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Leaf water content (LWC) encapsulates critical aspects of tree physiology and is considered a proxy for assessing tree drought stress and the risk of forest decline; however, its measurement relies on destructive sampling and is thus less efficient. Advancements in hyperspectral imaging technology present new prospects for noninvasively evaluating LWC and mapping drought severity across forested regions. In this study, leaf samples were obtained from Populus alba var. pyramidalis, a species widely employed for constructing farmland shelterbelts in water-limited regions of northern China but notably susceptible to drought. These samples were dehydrated to varying degrees to generate concurrent LWC measurements and hyperspectral images, enabling the development of narrow-band and multivariate spectral prediction models for LWC estimation. Two visible-spectrum narrow-band indices identified, the single-band index (R627) and the band subtraction index (R437 − R444), demonstrated a strong correlation with LWC. Despite certain influences of variable preprocessing and selection on multivariate model performance, most models exhibited robust predictive accuracy for LWC. The FDRL-UVE-PLSR combination emerged as the optimal multivariate model, with R2 values reaching 0.9925 and 0.9853 and RMSE values below 0.0124 and 0.0264 for the calibration and validation datasets, respectively. Using this optimal model, along with localized spectral smoothing, moisture distribution across leaf surfaces was visualized, revealing lower water retention at the leaf margins compared to central regions. These methodologies provide critical insights into subtle water-associated physiological processes at the leaf scale and facilitate high-frequency, large-scale assessments and monitoring of drought stress levels and the risk of drought-induced tree mortality and forest degradation in drylands. [ABSTRACT FROM AUTHOR]

Summary Understanding isotope fractionation mechanisms is fundamental for analyses of plant ecophysiology and paleoclimate based on tree‐ring isotope data. To gain new insights into isotope fractionation, we analysed intramolecular 13C discrimination in tree‐ring glucose (Δi′, i = C‐1 to C‐6) and metabolic deuterium fractionation at H1 and H2 (εmet) combinedly. This dual‐isotope approach was used for isotope‐signal deconvolution. We found evidence for metabolic processes affecting Δ1′ and Δ3′, which respond to air vapour pressure deficit (VPD), and processes affecting Δ1′, Δ2′, and εmet, which respond to precipitation but not VPD. These relationships exhibit change points dividing a period of homeostasis (1961–1980) from a period of metabolic adjustment (1983–1995). Homeostasis may result from sufficient groundwater availability. Additionally, we found Δ5′ and Δ6′ relationships with radiation and temperature, which are temporally stable and consistent with previously proposed isotope fractionation mechanisms. Based on the multitude of climate covariables, intramolecular carbon isotope analysis has a remarkable potential for climate reconstruction. While isotope fractionation beyond leaves is currently considered to be constant, we propose significant parts of the carbon and hydrogen isotope variation in tree‐ring glucose originate in stems (precipitation‐dependent signals). As basis for follow‐up studies, we propose mechanisms introducing Δ1′, Δ2′, Δ3′, and εmet variability. [ABSTRACT FROM AUTHOR]

Hollyhock (Alcea rosea L.) is an aromatic, ornamental/medicinal plant species for which the selection of drought-tolerant varieties based on physio-chemical traits is desirable. The data presented resulted from a field experiment. This experiment was designed as a split-plot, based on a randomized complete block design, in which the main plots consisted of the three irrigation regimes (30, 60 and 80% permissible discharge moisture available in the soil), and the subplots consisted of nine hollyhock varieties. Photosynthetic pigments, Fv/Fm, proline content and selected antioxidant enzymes were measured throughout the period of induced drought stress. The data obtained illustrate the nature of the physiological response of hollyhock to drought stress. Based on the measured traits the varieties Isfahan 1, Shiraz 1 and Tabriz were shown to display the highest degree of resistance to drought stress. These data suggest that the effect of drought stress is dependent upon the drought level, variety and the trait in question. In this regard, future plant breeders for this species may find it useful to utilize ascorbate peroxidase (APX), catalase (CAT) and guayacol peroxidase (POX) activities as biochemical markers to select for drought-tolerant genotypes. As such, hollyhock can be considered a promising ornamental/medicinal species for cultivation in semi-arid environments. [ABSTRACT FROM AUTHOR]

Hollyhock (Alcea rosea L.) is an aromatic, ornamental/medicinal plant species for which the selection of drought-tolerant varieties based on physio-chemical traits is desirable. The data presented resulted from a field experiment. This experiment was designed as a split-plot, based on a randomized complete block design, in which the main plots consisted of the three irrigation regimes (30, 60 and 80% permissible discharge moisture available in the soil), and the subplots consisted of nine hollyhock varieties. Photosynthetic pigments, Fv/Fm, proline content and selected antioxidant enzymes were measured throughout the period of induced drought stress. The data obtained illustrate the nature of the physiological response of hollyhock to drought stress. Based on the measured traits the varieties Isfahan 1, Shiraz 1 and Tabriz were shown to display the highest degree of resistance to drought stress. These data suggest that the effect of drought stress is dependent upon the drought level, variety and the trait in question. In this regard, future plant breeders for this species may find it useful to utilize ascorbate peroxidase (APX), catalase (CAT) and guayacol peroxidase (POX) activities as biochemical markers to select for drought-tolerant genotypes. As such, hollyhock can be considered a promising ornamental/medicinal species for cultivation in semi-arid environments.

Argan tree growth and production are both affected by drought stress, which is recognized as a critical and serious environmental issue worldwide. This study aims to examine the effect of a multi-species consortium of arbuscular mycorrhizal fungi (AMF) "Rhizargan consortium", on the leaf water status and photosynthesis in drought-stressed argan seedlings. The performances of Rhizargan consortium were compared to those of a single pure commercialized strain of Rhizophagus irregularis. Seedlings of two argan tree ecotypes were subjected to three water regimes: 30, 60, and 100% field capacity (FC). After twelve months of drought stress, mycorrhizal argan seedlings showed a significant increase in leaf water potential, stomatal conductance, and maximum efficiency of PSII (Fm/Fv) than those without mycorrhiza inoculation. Moreover, AMF inoculation led to significant leaf accumulation of chlorophyll and carotenoid upon drought imposition. Nonetheless, severe drought stress (30% FC) decreased these physiological/photochemical attributes as well as both frequency and intensity of mycorrhization, but to a lesser extent in the argan seedlings inoculated with "Rhizargan consortium". This study contributes to advances in the knowledge of the indigenous Rhizargan consortium's ability to induce drought tolerance in argan trees. [ABSTRACT FROM AUTHOR]

Frequent discharge of cobalt in ionic form (Co2+) during industrial processes is contaminating agricultural soil through the addition of industrial effluent. Cobalt is beneficial element in trace amounts but its higher concentrations in soil severely damage the growth and development of plants. In this two-year study, the pre-selected sublethal level (0.5 mM) concentration of Co2+ was applied in soil to induce toxicity on two elite maize (Zea mays L.) hybrids ('Hycorn11plus' and 'P-1429'). To encounter the toxic effects of selected sub-lethal (0.5 mM) Co2+ level (applied using CoCl2·6H2O), pre-optimized levels of three stress protective chemicals (SPCs) i.e., ascorbic acid (0.5 mM), salicylic acid (0.5 mM) and thiourea (1.0 mM) were foliar sprayed. The Co2+ and SCPs treatments were applied 10 days after seedling emergence. After ten days of treatment application, the data were recorded for the growth, nutrients and leaf water status. The shoot and root dry weights and shoot-to-root (S/R) ratio were substantially reduced by the Co2+ stress. Co2+ intoxication also enhanced the leaf water loss (LWL) while relative water contents (RWC) were reduced in Co2+ stressed plants. The Co2+ treatment reduced the intake of nitrate-N, sulfate-S, phosphate-P, K+, Ca2+, Mg2+, Zn2+, and Fe2+ contents significantly both in the shoot and root. However, from the correlation matrix, it was noted that the foliar spray of SPCs effectively alleviated the Co2+damage by preventing the influx of Co2+ ions and enhanced the growth, water and nutrient contents except for LWL. From the reduced RWC and shoot and root nutrient contents, as well as increased LWL and Co2+ contents, it is evident that Co2+ interfered with either the function or structure of water and ion-transport systems located on the plasma lemma and tonoplast of root cells. AsA was more effective among the foliar applied SPCs due to its multiple metabolic roles in plants. The foliar spray of SPCs improved the root mass and tendency to absorb essential nutrients under Co2+toxicity indicating an intimate communication between shoot and root. The use of SPCs at the selected levels is a pragmatic strategy to counteract the Co2+ damage to maize in the marginally contaminated areas. [ABSTRACT FROM AUTHOR]

Cooperative interactions may frequently be reinforced by "partner fidelity feedback," in which high‐ or low‐quality partners drive positive feedbacks with high or low benefits for the host, respectively. Benefits of plant–animal mutualisms for plants have been quantified almost universally in terms of growth or reproduction, but these are only two of many sinks to which a host‐plant allocates its resources. By investigating how partners to host‐plants impact two fundamental plant resources, carbon and water, we can better characterize plant–partner fidelity and understand how plant–partner mutualisms may be modulated by resource dynamics. In Laikipia, Kenya, four ant species compete for Acacia drepanolobium host‐plants. These ants differ in multiple traits, from nectar consumption to host‐plant protection. Using a 5‐year ant removal experiment, we compared carbon fixation, leaf water status, and stem non‐structural carbohydrate concentrations for adult ant–plants with and without ant partners. Removal treatments showed that the ants differentially mediate tree carbon and/or water resources. All three ant species known to be aggressive against herbivores were linked to benefits for host‐plant resources, but only the two species that defend but do not prune the host, Crematogaster mimosae and Tetraponera penzigi, increased tree carbon fixation. Of these two species, only the nectivore C. mimosae increased tree simple sugars. Crematogaster nigriceps, which defends the tree but also castrates flowers and prunes meristems, was linked only to lower tree water stress approximated by pre‐dawn leaf water potential. In contrast to those defensive ants, Crematogaster sjostedti, a poor defender that displaces other ants, was linked to lower tree carbon fixation. Comparing the effects of the four ant species across control trees suggests that differential ant occupancy drives substantial differences in carbon and water supply among host trees. Our results highlight that ant partners can positively or negatively impact carbon and/or water relations for their host‐plant, and we discuss the likelihood that carbon‐ and water‐related partner fidelity feedback loops occur across ant–plant mutualisms. [ABSTRACT FROM AUTHOR]

Understanding the relationship between plant water status and productivity and between plant water status and plant mortality is required to effectively quantify and predict the effects of drought on plants. Plant water status is closely linked to leaf water content that may be estimated using remote sensing technologies. Here, we used an inexpensive miniature hyperspectral spectrometer in the 1550–1950 nm wavelength domain to measure changes in silver birch (Betula pendula Roth) leaf water content combined with leaf gas exchange measurements at a sub-minute time resolution, under increasing vapor pressure deficit, CO2 concentrations, and light intensity within the measurement cuvette; we also developed a novel methodology for calibrating reflectance measurements to predict leaf water content for individual leaves. Based on reflectance at 1550 nm, linear regression modeling explained 98–99% of the variation in leaf water content, with a root mean square error of 0.31–0.43 g cm−2. The prediction accuracy of the model represents a c. ten-fold improvement compared to previous studies that have used destructive sampling measurements of several leaves. This novel methodology allows the study of interlinkages between leaf water content, transpiration, and assimilation at a high time resolution that will increase understanding of the movement of water within plants and between plants and the atmosphere. [ABSTRACT FROM AUTHOR]

Background: Salinity stress (SS) is a serious detrimental factor for crop growth and productivity and its intensity it is continuously increasing which is posing serious threat to global food security. Hydrogen peroxide (H2O2) priming has emerged as an excellent strategy to mitigate the adverse impacts of SS. However, the role of H2O2 priming in mitigating the salinity induced toxicity is not fully explored. Methods and results: Therefore, in this context the present study was conducted in complete randomized design (CRD) in factorial combination to determine the impact of H2O2 priming on germination, growth, physiological and biochemical traits, osmo-regulating compounds, hormonal balance and ionic homeostasis. The experiment was based on different levels of SS; control, 6 and 12 dS m−1 SS and priming treatments, control and H2O2 priming (2%). Salinity stress significantly reduced the growth, leaf water status (− 15.55%), calcium (Ca2+), potassium (K+) and magnesium (Mg2+) accumulation and increased malondialdehyde (MDA: + 29.95%), H2O2 (+ 21.48%) contents, osmo-regulating compounds (proline, soluble sugars), indole acetic acid (IAA), anti-oxidant activities (ascorbate peroxidase: APX, catalase: CAT, peroxidase: POD and ascorbic acid: AsA) and accumulation of sodium (Na+) and chloride (Cl−.). H2O2 priming effectively reduced the effects of SS on germination and growth and strengthen the anti-oxidant activities through reduced MDA (− 12.36%) and H2O2 (− 21.13%) and increasing leaf water status (16.90%), soluble protein (+ 71.32%), free amino acids (+ 26.41%), proline (+ 49.18%), soluble sugars (+ 71.02%), IAA (+ 57.59%) and gibberlic acid (GA) (+ 21.11%). Above all, H2O2 priming reduced the massive entry of noxious ions (Na+ and Cl−) while increased the entry of Ca2+, K+ and Mg2+ thus improved the plant performance under SS. Conclusion: In conclusion H2O2 priming was proved beneficial for improving maize growth under SS thorough enhanced anti-oxidant activities, photosynthetic pigments, leaf water status, accumulation of osmo-regulating compounds, hormonal balance and ionic homeostasis. [ABSTRACT FROM AUTHOR]

Invasive alien species (IAS) are a problem, especially in drought-prone environments such as the Mediterranean Basin where the exacerbation of the already severe conditions could constrain the native species acclimatation degree, creating new opportunities for IAS. Climate change may drive IAS expansions, even if different IAS can vary in their acclimatation response. Thus, it is important to obtain a broader insight of how the different IAS face abiotic stress. This research aimed to compare the effect of the imposed water stress on physiological and morphological leaf traits of Ailanthus altissima (AA), Robinia pseudoacacia (RP), and Phytolacca americana (PA), which are widely spread IAS in the Mediterranean Basin. Our results showed a species-dependent effect of the water stress at a physiological and morphological level, as well as an interaction between species and stress duration. Despite a common strategy characterized by low stomatal control of the photosynthesis, AA, PA, and RP differ in their sensitivity to water stress. In particular, even if AA was characterized by a more water-spending strategy, it was more resistant to water stress than PA and RP. In this view, the key factor was its plasticity to increase leaf mass per area (LMA) in response to water stress. [ABSTRACT FROM AUTHOR]

Remote-sensing using normalized difference vegetation index (NDVI) has the potential of rapidly detecting the effect of water stress on field crops. However, this detection has typically been accomplished only after the stress effect led to significant changes in crop green biomass, leaf area index, angle and position, and few studies have attempted to estimate the uncertainties of the regression models. These have limited the informed interpretation of NDVI data in agricultural applications. We built a ground-based sensing cart and used it to calibrate the relationships between NDVI and leaf water potential (LWP) for wheat, corn, and cotton growing under field conditions. Both the methods of ordinary least-squares (OLS) and weighted least-squares (WLS) were employed in data analysis, and measurement errors in both LWP and NDVI were considered. We also used statistical resampling to test the effect of measurement errors of LWP on the uncertainties of model coefficients. Our data showed that obtaining a high value of the coefficient of determination did not guarantee a high prediction precision in the obtained regression models. Large prediction uncertainties were estimated for all three crops, and the regressions obtained were not always significant. The best models were obtained for cotton with a prediction uncertainty of 27%. We found that considering measurement errors for both LWP and NDVI led to reduced uncertainties in model coefficients. Also, reducing the sample size of LWP measurement led to significantly increased uncertainties in the coefficients of the linear models describing the LWP-NDVI relationship. Finally, potential strategies for reducing the uncertainty relative to the range of NDVI measurement are discussed.

Drought and water shortages have always been great challenges for agricultural production in the North China Plain. To explore appropriate irrigation regimes and planting patterns in this area, a field experiment was conducted for winter wheat (Triticum aestivum L.) from 2014 to 2016. Three irrigation treatments of 50 mm irrigation at growth stage of jointing (GS34) and heading (GS48, W1), 100 mm irrigation at GS34 (W2) and 100 mm irrigation at GS34 and GS48 (W3) combined with uniform (U), double–double (DD) and furrow‐ridge (F) planting patterns were designed. The tillers number, leaf water status, spike characteristics and radiation use efficiency (RUE) were measured. Results showed that compared with W2, W3 significantly reduced leaf abscisic acid (ABA) content and increased tillers number, spikelets spike−1, yield components and RUE, while W1 produced more tillers number, leaf relative water content (LRWC) and water potential (Lψ) only in the late growth stage, yield components and RUE. The DD significantly increased tillers number, LRWC, Lψ, leaf osmotic potential, spike length, spikes m−2, grains spike−1 and RUE, and reduced the ABA content compared with U. Considering the serious water shortage in the North China Plain, 50 mm irrigation at jointing and heading stages combined with DD is a worthy cultivation measure for sustainable agriculture at water‐deficit condition. [ABSTRACT FROM AUTHOR]

The agronomic and physiological traits, drought tolerance indexes, principal component analysis and Ward`s method were applied to assess the differences among 20 wheat genotypes in response to drought. Statistically significant correlation was observed for measured traits. Drought susceptibility index (DSI), stress tolerance index (STI) and stress index (SI) were most useful to identify genotypes differing in their response to drought. Utility of the indexes was confirmed by physiological markers of drought tolerance i.e. membrane injury and leaf water status. Variation of the genotypes in biomass and grain yield during drought stress was also verified by clustering methods. Finally, integration of physiological and statistical methods presented in this work, allows to both, indicate that tolerance to drought in wheat has a common genetic background, and select the most diverse genotypes. Based on the results, we recommend a tool for breeders, useful to select the genotypes resistant and sensitive to drought.

Invasive alien species (IAS) are a problem, especially in drought-prone environments such as the Mediterranean Basin where the exacerbation of the already severe conditions could constrain the native species acclimatation degree, creating new opportunities for IAS. Climate change may drive IAS expansions, even if different IAS can vary in their acclimatation response. Thus, it is important to obtain a broader insight of how the different IAS face abiotic stress. This research aimed to compare the effect of the imposed water stress on physiological and morphological leaf traits of Ailanthus altissima (AA), Robinia pseudoacacia (RP), and Phytolacca americana (PA), which are widely spread IAS in the Mediterranean Basin. Our results showed a species-dependent effect of the water stress at a physiological and morphological level, as well as an interaction between species and stress duration. Despite a common strategy characterized by low stomatal control of the photosynthesis, AA, PA, and RP differ in their sensitivity to water stress. In particular, even if AA was characterized by a more water-spending strategy, it was more resistant to water stress than PA and RP. In this view, the key factor was its plasticity to increase leaf mass per area (LMA) in response to water stress.

Our aim was to understand how moderately increased light intensities influenced the response of chickpea to high temperature. Three chickpea genotypes (Acc#3, Acc#7 and Acc#8) were treated at control (26 °C and 300 μmol m−2 s−1 photosynthetic photon flux density/PPFD), high temperature (38 °C and 300 μmol m−2 s−1 PPFD), increased light intensity (26 °C and 600 μmol m−2 s−1 PPFD) and combination of increased light and temperature (38 °C and 600 μmol m−2 s−1 PPFD). The net photosynthetic rate (P N) of Acc#3 and Acc#8 significantly decreased at high temperature regardless of light intensity. The P N of all three genotypes at increased light intensity was significantly higher than that at high temperature. The intracellular CO 2 concentration (C i), stomatal conductance (g s) and transpiration rate (E) of Acc#3 and Acc#8 at increased light intensity with or without high temperature significantly decreased in comparison with control and individually high temperature treatment. The relative water content of Acc#3 at high temperature and the combination treatment decreased as compared with control. The relative water content of Acc#7 at control was higher than the other three treatments. The F v /F m (Maximum quantum efficiency of photosystem II) of leaves from the three genotypes at 38 °C were lower than at 26 °C regardless of light intensity. The high temperature decreased chlorophyll content in the lower bottom leaf of Acc#7 and Acc#8 than control. In conclusion, chickpeas showed a higher net photosynthetic rate at increased light intensity to withstand heat stress, which was genotype-dependent. Physiological responses of different chickpea genotypes to increased temperature and light intensity indicated that distinct responsive mechanism of photosynthesis. This study provides information on how chickpea respond to high temperature and increased light intensity, which will help us to improve chickpea to deal with future climate changes. • Moderately increased light intensity decreased C i , g s and E regardless of temperature. • Chickpeas showed a higher P N at increased light intensity to withstand heat stress. • Physiological responses of the chickpea to increased temperature and light intensity was genotype-dependent. [ABSTRACT FROM AUTHOR]

Flag leaf and shoot growth at heading stage as well as ultimate yield capacity of ten wheat cultivars were assessed in a pot experiment under normal and drought conditions. Drought was imposed by withholding 25% of field capacity from the 45- day old plants for 21 days followed by normal irrigation until maturity. Leaf succulence degree and stomatal opening area as well as shoot biomass, density and distribution decreased in all cultivars in response to drought but to different degrees. On contrary, leaf sclerophylly degree and water saturation deficit increased in all cultivars as a result of drought. At the same time, drought caused marked alterations in leaf transpiration rate, hair features, abscisic acid content, osmotic adjustment and fatty acid profile of the concerned cultivars; with ultimate variable capacity for yield. The drought- induced changes in the estimated traits were graphically represented in a single map then they were correlated with each other. The considered cultivars could be eventually clustered based on their drought response; with Sids cultivars being the most drought tolerant whereas Shandaweel 1 and Giza 168 being the most sensitive. [ABSTRACT FROM AUTHOR]

The field experiment was conducted to evaluate the effect of foliar spray of calcium lactate (Ca) on fresh yield and biochemical attribute of lettuce (Lactuca sativa L.) under water deficit stress, in a split plot form based on a randomized complete block design with three Irrigation regimes (70, 85 and 100% ETc) and three calcium lactate treatment levels (0, 0.75 and 1.5 g L-1) in three replicates. Results revealed that water deficit stress significantly reduced the growth and yield of plant, leaf relative water contents, excised leaf water retention and N, P and Mg absorption while led to increase anthocyanin, phenol and flavonoids contents, antioxidant activity, peroxidase and catalase activity and water use efficiency. The results of our research indicated that the application of CaL 1.5 g L-1 is capable of increasing lettuce yield, under field conditions with 30% less than optimal irrigation. CaL treatment showed a clearly protective effect in stressed plants, enhancing their leaf water status, antioxidant capacity and N and Ca contents in comparison to untreated plants. Therefore, feeding leaves by CaL with increasing antioxidant activity and nutrients content especially N led to increase growth and fresh yield of lettuce under normal irrigation and water deficit conditions.

The field experiment was conducted to evaluate the effect of foliar spray of calcium lactate (Ca) on fresh yield and biochemical attribute of lettuce (Lactuca sativa L.) under water deficit stress, in a split plot form based on a randomized complete block design with three Irrigation regimes (70, 85 and 100% ETc) and three calcium lactate treatment levels (0, 0.75 and 1.5 g L-1) in three replicates. Results revealed that water deficit stress significantly reduced the growth and yield of plant, leaf relative water contents, excised leaf water retention and N, P and Mg absorption while led to increase anthocyanin, phenol and flavonoids contents, antioxidant activity, peroxidase and catalase activity and water use efficiency. The results of our research indicated that the application of CaL 1.5 g L-1 is capable of increasing lettuce yield, under field conditions with 30% less than optimal irrigation. CaL treatment showed a clearly protective effect in stressed plants, enhancing their leaf water status, antioxidant capacity and N and Ca contents in comparison to untreated plants. Therefore, feeding leaves by CaL with increasing antioxidant activity and nutrients content especially N led to increase growth and fresh yield of lettuce under normal irrigation and water deficit conditions. [ABSTRACT FROM AUTHOR]

The agronomic and physiological traits, drought tolerance indexes, principal component analysis and Ward's method were applied to assess the differences among 20 wheat genotypes in response to drought. Statistically significant correlation was observed for measured traits. Drought susceptibility index (DSI), stress tolerance index (STI) and stress index (SI) were most useful to identify genotypes differing in their response to drought. Utility of the indexes was confirmed by physiological markers of drought tolerance i.e. membrane injury and leaf water status. Variation of the genotypes in biomass and grain yield during drought stress was also verified by clustering methods. Finally, integration of physiological and statistical methods presented in this work, allows to both, indicate that tolerance to drought in wheat has a common genetic background, and select the most diverse genotypes. Based on the results, we recommend a tool for breeders, useful to select the genotypes resistant and sensitive to drought. Abbreviations: DM: dry matter; DSI: drought susceptibility index; FWC: field water capacity; GY: grain yield; GMP: geometric mean productivity index; H: plant height; LI: leakage index related to membrane injury; MPRO: mean productivity index; MHAR: harmonic mean index; NoT: number of tillers; NoG, W-1000: number of grains and weight of 1000 grains, respectively; NoLMT, NoLAT, NoLT: number of leaves on main tiller, adventitious tillers and total leaf number, respectively; PCA: principal component analysis; RTC: relative trait change; RWC, RT, WD: relative water content, relative turgidity and water deficit, respectively SI: stress index; SPAD: leaf greening; STI: stress tolerance index; TI: tolerance index; WCA: Ward's cluster analysis. [ABSTRACT FROM AUTHOR]

In regions with sandy soil texture and water scarcity, it is little to know the coupling effect of deficit irrigation with fertilization on soybean growth. The three combined effects of deficit irrigation (DI) and nitrogen fertilization (NF) on the leaf-level physiological and morphological parameters were identified. Irrigation was started once soil water content (SWC) was below 60% (T1), 50% (T2), 40% (T3), or 70% (CK) of field capacity (FC), respectively; meanwhile, 54 kg N ha-1 (T1), 67.5 kg N ha-1 (T2), or 81 kg N ha-1 (T3) was assigned at the beginning of the blooming stage. The results showed that the net photosynthetic rate (PN) and leaf water use efficiency (LWUE) was highest in T3. The leaf area (LA), plant height (SH), and leaf fresh mass (LFM) of T1, T3 increased by 32.69%, 16.05%, 29.10%, 14.93%, 62.49%, 71.43%, respectively, in comparison to CK. Relative water content (RWC, including leaf and pod) was lower in T1, T3 than in CK significantly, which was negative linear relationship with leaf water potential (ψw), and decreased continuously across growth stage. Ultimately, the average pod dry mass (PDM) in T3, T1 was up to 1.93g, 1.85g, CK just was 0.26g. Our results suggested that combination of 324mm irrigation and 54 kg N ha-1 optimally elevated VG, and 81mm water combining with 81 kg N ha-1 coupling most favoured RG and dry matter accumulation (DM) in comparison to single 405mm irrigation, maximizing the use efficiency of water, nitrogen and increasing vegetative growth (VG) and reproductive growth (RG). [ABSTRACT FROM AUTHOR]

Although potassium (K) is a macronutrient few studies have evaluated the response of olive tree to K fertilization. In this work results of two field and two pot K fertilizer experiments are presented. One of the field trials was conducted in a commercial young olive grove. The second was conducted in a plantation purposely established for this study. In the two field and the first pot experiment, the K supply was the single variation factor. The second pot experiment was arranged as a factorial with two K rates, two water regimes and two cultivars (‘Arbequina’ and ‘Cobrançosa’). K supply did not increase olive tree growth or yield. Accumulated olive yield in the first field experiment, for instance, varied from 2.46 and 2.84 kg tree−1, respectively in K treated and untreated plants. K supply increased the shoot/root ratio (1.6-2.0 from the control to the most fertilized treatment) and the concentration of K in roots (2.9-11.2 g kg−1) to a greater extent than in leaves (7.0-11.9 g kg−1), suggesting that shoots are a priority sink for K and roots may store the nutrient as a reserve. Plant water status and chlorophyll a fluorescence were not significantly affected by K applications. Plants suffering from water stress yielded less phytomass (40.2-56.4 g pot−1, respectively in control and well-watered plants) and showed higher K concentrations in leaves (14.2-11.6 g kg−1) and lower in roots (4.9-6.8 g kg−1) which is probably due to the reduction of K uptake from the dry soil. ‘Cobrançosa’ appeared to be more tolerant to water stress than ‘Arbequina’. These experiments showed a poor response of olive tree to K fertilization. Considering that K is usually applied by farmers every year, it seems that further studies on K fertilization in olive are needed in order to adjust K fertilizer rates to crop needs. [ABSTRACT FROM AUTHOR]

CO 2 concentration [CO 2 ] level in artificial ecosystems such as greenhouse agriculture and space farming can easily exceed 1000 μmol mol −1 (or ppm). In order to understand how the growth and development in crop plants may respond to elevated CO 2 , it is necessary to determine if crop leaves in the closed artificial ecosystem have a fully developed photosynthetic apparatus, and whether or not photosynthesis in these leaves is more responsive to elevated CO 2 concentration. To address this issue, we evaluated the response of photosynthetic characteristics, leaf water status and antioxidant capacity of Chufa ( Cyperus esculentus L.), which is a sedge-like plant with 1–2 cm small sweet tubers in length, under elevated CO 2 concentrations in an artificial closed ecosystem. The results showed that Chufa plants cultivated in the elevated CO 2 environment from the seedling stage to the maturity stage were characterized by more appropriate chlorophyll content and photosynthetic rate. The photosynthetic rate of Chufa plants in the 1000 and 3000 ppm treatments was no significant difference with that in 500 ppm CO 2 condition both at seedling stage and rapid growth stage. All the treatments had a high relative water content (RWC) about 60% at the maturity stage. However, there was no significant difference in membrane stability index (MSI) at the rapid growth stage. The antioxidase enzymes activities experienced a rise and a drop and reached the peak at the rapid growth stage. Elevated CO 2 , especially more than 1000 ppm conditions, may accelerant Chufa plants aging process. [ABSTRACT FROM AUTHOR]

ENSO (El Nino Southern Oscillation) occurring in 2015 in Indonesia caused drought stress and the decrease in the percentage of production and even death of plants. One effective and relatively inexpensive way of reducing damage and economic losses due to drought is the availibility of tolerant cocoa. The objective of this research was to obtain tolerant clones based on morpho-physiological characters under drought stress. The experiment was conducted in Kaliwining Experimental Station of Indonesian Coffee and Cocoa Research Institute (ICCRI) during dry season (El Nino period with 5 consecutive dry months, from May to October 2015). Stomata, proline, leaf water status was measured at the peak of dry season on tested cocoa clones. The cocoa clones that predicted tolerant against to drought stress were KW 641, KW 514, KW 535, KW 619, and KW 516, whereas the cocoa clones that predicted susceptible under drought stress were KW 609, KW 614, KW 635, KW 606, and KW 651. The treatment clones had higher values of RWC, leaf proline content, narrower width and length of stomata openings, but smaller value of WSD compared to susceptible clones. Meanwhile, the character of leaf thickness might not significanly different to the character of drought tolerance.

Reduced growth and stomatal closure are the two main responses of plants to drought stress. The extent to which these processes are connected and whether different genotypes prefer one over the other remains unclear. To understand the genotype-specific interconnections of these two processes and evaluate potential utilisation of this knowledge for drought tolerance phenotyping, six natural accessions of Arabidopsis thaliana (L.) Heynh. were exposed to drought stress for 10 days. Projected leaf area of rosette, light-saturated CO2 assimilation rate (Amax), relative water content (RWC), leaf temperature (thermal imaging), and spectral reflectance were measured through the course of induced drought stress. Three types of acclimation were identified: (i) growth not affected but Amax significantly reduced, (ii) both growth and Amax significantly reduced, and (iii) growth significantly reduced but only small decrease in Amax. Within the last type, the smallest decline in RWCwas evident. These results show that a substantial reduction in leaf areamaycause a decline in transpiration that enables maintenance of both RWC and physiological processes. Both non-invasive thermal imaging and spectral reflectance measurements proved reliable tools for tracking drought-induced changes in Amax andRWCacross all accessions tested and thus are effective tools for phenotyping stress tolerance. [ABSTRACT FROM AUTHOR]

The Leaf Water Relations, Photosynthetic Parameters and Shoot Growth of Five Snap Bean Cultivars Were Assessed During The Drought Period To Determine Their Role In Alleviating Plant Water Deficit Imposed By Withholding Irrigation At Flowering. Soil Water Content of Irrigated Plants Was 18-20% While That of Unirrigated Plants Was 6-10% At 60 Days After Seeding (Das). Leaf Water Potential Was Approximately 0.15Mpa Lower and Relative Water Content Was Approximately 5% Lower In Unirrigated Plants Than In Irrigated Plants At 57 Das. Unirrigated Plants Had A Lower Stomatal Conductance (Gs) and Intercellular Co2 Concentration (Ci). Reduced Leaf Water Potential and Relative Water Content Were Associated With A Decreased Stem Elongation Rate. Plants With A Lower Stem Elongation Rate Had A Higher Specific Leaf Weight and Succulence Index (Suci). Significant Differences Among Five Cultivars of Snap Bean Were Found For All Parameters Measured. Decreased Leaf Water Potential and Stem Elongation Rate Resulting From Drought Participated In Preserving Relative Water Content and Improving Specific Leaf Weight and Suci. Maintenance of Higher Relative Water Content Increased Gs and Ci. Cultivars That Maintained A High Relative Water Content When Leaf Water Potential and Stem Elongation Rate Were Decreased Markedly, Were More Tolerant To Drought Than Those Which A Reduced Relative Water Content and The Leaf Water Potential and Stem Elongation Rate Were Only Slightly Lowered. Reduced Yield (Pods Per Plant and Seed Biomass) Resulting From Drought Was Associated With Reduced Relative Water Content.

The chickpea genotypes alongwith F4 progeny lines differing in their behavior towards drought stress were evaluated for seed yield, yield attributes and physiological traits related to drought tolerance. Parental genotypes, HC 1 and ICC 4958 were grown under both irrigated and drought conditions and progenies were grown under drought conditions only. Plant water status, relative stress injury (RSI), canopy temperature depression (CTD) and chlorophyll fluorescence (Fv/Fm) were measured at 50% flowering stage under drought conditions. Drought stress decreased the leaf water potential (LWP), leaf osmotic potential (LOP) and relative water content (RWC) in the plants. The water potential, osmotic potential, relative water content and relative stress injury in HC 1 were -1.20 MPa, -1.31 MPa, 59.2% and 31.28% respectively and in ICC 4958 were -1.00 MPa, -1.74 MPa, 66.58% and 20.93% respectively, under drought condition. Increase in CTD was 0.9 0C in ICC 4958 as compared to 2.06 0C in HC 1. The ICC 4958 maintained higher Fv/Fm ratio than HC 1 in both irrigated and drought conditions. There is a significant positive correlation between water potential, osmotic potential and RWC with seed yield, whereas, RSI and seed yield were negatively correlated. CTD has a significant negative correlation with WP, OP, RWC and seed yield. The seed yield of HC 1 and ICC 4958 were decreased under drought condition but decrease in yield of genotype ICC 4958 (24.96%) was less than genotype HC 1 (37.32%).

The effects of salt stress (0, 200, 400 and 600 mM NaCl) on water status, ion contents, chlorophyll contents and gas exchange characteristics in the leaves of Atraphaxis bracteata seedlings were studied in this paper. Results showed that relative water content (RWC) and leaf water potential (Ψw) 600 mM NaCl. Salinity also induced an excessive accumulation of Na+ in the leaves of plants, accompanied by a notable decrease of K+ content. Both Chlorophyll (Chl) a and Chl b contents in the leaves reduced remarkably compared with the controls, whereas the Chl a/b ratio went up throughout the experiment. Salt stress also led to a significant reduction in net photosynthetic rate (PN), transpiration rate (E), and stomatal conductance (gs) with the increase of salinity and time. However, intercellular CO2 concentration (Ci) and stomatal limiting value (Ls) showed markedly different trends in the experiment. Before the 15th day, Ci decreased sharply at 200, 400 and 600 mM NaCl; thereafter, it increased dramatically. On the contrary, rapid increases of Ls before the 15th day and great decreases after the 15th day were observed under different salinities. Moreover, our results suggest that the factors inducing the reduction of PN are different duo to the different salinities and different time. The higher the salinity is, the sooner the transform of stomatal limitation to non-stomatal limitation is. [ABSTRACT FROM AUTHOR]

Dois experimentos foram conduzidos, sendo um instalado em área de encosta e outro em área de baixada. Objetivou-se avaliar a tolerância à seca e ao alagamento de três espécies comerciais de Brachiaria (B. decumbens cv. Basilisk, B. brizantha cv. Marandu e B. mutica) e três acessos (B. brizantha B-11, B. humidicola cv. Tupi e B. dictyoneura), a partir de suas características morfogênicas, produtivas e relações hídricas. O delineamento experimental foi o de blocos ao acaso, com seis repetições. As parcelas, com 4 m² de área total, foram constituídas de oito linhas de 2 m de comprimento, com espaçamento entre linhas de 0, 25 m. Dezenove dias após corte de uniformização, a área localizada na baixada foi submetida ao alagamento de uma lámina d'àgua de 56 mm de água, por 30 dias; simultaneamente, suspendeu-se a irrigação na área de encosta sob déficit hídrico. O alagamento foi mais prejudicial às características morfogênicas que déficit hídrico. Enquanto a taxa de alongamento foliar de todas as espécies foi mais baixa sob alagamento, as taxas de aparecimento e senescência foliares responderam ao estresse hídrico conforme a espécie. A taxa de aparecimento de folhas foi mais comprometida pelo alagamento apenas em B. dictyoneura, B. mutica e B. brizantha cv. Marandu. As maiores taxas de senecência de folhas ocorreram sob alagamento, particularmente em B. decumbens, B. brizantha cv. Marandu e B-11. Os estresses hídricos tiveram efeitos diferenciados sobre as características produtivas das espécies. A produção de biomassa verde aérea foi maior em B-11 sob regime de déficit hídrico, enquanto em B. dictyoneura e B. mutica, observou-se tendência de valores mais altos sob regime de alagamento. O índice de área foliar foi mais alto sob deficit hídrico, apenas em B. brizantha Marandu e B-11. A população de perfilhos basilares foi maior sob alagamento apenas em B. dictyoneura.Two experiments were carried out from December/1997 to June/1998. One experiment was performed on hilly area e and the second one on lowland area. These experiments aimed to evaluate the tolerance to flooding and low soil water potential of three commercial Brachiaria species (B. decumbens cv. Basilisk, B. brizantha cv. Marandu e B. mutica) and three acesses (B. brizantha B-11, B. humidicola cv. Tupi and B. dictyoneura). Morphogenetical, productive and plant water status were the variables assessed. In each experiment the species were distributed in randomized blocks with six replications. Each plot had eight 2 m rows, spaced 0.25 m from each other. During the establishment phase both experimental areas were irrigated, if required. Nineteen days after uniformization clipping, the experiment on the lowland was daily flooded with a 56 mm of water lamina over 30 days, while the irrigation was supressed on the hilly area. Flooding was more detrimental to the morphogenetic traits of the Brachiaria species than water deficit. All species exhibited lower rate of leaf elongation under flooding but their leaf appearance and senescence rate responses to flooding varied with the species. Rate of leaf blade appearance in B. dictioneura, B. mutica and B. brizantha cv. Marundu was higher under water deficit than under flooding; leaf blade senecence rate was higher under flooding, particularly in B. decumbens and B. brizantha cv. Marandu and B-11. Flooding and water deficit effects on the productive traits varied with species. Green shoot biomass production was higher in B-11 under water deficit but in B. dictyoneura and B. mutica these values tended to be higher under flooding. Higher leaf area index figures were observed under water deficit only for B. brizantha Marandu and B-11. Under flooding basal tiller population was higher in B. dictyoneura. B. humidicola showed little variation with stress situation for most studied traits, while B. brizantha B-11 performed better under water deficit than under flooding.

Leaf water status information is highly needed for monitoring plant physiological processes and assessing drought stress. Retrieval of leaf water status based on hyperspectral indices has been shown to be easy and rapid. However, a universal index that is applicable to various plants remains a considerable challenge, primarily due to the limited range of field-measured datasets. In this study, a leaf dehydration experiment was designed to obtain a relatively comprehensive dataset with ranges that are difficult to obtain in field measurements. The relative water content (RWC) and equivalent water thickness (EWT) were chosen as the surrogates of leaf water status. Moreover, five common types of hyperspectral indices including: single reflectance (R), wavelength difference (D), simple ratio (SR), normalized ratio (ND) and double difference (DDn) were applied to determine the best indices. The results indicate that values of original reflectance, reflectance difference and reflectance sensitivity increased significantly, particularly within the 350–700 nm and 1300–2500 nm domains, with a decrease in leaf water. The identified best indices for RWC and EWT, when all the species were considered together, were the first derivative reflectance based ND type index of dND (1415, 1530) and SR type index of dSR (1530, 1895), with R 2 values of 0.95 ( p < 0.001) and 0.97 ( p < 0.001), respectively, better than previously published indices. Even so, different best indices for different species were identified, most probably due to the differences in leaf anatomy and physiological processes during leaf dehydration. Although more plant species and field-measured datasets are still needed in future studies, the recommend indices based on derivative spectra provide a means to monitor drought-induced plant mortality in temperate climate regions. [ABSTRACT FROM AUTHOR]

Tomato meets the dietary nutrient and antioxidant requirements of diverse populations. Being a C crop and an important vegetable, it is likely to be influenced by increased CO concentrations under climate change situation. This study was conducted to investigate the effects of elevated CO on overall physiology, water relations, growth, yield, and fruit quality of tomato ( Lycopersicon esculentum Mill) cv. Arka Ashish. Plants were grown at elevated CO [550 (EC) and 700 (EC) ppm of CO] in open top chambers. Increased assimilation rate, decreased stomatal conductance and transpiration rate were observed at elevated CO (EC) concentrations. Reduced leaf osmotic potential and increased water potential were observed at EC compared with the control (380 ppm of CO) in flowering and fruiting stages. Lower total chlorophyll content was recorded at EC. Plant height was significantly higher at EC compared with EC. Higher number of branches was observed at EC as compared with plants grown at EC and the control. Leaf area was lower at EC compared with EC but specific leaf mass was higher at EC. Due to higher leaf dry mass and root dry mass, the plants grown at EC exhibited higher total dry mass compared to EC and the control. Increased number of flowers and fruits together with higher fruit set led to higher fruit yield at both EC concentrations. The highest yield increase was observed at EC. The fruits showed a lower content of phenols, flavonoids, ferric reducing antioxidant potential, total soluble solids, and titratable acidity in plants grown at EC as compared with the control. The ascorbic acid content was high at both EC and EC. Carotenoids and lycopene content was low at EC compared to higher content observed at EC and the control. [ABSTRACT FROM AUTHOR]

Traditional crops are extremely important for food production in low income, food-deficit countries (LIFDCs) where they continue to be maintained by socio-cultural preferences and traditional uses. Significant potential exists to improve these crops, one of which is to select for improved productivity during moisture stress conditions. Germplasm of Amaranthus tricolor , Amaranthus hypochondriacus and Amaranthus hybridus were subjected to various screening methods to measure metabolic and physiological changes during water stress. The activities of enzymes involved in the oxygen-scavenging system during abiotic stress conditions (superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR)), free proline production, leaf area (LA), cell membrane stability (CMS), leaf water potential (LWP) and relative water content (RWC) were measured in these three amaranth species during induced water stress. This study showed significant differences in metabolic responses during water deficit of the three species tested. Moisture stress and a decrease in RWC and LWP were first experienced in A. hybridus and A. hypochondriacus , followed by A. tricolor . There was an indirect correlation between leaf water status (RWC and LWP), enzyme activity, proline production and leaf area. The combined effect of GR, APX and SOD could ensure higher levels of regulation of the toxic effect of H 2 O 2 which could be associated with drought tolerance in Amaranthus . Distinct differences in onset of proline accumulation and the amount of accumulated in leaves upon induced water stress was noticed for the three amaranth species tested. Proline accumulation during water stress conditions in amaranth seems to be indirect and could possibly have a protective role apart from osmoregulation during stress conditions. This contention is supported by the decrease in leaf area and high cell membrane stability for two of the species tested. This study forms part of a project aimed at the development of improved traditional crops to contribute to food production and quality for subsistence farmers in areas with low precipitation or variable rainfall patterns. [ABSTRACT FROM AUTHOR]

Abstract: The analysis of dynamic laser speckle is widely known as an effective non-contact technique for detecting micro-activity on a sample surface. However, the analysis obtained using conventional statistical methods is heavily influenced by the properties of the sample, laser beam and ambient lighting. Recently, we proposed a new normal vector based dynamic speckle analysis method and demonstrated its ability to remove interference due to non-uniform reflectivity, illumination, and time-varying ambient lighting. In this paper, the normal vector based statistical technique for dynamic speckle analysis is further justified by the application to leaf surface micro-motion detection for monitoring plant water status. We carried out experiments for surface activity detection of attached leaves to monitor variation of leaf water status. The presented results highlight the advantage of the normal vector based analysis over image intensity based methods and demonstrate the potential of measuring plant water status via dynamic laser speckle analysis. [Copyright &y& Elsevier]

It is important to determine the plant water stress before it can reduce the yield or becomes visible. The aim of this study was to investigate the relationship between remotely sensed hyperspectral reflectance indices and leaf water status (LWS) of olive seedlings (Olea europaea L. ev. 'Ayvalık', 'D9' 'D36' 'Erdek Yaglik', 'Frantoio' and 'Gemlik') at different irrigation regime. A pot experiment was conducted in field conditions with 2-years old olive seedlings for the seasons 2011 and 2012. Four levels of water treatment were applied to the pots to bring about different stress conditions; no stress (1-100), mild stress (I-66), severe stress (1-33) and full stress (1-0). Leaf water potential (LWP) and relative water content (RWC) were determined to assess the LWS of the plants. In addition, canopy spectral reflectance was measured with a handheld spectroradiometer and several spectral vegetation indices were calculated using canopy reflectance data. Analysis showed that the irrigation requirement of Frantoio cultivar was the highest when compared to that of other cultivars, while the lowest amount of water was required by Ayvalık cultivar. According to the stepwise multiple linear regression (SMLR) analysis between spectral indices and LWS of olive seedlings, the coefficient of determination (R2) of model between RWC and Photochemical Reflectance Index (PRI) was 0.70, while it was 0.81 between LWP and PRI, Soil Adjusted Vegetation Index (SAVI), Normalized Difference Vegetation Index (NDVI) and Normalized Pigment Chlorophyll Index (NPCI). Accordingly, it appeared that LWP could be detected more accurately than RWC using spectral indices. Results of this study indicated that the olive plant was very susceptible to water stress and the remotely sensed spectral data could be used to determine RWC and LWP as an indicator of water stress. [ABSTRACT FROM AUTHOR]

Abstract: Daily dynamics of leaf (K L) and soil-to-branch hydraulic conductance (K S–B) was investigated in silver birch (Betula pendula Roth.) using evaporative flux method in situ: water potential drop was measured with a pressure chamber and evaporative flux was estimated as sap flux density measured with sap flow gauges. Canopy position had a significant (P < 0.001) effect on both K L and K S – B. Upper-canopy leaves exhibited 1.7 and soil-to-branch pathway 2.3 times higher hydraulic efficiency than those for lower-canopy. K L varied significantly with time of day: K L for both upper- and lower-canopy leaves was lowest in the morning and rose gradually achieving maximal values in late afternoon (4.75 and 3.38 mmol m−2 s−1 MPa−1, respectively). Relevant environmental factors affecting K L were photosynthetic photon flux density (Q P), air relative humidity (RH) and air temperature (T A). K S – B started rising in the morning and reached maximum in the lower canopy (1.44 mmol m−2 s−1 MPa−1) at 1300 h and in the upper canopy (2.52 mmol m−2 s−1 MPa−1) at 1500 h, decreasing afterwards. Environmental factors controlling K S – B were Ψ S and Q P. The diurnal patterns of K L reflect a combination of environmental factors and endogenous rhythms. The temporal pattern of K S – B refers to daily up- and down-regulation of hydraulic conductance of water transport pathway from soil–root interface to leaves with respect to changing irradiance. [Copyright &y& Elsevier]

A very high percentage (around 70%) of the agronomic area in Switzerland is covered by grasslands at various altitudes where environmental conditions, management, community structure and productivity vary widely. As heat waves and drought are predicted to increase in future climate, survival of plant species in grasslands is a major issue of concern in Central Europe. The effect of summer drought on representative grasslands in Switzerland was studied through drought experiments (using rain-out shelters avoiding natural precipitation) to understand the response of predominant species to changed climatic conditions. The physiological performance (gas exchange, leaf water potential) of selected species was investigated at three locations in Switzerland. The pre-dawn leaf water potential of all species was lower (more negative) under the dryer conditions at the three sites. Net photosynthesis and stomatal conductance of forb and legume species did not show major changes under drought, while grass species showed large decreases at the lowland site. These differences between forb-legume and grass species were not observed at the pre-alpine and alpine site. The apparent drought tolerance of the forb-legume species seems to be due-at least partially-to increased water use efficiency under drought conditions. [ABSTRACT FROM AUTHOR]

Abstract: This study investigated the effects of cinnamic acid (CA) on growth, biochemical and physiological responses of Lactuca sativa L. CA (0.1, 0.5, 1.0 and 1.5 mM) treatments decreased plant height, root length, leaf and root fresh weight, but it did not affect the leaf water status. CA treatment (1.5 mM) significantly reduced F v, F m, photochemical efficiency of PSII (F v/F m) and quantum yield of PSII (ΦPSII) photochemistry in L. sativa. The photochemical fluorescence quenching (qP) and non-photochemical quenching (NPQ) were reduced after treatment with 1.5 mM CA. Fraction of photon energy absorbed by PS II antennae trapped by “open” PS II reaction centers (P) was reduced by CA (1.5 mM) while, portion of absorbed photon energy thermally dissipated (D) and photon energy absorbed by PSII antennae and trapped by “closed” PSII reaction centers (E) was increased. Carbon isotope composition ratios (δ13C) was less negative (−27.10) in CA (1.5 mM) treated plants as compared to control (−27.61). Carbon isotope discrimination (Δ13C) and ratio of intercellular CO2 concentration (ci/ca) from leaf to air were also less in CA treated plants. CA (1.5 mM) also decreased the leaf protein contents of L. sativa as compared to control. [Copyright &y& Elsevier]

Abstract: The effects are reported here of Benzoxazolin-2(3H)-one (BOA), an allelopathic compound, on plant water relations, growth, components of chlorophyll fluorescence, and carbon isotope discrimination in lettuce (Lactuca sativa L.). Lettuce seedlings were grown in 1:1 Hoagland solution in perlite culture medium in environmentally controlled glasshouse. After 30 days, BOA was applied at concentration of 0.1, 0.5, 1.0 and 1.5 mM and distilled water (control). BOA, in the range (0.1–1.5 mM), decreased the shoot length, root length, leaf and root fresh weight. Within this concentration range, BOA significantly reduced relative water content while leaf osmotic potential remained unaltered. Stress response of lettuce was evaluated on the basis of six days of treatment with 1.5 mM BOA by analyzing several chlorophyll fluorescence parameters determined under dark-adapted and steady state conditions. There was no change in initial fluorescence (Fo) in response to BOA treatment while maximum chlorophyll fluorescence (Fm) was significantly reduced. BOA treatment significantly reduced variable fluorescence (Fv) on first, second, third, fourth, fifth and sixth day. Quantum efficiency of open PSII reaction centers (Fv/Fm) in the dark-adapted state was significantly reduced in response to BOA treatment. Quantum yield of photosystem II (ΦPSII) electron transport was significantly reduced because of decrease in the efficiency of excitation energy trapping of PSII reaction centers. Maximum fluorescence in light-adapted leaves (F′m) was significantly decreased but there was no change in initial fluorescence in light-adapted state (F′o) in response to 1.5 mM BOA treatment. BOA application significantly reduced photochemical fluorescence quenching (qP) indicating that the balance between excitation rate and electron transfer rate has changed leading to a more reduced state of PSII reaction centers. Non photochemical quenching (NPQ) was also significantly reduced by BOA treatment on third, fourth and fifth day. BOA had dominant effect on C isotope ratios (δ 13C) that was significantly less negative (−26.93) at 1.0 mM concentration as compared to control (−27.61). Carbon isotope discrimination (Δ13C) values were significantly less (19.45) as compared to control (20.17) at 1.0 mM. BOA also affect ratio of intercellular to air CO2 concentration (ci/ca) that was significantly less (0.66) as compared to control (0.69) when treated with 1.0 mM BOA. Protein content of lettuce leaf tissue decreased under BOA treatment at 1.5 mM concentration as compared to control. [Copyright &y& Elsevier]

Permanent xylem blockage is a common result of attacks by herbivores and fungi. The mitosporic fungus Phoma tracheiphila (Petri) Kantschaveli et Gikachvili, is the agent of a Citrus tracheomycosis ("malsecco disease") causing xylem impairment and leading to leaf shedding and plant dieback. In the present study, this pathogen was used for monitoring the effects of increasing levels of stem hydraulic resistance (Rstem) on leaf water status and gas exchange. In this view, measurements are reported of changes in the hydraulic resistance of infected stems (Rstem) of C. aurantium (sour orange) during progressive and irreversible xylem blockage with parallel measurements of leaf water potential and conductance to water vapour. Leaves were highly responsive to increasing Rstem as due to fungal infection, with substantial stomatal closure and drop in water potential. [ABSTRACT FROM AUTHOR]

Drought stress hampers rice performance principally by disrupting the plant–water relations and structure of biological membranes. This study appraised the role of polyamines (PAs) in improving drought tolerance in fine grain aromatic rice ( Oryza sativa L.). Three PAs [putrescine (Put), spermidine (Spd) and spermine (Spm)] were used each at 10 μM as seed priming (by soaking seeds in solution) and foliar spray. Primed and non-primed seeds were sown in plastic pots with normal irrigation in a phytotron. At four-leaf stage, plants were subjected to drought stress by bringing the soil moisture down to 50% of field capacity by halting water supply. For foliar application, 10 μM solutions each of Put, Spd and Spm were sprayed at five-leaf stage. Results revealed that drought stress severely reduced the rice fresh and dry weights, while PAs application improved net photosynthesis, water use efficiency, leaf water status, production of free proline, anthocyanins and soluble phenolics and improved membrane properties. PAs improved drought tolerance in terms of dry matter yield and net photosynthesis was associated with the maintenance of leaf water status and improved water use efficiency. Among the antioxidants, catalase activity was negatively related to H2O2 and membrane permeability, which indicated alleviation of oxidative damage on cellular membranes by PAs application. Foliar application was more effective than the seed priming, and among the PAs, Spm was the most effective in improving drought tolerance. [ABSTRACT FROM AUTHOR]

• This study assesses how different phases of shoot growth underlie seasonal change in leaf and stem dry matter content (LDMC and SDMC, respectively) of 12 woody Mediterranean species. The relationship between LDMC and nonstructural carbohydrate (NSC) concentrations is also explored and the seasonal vs interspecies variability of LDMC compared. • LDMC, SDMC and shoot elongation rate (SER) were measured on a monthly basis for a minimum of 12 months. Bud growth rate (BGR) and NSC concentrations were also assessed in several of the study species. • LDMC and SDMC decreased during shoot elongation in spring and increased in summer, showing a significant negative correlation with SER, but were unrelated to BGR. Half of the species analysed showed a positive relationship between LDMC and NSC. Seasonal fluctuations of LDMC within species were higher than interspecies differences, and species ranking was significantly affected by the month of sampling, except during winter months. • Seasonal changes in LDMC and SDMC are mainly related to shoot elongation phenology, and NSC sink–source relationships between old and growing organs can explain this relationship in some species. Owing to the high seasonal variability in LDMC, it is recommended that samples for comparative purposes should be collected as close to the winter as possible. [ABSTRACT FROM AUTHOR]

Abstract: There is an ongoing debate about how European beech might be affected by a future drier climate. While numerous studies have examined the effects of soil drought on beech growth and development, studies investigating the effects of elevated atmospheric water vapour pressure deficit (VPD) are lacking. By increasing VPD in climate and open-top chamber experiments, with moisture in the rooting medium near optimum, we tested the hypothesis that increased VPD negatively affects the growth and development of European beech saplings. In the climate chambers, a reduction in relative air humidity by 40% resulted in a 68% reduction in productivity. Similarly, in the open-top chamber experiment conducted on the forest floor, biomass declined by 30% when relative air humidity was 15% lower. The reduction in biomass was mainly a consequence of a dramatically reduced leaf growth of beech in the elevated VPD treatments. Our results show that growth and development of beech saplings strongly depend not only on soil moisture but also on the prevailing VPD level. We conclude that the vapour pressure deficit is a widely ignored factor which influences the growth and vitality, and possibly also the distribution of European beech. Future forest management schemes under an altered climate should take this factor into account. [Copyright &y& Elsevier]

Abstract: In the northeast of Brazil the drought period determines the yield period of the sugar apple (Annona squamosa L.). As a result, the use of irrigation is essential to stagger production over the course of the year. The results shown here represent an analysis of water status levels in sugar apples in daylight and seasonal periods in semi-arid regions. Two plant groups were studied: one without irrigation and the other with irrigation during drought months. This study showed that younger leaves displayed greater stomatal conductance and transpiration. In drought months, even in irrigated plants, the high air moisture deficit had a strong influence on the stomatal closure, which did not translate into a reduction in transpiration. Over the same period, the leaf water potential was −1.8 and −2.9MPa at mid-day in irrigated and non-irrigated plants, respectively, and only the irrigated plants could recover their leaf hydration level at night. With a water deficit, plants showed greater control of transpiration through stomatal closure, with a linear relationship between stomatal conductance and transpiration. [Copyright &y& Elsevier]

Phenotypes more or less deficient in photosynthetic pigments show reduced productivity. Not much is known, however, about the influence of pigment-less twigs on the water balance of whole trees. We studied the water relations and hydraulic properties of normal and pigment-less (white) and 1-year-old shoots of 12-year-old Citrus sinensis L. trees. Compared with green leaves, white leaves showed a pronounced deficiency of pigments, higher stomatal density, the absence of chloroplasts in the guard cells and a different organization of leaf parenchyma. Stomatal conductance (gL) and transpiration rate (EL) were higher in white leaves than in green leaves during the hottest hours of the day, especially in July and September. The absence of chloroplasts in the stomatal guard cells seemed to be one of the factors causing insufficient stomatal control. Hydraulic conductance (KL) was higher in white leaves than in green leaves (16.96 ± 2.24 x 10-5 versus 11.26 ± 0.66 x 10-5 kg s-1m-2 MPa). The ratio between the sum of the fourth power of xylem conduit radius (Σr4) (which determines theoretical conductance) and the total leaf area supplied by petioles and midribs was higher in white leaves than in green leaves. This was because of a smaller leaf area in white leaves and a statistically different distribution of lumen diameters of the conduits in midribs and petioles. The hydraulic properties of white twigs profoundly disturbed the water balance and physiology of the whole tree. [ABSTRACT FROM AUTHOR]