water deficit method to study plant responses to drought stress.

Data-Driven Models for Canopy Temperature-Based Irrigation Scheduling

HighlightsArtificial neural network modeling was used to predict crop water stress index lower reference canopy temperature.Root mean square error of predicted lower reference temperatures was <1.1°C for sugarbeet and Pinot noir wine grape.Energy balance model was used to dynamically predict crop water stress index upper reference canopy temperature.Crop water stress index for sugarbeet was well correlated with irrigation and soil water status.Crop water stress idex was well correlated with midday leaf water potential of wine grape.Abstract. Normalized crop canopy temperature, termed crop water stress index (CWSI), was proposed over 40 years ago as an irrigation management tool but has experienced limited adoption in production agriculture. Development of generalized crop-specific upper and lower reference temperatures is critical for implementation of CWSI-based irrigation scheduling. The objective of this study was to develop and evaluate data-driven models for predicting the reference canopy temperatures needed to compute CWSI for sugarbeet and wine grape. Reference canopy temperatures for sugarbeet and wine grape were predicted using machine learning and regression models developed from measured canopy temperatures of sugarbeet, grown in Idaho and Wyoming, and wine grape, grown in Idaho and Oregon, over five years under full and severe deficit irrigation. Lower reference temperatures (TLL) were estimated using neural network models with Nash-Sutcliffe model efficiencies exceeding 0.88 and root mean square error less than 1.1°C. The relationship between TLL minus ambient air temperature and vapor pressure deficit was represented with a linear model that maximized the regression coefficient rather than minimized the sum of squared error. The linear models were used to estimate upper reference temperatures that were nearly double the values reported in previous studies. A daily CWSI, calculated as the average of 15 min CWSI values between 13:00 and 16:00 MDT for sugarbeet and between 13:00 and 15:00 local time for wine grape, were well correlated with irrigation events and amounts. There was a significant (p < 0.001) linear relationship between the daily CWSI and midday leaf water potential of Malbec and Syrah wine grapes, with an R2 of 0.53. The data-driven models developed in this study to estimate reference temperatures enable automated calculation of the CWSI for effective assessment of crop water stress. However, measurements taken under conditions of wet canopy or low solar radiation should be disregarded as they can result in irrational values of the CWSI. Keywords: Canopy temperature, Crop water stress index, Irrigation scheduling, Leaf water potential, Sugarbeet, Wine grape.

Early defoliation effects on water status, fruit yield and must quality of ‘Nerello mascalese’ grapes

ABSTRACT: The effect of basal zone defoliation on vines influences yield and ripening depending on the phenological stage and its intensity. Early basal defoliation (EBD) was carried out at flowering on the autochthonous Vitis vinifera (L.) cultivar ‘Nerello mascalese’ grown on the eastern slopes of Mount Etna, Sicily. The effects were evaluated over a two-year period. In the first year, the canopy retained 67 % of its original leaf area after EBD and in the second year, 58 %. Compared with control vines, mid-day leaf water potentials in the EBD vines enjoyed higher water status throughout the growing seasons in both years. EBD had no significant negative effects on yield but did have significant positive effects on the levels of total polyphenols, total flavonols and total anthocyanins. Yield and its components are conditioned by a number of factors mainly linked to climate and to the vines’ general condition during berry growth and ripening. Even after two consecutive years of treatment, EBD does not have any negative effects on yield. However, EBD does have strong positive effects on berry quality attributes as a consequence of the following: greater exposure of the cluster to sunlight, higher vine water status and avoidance of high temperature stresses in the last phase of ripening during the analysis of anthocyanin.

Interspecific variations in tree allometry and functional traits in subtropical plantations in southern China.

Mechanical stability against buckling and water transport resistance through xylem vary with increasing tree height. To explore interspecific allometry based on morphological and physiological traits can play a crucial role in revealing their ecological adaptation. Four architectural traits (tree height, diameter at the breast height (DBH), crown width and crown depth) and seven functional traits (specific leaf area (SLA), leaf total carbon concentration (TC), midday leaf water potential, leaf δ13C and δ18O, wood density and xylem water transport efficiency) were measured in Schima superba, Acacia auriculiformis and Eucalyptus citriodora plantations in the subtropical region of China. The mechanical stability declined in the order of S. superba > A. auriculiformis > E. citriodora. Taller species at a given DBH had slender stems and narrower crowns. Smaller leaf δ18O and more efficient xylem water transport were observed in two taller tree species, A. auriculiformis and E. citriodora. Smaller SLA, higher leaf TC and larger leaf area indicated more carbon allocation to leaves of S. superba. The variations in architectural and functional traits with tree allometry among tree species may provide a more complete understanding of species-specific growth strategies in this subtropical region.

Sap flow changes and climatic responses over multiple-year treatment of rainfall exclusion in a sub-humid black locust plantation

Black locust (Robinia pseudoacacia) plantations have been widely established in the semiarid and sub-humid areas of central China. Under the condition of global climate change, which is introducing much uncertainty of precipitation patterns in this region, it is of special significance to investigate their responses to precipitation. Here, we investigated sap flow response to reduced throughfall. Stem sap flow was measured from 2011 to 2017 using Granier-type sensors. By placing waterproof panels within tree rows, about 47.5% precipitation was excluded from treated plots since April 2015. Differences in soil water content gradually increased to 4.3% between treated and control plots with continued throughfall exclusion. Decreased precipitation input significantly reduced the average sap flux density in treated plots by 9.1%–45.3%. The extent of this reduction depended on precipitation in the previous and current years. Transpiration and forest growth were negatively affected by the treatment. Furthermore, sap flow response to environmental factors became insensitive, with the discrepancy increasing with increasing drought duration, but was regained by rainfall recharge to soil water in the first two treatment years. However, prolonged drought might damage transpiration resilience capacity, as the saturated sap flux after soil water recharging during the wet period was still lower than that in the control plot in the latter year. Predawn leaf water potential was significantly lower in the treated plot compared to the control plot, whereas midday leaf water potential was similar. Whole tree hydraulic conductance (GP) was also similar between the two plots, except in extreme drought months when GP was much lower in the treated plot. In addition, the specific leaf area and stomatal density decreased in the treated plot. Therefore, decreases in precipitation would cause a transpiration reduction, weakening the tree’s response to meteorological variables and lowering growth and productivity, potentially damaging transpiration resilience. These results suggest that black locust is sensitive to water changes, its capacity of drought tolerant is restrained by the drought time scale or drought severity, the use of such species in reforestation in semiarid regions should be implemented with caution.

Large hydraulic safety margins protect Neotropical canopy rainforest tree species against hydraulic failure during drought

Key messageAbundant Neotropical canopy-tree species are more resistant to drought-induced branch embolism than what is currently admitted. Large hydraulic safety margins protect them from hydraulic failure under actual drought conditions.ContextXylem vulnerability to embolism, which is associated to survival under extreme drought conditions, is being increasingly studied in the tropics, but data on the risk of hydraulic failure for lowland Neotropical rainforest canopy-tree species, thought to be highly vulnerable, are lacking.AimsThe purpose of this study was to gain more knowledge on species drought-resistance characteristics in branches and leaves and the risk of hydraulic failure of abundant rainforest canopy-tree species during the dry season.MethodsWe first assessed the range of branch xylem vulnerability to embolism using the flow-centrifuge technique on 1-m-long sun-exposed branches and evaluated hydraulic safety margins with leaf turgor loss point and midday water potential during normal- and severe-intensity dry seasons for a large set of Amazonian rainforest canopy-tree species.ResultsTree species exhibited a broad range of embolism resistance, with the pressure threshold inducing 50% loss of branch hydraulic conductivity varying from − 1.86 to − 7.63 MPa. Conversely, we found low variability in leaf turgor loss point and dry season midday leaf water potential, and mostly large, positive hydraulic safety margins.ConclusionsRainforest canopy-tree species growing under elevated mean annual precipitation can have high resistance to embolism and are more resistant than what was previously thought. Thanks to early leaf turgor loss and high embolism resistance, most species have a low risk of hydraulic failure and are well able to withstand normal and even severe dry seasons.

The leaf miner Phyllocnistis populiella negatively impacts water relations in aspen.

Within the North American boreal forest, a widespread outbreak of the epidermal leaf miner Phyllocnistis populiella Cham. has damaged quaking aspen (Populus tremuloides Michx.) for nearly 20years. In a series of experiments, we tested the effects of feeding damage by P. populiella on leaf water relations and gas exchange. Relative to insecticide-treated trees, the leaves of naturally mined trees had lower photosynthesis, stomatal conductance to water vapor, transpiration, water-use efficiency, predawn water potential and water content, as well as more enriched foliar δ13C. The magnitude of the difference between naturally mined and insecticide-treated trees did not change significantly throughout the growing season, suggesting that the effect is not caused by accumulation of incidental damage to mined portions of the epidermis over time. The contributions of mining-related stomatal malfunction and cuticular transpiration to these overall effects were investigated by restricting mining damage to stomatous abaxial and astomatous adaxial leaf surfaces. Mining of the abaxial epidermis decreased photosynthesis and enriched leaf δ13C, while increasing leaf water potential and water content relative to unmined leaves, effects consistent with stomatal closure due to disfunction of mined guard cells. Mining of the adaxial epidermis also reduced photosynthesis but had different effects on water relations, reducing midday leaf water potential and water content relative to unmined leaves, and did not affect δ13C. In the laboratory, extent of mining damage to the adaxial surface was positively related to the rate of water loss by leaves treated to prevent water loss through stomata. We conclude that overall, despite water savings due to closure of mined stomata, natural levels of damage by P. populiella negatively impact water relations due to increased cuticular permeability to water vapor across the mined portions of the epidermis. Leaf mining by P. populiella could exacerbate the negative effects of climate warming and water deficit in interior Alaska.

A continuum of stomatal responses to water deficits among 17 wine grape cultivars (Vitis vinifera).

Vitis vinifera L. cultivars have been previously classified as isohydric, near-isohydric, anisohydric or isohydrodynamic, depending on the study. To test the hypothesis that V. vinifera cultivars' stomatal behaviour can be separated into distinct classes, 17 cultivars grown in a replicated field trial were subjected to three irrigation treatments to manipulate vine water status across multiple years. Predawn (ΨPD) and midday (Ψl) leaf water potential and midday stomatal conductance (gs) were measured regularly throughout several seasons. The relationship of gs to Ψl was best modelled as a sigmoidal function and maximum stomatal conductance (gmax), water status at the onset of stomatal closure (Ψl95), sensitivity of closure (gsensitivity) and water status at the end of closure (Ψl25) were compared. There were no significant differences in gmax among cultivars. Cultivar-specific responses of gs to Ψl were broadly distributed along a continuum based on the relationship between Ψl95 and gsensitivity. Season-long cultivar mean Ψl values were positively related to Ψl25. In general, cultivars responded similarly to one another at high and low water status, but their stomatal behaviour differed at moderate water deficits. The results show that V. vinifera cultivars possess both iso- and anisohydric stomatal behaviours that depend on the intensity of water deficits, and call into question previous classifications assuming a single behaviour.

Water Status and Yield Response to Deficit Irrigation and Fertilization of Three Olive Oil Cultivars under the Semi-Arid Conditions of Tunisia

Sustainability of olive production is possible by adopting the modern techniques of irrigation and fertilization. In Tunisia, olive trees are usually cultivated in poor soils, under semi-arid conditions characterized by water scarcity. This study investigated the effects of different water supply and fertilization on leaf water status and crop yield of three different olive oil varieties cultivated in central Tunisia, during four experimental seasons (2014–2017). Three treatments were examined: trees conducted under rainfed conditions (TRF), which represented the control treatment, trees irrigated with 50% ETc (T50) and, finally, trees irrigated with 50% ETc and with additional fertilization (T50F). Leaf water content and potential, yield and water use efficiency have been monitored on three different varieties, Chetoui, Chemlali, and Koroneiki, which are quite typical in the considered region. For all the growing seasons, midday leaf water potentials were measured from April to September. Midday leaf water potentials (MLWP) were generally higher for the two irrigated treatments (T50 and T50F) than for non-irrigated trees (TRF). As the season proceeded, MLWPs tended to decrease during summer for all the treatments and varieties. The lowest values were observed for the non-irrigated trees, varying between −3.25 MPa to −4.75 MPa. Relative leaf water content followed the same trends of midday leaf water potentials. Chetoui showed the lowest yield, which did not exceed 1530 Kg/(ha year), even for irrigated and fertilized trees. On the other hand, the yields of Chemlali and Koroneiki, cumulated in the four years, reached the maximum value of about 20 tons/ha. For these two varieties, the cumulated yield obtained in the control treatment (TRF) resulted significantly lower than the corresponding of the other two treatments (T50 and T50F). The highest irrigation water use efficiency (WUE) was estimated for Chemlali (T50) and (TRF). WUE was equal to 1.22 Kg/m3 for Koroneiki under fertigated treatment (T50F). Application of the only water supply (50% ETc) or associated with fertilizer improved the tree water status and increased the productivity of Chemlali and Koroneiki varieties.

Drought tolerance of a Pinus palustris plantation

Longleaf pine (Pinus palustris Mill.) forests are thought to be drought tolerant and if so, planting longleaf pine presents a forest management strategy for climate change adaptation in the southeastern United States (U.S.). To better understand how longleaf pine copes with drought, leaf water relations, sap flow, canopy stomatal conductance (GS), and growth were studied over three growing seasons in response to ambient throughfall (ambient treatment) versus an approximate 40% reduction in throughfall (drought treatment) in a 13-year-old plantation. An exceptional drought occurred the first year of the study and decreased mean predawn (ΨPD) and midday (ΨMD) leaf water potential to −2.9 MPa and −3.6 MPa, respectively, and decreased average monthly midday Gs to near zero for at least one month in both treatments. Stomatal closure occurred at a ΨMD of −3.0 MPa in both treatments. Leaf water potentials and transpiration recovered quickly following significant rain events that terminated the drought and mortality was similar among years and treatments (2.8%). Longleaf pine responded to drought treatment with greater stomatal control of plant water loss rather than adjustments in leaf area, the sapwood to leaf area ratio, or leaf water potential at the turgor loss point (ΨTLP). Annual transpiration per unit leaf area was reduced 16% by drought treatment, but greater stomatal control of water loss in response to drought treatment was associated with decreases in growth efficiency and volume, and no improvement in water use efficiency.

Linking reliance on deep soil water to resource economy strategies and abundance among coexisting understorey shrub species in subtropical pine plantations

Strategies for deep soil water acquisition (WAdeep ) are critical to a species' adaptation to drought. However, it is unknown how WAdeep determines the abundance and resource economy strategies of understorey shrub species. With data from 13 understorey shrub species in subtropical coniferous plantations, we investigated associations between the magnitude of WAdeep , the seasonal plasticity of WAdeep , midday leaf water potential (Ψmd ), species abundance and resource economic traits across organs. Higher capacity for WAdeep was associated with higher intrinsic water use efficiency, but was not necessary for maintaining higher Ψmd in the dry season nor was it an ubiquitous trait possessed by the most common shrub species. Species with higher seasonal plasticity of WAdeep had lower wood density, indicating that fast species had higher plasticity in deep soil resource acquisition. However, the magnitude and plasticity of WAdeep were not related to shallow fine root economy traits, suggesting independent dimensions of soil resource acquisition between deep and shallow soil. Our results provide new insights into the mechanisms through which the magnitude and plasticity of WAdeep interact with shallow soil and aboveground resource acquisition traits to integrate the whole-plant economic spectrum and, thus, community assembly processes.