Reduced Chlorophyll Fluorescence Research Articles

Silencing ZmPP2C-A10 with a foxtail mosaic virus (FoMV) derived vector benefits maize growth and development following water limitation.

Global climate change is causing more frequent and severe droughts, which can have negative impacts on plant growth and crop productivity. Under drought conditions, plants produce the hormone ABA (abscisic acid), which regulates adaptive responses, such as stomatal closure and root elongation. Plant viruses have been used in the lab to convey new traits to plants and could also be used to increase production of ABA or to enhance downstream plant drought resistance responses. In this study, foxtail mosaic virus (FoMV) was used to silence ZmPP2C-A10, a negative regulator of ABA signalling, in maize (Zea mays L.). Both silenced and control plants were exposed to an 8-day drought treatment, followed by a 30-day period of rewatering, after which indicators of drought resistance were measured. After drought treatment, we observed a nearly twofold increase in expression of a stress-mitigation gene, ZmRAB17, reduced chlorophyll fluorescence changes (indicator of stress), and increased plant biomass and development in the ZmPP2C-A10-silenced maize compared to controls. These results demonstrate that the FoMV systemcan be used to silence endogenous expression of ZmPP2C-A10 and increase maize tolerance to drought. This could offer a useful tool to improve crop traits and reduce yield loss during the growing season.

Iono-metabolomic guided elucidation of arsenic induced physiological and metabolic dynamics in wheat genotypes

Despite the growing concerns about arsenic (As) toxicity, information on wheat adaptability in such an aggravating environment is limited. Thus, the present investigation based on an iono-metabolomic approach is aimed to decipher the response of wheat genotypes towards As toxicity. Wheat genotypes procured from natural conditions were characterized as high As-contaminated (Shri ram-303 and HD-2967) and low As-contaminated (Malviya-234 and DBW-17) based on ICP-MS As accumulation analysis. Reduced chlorophyll fluorescence attributes, grain yield and quality traits, and low grain nutrient status were accompanied by remarkable grain As accumulation in high As-contaminated genotypes, thus imposing a higher potential cancer risk and hazard quotient. Contrarily, in low As-contaminated genotypes, the richness of Zn, N, Fe, Mn, Na, K, Mg, and Ca could probably have supported less grain As accumulation, imparting better agronomic and grain quality traits. Additionally, from metabolomic analysis (LC-MS/MS and UHPLC), abundances of alanine, aspartate, glutamate, quercetin, isoliquiritigenin, trans-ferrulic, cinnamic, caffeic, and syringic bestow Malviya-234 as the best edible wheat genotype. Further, the multivariate statistical analysis (HCA, PCA, and PLS-DA) revealed certain other key metabolites (rutin, nobletin, myricetin, catechin, and naringenin) based genotypic discrimination that imparts strength to genotypes for better adaptation in harsh conditions. Out of the 5 metabolic pathways ascertained through topological analysis, the two main pathways vital for plant's metabolic adjustments in an As-induced environment were: 1. The alanine, aspartate and glutamate metabolism pathway, and 2. The flavonoid biosynthesis pathway. This is also evident from network analysis, which stipulates amino acid metabolism as a prominent As regulatory factor closely associated with flavonoids and phenolics. Therefore, the present findings are useful for wheat breeding programs to develop As adaptive genotypes that are beneficial for crop improvement and human health.

Integrated cytological, physiological, and transcriptome analysis of the bud mutant of jujube (Ziziphus jujuba Mill.) with non-lethal albino phenotype

Although the underlying mechanisms of the albino phenotype have been deciphered in seedlings of model plants, leaf albinism of bud mutants in woody species has been less extensively studied. In this study, a bud mutant of jujube (Ziziphus jujuba Mill.) with non-lethal albino phenotype was characterized. Compared with the normal leaves, the albino leaves showed lower chlorophyll and carotenoid contents, and higher POD activity and proline content to respond to oxidative damage. The impaired chloroplasts with ruptured thylakoid membranes and vacuoles with excess autophagosomes were observed in albino leaves. The decreased photosynthetic capacity in albino leaves was manifested as negative net photosynthetic rate and reduced chlorophyll fluorescence. The molecular mechanism of the albino leaves during development was explored through transcriptome analysis. A total of 3213, 3348, 8072 differentially expressed genes (DEGs) were identified in leaf buds, young leaves and mature leaves of normal plant and albino mutant, respectively. Further analysis indicated that most DEGs related to the biosynthesis of chlorophyll and carotenoid, chloroplast development, and photosynthesis were down-regulated in albino leaf buds, which were likely the main factors responsible for albino phenotype at early stage. Contrarily, DEGs involved in chloroplast development, including PPR, FtsH, mTERF, were mainly up-regulated in albino mature leaves, suggesting different regulatory mechanism for defective chloroplast structure at various stages. In addition, DEGs were significantly enriched in biosynthesis of phenylpropanoids and flavonoids in young and mature leaves of the albino mutant Moreover, transcription factor family genes, involving bHLH, MYB_related, NAC, ERF, B3, and WRKY, were identified as DEGs at three stages, indicating the promoted secondary metabolism production and senescence of the albino leaves. These findings provided new insights into the molecular mechanism of leaf albinism in woody plants.

Modulation of grape cuticular wax composition following multiple heatwaves influences grape transpiration

Heat stress events (heatwaves) significantly impair grapevine leaf and berry physiology. The prevalence and frequency of heatwaves are predicted to increase in the coming decades, even in moderate climates. Despite this, many facets of heatwave effects on grapevine physiology remain unstudied. In this work, we subjected potted Gewürztraminer grapevines to a single heatwave event at mid-ripening or a double heatwave event at both the onset of ripening and mid-ripening and compared them to respective untreated control vines. The recovery of leaf and grape physiology from both events were analyzed on the day following the event and at harvest maturity through measurements of leaf gas exchange and chlorophyll fluorescence, and grape size, total soluble solids, and cuticular wax composition. Both single heatwave (S-HW) and double heatwave ( D -HW) treatments reduced chlorophyll fluorescence ( Fv/Fm ) by 12.8 % and 6.1 % on the day following the heatwave, respectively. However, values recovered at harvest maturity only by S-HW. Photosynthetic rate (Pn) was not affected by treatments on the day following the heatwave, but was reduced in D -HW by 48 % at harvest maturity. Total soluble solids were also decreased only by D -HW at harvest maturity. Following the D -HW, total berry wax (by 11.8 %), as well as the total contents of triterpenoids (by 11.7 %) and aldehydes (by 14.3 %) were increased significantly at harvest maturity. Fruit cuticular transpiration was reduced by D -HW. Interestingly, this decrease in transpiration was correlated with an increase in the ratio between the two most abundant wax compounds, oleanolic acid and ursolic acid, which are both triterpenoids. This data corroborates to suggest that grapevines are resilient to a single but not a double heatwave event. Future work will further explore the effects of heatwave frequency and recovery on additional facets of leaf physiology and grape quality. • Grapevines were exposed to a single or double heatwave event during ripening. • The double heatwave reduced leaf chlorophyll fluorescence and berry soluble solids. • The double heatwave raised total wax and triterpenoid contents in berries at harvest. • The double heatwave increased the ratio of oleanolic to ursolic acid at harvest. • The oleanolic to ursolic acid ratio correlated with lower cuticular transpiration.

Quantification of Multiple Herbicide Resistance in Phalaris minor Populations of the North-Western Indo-Gangetic Plains of India

Multiple resistance to different herbicides used for management of Phalaris minor Retz. in Northern India was quantified for its two populations—one susceptible and the other resistant to acetyl-CoA carboxylase (ACCase) inhibitor herbicide clodinafop-propargyl. Clodinafop-propargyl and pinoxaden at their recommended dose recorded complete control of clodinafop-propargyl susceptible P. minor population, whereas sulfosulfuron and mesosulfuron plus iodosulfuron at their recommended dose exhibited 48.5 and 51.5% control of this population. In clodinafop-propargyl-resistant P. minor population, sulfosulfuron and mesosulfuron plus iodosulfuron even at 4X dose did not cause any mortality; however, pinoxaden at 4X dose caused complete mortality at 30 DAS. Metribuzin plus clodinafop-propargyl applied at all the doses (0.25X, 0.5X, X, 2X and 4X) recorded complete mortality of both the populations. Application of different herbicides caused reduction in chlorophyll fluorescence and chlorophyll content index in leaves of both the populations in a dose-dependent manner. But the magnitude of reduction was higher in susceptible population as compared to the resistant population.

Physiological and Yield Responses of Green-Shelled Beans (Phaseolus vulgaris L.) Grown under Restricted Irrigation

Common bean is an important crop, consumed as green-shelled bean in several countries. In Chile, green-shelled beans are cultivated often as a dry land crop, vulnerable to drought. The objective of this study was to characterize the hydric and productive responses of four green-shelled bean genotypes subjected to deficit irrigation in order to outline production strategies in the face of increasing water scarcity. Two experiments were evaluated: one pot experiment with three irrigation treatments, supplying 100% of the crop evapotranspiration (ETc) (T100), 50% (T50), and 30% (T30); and an open field experiment with two treatments: 100% (I100) and 40% of ETc (I40). Treatments were applied during reproductive stage in determinate cultivars and vegetative stage in indeterminate plants. Severe water restriction (T30 and I40) in both experiments showed a significant decrease in stomatal conductances, as well as biomass and number of grains per pod; I40 treatment also showed a reduction in chlorophyll fluorescence. Water use efficiency (WUE) was higher under water stress in field (I40), but lower on the T30 treatment from the pot experiment. Determinate cultivars showed 22.7% higher of 100-seed weight compared to indeterminate type, and, thus, higher tolerance to drought. Our results indicate that severe water stress is highly harmful in terms of yield, and a moderate controlled deficit irrigation plus the use of determinate genotypes may be a strategy for producing green-shelled bean successfully under a drought scenario.

Exogenous Melatonin Alleviates Heat‐Induced Oxidative Damage in Strawberry (Fragaria × ananassa Duch. cv. Ventana) Plant

Melatonin is a signaling molecule that is involved in inducing plantsʼ abiotic stress tolerance. To determine the possible effects of the melatonin pre-treatment on thermotolerance in strawberry (Fragaria × ananassa Duch.), the heat-sensitive cultivar Ventana was subjected to high temperatures (35 °C and 40 °C) for 10 h after pre-treatment with 0, 50, and 100 μM melatonin. High temperature increased malondialdehyde and H2O2 contents and reduced relative water content, carotenoid content, and catalase and ascorbate peroxidase activities, which led to a marked reduction in chlorophyll fluorescence. However, pre-treatment with melatonin at 100 μM decreased heat injury symptoms and induced antioxidant mechanisms in heat-sensitive cultivar Ventana, increasing heat tolerance. The results showed that when the melatonin pre-treated strawberry plants were exposed to high temperature (40 °C) for 2 h, the levels of FaTHsfA2a and HSP90 mRNA significantly increased, but after heat treating at 40 °C for 5 and 10 h, their mRNA levels were as similar as the control. The results support the hypothesis that melatonin acts as an important signaling molecule during heat stress to induce protective mechanisms via up-regulating the expression of defense HSF (FaTHsfA2a, FaTHSFB1a) and HSP (HSP90) genes.

MYB134-RNAi poplar plants show reduced tannin synthesis in leaves but not roots, and increased susceptibility to oxidative stress.

The importance of the poplar MYB134 gene in controlling condensed tannin (CT) biosynthesis was tested by suppressing its expression using RNA interference (RNAi). MYB134-RNAi plants grew normally but showed reduced accumulation of stress-induced CTs in leaves. RNA-seq analysis indicated that flavonoid- and CT-related genes, as well as additional CT regulators, were strongly and specifically down-regulated by MYB134 suppression. This confirmed that the primary MYB134 target is the leaf flavonoid and CT pathway. Root CT accumulation was not impacted by MYB suppression, suggesting that additional CT regulators are active in roots and emphasizing the complexity of the regulation of CTs in poplar. To test the effect of CT down-regulation on oxidative stress resistance, leaves of MYB134-RNAi and control plants were exposed to the reactive oxygen species generator methyl viologen. MYB134-RNAi leaves sustained significantly more photosystem II damage, as seen in reduced chlorophyll fluorescence, compared with wild-type leaves. MYB134-RNAi leaves also contained more hydrogen peroxide, a reactive oxygen species, compared with the wild type. Our data thus corroborate the hypothesis that CT can act as an antioxidant in vivo and protect against oxidative stress. Overall, MYB134 was shown to be a central player in the regulation of CT synthesis in leaves.

Quantifying the Effect of Water Deficit on Cotton Genotypes Using Agro-physiological and Biochemical Parameters

ABSTRACT To investigate the water-deficit tolerance, 45 cotton genotypes were grown under normal irrigation and water-deficit conditions for 2 years. Genotype × treatment × year interaction was determined for seed cotton yield, number of bolls, boll weight, chlorophyll fluorescence, proline contents, and total soluble proteins. Apart from proline levels, all traits showed a reduction under water-deficit conditions. The mean percentage reduction in seed cotton yield due to water deficit conditions was 52.83% and 42.19%, for number of bolls was 48.44% and 39.30%, for boll weight was reduced by 8.94% and 6.03% in 2013 and 2014 respectively. Reduction in chlorophyll fluorescence was 13.87% and 16.46% while soluble protein levels decreased by 25.57% and 21.09% during 2013 and 2014 respectively. For proline contents went up by 38.68% and 37.70% in 2013 and 2014 respectively. Relatively small changes in these parameters under water-deficit conditions were recorded for varieties FH-155, FH-207, FH-322, FH-329 IUB-13 and IUB-222 making these genotypes best suited for cultivation under water-deficit conditions. The positive correlation of seed cotton yield with proline contents and chlorophyll fluorescence under water-deficit condition indicates that these two traits can be considered to select cotton genotypes at early growth stages.

Effects of drought stress on root development and physiological characteristics of sweet potato at seedling stage

The effects of drought stress on root morphology, endogenous hormones, chlorophyll fluorescence and active oxygen metabolism in three different stages of sweet potato rooting, branching and tubering stage were studied by sand culture method with 10% PEG-6000 simulating drought stress. The results showed that the biomass of sweet potato decreased significantly under drought stress in different periods, with the degree of drought stress being 10 days > 20 days > 30 days after transplantation. Drought stress significantly reduced the average diameter and root volume at the 10 days after transplantation, followed by the 20 days and 30 days. Both the main and interactive effects of different periods and drought stress significantly affected root morphological characteristics. Drought stress at different stages significantly reduced chlorophyll fluorescence characteristics, resulting in blocked photosynthate formation, and inhibited root differentiation. Drought stress affected the proportion of endogenous hormones in root (with decreases of indoleacetic acid and zeatin riboside contents but increases of abscisic acid contents) and thus inhibiting root differentiation of sweet potato. The earlier the stress time, the more serious the root differentiation of sweet potato was hindered. Across different drought-tolerant varieties, the severity of root differentiation blocked in Jishu 26 was significantly lower than that in Guangshu 87. Root endogenous hormones and chlorophyll fluorescence were the key drivers for the average diameter and root volume (R1=0.936, R2=0.972). Zeatin riboside, maximal photochemical efficiency, and abscisic acid had greater direct effects on average diameter and root volume of sweet potato. Sweet potato was more sensitive to drought stress in the 10th day after transplanting. Therefore, proper irrigation should be considered in case of drought in seedling stage of sweet potato.

Effects of spermidine and salinity stress on growth and biochemical response of paraquat‐susceptibe and ‐resistant goosegrass (Eleusine indica L.)

This study aimed to investigate the interaction effect of spermidine (Spd) and salinity stress on growth, photosynthetic rate, antioxidant system and free polyamines (PAs) contents of goosegrass (Eleusine indica L.) seedlings. E. indica was raised in a growth chamber under normal and toxic salt stress (100 mM of NaCl) and sprayed with 0 and 1.00 mM of Spd. The degree of growth inhibition caused by salt stress was lower in a paraquat‐resistant (R) biotype compared to a paraquat‐susceptible (S) biotype. Salt stress significantly elevated the accumulation of malondialdehyde, electrolyte leakage and proline and resulted in the degradation of chlorophyll; reduction in chlorophyll fluorescence; and a decrease in photosynthetic rate, relative water content and biomass. Spd‐treated plants maintained higher activities of antioxidant enzymes (catalase, superoxide dismutase and peroxidase), a greater rate of photosynthesis and lower osmotic pressure than untreated plants in the S biotype. Endogenous Spd content was reduced significantly in response to salt stress in both biotypes, but free PAs content in the S biotype was remarkably enhanced with exogenous Spd application under normal or salinity stress conditions. The result indicated that the S biotype was more sensitive to salinity than the R biotype; meanwhile, exogenous Spd maybe play an important role in protecting S biotype plants from salt stress.

Green synthesis of silver nanoparticles with extract of Mimusops coriacea and light

Biological methods of nanoparticle synthesis using plant extracts have been suggested as promising ecofriendly alternative to chemical and physical methods. In this study, spherical silver nanoparticles (AgNP) were synthesized from the aqueous extract of Mimusops coriacea leaves at room temperature. To accelerate the reduction of Ag+ ions was used photoreduction process with Xenon lamp. A presence of resonant surface plasmon band at approximately 415 nm confirms the formation of the nanoparticles. The shape and size of the particles were determined by transmission electron microscopy images indicating sizes from 10 to 30 nm in diameter. Zeta potential indicates good stability. To identify the products for the reduction of Ag+ ions and stability of AgNP, FTIR analysis were performed. An intense reduction in chlorophyll fluorescence was observed after formation of the nanoparticles.

Snapshot Transient Absorption Spectroscopy of Carotenoid Radical Cations in High-Light-Acclimating Thylakoid Membranes.

Nonphotochemical quenching mechanisms regulate light harvesting in oxygenic photosynthesis. Measurement techniques for nonphotochemical quenching have typically focused on downstream effects of quenching, such as measuring reduced chlorophyll fluorescence. Here, to directly measure a species involved in quenching, we report snapshot transient absorption (TA) spectroscopy, which rapidly tracks carotenoid radical cation signals as samples acclimate to excess light. The formation of zeaxanthin radical cations, which is possible evidence of zeaxanthin-chlorophyll charge-transfer (CT) quenching, was investigated in spinach thylakoids. Together with fluorescence lifetime snapshot data and time-resolved high-performance liquid chromatography (HPLC) measurements, snapshot TA reveals that Zea•+ formation is closely related to energy-dependent quenching (qE) in nonphotochemical quenching. Quantitative and dynamic information on CT quenching discussed in this work give insight into the design principles of photoprotection in natural photosynthesis.

Reduction of Chlorophyll Fluorescence in Zoysiagrasses at Chilling and High Temperatures with Moderate Light

Reduction of Chlorophyll Fluorescence in Zoysiagrasses at Chilling and High Temperatures with Moderate Light

Physiological and biochemical responses in rice (Oryza sativaL.) to high temperature: A review

Rice is the staple food crop and is the livelihood for most of the people across the globe. Keeping the present climate change scenario in view, there is a severe threat due to rise in temperature that can affect rice yield potential. Heat stress is one of the major abiotic stresses hampering the growth of rice. Temperature at every growth stage plays a critical role in deciding the rice yields. The major effects of heat stress in rice on its morphoagronomical parameters include reduced germination, poor seedling growth, reduction in plant height and tillering, reduction in number of pollen grains, poor anther dehiscence, increased sterility, reduced grain filling and poor grain quality that ultimately lead to yield reduction. From the physiological point of view, there is an inhibition of photosynthesis and related gas exchange traits, reduction in chlorophyll content and other pigments, reduction in chlorophyll fluorescence (Fv/Fm), reduction in cell membrane thermostability as well as an imbalance between photosynthesis and respiration. Biochemically, there is an increase in accumulation of osmoprotectants (praline and glycine betaine), increase in activity of antioxidants and increase in hormone accumulation (abscisic acid and ethylene). A complete understanding of mechanisms conferring thermotolerance and identification of genotypes possessing tolerance is the pre-requisite.

Modified atmosphere generated during storage under light conditions is the main factor responsible for the quality changes of baby spinach

Minimally processed products are generally exposed to low temperature and uncontrolled light conditions during the supply chain. The positive effect of low temperature on quality of baby spinach is widely reported, but there is little information available about the light effect. The objective of this study was to obtain insight about the cause-effect of light exposure of baby spinach on leaf quality and senescence parameters. Minimally processed baby spinach was stored in passive Modified Atmosphere Packaging (MAP) and in Controlled Atmosphere (CA) under different light conditions. In passive MAP, three very different headspace gas compositions within the bags due to photosynthesis and respiration reactions were generated that strongly affected the quality characteristics. To isolate the light effect from the atmosphere composition influence, and thus understand the mechanisms causing the quality changes, baby spinach was stored under two CA of 0.5kPa O2+10kPa CO2 (low O2+high CO2 levels) and air combined with 2 light conditions (continuous light and darkness). The changes observed under the different light conditions were mainly caused by the differences in gas composition. Under light, MAP with high O2 partial pressure (pO2) and low CO2 partial pressure (pCO2) was detrimental because of the growth of Pseudomonas spp. and the progress in tissue senescence due to oxidative stress, increasing cell damage, lipid peroxidation and chlorophyll degradation. Under darkness, MAP with low pO2 and high pCO2 was also detrimental because of the intense off-odour developments, the increase in pH and electrolyte leakage and the reduction in chlorophyll fluorescence. Our results showed that the modified atmosphere generated with exposure to the different light conditions affects the quality of baby spinach mainly because of the high pO2 under light and high pCO2 under darkness.

Salinity stress effects on direct and indirect defence metabolites in maize

In nature, plants are often exposed to multiple stress factors at the same time. The effects of single biotic or abiotic stresses on plant metabolism are well documented but how plants respond to a combination of these is little researched. Here we studied the effects of high salinity and herbivory on levels of secondary compounds and gene expression associated with defences against insects. Hydroponically grown maize plants were subjected to sodium chloride (1, 50, 100mM NaCl) and/or damage by caterpillars of Spodoptera exigua. Salt-stressed plants showed stunted growth, reduced chlorophyll fluorescence and enhanced levels of reactive oxygen species and 1,4-benzoxazin-3-one aglycones (aBX). Herbivory induced higher transcript levels of the Zm-Bx1 gene involved in aBX biosynthesis and of the Zm-SerPIN gene coding for a serine proteinase inhibitor which might affect plant feeding insects. Herbivory also triggered the emission of volatile organic compounds (VOCs) that are attractive signals for parasitoids and predators and thus regarded as an indirect defence. Herbivore-induced metabolites were differentially affected in salt-stressed plants. High salinity resulted in transient priming of jasmonic acid while aBX levels were reduced in double-stressed plants. Salt stress led to lower herbivore-induced VOC emission per plant but not per unit biomass. However, quantitative shifts in individual compounds were found in both cases. Our study confirms the notion that combined stresses produce a unique phenotype that cannot be derived from single-stress effects. The ecological implications of these changes for organisms from different trophic levels and for plant fitness remain to be tested.

Carotenoid-chlorophyll coupling and fluorescence quenching in aggregated minor PSII proteins CP24 and CP29.

It is known that aggregation of isolated light-harvesting complex II (LHCII) in solution results in high fluorescence quenching, reduced chlorophyll fluorescence lifetime, and increased electronic coupling of carotenoid (Car) S1 and chlorophyll (Chl) Qy states, as determined by two-photon studies. It has been suggested that this behavior of aggregated LHCII mimics aspects of non-photochemical quenching processes of higher plants and algae. However, several studies proposed that the minor photosystem II proteins CP24 and CP29 also play a significant role in regulation of photosynthesis. Therefore, we use a simple protocol that allows gradual aggregation also of CP24 and CP29. Similarly, as observed for LHCII, aggregation of CP24 and CP29 also leads to increasing fluorescence quenching and increasing electronic Car S1-Chl Qy coupling. Furthermore, a direct comparison of the three proteins revealed a significant higher electronic coupling in the two minor proteins already in the absence of any aggregation. These differences become even more prominent upon aggregation. A red-shift of the Qy absorption band known from LHCII aggregation was also observed for CP29 but not for CP24. We discuss possible implications of these results for the role of CP24 and CP29 as potential valves for excess excitation energy in the regulation of photosynthetic light harvesting.

Alternate wetting and drying irrigation-mediated changes in the growth, photosynthesis and yield of the medicinal plant Tulipa edulis

Tulipa edulis is an important medicinal plant with a variety of anti-cancer properties. There is an urgent need to reduce water consumption in T. edulis under greenhouse cultivation. A greenhouse experiment was performed to study the effect of well-watered (80% of field capacity, Control), persistent drought (50% of field capacity, D) and alternate wetting and drying (50% and 80% of field capacity, AWD) regimes on the growth traits, photosynthetic pigment contents, chlorophyll fluorescence parameters, photosynthetic characteristics and yield of T. edulis. The results showed that compared with the well-watered control, persistent drought inhibited plant growth and yields dramatically, presumably due to the significantly lower photosynthetic rate caused by a decrease in photosynthetic pigments and a reduced chlorophyll fluorescence efficiency (Fv/Fm, Fv/F0). In contrast, the AWD plants showed a capacity for photosynthesis comparable to the well-watered control, which could be associated with similar photosynthetic pigment levels and chlorophyll fluorescence parameters (Fv/Fm, Fv/F0). AWD reduced the irrigation water input by 25.09% while leading to comparable yields and increased water productivity by 21.21% compared with the well-watered control. The results suggested that an alternate wetting and drying (50% and 80% of field capacity) regime can be an effective means of saving water, promoting bulb production, and improving water production for T. edulis.

Sublethal effects of environmentally relevant run‐off concentrations of glyphosate in the root zone of Ludwigia peploides (creeping water primrose) and Polygonum hydropiperoides (smartweed)

As one of the most widely applied agricultural chemicals in the world, glyphosate has many effects on the environment. The present study quantified plant responses to exposure by glyphosate through the root zone for a range of concentrations (0, 10, 100 and 1000 μg L−1). Ludwigia peploides and Polygonum hydropiperoides were grown in a greenhouse and given a single exposure to glyphosate via the root zone. The growth and physiological parameters were measured before exposure and for 18 days postexposure. The growth variables that were measured included the relative growth rate, stem length increase, biomass and root‐to‐shoot‐ratios. The physiological variables that were measured were the chlorophyll content index and chlorophyll fluorescence. The data analyses revealed that the root‐zone glyphosate affected some of the measured variables in P. hydropiperoides more than for L. peploides. Polygonum hydropiperoides showed a significant decrease in the root‐to‐shoot ratios for the 100 μg L−1 treatment, compared to the 10 μg L−1 treatment. The chlorophyll content index of the treated plants was significantly reduced in P. hydropiperoides, compared to the untreated plants on Days 7 and 18. Ludwigia peploides was affected only on the day after exposure, with the chlorophyll fluorescence parameters being significantly less for the 1000 μg L−1 treatment, compared to the 10 μg L−1 treatment. Glyphosate‐treated P. hydropiperoides showed a decreased chlorophyll content and reduced chlorophyll fluorescence parameters. In contrast, L. peploides showed a decrease in the chlorophyll fluorescence parameters but no reduction in its chlorophyll content. In addition to demonstrating the adverse effects of root exposure to glyphosate for the study species, these data help to partially explain the highly invasive and persistent nature of L. peploides in marginal aquatic environments, such as agricultural ditches.