Photosynthetic Responses Research Articles

Photosynthetic responses of a golden tide alga (Sargassum horneri) to ultraviolet radiation

In recent years, massive Sargassum drifting on the sea surface, known as “golden tides,” negatively impacted on the local marine ecology. However, the physiological mechanisms of its formation remain unclear. To investigate the photosynthetic responses of golden tide algae to UVR, one key factor for drifting Sargassum population, we cultivated thalli of S. horneri, a golden tide alga, under three light treatments: P (photosynthetically active radiation, PAR), PA (PAR+UVA) and PAB (PAR+UVA+UVB) for 120 mins, followed by low light recovery for 240 mins. The photosynthetic characteristics of alga were determined. The results showed that UVR exposure decreased photosynthetic activity, reflected by depressed maximum photochemical quantum yield (Fv/Fm) and contents of Chla and Chlc in the PA and PAB treatments. Higher content of malondialdehyde (MDA) was found in thalli exposed to UVR, which verified the damage of UVR. Electron transfer rate (ETR) was slowed down by UVR, accompanied by the increments of net closing rate of the reaction center and the energy absorbed and dissipated by unit reaction center in PSII. In these effects on photosynthesis of UVR, the PAB treatment expressed more significant inhibition, indicating a remarkable role of UVB. However, based on our results, S. horneri also took some strategies to protect itself from photodamage of UVR. UVR exposure enhanced the contents of UV-absorbing compounds (UVACs) and carotenoid, and simultaneously expedited heat consumption of excess light energy, indicated by the increased non-photochemical quenching coefficient (NPQ) in the PA and PAB treatments. Increased activities of superoxide dismutase (SOD) and peroxidase (POD), and higher content of PsbA (D1) protein were found in the treatments with UVR, which suggested that antioxidant system and the turnover of D1 protein played important roles in protection from UV-induced damages. Due to the above protection pathways, Fv/Fm and ETR gradually recovered when thalli were transferred to low light recovery. Therefore, we suggest that various protection and restoration pathways in S. horneri work together to effectively protect against UVR damage, which may be the reason why drifting populations can adapt to UVR on the seawater surface and form golden tide in case of suitable temperature and nutrients.

Impact of warmer and drier conditions on tree photosynthetic properties and the role of species interactions.

Increased temperature and prolonged soil moisture reduction have distinct impacts on tree photosynthetic properties. Yet, our knowledge of their combined effect is limited. Moreover, how species interactions alter photosynthetic responses to warming and drought remains unclear. Using mesocosms, we studied how photosynthetic properties of European beech and downy oak were impacted by multi-year warming and soil moisture reduction alone or combined, and how species interactions (intra- vs inter-specific interactions) modulated these effects. Warming of +5°C enhanced photosynthetic properties in oak but not beech, while moisture reduction decreased them in both species. Combined warming and moisture reduction reduced photosynthetic properties for both species, but no exacerbated effects were observed. Oak was less impacted by combined warming and limited moisture when interacting with beech than in intra-specific stands. For beech, species interactions had no impact on the photosynthetic responses to warming and moisture reduction, alone or combined. Warming had either no or beneficial effects on the photosynthetic properties, while moisture reduction and their combined effects strongly reduced photosynthetic responses. However, inter-specific interactions mitigated the adverse impacts of combined warming and drought in oak, thereby highlighting the need to deepen our understanding of the role of species interactions under climate change.

Low Red to Far-red ratio increases resistance to CO2 diffusion and reduces photosynthetic efficiency in low light grown tomato plants

Application of light-emitting diode technology has opened opportunities to optimize light spectrum for crop production greenhouses and vertical farms. In addition to photosynthetically active radiation, far-red (FR) light has shown potential for enhancing leaf photosynthesis. However, additional FR also alters the red to far-red ratio (R:FR) and induces a shade-avoidance response (SAR) that changes leaf nitrogen, thickness and mass. These acclimations can potentially also alter the resistance to CO 2 diffusion, which can limit photosynthesis. Tomato plants were grown with and without additional FR at two light levels. Changes in photosynthetic responses to light and CO 2 diffusion resistance, as well as leaf mass, thickness and nitrogen content were assessed. At low light additional FR strongly reduced leaf maximum photosynthesis, leaf mass, thickness and nitrogen, and increased the resistance to CO 2 diffusion. These effects were to a much lesser extent present in plants grown at high light intensity. Tomato leaves grown under low light intensity supplemented with FR, show much stronger SAR and a larger increase in CO 2 diffusion resistance than plants grown under high light, which negatively influences their photosynthesis at increasing light intensity. Only if the negative effects of sensitivity to FR and SAR response can be avoided, supplemental FR light may be beneficial to enhance photosynthesis in greenhouse and vertical farm systems.

Melatonin Influences Stomatal Behavior, Root Morphology, Cell Viability, Photosynthetic Responses, Fruit Yield, and Fruit Quality of Tomato Plants Exposed to Salt Stress

Melatonin Influences Stomatal Behavior, Root Morphology, Cell Viability, Photosynthetic Responses, Fruit Yield, and Fruit Quality of Tomato Plants Exposed to Salt Stress

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.

Heat-Induced Photosynthetic Responses of Symbiodiniaceae Revealed by Flash-Induced Fluorescence Relaxation Kinetics

Symbiodiniaceae live in endosymbiosis with corals. In the last few decades, mass bleaching events have occurred in the coral reefs, causing damage in the ecosystem and the associated species. Global temperature increase is affecting the algae, disturbing the whole symbiosis and leads to coral bleaching. However, the heat tolerance is strongly determined by the species (formerly genetic clades) harbored by the coral host. We assessed three different strains of Symbiodiniaceae family, i.e., Fugacium kawagutii (CS156), Symbiodinium tridacnidorum (2465), and Symbiodinium microadriaticum (2467), which display different heat tolerance under heat stress conditions. Flash-induced chlorophyll fluorescence relaxation is a useful tool to monitor various components of the photosynthetic electron transport chain and the redox reactions of plastoquinone pool. We observed the appearance of a wave phenomenon in the fluorescence relaxation by heating the strains in combination with microaerobic conditions. The characteristics of this fluorescence wave were found to be strain-specific and possibly related to the transient oxidation and re-reduction of the plastoquinone pool. The appearance of the wave phenomenon appears to be related to cyclic electron flow as well because it is accompanied with enhanced post-illumination chlorophyll fluorescence rise. These results will potentially reveal further details of the role of cyclic electron transport in Symbiodiniaceae and its relevance in heat stress tolerance.

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.

Synchronization between photosynthetic responses to seasonality during fruit development and fatty acid profile of mesocarp oil in macauba (Acrocomia aculeata)

Macauba palm (Acrocomia aculeata (Jacq.) Lodd. ex Mart. Arecaceae) is a novel oil crop with wide industrial applicability. However, little is known about the photosynthetic responses to seasonality during fruit development in macauba palm and its effects on the fatty acid profile of mesocarp oil and its physicochemical and spectroscopic characteristics. The fatty acid profile changed in six fruit developmental stages (ranging from 180 days after anthesis to full ripening and dispersion). This occurred during the transition from dry to rainy season concomitant with adjustments in photosynthetic responses. The increase in mesocarp oil yield in the fruit was synchronized with the higher photosynthetic capacity at the beginning of the rainy season, being characterized by a raise in oleic acid. The dynamics of soluble solids, acidity, pH, total sugars and starch were proportional to the spectroscopic changes and allowed to determine the ideal harvest point: 360 days after anthesis, with fruits still in the bunch. The macauba palm fruits in this stage showed suitable physical and chemical characteristics for industrial use, as well as higher oil yield. The monitoring of chemical changes with Fournier transformed infrared spectroscopy techniques would aid fast and precise detection of the fruit development and its ideal harvest point.

Integrated physiological and transcriptomic analyses reveal differential photosynthetic responses to low-light stress in tall fescue cultivars

Tall fescue (Festuca arundinacea Schreb.) is the predominant cool-season turfgrass species worldwide, but low-light (LL) stress is a primary limiting factor for turfgrass management. Studies on two tall fescue cultivars, Arid 3 and Airlie, showed that Airlie is more susceptible to LL stress than Arid 3. However, the underlying susceptibility mechanism is obscure. In this study, we investigated the physiological and transcriptional changes of two tall fescue cultivars under LL stress. Arid 3 showed better growth characteristics, higher chlorophyll contents and photosynthetic gas exchange than Airlie. A total of 136,925 unigenes were obtained from our RNA-sequencing. There were 24,944 and 30,816 differentially expressed genes (DEGs) between LL stress and the control in Arid 3 and Airlie, respectively. Meanwhile, there were 20,599 DEGs detected between Arid 3 and Airlie under the control, and under LL stress the DEGs between two cultivars were 20,783. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis suggested that the DEGs were mainly involved in ‘cell part’ and ‘glutathione metabolism’. Furthermore, vital transcription factors obtained different expression level in two cultivars. FaPhyA and FaPhyB were higher expressed in Arid 3 than that in Airlie, which played positive roles in regulating photomorphogenesis of tall fescue under LL stress. On the contrary, the expression levels of negative regulatory factor FaPIF5 and FaCOP1 were higher in Airlie. Additionally, genes related to chlorophyll metabolism and photosynthesis were also affected by LL stress, there were 26 genes significantly higher expressed in Arid 3. This study revealed two tall fescue cultivars develop different physiological and transcriptional changes, and provided an insight into different photosynthetic responses in two tall fescue cultivars responding to LL stress.

Photosynthetic response and antioxidative activity of ‘Hass’ avocado cultivar treated with short-term low temperature

To investigate the effects of short-term low temperatures, three-year-old avocado (Persea americana cv. Hass) seedlings were treated with 1, − 2, or − 5 °C for 1 h and subsequently recovered in ambient condition for 24 h. Leaf color changes were investigated with chlorophyll, carotenoid, and phenolic contents. Photosynthetic responses were examined using gas exchange analysis. With H2O2 contents as oxidative stresses, enzymatic (ascorbate peroxidase, APX; glutathione reductase, GR; catalase, CAT; peroxidase, POD) and non-enzymatic antioxidant activities were determined using spectrophotometry. Leaves in the avocado seedlings started to be discolored with changes in the contents of chlorophyll a, carotenoids, and phenolics when treated with − 5 °C. However, the H2O2 content was not different in leaves treated with low temperatures. Photosynthetic activities decreased in leaves in the seedlings treated with − 5 °C. Of antioxidant enzymes, APX and GR have high activities in leaves in the seedlings treated with 1 and − 2 °C. In leaves in the seedlings treated with − 5 °C, the activities of all enzymes decreased. Non-enzymatic antioxidant activity was not different among leaves treated with low temperatures. These results indicated that APX and GR would play a critical role in withstanding chilling stress in ‘Hass’ avocado seedlings. However, under lethal temperature, even for a short time, the plants suffered irreversible damage with the breakdown of photosystem and antioxidant system.

Delayed Leaf Senescence by Upregulation of Cytokinin Biosynthesis Specifically in Tomato Roots.

Cytokinins (CKs) regulate numerous plant developmental processes, including photosynthesis and leaf senescence. Isopentenyltransferase (IPT) is a rate-limiting enzyme in the CK-biosynthesis pathway. We overexpressed ipt under tissue-specific promoters to study the long-range effect of CK on the functioning of tomato source leaves. Photosynthetic activity over time provided the measure for leaf aging. Significantly delayed leaf senescence was observed in plants expressing ipt under a root-specific promoter, but not in those expressing the gene under a source leaf-specific promoter. The root-derived influence on leaf aging was further confirmed by grafting experiments. CK concentration in source leaves of both transgenic lines increased significantly, with different proportions of its various derivatives. On the other hand, root CK concentration was only slightly elevated. Nevertheless, the significant change in the proportion of CK derivatives in the root indicated that CK biosynthesis and metabolism were altered. Partial leaf defoliation upregulates photosynthetic rate in the remaining leaf; however, overexpression of ipt in either tissues eliminated this response. Interestingly, stem girdling also eliminated the photosynthetic response. Taken together, our findings suggest that leaf senescence is regulated by a CK-mediated root–shoot communication network. We propose that CK-mediated signal is translocated to the leaf via the xylem where it alters CK biosynthesis, resulting in delayed senescence.

Stomatal and photosynthetic responses of soybean with two types of mulch under different soil water conditions

Soybean was planted in clay pots with living mulch of white clover (CL) or shredded paper mulch (SP). Soil moisture in the pots was individually controlled at five levels from around 20% of volumetric soil water content (SWC) to near-saturated, by monitoring SWC every morning and irrigating intermittently. This study focussed on the growth period of the soybean when plant height and LAI reached around maximum. The lower evapotranspiration (ET) and lower stomatal conductance (gs) of the soybean in lower SWC with both SP and CL were caused by water stress. The significantly higher ET but lower gs for CL compared with SP at the same SWC levels revealed that the soybean with CL competed with the clover for water and that the clover extracted water even at the lower SWC. The lowest electron transport rate (ETR) and non-photochemical quenching (NPQ) at the lowest SWC level with both SP and CL were regarded as being caused by water stress, under which the thermal dissipation processes could not be activated under strong light with photoinhibition. The lower ETR and the higher NPQ under the low PPFD condition for CL compared with SP could be interpreted as the soybean with CL having both water and nutrient stresses, even under the low PPFD condition, but the soybean with CL activated NPQ to protect PhSII by reaching the maximum NPQ under lower PPFD compared with the soybean with SP. The lower photosynthetic rate (P) of the soybean at the lower SWC level for both SP and CL resulted from the lower gs and ETR caused by water stress. The lower P for CL compared with SP at the same SWC level resulted from the lower gs and ETR and severer photoinhibition despite the activated function of NPQ caused by the water stress and by the nutrient stress.

Is Tempranillo Blanco Grapevine Different from Tempranillo Tinto Only in the Color of the Grapes? An Updated Review.

Tempranillo Blanco is a somatic variant of Tempranillo Tinto that appeared as a natural, spontaneous mutation in 1988 in a single shoot of a single plant in an old vineyard. It was vegetatively propagated, and currently wines from Tempranillo Blanco are commercially available. The mutation that originated Tempranillo Blanco comprised single-nucleotide variations, chromosomal deletions, and reorganizations, losing hundreds of genes and putatively affecting the functioning and regulation of many others. The most evident, visual change in Tempranillo Blanco is the anthocyanin lost, producing this grapevine variety bunches of colorless grapes. This review aims to summarize from the available literature differences found between Tempranillo Blanco and Tinto in addition to the color of the grapes, in a climate change context and using fruit-bearing cuttings grown in temperature-gradient greenhouses as research-oriented greenhouses. The differences found include changes in growth, water use, bunch mass, grape quality (both technological and phenolic maturity), and some aspects of their photosynthetic response when grown in an atmosphere of elevated CO2 concentration and temperature, and low water availability. Under field conditions, Tempranillo Blanco yields less than Tempranillo Tinto, the lower weight of their bunches being related to a lower pollen viability and berry and seed setting.

Fine scale variability in Green Vegetation Fraction Over the Southern Great Plains using Sentinel-2 satellite: A case study

We estimate the green vegetation fraction (GVF) at high spatial resolution (10 m) by applying a new method based on image histogram equalization and utilizing images with multiple spectral bands from Sentinel-2 satellite observations. True color and multi-spectral images at 10 m resolution are used over 50 × 50 km2 domain centered on the US Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) site over the Southern Great Plains to recognize green pixels and estimate the vegetation fraction. The GVF retrieved from several spectral bands is compared with Sentinel-2 true color images, Sentinel-3, MODIS vegetation products, and observations from the US DOE research aircraft on selected days from the Holistic Interactions of Shallow Clouds, Aerosols, and Land-Ecosystems (HI-SCALE) campaign. Unlike MODIS or Sentinel-3, our approach to retrieve the GVF is independent of absolute reflectance or photosynthetic response. Spatial patterns in vegetation distribution are similar in all three satellite approaches, however MODIS underestimates the vegetation cover by about 10% compared to the Sentinel-2, -3 retrievals over the study domain. The largest contrast in MODIS and Sentinel-2, -3 is found when the GVF is less than 0.2 or greater than 0.9, likely as a result of different retrieval approaches and spectral bands used to estimate the vegetation products. The NDVI retrieved from MODIS is also underestimated compared to the aircraft observations suggesting that MODIS underestimates both NDVI and GVF. In the past, various satellite observations have been used to retrieve the vegetation fraction at medium (0.25–0.50 km) and coarser resolutions (15 km) but our approach is extended to a much higher (10 m) resolution. Our analysis from Sentinel-2 shows large spatial variability in GVF and a clear disparity with estimates from MODIS and Sentinel-3 satellites. The new approach to estimate GVF has the potential to increase spatial accuracy and precision of surface properties relevant for crop and forest management, surface and energy balance processes, and land surface parameterizations in atmospheric models.

Interplay between LHCSR proteins and state transitions governs the NPQ response in Chlamydomonas during light fluctuations.

Photosynthetic organisms use sunlight as the primary energy source to fix CO2. However, in nature, light energy is highly variable, reaching levels of saturation for periods ranging from milliseconds to hours. In the green microalga Chlamydomonas reinhardtii, safe dissipation of excess light energy by nonphotochemical quenching (NPQ) is mediated by light‐harvesting complex stress‐related (LHCSR) proteins and redistribution of light‐harvesting antennae between the photosystems (state transition). Although each component underlying NPQ has been documented, their relative contributions to NPQ under fluctuating light conditions remain unknown. Here, by monitoring NPQ in intact cells throughout high light/dark cycles of various illumination periods, we find that the dynamics of NPQ depend on the timescales of light fluctuations. We show that LHCSRs play a major role during the light phases of light fluctuations and describe their role in growth under rapid light fluctuations. We further reveal an activation of NPQ during the dark phases of all high light/dark cycles and show that this phenomenon arises from state transition. Finally, we show that LHCSRs and state transition synergistically cooperate to enable NPQ response during light fluctuations. These results highlight the dynamic functioning of photoprotection under light fluctuations and open a new way to systematically characterize the photosynthetic response to an ever‐changing light environment.

Impacts of drought intensity and weed competition on drought-tolerant corn performance

AbstractWater stress and weed competition are critical stressors during corn (Zea mays L.) development. Genetic improvements in corn have resulted in hybrids with greater tolerance to abiotic and biotic stressors; however, drought stress remains problematic. Therefore, in light of the anticipated change in precipitation throughout the Great Lakes Region, greenhouse experiments were conducted to evaluate water stress and weed competition on drought-tolerant corn performance. The study followed a completely randomized block design with four replications. Factorial treatment combinations consisted of drought-tolerant corn competition (presence or absence), water stress (100% or 50% volumetric water content [VWC]), and nine corn:common lambsquarters (Chenopodium album L., CHEAL) densities. Corn and C. album growth parameters were measured at 14 and 21 d after water-stress initiation. To explore the impact of reduced soil moisture and weed competition on corn and C. album growth parameters, photosynthetic response, and biomass, linear mixed-effects and nonlinear regression models were constructed in R. Chenopodium album biomass was reduced by 46% and 50% under corn competition at 2 and 4 weeds pot−1 (P = 0.0003, 0.0004). However, introducing crop competition under 6 and 9 weeds pot−1 did not reduce C. album biomass (P = 0.90, 1.00). Averaged across weed pressures, corn biomass was 22% less when grown under 50% compared with 100% VWC (P = 0.0003). However, averaged across VWC values, increasing weed competition from 0 to 2 (P = 0.04), 4 (P = <0.0001), 6 (P = 0.0002), or 9 (P = 0.0002) weeds pot−1 reduced biomass by 22%, 38%, 35%, and 36%. Overall, water stress and C. album competition negatively affected the parameters measured in this study; however, the magnitude of reduction is stronger under drought stress than increasing weed competition when water is not limiting. Therefore, field crop growers must modify current integrated weed management programs to maintain yield under future climate stress.

Assessment of different salt concentrations on the growth and phytochemical change of the ice plants

The ice plant (Mesembryanthemum crystallinum L.) has become a halophyte model to study the plant photosynthetic responses C3 photosynthesis to crassulacean acid metabolism (CAM), which is accelerated by salt stress. However, this adaptive mechanism improves water use efficiency, and water stress tolerance is still poorly known. This study examined the effect of individual and mixture of NaCl and CaCl2 concentrations on morphological parameters and bioactive component contents of ice plants in a plant factory system. Eight salt treatments individually and a combination of sodium chloride (NaCl) and calcium chloride (CaCl2), and Hoagland solutions were applied after the transplanting of ice plants. Morphological parameters like the number of leaves and lateral stems, leaf chlorophyll content (SPAD value), fresh weight, and dry weight of shoots and roots were measured at the adult stage. Concurrently, in the juvenile phase, the area of a canopy was evaluated using an image processing technique in HSV (hue, saturation, value) colour space. Correspondingly, ice plant secondary metabolites such as cations, anions, and radical scavenging activity were assayed in the adult phase correlated to the salt stress. The effects of salt stress on the growth of ice plants and secondary metabolite production were analysed using completely randomized block designs through the variance by one-way ANOVA with a significance level of p < 0.05. This study demonstrated that 400 mM CaCl2 (T4) enhanced the biomass and high sodium (Na+) and calcium (Ca2+) accumulations, and 200 mM CaCl2 (T3) accelerated the potassium (K+), magnesium (Mg2+), phosphate (PO43−), and sulfate (SO42−) accumulations. Moreover, NaCl 400 mM (T1) and combination of 100 mM NaCl and 300 mM CaCl2 (T5) positively influenced the chloride (Cl−) deposition and combination of 200 mM NaCl and 200 mM CaCl2 (T6) improved nitrate (NO3–) accretion. Furthermore, 100 mM CaCl2 (T2) exhibited the highest antioxidant activity in ice plants grown under the plant factory system.

Nutrient uptake, physiological responses and growth of tobacco (Nicotiana tabacum L.) in soil under composite salt stress

Higher soil salinity imposes osmotic stress and ion toxicity in plants, leading to substantial crop yield loss worldwide. Understanding of the quantitative and dynamic physiological responses to composite soil salinity (CSS) is limited and needs to be expanded. In this study, physiological, nutritional, and biomass yield parameters of tobacco ( Nicotiana tabacum L.) grown in soil with five levels of CSS, basal CSS level (untreated control, CK) and 3 (T 1 ), 6 (T 2 ), 9 (T 3 ), and 12 (T 4 ) times the basal CSS level, grown under greenhouse were determined and studied at 30-, 60-, and 90-d growth periods. Leaf dry biomass was significantly ( P < 0.05) increased by the low salinity levels applied (T 1 and T 2 ) at all three time points, whereas it progressively declined as the CSS level further increased. The leaf physiological and photosynthetic responses were more adversely affected by CSS at the early growth stage (day 30). A path-coefficient analysis demonstrated that leaf proline concentration had the largest direct effect (–0.66), and leaf Cu content had the most significant indirect effect (0.49) on leaf dry biomass of plants. The results suggest that lower CSS levels (T 1 and T 2 ) could stimulate tobacco growth (leaf biomass yield, in particular), and higher leaf proline and Cu levels at the early growth stage may potentially increase the ability of tobacco plants to withstand the adverse effects of salinity, which could be considered for future research and development of salinity management strategies.

Respiratory and Photosynthetic Responses of Antarctic Vascular Plants Are Differentially Affected by CO2 Enrichment and Nocturnal Warming

Projected rises in atmospheric CO2 concentration and minimum night-time temperatures may have important effects on plant carbon metabolism altering the carbon balance of the only two vascular plant species in the Antarctic Peninsula. We assessed the effect of nocturnal warming (8/5 °C vs. 8/8 °C day/night) and CO2 concentrations (400 ppm and 750 ppm) on gas exchange, non-structural carbohydrates, two respiratory-related enzymes, and mitochondrial size and number in two species of vascular plants. In Colobanthus quitensis, light-saturated photosynthesis measured at 400 ppm was reduced when plants were grown in the elevated CO2 or in the nocturnal warming treatments. Growth in elevated CO2 reduced stomatal conductance but nocturnal warming did not. The short-term sensitivity of respiration, relative protein abundance, and mitochondrial traits were not responsive to either treatment in this species. Moreover, some acclimation to nocturnal warming at ambient CO2 was observed. Altogether, these responses in C. quitensis led to an increase in the respiration-assimilation ratio in plants grown in elevated CO2. The response of Deschampsia antarctica to the experimental treatments was quite distinct. Photosynthesis was not affected by either treatment; however, respiration acclimated to temperature in the elevated CO2 treatment. The observed short-term changes in thermal sensitivity indicate type I acclimation of respiration. Growth in elevated CO2 and nocturnal warming resulted in a reduction in mitochondrial numbers and an increase in mitochondrial size in D. antarctica. Overall, our results suggest that with climate change D. antarctica could be more successful than C. quitensis, due to its ability to make metabolic adjustments to maintain its carbon balance.

Biochemical, gas exchange, and chlorophyll fluorescence analysis of maize genotypes under drought stress reveals important insights into their interaction and homeostasis

Many studies have been conducted on maize to study the effect of drought on yield at the flowering stage, but understanding biochemical and photosynthetic response against drought at the seedling stage needs to be well established. Thus, to understand differential changes and interaction of biochemical and photosynthetic parameters at the seedling stage under drought, a greenhouse experiment with twelve maize genotypes under severe drought (30% field capacity) and irrigated (90-100% field capacity) conditions were performed. Drought differentially altered biochemical and photosynthetic parameters in all genotypes. A sharp increase in hydrogen peroxide, malondialdehyde (MDA), and total antioxidant capacity (TAOC) were seen and a positive association between H2O2 and TAOC, and MDA and transpiration rate (E) was observed under drought. Nonphotochemical quenching increased under drought to avoid the photosystem damage. PCA biplot analysis showed that reducing E and increasing photosynthetic efficiency would be a better drought adaptation mechanism in maize at the seedling stage.