Net Photosynthetic Assimilation Research Articles

Impact of lead and zinc heavy metal pollution on the growth and phytoremediation potential of Sulla carnosa in Sebkha el Kalbia, Tunisia.

Heavy metal pollution from human and natural activities poses significant environmental and health concerns for wildlife and humans, with lead and zinc being particularly threatening. This study focuses on Sebkha el Kalbia in Tunisia, highlighting the challenges faced by local communities in addressing heavy metal pollution. The area is prone to contamination through rivers and streams that transport pollutants from industrial zones and rural areas into the salt pan. The recent establishment of an industrial zone has worsened pollution levels, calling for strict regulatory measures and clean technologies to limit heavy metal pollution and protect human health and the environment. The study assesses the impact of lead and zinc pollution on the growth of Sulla carnosa and its potential for phytoremediation. Soil and plant samples from contaminated areas were analyzed, revealing high levels of heavy metal contamination. The growth parameters of Sulla carnosa, such as plant height, weight, and enzymatic activity, were examined, showing a significant reduction in plant growth when exposed to high metal concentrations. Specifically, in the presence of 100ppm of lead (Pb), net photosynthetic assimilation (An) decreased by 52%, while the amount of Pb increased by 78%. At 800ppm of Pb, An decreased by 87%, and the amount of Pb increased by over 800%. Furthermore, the relationship between net photosynthetic assimilation and lead (Pb) content remained significant but negative. At high doses (800ppm), the biomass produced decreases by 64%, while the amount of Zn increases 2.7 times. These results suggest that at low doses, zinc is not toxic. These findings highlight Sulla carnosa as a potential candidate for phytoremediation with preferential metal accumulation in the roots and improved enzymatic activity, underscoring the urgency of addressing heavy metal pollution in Sebkha el Kalbia.

Morpho-physiological and metabolites alteration in the susceptible and tolerant genotypes of sesame under waterlogging stress and post-waterlogging recovery

Among the oil-seed crops, Sesamum indicum L. is an important nutritionally rich crop, well adapted to grow in semi-arid regions. Waterlogging stress adversely affects the growth of sesame by limiting diffused oxygen availability in soil and generating hypoxic, subsequently anoxic conditions. The present study aimed to screen the 1,006 accessions for waterlogging stress response at the seedling stage to identify the most tolerant and susceptible genotype. The investigation revealed that, 48 h of stress are detrimental and 10 days post-waterlogging impede crop survival. The screened accessions were narrowed down by 8 to detect the morphological alterations, and the morphological characteristics such as shoot height, root length, SPAD, branches per plant and relative water content r) were significantly higher in check and EC377024. Enzymatic (SOD, CAT and APX) and non-enzymatic (TFC, TPC, DPPH, FRAP, TAA, MDA and proline) antioxidant activity was notably higher in check and EC377024 and lower in IC129289. DAB and NBT assay confirmed lower damages from free radicals in EC377024 compared to IC129289. Moreover, contrasting gene expression profiling of free radicals (POD and RBOHC), carbohydrate metabolism (SuSy2 and StSy1), phosphate group gene (PSRG), and plant hormone (ERF RAP 2–7, ACC) confirmed the tolerance in EC377024 under waterlogging stress conditions. Besides, metabolomics study in EC377024 at control and 48 h of waterlogging stress indicate the significant accumulated metabolites in fatty acid (decanoate), carbohydrate, amino acid, Shikimate, MEP (5-enolpyruvoyl-shikimate-3-phosphate) Krebs cycle and Xanthophyll pathways. This comprehensive combination of morpho-physiological, biochemical, molecular and metabolomic characterizations highlight the stress responsive mechanisms between the tolerant (EC377024) and susceptible (IC129289) genotypes.

Exploring carbon sequestration in broad-leaved Korean pine forests: Insights into photosynthetic and respiratory processes

A comprehensive understanding of carbon assimilation and sequestration in broad-leaved Korean pine forests is crucial for accurately estimating this significant aspect of temperate forests at a regional scale. In this study, we introduced a high-temporal resolution model designed for carbon assimilation insights at the plot scale, focusing on specific parameters such as leaf area dynamics, vertical leaf distribution, photosynthetically active radiation (PAR) fluctuations, and the photosynthetic traits of tree species. The findings reveal that most tree species in broad-leaved Korean pine forests exhibit an inverted U-shaped pattern in leaf area dynamics, with shorter leaf drop periods than leaf expansion events. Leaf distribution varies significantly among different canopy heights, with approximately 80 % of the leaves above 15 m. PAR decreases as canopy height decreases, with PAR at 25 m accounting for about 60 % of the PAR above the canopy. Our framework incorporates a leaf-scale light-response curve and empirical photosynthesis-temperature relationships to estimate forest carbon assimilation on daily and hourly scales accurately. Using the model, we assess the gross primary productivity (GPP), leaf net photosynthetic assimilation (LNPA), and carbon increment (ΔC) of broad-leaved Korean pine forests from 2017 to 2020. The results demonstrate GPP, LNPA, and ΔC values of 21.4 t·ha−1·a−1, 17.4 t·ha−1·a−1, and 4.0 t·ha−1·a−1, respectively. Regarding efficiency, GPP, LNPA, and ΔC per square meter of leaf per year are 179 g, 146 g, and 33 g, respectively. Notably, tree species in the canopy layer of the forest exhibit significantly higher efficiency than those in the understory layer. This research significantly contributes to our understanding of carbon cycling and the responses of forest ecosystems to climate change. Moreover, it provides a practical tool for forest management and the development of carbon sequestration strategies.

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.

Effects of salinity and iron deficiency on growth and physiological attributes of Avicennia marina (Forssk.) Vierh

ABSTRACT The grey mangrove, Avicennia marina, grows in coastal zones in which salinity is frequently associated with iron deficiency. Its response to these combined stresses has not yet explored. The current study aims to assess the physiological and biochemical effects of iron deficiency (ID), salt stress (SS) and their combination (ID + SS) on A. marina seedlings. Iron deficiency reduced growth at non-saline treated plants by 27% while its deleterious effect was mitigated by the supply of 600 mM NaCl, mainly through the increase of photosynthetic pigment contents, iron accumulation in leaves, and intrinsic water use efficiency (iWUE), and the maintain of iron use efficiency (FeUE). Iron deficiency restricted iron accumulation in leaves (31%), iron absorption efficiency (FeAE) (38%), photosynthetic activity and pigment contents, and enhanced FeUE (48%) at saline treated plants. Otherwise, salinity enhanced growth (47%), root volume (20%), Fe accumulation in leaves (8%), and pigment contents at Fe-deficient plants. However, it reduced their FeAE (18%), transpiration rate (77%) and stomatal conductance (86%). Equally, it increased Na and Cl accumulation, the net photosynthetic assimilation rate and iWUE at Fe-deficient. Interestingly, the combined stresses had no additive effects and stressed plants (ID +SS) had comparable biomass to that of the control.

Tradeoff in the supply and demand for CO2dominates the divergence of net photosynthesis rates of functional plants in alpine ecosystems

AbstractThe responses of photosynthesis to change of temperature and CO2concentration are divergent among various alpine plant species at high altitude regions; however, very few direct in situ measurements have been conducted to compare photosynthetic capacity among different functional plants along altitude gradients in the Qinghai‐Tibet Plateau (QTP). This study measured the net photosynthetic assimilation rate (An), maximum carboxylation rate (Vcmax), maximum electron transport rate (Jmax), stomatal conductance (gs) and mesophyll conductance (gm) for CO2of three plant functional types (PFTs, sedge, grass and shrub) and functional traits at different altitudes in the Qinghai Lake watershed during growing season. Meanwhile we simulated An of the PFTs under potential future scenario. Results indicate that grass maintain a relatively stable An by decreasingVcmax,Jmax, ratio ofJmaxtoVcmax(J/V) andgs, while slightly increasinggmwith increasing altitudes. In contrast, the An of sedge and shrubs increased with risingVcmax,Jmax,gsandgmvalues, resulting in a large increment in the An at low altitudes. Grass was less sensitive to temperature by reducing the supply of CO2, while sedge and shrub increased.Cawas a more dominant factor thanTain affecting the An of grass. The order of rising An in PFTs was shrub > sedge > grass, and the An of alpine meadow was found to increase more under the Representative Concentration Pathways (RCP) 4.5 and 8.5 scenarios. Our results indicate that grass may be more resistant to future warming and suggested that considering PFTs is of great significance for improving the simulating of the response of vegetation physiological and ecological processes to future climate change in alpine regions.

Photosynthetic performance of Terminalia arjuna Roxb towards different doses of 60Co γ-irradiation

The air dried seeds of T. arjuna were exposed to 100Gy, 200Gy, 400Gy and 600Gy gamma irradiation doses from a 60Co γ-irradiation source. The results showed that, the chlorophylla, chlorophyllb and total chlorophyll content in the leaves of T. arjuna raised significantly (p≤ 0.05) by lower γ-irradiation doses (100Gy & 200Gy). Under all the treatments and in control, the carbon assimilation rate (photosynthetic rate) raised to its maximum value around 11:00am where from a steady fall in it was observed respectively. Stimulation in the net photosynthetic assimilation rate was recorded under 100Gy and 200Gy doses. The stomatal conductance (GS) and average transpiration rate was increased by 100Gy and 200Gy treatment. In contrast, the higher γ-irradiation dose (above 200Gy) decreased these parameters significantly (p ≤ 0.05). This study provides the basic information of the impact of gamma radiations on the photosynthetic responses of T. arjuna and its radiosensitivity.

The Absence of the AtSYT1 Function Elevates the Adverse Effect of Salt Stress on Photosynthesis in Arabidopsis.

Arabidopsis thaliana SYNAPTOTAGMIN 1 (AtSYT1) was shown to be involved in responses to different environmental and biotic stresses. We investigated gas exchange and chlorophyll a fluorescence in Arabidopsis wild-type (WT, ecotype Col-0) and atsyt1 mutant plants irrigated for 48 h with 150 mM NaCl. We found that salt stress significantly decreases net photosynthetic assimilation, effective photochemical quantum yield of photosystem II (ΦPSII), stomatal conductance and transpiration rate in both genotypes. Salt stress has a more severe impact on atsyt1 plants with increasing effect at higher illumination. Dark respiration, photochemical quenching (qP), non-photochemical quenching and ΦPSII measured at 750 µmol m−2 s−1 photosynthetic photon flux density were significantly affected by salt in both genotypes. However, differences between mutant and WT plants were recorded only for qP and ΦPSII. Decreased photosynthetic efficiency in atsyt1 under salt stress was accompanied by reduced chlorophyll and carotenoid and increased flavonol content in atsyt1 leaves. No differences in the abundance of key proteins participating in photosynthesis (except PsaC and PsbQ) and chlorophyll biosynthesis were found regardless of genotype or salt treatment. Microscopic analysis showed that irrigating plants with salt caused a partial closure of the stomata, and this effect was more pronounced in the mutant than in WT plants. The localization pattern of AtSYT1 was also altered by salt stress.

Yield Response and Physiological Adaptation of Green Bean to Photovoltaic Greenhouses.

The cultivation of the horticultural crops inside photovoltaic greenhouses (PVG) should be studied in relation to the shading cast by the photovoltaic (PV) panels on the roof. This work evaluated the green bean cultivation inside PVGs with a percentage of the greenhouse area covered with PV panels (PV cover ratio, PVR) ranging from 25 to 100%. Three dwarf green bean cycles (Phaseolus vulgaris L., cv. Valentino) were conducted inside an iron–plastic PVG with a PVR of 50%. The average yield was 31% lower than a conventional greenhouse. Adverse effects on quality were noticed under the PV roof, including a reduction of pod weight, size, and caliber. Negative net photosynthetic assimilation rates were observed on the plants under the PV roof, which adapted by relocating more resources to the stems, increasing the specific leaf area (SLA), leaf area ratio (LAR), and the radiation use efficiency (RUE). The fresh yield increased by 0.44% for each additional 1% of cumulated PAR. Based on the linear regressions between measured yield and cumulated PAR, a limited yield reduction of 16% was calculated inside a PVG with maximum PVR of 25%, whereas an average yield loss of 52% can occur with a PVR of 100%. The economic trade-off between energy and green bean yield can be achieved with a PVR of 10%. The same experimental approach can be used as a decision support tool to identify other crops suitable for cultivation inside PVGs and assess the agricultural sustainability of the mixed system.

Soil moisture sensor-based automated irrigation of Cymbidium under various substrate conditions

Most orchid growers use bark as substrate to avoid too wet conditions, although it requires excessive water use of leaching. We conducted research to investigate the applicability of a soil moisture sensor-based automated irrigation system in Cymbidium production for efficient irrigation management and compared the growth and water use of Cymbidium under various substrate conditions. One-year-old Cymbidium ‘Hoshino Shizuku’ plantlets were grown in bark, coconut husk chips, coir dust, or a commercial growing mix at a similar matric potential within the easily available water range. Irrigation occurred when the substrate dried below the volumetric water content thresholds at 0.25, 0.30, 0.35, and 0.40 m3 m−3 in the bark, coconut husk chips, coir dust, and the commercial growing mix, respectively. Pseudobulb size, net photosynthetic assimilation rate, fresh shoot, and root weight of the Cymbidium showed no differences among the substrates, although Cymbidium grown in the commercial growing mix had better shoot growth than plants in the other substrates. The amount of irrigation was higher (ca. 6 times) in coarse substrates (bark and coconut husk chips) than fine substrates (coir dust and the commercial growing mix), indicating that fine substrates with higher water-holding capacity could use water more efficiently. The amount of irrigation and nutrient availability of the substrate in the coarse substrates were much lower than those in the fine substrates, producing a difference in growth of the Cymbidium among the substrates. Water use efficiency was 8–9.5 times higher in Cymbidium grown in fine substrates than plants grown in coarse substrates. Overall, the soil moisture sensor-based automated irrigation system could provide an appropriate moisture level for Cymbidium grown in fine substrates, avoiding too wet conditions, and produced quality Cymbidium with more efficient water and nutrient use than orchids produced in coarse substrates.

Functional relationship between photosynthetic leaf gas exchange in response to silicon application and water stress mitigation in sugarcane

BackgroundWater stress is one of the serious abiotic stresses that negatively influences the growth, development and production of sugarcane in arid and semi-arid regions. However, silicon (Si) has been applied as an alleviation strategy subjected to environmental stresses.MethodsIn this experiment, Si was applied as soil irrigation in sugarcane plants to understand the mitigation effect of Si against harmful impact of water stress on photosynthetic leaf gas exchange.ResultsIn the present study we primarily revealed the consequences of low soil moisture content, which affect overall plant performance of sugarcane significantly. Silicon application reduced the adverse effects of water stress by improving the net photosynthetic assimilation rate (Anet) 1.35–18.75%, stomatal conductance to water vapour (gs) 3.26–21.57% and rate of transpiration (E) 1.16–17.83%. The mathematical models developed from the proposed hypothesis explained the functional relationships between photosynthetic responses of Si application and water stress mitigation.ConclusionsSilicon application showed high ameliorative effects on photosynthetic responses of sugarcane to water stress and could be used for mitigating environmental stresses in other crops, too, in future.

Leaf gas exchange and foliar macronutrients vary in Quercus bicolor but not Quercus phellos between a designed soil pavement system and open lawn

Structural soils are a type of designed soil intended to improve tree growth in the built environment by increasing the rooting volume available to trees underneath pavement. While urban trees can experience multiple environmental stressors, tree water relations and leaf nutrients are not well studied in structural soil systems. We examined leaf level gas exchange, foliar nutrient concentrations, and crown condition to evaluate the potential effects of water and nutrient related stressors in this setting. Located in Brooklyn, NY, USA, the study site included Quercus bicolor and Q. phellos planted in both sidewalk pits underlain with structural soil and in open lawn areas. Tree size measurements indicate that around 16–20 years post-installation, lawn trees have started to become larger than those in the sidewalk, though the size differences are comparatively small. Leaf level net photosynthetic assimilation and stomatal conductance of Q. bicolor were significantly lower in sidewalk trees compared to lawn trees in 2016. Yet no differences in gas exchange were observed for Q. phellos which suggests the two species likely have different water use strategies. Out of 27 elements measured in leaf tissue, Ca, K, Ba, and Sr were significantly lower in Q. bicolor sidewalk trees. Both species appeared to have elevated foliar concentrations of Na. For Q. phellos, sidewalk trees had significantly lower crown vitality (fine twig dieback) scores, though no differences were observed for Q. bicolor. These findings suggest Q. bicolor may be more sensitive to water and nutrient stress in the structural soil system compared to Q. phellos.

Growth and Photosynthesis of Young Cymbidium as Influenced by Supplemental Lighting Timing

The effects of supplemental lighting (SL) timing on vegetative growth and the photosynthetic assimilation rate of young Cymbidium hybrids were examined. Nine month old C. ‘Yang Guifei’ and ‘Wine Shower’ were treated with four different SL timings: 22:00 – 02:00 (middle of the night, MN); 17:00 – 21:00 (end of day extension, DE); 07:00 – 09:00 plus 17:00 – 19:00 (both beginning and end of the night as split day extension, SDE), and non SL (8/16 h, short day, SD) for 4 months. All SL were provided by two types of 100% red LEDs (640 and 660 nm), with 150 μmol･m-2 ･s-1 and 800 μmol･mol-1 of CO2 supplied during the night (16 h). Pseudobulb diameters were significantly higher under SL treatments compared with the SD of both cultivars, irrespective of SL timing. Net photosynthetic assimilation rates were enhanced with increased SL, due to the additional photosynthesis and reduction of dark respiration. Thus, daily net photosynthetic amounts of SL treatments effectively increased photosynthesis compared to the SD. These results indicate that SL helps promote vegetative growth by enhancing photosynthesis. Since there were no significant differences among the SL timings when CO2 was provided uniformly during the night, we concluded that growth and photosynthesis of young Cymbidium do not depend on the timing of SL application, but are related to the daily light integrals, which is the amount of photosynthetically active photons delivered over 24 hours.

Xenon lamps used for fruit surface sterilization can increase the content of total flavonols in leaves of Lactuca sativa L. without any negative effect on net photosynthesis.

One (1P), two (2P), three (3P) or four (4P) pulses of light supplied by a xenon lamp, were applied to young lettuce plants grown in pots. The lamp used in the trial was similar to those used for fruit surface sterilization. Total flavonols were measured in leaves using the Dualex method. In a first trial conducted in greenhouse conditions, 6 days after the pulsed light (PL) treatment, flavonols were increased by 312% and 525% in the 3P and 4P treatments, respectively, in comparison to the those in the untreated control. Changes in the chlorophyll fluorescence parameters suggest that the PL treatment may induce limited and transient damage to the photosynthetic machinery and that the damage increases with the increasing number of pulses. The performance parameters were not significantly affected by PL and recovered fully by 6 days after the treatments. The 1P and the 2P treatments 6 days after the treatment showed a 28.6% and a 32.5% increase, respectively, in net photosynthetic assimilation, when compared to that of the control. However, 8 days after the treatment, there was no longer a difference between the treatments and the control in net photosynthetic assimilation. Eight days after the light treatment, the 3P treatment showed a 38.4% increase in maximal net photosynthetic assimilation over that of the control, which is an indication of positive long-term adaptation of photosynthetic capacity. As a whole, our observations suggest that PL could be used on field or greenhouse crops to increase their phytochemical content. No long-lasting or strong negative effects on photosynthesis were associated with PL within the range of doses we tested; some observations even suggest that certain treatments could result in an additional positive effect. This conclusion is supported by a second trial conducted in phytotrons. More studies are required to better understand the roles of the different wavelengths supplied by PL and their interactions.

Net photosynthetic CO2 assimilation: more than just CO2 and O2 reduction cycles.

Net photosynthetic assimilation in C3 plants is mostly viewed as a simple balance between CO2 fixation by Rubisco-catalyzed carboxylation and CO2 production by photorespiration (and to a lower extent, by day respiration) that can be easily manipulated during gas exchange experiments using the CO2 :O2 ratio of the environment. However, it now becomes clear that it is not so simple, because the photosynthetic response to gaseous conditions involves 'ancillary' metabolisms, even in the short-term. That is, carbon and nitrogen utilization by pathways other than the Calvin cycle and the photorespiratory cycle, as well as rapid signaling events, can influence the observed rate of net photosynthesis. The potential impact of such ancillary metabolisms is assessed as well as how it must be taken into account to avoid misinterpretation of photosynthetic CO2 response curves or low O2 effects in C3 leaves.

Photosynthetic regulation in seed heads and flag leaves of sagebrush-steppe bunchgrasses.

Native sagebrush-steppe bunchgrass populations are threatened by the spread and dominance of exotic invasive annual grasses, in part due to low, episodic seed production. In contrast, the widespread exotic bunchgrass, crested wheatgrass, readily produces viable seed cohorts. The mechanisms underlying these differences are unclear. To address this, we measured seed head specific mass (gm-2) and net photosynthetic assimilation (A net) as a function of internal [CO2] (A/Ci curves) in pre- and post-anthesis seed heads and flag leaves of crested wheatgrass and four native bunchgrasses to determine if differences in allocation and photosynthetic characteristics of seed heads was consistent with differential reproductive success. Crested wheatgrass seed heads had 2-fold greater specific mass compared to the native grasses, concurrent with greater CO2-saturated photosynthesis (A max), mesophyll carboxylation efficiency (CE), and higher intrinsic water-use efficiency (WUE i ; A net/stomatal conductance (g s)), but with similar relative stomatal limitations to photosynthesis (RSL). Post-anthesis seed head A max, CE, RSL and g s decreased in native grasses, while crested wheatgrass RSL decreased and CE increased dramatically, likely due to tighter coordination between seed head structural changes with stomatal and biochemical dynamics. Our results suggest native sagebrush-steppe bunchgrasses have greater stomatal and structural constraints to reproductive photosynthesis, while the exotic grass has evolved seed heads functionally similar to leaves. This study shows elucidating reproduction-related ecophysiological mechanisms provide understanding of plant attributes that underlie restoration success and could help guide the development of native plant materials with functional attributes needed to overcome demographic bottlenecks that limit their restoration into degraded sagebrush-steppe.

Canola Responses to Drought, Heat, and Combined Stress: Shared and Specific Effects on Carbon Assimilation, Seed Yield, and Oil Composition.

Photosynthetic assimilation is remarkably altered by heat and drought, and this depends on the individual or combined occurrence of stressors and their respective intensities and durations. Abiotic stressors may also alter the nutritional quality and economic value of crops. In this controlled greenhouse study, we evaluated the response of Brassica napus L., from flowering to seed development, to two temperature and water treatments and a combination of these treatments. The diffusional limitations of stomatal conductance and mesophyll conductance on photosynthesis, as well as resource-use efficiency (particularly water and nitrogen), were assessed. In addition, the effects of stressors on the seed fatty acid content and composition and the total protein content were examined. The results showed that the reduction in the net photosynthetic assimilation rate was caused by combinations of heat and drought (heat + drought) treatments, by drought alone, and, to a lesser extent, by heat alone. The stomatal conductance decreased under drought and heat + drought treatments but not under heat. Conversely, the mesophyll conductance was reduced significantly in the plants exposed to heat and heat + drought but not in the plants exposed to drought alone. The carboxylation efficiency rate and the electron transport rate were reduced under the heat treatment. The seed yield was reduced by 85.3% under the heat treatment and, to a lesser extent, under the drought treatment (31%). This emphasizes the devastating effects of hotter weather on seed formation and development. Seed oil content decreased by 52% in the plants exposed to heat, the protein content increased under all the stress treatments. Heat treatment had a more deleterious effect than drought on the seed oil composition, leading to enhanced levels of saturated fatty oils and, consequently, desaturation efficiency, a measure of oil frying ability. Overall, this study showed that except for the photosynthetic assimilation rate and stomatal conductance, heat, rather than drought, negatively affected the photosynthetic capacity, yield, and oil quality attributes when imposed during the flowering and silique-filling stages. This result highlights the necessity for a better understanding of heat tolerance mechanisms in crops to help to create germplasms that are adapted to rapid climate warming.

Water relations and photo-protection mechanisms during drought stress in four coffee (Coffea arabica) cultivars from southwestern Saudi Arabia

This study investigated for the first time the effect of drought on water relations, gas exchange, osmotic adjustment, and photoprotection mechanisms of local Arabica coffee cultivars namely, Dawairi, Tufahi, Kholani and Tessawi grown in Southwestern Saudi Arabia. Two-year-old plants growing in pots were subjected to water stress by withholding watering for four weeks. Water relations and gas exchange measurements revealed that the severity of the stress varied among cultivars. The most contrasting behavior was between the two cultivars Dawairi (drought-tolerant) and Kholani (drought-sensitive). Tufahi and Tessawi, however, showed intermediate tolerance. Under drought stress, Dawairi trees were able to maintain higher leaf water content (WC), plant turgor potential (Ψp) and net photosynthetic assimilation rate (Anet) at a given predawn leaf water potential (Ψpd) than the other three cultivars. Irreversible wilting (turgor loss) occurred at leaf Ψpd of about −2.5 MPa for Kholani and about −3.5 MPa or lower for the other cultivars. The drought tolerant cultivar also showed the highest increase in instantaneous water-use efficiency (iWUE) under drought stress. All coffee cultivars were able to slow the onset of water stress by controlling transpiration (avoidance). But they did vary in their ability to avoid tissue dehydration under such stress. The reduction in Anet, transpiration rate (E) and stomatal conductance (gs) with decreasing Ψpd was earlier and more marked in Kholani and Tufahi than in Dawairi and Tessawi. Besides, the fluctuations in Ψpd and Ψmid revealed a contrasting behavior among the four cultivars. Under drought stress, Dawairi maintained the highest diurnal range of ∆Ψpd-mid and showed the highest daily re-saturation capability. Moreover, it had a greater capacity for osmotic adjustment through solute accumulation. In contrast, in Kholani and Tufahi the drought-induced accumulation of solutes was mainly passive due to dehydration of the leaves. Moreover, Dawairi and Tessawi accumulated more proline in their leaves than the two other cultivars under stress. Drought stress considerably altered total soluble sugar (TSS) concentration in most cultivars. Surprisingly, the decrease in TSS content was more pronounced in drought tolerant cultivars. Photoinhibition occurred in all four cultivars when subjected to drought stress albeit with variable severity. Moderate stress decreased the quantum efficiency of PSII (ΦPSII), photochemical fluorescence quenching (qP) and electron transport rate (ETR), and increased the non-photochemical quenching (NPQ); this implies dynamic photoinhibition in all cultivars. However, when drought became severe towards the end of the experiment, the decrease in ΦPSII, qP and ETR was accompanied by a decline in Fv/Fm indicating the occurrence of chronic photoinhibition in most cultivars. Still photoinhibition was more obvious in Kholani and Tufahi. Interesting genetic differences in drought tolerance appear to exist among these four economically important Arabica coffee cultivars.

Effects of increased soil fertility and plant growth-promoting rhizobacteria inoculation on biomass yield, energy value, and physiological response of poplar in short-rotation coppices in a reclaimed tideland: A case study in the Saemangeum area of Korea

This study aims to investigate the physiological response, biomass yield and its bio-energy value to charcoal mineral fertilizer and Bacillus subtilis strain JS, a plant growth-promoting rhizobacteria, under nine different soil-enrichment procedures, and to provide a reference for suitable management strategies for short-rotation coppices on the marginal soils of reclaimed tidelands in Saemangeum area of Korea. The treatments used in this experiment were as follows: 1) 1:100 (volume basis) diluted rhizobacteria inoculation {B1, (B. subtilis: double-distilled water, v/v)}, 2) 1:50 diluted rhizobacteria inoculation (B2), 3) mineral fertilization {F1, (charcoal 200 kg ha−1)}, 4) additional mineral fertilization {F2, (charcoal 300 kg ha−1)}, 5) F1+B1, 6) F2+B1, 7) F1+B2, 8) F2+B2, and 9) control plot with no soil enrichment (C). The plant species used in this study is Populus euramericana. Net photosynthetic assimilation using leaves acclimated for 2 min at 1500 μmol m−2 s−1 was the highest in F1+B2, followed by B2+F2 and B2. Total biomass yield in F2+B2 was the highest by a significant margin among the nine soil-enrichment procedures, whereas that in the control soil was lowest. Plants in all soil conditions provided similar net calorific values of dry mass, and they all fell within the third grade of wood pellet quality criteria of the National Institute of Forest Science standard specification (Korea), within the premium category in the Pellet Fuels Institute standard specification (US), and within the A1 category in the EN-Plus standard specification (EU). Moreover, it was confirmed that the poplar was suited to produce wood pellets for heating energy.

TROCAS GASOSAS DE PLANTAS JOVENS DE TAXI-BRANCO SUBMETIDAS À VARIAÇÃO DE TEMPERATURA FOLIAR E SUSPENSÃO DA IRRIGAÇÃO

O objetivo deste trabalho foi investigar a influência da variação de temperatura foliar associada à suspensão de irrigação sobre as trocas gasosas de plantas jovens de taxi-branco (Sclerolobium paniculatum Vogel). O estudo foi realizado em casa de vegetação na área experimental da Embrapa Amazônia Ocidental. As plantas cresceram em casa de vegetação e depois de quatro meses de aclimatização foram submetidas a três regimes hídricos (mantidas irrigadas até a capacidade de campo do solo, irrigação suspensa por oito e 14 dias). Foram avaliados os parâmetros fisiológicos de trocas gasosas, taxa de assimilação líquida de CO2 (A), transpiração foliar (E), condutância estomática (gs) e eficiência no uso da água (EUA) os quais foram obtidos por meio do medidor portátil de fotossíntese (CI-340, CID, Inc.). Os resultados mostraram que houve redução das taxas de assimilação líquida de CO2 em função da elevação da temperatura foliar e da suspensão da irrigação. Após oito dias de suspensão da irrigação houve redução das taxas de assimilação líquida de CO2 fotossintéticas em 62, 65, 75, 58, 50 e 64% e aos 14 dias esta redução foi de 80, 85, 85, 84, 86 e 93% em comparação as plantas mantidas irrigadas, nas temperaturas de 25, 30, 35, 40, 45 e 50°C, respectivamente. O comportamento das taxas de transpiração foliar foi inversamente proporcional às taxas de fotossíntese líquida, mostrando incremento em função do aumento da temperatura foliar. O comportamento fisiológico de trocas gasosas de Sclerolobium paniculatum apresentou variações tanto em relação ao efeito da temperatura foliar, quanto da suspensão de irrigação.