Net CO2 Assimilation Rate Research Articles

Common bean SNP alleles and candidate genes affecting photosynthesis under contrasting water regimes

Water deficit is a major worldwide constraint to common bean (Phaseolus vulgaris L.) production, being photosynthesis one of the most affected physiological processes. To gain insights into the genetic basis of the photosynthetic response of common bean under water-limited conditions, a collection of 158 Portuguese accessions was grown under both well-watered and water-deficit regimes. Leaf gas-exchange parameters were measured and photosynthetic pigments quantified. The same collection was genotyped using SNP arrays, and SNP-trait associations tested considering a linear mixed model accounting for the genetic relatedness among accessions. A total of 133 SNP-trait associations were identified for net CO2 assimilation rate, transpiration rate, stomatal conductance, and chlorophylls a and b, carotenes, and xanthophyll contents. Ninety of these associations were detected under water-deficit and 43 under well-watered conditions, with only two associations common to both treatments. Identified candidate genes revealed that stomatal regulation, protein translocation across membranes, redox mechanisms, hormone, and osmotic stress signaling were the most relevant processes involved in common bean response to water-limited conditions. These candidates are now preferential targets for common bean water-deficit-tolerance breeding. Additionally, new sources of water-deficit tolerance of Andean, Mesoamerican, and admixed origin were detected as accessions valuable for breeding, and not yet explored.

Integration of electron flow partitioning improves estimation of photosynthetic rate under various environmental conditions based on chlorophyll fluorescence

Electron transport rate (ETR), estimated from chlorophyll fluorescence, is a widely-used indicator of photosynthetic activity. However, net photosynthetic CO2 assimilation rate (A) does not linearly correlate with ETR when the fraction of electron partitioning into photosynthesis and photorespiration changes under fluctuating environmental conditions (CO2, light, temperature and soil moisture).Here, we propose a practical approach to estimate A based on ETR with integration of stomatal conductance (gs) and leaf temperature, taking intercellular CO2 concentration (Ci)- and temperature-dependent electron partitioning into account.A estimated with the present approach was in good agreement with A measured under i) various CO2 concentrations and light intensities in seedlings of Japanese beech and Japanese white birch, and ii) under 400 and 800 μmol mol−1 CO2 and temperatures of 15–40 °C, and iii) in progress of drought stress after a water withholding in seedlings of Japanese white birch. Furthermore, canopy-level CO2 uptake could be estimated based on the spectroscopic and flux observations over a Japanese beech stand, under a wide range of environmental conditions.The present approach is advantageous because it does not require biochemical information, such as the maximum rates of Rubisco carboxylation and electron transport, providing a more forward approach to estimate terrestrial carbon flux through remote sensing approaches.

Intrinsic Fluctuations in Transpiration Induce Photorespiration to Oxidize P700 in Photosystem I

Upon exposure to environmental stress, the primary electron donor in photosystem I (PSI), P700, is oxidized to suppress the production of reactive oxygen species that could oxidatively inactivate the function of PSI. The illumination of rice leaves with actinic light induces intrinsic fluctuations in the opening and closing of stomata, causing the net CO2 assimilation rate to fluctuate. We examined the effects of these intrinsic fluctuations on electron transport reactions. Under atmospheric O2 conditions (21 kPa), the effective quantum yield of photosystem II (PSII) (Y(II)) remained relatively high while the net CO2 assimilation rate fluctuated, which indicates the function of alternative electron flow. By contrast, under low O2 conditions (2 kPa), Y(II) fluctuated. These results suggest that photorespiration primarily drove the alternative electron flow. Photorespiration maintained the oxidation level of ferredoxin (Fd) throughout the fluctuation of the net CO2 assimilation rate. Moreover, the relative activity of photorespiration was correlated with both the oxidation level of P700 and the magnitude of the proton gradient across the thylakoid membrane in 21 kPa O2 conditions. These results show that photorespiration oxidized P700 by stimulating the proton gradient formation when CO2 assimilation was suppressed by stomatal closure.

Plasticity of the Root System Architecture and Leaf Gas Exchange Parameters Are Important for Maintaining Bottle Gourd Responses under Water Deficit.

The evaluation of root system architecture (RSA) development and the physiological responses of crop plants grown under water-limited conditions are of great importance. The purpose of this study was to examine the short-term variation of the morphological and physiological plasticity of Lagenaria siceraria genotypes under water deficit, evaluating the changes in the relationship between the root system architecture and leaf physiological responses. Bottle gourd genotypes were grown in rhizoboxes under well-watered and water deficit conditions. Significant genotype-water regime interactions were observed for several RSA traits and physiological parameters. Biplot analyses confirmed that the drought-tolerant genotypes (BG-48 and GC) showed a high net CO2 assimilation rate, stomatal conductance, transpiration rates with a smaller length, and a reduced root length density of second-order lateral roots, whereas the genotypes BG-67 and Osorno were identified as drought-sensitive and showed greater values for average root length and the density of second-order lateral roots. Consequently, a reduced length and density of lateral roots in bottle gourd should constitute a response to water deficit. The root traits studied here can be used to evaluate bottle gourd performance under novel water management strategies and as criteria for breeding selection.

PHOTOSYNTHETIC EFFICIENCY OF TOMATO PLANTS SUBMITTED TO CALCIUM SILICATE APPLICATION

The objective was to evaluate the effect of calcium silicate on the chlorophyll content and gas exchange of two tomato hybrids. The design used was in randomized blocks in a 2x5 factorial scheme, with four replications. The first factor was composed of two tomato hybrids: Ivety and Natália, and the second factor was composed of five doses of calcium silicate (0, 150, 300, 450, and 600 kg ha-1), applied to the substrate before planting the seedlings. Gas exchange: net CO2 assimilation rate (A), leaf transpiration rate (E), stomatal conductance (gs), internal CO2 concentration (Ci), water-use efficiency (WUE), intrinsic efficiency water use (iWUE), and instant carboxylation efficiency (ACi); SPAD index and the levels of chlorophylls a, b, and total were evaluated. The analyzes were performed in the stages of first flowering (17 days after transplanting - DAT), full flowering (58 DAT), and full fruiting (78 DAT). At 17 DAT, no difference was observed for gas exchange variables and photosynthetic pigments. The application of calcium silicate reduced gas exchange and photosynthetic pigments at 58 DAT. The hybrid Natália had the highest A, WUE, iWUE, and ACi at 78 DAT. However, the hybrid Ivety in the same growth stage, in full fruiting, was superior only for the internal concentration of CO2 and SPAD index, with no difference for photosynthetic pigments.

Salinity-Induced Physiological Responses of Three Putative Salt Tolerant Citrus Rootstocks

Our study aimed to evaluate the physiological responses following salinity treatment of three putatively salt-tolerant Citrus rootstocks recently developed by the University of Florida’s Citrus breeding program. Four-month-old seedlings from each of the three rootstocks (HS1, HS17, and HC15) were irrigated with 0, 60, 80, and 100 mm NaCl solution. The seedlings were evaluated together with the salt-tolerant Cleopatra mandarin as a positive control, Volkamer lemon as a moderately salt-tolerant rootstock, and the salt-sensitive Carrizo rootstock as a negative control. Our results demonstrated that chlorophyll content, net CO2 assimilation rate (A), transpiration rate (E), and stomatal conductance (gsw) significantly decreased in response to salinity. Na+ and Cl− levels were higher in leaf tissues than in the roots. Relatively little damage to the cellular membrane was recorded in HC15 and Cleopatra rootstocks under the 100 mm NaCl treatment, along with high accumulation of total phenolic content (TPC), while HS17 had the highest proline levels. Our results indicate that HC15 and HS17 rootstocks exhibited salt tolerance capacity via different strategies under salt stress and could be suitable replacements to the commercially available, salt-tolerant Cleopatra rootstock.

Salicylic acid and H2O2 seed priming alleviates Fe deficiency through the modulation of growth, root acidification capacity and photosynthetic performance in Sulla carnosa

Iron (Fe) is one of the essential nutrients for plant growth which is involved in several physiological functions. Hence, there are intensive efforts to improve plant tolerance to Fe deficiency, by genotypic screening and by the use of adapted physiological tools. The intend of the current study was to explore the seed priming effect with salicylic acid (SA 0.25 mM) and hydrogen peroxide (H2O2 20 mM), either separately applied or combined, on plant growth, nutritional elements status (Fe and potassium K), root acidification and photosynthetic activity in two S. carnosa cultivars (Sidi Khlif and Kalbia) with different tolerance to such constraint. Under unprimed conditions, Fe deficiency decreased plant growth, chlorophyll concentration, in addition to Fe and K contents. Moreover, it affected the photosynthetic activity by inhibiting the net CO2 assimilation rate and increasing the transpiration rate of both cultivars, following a reduced water use efficiency. The changes above described were much less pronounced in Sidi Khlif than in Kalbia. The stomatal conductance increased in Fe-deficient leaves of both cultivars, suggesting that the photosynthesis impairment should be attributed to non-stomatal factors. Interestingly, priming seeds with both agents significantly improved the growth performance and the rhizosphere acidification of deficient S. carnosa plants. However, the D + SA + H2O2 treatment had the most beneficial effect on S. carnosa plant growth. The degree of this stimulation may vary depending on the cultivar, the tissue and the priming agent applied. This could be owing to the photosynthetic performance modulation, leading to more efficient nutrient uptake.

Enhanced Tolerance to Cold in Common Bean Treated with Biostimulant

Plants exposed to suboptimal temperatures suffer damage to physiological processes, growth, development and yield. Acting as enhancers of physiological and metabolic performance of plants, biostimulants have been used to mitigate crop damage caused by abiotic stresses. This study aimed to determine which formulation and dosage of FH Attivus® biostimulant have the best effects on the development of bean plants exposed to suboptimal temperatures (<20 °C). The experiment was conducted in a greenhouse under suboptimal temperatures in a randomized block design with four replications and ten treatments, consisting of three formulations and dosages of the biostimulant, applied at V4 stage, besides a control without biostimulant application. Growth, physiological and biochemical variables were evaluated. The application of biostimulant made bean plants more tolerant to low temperatures by maintaining CO2 net assimilation rate (A) and increasing the activity of antioxidant enzymes. The relative chlorophyll content (SPAD index), PSII effective quantum yield of linear electron flux (ϕPSII), apparent electron transport rate (ETR) and photochemical extinction coefficient (qP) were higher in all treatments compared to the control, as well as the lowest values of A and ETR were observed in the control. In addition, the activities of all evaluated antioxidant enzymes were superior to the control at the lowest dosages of formulation 2, and at all dosages of formulation 3, indicating, in these treatments, greater protection of cells against oxidative damage. The use of biostimulant is, therefore, a management that makes plants less susceptible to low temperatures in the growing environment.

Night temperature determines flowering time and quality of Chrysanthemum morifolium during a high day temperature

ABSTRACT The effects of controlling night temperatures (NTs) during summer-season on flowering and photosynthetic characteristics in Chrysanthemum morifolium were investigated at NTs of 20, 23, 26, or 29°C and a day temperature (DT) of 35°C. Days to budding and flowering increased more in the plants grown at NTs of 26 or 29°C than those of 20 or 23°C, regardless of cultivar. The flowers appeared as a withered state in ‘Swifty Rosso’ grown at a 26°C NT and ‘Swifty Yellow’ at 26 or 29°C NTs. The percentage of abnormal flowers reached 100% in ‘Swifty Rosso’ grown at a 26°C NT and 26 and 29°C NTs in ‘Swifty Yellow’. Flower size were the largest in the plants grown at 20 or 23°C NTs than those at 26 and 29°C NTs. The net CO2 assimilation rates had average high values in the plants grown at 20 or 23°C NTs. Low photosynthetic efficiency was found in the plants grown at 26 or 29°C NTs. At the high DT that occurs during the summer season with high NTs ≥26°C delays budding and causes abnormal and withered flowering. Since it is year-around plant, techniques of controlling NTs can be used effectively while maintaining quality levels.

Silicon Application Increases Biomass Yield in Sunflower by Improving the Photosynthesizing Leaf Area

Sunflower is an oilseed plant important for food and biodiesel production. One cheap way to increase sunflower production is by the application of silicon (Si), which has shown to be beneficial in plants under a series of stresses. We analyzed if the application of Si in sunflower affected the CO2 assimilation, N uptake, leaf quantity and quality, and total biomass yield. No difference was observed in the gas exchange measurements or in leaf N concentration. The total leaf area increased in plants applied with even the lowest dose of Si, with no loss to the net CO2 assimilation rate or leaf N concentration. The higher total leaf area of the plants treated with Si resulted in an increase of the total CO2 assimilation by the plant. Plants treated with any dose of Si had an increase of 24–39% in biomass yield. Statistically, the increase in biomass was explained by the total CO2 assimilation in the plant. If the increment in biomass yield is proportional to the oilseed production, we estimate that Si application in sunflower can increase profit by up to 22%. Large-scale experiments are needed to better determine the proper Si dose to be applied and the oilseed production.

Papaya (Carica papaya L.) Leaf Area Estimation and Single-leaf Net Photosynthetic CO2 Assimilation Rate Following Leaf Defoliation and Fruit Thinning

Papaya (Carica papaya L.) leaves are large, up to 70 cm wide, and frequently deeply lobed, with seven to 13 major veins. The scan width of current handheld digital leaf area instruments is generally less than 15 cm. A rapid method is needed to estimate the total leaf area of a plant in the field with leaves at different stages of growth from the apex. The length of the main and side veins of papaya leaves can be used to estimate the area of a single leaf and the total leaf area of the plant. The relationship between main vein lengths and total leaf area was determined for mature leaves from the cultivars Sunset, Line-8, and Kapoho. A simple relationship exists between leaf area and the length of the two main side midribs (L3 and L4): Leaf area (cm2) = −2280 + 87.7*L3 + 55.6*L4 (P &gt; F = 0.0001; r2 = 0.969), explaining ≈94% of the variation between estimated leaf area and leaf area. The most recently matured leaf is the third or fourth discernable leaf from the apex, with a positive net photosynthetic CO2 assimilation rate and an average area of 2331 cm2 that could fix up to 1.6 g carbon per 10-hour day under full sun. The rate of photosynthesis declined with leaf age, and the overall net photosynthetic CO2 assimilation rate of the plant can be predicted. Following 80% leaf defoliation of the plant, the net photosynthetic CO2 assimilation rate of the most recently matured leaf increased 30% to 50% on days 11 and 19 after treatment when the photosynthetic active radiation (PAR) was approximately half of that on day 15 under full sun when no difference in net photosynthetic CO2 assimilation rate was seen. Fruit removal did not affect the net photosynthetic CO2 assimilation rate. Papaya adjusts its single-leaf net photosynthetic CO2 assimilation rate under lower light levels to meet plant growth and fruit sink demand.

Leaf morphophysiological changes induced by long-term drought in Jatropha curcas plants explain the resilience to extreme drought

Jatropha curcas plants were cultivated during 4 months in pots containing soil at 90% of field capacity (FC), in permanent drought at 30% of FC and in extreme drought without any irrigation. The permanent drought clearly resulted in significant reductions of 43% on spongy parenchyma thickness and increase of 170% on stomatal index and 80% in photosynthetic pigments content. The measurements of leaf gas showed that growing in permanent drought condition resulted in decreases of 38% on net CO2 assimilation rate, 81% on stomatal conductance, 69% on transpiration, 30% on intercellular carbon concentration (Ci) and reductions on the capacity to refresh leaves. The plants subjected to extreme drought took a period of 12 days of re-irrigation to recover values of CO2 assimilation and stomatal conductance similar to well-irrigated plants. Some of these morphophysiological changes look as though not to directly result from drought, but from secondary variations unleashed by stomatal closure and intensified by long duration of stressful conditions. This seems to result in plants photosynthetically more efficient with competitive advantage in arid situations. Besides these variations, it was possible to show and evaluate the resilience and extreme tolerance of these plants to survive in harsh environment.

Spatial arrangement of maize plants aiming to maximize grain yield in the hybrid BRS-3046

The objectives of this study were to: (i) evaluate the effect of different spatial arrangements on morpho-physiological characteristics and (ii) determine the optimal spatial arrangement to maximize grain yield of the maize hybrid BRS-3046 grown in the Mid-North region of Brazil. We tested two row spacings (0.5 and 1 m) and five plant densities (2, 4, 6, 8, 10 plants m-2), which corresponded to 10 different plant spatial arrangements. Different morphophysiological variables, gas exchange rates and grain yield were measured. The increased planting density led to a linear increase in LAI, regardless of row spacing, while the net CO2 assimilation rate increased until the density of 4 and 6 plants m-2, under a row spacing of 0.5 and 1.0 m, respectively. On the other hand, we found a linear reduction in the stomatal conductance with increasing planting density. The intercellular CO2 concentration and the transpiration rate were higher in the widest row spacing. The instantaneous efficiency of carboxylation, in turn, showed a slight increase up to the density of six plants m-2, then falling, regardless of row spacing. Increasing plant density resulted in a linear increase in plant height and ear insertion height, regardless of row spacing. However, it had an opposite effect on stem diameter. Grain yield, in turn, increased up to 7.3 plants m-2 at a row spacing of 0.5 m and 8 plants m-2 at a row spacing of 1.0 m. This spatial arrangement was considered as ideal for achieving maximum yield

Influence of drought on the photosynthetic apparatus activity, senescence rate, and productivity in wheat plants

Effects of soil drought at flowering stage on the functional state of photosynthetic apparatus and chloroplast enzymatic antioxidant defense systems in flag leaf during reproductive period, and the productivity of winter wheat plants of high-protein Natalka variety and drought-tolerant Podolyanka variety were studied in pot experiment. Until flowering and for the control plants during the entire vegetation, the soil moisture content was maintained at a level of 60—70 % of field capacity (FC). Drought treatment (soil moisture 30 % FC) was applied for 7 days covering flowering—early kernel watery ripe period (BBCH 61—71). After that, watering of plants was resumed to a control level which was maintained until the end of the growing season. The estimation of the chlorophyll and Rubisco content, the chloroplast antioxidant enzymes activity, and the net CO2 assimilation and transpiration rates was carried out on flag leaves. The measurements were taken on the third day of watering cessation (the first day the soil moisture reached 30 % FC, BBCH 61), at the end of the drought period (seventh day at 30 % FC, BBCH 71), and after watering resumed at the medium milk (BBCH 75) and late milk (BBCH 77) stages. The components of plant grain productivity were determined by weighing air-dry material at grain full ripeness. It was revealed, that drought stress during flowering inhibited CO2 assimilation and accelerated induction of senescence processes in wheat plants associated with degradation of photosynthetic apparatus and manifested in quicker ontogenetic drop in chlorophyll and Rubisco contents and loss of leaf photosynthetic activity. This exacerbated the drought impact on the plant organism so that after optimal watering return, the physiological and biochemical parameters were not restored to the values of control plants that were all time under optimal moisture supply. Stress-induced premature senescence reduced the supply of plants with assimilates and ultimately led to a decrease in their grain productivity. Impact of drought on flag leaf photosynthetic activity and especially on senescence induction were much more pronounced in the high-protein wheat variety Natalka with a genetically programmed earlier start of the nitrogen-containing compounds remobilization from leaves than in Podolyanka variety. The drought-tolerant variety Podolyanka keep ability to maintain much higher CO2 assimilation activity during drought period and to preserve photosynthetic apparatus from early induction of senescence due to likely more efficient chloroplast antioxidant defense systems, thereby gaining a better assimilates supply for yield formation.

Drought stress strengthens the link between chlorophyll fluorescence parameters and photosynthetic traits.

Chlorophyll fluorescence (ChlF) has been used to understand photosynthesis and its response to climate change, particularly with satellite-based data. However, it remains unclear how the ChlF ratio and photosynthesis are linked at the leaf level under drought stress. Here, we examined the link between ChlF ratio and photosynthesis at the leaf level by measuring photosynthetic traits, such as net CO2 assimilation rate (An), the maximum carboxylation rate of Rubisco (Vcmax), the maximum rate of electron transport (Jmax), stomatal conductance (gs) and total chlorophyll content (Chlt). The ChlF ratio of the leaf level such as maximum quantum efficiency of PSII (Fv/Fm) is based on fluorescence kinetics. ChlF intensity ratio (LD685/LD740) based on spectrum analysis was obtained. We found that a combination of the stomatal limitation, non-stomatal limitation, and Chlt regulated leaf photosynthesis under drought stress, while Jmax and Chlt governed the ChlF ratio. A significant link between the ChlF ratio and An was found under drought stress while no significant correlation in the control, which indicated that drought stress strengthens the link between the ChlF ratio and photosynthetic traits. These results suggest that the ChlF ratio can be a powerful tool to track photosynthetic traits of terrestrial ecosystems under drought stress.

Improved Porosity of Insect Proof Screens Enhances Quality Aspects of Zucchini Squash without Compromising the Yield.

In a global climate change environment, assuring optimal growing conditions is a difficult challenge, compromising the food supply for a rapidly rising population. The climatic conditions in the protected environment lead to high temperatures and fast insect development, impacting productivity and vegetables qualitative attributes. Consumers’ interest in healthy food requires sustainable tools to manage biotic and abiotic factors and, from this perspective, anti-insect nets represent an excellent “green” solution. For this purpose, our goal was to compare two different anti-insect nets on microclimate, production, and qualitative traits of Cucurbita pepo L. fresh fruits. The experiment was conducted in three separate polyethylene high tunnels, with 50 mesh anti-insect nets of different porosities being installed on the openings of two tunnels, while the third tunnel was a control without nets. Microclimate measurements, as well as yield, physiological, and phytochemicals variables, were assessed. The 50 mesh net led to a decrease in marketable yield (22.5%), fruit number (18.0%), CO2 net assimilation rate (6.0%), and transpiration rate (29.5%). Total soluble solids, antioxidant activities and total ascorbic acid concentration had an opposite trend. The 50 mesh AirPlus net improved quality aspects of zucchini fruits by increasing total ascorbic acid, total phenols, and antioxidant compounds, with no negative impact on yield.

Effect of phosphorus on iron toxicity: photosynthetic and antioxidant responses of rice cultivars

Iron (Fe) toxicity is a problem that affects many rice areas in lowland environments. The aim of this study was to investigate, through photosynthetic and antioxidant responses, the effect of phosphorus (P) nutrition as a mitigator of iron (Fe) toxicity in rice cultivars. The experimental design used was in randomized blocks, with four replications Three rice cultivars (Br/Irga 409, Irga 424, and Irga 425) were exposed to two concentrations of Fe (2 and 200 mg L-1) combined with two concentrations of P (2.5 and 15 mg L-1) in a nutrient solution, for 60 days. The results show that the excess of Fe reduced the root dry matter of all cultivars, but only the cultivar Br/Irga 409 showed a decrease in the shoot dry matter. The antioxidant enzymatic activity was not efficient to attenuate the toxicity by Fe due to the higher lipid peroxidation and decrease in the net CO2 assimilation rate. The cultivar Irga 425 showed greater tolerance to conditions of toxicity by Fe when associated with the increase in P availability, with high photosynthetic responses and enzymatic activity (superoxide dismutase). The cultivar Br/Irga 409 showed greater sensitivity to toxicity by Fe compared to other cultivars.

Differing precision irrigation thresholds for kale (Brassica oleracea L. var. acephala) induces changes in physiological performance, metabolites, and yield

Kale originates from the eastern Mediterranean and Asia Minor, being cultivated worldwide and is considered as global cash crop to high nutrients as well as cold tolerance in the fall, winter, and spring. Although kale production is gradually increasing, there is limited research on physiological and metabolism changes by different levels of irrigation. Here, we comprehensively investigated yield, metabolism, and physiological changes by different levels of precision irrigation based on soil moisture sensor. Kales were grown at three different levels of volumetric water content (VWC) which included 0.15, 0.25, or 0.35 m3 m3, corresponding to well-watered, intermediate drought, and drought stressed conditions. There was a 22.5% increase in fresh weight when comparing the 0.15 to 0.35 m3 m3 VWC treatments. Leaf transpiration (E), net CO2 assimilation rate (A), intercellular CO2 concentration (Ci), tand stomatal conductance (gs) to water vapor were significantly different between 0.15 and 0.35 m3 m3 VWC treatments. The carotenoids neoxanthin and antheraxanthin were significantly decreased when comparing the 0.15 to 0.35 m3 m3 VWC treatments. Additionally, aspartic acid and glutamate were highest concentration at 0.35 VWC, implying well-watered condition has a high assimilation capacity from nitrate and ammonium in the kale plant leaf tissue. Glycine, histidine, proline, fructose, and glucose were increased as VWC decreased, indicating that these metabolites are indicators of drought stress. Linoleic acid, and the glucosinolates glucoiberin, progoitrin, sinigrin, and total phenolic content were the highest concentration in the 0.25 m3 m3 VWC, indicating moderate drought stress may increase these specific metabolites. From the pathway analysis, drought stress significantly increased alanine, aspartate, and glutamate metabolism and glycine, serine, and threonine metabolism. Deficit irrigation that induce drought stress impacted kale plants by decreasing physiological (A, E, and gs) parameters and metabolite (carotenoids, chlorophylls) concentrations, while increase stress induced metabolites such as proline and glutamate. Thus, this study utilized a comprehensive research methodology that connects morphophysiological and biochemical metabolite information and demonstrates how kale plants may integrate growth in drought conditions.

Improving Net Photosynthetic Rate and Rooting Depth of Grapevines Through a Novel Irrigation Strategy in a Semi-Arid Climate.

Direct root-zone irrigation (DRZ) is a novel subsurface irrigation strategy initially tested in vineyards for economizing water and securing grape production in arid regions with unstable climatic patterns. However, studies are lacking on the responses of grapevine leaf carbon assimilation and deep rooting patterns to the novel irrigation strategy, which are essential for optimizing grapevine growth and alleviating extreme water stress during periods of heat and drought. Thus, a two-year field study was conducted in a commercial vineyard of Cabernet Sauvignon (Vitis vinifera L.) under a semi-arid climate in Washington, USA to compare the differences in leaf gas exchange and root distribution along the 0–160 cm soil profile, combined with measurements of specific leaf area and total carbon and nitrogen content in leaves and shoots to compare DRZ and traditional surface drip irrigation (SD) under three watering regimes. Compared to SD, significantly higher rates of net CO2 assimilation, stomatal conductance and transpiration in leaves, which positively correlated to midday stem water potential, were found in grapevines irrigated through DRZ in both years. Meanwhile, DRZ reduced total root number by 50–60% and root length density (RLD) by 30–40% in the upper 60 cm soil at high (0.75–0.80 crop evapotranspiration) and moderate (0.60–0.65 crop evapotranspiration) irrigation rates, but no significant differences were found at low (0.45–0.50 crop evapotranspiration) irrigation rate between DRZ and SD. Higher root number and RLD were detected under DRZ within 60–160 cm soil depths, accompanied by a decreased ratio of total carbon to nitrogen content in leaves with slightly increased specific leaf area. Decreased rainfall and increased temperature in 2018 possibly amplified the positive effects of DRZ. Our study indicates that grapevines under DRZ could develop deeper roots for water uptake, which helps ameliorate water stress and improve the photosynthetic rate as well as enhance grapevine adaptation to semi-arid climates.

Effects of Postharvest Water Deficits on the Physiological Behavior of Early-Maturing Nectarine Trees.

The physiological performance of early-maturing nectarine trees in response to water deficits was studied during the postharvest period. Two deficit irrigation treatments were applied, moderate and severe, and these were compared with a control treatment (fully irrigated). Stem water potential and leaf gas exchange (net CO2 assimilation rate, ACO2; transpiration rate, E; and stomatal conductance, gs) were measured frequently. Drought avoidance mechanisms included a decrease in stomatal conductance, especially in the case of the severe deficit treatment, which also showed a strong dependence of ACO2 on gs. Intrinsic water-use efficiency (ACO2/gs) was more sensitive than instantaneous water-use efficiency (ACO2/E) as an indicator to detect water deficit situations in nectarine trees. However, in contrast to the results obtained for other deciduous fruit trees, a poor correlation was found between ACO2/E and ACO2/gs, despite the important relation between E and gs. ACO2/E was also weakly correlated with gs, although this relationship clearly improved when the vapor pressure deficit (VPD) was included, along with gs as the independent variable. This fact reveals that apart from stomatal closure, E depends on the boundary layer conductance (gb), which is mediated by VPD through changes in wind speed. This suggests low values of the decoupling coefficient for this water-resilient species.