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Background The objective was to determine how molasses and Lactobacillus plantarum affect chemical composition, fermentation quality, aerobic stability, and the microbial community of an ensiled mixture of amaranth (Amaranthus hypochondriaus, AF) and rice straw. Treatments were control (C, no addition), L. plantarum (L; 2 × 105 cfu g-1 fresh weight), molasses (M; 40 g kg-1 fresh matter), and their combination (LM). All treatments were ensiled for 1, 3, 5, 7, and 30 days. Results All additives improved fermentation quality with greater lactic acid (LA), acetic acid, and lower pH than C silage over the ensiling period. The LM silage combination optimized fermentability, manifested as greater LA contents and a more rapid pH reduction during the first 7 days of ensiling than L or M silages. After 30 days of ensiling, inoculant L. plantarum increased Lactobacillus abundance and reduced bacterial diversity and Enterobacteriaceae abundance compared with silage treated with molasses. Molasses addition reduced the relative concentration of structural carbohydrates (neutral and acid detergent fiber, and hemicellulose) after 30 days of ensiling. Finally, there was spoilage after 2 days and 4 days of aerobic exposure in C and LM silages respectively, whereas L silage had not spoiled after 4 days. Conclusions Although the combination of L. plantarum and molasses further optimized fermentation characteristics, L silage had better aerobic stability. © 2021 Society of Chemical Industry.

Phytoremediation has been increasingly used as a green technology for the remediation of heavy metal contaminated soils. Microorganisms could enhance phytoremediation efficiency by solubilizing heavy metal and improve plant growth by producing phytohormones in the heavy metal contaminated soils. In this study, we investigated the abundance and composition of soil microbial communities in heavy metal contaminated soils. Furthermore, we identified a Cd-resistant fungal strain Penicillium janthinellum ZZ-2 and assessed its potential in improving plant growth, Cd accumulation and Cd tolerance in bermudagrass. The results indicated that long-term heavy metal pollution decreased microbial biomass and activity by inhibiting microbial community diversity, but did not significantly affect community composition. Mainly, the relative abundance of some specific bacterial and fungal taxa, such as Actinobacteria, Chloroflexi, Bacteroidetes, Ascomycota and Basidiomycota, changes under metal pollution. Furthermore, at genus level, certain microbial taxa, such as Pseudonocardiaceae, AD3, Latescibacteria, Apiotrichum and Paraboeremia, only exist in polluted soil. One Cd-resistant fungus ZZ-2 was isolated and identified as Penicillium janthinellum. Further characterization revealed that ZZ-2 had a greater capacity for Cd2+ absorption, produced indole-3-acid (IAA), and facilitated plant growth in the presence of Cd. Interestingly, ZZ-2 inoculation significantly increased Cd uptake in the stem and root of bermudagrass. Thus, ZZ-2 could improve plant growth under Cd stress by reducing Cd-toxicity, increasing Cd uptake and producing IAA. This study suggests a novel fungus-assisted phytoremediation approach to alleviate Cd toxicity in heavy metals contaminated soils.

The objective was to evaluate effects of Lactobacillus plantarum and/or cellulase on fermentation, aerobic stability and bacterial community of mixed high-moisture amaranth (AF) and rice straw (RS) silage. The mixtures were treated with no addition (C), L. plantarum (L), cellulase (F) and their combination (LF). Additives increased the abundances of Lactobacillus and reduced the abundances of Weissella, Pediococcus, Lactococcus, decreased pH, acetic acid, ammonia nitrogen and increased lactic acid concentration as compared to C silage over the ensiling period. The LF silage had the highest lactic acid concentration among all silages over the 7 d of ensiling and also the lowest abundance of Enterobacteriaceae over 30 d of ensiling. Aerobic spoilage occurred in C and LF silages after 2 d of aerobic exposure, whereas the L and F silages remained stable > 4 d. In conclusion, silage treated with LF showed best silage quality.

A novel composite, CdS/MIL-53(Fe), was successfully fabricated via a facile solvothermal method and characterized with XRD, SEM, TEM, XPS, FT-IR and UV–vis DRS. The results showed that the fabrication was able to result in a good dispersion of CdS nanoparticles onto MIL-53(Fe). The photocatalytic activities of the as-synthesized composite were investigated through the degradation of Rhodamine B (RhB) in water under visible light irradiation. It was found that the composite prepared at the mass ratio of CdS to MIL-53(Fe) of 1.5:1 displayed the highest photocatalytic activity. An approximately 92.5% of photocatalytic degradation of RhB was achieved at 0.5 g/L of 1.5-CdS/MIL dosage, 10 mg/L of initial RhB concentration and 23 °C of reaction temperature under visible light irradiation. The RhB photocatalytic degradation followed well the first-order kinetics equation and the increased catalyst dosage and optimal initial RhB concentration were responsible for the enhanced photocatalytic degradation. Quenching tests revealed that the predominant free radicals in the CdS/MIL-(53)-RhBaq-visible light system was O2− ; nevertheless, h+ and OH also contributed to a certain degree. The enhanced photocatalytic performance was ascribed to the formation of heterojunction structure between CdS and MIL-53(Fe) which significantly suppressed the recombination of photogenerated electron-hole pairs. Moreover, the reusability of 1.5-CdS/MIL composite was also studied.

Alfalfa (Medicago sativa) is the most widely grown and most important forage crop in the world. However, alfalfa is susceptible to waterlogging stress, which is the major constraint for its cultivation area and crop production. So far, the molecular mechanism of alfalfa response to the waterlogging is largely unknown. Here, comparative transcriptome combined with proteomic analyses of two cultivars (M12, tolerant, M25, sensitive) of alfalfa showing contrasting tolerance to waterlogging were performed to understand the mechanism of alfalfa in response to waterlogging stress. Totally, 748 (581 up- and 167 down-regulated) genes were differentially expressed in leaves of waterlogging-stressed alfalfa compared with the control (M12_W vs. M12_CK), whereas 1193 (740 up- and 453 down-regulated) differentially abundant transcripts (DATs) were detected in the leaves of waterlogging-stressed plants in comparison with the control plants (M25_W vs. M25_CK). Furthermore, a total of 187 (122 up- and 65 down-regulated) and 190 (105 up- and 85 down-regulated) differentially abundant proteins (DAPs) were identified via isobaric tags for relative and absolute quantification (iTRAQ) method in M12_W vs. M12_CK and M25_W vs. M25_CK comparison, respectively. Compared dataset analysis of proteomics and transcriptomics revealed that 27 and eight genes displayed jointly up-regulated or down-regulated expression profiles at both mRNA and protein levels in M12_W vs. M12_CK comparison, whereas 30 and 27 genes were found to be co-up-regulated or co-down-regulated in M25_W vs. M25_CK comparison, respectively. The strongly enriched Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways for co-up-regulated genes at mRNA and protein levels in M12_W vs. M12_CK comparison were ‘Amino sugar and nucleotide sugar metabolism’, ‘Arginine and proline metabolism’ and ‘Starch and sucrose metabolism’, whereas co-up-regulated protein-related pathways including ‘Arginine and proline metabolism’ and ‘Valine, leucine and isoleucine degradation’ were largely enriched in M25_W vs. M25_CK comparison. Importantly, the identified genes related to beta-amylase, Ethylene response Factor (ERF), Calcineurin B-like (CBL) interacting protein kinases (CIPKs), Glutathione peroxidase (GPX), and Glutathione-S-transferase (GST) may play key roles in conferring alfalfa tolerance to waterlogging stress. The present study may contribute to our understanding the molecular mechanism underlying the responses of alfalfa to waterlogging stress, and also provide important clues for further study and in-depth characterization of waterlogging-resistance breeding candidate genes in alfalfa.

Plants growing in salt-affected soils may have retarded growth and inhibited or altered metabolic processes. This study aims at investigating the impact of subsurface soil salinity on root growth and metabolic processes in perennial ryegrass (Lolium perenne). The seeds of perennial ryegrass (cv. Quick Start II) were planted in polyvinyl chloride (PVC) tubes (10 cm diameter × 42 cm long) for 2 months. The experiment consisted of three treatments: 1) control, 40 cm filled with sand–peat mixture (7 sand : 3 peat wt/wt); 2) T20, a 20-cm-deep layer of saline soil covered with a 20-cm-deep layer of sand–peat mixture; and 3) T30, a 30-cm-deep layer of saline soil covered with a 10-cm-deep layer of sand–peat mixture. Our study showed that soil salinity at the subsurface inhibited the growth of perennial ryegrass roots. Compared with the control, the root activity in saline soil layer decreased, whereas it remained high in the mixture-soil zone. The content of amino acids in the roots obtained from the surface soil (0–10 cm) in T30 was greater than that in both the T20 and the control regimes. The content of soluble sugars in the roots went up with the decrease of the depth of sand–peat mixture. The increased root activity and free amino acids content in the roots sampled from the upper soil layers coupled with the increased soluble sugars in the roots subjected to soil salinity stress in the bottom soil layer represents some adaptive responses and regulative mechanisms in perennial ryegrass.

Melatonin (MT), polyamines (PAs), and ethylene have been suggested to play key roles in plant growth and development in response to environmental abiotic stresses. However, the effect of melatonin on polyamine and ethylene metabolism under waterlogging stress has rarely been elucidated. The main purpose of this study was to investigate the effect of melatonin pretreatment on waterlogging stress in alfalfa. The experiment was arranged into four treatment groups control with water pretreatment (CK-MT), control with melatonin pretreatment (CK+MT), waterlogging pretreated with water (WL-MT) and waterlogging pretreated with melatonin (WL+MT), with three replications. Six-week-old alfalfa seedlings were pretreated with 100 μM melatonin and exposed to waterlogging stress for 10 days. Plant growth rate, different physiological characteristics, and gene expression level were measured. Results showed that waterlogging induced melatonin accumulation, and melatonin pretreatment increased endogenous MT levels for the control and water-logged plants. Waterlogging stress caused a significant reduction in plant growth, chlorophyll content, photochemical efficiency (Fv/Fm) and net photosynthetic rate (Pn), while also causing increased leaf electrolyte leakage (EL) and malondialdehyde (MDA) content. Pretreatment with melatonin alleviated the waterlogging-induced damage and reduction in plant growth, chlorophyll content, Fv/Fm and Pn. Waterlogging stress significantly increased leaf polyamines (Put, Spd, Spm) and ethylene levels, and the increased PAs and ethylene levels are coupled with higher metabolic enzymes and gene expressions. While pretreatment with melatonin further increased Put, Spd and Spm levels, it also decreased ethylene levels under waterlogging, and those increased PAs levels or decreased ethylene levels are regulated by the metabolic enzymes and gene expressions. The results in this study provide more comprehensive insight into the physiological and molecular mechanisms of melatonin-improved waterlogging tolerance in alfalfa. Furthermore, they suggested that melatonin improved waterlogging tolerance in alfalfa at least partially by reprogramming ethylene and PA biosynthesis, attributable to the increased PAs and decreased ethylene levels, which leads to more enhanced membrane stability and photosynthesis as well as less leaf senescence caused by ethylene.

A novel nanocomposite, SnO 2 /ZnS, was successfully synthesized via a one-step hydrothermal method. The composite was characterized by several techniques such as XRD, SEM, TEM, XPS and UV–vis spectrum, and utilized for photocatalytic degradation of refractory dye Rhodamine B (RhB) under simulated and natural sunlight. It was found that the composite prepared at the molar ratio of n(SnCl 4 ·5H 2 O)/ n (Zn(NO 3 ) 2 ·6H 2 O) = 1.5 and hydrothermal temperature of 180 °C showed the highest photocatalytic activity. The photocatalytic degradation of RhB reached the maximum of 95% at the 1 g/L SnO 2 /ZnS dosage, 10 mg/L initial RhB concentration, 4.59 initial solution pH and 23 °C. The RhB photocatalytic degradation fitted well to the first-order kinetics model, and the increased SnO 2 /ZnS dosage, decreased initial RhB concentration and optimal initial solution pH were responsible for the increase of RhB photocatalytic degradation rate. The composite also displayed stable performance during 5 runs of reuse. Quenching tests demonstrated that the dominant active species generated in SnO 2 /ZnS-RhB-H 2 O-simulated sunlight system was O 2 − ; nevertheless, h + and OH also contributed to RhB degradation. The formation mechanism of the SnO 2 /ZnS nanosphere and RhB photocatalytic degradation mechanism were proposed. Moreover, the composite has proved to have the high efficiency for the degradation of RhB under natural sunlight irradiation.

A novel composite, Ag@AgBr/SBA-15, was successfully synthesized by dispersion of AgBr on mesoporous silica SBA-15, characterized by several techniques, such as XRD, N2 adsorption−desorption, SEM & EDS, UV−vis spectrum and XPS, and utilized for visible light photocatalytic degradation of dye Rhodamine B (RhB) in aqueous solutions. The results showed that for the various AgBr loadings in the composites, RhB photocatalytic degradation efficiency arrived at the maximum of 77% at 50% loading, or with 50Ag@AgBr/SBA-15. Under the combined mode, the RhB removal reached 88% at 0.3 g/L of 50Ag@AgBr/SBA-15 dosage, 20 mg L−1 of initial RhB concentration, 4.28 of unadjusted initial pH and 20 °C. The RhB photocatalytic degradation followed well with the second-order kinetics, and the increase of the 50Ag@AgBr/SBA-15 dosage, the decrease of the initial RhB concentration and the optimal initial solution pH would be favorable to RhB photocatalytic degradation. The quenching tests demonstrated that the RhB photocatalytic degradation was mainly attributed to the generation of active species such as O2−, OH and h+. Moreover, the adsorption characteristics of 50Ag@AgBr/SBA-15 were investigated, with its pHpzc of 6.21 acquired and the conclusion that the RhB adsorption isotherm well followed Langmuir model drawn. Additionally, photocatalyst 50Ag@AgBr/SBA-15 can be effectively regenerated with the H2O2 solutions under visible light irradiation, and reused for up to five runs for the degradation of RhB in the presence of visible light, with RhB removal more than 75% and Ag+ leaching undetected for each run.

Glycinebetaine (GB) is an important organic osmolyte that accumulates in many plant species in response to abiotic stresses including heavy metals. The objective of this study was to investigate whether exogenous GB would ameliorate the adverse effect of cadmium (Cd) stress on perennial ryegrass (Lolium perenne). Fifty-three days old seedlings were exposed to hydroponic culture for 7 days with six treatments: T1 (control), T2 (0 mM Cd + 20 mM GB), T3 (0 mM Cd + 50 mM GB), T4 (0.5 mM Cd + 0 mM GB), T5 (0.5 mM Cd + 20 mM GB), T6 (0.5 mM Cd + 50 mM GB). Cd stress resulted in a remarkable decrease in turf quality, vertical shoot growth rate (VSGR), normalized relative transpiration (NRT) and Chlorophyll (Chl) content; with significant increases in electric conductivity (EL), malondialdehyde (MDA) content, superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) activity, oxalic and tartaric acid content. Exogenous application of GB decreased EL and MDA content in Cd stressed plants, and increased turf quality, VSGR, NRT, Chl content, SOD, CAT, POD activity, oxalic, tartaric acid content, and the gene expression level of SOD and POD when compared with Cd stressed without GB. Perennial ryegrass with 20 mM GB application suppressed the Cd accumulation in both shoots and roots. A lower translocation factor of Cd was found in GB treated plants than non-GB treated plants, and the lowest translocation factor was observed in the 20 mM GB application. These results suggested that GB could alleviate the detrimental effect of Cd on perennial ryegrass and the amelioration was mainly related to the elevation in SOD, CAT, and POD at enzyme and gene expression levels, which reduced Cd content in shoots and improved cell membrane stability by reducing oxidation of membrane lipids. These findings lead us to conclude that application of GB with 20 mM is the best strategy to ameliorate the detrimental impacts of Cd stress on perennial ryegrass.

Clonal plants can consist of connected individual ramets that enhance resource sharing through physiological integration. This integration enables the whole clone to tolerate environmental stresses. The objective of this research was to investigate the effects of physical ramet connections on the integration of antioxidant enzymes in clonal common bermudagrass (Cynodon dactylon) growing under heterogeneously distributed water; i.e., nonuniform distribution of water due to 20% polyethylene glycol (PEG 6000) treatment on some ramets and not others. The bottom, middle, upper and three fragments of clonal common bermudagrass were subjected to 20% PEG 6000 with water potential of −1.8 MPa to induce heterogeneous and homogeneous drought stress. The control was not treated with 20% PEG 6000. Within the heterogeneous treatment, water stressed clonal fragments generally had higher leaf and root antioxidant enzyme activities with respect to superoxide dismutase, catalase, peroxidase (except for root peroxidase). There was no difference in antioxidant enzyme activity within the connected clonal ramets for homogeneous treatment; i.e., three connected ramets treated with 20% PEG 6000. Osmotically stressed clonal fragments under heterogeneous environments had a lower level of malonaldehyde (MDA) compared with those in homogeneous regimes. The antioxidant enzyme integration was affected by directionality and water availability contrast. This was indicated by significant decline in MDA levels within the heterogeneous treatments as compared with homogeneous treatment, which suggested reduced lipid peroxidation. These results suggested that ramet connections facilitate integration of antioxidant enzymes within clonal plants growing in heterogeneously available water. Enzymes were integrated from clonal fragments growing in water sufficient environment to those in water stressed regimes. This enhanced reactive oxygen species scavenging capacity of the entire clone hence improved drought tolerance.

ERF (ethylene-responsive factor) transcription factors play important roles in plant stress signaling transduction pathways. However, their specific roles during diverse abiotic stresses tolerance in Gossypium hirsutum are largely unknown. Here, a novel ERF transcription factor, designated GhERF38, homologous to AtERF38 in Arabidopsis, was isolated from cotton (Gossypium hirsutum L). GhERF38 expression was up-regulated by salt, drought and ABA treatments. Subcellular localization results indicated that GhERF38 was localized in the cell nucleus. Over-expression of GhERF38 in Arabidopsis reduced plant tolerance to salt and drought stress as indicated by a decline of seed germination, plant greenness frequency, primary roots length and the survival rate in transgenic plants compared to those of wild type plants under salt or drought treatment. Besides, stress tolerance related physiological parameters such as proline content, relative water content, soluble sugar and chlorophyll content were all significantly lower in transgenic plants than those of wild type plants under salt or drought treatment. Furthermore, over-expression of GhERF38 in Arabidopsis resulted in ABA sensitivity in transgenic plants during both seed germination and seedling growth. Interestingly, the stomatal aperture of guard cells in the transgenic plants was larger than that in transgenic plant after ABA treatment, suggesting that GhERF38-overexpressing plants were insensitive to ABA in terms of stomatal closure. Furthermore, expressions of the stress-related genes were altered in the GhERF38 transgenic plants under high salinity, drought or ABA treatment. Together, our results revealed that GhERF38 functions as a novel regulator that is involved in response to salt/drought stress and ABA signaling during plant development.

Salinity is one of the major environmental factors affecting plant growth and survival by modifying source and sink relationships at physiological and metabolic levels. Individual metabolite levels and/or ratios in sink and source tissues may reflect the complex interplay of metabolic activities in sink and source tissues at the whole-plant level. We used a non-targeted gas chromatography-mass spectrometry (GC-MS) approach to study sink and source tissue-specific metabolite levels and ratios from bermudagrass under salinity stress. Shoot growth rate decreased while root growth rate increased which lead to an increased root/shoot growth rate ratio under salt stress. A clear shift in soluble sugars (sucrose, glucose and fructose) and metabolites linked to nitrogen metabolism (glutamate, aspartate and asparagine) in favor of sink roots was observed, when compared with sink and source leaves. The higher shifts in soluble sugars and metabolites linked to nitrogen metabolism in favor of sink roots may contribute to the root sink strength maintenance that facilitated the recovery of the functional equilibrium between shoot and root, allowing the roots to increase competitive ability for below-ground resource capture. This trait could be considered in breeding programs for increasing salt tolerance, which would help maintain root functioning (i.e. water and nutrient absorption, Na+ exclusion) and adaptation to stress.

Plants may survive salinity and alkalinity with differential metabolic responses. The aim of this study was to gain further insights into the differential response to salinity and alkalinity stress at the metabolic level. Two Kentucky bluegrass, ‘Midnight’ (tolerant) and ‘Voyager II’ (sensitive), were subjected to salinity (NaCl, 75 mM Na+, pH 5.41) and alkalinity (Na2CO3 and NaHCO3, 75 mM Na+, pH 9.5) in hydroponics. The leaf metabolite profile was determined using gas chromatography–mass spectrometry (GC-MS). Alkaline salts caused more severe damages than neutral salt as indicated by the vertical shoot growth rate (VSGR), turf quality, electrolyte leakage (EL) and lipid peroxidation (MDA content). Adaptation of plants to salinity was mainly associated with the accumulation of amino acids (proline, valine, glutamate, asparagine, glutamine, phenylalanine and lysine) and sugars (sucrose, trehalose). In contrast, the metabolic response to alkalinity stress was mostly associated with the accumulation of organic acids that are mainly sugar acids (gluconate, galactarate, glucarate) and those involved in the citric acid cycle (malate, citrate, isocitrate, succinate, maleiate, aconitate). The differential accumulation of the amino acids, organic acids, sugars and fatty acids may contribute to the differential adaptation strategies due to their roles in the stress response pathways such as osmotic adjustment, membrane stability, respiration for energy production, carbon/nitrogen assimilation, regulation of the intracellular pH and the pH outside roots.

Plants possess abiotic stress responses that alter photosynthetic metabolism under salinity stress. The objective of this study was to identify the stomatal and metabolic changes associated with photosynthetic responses to NaCl stress in perennial ryegrass (Lolium perenne). Five-week-old seedlings of two perennial ryegrass genotypes, PI 516605 (salt-sensitive) and BARLP 4317 (salt-tolerant), were subjected to 0 and 250 mm NaCl for 8 days. The salt tolerance in perennial ryegrass was significantly associated with leaf relative water content (RWC) and photosynthetic capacity through the maintenance of greater metabolic activities under prolonged salt stress. BARLP 4317 maintained greater turf quality, RWC, and stomatal limitations but a lower level of lipid peroxidation [malondialdehyde (MDA)] and intercellular CO2 concentration than PI 516605 at 8 days after treatment (DAT). Ribulose-1, 5-bisphosphate carboxylase:oxygenase (Rubisco) activity and activation state, transcriptional level of rbcL gene, and expression level of Rubisco large subunit (LSU) declined in stressed perennial ryegrass but were higher in salt-tolerant genotype at 8 DAT. Furthermore, photosynthetic rate increased linearly with increasing Rubisco activity, Rubisco activation state, and RWC in both genotypes. The same linear relationship was found between RWC and Rubisco activity. However, MDA content decreased linearly with increasing RWC in both genotypes. Salinity-induced inhibition of photosynthesis in perennial ryegrass was mainly the result of stomatal limitation during early salt stress and metabolic limitation associated with the inhibition of RWC, activity of Rubisco, expression level of rbcL gene, and LSU under a prolonged period of severe salinity.

A novel heterogeneous Co catalyst CoMg/SBA-15 was prepared through a two-step incipient wetness impregnation of Mg and Co into mesoporous silica SBA-15 and used for the activation of oxone to generate sulphate radicals for degrading Rhodamine B (RhB) in aqueous solution. The CoMg/SBA-15 was characterized by several techniques such as XRD, N 2 adsorption–desorption, CO 2 -TPD, TEM and SEM. It was found that the CoMg/SBA-15 existed as agglomerates with the particle size more than 0.3 μm, and Co and Mg occurred mainly both inside and outside the support pores in the form of cubic spinel Co 3 O 4 and Mg oxide crystallites, respectively. Loading Mg into the support increased the dispersion of Co 3 O 4 on the support and generated the remarkable basicity of the catalyst surface promoting the formation of surface Co–OH complex. The CoMg/SBA-15 still displayed the long-range ordered arrangement of the channels in structure with the reduced pore diameter and surface area compared with the SBA-15. The Co/SBA-15–oxone–RhB system, as a test control, was demonstrated to be efficient for the activation of oxone producing sulphate radicals for the degradation of RhB in solution. And the increase of Co/SBA-15 and oxone dosages had the positive effect on the degradation efficiency and rate, with the almost complete RhB degradation in 60 min and the Co leaching concentration less than 43 μg/L and the leaching percent less than 0.40% at appropriate Co/SBA-15 and oxone dosages. In addition, the degradation followed the first-order kinetics. The CoMg/SBA-15 exhibited much higher activity than Co/SBA-15 and Co/MgO with the same Co loading in degrading RhB by sulphate radicals from oxone, with nearly 100% degradation in 5 min, the Co leaching concentration of 80 μg/L and the leaching percent of 0.96%, and almost 100% TOC removal under appropriate conditions achieved. The CoMg/SBA-15 also displayed stable performance during 25 runs of reuse. Based on the UV–vis spectra and TOC measurement, the degradation mechanism of RhB in the presence of CoMg/SBA-15 and oxone was proposed. It is believed that CoMg/SBA-15 can be widely applied in the catalytic oxidation with oxone for the degradation of the refractory organic pollutants such as dye RhB in water.

Little is known about the interplay between Ca2+ and H2O2 signaling in stressed cool-season turfgrass. To understand better how Ca2+ and H2O2 signals are integrated to enhance grass acclimation to stress conditions, we analyzed the rearrangements of endogenous ion accumulation, antioxidant systems and secondary metabolism in roots, stems and leaves of perennial ryegrass (Lolium perenne L.) treated with exogenous Ca2+ and H2O2 under salinity. Ca2+ signaling remarkably enhanced the physiological response to salt conditions. Ca2+ signaling could maintain ROS homeostasis in stressed grass by increasing the responses of antioxidant genes, proteins and enzymes. H2O2 signaling could activate ROS homeostasis by inducing antioxidant genes but weakened Ca2+ signaling in leaves. Furthermore, the metabolic profiles revealed that sugars and sugar alcohol accounted for 49.5–88.2% of all metabolites accumulation in all treated leaves and roots. However, the accumulation of these sugars and sugar alcohols displayed opposing trends between Ca2+ and H2O2 application in salt-stressed plants, which suggests that these metabolites are the common regulatory factor for Ca2+ and H2O2 signals. These findings assist in understanding better the integrated network in Ca2+ and H2O2 of cool-season turfgrass’ response to salinity.

Soil alkalization is one of the most prominent adverse environmental factors limiting plant growth, while alkali stress affects amino acids and carbohydrates metabolism. The objective of this study was conducted to investigate the effects of alkali stress on growth, amino acids and carbohydrates metabolism in Kentucky bluegrass (Poa pratensis). Seventy-day-old plants were subjected to four pH levels: 6.0 (control), 8.0 (low), 9.4 (moderate) and 10.3 (severe) for 7 days. Moderate to severe alkali stress (pH >9.4) caused a significant decline in turf quality and growth rate in Kentucky bluegrass. Soluble protein was unchanged in shoots, but decreased in roots as pH increased. The levels of amino acids was kept at the same level as control level at 4 days after treatment (DAT) in shoots, but greater at 7 DAT, when plants were subjected to severe (pH 10.3) alkali stress. The alkali stressed plants had a greater level of starch, water soluble carbohydrate and sucrose content, but lower level of fructose and glucose. Fructan and total non-structural carbohydrate (TNC) increased at 4 DAT and decreased at 7 DAT for alkali stressed plants. These results suggested that the decrease in fructose and glucose contributed to the growth reduction under alkali stress, while the increase in amino acids, sucrose and storage form of carbohydrate (fructan, starch) could be an adaptative mechanism in Kentucky bluegrass under alkali stress.

Plant adaptation to salt stress may be associated with morphological, physiological, and gene expression alterations. The objective of this study was to investigate the effect of salt stress on morphological and antioxidant enzyme changes and its gene expressions in bermudagrass (Cynodon dactylon). Salt-tolerant ‘C43’ and salt-sensitive ‘C198’, previously determined in our preliminary study, were subjected to four salinity levels: 0 mm (control), 100 mm (low), 200 mm (moderate), and 400 mm (high) NaCl for 21 days. Salt stress decreased turf quality and canopy height, especially in ‘C198’. Salt stress increased root length, root number, root fresh weight, and root/shoot length ratio, to a greater extent in salt-tolerant genotype. Salt stress increased Na+ and decreased K+ content, which resulted in a higher Na+/K+ ratio in bermudagrass, to a great extent in shoot and root of ‘C198’. Moderate (200 mm) and high (400 mm) salt concentration increased malondialdehyde and hydrogen peroxide content in old leaves of ‘C198’. ‘C43’ exhibited a greater activity of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and dehydro-ascorbate reductase (DHAR) than ‘C198’ in old leaves subjected to 200 and 400 mm NaCl. Antioxidant gene expressions were upregulated in new leaves and downregulated in old leaves with increasing salinity levels for both genotypes. Salt-tolerant genotypes exhibited a relatively greater antioxidant gene expression than salt-sensitive ones when exposed to the same level of salt stress. These results suggested that SOD, CAT, APX, and DHAR might be involved in scavenging salt stress-induced reactive oxygen species in bermudagrass at the level of gene expression. Salt tolerance might be attributed to the development and maintenance of a more extensive root system under saline conditions and induced antioxidant gene expressions, leading to more efficient enzyme stimulation and protection in bermudagrass.

The magnetic mesoporous material Fe/CMK-3 acting as a catalyst–sorbent was synthesized by using ordered mesoporous carbon CMK-3 as the supporter, Fe(NO 3 ) 3 as the iron source, and glycol as the reducing agent. The samples synthesized were characterized by powder X-ray diffraction (XRD), N 2 adsorption–desorption, scanning electron microscope (SEM) and transmission electron microscopy (TEM). The results show that the prepared Fe/CMK-3 preserved the ordered mesoporous structure of CMK-3, and magnetic species was mainly Fe 3 O 4 , which was dispersed inside channels of CMK-3 as nanoparticles with the diameter of around 10 nm. The adsorption and catalytic dry oxidation efficiency of the prepared Fe/CMK-3 were determined. The results also show that Fe/CMK-3 had good adsorption performance of phenol in aqueous solution and could be easily separated from water and recycled due to its ferromagnetic nature. Iron oxides supported on CMK-3 were excellent catalysts for dry oxidation of phenol. After 15 adsorption–catalytic oxidation cycles, the phenol adsorption capacity of Fe/CMK-3 only decreased a little, suggesting the good practicality. Combined thermogravimetry and mass spectrum (TG–MS) instrument was used to investigate the catalytic oxidation of phenol on Fe/CMK-3 and the ignition characteristics of the catalyst–sorbent. The supported Fe 3 O 4 was found to be not only the magnetic component but also the active catalyst for the oxidation of phenol. The adsorbed phenol could be oxidized into CO 2 and H 2 O at 220 °C at which no obvious phenol desorption or CMK-3 ignition occurred.

Salinity stress may involve the accumulation of glycine betaine (GB). The objective of this study was to examine whether exogenous GB would ameliorate the detrimental effect of salinity stress on perennial ryegrass (Lolium perenne). The grass was subjected to two salinity levels (0 and 250 mm NaCl) and three GB levels (0, 20, and 50 mm). Salinity resulted in a remarkable decrease in vertical shoot growth rate (VSGR), shoot and root fresh weight, relative water content (RWC), relative transpiration rate (Tr), and chlorophyll (Chl) content, superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) activities. Plants subjected to salt exhibited an increase in leaf electrolyte leakage (EL), lipid peroxidation (MDA), and proline content. Application of GB reduced EL, MDA, and proline content in salt-stressed plants. Perennial ryegrass subjected to salt stress plus GB had a greater level of VSGR, RWC, relative Tr, Chl content, and activities of SOD, CAT, and APX when compared with salt-stressed without GB. Salt stress increased Na+ and decreased K+ content, which resulted in a higher Na+/K+ ratio in perennial ryegrass. Application of 20 mm GB suppressed Na+ accumulation, whereas the K+ content was significantly increased in shoot, which led to a higher K+/Na+ ratio under saline conditions. These results suggested that GB-enhanced salt tolerance in perennial ryegrass was mainly related to the elevated SOD, CAT, and APX activity and alleviation of cell membrane damage by reducing oxidation of membrane lipid and improving the ion homeostasis under salt stress.

A powder Co/SBA-15 catalyst for the activation of peroxymonosulfate (PMS) and the subsequent degradation of phenol was prepared through an incipient wetness impregnation technique using SBA-15 as the support, Co(NO 3 ) 2 ·6H 2 O as the precursor. A facile way to make a recyclable Co/SBA-15 catalyst was tested. The samples synthesized were characterized by X-ray diffraction (XRD), N 2 adsorption–desorption, high-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM) techniques. Effects of Co loading, calcination temperature and time on the performance of the powder catalyst were investigated. The results show that Co 3 O 4 was the main cobalt species present both inside and outside the support. Heat treatment led to the formation of Co–O–Si species during the calcinations and significantly inhibited Co leaching. The 10 wt%Co/SBA-15 calcined at 400 °C for 5 h had the best performance, with the phenol removal of more than 98% and total organic carbon (TOC) reduction of approximately 98%. The complete mineralization of phenol degradation was demonstrated, and the degradation mechanism was analyzed. Moreover, effects of PMS dosages and phenol concentrations on phenol degradation were also investigated. The results show that the appropriately high PMS dosage and the low phenol concentration were favorable to phenol removal. During 25 runs of recycling tests, the powder Co/SBA-15 wrapped with polytetrafluoroethylene (PTFE) membranes always maintained high catalytic activity with the phenol removal more than 90% in 2 h and Co leaching of less than 85 μg/L. Consequently, it is an easily recyclable catalyst.

Stomatal closure and metabolic impairment under drought stress limits photosynthesis. The objective of this study was to determine major stomatal and metabolic factors involved in photosynthetic responses to drought and recovery upon re-watering in a C(3) perennial grass species, Kentucky bluegrass (Poa pratensis L.). Two genotypes differing in drought resistance, 'Midnight' (tolerant) and 'Brilliant' (sensitive), were subjected to drought stress for 15 days and then re-watered for 10 days in growth chambers. Single-leaf net photosynthetic rate (A), stomatal conductance (g(s)) and transpiration rate (Tr) decreased during drought, with a less rapid decline in 'Midnight' than in 'Brilliant'. Photochemical efficiency, Rubisco activity and activation state declined during drought, but were significantly higher in 'Midnight' than in 'Brilliant'. The relationship between A and internal leaf CO(2) concentration (A/Ci curve) during drought and re-watering was analyzed to estimate the relative influence of stomatal and non-stomatal components on photosynthesis. Stomatal limitation (Ls %), non-stomatal limitation (Lns %), CO(2) compensation point (CP) and dark respiration (Rd) increased with stress duration in both genotypes, but to a lesser extent in 'Midnight'. Maximum CO(2) assimilation rate (A(max)), carboxylation efficiency (CE) and mesophyll conductance (g(m)) declined, but 'Midnight' had significantly higher levels of A(max), CE and g(m) than 'Brilliant'. Maximum carboxylation rate of Rubisco (V(cmax)) and ribulose-1,5-bisphospate (RuBP) regeneration capacity mediated by maximum electron transport rate (J(max)) decreased from moderate to severe drought stress in both genotypes, but to a greater extent in 'Brilliant' than in 'Midnight'. After re-watering, RWC restored to about 90% of the control levels in both genotypes, whereas A, g(s), Tr and Fv/Fm was only partially recovered, with a higher recovery level in 'Midnight' than in 'Brilliant'. Rubisco activity and activation state restored to the control level after re-watering, with more rapid increase in 'Midnight' than in 'Brilliant'. The values of Ls, Lns, CP and Rd declined, and A(max), CE, V(cmax), J(max) and g(m) increased after re-watering, with more rapid change in all parameters in 'Midnight' than in 'Brilliant'. These results indicated that the maintenance of higher A and A(max) under drought stress in drought-tolerant Kentucky bluegrass could be attributed to higher Rubico activation state, higher CE and less stomatal limitation. The ability to resume metabolic activity (A(max), CE, Fv/Fm and Rubisco) was observed in the drought-tolerant genotype and is the most likely cause for the increased recuperative ability of photosynthesis. Incomplete recovery of photosynthesis upon re-watering could be attributable to lasting stomatal limitations caused by severe drought damage in both genotypes. Promoting rapid stomatal recovery from drought stress may be critical for plants to resume full photosynthetic capacity in C(3) perennial grass species.

Expression of dehydrin proteins may be induced or enhanced by environmental stresses that lead to cell dehydration. The objective of the this study was to investigate genetic variation in dehydrin protein accumulation in response to drought stress of whole-plants or dehydration of detached leaves and to identify dehydrins differentially expressed in bermudagrass ( Cynodon spp.) genotypes differing in drought tolerance. Plants of four hybrid bermudagrass ( Cynodondactylon L. × Cynodontransvaalensis L.) (‘Tifway’, ‘Tifdwarf’, ‘Tifeagle’, ‘Kan1’) and four common bermudagrass ( Cynodon dactylon ) (‘C299’, ‘Sportbermuda’, ‘H10’, and ‘H19’) genotypes were subjected to 14 d of drought stress and detached leaves of two genotypes were exposed to dehydration in growth chambers. Turf quality and leaf relative water content (RWC) decreased while electrolyte leakage (EL) increased during whole-plant drought stress for all genotypes, with more pronounced changes in each parameter for ‘C299’ and ‘Tifeagle’ than those for other genotypes (‘Tifway’, ‘Kan 1’, ‘Sportbermuda’, ‘H10’, and H19’), suggesting that the former two genotypes were more sensitive to drought stress than the other genotypes. During dehydration of detached leaves, relative water loss rate (RWL) was significantly lower in drought-tolerant ‘Tifway’ than in drought-sensitive ‘C299’. Immunoblotting analysis indicated that no dehydrin polypeptides were detected in all genotypes under well-watered conditions. A 24-kDa polypeptide was detected in ‘C299’ at 6 d of drought, but not in the other genotypes. The dehydrin polypeptides of about 14–74 kDa accumulated at 10 d of drought stress and in a range of RWL for detached leaves, and two dehydrins (31 and 40 kDa) exhibited differential accumulation in the drought-sensitive ‘C299’ and tolerant ‘Tifway’, as demonstrated by the whole-plant drought responses. The 31-kDa dehydrin polypeptide was present only in ‘Tifway’ and ‘H19’ at 10 d of drought stress, and accumulated with the increasing RWL in detached leaves of ‘Tifway’. The expression level of 40-kDa dehydrin polypeptides was greater in ‘Tifway’’ than in ‘C299’ at the same level of water deficit (from 10% to 65% RWL). These results indicated that the accumulation of 31- and 40-kDa dehydrins may contribute to drought or dehydration tolerance in warm-season bermudagrass.

Plants may survive drought stress by altering photosynthetic metabolism. This study was designed to investigate stomatal and metabolic changes associated with photosynthetic responses to drought for bermudagrass. A hybrid bermudagrass [Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt Davy, cv. Tifway] and a common bermudagrass (C. dactylon, cv. C299) were subjected to drought by withholding irrigation in growth chambers. Tifway maintained higher relative water content and lower electrolyte leakage than C299 under drought. Net photosynthetic rate (P n) and stomatal conductance (g s ) decreased, with more rapid decline in C299, but P n was significantly greater in Tifway than in C299, while g s did not differ between the two genotypes during 14 d of drought. Photochemical efficiency, ribulose-1,5-bisphosphate carboxylase:oxygenase (Rubisco) activity, and activation state declined during drought stress, but were higher in Tifway than in C299 within 14 d of treatment. Electrophoretic analysis revealed that at 14 and 18 d of drought, pyruvate orthophosphate dikinase (98 kDa) and Rubisco protein (49 kDa) exhibited severe degradation in C299 but to a lesser extent in Tifway. These results indicated that the superior drought resistance in Tifway could be attributed to higher photosynthetic capacity through the maintenance of higher metabolic activities, as manifested by more active Rubisco enzyme and Rubisco activase and more stable photosynthetic proteins.

Apomixis is a special asexual reproduction that plants can form embryo and produce progenies via seeds without sperm-egg fusion. Since apomitic embryo is a complete genetic clone of maternal parent without the participation of sperm, it is an ideal pathway to fix and utilize hybrid vigor and has unpredictable potential value in crop breeding, thus be called "the asexual revolution". According to the formation of the apomitic embryos, apomixis could be divided into three major types: diplospory, apospory and adventive embryony. This review is focused on the recent research progresses of related genes in the development of embryo, endosperm, and miosis, and several genes may involved in the regulation of apomitic development.

Citric acid may be involved in plant response to high temperature. The objective of this study was to investigate whether exogenous citric acid could improve heat tolerance in a cool‐season turfgrass species, tall fescue (Lolium arundinaceum), and to determine the physiological mechanisms of citric acid effects on heat stress tolerance. The grasses were subjected to four citric acid levels (0, 0.2, 2 and 20 mM) and two temperature levels (25/20 and 35/30 ± 0.5 ̊C, day/night) treatments in growth chambers. Heat stress increased an electrolyte leakage (EL) and malonaldehyde (MDA) content, while reduced plant growth, chlorophyll (Chl) content, photochemical efficiency (Fv/Fm), root activity and antioxidant enzyme activities (superoxide dismutase, SOD; catalase, CAT; peroxidase, POD). External citric acid alleviated the detrimental effects of heat stress on tall fescue, which was evidenced by decreased EL and MDA content, and improved plant growth under stress conditions. Additionally, the reduction in Chl content, Fv/Fm, SOD, POD, CAT and root activity were ameliorated in citric acid treated plants under heat stressed conditions. High temperature induced the expression of heat shock protein (HSP) genes, which exhibited greater expression levels after citric acid treatment under heat stress. These results suggest that exogenous citric acid application may alleviate growth and physiological damage caused by high temperature. In addition, the exogenously applied citric acid might be responsible for maintaining membrane stability, root activity, and activation of antioxidant response and HSP genes which could contribute to the protective roles of citric acid in tall fescue responses to heat stress.

Little is known about the interplay between Ca2+ and H2O2 signaling in stressed cool-season turfgrass. To understand better how Ca2+ and H2O2 signals are integrated to enhance grass acclimation to stress conditions, we analyzed the rearrangements of endogenous ion accumulation, antioxidant systems and secondary metabolism in roots, stems and leaves of perennial ryegrass (Lolium perenne L.) treated with exogenous Ca2+ and H2O2 under salinity. Ca2+ signaling remarkably enhanced the physiological response to salt conditions. Ca2+ signaling could maintain ROS homeostasis in stressed grass by increasing the responses of antioxidant genes, proteins and enzymes. H2O2 signaling could activate ROS homeostasis by inducing antioxidant genes but weakened Ca2+ signaling in leaves. Furthermore, the metabolic profiles revealed that sugars and sugar alcohol accounted for 49.5–88.2% of all metabolites accumulation in all treated leaves and roots. However, the accumulation of these sugars and sugar alcohols displayed opposing trends between Ca2+ and H2O2 application in salt-stressed plants, which suggests that these metabolites are the common regulatory factor for Ca2+ and H2O2 signals. These findings assist in understanding better the integrated network in Ca2+ and H2O2 of cool-season turfgrass’ response to salinity.

The details of DTGs associated with CIPK. (doc 114 KB)

Phytoremediation utilizing plants and microbes has been increasingly adopted as a green technology for cleaning up heavy metal polluted soils. Cd polluted soil and native bermudagrass from Liuyang and Zhuzhou in Hunan province of China were collected to investigate microbial diversity and isolate Cd resistant fungi, and then to determine the effect of Cd resistant fungi on Cd tolerance and transportation of bermudagrass. The functional diversity of microorganisms was evaluated using the BIOLOG Eco method. Cd-resistant fungi strain was isolated and identified as Aspergillus aculeatus based on the ribosomal internal transcribed spacer region sequence analysis. Bermudagrass was exposed to control, Cd only, and Cd plus A. aculeatus (Cd + A. aculeatus) with growth matrix (sawdust/sand = 3/1 in volume). Results indicated that Cd + A. aculeatus treated bermudagrass exhibited a higher photosynthetic activity compared to Cd only treated plants. Inoculation of A. aculeatus resulted in a decrease in stem and leaf Cd concentrations, to a greater extent for Cd-sensitive than for Cd-tolerant genotype. However, inoculation of A. aculeatus increased root Cd concentration under Cd stress conditions, significantly elevated soil pH, and decreased soil water-soluble Cd concentration. These results suggested that A. aculeatus might be potentially applied to improve Cd tolerance and to reduce Cd transportation to shoot of bermudagrass.

Cadmium (Cd) is one of the most toxic pollutants that caused severe threats to animal and human health. Bermudagrass is a dominant species in Cd contaminated soils, which can prevent Cd flow and spread. The objectives of this study were to determine the genetic variations in major physiological traits related to Cd tolerance in six populations of Bermudagrass collected from China, and to examine the genetic diversity and relationships among these accessions that vary in Cd tolerance using molecular markers. Plants of 120 accessions (116 natural accessions and 4 commercial cultivars) were exposed to 0 (i.e. control) or 1.5 mM CdSO4·8/3H2O for 3 weeks in hydroponic culture. Turf quality, transpiration rate, chlorophyll content, leaf water content and growth rate showed wide phenotypic variation. The membership function method was used to comprehensively evaluate Cd-tolerance. According to the average subordinate function value, four accessions were classified as the most tolerant genotypes and four accessions as Cd-sensitive genotypes. The trend of Cd tolerance among the six studied populations was as follows: Hunan > South China > North China > Central China > West South China and Xinjiang population. Phylogenetic analysis revealed that the majority of accessions from the same or adjacent regions were clustered into the same groups or subgroups, and the accessions with similar cadmium tolerance displayed a close phylogenetic relationship. Screening genetically diverse germplasm by combining the physiological traits and molecular markers could prove useful in developing Cd-tolerant Bermudagrass for the remediation of mill tailings and heavy metal polluted soils.

Metabolic responses to cadmium (Cd) may be associated with variations in Cd tolerance in plants. The objectives of this study were to examine changes in metabolic profiles in bermudagrass in response to Cd stress and to identify predominant metabolites associated with differential Cd tolerance using gas chromatography-mass spectrometry. Two genotypes of bermudagrass with contrasting Cd tolerance were exposed to 0 and 1.5 mM CdSO4 for 14 days in hydroponics. Physiological responses to Cd were evaluated by determining turf quality, growth rate, chlorophyll content and normalized relative transpiration. All these parameters exhibited higher tolerance in WB242 than in WB144. Cd treated WB144 transported more Cd to the shoot than in WB242. The metabolite analysis of leaf polar extracts revealed 39 Cd responsive metabolites in both genotypes, mainly consisting of amino acids, organic acids, sugars, fatty acids and others. A difference in the metabolic profiles was observed between the two bermudagrass genotypes exposed to Cd stress. Seven amino acids (norvaline, glycine, proline, serine, threonine, glutamic acid and gulonic acid), four organic acids (glyceric acid, oxoglutaric acid, citric acid and malic acid,) and three sugars (xylulose, galactose and talose) accumulated more in WB242 than WB144. However, compared to the control, WB144 accumulated higher quantities of sugars than WB242 in the Cd regime. The differential accumulation of these metabolites could be associated with the differential Cd tolerance in bermudagrass.

Salinity could damage cellular membranes through overproduction of reactive oxygen species (ROS), while antioxidant capacities play a vital role in protecting plants from salinity caused oxidative damages. The objective of this study was to investigate the toxic effect of salt on the antioxidant enzyme activities, isoforms and gene expressions in perennial ryegrass (Lolium perenne L.). Salt-tolerant 'Quickstart II' and salt-sensitive 'DP1' were subjected to 0 and 250 mM NaCl for 12 d. Salt stress increased the content of lipid peroxidation (MDA), electrolyte leakage (EL) and hydrogen peroxide (H₂O₂), to a greater extent in salt-sensitive genotype. Salt-stressed plant leaves exhibited a greater activity of superoxide dismutase (SOD, EC 1.15.1.1), peroxidase (POD, EC 1.11.1.7), ascorbate peroxidase (APX, EC 1.11.1.11) at 4d after treatment (DAT), but a lower level of enzyme activity at 8 and 12d, when compared to the control. Catalase (CAT, EC 1.11.1.6) activity was greater at 4 DAT and thereafter decreased in salt tolerant genotype relative to the control, whereas lower than the control during whole experiment period for salt-sensitive genotype. There were different patterns of five isoforms of SOD, POD and two isoforms of APX between two genotypes. Antioxidant gene expression was positively related to isoenzymatic and total enzymatic activities during 12-d salt-treated leaves of two genotypes, with a relatively higher level in salt-tolerant genotype. Thus, salt tolerance could be related to the constitutive/induced antioxidant gene, leading to more efficient enzyme stimulation and protection in perennial ryegrass.

Stomatal closure and metabolic impairment under drought stress limits photosynthesis. The objective of this study was to determine major stomatal and metabolic factors involved in photosynthetic responses to drought and recovery upon re-watering in a C(3) perennial grass species, Kentucky bluegrass (Poa pratensis L.). Two genotypes differing in drought resistance, 'Midnight' (tolerant) and 'Brilliant' (sensitive), were subjected to drought stress for 15 days and then re-watered for 10 days in growth chambers. Single-leaf net photosynthetic rate (A), stomatal conductance (g(s)) and transpiration rate (Tr) decreased during drought, with a less rapid decline in 'Midnight' than in 'Brilliant'. Photochemical efficiency, Rubisco activity and activation state declined during drought, but were significantly higher in 'Midnight' than in 'Brilliant'. The relationship between A and internal leaf CO(2) concentration (A/Ci curve) during drought and re-watering was analyzed to estimate the relative influence of stomatal and non-stomatal components on photosynthesis. Stomatal limitation (Ls %), non-stomatal limitation (Lns %), CO(2) compensation point (CP) and dark respiration (Rd) increased with stress duration in both genotypes, but to a lesser extent in 'Midnight'. Maximum CO(2) assimilation rate (A(max)), carboxylation efficiency (CE) and mesophyll conductance (g(m)) declined, but 'Midnight' had significantly higher levels of A(max), CE and g(m) than 'Brilliant'. Maximum carboxylation rate of Rubisco (V(cmax)) and ribulose-1,5-bisphospate (RuBP) regeneration capacity mediated by maximum electron transport rate (J(max)) decreased from moderate to severe drought stress in both genotypes, but to a greater extent in 'Brilliant' than in 'Midnight'. After re-watering, RWC restored to about 90% of the control levels in both genotypes, whereas A, g(s), Tr and Fv/Fm was only partially recovered, with a higher recovery level in 'Midnight' than in 'Brilliant'. Rubisco activity and activation state restored to the control level after re-watering, with more rapid increase in 'Midnight' than in 'Brilliant'. The values of Ls, Lns, CP and Rd declined, and A(max), CE, V(cmax), J(max) and g(m) increased after re-watering, with more rapid change in all parameters in 'Midnight' than in 'Brilliant'. These results indicated that the maintenance of higher A and A(max) under drought stress in drought-tolerant Kentucky bluegrass could be attributed to higher Rubico activation state, higher CE and less stomatal limitation. The ability to resume metabolic activity (A(max), CE, Fv/Fm and Rubisco) was observed in the drought-tolerant genotype and is the most likely cause for the increased recuperative ability of photosynthesis. Incomplete recovery of photosynthesis upon re-watering could be attributable to lasting stomatal limitations caused by severe drought damage in both genotypes. Promoting rapid stomatal recovery from drought stress may be critical for plants to resume full photosynthetic capacity in C(3) perennial grass species.