Effect of water stress and NaCl triggered changes on yield,physiology, biochemistry of broad bean (Vicia faba) plants and on quality of harvested pods

Salinity and drought are the most important abiotic stresses affecting crop yield. Broad bean was chosen as model plant for assessing the impact of salt stress and its interaction with drought in the field experiments. The factors examined in the experiments were the two irrigation rates (normal watering — NW with 3 L plant^?1 and drought — D) and three salinity rates imposed by foliar application (0, 50, 100 mg L^?1 NaCl). Highest NaCl level with normal water irrigation caused maximum reduction in plant height and production, which it was due to photosynthetic disturbances. Salt injuries were alleviated by increasing water stress. The control plants exposed to NaCl lost their ability over water control. The increased malondialdehyde (MDA) and H₂O₂ indicate the prevalence of oxidative stress due to salinity. The levels of proline and carbohydrates were higher under salinity alone than under simultaneous exposure to drought and NaCl. The protein concentration of immature and mature broad bean pods was more inhibited more by NaCl supply than by drought alone. The combination of drought and NaCl resulted in a significant increase in proteins, glucose, fructose and sucrose content. Overall, the ameliorative effect of drought under NaCl supply was quantified.     

Abscisic acid, indole-3-acetic acid and mineral–nutrient changes induced by drought and salinity in longan (Dimocarpus longan Lour.) plants

Longan species (Dimocarpus longan Lour.) exhibit a high agronomic potential in many subtropical regions worldwide; however, little is known about its responses to abiotic stress conditions. Drought and salinity are the most environmental factors inducing negative effects on plant growth and development. In order to elucidate the responses of longan to drought and salinity, seedlings were grown under conditions of drought and salt stresses. Drought was imposed by suspending water supply leading to progressive soil dehydration, and salinity was induced using two concentrations of NaCl, 100 and 150 mM in water solution, for 64 days. Data showed that salt concentrations increased foliar abscisic acid (ABA) and only 150 mM NaCl reduced indole-3-acetic acid (IAA) and increased proline levels. NaCl treatments also increased Na⁺ and Cl^? content in plant organs proportionally to salt concentration. Drought increased leaf ABA but did not change IAA concentrations, and also increased proline synthesis. In addition, drought and salt stresses reduced the photosynthesis performance; however, only drought decreased leaf growth and relative leaf water content. Overall, data indicate that under severe salt stress, high ABA accumulation was accompanied by a reduction of IAA levels; however, drought strongly increased ABA but did not change IAA concentrations. Moreover, drought and high salinity similarly increased (or maintained) ion levels and proline synthesis. Data also suggest that ABA accumulation may mitigate the impact of salt stress through inducing stomatal closure and delaying water loss, but did not mediate the effects of long-term drought conditions probably because leaves reached a strong dehydration and the role of ABA at this stage was not effective to detain leaf injuries.     

Adjusting Nitrogen Application in Accordance with Soil Water Availability Enhances Yield and Water Use by Regulating Physiological Traits of Maize under Drip Fertigation

Knowledge of the interactive effects of water and nitrogen (N) on physio-chemical traits of maize (Zea mays L.) helps to optimize water and N management and improve productivity. A split-plot experiment was conducted with three soil water conditions (severe drought, moderate drought, and fully water supply referring to 45%–55%, 65%–75%, and 85%–95% field capacity, respectively) and four N application rates (N₀, N₁₅₀, N₂₄₀, and N₃₃₀ referring to 0, 150, 240, 330 kg N ha^–1 respectively) under drip fertigation in 2014 and 2015 in the Huang-Huai-Hai Plain of China. The results indicated that drought stress inhibited physiological activity of plants (leaf relative water content, root bleeding sap, and net photosynthetic rate), resulting in low dry matter accumulation after silking, yield, and N uptake, whereas increased WUE and NUE. N application rates over than 150 kg ha^–1 aggravated the inhibition of physiological activity under severe drought condition, while it was offset under moderate drought condition. High N application rates (N₃₃₀) still revealed negative effects under moderate drought condition, as it did not consistently enhance plant physiological activity and significantly reduced N uptake as compared to the N₂₄₀ treatment. With fully water supply, increasing N application rates synergistically enhanced physiological activity, promoted dry matter accumulation after silking, and increased yield, WUE, and N uptake. Although the N₂₄₀ treatment reduced yield by 5.4% in average, it saved 27.3% N under full water supply condition as compared with N₃₃₀ treatment. The results indicated that N regulated growth of maize in aspects of physiological traits, dry matter accumulation, and yield as well as water and N use was depended on soil water status. The appropriate N application rates for maize production was 150 kg ha^–1 under moderate drought or 240 kg ha^–1 under fully water supply under drip fertigation, and high N supply (>150 kg ha^–1) should be avoided under severe drought condition.     

Morpho-physiological responses of sugar beet (Beta vulgaris L.) genotypes to drought stress

The identification of morpho-physiological traits related to drought tolerance and high yield potential is a challenge when selecting sugar beet genotypes with greater tolerance to water stress. In this paper, root morphological parameters, antioxidant systems, leaf relative water content (RWC) and H⁺-ATPase activity as key morpho-physiological traits involved in drought tolerance/susceptibility of sugar beet were studied. Genotypes showing a different drought tolerance index (DTI) but a similar yield potential, under moderate (?0.6 Mpa) and severe (?1.2 MPa) water stress, were selected and their morpho-physiological traits were investigated. The results showed a wide genetic variation in morpho-physiological parameters which demonstrated the different adaptive strategies under moderate and severe drought conditions in sugar beet. In particular, an efficient antioxidant system and redox signalling made some sugar beet genotypes more tolerant to drought stress. The alternative strategy of other genotypes was the reduction of root tissue density, which produced a less dense root system improving the axial hydraulic conductivity. These results could be considered as interesting challenge for a better understanding of the drought tolerance mechanisms in sugar beet.     

Leaf tensity: a method for rapid determination of water requirement information in Brassica napus L.

Water regulation caused by enzymes, such as carbonic anhydrase (CA), changes the water status, making it difficult to diagnose water deficit using leaf water potential (ψ_L) or stomatal conductance (g_s). Therefore, new methods for timely and accurately determining plant water status should be established. In this study, CA activity, ψ_L, leaf tensity (T_d), photosynthetic characteristics and plant growth of Brassica napus L. seedlings under drought and subsequent rewatering were analysed. Results indicated that T_d could reflect the plant water status better than ψ_L or g_s and played an important role in the photosynthesis of B. napus. B. napus exhibited good restorability at the 40?g?L^?1 polyethylene glycol level. The rewatering strategy for B. napus was excellent at 40?g?L^?1 (?0.15?MPa) →20?g?L^?1 (?0.11?MPa). T_d could be used for the rapid determination of water requirement information in B. napus during winter drought period.     

Salt sensitivity in chickpea is determined by sodium toxicity

Main conclusion

Salt sensitivity in chickpea is determined by Na⁺ toxicity, whereas relatively high leaf tissue concentrations of Cl^? were tolerated, and the osmotic component of 60-mM NaCl was not detrimental.Chickpea (Cicer arietinum L.) is sensitive to salinity. This study dissected the responses of chickpea to osmotic and ionic components (Na⁺ and/or Cl^?) of salt stress. Two genotypes with contrasting salt tolerances were exposed to osmotic treatments (?0.16 and ?0.29 MPa), Na⁺-salts, Cl^?-salts, or NaCl at 0, 30, or 60 mM for 42 days and growth, tissue ion concentrations and leaf gas-exchange were assessed. The osmotic treatments and Cl^?-salts did not affect growth, whereas Na⁺-salts and NaCl treatments equally impaired growth in either genotype. Shoot Na⁺ and Cl^? concentrations had markedly increased, whereas shoot K⁺ had declined in the NaCl treatments, but both genotypes had similar shoot concentrations of each of these individual ions after 14 and 28 days of treatments. Genesis836 achieved higher net photosynthetic rate (64–84 % of control) compared with Rupali (35–56 % of control) at equivalent leaf Na⁺ concentrations. We conclude that (1) salt sensitivity in chickpea is determined by Na⁺ toxicity, and (2) the two contrasting genotypes appear to differ in ‘tissue tolerance’ of high Na⁺. This study provides a basis for focus on Na⁺ tolerance traits for future varietal improvement programs for salinity tolerance in chickpea.

     

Comparison of salinity tolerance of three Atriplex spp. in well-watered and drying soils

Members of the Chenopodiaceae are well adapted to both salt and drought stress and can serve as model species to understand the mechanisms of tolerance in plants. We grew Atriplex hortensis (ATHO), A. canescens (ATCA), and A. lentiformis (ATLE) along a NaCL salinity gradient under non-water-limited conditions and in drying soils in greenhouse experiments. The species differed in photosynthetic carbon fixation pathway, capacity for sodium uptake, and habitat preferences. Under non-water-limited conditions, ATLE (C4) maintained high growth rates up to 30 g L⁻¹ NaCl. ATHO (C3) had lower growth than ATLE at high salinities, while ATCA (C4) grew more slowly than either ATLE or ATHO and showed no net growth above 20 g L⁻¹ NaCl. ATHO and ATLE accumulated twice as much sodium in their shoots as ATCA, but all three species had increasing sodium levels at higher salinities. Potassium, magnesium and calcium levels were relatively constant over the salinity gradient. All three species showed marked accumulation of chloride across the salinity gradient, whereas nitrate, phosphorous and sulfate decreased with salinity. The effect of drought was simulated by growing plants in sealed pots with an initial charge of water plus NaCl, and allowing them to grow to the end point at which they no longer were able to extract water from the soil solution. Drought and salinity were not additive stress factors for Atriplex spp. in this experiment. NaCl increased their ability to extract water from the soil solution compared to fresh water controls. ATLE showed increased shoot dry matter production and increased water use efficiency (WUE) as initial salinity levels increased from 0 to 30 g L⁻¹ NaCl, whereas dry matter production and WUE peaked at 5 g L⁻¹ for ATHO and ATCA. Final soil moisture salinities tolerated by species were 85 g L⁻¹, 55 g L⁻¹ and 160 g L⁻¹ NaCl for ATHO, ATCA and ATLE, respectively. C4 photosynthesis and sodium accumulation in shoots were associated with high drought and salt tolerance.     

Proteomics reveals the adaptability mechanism of Brassica napus to short-term boron deprivation

The application of pyrogenic carbon, biochar, to agricultural soils is currently discussed as a win-win strategy to sequester carbon in soil, thus improving soil fertility and mitigate global warming. Our aim was to investigate if biochar may improve plant eco-physiological responses under sufficient water supply as well as moderate drought stress. A fully randomized greenhouse study was conducted with the pseudo-cereal Chenopodium quinoa Willd, using three levels of biochar addition (0, 100 and 200?t ha^?1) to a sandy soil and two water treatments (60% and 20% of the water holding capacity of the control), investigating growth, water use efficiency, eco-physiological parameters and greenhouse gas (GHG) fluxes. Biochar application increased growth, drought tolerance and leaf-N- and water-use efficiency of quinoa despite larger plant?Cleaf areas. The plants growing in biochar-amended soil accumulated exactly the same amount of nitrogen in their larger leaf biomass than the control plants, causing significantly decreased leaf N-, proline- and chlorophyll-concentrations. In this regard, plant responses to biochar closely resembled those to elevated CO₂. However, neither soil- nor plant?Csoil-respiration was higher in the larger plants, indicating less respiratory C losses per unit of biomass produced. Soil-N₂O emissions were significantly reduced with biochar. The large application rate of 200?t ha^?1 biochar did not improve plant growth compared to 100?t ha^?1; hence an upper beneficial level exists. For quinoa grown in a sandy soil, biochar application might hence provide a win-win strategy for increased crop production, GHG emission mitigation and soil C sequestration.     

Growth,photosynthesis and water relations as affected by different drought regimes and subsequent recovery in <Emphasis Type="Italic">Medicago laciniata</Emphasis> (L.) populations

The aims of this study were to investigate the effects of water deficit and recovery on growth, photosynthesis and water relations in four Medicago laciniata populations from saharian (Ml-90), inferior arid (Ml-204), superior arid (Ml-306) and semi-arid (Ml-376) Tunisian regions. After 28 d of sowing with ample irrigation, the plants were subjected to 4 water regimes: optimal irrigation (100% of field capacity, FC), moderate drought (75% FC), severe drought (35% FC) and rewatering (plants submitted to 35% FC during 7 d, afterwards the plants were rewatered to 100% FC). Harvest was carried out after 28 d of treatments. The drought tolerance in M. laciniata populations was found to be increased particularly with increasing temperatures of collection site of the population. The Ml-204 and Ml-90 populations used mainly physiological strategies for survival under moderate water shortage. Higher severe drought tolerance in both signaled populations would be related to their lower photosynthesis metabolic impairment, relatively higher leaf RWC and greater osmotic potential decrease. The results suggest that plants with low values of leaf features are likely to maintain higher leaf RWC under sever drought. The largest decrease of osmotic potential was found associated with the solute accumulations such as proline and K⁺.     

Morphological and physiological responses of Triglochin buchenaui K?cke, Mering & Kadereit to various combinations of water and salinity: implications for resilience to climate change

Impacts of abiotic factors on low lying salt marsh species have been closely evaluated as unique stressors, but few studies have determined the physiological and morphological responses to predicted climate change conditions. This study investigated the effects of water state (tidal, flooded and drought) and salinity on Triglochin buchenaui K?cke, Mering and Kadereit, newly separated from the Triglochin bulbosa L. complex. Growth, proline concentration, relative water content, electrolyte leakage, chlorophyll concentration and morphological analyses were done following 3?months of treatments. Results showed significant variation in height (7.57?±?0.5?C29?±?1.55?cm, p?<?0.005, df?=?55), leaf area increments and relative growth rates which decreased with increasing salinity under all water states. There was almost a cessation of growth under submergence which reduces the plant??s regeneration potential under these conditions. Proline accumulation (1.84?±?0.23?C3.36?±?0.38?mg?g^?1 DW), response of photosynthetic pigments and electrolyte leakage (8.17?±?0.80?C38.36?±?7.42?%???S?g^?1?FW) were fundamental to osmotic and membrane response regulation. Plants survived in all water states at salinity up to 45?ppt, but the optimum range was 0?C18?ppt, and best water state was the tidal condition. Viable rhizomes were produced under drought conditions but in the absence of seed banks, regeneration of the species following prolonged submergence may not be possible due to absence of both rhizomes and seeds. In their natural habitat, highly succulent T. buchenaui plants (29?±?1.55?cm tall and above) are indicative of freshwater conditions.     

Environmental controls on growth and lipid content for the freshwater diatom, Fragilaria capucina: A candidate for biofuel production

The use of microalgae for biofuel production has the potential to reduce fossil fuel consumption. Ideal candidate species of microalgae for bio-oil production need both relatively high growth rates and lipid content. Here, we report on the effects of temperature, nutrients (N, Si), and salinity on growth rates and lipid content of the common freshwater diatom, Fragilaria capucina (Desm), isolated from western Lake Erie. At low NaCl salinity, growth rate increased rapidly from 10 to 20°C, and then further increased slowly from 20 to 30°C, with a maximum specific growth rate of 0.61?day^?1. Growth rate declined with increasing salinity (e.g., reduced by ca. 50 and 100% at 137 and 274?mmol?L^?1 NaCl, respectively), and increased with increased N and Si concentration until ca. 100?μmol?L^?1 for each (with >85% of maximum growth rate at 10?μmol?L^?1). Lipid content (% total lipid per dry mass) in nutrient-replete cultures was 14% and (1) increased to >30% at low N and, especially, low Si; (2) was lower at 30°C vs. 20 or 10°C; and (3) decreased with salinity. Thus, F. capucina accumulates lipid to high levels even under N, Si, and temperature levels that permit a high growth rate for this species, and hence, this species is a candidate for use in biofuel production.     

Drought Responses of Foliar Metabolites in Three Maize Hybrids Differing in Water Stress Tolerance

Maize (Zea mays L.) hybrids varying in drought tolerance were treated with water stress in controlled environments. Experiments were performed during vegetative growth and water was withheld for 19 days beginning 17 days after sowing. Genotypic comparisons used measured changes of leaf water potential or results were expressed by time of treatment. Total dry matter of the drought tolerant hybrid on the final harvest was 53% less than that of the intermediate and susceptible maize hybrids when plants were water sufficient. This showed that maize hybrids selected for extreme drought tolerance possessed a dwarf phenotype that affected soil water contents and leaf water potentials. Changes of shoot and root growth, leaf water potential, net photosynthesis and stomatal conductance in response to the time of water stress treatment were diminished when comparing the drought tolerant to the intermediate or susceptible maize hybrids. Genotypic differences were observed in 26 of 40 total foliar metabolites during water stress treatments. Hierarchical clustering revealed that the tolerant maize hybrid initiated the accumulation of stress related metabolites at higher leaf water potentials than either the susceptible or intermediate hybrids. Opposite results occurred when changes of metabolites in maize leaves were expressed temporally. The above results demonstrated that genotypic differences were readily observed by comparing maize hybrids differing in drought tolerance based on either time of treatment or measured leaf water potential. Current findings provided new and potentially important insights into the mechanisms of drought tolerance in maize.     

Excessive rainfall leads to maize yield loss of a comparable magnitude to extreme drought in the United States

Increasing drought and extreme rainfall are major threats to maize production in the United States. However, compared to drought impact, the impact of excessive rainfall on crop yield remains unresolved. Here, we present observational evidence from crop yield and insurance data that excessive rainfall can reduce maize yield up to ?34% (?17 ± 3% on average) in the United States relative to the expected yield from the long‐term trend, comparable to the up to ?37% loss by extreme drought (?32 ± 2% on average) from 1981 to 2016. Drought consistently decreases maize yield due to water deficiency and concurrent heat, with greater yield loss for rainfed maize in wetter areas. Excessive rainfall can have either negative or positive impact on crop yield, and its sign varies regionally. Excessive rainfall decreases maize yield significantly in cooler areas in conjunction with poorly drained soils, and such yield loss gets exacerbated under the condition of high preseason soil water storage. Current process‐based crop models cannot capture the yield loss from excessive rainfall and overestimate yield under wet conditions. Our results highlight the need for improved understanding and modeling of the excessive rainfall impact on crop yield.     

Over-expression of Osmotin Induces Proline Accumulation and Confers Tolerance to Osmotic Stress in Transgenic Tobacco

Osmotin has been implicated in conferring tolerance to drought and salt stress in plants. We have over-expressed the osmotin gene under the control of constitutive CaMV 35S promoter in transgenic tobacco, and studied involvement of the protein in imparting tolerance to salinity and drought stress. The transgenic plants exhibited retarded leaf senescence and improved germination on a medium containing 200mM NaCl. Further, the transgenics maintained higher leaf relative water content (RWC), leaf photosynthesis and free proline content than the wild type plants during water stress and after recovery from stress. When subjected to salt stress (200mM NaCl), the transgenic plants accumulated significantly more proline than the wild type plants. These results suggest the involvement of the osmotin-induced increase in proline in imparting tolerance to salinity and drought stress in transgenic plants over-expressing the osmotin gene.     

Photosynthetic and wood anatomical responses of Tamarix africana Poiret to water level reduction after short-term fresh- and saline-water flooding

In the Mediterranean basin, Tamarix spp. constitute important populations along rivers and sea coasts, and might be primarily subjected to water level fluctuations and salinization, as a consequence of global climate change. Here, we analyze leaf gas exchange and xylem anatomy during a water level decrease below the soil surface after short-term flooding with fresh- and saline-water (200?mM) in order to predict Tamarix africana Poiret responses under future environmental conditions. Fresh-water level reduction negatively affected stomatal conductance (?56.3?%), but only when water decreased to the lowest level (15?cm below the soil surface). No effects on assimilation rates and xylem vessel dimensions occurred. Under saline conditions, the rate of the water level decrease was lower compared to the non-saline treatment, as stomatal conductance was negatively affected by salinity (?59.5?%) and significantly declined over time. Moreover, decreases in mean xylem vessel area (?51.3?%), assimilation rates (?52.2?%) and stomatal conductance (?76.0?%) were also observed compared to the control, indicating both an osmotic stress and a toxic effect of NaCl on leaf gas exchange. These leaf responses were probably induced by greater belowground-root salt absorption and transport compared to previous flooding conditions, as confirmed by the increase in salt excretion (+473.2?%). The results emphasize the survival risk of Tamarix spp. to water level variation under both saline and non-saline conditions, and the need of management practices focused on the conservation of these populations.     

Foliar Application of Cytokinin Modulates Gas Exchange Features,Water Relation and Biochemical Responses to Improve Growth Performance of Maize under Drought Stress

Improvement of plant performance under drought stress is crucial to sustaining agricultural productivity. The current study investigated the ameliorative effects of foliar-applied kinetin, an adenine-type cytokinin (CK), on growth and gas exchange parameters, water relations and biochemical attributes of maize plants under drought stress. Eighteen-day-old maize plants were subjected to drought by maintaining soil moisture content at 25% field capacity for 8 days followed by foliar application of kinetin at 0, 75, 150 and 225 mg L⁻¹ (CK0, CK75, CK150 and CK225, respectively) to the plants for two-times at the 9-day interval. Results revealed that drought stress markedly reduced stem diameter, dry weight, chlorophyll content, gas exchange parameters and water balance but increased proline, malondialdehyde and soluble sugar contents, electrolyte leakage and senescence in maize leaves. Application of exogenous CK remarkably improved maize performance by modulating growth, gas exchange- and water relation-related parameters in a dose-dependent manner under drought stress. CK225 increased chlorophyll content (by 61.54%), relative water content (by 49.14%), net photosynthesis rate (by 39.94%) and transpiration rate (by 121.36%) and also delayed leaf senescence but decreased internal CO₂ concentration (by 7.38%), water saturation deficit (by 40.40%) and water uptake capacity (by 42.49%) in both well-watered and drought-stressed plants. Nevertheless, CK application considerably decreased electrolyte leakage, proline, malondialdehyde and soluble sugar levels in drought-stressed maize plants, as also supported by heatmap and cluster analyses. Taken together, exogenous CK at proper concentration (225 mg L⁻¹) successfully improved maize performance under drought conditions, thereby suggesting CK application as a useful approach to alleviate drought-induced adverse effects in maize plants, and perhaps in other important crop plants.     

Physiological response of Nannochloropsis sp. to saline stress in laboratory batch cultures

In the present paper, we investigated the physiological response of the marine microalga Nannochloropsis sp. to salt stress (13, 27, 54, and 81 g L^?1 NaCl). Increasing the sodium chloride concentration caused up to a 70 % decrease in the chlorophyll a concentration, cell growth, and net photosynthesis rate. The chlorophyll a fluorescence measurements indicated a strong reduction in the effective quantum yield of photosystem II (?60 %) and an increase in nonphotochemical quenching when the cells were exposed to NaCl concentrations greater than 27 g L^?1 (control). In contrast, the specific lipid content increased up to 80 % when the sodium chloride concentration was increased from 27 to 54–81 g L^?1. These results are relevant for the outdoor cultivation of this microalga using open photobioreactors, in which microalgae are subjected to strong changes in salinity concentration caused by water evaporation.     

Differences in physiological and biochemical characteristics in response to single and combined drought and salinity stresses between wheat genotypes differing in salt tolerance

The combined drought and salinity stresses pose a serious challenge for crop production, but the physiological mechanisms behind the stresses responses in wheat remains poorly understood. Greenhouse pot experiment was performed to study differences in genotype response to the single and combined (D + S) stresses of drought (4% soil moisture, D) and salinity (100 mM NaCl, S) using two wheat genotypes: Jimai22 (salt tolerant) and Yangmai20 (salt‐sensitive). Results showed that salinity, drought and/or D + S severely reduces plant growth, biomass and net photosynthetic rate, with a greater effect observed in Yangmai20 than Jimai22. A notable improvement in water use efficiency (WUE) by 239, 77 and 103% under drought, salinity and D + S, respectively, was observed in Jimai22. Moreover, Jimai22 recorded higher root K⁺ concentration in drought and salinity stressed condition and shoot K⁺ under salinity alone than that of Yangmai20. Jimai22 showed lower increase in malondialdehyde (MDA) accumulation, but higher activities of superoxide dismutase (SOD, EC 1.15.1.1) and guaicol peroxidase (POD, EC 1.11.1.7), under single and combined stresses, and catalase (CAT, EC 1.11.1.6) and ascorbate peroxidase (APX, EC 1.11.1.11) under single stress. Our results suggest that high tolerance of Jimai22 in both drought and D + S stresses is closely associated with larger root length, higher Fv/Fm and less MDA contents and improved capacity of SOD and POD. Moreover, under drought Jimai22 tolerance is firmly related to higher root K⁺ concentration level and low level of Na⁺, high‐net photosynthetic rate and WUE as well as increased CAT and APX activities to scavenge reactive oxygen species.     

Responses to UV-B radiation in Trifolium repens L. – physiological links to plant productivity and water availability

This study used comparisons across nine populations of Trifolium repens (white clover) in conjunction with drought to examine physiological responses to ultraviolet‐B radiation (UV‐B). Plants were exposed for 12 weeks to supplementation with 13.3 kJ m^?2 d^?1 UV‐B, accompanied by 4 weeks of drought under controlled environmental conditions. UV‐B increased the levels of UV‐B‐absorbing compounds and of flavonol glycosides and this effect was synergistically enhanced by water stress. These changes were more pronounced for the ortho‐dihydroxylated quercetin, rather than the monohydroxylated kaempferol glycosides. UV‐B increased leaf water potential (ψ_L) by 16% under drought and proline levels by 23% under well‐watered conditions. The intraspecific comparisons showed that higher UV‐B‐induced levels of UV‐B‐absorbing compounds, of quercetin glycosides and of ψ_L were linked to lower plant productivity and to higher UV‐B tolerance under well‐watered conditions. These findings suggest that: (1) slow‐growing T. repens ecotypes adapted to other stresses have higher capacity for physiological acclimation to UV‐B; and (2) that these attributes also contribute to decreased UV‐B sensitivity under drought.