Decrease In Stomatal Conductance Research Articles

Endophyte mediated Populus trichocarpa water use efficiency is dependent on time of day and plant water status

Endophytes are potential partners for improving the resource use efficiency of bioenergy feedstock systems such as short rotation coppiced Populus. Endophytes isolated from members of the Salicaceae family have broad host compatibility and can improve water use efficiency (WUE) through decreases in stomatal conductance. However, the literature is inconsistent with regards to the environmental conditions and temporal patterns of these benefits. This study investigates how endophyte mediated changes in Populus trichocarpa (Torr. and Gray) ‘Nisqually-1’ stomatal conductance and WUE shift with time and scale in response to water-deficit stress. Leaf gas exchange and above-ground productivity were used to evaluate the carbon and water balances of glasshouse grown plants in response to endophyte inoculation and water-deficit. Differences in stomatal conductance between control and inoculated plants were more pronounced (39.7 % decrease, Welch’s two-sample t(14.34 dfadj) = -2.358, p-value = 0.033) under water-deficit conditions in the late morning during a period of higher light intensity. The decrease in stomatal conductance accompanied a substantial increase in intrinsic WUE (iWUE) for water-deficit inoculated plants. However, increases in iWUE did not result in improvements in aboveground productivity or shoot biomass WUE (WUEsb) for water-deficit inoculated plants. This decoupling between iWUE and aboveground productivity may be an indicator of assimilate allocation to microbial metabolism as an additional carbon sink or a shift in carbon allocation towards belowground biomass. Future work should take a whole-plant approach that accounts for diurnal patterns in incident irradiance to evaluate the impact of endophyte inoculation on host WUE and stress tolerance.

Differential impact of decreasing relative humidity on photosynthesis under fluctuating light between maize and tomato

AbstractPhotosynthetic CO2 assimilation (AN) under fluctuating light (FL) plays a critical role in plant growth and crop yield. C4 crops usually reach greater yields than C3 crops when grown in regions with low relative humidity, which might be partly due to the CO2 concentration mechanism and higher AN under FL of C4 crops. To test this hypothesis, we measured gas exchange and chlorophyll fluorescence under different changing frequencies of FL at contrasting relative air humidity (60% and 15%) for leaves of maize (Zea mays, C4) and tomato (Solanum lycopersicum, C3). In general, a more rapid changing frequency of FL would cause a larger loss in AN during shade‐sun transitions, with 20–38% in maize and 16–52% in tomato. Low relative humidity induced a larger decrease of stomatal conductance (gs) under FL in tomato than in maize, leading to a much stronger loss in AN in tomato than in maize. After transition from low to high light, AN of maize was mainly limited by gs with negligible non‐stomatal limitation, and the stomatal limitation was slightly affected by relative humidity. By comparison, low relative humidity significantly increased the stomatal limitation of AN in tomato but hardly affected non‐stomatal limitation. These results highlight the differential impact of decreasing relative humidity on dynamic photosynthesis and productivity between C3 and C4 crops.

Influence of Incremental Short Term Salt Stress at the Seedling Stage on Root Plasticity, Shoot Thermal Profile and Ion Homeostasis in Contrasting Wheat Genotypes

Understanding the component traits determining salt stress tolerance is a major breeding target in wheat. The lack of genetic resources suited to salt-affected regions and the complexity of the traits involved impede progress in breeding salt-tolerant wheat varieties. This study was conducted with four bread wheats, namely (Triticum aestivum) Kharchia-65 (K-65), BT-Schomburgk (BTS), HD-2687, and HD-3298. Treatments were imposed on plants with varying electrical conductivity (control, 5 dS m−1, 10 dS m−1, and 15 dS m−1) with a combination of three different salts NaCl, CaCl2·2H2O, and Na2SO4. We evaluated variations in root system architecture, canopy temperature (depicted as a thermal image), reactive oxygen species (ROS) homeostasis, and leaf stomatal density in response to incremental doses of salt stress in a hydroponic experiment. As the plants were sampled after short-term exposure to stress (within 3 weeks of stress imposition), the plants were expected to be in a quiescent state. Due to the osmotic effect, the growth of the plants was compromised, and the associated decrease in stomatal conductance increased the canopy temperature. ROS accumulation and antioxidant enzyme activity did not follow a definite pattern. The antioxidant system’s tolerance to ROS comes into action much later in the tolerance mechanism. That could probably be the reason behind the varied response in ROS accumulation and antioxidant enzymes after short-term exposure to salt stress. Thermal images could effectively differentiate between salt-tolerant (K65) and sensitive (HD2687) genotypes. The variation in Na+/K+ ratio also suggested a genotypic variation in salt tolerance. The genotypes of K-65 maintained a better root system, while HD2687 showed severe reduction in root biomass and other root traits under salt stress. The PCA data also point out genotypic variation in lateral and main root traits in response to different salt stress levels. For salt tolerance in wheat, the main contributing root traits were total root length, total surface area, total root volume, tips, and other main, lateral root traits. The idea of differential control of RSA dynamics is novel and can be further explored to understand natural variation in salt stress tolerance.

Impacts on South America moisture transport under Amazon deforestation and 2 °C global warming

The increase in greenhouse gasses (GHG) anthropogenic emissions and deforestation over the last decades have led to many chemical and physical changes in the climate system, affecting the atmosphere's energy and water balance. A process that could be affected is the Amazonian moisture transport in the South American continent (including La Plata basin), which is crucial to the southeast Brazilian water regime. The focus of our research is on evaluating how local (i.e. Amazon deforestation) and global forcings (increase of atmospheric GHG concentration) may modify this moisture transport under climate change scenarios. We used two coupled land-atmosphere models forced by CMIP6 sea surface temperatures to simulate these processes for two scenarios: i) increase in carbon dioxide (CO2) — RCP8.5 atmospheric levels (00DEF), and ii) total Amazon deforestation simultaneous with atmospheric CO2 levels increased (100DEF). These scenarios were compared with a control simulation, set with a constant CO2 of 388 ppm and present-day Amazon Forest cover. The 30-year Specific Warming Level 2 (SWL2) index evaluated from the simulations is set to be reached 2 years earlier due to Amazon deforestation. A reduction in precipitation was observed in the Amazon basin (−3.1 mm·day−1) as well as in La Plata Basin (−0.5 mm·day−1) due to reductions in the Amazon evapotranspiration (−0.9 mm·day−1) through a stomatal conductance decrease (00DEF) and land cover change (100DEF). In addition, the income moisture transport decreased (22 %) in the northern La Plata basin in both scenarios and model experiments. Our results indicated a worse scenario than previously found in the region. Both Amazon and La Plata hydrological regimes are connected (moisture and energy transport), indicating that a large-scale Amazon deforestation will have additional climate, economic and social implications for South America.

Sustainable Use of Treated Municipal Wastewater after Chlorination: Short-Term Effects on Crops and Soils

Due to the scarcity of fresh water for crop irrigation in semi-arid areas, sustainable use of treated municipal wastewater is essential. Chlorine for wastewater disinfection added in wastewater treatment plants may be toxic for crops and can degrade cultivated soils. This study evaluates the crop and soil response to irrigation with treated municipal wastewater (with or without chlorination) in comparison to clear water. Small plants of tomato and cabbage and young bergamot trees were irrigated in pots throughout two months. The use of chlorinated or non-chlorinated wastewater did not significantly change biomass growth, morphological parameters and the efficiency of energy transfer. Significant reductions (40–50%) in the stem diameter of tomato and bergamot plants and differences (−25% to 53%) in all physiological parameters were measured for tomato immediately after the irrigation start. A decrease (−55%) in stomatal conductance and transpiration rate together with an increase (+80%) in water use efficiency were also recorded in bergamot after 30 days of irrigation. This type of irrigation water did not induce significant changes in soil properties, except for a decrease in pH (−20%) in bergamot soils after the irrigation start and in electric conductivity (EC, −40%) at the end of the irrigation period for all species. Irrigation of plants with chlorinated wastewater increased the weight of the fresh biomass (+56%) of leaves and the stem diameter (−60%) of tomato and decreased water use efficiency (+67%) in bergamot after the irrigation start. After two months, decreases in stomatal conductance and transpiration rate in cabbage (over 50%) and increases in water use efficiency in cabbage and bergamot (by 40% and 70%, respectively) were evident. Among the studied soil properties, land application of chlorinated wastewater only reduced electrical conductivity (−47%). Overall, this study demonstrated that the use of treated municipal wastewater (with or without chlorination) does not have detrimental impacts on both plant growth (at least for tomato, cabbage and bergamot) and soil health in the short term.

Effect of high salinity and of priming of non-germinated seeds by UV-C light on photosynthesis of lettuce plants grown in a controlled soilless system.

High salinity results in a decrease in plant photosynthesis and crop productivity. The aim of the present study was to evaluate the effect of UV-C priming treatments of lettuce seeds on photosynthesis of plants grown at high salinity. Non-primed and primed seeds were grown in an hydroponic system, with a standard nutrient solution, either supplemented with 100 mM NaCl (high salinity), or not (control). Considering that leaf and root K+ concentrations remained constant and that chlorophyll fluorescence parameters and root growth were not affected negatively in the high salinity treatment, we conclude that the latter was at the origin of a moderate stress only. A substantial decrease in leaf net photosynthetic assimilation (Anet) was however observed as a consequence of stomatal and non-stomatal limitations in the high salinity treatment. This decrease in Anet translated into a decrease in growth parameters; it may be attributed partially to the high salinity-associated increase in leaf concentration in abscisic acid and decrease in stomatal conductance. Priming by UV-C light resulted in an increase in total photosynthetic electron transport rate and Anet in the leaves of plants grown at high salinity. The increase of the latter translated into a moderate increase in growth parameters. It is hypothesized that the positive effect of UV-C priming on Anet and growth of the aerial part of lettuce plants grown at high salinity, is mainly due to its stimulating effect on leaf concentration in salicylic acid. Even though leaf cytokinins' concentration was higher in plants from primed seeds, maintenance of the cytokinins-to-abscisic acid ratio also supports the idea that UV-C priming resulted in protection of plants exposed to high salinity.

Photosynthetic traits and plant hydraulic dynamics in Gamhong apple cultivar under drought, waterlogging, and stress recovery periods

Drought and waterlogging are major abiotic stresses in fruit cultivation that should both be considered when establishing an orchard as the frequency and severity of extreme climate events continue to rise. This study investigated the photosynthetic traits and plant–water relations of Gamhong/M.9 apple cultivar during and after drought (DT) and waterlogging (WT) treatments. Both stresses adversely affected the photosynthetic and plant hydraulic traits, with stress-specific effects. Drought significantly increased the leaf mass per area, indicating that the cultivar allocated more resources to structural investment than to photosynthesis upregulation. The net photosynthetic rate and stomatal conductance were reduced at an earlier stage under DT (day 3) than under WT (day 6). The recovery of these photosynthetic traits was slower under DT than that under WT, with the net photosynthetic rate recovering 12 days after DT and 9 days after WT, whereas the stomatal conductance recovered 11 days after DT and 7 days after WT. Additionally, the progressive increase in xylem sap abscisic acid concentration resulted in a linear decrease in stomatal conductance, with a greater under DT than under WT. The leaf water potential and sap flow followed similar decreasing trends as that of the photosynthetic traits; however, hydraulic traits recovered earlier than photosynthetic traits under both stress conditions. The leaf water potential was reduced on day 4 of DT and recovered 6 days after watering was resumed. Contrastingly, under WT, this trait was reduced on day 7 of the treatment and recovered 4 days after its end. Our findings highlight that the Gamhong cultivar has higher acclimation potential to waterlogging and can alleviate the adverse effects of excess water while maintaining its physiological traits and improving plant–water relations.

Sarcocornia fruticosa recovery capacity after exposure to co-existed water and salinity stress

The capacity of halophytes species to resist abiotic stress has been tested on multiple occasions. The ability of these species such as Sarcocornia fruticosa to cope with severe stress conditions has been shown, as well as their utility as a phytoremediation tool or even as potential crop species. However, there is a lack of literature on the effect that these abiotic factors have on their physiological response after a recovery period. In a greenhouse experiment, S. fruticosa plants were subjected to a combination of water regimen (water stress/field capacity) and salinity concentration (171/510 mM NaCl) grown conditions for 30 days. After these stress periods, plants were left 15 days in recovery conditions (field capacity and 171 mM NaCl). To study the effect of stress during both periods, osmotic potential, net photosynthetic rate, stomatal conductance, intercellular CO2 concentration, quantum efficiency of PS II, OJIP-derived parameters and photosynthetic pigment concentrations were measured. Our results show the already known resistance of this species to drought and salinity stress. However, the combination of both factors did affect the ability of S. fruticosa to maintain its level of carbon assimilation due to a decrease in stomatal conductance. In addition, the recovery period helped us to describe a synergic effect of both abiotic factors showing that plants subjected to both stresses received a better response during the recovery period than those only affected by salinity stress.

Independent and combined influence of drought stress and nitrogen deficiency on physiological and proteomic changes of barley leaves

Drought stress and nitrogen (N) deficiency often interact mutually during crop growth, yet the combinational effects of both stresses are still poorly understood. In the present study, physiological changes of barley were determined under drought stress, N deficiency and combined both stresses. Barley leaf proteomes were detected by label-free proteomic techniques under drought stress or/and N deficiency. The results showed that few proteins involved in photosynthesis were changed, and the main reason for the reduction in photosynthetic rate (An) was the decrease in stomatal conductance (gs) under drought stress. The increased photorespiration as well as decreased gs and chlorophyll reduced An under combined stresses. Compared to drought stress and N deficiency, the combined stresses led to the greater expression of proteins related to energy, carbohydrate and amino acid metabolism, causing the development of more extensive signaling pathways. Barley plants generated more energy by enhancing aerobic respiration to maintain growth under combined stresses. The synthesis of proteins in plant leaves was decreased under drought stress or/and N deficiency, while the degradation of proteins was enhanced to provide free amino acids under N deficiency and combined stresses. Our results provided further information for the mechanisms of crop response to combined drought stress and N deficiency, and helped to understand the response and adaptation of plants to adverse environmental conditions.

Reduction of photosynthesis under P deficiency is mainly caused by the decreased CO2 diffusional capacities in wheat (Triticum aestivum L.)

Phosphorus is one of the most important essential mineral elements for plant growth and development. It has been widely recognized that phosphorus deficiency can lead to the significant declines in leaf photosynthetic rate and leaf area. However, the internal mechanism associated with the leaf anatomical traits has not been well understood. In present study, a hydroponic experiment was conducted to study the effect of phosphorus deficiency on leaf growth and photosynthesis in Jimai 22 (JM22, Triticum aestivum L.) and Suk Landarace 26 (SL26, Triticum aestivum L.). With the decrease in phosphorus concentration, leaf photosynthetic rate and leaf area in SL26 and JM22 all decreased significantly, but the decrease in leaf area occurred earlier than that in leaf photosynthetic rate. The thresholds of phosphorus concentration to maintain a high photosynthesis were 145.5 and 138.7 mg m−2, respectively, in SL26 and JM22; and they were 197.5 and 212.0 mg m−2, respectively, for leaf growth. The decrease in leaf photosynthetic rate under low P conditions was mainly caused by the lowered stomatal conductance and mesophyll conductance, and to a less extent by the decrease in biochemical capacities. The decrease in stomatal conductance was attributed to the smaller vascular bundle area, xylem conduits area and the lower leaf hydraulic conductance. However, the reduction in mesophyll conductance was not related to either the cell wall thickness or the development of chloroplast.

Photosynthesis, Respiration, and Thermal Energy Dissipation in Leaves of Two Phenotypes of Plantago media L. under Environmental Conditions

The ability to maintain the balance between the absorbed light energy and energy used in photosynthesis is a key factor of plant adaptation to variable environmental conditions. In this work, diurnal variations in photosynthesis, respiration, thermal energy dissipation, and the activity of the antioxidant system were studied in hoary plantain (Plantago media L.) growing on an open slope (sun plants) and under natural shading in the herbage (shade plants). The highest leaves net photosynthetic rate (Pn) was observed early in the morning and amounted to 2.6 and 9.2 μmol CO2/m2 s in shade and sun plants, respectively. In the daytime, the Pn values of sun plants decreased significantly (threefold) along with the decrease in stomatal conductance; changes of both parameters developed concurrently with the increase in insolation and air temperature. The Pn changes in leaves of shade plants were less pronounced and weakly dependent on stomatal conductance. The leaves of shade plants contained comparatively high amounts of soluble carbohydrates, whereas the sun plant leaves accumulated larger amounts of starch. In the daytime, nonphotochemical quenching (NPQ) of chlorophyll a fluorescence in photosystem II of sun plant leaves could be as large as 2.6 rel. units, which was four- to fivefold higher than NPQ in shade plants. In leaves of sun plants in the morning and evening hours, the ratio of cytochrome pathway (CP) and the alternative (AP) respiratory pathways was approximately 1.0, whereas this ratio decreased to 0.4 during the day, synchronously with an increase in NPQ. The CP/AP ratio in shade plant leaves remained constant throughout the diurnal cycle and equaled 1.4, indicating a comparatively high energy efficiency of respiration in shaded plants growing under the grass canopy. The leaves of sun plants featured an increased content of superoxide anion radical and hydrogen peroxide as well as the elevated activity of antioxidant enzymes (superoxide dismutase, guaiacol peroxidase) that control the accumulation of reactive oxygen species. The results emphasize the importance of coordinated changes in energy-dissipating processes and the activity of the antioxidant system for maintaining the energy and redox balance in phototrophic tissues during long-term adaptation of plants to environmental conditions, excessive insolation in particular.

Single and combined effects of fertilization, ectomycorrhizal inoculation, and drought on container-grown Japanese larch seedlings

Climate change can intensify drought in many regions of the world and lead to more frequent drought events or altered cycles of soil water status. Therefore, it is important to enhance the tolerance to drought and thus health, vigor, and success of transplantation seedlings used in the forestry by modifying fertilization and promoting mycorrhization. Here, we sowed seeds of Japanese larch (Larix kaempferi) in 0.2-L containers with 0.5 g (low fertilization; LF) or 2 g (high fertilization; HF) of slow-release fertilizer early in the growing season. One month later, we irrigated seedlings with non-sterilized ectomycorrhizal inoculum (ECM) or sterilized solution (non-ECM), and after about 2 months, plants were either kept well watered (WW; 500 mL water/plant/week) or subjected to drought (DR; 50 mL water per plant/week) until the end of the growing season. HF largely stimulated plant growth and above- and belowground biomass production, effects that are of practical significance, but caused a small decrease in stomatal conductance (Gs390) and transpiration rate (E390), which in practice is insignificant. ECM treatment resulted in moderate inhibition of seedling growth and biomass and largely canceled out the enhancement of biomass and foliar K content by HF. DR caused a large decrease in CO2 assimilation, and enhanced stomatal closure and induced senescence. DR also largely depleted foliar Mg and enriched foliar K. Although DR caused a large decrease in foliar P content in LF, it moderately increased P in HF. Likewise, DR increased foliar K in HF but not in LF, and decreased foliar P in ECM plants but not in non-ECM plants. Conversely, ECM plants exhibited a large enrichment in foliar P under WW and had a lower water potential under DR when grown in LF. These results indicate that the drought tolerance and health and vigor of Japanese larch seedlings can be modified by soil fertility and soil microorganisms. This study provides a basis for new multifactorial research programs aimed at producing seedlings of superior quality for forestation under climate change.

Vapor pressure deficit constrains transpiration and photosynthesis in holm oak: A comparison of three methods during summer drought.

High rates of vapor pressure deficit (VPD) can severely decrease plant productivity by reducing stomatal conductance, which might be exacerbated during Mediterranean summers due to soil water deficit. In this study, we monitored the response of holm oak, the archetype of Mediterranean trees, to changes in VPD during a summer drought period to evaluate the effects and consequences on gas exchange of the two water stresses (atmospheric and soil). Measurements were performed on trees growing in an experimental plantation over two summers with moderate drought stress by using three different methods: at the leaf level with an infrared gas analyzer, using a whole-plant chamber for short-term monitoring at the tree level, and measuring the canopy temperature for long-term monitoring. The three methods provided negative relationships between leaf conductance and VPD but with discrepancies probably associated with the measurement scale. Overall, the results showed that atmospheric and soil water stress had an additive effect. Under well-watered conditions, an increase in VPD was partially compensated by a reduction in stomatal conductance, resulting in a slight increase in the transpiration rates. With soil water deficit, the response to VPD resulted in a further decrease in stomatal conductance, reducing transpiration as a water saving strategy. The decrease in conductance in response to VPD was transitory, recovering to initial values as soon as the VPD decreased, both under well-watered and drought conditions. Due to this high sensitivity to atmospheric drought, the maximum carbon gain rates of holm oak were restricted to a short environmental window, which might modulate its physiological performance and natural distribution.

Short waterlogging events differently affect morphology and photosynthesis of two cucumber (Cucumis sativus L.) cultivars.

Waterlogging induces growth and developmental changes in sensitive crops such as cucumber (Cucumis sativus L.) during early plant development. However, information on the physiological mechanisms underpinning the response of cucumber plants to waterlogging conditions is limited. Here, we investigated the effects of 10-day waterlogging stress on the morphology, photosynthesis, and chlorophyll fluorescence parameters in two cultivars of cucumber seedlings. Waterlogging stress hampered cultivars’ growth, biomass accumulation, and photosynthetic capacity. Both cultivars also developed adventitious roots (ARs) after 10 days of waterlogging (DOW). We observed differential responses in the light- and carbon-dependent reactions of photosynthesis, with an increase in light-dependent reactions. At the same time, carbon assimilation was considerably inhibited by waterlogging. Specifically, the CO2 assimilation rate (A) in leaves was significantly reduced and was caused by a corresponding decrease in stomatal conductance (gs). The downregulation of the maximum rate of Rubisco efficiency (Vcmax) and the maximum rate of photosynthetic electron transport (Jmax) were non-stomatal limiting factors contributing to A reduction. Exposure of cucumber to 10 DOW affected the PSII photochemistry by downregulating the PSII quantum yield (ΦPSII). The redox state of the primary quinone acceptor in the lake model (1-qL), a measure of the regulatory balance of the light reactions, became more oxidized after 10 DOW, indicating enhanced electron sink capacity despite a reduced A. Overall, the results suggest that waterlogging induces alterations in the photochemical apparatus efficiency of cucumber. Thus, developing cultivars that resist inhibition of PSII photochemistry while maintaining carbon metabolism is a potential approach for increasing crops’ tolerance to waterlogged environments.

Photosynthetic Responses, Growth, Production, and Tolerance of Traditional Varieties of Cowpea under Salt Stress.

HighlightsSalinity tolerance among traditional varieties of cowpea is variable.High net photosynthesis is observed in cowpea-tolerant varieties under salt stress.The decrease in photosynthesis is caused by stomatal restriction and low photochemical efficiency.Cowpea varieties are similar in photochemical efficiency and photochemical quenching.The decrease in pod number and seeds per pod are the main effects of salinity on cowpea production.Cowpea is the main subsistence crop—protein source—for the Brazilian semi-arid region. The use of salt-stress-tolerant varieties can improve crop yields. We evaluated the effect of irrigation with brackish water on the growth, photosynthetic responses, production, and tolerance of fifteen traditional varieties of cowpea. The experiment was conducted in randomized blocks, in a 15 × 2 factorial scheme, composed of 15 traditional varieties of cowpea and two salinity levels of irrigation water (0.5 and 4.5 dS m−1), with five replicates. Plants were grown in pots containing 10 dm3 of soil for 80 days. The reduction in the photosynthetic rate of cowpea varieties occurs mainly due to the decrease in stomatal conductance caused by salt stress. Salt stress increased the electron transport rate and photochemical quenching of cowpea varieties, but stress-tolerant varieties increased the CO2 assimilation rate and instantaneous carboxylation efficiency. The Ceará, Costela de Vaca, Pingo de Ouro, Ovo de Peru, and Sempre Verde varieties are tolerant to salt stress. Salt stress decreases 26% of the production of tolerant varieties to salt stress and 54% of susceptible varieties. The present findings show the existence of variability for saline stress tolerance in traditional varieties of cowpea and that Ceará, Costela de Vaca, Pingo de Ouro, and Ovo de Peru varieties are more suitable for crops irrigated with saline water.

Effects of biogenic silver and iron nanoparticles on soybean seedlings (Glycine max)

BackgroundBiogenic metallic nanoparticles have been emerging as a promising alternative for the control of phytopathogens and as nanofertilizers. In this way, it is essential to investigate the possible impacts of these new nanomaterials on plants. In this study, the effects of soil contamination with biogenic silver (AgNPs) and iron (FeNPs) with known antifungal potential were investigated on morphological, physiological and biochemical parameters of soybean seedlings.ResultsThe exposure of plants/seedlings to AgNPs induced the reduction of root dry weight followed by oxidative stress in this organ, however, adaptive responses such as a decrease in stomatal conductance without impacts on photosynthesis and an increase in intrinsic water use efficiency were also observed. The seedlings exposed to FeNPs had shown an increase in the levels of oxygen peroxide in the leaves not accompanied by lipid peroxidation, and an increase in the expression of POD2 and POD7 genes, indicating a defense mechanism by root lignification.ConclusionOur results demonstrated that different metal biogenic nanoparticles cause different effects on soybean seedlings and these findings highlight the importance of investigating possible phytotoxic effects of these nanomaterials for the control of phytopathogens or as nanofertilizers.

Impacts of zebra chip disease and irrigation on leaf physiological traits in potato

Zebra chip disease (ZC) is caused by the fastidious, phloem-limited, bacterial pathogen ‘Candidatus Liberibacter solanacearum (Lso), which is transmitted from plant to plant by the potato psyllid (Bactericera cockerelli (Sulc)). Understanding how ZC impacts potato (Solanum tuberosum L.) physiology, could help growers in making more informed crop management decisions. Measurements of instantaneous leaf physiological responses, such as photosynthetic CO2 uptake and transpiration on the leaf surface, can be used not only for fast screening of affected plants in the field but also for optimizing irrigation management. Over the 2019 and 2020 field seasons, we characterized time-course photosynthetic physiological responses of potato plants infested by potato psyllids (B. cockerelli (Sulc)) carrying the Lso haplotypes A+B. Potato plants were subjected to different variable-rate irrigation (VRI) treatments (100%, 80%, and 60% of field capacity of the soil) through a center-pivot sprinkler system to examine the impact of the disease on key physiological parameters of photosynthesis and transpiration. Leaf and air temperatures, and hyperspectral profiles of the canopy were also measured and compared. The measurements were made during midday weekly from 25 to 50 days after plant infestation (DAI) with bacteriliferous psyllids. The results showed that many of the measured variables, including stomatal conductance, photosynthesis rate, transpiration rate, quantum yields, and normalized difference in vegetation index started to decrease beginning approximately 28–35 DAI, gradually worsening until 50 DAI, in both 2019 and 2020, as the infection proceeded. The decreases in stomatal conductance in infected plants led to decreases in photosynthesis and transpiration. In turn, reduced transpiration resulted in increased leaf temperature due to decrease in evaporative cooling on the leaf surface. Higher leaf temperatures under hot and dry conditions with high light intensity during the daytime would further reduce photosynthetic light harvesting, which is supported by our data, indicating the damage to the photosynthetic pigment formation and machinery. These findings support the previous report that increased leaf temperature in infected plants may have been derived from the closure of stomata in hypersensitive reactions to infection. These stomatal responses were detected within 28 DAI, a week earlier than the differences in hyperspectral profiles observed 35 DAI, and could be implemented in early disease detection strategiesusing measurements of leaf temperature.

Fig (Ficus carica L.) vulnerability to climate change: Combined effects of water stress and high temperature on ecophysiological behaviour of different cultivars

Climate change scenarios predict that drought and high temperatures will become the main stress factors affecting fruit tree's production. This study was undertaken in order to evaluate ecophysiological behaviour of young fig plants of cultivars Zidi and Bither Abiadh under two water regimes (‘T50’ and ‘T100’, supply of respectively 50% and 100% of water requirement) in different growing conditions (open-air, tunnel covered with insect proof and polyethylene greenhouse). During the first cycle of measurements, it has been concluded that the decrease of stomatal conductance was the primary response to water stress, which controlled transpiration and photosynthesis rates and regulated leaf temperature. Fig cultivars reduced leaf stomatal conductance after 7 days of changing environments and reducing irrigation to 50% of required water supply. Measurements carried out after 15 days showed a decrease of photosynthetic parameters even for fig plants irrigated with 100% of their water requirement, due to the effect of high temperatures associated with low air humidity in the different growing conditions. During the second cycle, measurements carried out on persistent leaves showed that fig cultivars were adapted to prolonged water stress. Overall, Zidi and Bither Abiadh responded almost similarly to water stress and exhibited the same ecophysiological behaviour in each growing condition during the first and the second cycle of measurements. Despite leaf abscission, fig plants revealed drought stress memorizing by showing a rapid growth recovery once the stress was relieved.

Assimilatory deficit and energy regulation in young Handroanthus chrysotrichus plants under flooding stress.

Flooding negatively influences the growth and development of several plant species. Here, we show that the flood tolerance of young Handroanthus chrysotrichus plants involves growth deficit, carbon assimilation reductions, starch remobilization, and energy regulation. The effect of hypoxia was evaluated in a controlled experiment consisting of plants subjected to normoxia and water-logging, with later recovery. We measured morphological changes, gas exchange, photosynthetic pigments, soluble carbohydrates and starch contents, the activity of the enzymes alcohol dehydrogenase (ADH), and pyruvate decarboxylase (PDC), and ATP and ADP levels. While control plants showed normal appearance and growth, flooded plants exhibited a drastic decrease in growth, necrosis of some root tips, hypertrophic lenticels on the stems, and foliar chlorosis. Oxygen deprivation in root cells led to a significant decrease in stomatal conductance. The low Amax rates caused a decline in foliar soluble sugar content at 20days and a subsequent increase in the leaves and roots, coinciding with starch degradation at 40days. We also observed increases of 220.5% in ADH and 292% in PDC activities in the roots at 20 and 40days of flooding. The activation of anaerobic metabolism in stressed plants was an essential mechanism for ATP regulation in both tissues used to maintain a minimal metabolism to cope with hypoxia to the detriment of growth. The post-stress recovery process in H. chrysotrichus occurred slowly, with gas exchange gradually resumed and anaerobic metabolism and sugar content maintained to improve energy regulation.

Ultraviolet radiation causes leaf warming due to partial stomatal closure.

Variation in solar ultraviolet radiation induces a wide-range of plant responses from the cellular to whole-plant scale. We demonstrate here for the first time that partial stomatal closure caused by ultraviolet radiation exposure results in significant increases in leaf temperature. Significant leaf warming in response to ultraviolet radiation was consistent in tomato (Solanum lycopersicum L.) across different experimental approaches. In field experiments where solar ultraviolet radiation was attenuated using filters, exposure to ultraviolet radiation significantly decreased stomatal conductance and increased leaf temperature by up to 1.5°C. Using fluorescent lamps to provide ultraviolet radiation treatments, smaller but significant increases in leaf temperature due to decreases in stomatal conductance occurred in both multi-day controlled environment growth room experiments and short-term (<2 hours) climate cabinet irradiance response experiments. We show that leaf warming due to partial stomatal closure is independent of any direct warming effects of ultraviolet radiation manipulations. We discuss the implications of ultraviolet radiation-induced warming both for horticultural crop production and understanding broader plant responses to ultraviolet radiation.