Leaf Cl Research Articles

Partial substitution of nitrate by chloride in fertigation recipes allows for lower nitrate input in hydroponic lettuce crops.

The management of nitrogen (N) fertilization is of fundamental importance in hydroponics. To reduce the supply of nitrate (NO3 -) in fertigation recipes for Batavia lettuce crops grown in closed hydroponics, partial replacement of nitrate by chloride (NO3 -/Cl-) at different ratios but with the same equivalent sum was experimentally tested. The experiment included four nutritional treatments in the replenishment nutrient solution, particularly T1; 0.7 mM Cl-/19 mM NO3 -, T2; 2 mM Cl-/17.7 mM NO3 -, T3; 4 mM Cl-/15.7 mM NO3 - and T4; 6 mM Cl-/13.7 mM NO3 -. The results showed that reducing nitrate supply combined with equivalent increase in chloride application gradually reduced the gap between nitrate input and nitrogen uptake concentrations, with the smallest differences occurring in T4 treatment, which reduced the nitrate concentration in the drainage by 50%. The tested treatments led to very small variations in plant water uptake, production of fresh biomass and nutritional quality, which is justified by the proper functioning of key physiological mechanisms, such as stomatal conductance, which was followed by an increased efficiency of nitrogen use up to 25% (kg fresh biomass kg-1 N supply). The steady level of C/N ratio in the plant tissue irrespective of NO3 -/Cl- supply ratio points to sufficiency in photosynthetic products and adequacy in the supply of nitrogen, although leaf Cl- content increased up to 19.6 mg g-1 dry weight in the lowest NO3 -/Cl- treatment. Nutrient uptake concentrations were determined as follows: 13.4 (N), 1.72 (P), 10.2 (K), 3.13 (Ca), 0.86 (Mg, mmol L-1), 27.8 (Fe), 5.63 (Mn), 5.45 (Zn) and 0.72 (Cu, μmol L-1). This study suggests that replacing 30% of NO3 - supply with Cl- in fertigation recipes for hydroponic lettuce crops reduces leaf nitrate content without affecting physiological processes, growth, and quality, verifying in parallel the role of chloride as a beneficial macronutrient. Finally, a relationship between Cl- uptake and its concentration in the root zone solution was established enabling the simulation of chloride to water consumption.

Meta-QTL and Candidate Gene Analyses of Agronomic Salt Tolerance and Related Traits in an RIL Population Derived from Solanum pimpinellifolium.

Breeding salt-tolerant crops is necessary to reduce food insecurity. Prebreeding populations are fundamental for uncovering tolerance alleles from wild germplasm. To obtain a physiological interpretation of the agronomic salt tolerance and better criteria to identify candidate genes, quantitative trait loci (QTLs) governing productivity-related traits in a population of recombinant inbred lines (RIL) derived from S. pimpinellifolium were reanalyzed using an SNP-saturated linkage map and clustered using QTL meta-analysis to synthesize QTL information. A total of 60 out of 85 QTLs were grouped into 12 productivity MQTLs. Ten of them were found to overlap with other tomato yield QTLs that were found using various mapping populations and cultivation conditions. The MQTL compositions showed that fruit yield was genetically associated with leaf water content. Additionally, leaf Cl- and K+ contents were related to tomato productivity under control and salinity conditions, respectively. More than one functional candidate was frequently found, explaining most productivity MQTLs, indicating that the co-regulation of more than one gene within those MQTLs might explain the clustering of agronomic and physiological QTLs. Moreover, MQTL1.2, MQTL3 and MQTL6 point to the root as the main organ involved in increasing productivity under salinity through the wild allele, suggesting that adequate rootstock/scion combinations could have a clear agronomic advantage under salinity.

Similar and divergent responses to salinity stress of jamun (Syzygium cumini L. Skeels) genotypes.

Genetic variation for salt tolerance remains elusive in jamun (Syzygium cumini). Effects of gradually increased salinity (2.0-12.0 dS/m) were examined in 20 monoembryonic and 28 polyembryonic genotypes of jamun. Six genotypes were additionally assessed for understanding salt-induced changes in gas exchange attributes and antioxidant enzymes. Salt-induced reductions in leaf, stem, root and plant dry mass (PDM) were relatively greater in mono- than in poly-embryonic types. Reductions in PDM relative to control implied more adverse impacts of salinity on genotypes CSJ-28, CSJ-31, CSJ-43 and CSJ-47 (mono) and CSJ-1, CSJ-24, CSJ-26 and CSJ-27 (poly). Comparably, some mono- (CSJ-5, CSJ-18) and poly-embryonic (CSJ-7, CSJ-8, CSJ-14, CSJ-19) genotypes exhibited least reductions in PDM following salt treatment. Most polyembryonic genotypes showed lower reductions in root than in shoot mass, indicating that they may be more adept at absorbing water and nutrients when exposed to salt. The majority of genotypes did not exhibit leaf tip burn and marginal scorch despite significant increases in Na+ and Cl-, suggesting that tissue tolerance existed for storing excess Na+ and Cl- in vacuoles. Jamun genotypes were likely more efficient in Cl- exclusion because leaf, stem and root Cl- levels were consistently lower than those of Na+ under salt treatment. Leaf K+ was particularly little affected in genotypes with high leaf Na+. Lack of discernible differences in leaf, stem and root Ca2+ and Mg2+ contents between control and salt treatments was likely due to their preferential uptake. Correlation analysis suggested that Na+ probably had a greater inhibitory effect on biomass in both mono- and poly-embryonic types. Discriminant analysis revealed that while stem and root Cl- probably accounted for shared responses, root Na+, leaf K+ and leaf Cl- explained divergent responses to salt stress of mono- and poly-embryonic types. Genotypes CSJ-18 and CSJ-19 seemed efficient in fending off oxidative damage caused by salt because of their stronger antioxidant defences. Polyembryonic genotypes CSJ-7, CSJ-8, CSJ-14 and CSJ-19, which showed least reductions in biomass even after prolonged exposure to salinity stress, may be used as salt-tolerant rootstocks. The biochemical and molecular underpinnings of tissue tolerance to excess Na+ and Cl- as well as preferential uptake of K+, Ca2+, and Mg2+ need to be elucidated.

Populus euphratica has stronger regrowth ability than Populus pruinosa under salinity stress.

Pest infestation and soil salinization levels are increasing due to climate change. Comprehending plant regrowth after insect damage and salinity stress is crucial to understanding climate change's multifactorial impacts on forest ecosystems. This study examined Populus euphratica and P. pruinosa regrowth after different defoliation levels combined with salinity stress. Specifically, the biomass and regrowth ability, non-structural carbohydrate (NSC) and nitrogen (N) pools in different organs and the whole plant, and the leaf Cl- concentration of both poplars were analyzed. Our results showed that after 50% defoliation and no salt addition, the regrowth of both species recovered similarly to the control level, while their regrowth was about 70% after 90% defoliation. However, under salinity stress, the regrowth (% leaf biomass) of P. euphratica was significantly higher than P. pruinose at either the 50% or 90% defoliation levels. Additionally, P. euphratica had more soluble sugar, starch, NSC and N pools in leaf, stem, root and whole plant than P. pruinose under salinity stress. The regrowth based on leaf biomass increased linearly with soluble sugar, starch, NSC and N pools, and decreased linearly with leaf Cl- concentration across different salinity and defoliation levels. These results indicated that defoliation significantly decreased NSC and N pools, limiting the growth of both poplars, and salinity stress exacerbated the negative effect. Furthermore, when suffering from salinity stress, P. euphratica with higher NSC and N pools exhibited stronger regrowth ability than P. pruinose.

Salt-excluder rootstock improves physio-biochemical responses of grafted grapevine plants subjected to salinity stress

This study tests the hypothesis that a more salt-excluder rootstock can attenuate salt stress in grapevine plants by enhancing photosynthesis and providing ionic and oxidative protection. Plants of ‘BRS Vitória’ variety, grafted with the rootstocks IAC 313 (salt-excluder) and SO4, were subjected to salinity by adding NaCl (0, 50, and 100 mM) for 30 days. Plants with SO4 showed more severe salt toxicity symptoms in leaves and lower chlorophyll content under salinity. Conversely, plants with IAC 313 showed improved photosynthesis and stomatal conductance, along with higher carboxylation efficiency under salt compared to SO4. Under salinity, plants with SO4 showed higher losses of K+ in stems, roots, and petioles, as well as increased accumulation of Na+ in these organs, relative to IAC 313. Furthermore, plants with IAC 313 had lower leaf Na+ content under salinity and reduced leaf Cl− content at 50 mM NaCl, a response associated with a higher Na+ allocation in petioles of IAC 313. At 50 mM, IAC 313 exhibited better photochemical activity, as indicated by electron transport rate and non-photochemical quenching. However, at 100 mM, both rootstocks showed similar trends, suggesting that the photosynthetic restriction was primarily due to stomatal disturbances. Plants with IAC 313 showed better APX activity and ascorbate balance under salinity. IAC 313 showed more salt-resistance traits than SO4, although the growth was similarly affected in both rootstocks. This response could be due to the reduced time of salt treatment (30 days). In summary, our data indicate that IAC 313 rootstock possesses better salt tolerance traits than SO4.

Nitrogen Fertilization Effects on Boron and Chloride Concentration, Yield and Quality in Potato

ABSTRACT Nitrogen (N) availability affects the boron (B) and chloride (Cl) concentrations in potato plants. The objective of our study was to evaluate: 1) the effect of nitrogen (N) fertilization on boron (B) and chloride (Cl) concentration in leaves and tubers, yield and tuber quality; and 2) the use of nitrogen nutrition index in shoot biomass (NNIsh) and in the tuber at harvest (NNItH) to estimate B and Cl nutrition status. Two trials were carried out (2009/10 and 2010/11). At each year, a split-plot randomized complete blotuber B uptakeck design with three replications was used. The main plot was the N rate applied at planting (0 or 50 kg N ha−1), and the subplots were the N rate applied at tuber initiation (0, 50 or 100 kg N ha−1). Our results showed that leaf B concentration and yield increased with N availability (13% and 5%, respectively). While leaf and tuber Cl concentration and DM decreased with N availability (16%, 18% and 3%, respectively). Moreover, the NNIsh was related to the leaf B and Cl concentration and relative yield. The NNItH was also closely related to dry matter (DM), B and Cl concentrations in tubers at harvest. This study demonstrated that N fertilization affected the concentration of B and Cl in leaf and tuber and that NNIsh and NNItH estimated the nutritional status of anionic micronutrients. Therefore, simultaneous N, B and Cl management is critical for increasing their use efficiencies and improving crop productivity.

Combining Genetic and Transcriptomic Approaches to Identify Transporter-Coding Genes as Likely Responsible for a Repeatable Salt Tolerance QTL in Citrus

The excessive accumulation of chloride (Cl−) in leaves due to salinity is frequently related to decreased yield in citrus. Two salt tolerance experiments to detect quantitative trait loci (QTLs) for leaf concentrations of Cl−, Na+, and other traits using the same reference progeny derived from the salt-tolerant Cleopatra mandarin (Citrus reshni) and the disease-resistant donor Poncirus trifoliata were performed with the aim to identify repeatable QTLs that regulate leaf Cl− (and/or Na+) exclusion across independent experiments in citrus, as well as potential candidate genes involved. A repeatable QTL controlling leaf Cl− was detected in chromosome 6 (LCl-6), where 23 potential candidate genes coding for transporters were identified using the C. clementina genome as reference. Transcriptomic analysis revealed two important candidate genes coding for a member of the nitrate transporter 1/peptide transporter family (NPF5.9) and a major facilitator superfamily (MFS) protein. Cell wall biosynthesis- and secondary metabolism-related processes appeared to play a significant role in differential gene expression in LCl-6. Six likely gene candidates were mapped in LCl-6, showing conserved synteny in C. reshni. In conclusion, markers to select beneficial Cleopatra mandarin alleles of likely candidate genes in LCl-6 to improve salt tolerance in citrus rootstock breeding programs are provided.

Salinity level influenced morpho-physiology and nutrient uptake of young citrus rootstocks

Soil and irrigation water salinity are major limiting factor to citrus industry in arid environments.The objective of this study was to assess the effects of different salt stress levels on growth and ion uptake of three-month-old citrus rootstocks; sour orange (Citrus aurantium) and Volkamer lemon (Citrus volkameriana). Six levels of NaCl-salinity were used, 0.7 (control), 2, 4, 8, 12 and 15 dS m−1. Salinity increment from 2.0 to 15.0 dS m−1 significantly reduced seedlings height, stem diameter, leaf area, root dry weight, leaf relative water content, chlorophyll content index and chlorophyll fluorescence by one to three folds. In addition, leaf and root N concentration reduced by 10%–50%, P 6%–50%, K 8%–47%, Ca+2 7%–51% and Mg+2 7%–50% when salt stress in the irrigation water increased from 2.0 to 15.0 dS m−1. Conversely, salt stress increment (2.0–15.0 dS m−1) increased leaf stomatal resistance (5 folds), proline concentration (1 fold), Na+ and Cl− in the leaf (10 fold) and root (4 fold) when compared to control (0.7 dS m−1). In term of rootstock, Volkamer had higher seedling height, stem diameter, and root constituents (length, fresh and dry weight) than sour orange. While sour orange had higher leaf Cl−, Ca+2 and Mg+2, Volkamer lemon had higher N, Na+, K+, and P. However, root nutrient (N, Na+, Cl−, P and Mg+2) from Volkamer had consistently higher concentration compared to sour orange at 4.0, 8.0, 12.0 and 15.0 dS m−1. Therefore, we believe that the Volkamer rootstock is more tolerant to salt stress than sour orange.

Populus euphratica males exhibit stronger drought and salt stress resistance than females

Much attention has been paid on dioecious plants and their responses to environmental stresses. However, little information is available on sexual dimorphism in Populus euphratica Oliver, which usually grows in arid desert areas and exposes to drought and salinity stress. In this study, we investigated female and male seedlings of P. euphratica and their growth and anatomical structure, gas exchange, water and nitrogen use, oxidative stress and antioxidants under drought, salinity, and the combined stress. We found that there were no significant sexual differences in P. euphratica under control conditions (well-watered and no salt addition). However, males showed stronger resistance to drought, salinity and especially to the combined stress, as they had protective structures, higher biomass, net photosynthetic rate (Pn), water and nitrogen use, osmotic adjustment and reactive oxygen species (ROS) scavenging ability, and a lower leaf Cl– content under stress conditions. The significant sex × drought × salinity interactions for biomass, Pn, water and nitrogen use, superoxide radicals (O2–), proline and free amino acids (FAA) indicated that sexual dimorphism occurs depending on the stress gradients, implying contrasting adaptive responses and life strategies in P. euphratica females and males under stress conditions. Due to the sexual dimorphism of P. euphratica under drought and salinity stress, more severe shifts in the sex ratio of P. euphratica forests may occur under future climate change with aggravated aridity and soil salinity.

Root system response to salt stress in grapevines (Vitis spp.): A link between root structure and salt exclusion

Accessing freshwater resources for agriculture becomes more complex due to increasing demands and declining water quality. Alternative water sources, such as saline water, require ad hoc solutions. Therefore, understanding roots' response to saline water is crucial for future agriculture. We examined the response of three grapevine rootstocks (Paulsen 1103, Richter 110 and SO4) to salt stress. The rootstocks were subjected to two salinity treatments: 10 mM and 30 mM NaCl (EC = 2 and 4 ds/m, respectively). Root and shoot samples were taken at the end of the experiment for morphologic and ionomic analyses. The specific root area (SRA) increased in response to salinity for all three rootstocks due to root tissue density and average root diameter reductions. Salinity also led to increased root Na+ and Cl- contents and reduced root K+/Na+ ratio, parallel to increased leaf Cl- but not Na+ contents. SO4 showed improved chloride and sodium exclusion, concomitant with its highest SRA, resulting from the increase in its thin roots' contribution to the total root system surface area. We suggest that enhanced SRA combined with decreased root tissue density and diameter may improve grapevines' salt exclusion by less salt uptake from the soil.

Physiological and Transcriptional Responses to Saline Irrigation of Young 'Tempranillo' Vines Grafted Onto Different Rootstocks.

The use of more salt stress-tolerant vine rootstocks can be a sustainable strategy for adapting traditional grapevine cultivars to future conditions. However, how the new M1 and M4 rootstocks perform against salinity compared to conventional ones, such as the 1103-Paulsen, had not been previously assessed under real field conditions. Therefore, a field trial was carried out in a young ‘Tempranillo’ (Vitis vinifera L.) vineyard grafted onto all three rootstocks under a semi-arid and hot-summer Mediterranean climate. The vines were irrigated with two kinds of water: a non-saline Control with EC of 0.8 dS m–1 and a Saline treatment with 3.5 dS m–1. Then, various physiological parameters were assessed in the scion, and, additionally, gene expression was studied by high throughput sequencing in leaf and berry tissues. Plant water relations evidenced the osmotic effect of water quality, but not that of the rootstock. Accordingly, leaf-level gas exchange rates were also reduced in all three rootstocks, with M1 inducing significantly lower net photosynthesis rates than 1103-Paulsen. Nevertheless, the expression of groups of genes involved in photosynthesis and amino acid metabolism pathways were not significantly and differentially expressed. The irrigation with saline water significantly increased leaf chloride contents in the scion onto the M-rootstocks, but not onto the 1103P. The limitation for leaf Cl– and Na+ accumulation on the scion was conferred by rootstock. Few processes were differentially regulated in the scion in response to the saline treatment, mainly, in the groups of genes involved in the flavonoids and phenylpropanoids metabolic pathways. However, these transcriptomic effects were not fully reflected in grape phenolic ripeness, with M4 being the only one that did not cause reductions in these compounds in response to salinity, and 1103-Paulsen having the highest overall concentrations. These results suggest that all three rootstocks confer short-term salinity tolerance to the scion. The lower transcriptomic changes and the lower accumulation of potentially phytotoxic ions in the scion grafted onto 1103-Paulsen compared to M-rootstocks point to the former being able to maintain this physiological response in the longer term. Further agronomic trials should be conducted to confirm these effects on vine physiology and transcriptomics in mature vineyards.

Growth, Gas Exchange, and Mineral Nutrients of Hydrangea Hybrids Irrigated with Saline Water

Hydrangeas are popular landscape plants that are widely grown in many parts of the world. The objective of this study was to evaluate the salinity tolerance of three novel Dichroa ×hydrangea hybrids [Dichroa febrifuga ‘Yamaguchi Hardy’ × Hydrangea macrophylla ‘Hamburg’ (YH × Hamburg), Dichroa febrifuga ‘Yellow Wings’ ×Hydrangea macrophylla ‘Nigra’ (YW × Nigra), and Dichroa febrifuga ‘Yellow Wings’ ×Hydrangea macrophylla ‘Oakhill’ (YW × Oakhill)]. A 52-day greenhouse study was conducted by irrigating container-grown plants with nutrient solution at an electrical conductivity (EC) of 1.1 dS·m−1 (control) or saline solution at an EC of 5.0 dS·m−1 (EC 5) or 10.0 dS·m−1 (EC 10). At harvest, YH × Hamburg and YW × Nigra in EC 5 and EC 10 still exhibited good quality with average visual scores greater than 4.1 (0 = dead; 5 = excellent). For YW × Oakhill, moderate foliar salt damage was observed with an average visual score of 2.9 in EC 5 and 2.2 in EC 10. Compared with control, the shoot dry weight of YH × Hamburg, YW × Nigra, and YW × Oakhill in EC 5 reduced by 35%, 35%, and 55%, respectively, whereas that in EC 10 decreased by 58%, 58%, and 67%, respectively. Elevated salinity also decreased plant height, leaf area, and leaf greenness [Soil Plant Analysis Development (SPAD) readings]; chlorophyll fluorescence (Fv/Fm); performance index (PI); and net photosynthetic rate (Pn). All these responses might result from excess accumulation of sodium (Na+) and chloride (Cl−) ions in hydrangea leaves. In this study, compared with control, leaf Na+ concentration of YH × Hamburg, YW × Nigra, and YW × Oakhill increased 11, 36, and 14 times, respectively, in EC 5, and 31, 53, and 18 times, respectively, in EC 10. Compared with control, leaf Cl− concentration increased 4, 9, and 7 times in EC 5, and 10, 11, and 8 times in EC 10 for YH × Hamburg, YW × Nigra, and YW × Oakhill, respectively. Leaf nitrogen (N), phosphorous (P), potassium (K+), and iron (Fe3+) concentrations decreased at elevated salinity levels but did not cause any nutrient deficiency. In summary, the three Dichroa ×hydrangea hybrids exhibited different salinity tolerance: YH × Hamburg and YW × Nigra were more tolerant than YW × Oakhill. Salt-tolerant hydrangea hybrids should be chosen for landscape use if soil and/or irrigation water are salty.

Dryland field validation of genotypic variation in salt tolerance of chickpea (Cicer arietinum L.) determined under controlled conditions

Chickpea ( Cicer arietinum L.) is a moderately salt-susceptible grain legume species. Genotypic differences in salt tolerance/susceptibility have been identified in chickpea genotypes grown in adequately-watered soil in pots with different salt concentrations, but few studies have been conducted in saline fields. This three-year study compared the growth and yield of chickpea genotypes to determine whether genotypic differences in salt tolerance/susceptibility identified in glasshouse pot experiments applied when grown in a dryland saline field. The emergence, phenology, growth, leaf ion concentration, yield and yield components of 10–20 chickpea genotypes were compared under controlled saline and water conditions in the glasshouse, and saline and non-saline conditions in the field in a semiarid environment. In the field, soil salinity and yields varied from year to year in the non-saline and saline treatments. Genotypic differences in salt tolerance and sensitivity were observed in the controlled salt and water conditions in the glasshouse. The salt tolerant and salt sensitive check genotypes, GENESIS 836 and RUPALI, respectively, grown in all three comparison years were similarly tolerant and sensitive in the glasshouse and dryland field in all three comparison years. However, other genotypes selected for salt tolerance under controlled conditions were not observed to be tolerant in the dryland field. While salinity slowed the rate of emergence and increased the time to flowering, the variation in saline yields among genotypes was associated with aboveground biomass, filled pod number and seed number at maturity in both the glasshouse and field, but not the number of emerged plants that survived to maturity or the delay in flowering. Salinity significantly increased the leaf Na + , K + and Cl - concentrations in the glasshouse and field (except in the glasshouse in 2010). Na + increased in young and old leaves by 28–84%, but the concentrations of Na + or K + in the leaves across genotypes was not correlated with yield in saline soil. Salinity increased leaf Cl – concentrations by 80–290%; the increase in young leaves had a significant association with reduced yield among genotypes only in the glasshouse in one year. We conclude that selection under controlled soil salinity and water content in pots can identify some genotypes that are salt tolerant, but for dryland saline environments verification of their tolerance in comparable environments is essential. • Chickpeas for dryland saline sites require phenotyping in appropriate environments. • Genotypic variation in water-limited yield confounds salt tolerance in the field. • Salt tolerant chickpeas do not universally exhibit cross-tolerance for water-limited yield. • Dryland salt tolerance is associated with increased biomass and reproductive success.

Nitrate supply limitations in tomato crops grown in a chloride-amended recirculating nutrient solution

Partial substitution of nitrate (NO3-) with chloride (Cl-) in the nutrient solution supplied to tomato crops (beefsteak and cherry types), grown in a closed hydroponic system, maintained nitrogen (N)- and carbon (C)- assimilation status in plants despite N-supply limitations. Lowering NO3- ions (90% of total N) supply to 2/3 of the standard recommendations, which was electrochemically compensated for by an equivalent increase of the Cl- concentration in the replenishment nutrient solution (RNS), increased N use efficiency (kg produce kg−1 N supply) and decreased NO3- in the drainage without compromising growth, yield and nutritional quality. Tomato plants supplied with Cl--amended RNS increased leaf Cl- content to macronutrient level (35 mg g−1 dry weight), retaining photosynthetic rates and crop yield potential at lower stomatal conductivity and transpiration. Nutrient to water uptake ratios (mass of nutrient per water volume absorbed), which are commonly termed ‘uptake concentrations’, were defined in different cropping seasons and ranged as follows: 12.1–13.5 (Nitrogen- NO3-+NH4+), 1.25–1.35 (Phosphorus-P), 6.1–6.3 (Potassium-K), 3.6–4.0 (Calcium-Ca), 1.0–1.3 (Magnesium-Mg, mmol L−1), 13.0–14.3 (Iron-Fe), 7.6–8.4 (Manganese-Mn), 5.1–5.2 (Zinc-Zn) and 0.7–0.9 (Copper-Cu, μmol L−1). The levels of N and Cl- supply had no impact on the uptake concentrations. This study suggests that replacing 1/3 of the standard NO3- supply by Cl- in closed hydroponic tomato crops enhances N use by two-fold and eliminates NO3- losses to one-half, with no significant effects on assimilation processes and fruit biomass production, suggesting that Cl- at appropriate concentrations is not only an essential micronutrient but also a beneficial macronutrient. The obtained uptake concentrations may be used through on-line operating decision support systems to optimize nutrient supply in hydroponic cultivations in Mediterranean greenhouses.

Contrasting Responses of Guar Genotypes Shed Light on Multiple Component Traits of Salinity Tolerance Mechanisms

Guar (Cyamopsis tetragonoloba (L.) Taub.) is a legume crop, and gum derived from its seeds has various industrial applications. Due to its tolerance to various abiotic stresses, guar can be grown under water-deficit or high-salinity conditions. In this investigation, four diverse guar genotypes that performed at a similar level in field conditions were evaluated in a salinity experiment in the greenhouse lysimeter system. Based on the salt tolerance index (STI) for shoot biomass, root biomass, shoot length, and root length, Matador and PI 268229 were classified as salt-tolerant, and PI 340261 and PI 537281 as salt-sensitive. Leaf Na concentrations were 4- to 5.5-fold higher, and leaf Cl concentrations were 1.6- to 1.9-fold higher in salt-sensitive lines than salt-tolerant lines under salinity. The strong associations between the leaf K concentrations under salinity compared to the control (K-salinity/K-control) ratio and STI for stem and root length advocate higher importance of K-salinity/K-control than total leaf K concentrations. The expression analyses of genes involved in Na+ and Cl− transport revealed the importance of different component traits of salinity tolerance mechanisms, such as the exclusion of Na+/Cl− from the root, sequestration of Cl− in root vacuoles, retrieval of Na+/Cl− from xylem during salinity stress, root-to-shoot Na+/Cl− translocation, and K+-Na+ homeostasis.

Effect of sea water substitution on growth, physiological and biochemical processes of coconut (Cocos nucifera L.) seedlings—A hydroponic study

Coconut is grown along the coasts and islands that are vulnerable to climate change-induced sea level rise. Though coconut is considered moderately salt tolerant, our understanding on the growth and physiological response to sea water, either inundation or subsurface water contamination, is very limited. This understanding will enable to effectively manage coconut in coastal systems under future climatic scenarios. In this study, ten month old hydroponically grown coconut seedlings were subjected to 0, 10, 25, 50, 75 and 100 % of sea water substitution (SWS), equivalent to 2.17, 8.32, 16.32, 30.03, 42.14 and 53.69 dS m−1 EC, respectively. Substituting Hoagland solution in hydroponic system by sea water of increasing concentration (>50 % SWS) significantly changed physiological processes; Fv/Fm decreased and rs increased as early as 7 and 18 days after treatment imposition (DAT), respectively which led to significant decline in leaf area and root length expansion as early as 24 DAT. At 25 % SWS, root system (root length and root biomass) was stable but the aerial part biomass was declined by 47 %. On the other hand plant height, leaf area, collar girth and biomass accumulation of seedlings under 10 % SWS (8.32 EC) was on par with the control plants suggesting coconut seedlings could tolerate 10 % SWS. Though, PN declined by 19 % and 43 % at 10 % and 25 % SWS, respectively and a similar decline in gs without a concomitant change in leaf water potential suggested that root-generated signals regulated the stomatal movement in coconut under salinity. Still the biomass accumulation at 10 % SWS was not affected by decline in PN. Under increasing sea water treatments, most of the Na+ absorbed was compartmentalized in root and shoot, while leaf had more accumulation of K+, that ensured high K+/Na+ ratio in the leaves which is an important salinity tolerant mechanism observed in coconut. The leaf Cl− content also had strong negative correlation with [PN] (r=-0.873) and biomass (r=-0.833), therefore in addition to K+ and Na+ homeostasis, the level of tolerance to the increased Cl− content in the leaves may also play an important role in salinity tolerance of coconut. This understanding will help in making appropriate strategies for managing coconut grown at coastal systems in the face of sea level rise under climate change.

Exogenous Salicylic Acid Modulates the Response to Combined Salinity-Temperature Stress in Pepper Plants (Capsicum annuum L. var. Tamarin).

Growers in the cultivated areas where the climate change threatens the agricultural productivity and livelihoods are aware that the current constraints for good quality water are being worsened by heatwaves. We studied the combination of salinity (60 mM NaCl) and heat shock stress (43 °C) in pepper plants (Capsicum annuum L. var. Tamarin) since this can affect physiological and biochemical processes distinctly when compared to separate effects. Moreover, the exogenous application of 0.5 mM salicylic acid (SA) was studied to determine its impacts and the SA-mediated processes that confer tolerance of the combined or stand-alone stresses. Plant growth, leaf Cl− and NO3− concentrations, carbohydrates, and polyamines were analyzed. Our results show that both salinity stress (SS) and heat stress (HS) reduced plant fresh weight, and SA only increased it for HS, with no effect for the combined stress (CS). While SA increased the concentration of Cl− for SS or CS, it had no effect on NO3−. The carbohydrates concentrations were, in general, increased by HS, and were decreased by CS, and for glucose and fructose, by SA. Additionally, when CS was imposed, SA significantly increased the spermine and spermidine concentrations. Thus, SA did not always alleviate the CS and the plant response to CS cannot be directly attributed to the full or partial sum of the individual responses to each stress.

Chloride Improves Nitrate Utilization and NUE in Plants.

Chloride (Cl–) has traditionally been considered harmful to agriculture because of its toxic effects in saline soils and its antagonistic interaction with nitrate (NO3–), which impairs NO3– nutrition. It has been largely believed that Cl– antagonizes NO3– uptake and accumulation in higher plants, reducing crop yield. However, we have recently uncovered that Cl– has new beneficial macronutrient, functions that improve plant growth, tissue water balance, plant water relations, photosynthetic performance, and water-use efficiency. The increased plant biomass indicates in turn that Cl– may also improve nitrogen use efficiency (NUE). Considering that N availability is a bottleneck for the plant growth, the excessive NO3– fertilization frequently used in agriculture becomes a major environmental concern worldwide, causing excessive leaf NO3– accumulation in crops like vegetables and, consequently, a potential risk to human health. New farming practices aimed to enhance plant NUE by reducing NO3– fertilization should promote a healthier and more sustainable agriculture. Given the strong interaction between Cl– and NO3– homeostasis in plants, we have verified if indeed Cl– affects NO3– accumulation and NUE in plants. For the first time to our knowledge, we provide a direct demonstration which shows that Cl–, contrary to impairing of NO3– nutrition, facilitates NO3– utilization and improves NUE in plants. This is largely due to Cl– improvement of the N–NO3– utilization efficiency (NUTE), having little or moderate effect on N–NO3– uptake efficiency (NUPE) when NO3– is used as the sole N source. Clear positive correlations between leaf Cl– content vs. NUE/NUTE or plant growth have been established at both intra- and interspecies levels. Optimal NO3– vs. Cl– ratios become a useful tool to increase crop yield and quality, agricultural sustainability and reducing the negative ecological impact of NO3– on the environment and on human health.

Influence of mycorrhizal or microbial complex inoculation on laurustinus plants irrigated with reclaimed water

ABSTRACT The application of microorganisms in crops has been proposed as a strategy to cope with adverse environmental conditions. Two separate experiments (I and II) were carried out in laurustinus plants in field conditions. For each experiment, half of the plants were irrigated with control water (C, EC <0.9 dS m−1) and the other half with reclaimed wastewater (RW, EC: 6 dS m−1). In experiment I, for each irrigation treatment, half of the plants were inoculated with Glomus iranicum (AMF). In experiment II, for each irrigation treatment, half of the plants were inoculated with a rhizosphere microbial complex (RMC). In experiment I, AMF increased leaf Ca/Na ratio and reduced leaf Cl concentration. In addition, stem water potential was enhanced in plants subjected to RW. Stomatal conductance was also improved by AMF in plants subjected to C and RW treatments. In experiment II, leaf K/Na and Ca/Na ratios were increased and leaf Cl concentration was reduced by RMC. The RMC increased stem water potential and relative chlorophyll content in both irrigation treatments. Under RW irrigation, plants with RMC showed better leaf stomatal conductance. These results highlight the importance of studying the microorganisms/species interaction in order to select the best combination.

Impact of Grafting, Salinity and Irrigation Water Composition on Eggplant Fruit Yield and Ion Relations

Scarcity of fresh water in arid and semi-arid regions means that we must use more saline waters for irrigation and develop tools to improve crop salt tolerance. The objectives of our study were to (1) Evaluate fruit production, salt tolerance and ion composition of eggplant cv Angela, both nongrafted and when grafted on tomato cv Maxifort rootstock and (2) Evaluate eggplant specific toxicity effect of Cl− and Na+ ions under saline conditions. We salinized the irrigation water with either a Na+-Ca2+- Cl− composition typical of coastal Mediterranean ground waters as well as a mixed Na+-Ca2+-SO42− Cl− type water, a composition more typical of interior continental basin ground. For each water type we evaluated 5 different salinity (osmotic) levels of –0.003 (control), –0.15, –0.30, –0.45 and –0.60 MPa. There were no statistically significant differences in the fruit yield relative to the water type, indicating that Cl− ion toxicity is not a major factor in eggplant yield associated with salinity. This conclusion was confirmed by the determination that leaf Cl content was not correlated with relative yield. The electrical conductivity of the saturation extract (ECe) at which yield is predicted to be reduced by 50% was 4.6 dS m−1 for the grafted plants vs. 1.33 dS m−1 for the nongrafted plants. The relative yield was very well correlated to leaf Na concentrations regardless of grafting status, indicating that Na is the toxic ion responsible for eggplant yield loss under saline conditions. The increased salt tolerance of cv Angela eggplant when grafted onto tomato Maxifort rootstock is attributed to a reduced Na uptake and increased Ca and K uptake with Maxifort rootstock.