Net CO2 Assimilation Rate Research Articles

Ultraviolet radiation underlies metabolic energy reprograming in Coffea arabica and Coffea canephora genotypes

Depletion of the stratospheric ozone layer enhances UV exposure to living organisms. We hypothesized that the adaptative physiological and bioenergetic responses of modern genotypes of Coffea arabica cv. Catuaí Amarelo IAC 62, and C. canephora (Conilon LB1) to actual UV levels would generate additional costs to the detriment of biomass formation and partitioning. Coffee plants were cultivated for six months in a mini greenhouse under either near ambient (UVam) or reduced (UVre) UV conditions, after which leaf gas exchanges, chlorophyll a fluorescence parameters and proton pump phosphohydrolase activities were analyzed. Growth under UVam did not affect the photochemical efficiency and net CO2 assimilation in both Coffea species, but reduced stomatal conductance (gs) and increased intrinsic water use efficiency (iWUE), maximum photosynthetic O2 evolution, and apparent quantum yield. Coffee plants under UVam showed decreased P-type H+-ATPase activity, whilst H+-PPase activity increased, preserving metabolic energy. Coffee biomass accumulation decreases under UVam were more pronounced in C. canephora, which generally invested more in the root system than in shoot biomass as compared to C. arabica. Reduced biomass in C. canephora under UVam susuggested restrained C-sequestration in plant biomass, which might be partly associated with gs reduction, along with a equilibrium between the ATP- and PPi-driven electrochemical H+ gradients, providing a mechanism for energy buffering and cellular robustness. The stability of fluorescence parameters and net CO2 assimilation rate under UVam, reduced gs and increased iWUE, oxygen-evolving complex activity, and elevated SPAD values, supported photomorphogenetic responses acclimation to actual UV in two modern coffee genotypes, with detrimental impact on shoot biomass, especially in C. canephora.

Kaolin Film Increases Gas Exchange Parameters of Coffee Seedlings During Transference From Nursery to Full Sunlight.

Increases in water use efficiency (WUE) and the reduction of negative impacts of high temperatures associated with high solar radiation are being achieved with the application of fine particle film of calcined and purified kaolin (KF) on the leaves and fruits of various plant species. KF was applied on young Coffea arabica and Coffea canephora plants before their transition from nursery to full sunlight during autumn and summer. The effects of KF were evaluated through the responses of leaf temperature (Tleaf), net CO2 assimilation rate (A), stomatal conductance (gs), transpiration (E), WUE, crop water stress index (CWSI), index of relative stomatal conductance (Ig), initial fluorescence (F0), and photosynthetic index (PI) in the first 2–3 weeks after the plant transitions to the full sun. All measurements were performed at midday. In Coffea plants, KF decreased the Tleaf up to 6.7°C/5.6°C and reduced the CWSI. The plants that were not protected with KF showed lower A, gs, E, and Ig than those protected with KF. C. canephora plants protected with KF achieved higher WUE compared with those not protected by 11.23% in autumn and 95.58% in summer. In both Coffea sp., KF application reduced F0, indicating reduced physical dissociation of the PSII reaction centers from the light-harvesting system, which was supported with increased PI. The use of KF can be recommended as a management strategy in the transition of Coffea seedlings from the nursery shade to the full sunlight, to protect leaves against the excessive solar radiation and high temperatures, especially in C. canephora during the summer.

Ecofisiologia de Mesosphaerum suaveolens (L.) Kuntze (Lamiaceae) sob estresse salino e ácido salicílico

ABSTRACT: Mesosphaerum suaveolens (L.) Kuntze is a species widely used in folk medicine and has a high aromatic and therapeutic potential. However, its cultivation in semi-arid regions can be limited by salts in the irrigation water. The objective of this study was to evaluate the effect of salicylic acid (SA) as a mitigator of saline stress on the growth and gas exchange of M. suaveolens. The experimental design used was the randomized blocks in an incomplete factorial scheme (Central Composite Design), with five electrical conductivities water (ECw = 0.5, 1.45, 5.0, 8.55, and 10.0 dS m-1) and five SA doses (0.0, 0.29, 1.0, 1.71, and 2.0 mM). Plant height, number of leaves, stem diameter, leaf area, root length, and height/diameter ratio, and gas exchange (stomatal conductance, net CO2 assimilation rate, transpiration rate, instantaneous, and intrinsic water use efficiency, instantaneous carboxylation efficiency, and leaf temperature) were evaluated. The application of 0.9 mM SA attenuates the negative effect of saline stress on the number of leaves and leaf area of M. suaveolens. The application of SA stimulates the number of leaves, plant height, and root growth, but does not affect the gas exchange of M. suaveolens. ECw reduces the growth and gas exchange of M. suaveolens plants.

Short daily ultraviolet exposure enhances intrinsic water-use efficiency and delays senescence in Micro-Tom tomato plants.

Ultraviolet (UV) radiation, unless present at high doses, is recognised as a regulator of plant growth and some specific processes. The present study investigated the influence of short daily UV irradiation (15min/day, 11days) on leaf gas exchange and some biochemical and molecular markers of leaf senescence (such as stomata movements, chlorophyll breakdown, anthocyanin production, senescence-associated genes) in Micro-Tom tomato plants. The UV-induced reduction of g s (stomatal conductance) during the treatment was associated with the modified expression of some genes involved in the control of stomatal movements. We hypothesise a two-step regulation of stomatal closure involving salicylic and abscisic acid hormones. The temporal changes of g s and A net (net photosynthetic CO2 assimilation rate) along with the pigment behaviour, suggest a possible delay of leaf senescence in treated plants, confirmed by the expression levels of genes related to senescence such as SAG113 and DFR . The UV potential to induce a persistent partial inhibition of g s without severely affecting A net led to an increased iWUE (intrinsic water-use efficiency) during the 11-day treatment, suggesting a priming effect of short daily UV radiation towards drought conditions potentially useful in reducing the excess water use in agriculture.

Pinus elliottii and P. elliottii x P. caribaea hybrid differently cope with combined drought and heat episodes

Extreme climate change events, such as long periods of drought and heat waves, are predicted to increase throughout this century. Pinus species are important economic resources. However, it remains unknown the vulnerability of most species to climate change-related stresses. We aimed to compare the performance reconfiguration of two resin/timber important species [Pinus elliottii var. elliottii (PE) and the hybrid Pinus elliottii var. elliottii × Pinus caribaea var. hondurensis (PE × PCH)] to face combined stress of drought+heat. Young PE and PE × PCH plants were grown at optimal conditions, then exposed to water deficit for 5 days, and in the last day of water deficit, plants were additionally exposed to a heat shock. The physiological responses, antioxidant capacity and oxidative stress were evaluated immediately and 5 days (recovery) after drought+heat treatment. Under control conditions, the hybrid displayed higher photosynthetic and biochemical performance (e.g. higher net CO2 assimilation rate, transpiration rate, photosynthetic pigments and anthocyanins levels, carbohydrates and antioxidant enzyme activities). Immediately after the drought+heat episode, plant water status decreased in both species, as well as the PSII photosynthetic parameters (ФPSII and Fv’/Fm’), while non-photochemical quenching increased. However, the gas-exchange parameters of PE and the hybrid responded differently to the combined stress. The hybrid suffered a stronger reduction on the net CO2 assimilation rate and transpiration rate, and presented higher levels of lipid peroxidation, but with no cell membrane permeability injuries. Principal component analysis supports that the different profile of both species is possibly associated to the stronger antioxidant capacity of PE under stress conditions. Moreover, these differences were still observed during recovery and photosynthesis was re-established totally only in PE. The hybrid clearly demonstrated less ability to restore the gas-exchange in the same period, possibly due to stomata re-opening limitations. The low net CO2 assimilation rates in the hybrid after stress relief could also result in the necessity to use the starch reserves to maintain TSS pools available for stress recovery. We conclude that the hybrid perform better under control conditions, and the PE seems better prepared to cope with the predictable global climate change scenarios forecast for the next decades. The hybrid is more affected by drought+heat, but is able to keep a photosynthetic performance close to the PE under stress, although less efficient during recovery.

Characterizing the development of photosynthetic capacity in relation to chloroplast structure and mineral nutrition in leaves of three woody fruit species

Plants have evolved different developmental patterns of photosynthetic capacity to better adapt to changing environmental conditions. Natural variation in photosynthetic development offers great potential for improving crop productivity. In this study, leaf developmental patterns were characterized in three woody fruit tree species with distinct photosynthetic capacity and growth habits. Changes in the photosynthetic rate, photosystem II (PSII) efficiency, chloroplast ultrastructure, activities of photosynthetic enzymes, and contents of carbohydrates and mineral nutrients were examined at five developmental stages to explore the interspecific variation in photosynthetic development. Rapid development of photosynthetic machinery and high photosynthetic capacity were found in Indian jujube (Ziziphus mauritiana) and apple (Malus domestica), whose net CO2 assimilation rate (A) peaked at full leaf expansion (FLE). Litchi (Litchi chinensis), a delayed-greening species, showed slow development of photosynthetic competence, with A peaked after FLE. The low photosynthetic capacity of litchi during early leaf expansion was associated with its delayed chloroplast development, low accumulation of starch, and low activities of ribulose-1,5-bisphosphate carboxylase/oxygenase and NADP-glyceraldehyde-3-phosphate dehydrogenase. Correlations between mineral contents and A across leaf stages and species identified manganese as the rate-limiting nutrients in photosynthetic development in new leaves. Foliar spray of MnSO4 solution (1gl-1) induced a short-term increase in photosynthesis in young leaves of litchi. These findings suggest that a better understanding of interspecific variation in photosynthetic development facilitates the development of new strategies for improving the photosynthetic efficiency of woody fruit trees.

Screening of ‘King’ Mandarin Hybrids as Tolerant Citrus Rootstocks to Flooding Stress

This work compares the tolerance to long-term anoxia conditions (35 days) of five new citrus ‘King’ mandarin (Citrus nobilis L. Lour) × Poncirus trifoliata ((L.) Raf.) hybrids (named 0501XX) and Carrizo citrange (CC, Citrus sinensis (L.) Osb. × Poncirus trifoliata (L.) Raf.), the widely used citrus rootstock in Spain. Growth parameters, chlorophyll concentration, gas exchange and fluorescence parameters, water relations in leaves, abscisic acid (ABA) concentration, and PIP1 and PIP2 gene expressions were assessed. With a waterlogging treatment, the root system biomass of most hybrids went down, and the chlorophyll a and b concentrations substantially dropped. The net CO2 assimilation rates (An) and stomatal conductance (gs) lowered significantly due to flooding, and the transpiration rate (E) closely paralleled the changes in gs. The leaf water and osmotic potentials significantly increased in most 0501 hybrids. As a trend, flooding stress lowered the ABA concentration in roots from most hybrids, but increased in the leaves of CC, 05019 and 050110. Under the control treatment (Ct) conditions, most 0501 hybrids showed higher PIP1 and PIP2 expressions than the control rootstock CC, but were impaired due to the flooding conditions in 05019 and 050110. From this study, we conclude that 0501 genotypes develop some adaptive responses in plants against flooding stress such as (1) stomata closure to prevent water loss likely mediated by ABA levels, and (2) enhanced water and osmotic potentials and the downregulation of those genes regulating aquaporin channels to maintain water relations in plants. Although these traits seemed especially relevant in hybrids 050110 and 050125, further experiments must be done to determine their behavior under field conditions, particularly their influence on commercial varieties and their suitability as flooding-tolerant hybrids for replacing CC, one of the main genotypes that is widely used as a citrus rootstock in Spain, under these conditions.

Physiological and Molecular Responses of 'Dusa' Avocado Rootstock to Water Stress: Insights for Drought Adaptation.

Avocado consumption is increasing year by year, and its cultivation has spread to many countries with low water availability, which threatens the sustainability and profitability of avocado orchards. However, to date, there is not much information on the behavior of commercial avocado rootstocks against drought. The aim of this research was to evaluate the physiological and molecular responses of ‘Dusa’ avocado rootstock to different levels of water stress. Plants were deficit irrigated until soil water content reached 50% (mild-WS) and 25% (severe-WS) of field capacity. Leaf water potential (Ψw), net CO2 assimilation rates (AN), transpiration rate (E), stomatal conductance (gs), and plant transpiration rates significantly decreased under both WS treatments, reaching significantly lower values in severe-WS plants. After rewatering, mild- and severe-WS plants showed a fast recovery in most physiological parameters measured. To analyze root response to different levels of drought stress, a cDNA avocado stress microarray was carried out. Plants showed a wide transcriptome response linked to the higher degree of water stress, and functional enrichment of differentially expressed genes (DEGs) revealed abundance of common sequences associated with water stress, as well as specific categories for mild-WS and severe-WS. DEGs previously linked to drought tolerance showed overexpression under both water stress levels, i.e., several transcription factors, genes related to abscisic acid (ABA) response, redox homeostasis, osmoprotection, and cell-wall organization. Taken altogether, physiological and molecular data highlight the good performance of ‘Dusa’ rootstock under low-water-availability conditions, although further water stress experiments must be carried out under field conditions.

Physiological responses of young oil palm (Elaeis guineensis Jacq.) plants to repetitive water deficit events

Stomatal and non-stomatal limitations to photosynthesis and acclimation of the photosynthetic machinery to repetitive water deficit (WD) events were investigated in oil palms (Elaeis guineensis Jacq.). For this, well-watered plants (control treatment) were compared with plants subjected to one, two, and three WD events imposed by withholding irrigation until their predawn leaf water potential (Ψpd) reached around −2.5 MPa. Treatment comparisons were performed over 28 days. The Ψpd decreased equally between WD treatments. Decreases in net CO2 assimilation rate (A) were similar between stressed plants until day 7. In the following days, the A was higher in plants thrice stressed than in those stressed once. Stomatal conductance decreased similarly between WD treatments, but mesophyll conductance to CO2 was lower in plants subjected to a single WD. Chloroplast CO2 concentration decreased similarly between plants subjected to one and three WD events until day 14, but it was lower in the former on subsequent days. Plants subjected to a single WD event showed lower Ribulose 1,5 bisphosphate carboxylase/oxygenase (Rubisco) activity, maximum rate of electron transport (Jmax), and higher rates of photorespiration and dark respiration than other treatments. Plants subjected to one WD event also showed lower maximum quantum efficiency of photosystem II (PSII) photochemistry and PSII maximum efficiency concomitantly with higher malondialdehyde content. The results support that repetitive WD events induce the acclimation of the photosynthetic machinery in oil palm through adjustments in carboxylase Rubisco activity, Jmax, photorespiration, and respiration rates, as well as attenuating oxidative damages to PSII and membrane lipids.

Use of physiological attributes to select native forest species for forest restoration in the southern Atlantic forest biome, Brazil

In subtropical regions, the selection of species for restoration is conducted as a part of phytosociological studies. This may be complemented by physiological characterization of the species in response to light. The objectives of this study were to identify the physiological attributes performance of native forest species that are conducive to restoration and to identify groups of species for planting in altered areas, under different light intensities south of the Atlantic Forest biome, in Brazil. Seedlings of 12 native species were cultivated in the nursery in full sun and shade, and the net CO2 assimilation rate (A), water use efficiency (WUE), and quantum yield potential of photosystem II (Fv/Fm) were determined for these seedlings. Cluster analysis allowed the differentiation of these species into three groups (Cl-I, Cl-II, and Cl-III) based on the similarity of physiological attributes. In Cl-I, we identified species with an A of 7 μmol CO2 m−2·s−1 and high Fv/Fm values when plants were growing in the shade. The Cl-II group had the highest A (≅12 μmol CO2 m−2·s−1) and WUE. The Cl-III group demonstrated an A of ≅ 5 μmol CO2 m−2·s−1 when the species was growing in full sun or under shade. The results demonstrate that forest species exhibit differences in terms of their A values in response to exposure to varying light intensities (that is, shade or full sun). The analysis of eco-physiological characteristics is fundamental in identifying the most suitable species for planting in forest restoration; this allows for adequate planning of recovery projects. Citharexylum montevidensis, Inga marginata, and Luehea divaricata are the species that were used for initial planting in full sun, which may complement the low density of Ceiba speciosa and Inga vera. For enrichment conditions in the southern Atlantic Forest biome, Cedrela fissilis, Handroanthus heptaphyllus, Vitex megapotamica, Ocotea puberula, Casearia sylvestris, Aspidosperma olivaceum, and Cupania vernalis are considered most appropriate for restoration.

Silicon mitigates the effects of moderate drought stress in cover crops

AbstractCover crops are important components of sustainable agricultural systems under no‐till conditions. However, in the Brazilian Cerrado region, plant growth and straw production on the soil surface have been hampered by insufficient soil water availability during off‐season. A pot experiment was conducted to investigate the effect of silicon fertilization on the morphological and physiological characteristics of cover crops under drought stress conditions. We hypothesized that silicon could mitigate the adverse effects of drought stress because of its role in improving the photosynthetic process and antioxidant defence mechanisms of plants. Thus, two silicon fertilizer levels (0 and 180 mg/kg of Silicon), three grass cover crops (Urochloa brizantha cv. BRS Piatã, U. brizantha cv. Marandu and Pennisetum glaucum cv. ADR 300) and three drought stress levels (100% pot capacity (PC): well‐watered conditions, 50% PC: moderate water stress and 25% PC: severe water stress) were laid out as a randomized block design in a factorial arrangement and replicated four times. Morphophysiological characteristics were recorded after 22 days of exposure to drought stress. Drought stress decreased the growth rate, leaf area (LA), net CO2 assimilation rate and stomatal conductance of the three cover crops. However, with the application of silicon fertilizer, a portion of the negative effects caused by water restriction could be mitigated, even though there were differences in the responses to silicon fertilization and water stress levels among the cover crop species. Silicon application potentiated the tillering and plant growth rate and increased the photosynthetic rate and water use efficiency of U. brizantha (cv. Marandu and cv. BRS Piatã) plants grown under moderate drought stress conditions.

Mitigating negative effects of long-term treated wastewater irrigation: Leaf gas exchange and water use efficiency response of avocado trees (Persea americana Mill.)

Declining performance of avocado orchards growing in a clayey soil irrigated with treated wastewater (TWW) for more than 5 years has been observed in Israel. Measures studied to mitigate this were freshwater (FW), blended TWW:FW in a 1:1 ratio (MIX), low-frequency TWW-irrigation (LFI), TWW irrigated tuff trenches (TUF) and TWW as the control treatment. This study reports on the response of avocado leaf gas exchange, intrinsic water use efficiency, leaf water potential and leaf hydraulic conductance (Kleaf) to the mitigation measures applied to a 'Hass' avocado orchard (Persea americana Mill.) previously irrigated with TWW for 7 years. Stomatal conductance (gs) of FW, MIX, TUF and LFI was greater than that for TWW on most measurement dates, which increased net leaf CO2 assimilation rate (Aleaf) and intercellular CO2 concentration (Ci). Increased gs reduced intrinsic water use efficiency [WUE, determined from either 13C discrimination (iWUE) or gas exchange (WUEi)] as compared to TWW. Although the WUE in TWW was higher than that in mitigation treatments on most measurement dates, the lower assimilation rates at leaf (Aleaf) and whole tree (Atree) levels observed in TWW indicate that TWW irrigation had negative effects on tree physiological performance. A strong negative relationship between WUEi (Aleaf/gs) and gs was found in all treatments, with highest WUEi and lowest gs in TWW. Leaf hydraulic conductance was also lowest for TWW, which may indicate that lower gas exchange was linked to lower water availability to the leaves. Overall, the increased gs, Aleaf, Atree and Kleaf in FW, MIX and TUF relative to TWW indicate that these mitigation measures are good candidates for improving orchard performance negatively affected by long-term irrigation with TWW in clayey soils. Comparing all treatments, FW was the most effective.

5-Aminolevulinic Acid Pretreatment Mitigates Drought and Salt Stresses in Poplar Plants

5-aminolevulinic acid (ALA), a key precursor in the biosynthesis of porphyrins, can improve plant tolerance to various environmental stresses. However, it is unclear whether ALA can improve tolerance in poplar. Here, we investigated the effects of ALA on poplars under drought and salt stresses. ALA pretreatment exhibited less morphological damage, reduced leaf malonaldehyde content (MDA) and electrolyte leakage (EL), and increased leaf relative water content (RWC), proline (PRO), superoxide dismutase (SOD), and peroxidase (POD) content under stresses. Furthermore, exogenous ALA mitigated the decrease in photosynthetic capacity, and restored the chlorophyll content (Chl), net CO2 assimilation rate, stomatal conductance (Gs), transpiration rate (Tr), maximal photochemical quantum yield of PSII (Fv/Fm), actual quantum yield of photosynthesis (YII), and electron transfer rate (ETR) of poplar under various stresses. qRT-PCR showed that ALA up-regulated the expression of antiporters and aquaporins genes, which are associated with Na+ exclusion in the leaf cells and the transport activity of aquaporins. In summary, ALA pretreatment significantly improved the stress tolerance of poplar, decreasing the degree of membrane lipid peroxidation and promoting the photosynthesis and antioxidant capacity of leaves. In addition, our results showed that ALA might mediate Na+ transporter and aquaporins activity, thereby increasing the salt tolerance of poplar.

Rapid growth in clonal Juglans nigra L. is most closely associated with early foliation, robust branch architecture, and protandry

The advantages of clonal forestry have been well described, but little progress has been made in the identification of phenotypes best suited to this method in high-value hardwood species. The genetic variation within, clonal repeatability (broad-sense heritability) of, and Pearson's correlations among phenological, morphological, physiological, and growth traits (N = 22) of black walnut (Juglans nigra L.) were investigated using 25 grafted clonal genotypes. The trees were grown at wide spacing (4.6 m × 6.1 m) in an intensively managed plantation in north-central Indiana, USA. Clonal effect was significant (p < 0.05) for most traits except gas exchange variables. Many phenological traits showed high clonal repeatability (Rc2 > 0.70), including foliation dates, first female bloom, first pollen shed, and crown retention rate (autumnal defoliation). Some traits showed moderate repeatability (0.35 < Rc2 < 0.7), such as branch angle, branch frequency, tree diameter, height, anthracnose severity, and foliar carbon and nitrogen concentration. Net CO2 assimilation rate and stomatal conductance had low repeatability (Rc2 < 0.35). We observed a previously unreported association between sexual morph and tree stem growth, i.e., protandrous trees generally grew faster than protogynous trees. This association between sexual morph and stem growth may be an evolutionary consequence of differences in reproductive costs in protandrous versus protogynous trees, and needs to be tested in other monoecious woody species. Overall, our analyses indicated that the following traits are associated with rapid stem growth: 1) early foliation; 2) early male flowering or late female flowering, i.e., more likely a protandrous variety; 3) large average branch diameter; 4) high branch frequency; 5) small (more vertical) average branch angle; 6) early leaf fall; 7) low later-season foliar carbon concentration; and 8) large number of small fruits and seeds. These traits may be used, with further testing, to define a biomass ideotype for J. nigra.

Molecular markers and GGE biplot analysis for selecting higher‐yield and drought‐tolerant maize hybrids

AbstractImproving maize (Zea mays L.) genotypes for higher productivity and tolerance to drought stress depends mainly on physiological and molecular markers. Therefore, this study aims at breeding maize for drought tolerance and high potentiality by selection based on molecular markers, photosynthetic parameters; and easy graphic methods that help in selecting elite genotypes across diverse environments. An 8 × 8 half diallel analysis was used at two locations involving drought and normal irrigation treatments to study parental genetic diversity (GD) and combining ability (general combing ability [GCA] and specific combining ability [SCA]) in F1 of maize. Fingerprinting of parents was made using simple sequence repeat (SSR) markers. Fifty‐eight alleles were ranged from two to five alleles per locus with an average of 0.63 alleles per locus. The average of polymorphic information content (PIC) was 0.63. Cuvette temperature (oc) was lowest by the cross L14 × L36. The cross L8 × L34 expresses the highest value for Quantum sensor (μmol m–2 s–1), net CO2 assimilation rate and chlorophyll content. As for leaf diffusive resistance (LDR) four crosses exhibited significant desirable LDR values. Concerning rate of leaf transpiration (LTR) (μg cm−2 S−1) the cross (L5 × L104) gave the lowest value. Most hybrids exhibited desirable values for drought susceptibility index. For grain yield plant–1, five F1 crosses, that is, L5 × L34, L8 × L14, L8 × L14, L30 × L104, and L36 × L104 expressed the most desirable SCA effects. These crosses are promising in maize breeding programs. Based on GGE biplot analysis, genotype nos. 8 and 10 exhibited the highest grain yield plant−1 and ranked the first across all environments.

Effects of shading and micro‐spray of canopy on photosynthetic characteristics, quality and yield of drip‐irrigated grapes*

AbstractGrapes are prone to midday depression of photosynthesis (MDP) under the action of high temperature and strong light, which can reduce the accumulation of organic matter, resulting in a decline in yield and quality. In this study, the grapes in Shanshan County, Xinjiang, China, were taken as an example to implement shading and micro‐spray measures. Shading degrees of 0, 15 and 30% were combined with micro‐spray flow rates of 20, 30 and 40 L h−1. Nine treatments and one control treatment (the control treatment is without shading and mist spraying) were designed through a combination of the shading and micro‐spray conditions. The photosynthetic prediction model of the multivariate nonlinear model was constructed and had high simulation accuracy. The decline of air temperature at the top of the canopy increased as the degree of shading and the amount of micro‐spray increased; MDP could be eliminated under the combined conditions of shading and micro‐spray. The mean daily net CO2 assimilation rate (An) increased by more than 0.53 μmol m−2 s−1. The combination of shading and micro‐spray conditions significantly increased fruit size and promoted greenness. The WP1 (15% and 40 L h−1) treatment had the highest mean daily An and the largest fruit volume. The vitamin C (VC) content of WP1 treatment was the highest, 4.13 mg kg−1, which was 1.2 times that of the control (CK) treatment. The yield of the WP1 treatment was the highest, which was 19.7% higher than that of the CK treatment. Thus, the WP1 treatment was the optimal treatment for promoting the An of grape leaves and improving the fruit quality of grapes. This research could provide a reference for improving the photosynthesis, fruit quality and yield of grapes and alleviating the photosynthetic MDP of crops.

The Impact of Photorespiratory Glycolate Oxidase Activity on Arabidopsis thaliana Leaf Soluble Amino Acid Pool Sizes during Acclimation to Low Atmospheric CO2 Concentrations.

Photorespiration is a metabolic process that removes toxic 2-phosphoglycolate produced by the oxygenase activity of ribulose-1,5-bisphosphate carboxylase/oxygenase. It is essential for plant growth under ambient air, and it can play an important role under stress conditions that reduce CO2 entry into the leaf thus enhancing photorespiration. The aim of the study was to determine the impact of photorespiration on Arabidopsis thaliana leaf amino acid metabolism under low atmospheric CO2 concentrations. To achieve this, wild-type plants and photorespiratory glycolate oxidase (gox) mutants were given either short-term (4 h) or long-term (1 to 8 d) low atmospheric CO2 concentration treatments and leaf amino acid levels were measured and analyzed. Low CO2 treatments rapidly decreased net CO2 assimilation rate and triggered a broad reconfiguration of soluble amino acids. The most significant changes involved photorespiratory Gly and Ser, aromatic and branched-chain amino acids as well as Ala, Asp, Asn, Arg, GABA and homoSer. While the Gly/Ser ratio increased in all Arabidopsis lines between air and low CO2 conditions, low CO2 conditions led to a higher increase in both Gly and Ser contents in gox1 and gox2.2 mutants when compared to wild-type and gox2.1 plants. Results are discussed with respect to potential limiting enzymatic steps with a special emphasis on photorespiratory aminotransferase activities and the complexity of photorespiration.

Low levels of TiO2-nanoparticles interact antagonistically with Al and Pb alleviating their toxicity

The contamination and bioavailability of deleterious metals in arable soils significantly limits crop development and yield. Aiming at mitigating Pb- and Al-induced phytotoxicity, this work explores the use of P25 titanium dioxide nanoparticles (nTiO2) in soil amendments. For that, Lactuca sativa L. plants were germinated and grown in the presence of 10 ppm Pb or 50 ppm Al, combined or not with 5 ppm nTiO2. Growth parameters, as well as endpoints of the redox state [cell relative membrane permeability (RMP), thiobarbituric acid reactive substances content, total phenolic content and photosynthesis (sugars and pigments levels, chlorophyll a fluorescence and gas exchange), were evaluated. Concerning Al, nTiO2 treatment alleviated the impairments induced in germination rate, seedling length, water content, RMP, stomatal conductance (gs), intercellular CO2 (Ci), and net CO2 assimilation rate (PN). It increased anthocyanins contents and effective efficiency of photosystem II (ΦPSII). In Pb-exposed plants, nTiO2 amendment mitigated the effects in RMP, PN, gs, and Ci. It also increased the pigment contents and the transpiration rate (E) comparatively to the control without nTiO2. These results clearly highlight the high potential of low doses of nTiO2 in alleviating metal phytotoxicity, particularly the one of Pb. Additionally, further research should explore the use of these nanoparticles in agricultural soil amendments.

Silicon fertilization increases gas-exchange and biomass by silicophytolith deposition in the leaves of contrasting drought-tolerant sugarcane cultivars under well-watered conditions

PurposeSilicon (Si) fertilization provides benefits to sugarcane. However, information remain scarce about the relationship between Si fertilization, gas exchange responses, biomass and silicophytolith accumulation in contrasting drought tolerant sugarcane cultivars under well-watered conditionsMethodsSugarcane cultivars (drought-tolerant and drought-sensitive) were grown in pots containing soil with low available Si and were treated (at rates equivalent to 0, 250, 500, 750, and 1000 kg ha−1 Si) with Si as silicate. The silicophytolith contents, morphotype descriptions, Si concentrations and gas exchange were evaluated in the top visible dewlap leaves. Stalk length and stalk biomass were also evaluated.ResultsThe silicophytolith, Si contents, net CO2 assimilation rate (A), plant transpiration (E), stomatal conductance (gs) and electron transport rate (ETR) of leaves and fresh biomass and length of stalks increased linearly as functions of the Si application rate, independent of cultivar. RB86-7515 showed the highest stalk length, fresh stalk and green leaf biomass, relative water content, and water potential, while RB85-5536 showed superior values for A, E, gs, and ETR.ConclusionsSi fertilization improved photosynthesis, transpiration, stalk length, and stalk biomass production in sugarcane. The highest silicophytolith content was reflected in a diversity of silicified cells, which may favor a higher photosynthesis and biomass. The increase of silicification in stomata complexes and trichomes with Si may be associated to a higher Si availability and transpiration. Contrasting drought-tolerant cultivars showed similar silicification and gas exchange responses with Si. Considering these benefits, Si should be included in the fertilization program of sugarcane.

Water Use Efficiency in Popcorn (Zea mays L. var. everta): Which Physiological Traits Would Be Useful for Breeding?

To ensure genetic gains in popcorn breeding programs carried out under drought conditions knowledge about the response of morphophysiological traits of plants to water stress for the selection of key traits is required. Therefore, the objective was to evaluate popcorn inbred lines with agronomically efficient (P2 and P3) and inefficient (L61 and L63) water use and two hybrids (P2xL61 and P3xL63) derived from these contrasting parents, cultivated under two water regimes (WW watered—WW; and water-stressed—WS) in a greenhouse, replicated five times, where each experimental unit consisted of one plant in a PVC tube. Irrigation was applied until stage V6 and suspended thereafter. Individual and combined analyses of variance were performed and the genotypic correlations and relative heteroses estimated. The water use efficient inbred lines were superior in root length (RL), root dry weight (RDW), and net CO2 assimilation rate (A), which were the characteristics that differentiated the studied genotypes most clearly. High heterosis estimates were observed for RL, SDW, leaf width (LW), leaf midrib length (LL), and agronomic water use efficiency (AWUE). The existence of a synergistic association between root angle and length for the characteristics A, stomatal conductance (gs), and chlorophyll concentration (SPAD index) proved most important for the identification and phenotyping of superior genotypes. Based on the study of these characteristics, the higher AWUE of the previously selected inbred lines could be explained. The results reinforced the importance of root physiological and morphological traits to explain AWUE and the possibility of advances by exploiting heterosis, given the morphophysiological superiority of hybrids in relation to parents.