Fraction Of Transpirable Soil Water Research Articles

Leaf emergence (phyllochron index) and leaf expansion response to soil drying in cowpea genotypes.

Drought can result in severely decreased leaf area development, which impacts plant growth and yield. However, rarely is leaf emergence or leaf expansion separated to resolve the relative sensitivity to water-deficit of these two processes. Experiments were undertaken to impose drought over approximately 2 weeks for eight cowpea (Vigna unguiculata) genotypes grown in pots under controlled environmental conditions. Daily measures of phyllochron index (PI, leaf emergence) and leaf area increase (leaf expansion) were obtained. Each of these measures was referenced against volumetric soil water content, i.e. fraction transpirable soil water. Although there was no clear difference between leaf emergence and leaf expansion in sensitivity to drying soil, both processes were more sensitive to soil drying than plant transpiration rate. Genotypic differences in the soil water content at the initiation of the decline in PI were identified. However, no consistent difference in sensitivity to water-deficit in leaf expansion was found. The difference in leaf emergence among genotypes in sensitivity to soil drying can now be exploited to provide guidance for plant improvement and crop yield increase.

Effects of water stress on emission of volatile organic compounds by Vicia faba, and consequences for attraction of the egg parasitoid Trissolcus basalis

When plants are damaged by herbivorous insects, blends of volatile organic compounds (VOCs) are induced and released and can also be used by parasitoids to locate hosts. The aim was to determine whether VOCs induced by water stress affect the plant–herbivore–parasitoid system represented by broad bean (Vicia faba; Fabales: Fabaceae) stink bug (Nezara viridula; Heteroptera: Pentatomidae) egg parasitoid (Trissolcus basalis; Hymenoptera: Platygastridae). The effects of water stress (expressed as the percentage fraction of transpirable soil water [FTSW] supplied) alone and in combination with N. viridula damage (feeding plus oviposition) were determined according to: (1) the behavioural response of the egg parasitoid in a Y-tube olfactometer and (2) the plant VOCs collected and analysed by thermal desorption–gas chromatography–mass spectrometry. With pot water capacity as FTSW100, water stress was applied as mild (FTSW80), moderate (FTSW50) and severe (FTSW10). Bioassays with plants under abiotic stress alone showed that egg parasitoids are more attracted by FTSW10 plants than by well-watered plants. When plants were under abiotic and biotic stress interactions, the egg parasitoids are more attracted by FTSW10 and FTSW50 plants than by well-watered plants infested with N. viridula. Considering VOCs emissions, projection to latent structures discriminant analysis (PLS-DA) separated treatments according to egg parasitoid responses. Water stress alone and in combination with biotic stress induced changes in VOC emissions of V. faba plants that attract egg parasitoids. These findings contribute to our understanding of how water stress affects the interactions between plants, insect pests and egg parasitoids.

Response of chickpea (Cicer arietinum L.) to terminal drought: leaf stomatal conductance, pod abscisic acid concentration, and seed set.

Flower and pod production and seed set of chickpea (Cicer arietinum L.) are sensitive to drought stress. A 2-fold range in seed yield was found among a large number of chickpea genotypes grown at three dryland field sites in south-western Australia. Leaf water potential, photosynthetic characteristics, and reproductive development of two chickpea genotypes with contrasting yields in the field were compared when subjected to terminal drought in 106kg containers of soil in a glasshouse. The terminal drought imposed from early podding reduced biomass, reproductive growth, harvest index, and seed yield of both genotypes. Terminal drought at least doubled the percentage of flower abortion, pod abscission, and number of empty pods. Pollen viability and germination decreased when the fraction of transpirable soil water (FTSW) decreased below 0.18 (82% of the plant-available soil water had been transpired); however, at least one pollen tube in each flower reached the ovary. The young pods which developed from flowers produced when the FTSW was 0.50 had viable embryos, but contained higher abscisic acid (ABA) concentrations than those of the well-watered plants; all pods ultimately aborted in the drought treatment. Cessation of seed set at the same soil water content at which stomata began to close and ABA increased strongly suggested a role for ABA signalling in the failure to set seed either directly through abscission of developing pods or seeds or indirectly through the reduction of photosynthesis and assimilate supply to the seeds.

Transpiration responses of warm-season turfgrass in relation to progressive soil drying

Developing turfgrass with good drought resistant is a major goal in breeding programs when water scarcity is one of the long-term challenges facing the turfgrass industry. It has been shown that plant transpiration does not decline until available soil water drops below a certain threshold. Studying the species and genotypic differences in this threshold may lead to turfgrass that conserve water and retain turfgrass quality during drought. The objective of this study was to characterize and compare the transpiration response of 19 warm-season turfgrass genotypes and cultivars in five species during soil drying and well-watered conditions in the greenhouse. The species included in the study were: Zoysia japonica (Steud), Zoysia matrella L., common bermudagrass (Cynodon dactylon L. Pers. var. dactylon), African bermudagrass (Cynodon transvaalensis Burtt-Davy), hybrid bermudagrass (C. dactylon L. var. dactylon×C. translvaalensis Burtt-Davy) and St. Augustinegrass [Stenotaphrum secundatum (Walter) Kuntze]. They were evaluated for evapotranspiration rate (ET) and the sensitivity of transpiration to soil drying which was indicated by a break point of the fraction transpirable soil water (FTSW). The range of break point during dry down was from 0.25 to 0.41, and genotypes within species had different ET when well-watered (ETck). Break point values were not correlated with the number of days to the endpoint, where ET declined below 10% of the control. Instead, the number of days to endpoint was negatively correlated with ETck (−0.59, P≤0.01). Thus, these results found significant variability in turfgrass break point and ETck that could contribute to water conservation, and a better understanding of drought responses in warm season turfgrasses.

Drought tolerance strategies highlighted by two Sorghum bicolor races in a dry-down experiment

Drought stress is the major environmental stress that affects more and more frequently plant growth and productivity due to the current climate change scenario. Unravelling the physiological mechanism underlying the response of plants to water stress and discover traits related to drought tolerance provide new and powerful tools for the selection in breeding programmes. Four genotypes of Sorghum bicolor (L.) Moench were screened in a dry-down experiment using different approaches to discover physiological and molecular indicators of drought tolerance.Different strategies were identified in response to drought among the four genotypes and the two Sorghum race allowing to state the tolerance of durra race compared to the caudatum one and, within the durra race, the drought tolerance of the genotype IS22330. It retained high biomass production and high tolerance index, it had a low threshold of fraction of transpirable soil water and high capacity to recover leaf apparatus after drought stress. Furthermore in this study, the expression levels of four genes highlighted that they could be used as proxy for drought tolerance. Dehdrine (DHN) could be used for screening drought tolerance both in durra and in caudatum races. NADP-Malic Enzyme, Carbonic Anhydrase (CA) and Plasma membrane Intrinsic Protein (PIP2-5), being up-regulated by drought stress only in durra race, have a more limited, though nonetheless useful application. In the tolerant durra genotype IS22330 in particular, the regulation of stomatal openings was strongly related to NADP-Malic Enzyme expression.

Physiological and metabolomic analysis of Punica granatum (L.) under drought stress

Punica granatum has a noticeable adaptation to drought stress. The levels of the green leaf volatile trans-2-hexenal increased in response to drought stress suggesting a possible role of this compound in drought stress response in pomegranate. Punica granatum (L.) is a highly valued fruit crop for its health-promoting effects and it is mainly cultivated in semi-arid areas. Thus, understanding the response mechanisms to drought stress is of great importance. In the present research, a metabolomics analysis was performed to evaluate the effects of drought stress on volatile organic compounds extracted from the leaves of pomegranate plants grown under water shortage conditions. The time course experiment (7 days of water deprivation and 24-h recovery) consisted of three treatments (control, drought stress, and rehydration of drought-stressed plants). Plant weights were recorded and control plants were irrigated daily at pot capacity to provide the lost water. Fraction of transpirable soil water has been evaluated as indicator of soil water availability in stressed plants. The levels of proline, hydrogen peroxide and lipid peroxidation as well as of the photosynthetic parameters such as photosynthesis rate (A), stomatal conductance (g s), photosynthetic efficiency of photosystem II, and photochemical quenching were monitored after the imposition of drought stress and recovery as markers of plant stress. Constitutive carbon volatile components were analyzed in the leaf of control and drought-stressed leaves using Head Space Solid Phase Micro Extraction sampling coupled with Gas Chromatography Mass Spectrometry. A total of 12 volatile compounds were found in pomegranate leaf profiles, mainly aldehydes, alcohols, and organic acids. Among them, the trans-2-hexenal showed a significant increase in water-stressed and recovered leaves respect to the well-watered ones. These data evidence a possible role of the oxylipin pathway in the response to water stress in pomegranate plants.

VALORES LIMÍTROFES PARA TRANSPIRAÇÃO, DESENVOLVIMENTO E CRESCIMENTO DE Corymbia citriodora (Hook.) K.D. Hill & L.A.S. Johnson EM RESPOSTA À DEFICIÊNCIA HÍDRICA NO SOLO1

RESUMO Quando a disponibilidade de água no solo é reduzida, as plantas respondem diminuindo a taxa de transpiração, o crescimento e o desenvolvimento, na tentativa de aclimatação à deficiência hídrica. Com o objetivo de quantificar essas respostas em mudas de Corymbia citriodora (Hook.) K.D. Hill & L.A.S. Johnson, foi utilizada a metodologia da fração de água transpirável no solo (FATS), em um experimento conduzido em casa de vegetação, sob o delineamento inteiramente casualizado, sendo dois níveis de suplementação hídrica, duas épocas de aplicação da deficiência hídrica e nove repetições. A FATS e os parâmetros de transpiração, crescimento e desenvolvimento foram medidos diariamente durante a aplicação da deficiência hídrica. A FATS crítica, em que a transpiração, o crescimento e desenvolvimento começam a ser reduzidos, foi distinta nas épocas de aplicação da deficiência hídrica devido à diferença das condições meteorológicas. Os valores elevados de FATS indicaram que a espécie possuiu boa aclimatação à deficiência hídrica no solo, quando comparada com as espécies anuais e outras perenes.

Leaf Expansion and Transpiration Responses of Millet Species to Soil Water Deficit

Plant processes, such as leaf expansion, stomatal conductance and transpiration, are affected by soil water, particularly in water–stressed environments. Quantifying the effects of soil water on plant processes, especially leaf expansion and transpiration, could be useful for crop modeling. In order to quantify the leaf expansion and transpiration in response to soil water deficit in three millet species, common (Panicum miliaceum L.), pearl (Pennisetum glaucum L.) and foxtail (Setaria italica L.) millets, a pot experiment was performed at the Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran. The soil water status was characterized by the fraction of transpirable soil water (FTSW). Leaf area and transpiration were measured daily. Relative leaf area expansion (RL) and relative transpiration (RT) data were plotted against FTSW. Finally the FTSW thresholds for RL and RT were calculated using linear–plateau and logistic models. The results showed that the thresholds for RL and RT were 0.68 and 0.62, respectively, based on all measured data of the three millet species using the linear–plateau model, indicating that RL and RT were constant when FTSW decreased from 1 to the threshold point. Thereafter, until FTSW = 0, RL and RT declined linearly with a slope of 1.48 and 1.43, respectively. Although millet is cultivated as a resistant crop in arid, semiarid and marginal lands, it showed an early response to soil water deficit at high FTSW thresholds. As leaf expansion and transpiration can be considered morphological and physiological variables, respectively, the results in this study indicate that millet has strong morphological flexibility when faced with soil water deficit.

Variation among Cowpea Genotypes in Sensitivity of Transpiration Rate and Symbiotic Nitrogen Fixation to Soil Drying

ABSTRACTCowpea (Vigna unguiculata L. Walp.) is often considered a crop species appropriate for drier environments. However, little or no information exists on two key physiological traits for drought conditions: early decrease in transpiration rate in the soil drying cycle and sustained N fixation activity under low soil‐water conditions. In this study, the responses of these two traits to soil drying were compared among 10 genotypes. The fraction of transpirable soil water at which transpiration rate began to decline varied from 0.59 to 0.24. The genotypes with the higher thresholds for the transpiration decrease offer a conservative water use strategy during soil drying and, hence, may be especially appropriate for very dry areas. The fraction of transpirable soil water at which N fixation rate began to decline ranged from 0.33 in one line to another line in which there was no decline in N fixation rate. Five lines had especially low thresholds for the decline in N fixation rate, which would be highly desirable in arid areas. In fact, N fixation tolerance to drought in these five lines is superior to any responses observed in other grain legumes. There was no correlation between the thresholds for decline in transpiration and N fixation.

Plant Survival of Drought During Establishment: An Interspecific Comparison of Five Grain Legumes

ABSTRACTSeedling establishment is obviously the first step in having successful crop production. In seasons and locations that experience early drought, potential differences among species in plant survival of drought could result in greater probability of crop establishment. In this study, plant survival capacity during crop establishment was tested for five grain legume species: soybean [Glycine max (L.) Merr.], common bean (Phaseolus vulgaris L.), groundnut (Arachis hypogaea L.), cowpea (Vigna unguiculata L. Walp.), and pigeon pea (Cajanus cajan L. Huth). Experiments were done for four sowing conditions (two soil textures × two initial soil‐water contents). Cowpea and pigeon pea had the greatest capacity for survival, while soybean, bean, and groundnut were more sensitive. Differences among species could not be explained by differences in the temporal dynamics of water use. Conversely, plant wilting and senescence in response to soil dehydration varied among species; initial wilting of cowpea and pigeon pea occurred at lower soil‐water contents. These two species also had the longest survival after fraction transpirable soil water (FTSW) reached zero. In a comparison of 10 genotypes of each species, genotypic variation in the wilting profile during the survival phase was observed in cowpea, bean, and, to a lesser extent, groundnut and pigeon pea, but no differences were found in soybean.

The use of soil electrical resistivity to monitor plant and soil water relationships in vineyards

Abstract. Soil water availability deeply affects plant physiology. In viticulture it is considered a major contributor to the "terroir" effect. The assessment of soil water in field conditions is a difficult task, especially over large surfaces. New techniques are therefore required in order to better explore variations of soil water content in space and time with low disturbance and with great precision. Electrical resistivity tomography (ERT) meets these requirements for applications in plant sciences, agriculture and ecology. In this paper, possible techniques to develop models that allow the use of ERT to spatialise soil water available to plants are reviewed. An application of soil water monitoring using ERT in a grapevine plot in Burgundy (north-east France) during the vintage 2013 is presented. We observed the lateral heterogeneity of ERT-derived fraction of transpirable soil water (FTSW) variations, and differences in water uptake depend on grapevine water status (leaf water potentials measured both at predawn and at solar noon and contemporary to ERT monitoring). Active zones in soils for water movements were identified. The use of ERT in ecophysiological studies, with parallel monitoring of plant water status, is still rare. These methods are promising because they have the potential to reveal a hidden part of a major function of plant development: the capacity to extract water from the soil.

Incorporating root distribution factor to evaluate soil water status for winter wheat

Many indicators have been developed to determine when and how much to irrigate to improve the irrigation efficiency. The relative available soil water (RASW) is an indicator that can be easily calculated but takes the availability of soil water to crops equally throughout the root zone profile without considering the soil water uptake ability as related to the root distribution. This study introduced a root parameter related to the relative root length abundance at different soil depth into RASW to evaluate the soil moisture conditions on crop performance (simplified as RASWr). The field study was carried out in the North China Plain (NCP) from 2010 to 2014 for four growing seasons of winter wheat (Triticum aestivum L.) under six irrigation treatments to create different soil moisture conditions. The results showed that RASWr was more closely related than RASW to the leaf water potential and stomatal conductance, and it was less affected by daily weather fluctuations as compared to crop water stress index (CWSI). Compared to the fraction of transpirable soil water (FTSW), RASWr was more easily obtained. The simple RASW indicator was improved by incorporating the relative root abundance factor which can be simulated by a form parameter of root distribution and maximum rooting depth at different growth stages of the crop.

Limite crítico no solo para transpiração e crescimento foliar em mandioca em dois períodos com deficiência hídrica

A cultura da mandioca geralmente é exposta a mais de um período de deficiência hídrica durante a estação de crescimento. O objetivo deste trabalho foi verificar se há diferença na Fração de Água Transpirável do Solo (FATS) crítica para transpiração e crescimento foliar em plantas de mandioca submetidas a um e dois períodos de deficiência hídrica no solo. Foram conduzidos dois experimentos com a cultura da mandioca, cultivar Fepagro RS 13. Os tratamentos foram quatro regimes hídricos subdivididos em dois períodos, período 1 (P1) e período 2 (P2): regimes hídricos RH1 e RH2 (sem e com deficiência hídrica nos dois períodos, respectivamente) e regimes hídricos RH3 e RH4 (com deficiência hídrica no P1 e P2, respectivamente). Usou-se o método da FATS para indicar os pontos críticos para transpiração e crescimento foliar. A FATS crítica foi 0,35, 0,38 e 0,37 para crescimento foliar e 0,28; 0,26; e 0,28 para transpiração no P1 do RH2 e RH3 e P2 do RH4, respectivamente. No P2 do RH2, a FATS crítica para crescimento foliar e transpiração foi 0,09 e 0,13, respectivamente. Concluiu-se que há diminuição na FATS crítica em mandioca no segundo período comparado ao primeiro período de deficiência hídrica no solo, que pode ser explicada pela menor área foliar, o que permitiu que o período de turgescência das folhas fosse maior e, com isso, demoraram mais a ativar seus mecanismos de controle estomático. A implicação prática desses resultados é que esses podem ser utilizados como parâmetros para irrigação da cultura, e também, na seleção de cultivares mais tolerantes à deficiência hídrica.

DREB1A overexpression in transgenic chickpea alters key traits influencing plant water budget across water regimes.

We demonstrate the role of DREB1A transcription factor in better root and shoot partitioning and higher transpiration efficiency in transgenic chickpea under drought stress Chickpea (Cicer arietinum L.) is mostly exposed to terminal drought stress which adversely influences its yield. Development of cultivars for suitable drought environments can offer sustainable solutions. We genetically engineered a desi-type chickpea variety to ectopically overexpress AtDREB1A, a transcription factor known to be involved in abiotic stress response, driven by the stress-inducible Atrd29A promoter. From several transgenic events of chickpea developed by Agrobacterium-mediated genetic transformation, four single copy events (RD2, RD7, RD9 and RD10) were characterized for DREB1A gene overexpression and evaluated under water stress in a biosafety greenhouse at T6 generation. Under progressive water stress, all transgenic events showed increased DREB1A gene expression before 50 % of soil moisture was lost (50 % FTSW or fraction of transpirable soil water), with a faster DREB1A transcript accumulation in RD2 at 85 % FTSW. Compared to the untransformed control, RD2 reduced its transpiration in drier soil and higher vapor pressure deficit (VPD) range (2.0-3.4 kPa). The assessment of terminal water stress response using lysimetric system that closely mimics the soil conditions in the field, showed that transgenic events RD7 and RD10 had increased biomass partitioning into shoot, denser rooting in deeper layers of soil profile and higher transpiration efficiency than the untransformed control. Also, RD9 with deeper roots and RD10 with higher root diameter showed that the transgenic events had altered rooting pattern compared to the untransformed control. These results indicate the implicit influence of rd29A::DREB1A on mechanisms underlying water uptake, stomatal response, transpiration efficiency and rooting architecture in water-stressed plants.

Effects of Root Water Uptake Efficiency on Soil Water Utilization in Wheat (Triticum aestivum L.) under Severe Drought Environments

AbstractImproving wheat production in drought‐prone areas is the key to meet the increasing global demand. The importance of root traits, especially, the structural traits such as root volume and rooting depth, has been well recognized to confer drought tolerance in wheat. However, generation of knowledge on root water uptake efficiency and its application in drought adaptation breeding had lagged behind. The main objective of this study was to evaluate the relevance of the root water uptake efficiency to biomass production under acute soil water deficit in six wheat genotypes. Pot experiments were conducted under polythene rainout shelters at Hokkaido University, Sapporo, Japan, in 2010 and 2011. Under drought that was measured as smaller critical fraction of transpirable soil water (FTSW), the root systems with less reduction water uptake efficiency were found to postpone the relative transpiration decline. This study also showed the existence of substantial genotypic variation on the root water uptake efficiency among the wheat genotypes. The expression of hydrophobic root morphology under drought environments, however, did not explain the results obtained on the relative root water uptake efficiency, indicating other regulative mechanisms in operation for the regulation of transverse water flow in the roots. These findings provide new understanding of drought adaptation in wheat through variations in the root water uptake efficiency.

Transpiration and leaf growth of potato clones in response to soil water deficit

Potato (Solanum tuberosum ssp. Tuberosum) crop is particularly susceptible to water deficit because of its small and shallow root system. The fraction of transpirable soil water (FTSW) approach has been widely used in the evaluation of plant responses to water deficit in different crops. The FTSW 34 threshold (when stomatal closure starts) is a trait of particular interest because it is an indicator of tolerance to water deficit. The FTSW threshold for decline in transpiration and leaf growth was evaluated in a drying soil to identify potato clones tolerant to water deficit. Two greenhouse experiments were carried out in pots, with three advanced clones and the cultivar Asterix. The FTSW, transpiration and leaf growth were measured on a daily basis, during the period of soil drying. FTSW was an efficient method to separate potato clones with regard to their response to water deficit. The advancedclones SMINIA 02106-11 and SMINIA 00017-6 are more tolerant to soil water deficit than the cultivar Asterix, and the clone SMINIA 793101-3 is more tolerant only under high solar radiation.

Modeling plant transpiration under limited soil water: Comparison of different plant and soil hydraulic parameterizations and preliminary implications for their use in land surface models

Accurate estimates of how soil water stress affects plant transpiration are crucial for reliable land surface model (LSM) predictions. Current LSMs generally use a water stress factor, β, dependent on soil moisture content, θ, that ranges linearly between β=1 for unstressed vegetation and β=0 when wilting point is reached. This paper explores the feasibility of replacing the current approach with equations that use soil water potential as their independent variable, or with a set of equations that involve hydraulic and chemical signaling, thereby ensuring feedbacks between the entire soil–root–xylem–leaf system. A comparison with the original linear θ-based water stress parameterization, and with its improved curvi-linear version, was conducted. Assessment of model suitability was focused on their ability to simulate the correct (as derived from experimental data) curve shape of relative transpiration versus fraction of transpirable soil water. We used model sensitivity analyses under progressive soil drying conditions, employing two commonly used approaches to calculate water retention and hydraulic conductivity curves. Furthermore, for each of these hydraulic parameterizations we used two different parameter sets, for 3 soil texture types; a total of 12 soil hydraulic permutations. Results showed that the resulting transpiration reduction functions (TRFs) varied considerably among the models. The fact that soil hydraulic conductivity played a major role in the model that involved hydraulic and chemical signaling led to unrealistic values of β, and hence TRF, for many soil hydraulic parameter sets. However, this model is much better equipped to simulate the behavior of different plant species. Based on these findings, we only recommend implementation of this approach into LSMs if great care with choice of soil hydraulic parameters is taken.

Soil water variability and its influence on transpirable soil water fraction with two grape varieties under different rainfall regimes

This research aims to analyse soil water variability and its influence on the amount of soil water available to rainfed vines under different rainfall patterns. Frequency domain reflectometry (FDR) sensors were used to measure soil volumetric water content on two plots planted with Chardonnay (CH) and Cabernet Sauvignon (CS) during two vegetative cycles. The Soil Water Assessment Tool (SWAT) model was used to simulate soil water during the period 2000–2012. The representativeness of the years analysed was then evaluated using multivariate techniques. The results obtained confirmed the high variability in soil water observed from year to year as a result of the rainfall and soil characteristics. The fraction of transpirable soil water (FTSW) reached almost 0.1 at the end of the growing season, but depended on the climatic and soil characteristics. Its effect on vines depended on variety, with early ripening varieties suffering most. The lack of water forced an advance in the harvest date and produced a significant decrease in yield. Although water deficits during the grape growing season are frequent, in the last decade, the most commonly observed pattern has been one of major water deficits recorded in the bloom-veraison and veraison-harvest periods. This has had a significant effect on yield, with reductions of up to 38% in the last year with respect to the 15-year average.

A water stress index based on water balance modelling for discrimination of grapevine quality and yield

<p style="text-align: justify;"><strong>Aims</strong>: A water stress index based on a water balance model was tested as a tool for classifying the water stress paths experienced by grapevines in various French Mediterranean vineyards. The relations between the index value and grapevine yield and berry quality (sugars, organic acids, anthocyanins) at harvest were investigated.</p><p style="text-align: justify;"><strong>Methods and results</strong>: A data set of 102 situations, each combining one location, one variety, one vintage and one water regime (irrigation or, most often, no irrigation), was collected for the study. The Fraction of Transpirable Soil Water (FTSW) was simulated by a unique-soil-reservoir water balance model at a daily time step. Five classes of water deficit were delimited from specific decreasing thresholds of FTSW over four periods between flowering and harvest. These thresholds were derived from predawn leaf water potential values because over decades, grapegrowers and researchers have shared references and built expertise by using this variable throughout the Mediterranean region. A water stress index resulting from the levels of water deficit reached at each of the four periods of the cycle was calculated. This index was correlated with yield per vine, berry weight, and berry sugar and organic acid contents but not with berry anthocyanin content.</p><p style="text-align: justify;"><strong>Conclusion</strong>: A simple water stress index, based on the water balance model, exhibited significant correlations with yield and berry quality for various cultivars and pedo-climatic conditions in Mediterranean vineyards.</p><p style="text-align: justify;"><strong>Significance and impact of the study</strong>: This water stress index is a valuable tool for explaining the variations in grape yield and quality among various locations and years because it reflects the vineyard water stress history in relation to rainfall regime and soil conditions. Improvement would come from the simulation of FTSW during winter, notably for soils of high Total Transpirable Soil Water. One potential application is the quantification of water stress change brought by irrigation in Mediterranean vineyards, and its relation to grapevine production.</p>

Effects of soil water deficits on three genotypes of potted Campanula medium plants during bud formation stage

Abstract: Potted ornamental plants are often exposed to drought stress during shipping and retailing, which decreases the value and postharvest quality. Thus, selection of genotypes which can better withstand soil water deficits is essential for sustainable production. Here, the response of three genotypes of potted Campanula medium (denoted as G100, G102 and G104) to progressive soil drying was investigated and their post-production performance was evaluated for four weeks. The potted plants were grown in a climate controlled greenhouse and were either well-watered (W) or drought-stressed (D) at floral bud formation stage. Soil water status was expressed as the fraction of transpirable soil water (FTSW). In the D pots, FTSW declined fastest in G100, followed by G102, and slowest in G104 after withholding irrigation. In the W plants, stomatal conductance ( g s ) was similar among the three genotypes, whereas transpiration rate ( T ) differed significantly among genotypes and was highest for G100, intermediate for G102, and lowest for G104. Estimated by a linear-plateau model, g s and T of G100 started to decrease at significantly higher FTSW thresholds than did G102 and G104. An earlier closure of stomata and decrease of T in G100 would allow the plant to conserve water in the soil; however, owing to its putative larger leaf area and greater stomatal density on the adaxial leaf surface, G100 quickly depleted soil water and resulted in severe drought stress to the plants as exemplified by the significantly lowered g s , leaf area, and relative water content (RWC). In contrast, a smaller leaf area and a lower stomatal density on the adaxial leaf surface of G104 enabled the plants to slowly deplete soil water and maintain high g s , T , leaf area, and RWC 8 days after withholding irrigation. Coincided with these, the floral bud abortion rate in the D plants was significantly higher for G100 as compared with G102 and G104. It is concluded that in potted ornamentals, a low transpiration rate, hereby a slow rate of soil water depletion, is crucial for maintaining postharvest quality under drought stress.