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Abstract Regrowth after defoliation is an essential mechanism of plant tolerance to grazing. In grasses, non-structural carbohydrates (NSC) contained in tiller bases constitute a major substrate for regrowth after defoliation. Using a multi-specific approach, the present study aimed at testing the effect of grazing intensity on NSC concentration in tiller bases. We selected five grazing-tolerant grass species (Agrostis stolonifera , Cynosurus cristatus , Hordeum secalinum, Lolium perenne and Poa trivialis) and collected plants in a grassland subjected to two cattle grazing intensities (intensive versus moderate) for years. We measured NSC concentrations (starch, fructans, sucrose, glucose and fructose) in tiller bases. We found that fructan and sucrose concentrations before the grazing season (April) were higher under intensive than moderate grazing. By contrast, no significant effect of the grazing intensity on these NSC concentrations in tiller bases remained at the end of the grazing season (October). These results suggest that the level of reserves available before the onset of disturbance caused by grazing as well as the reserve replenishment capacity during the grazing season are modified by the intensity of grazing. Highlights • Response of NSC concentrations to grazing intensity was measured for 5 grass species. • Before grazing season, fructan and sucrose concentrations were higher under intensive grazing. • After grazing season, there was no effect of grazing intensity on most NSCs. • Grazing intensity affects both formation and replenishment of NSC reserves. [ABSTRACT FROM AUTHOR]

Stolon is crucial for competitive ability, stresses tolerance, as well as carbohydrate and nutrition storage in plants. In our previous study, stolon growth as well as the content of both indole-3-acetic acid (IAA) and carbohydrates (glucose, sucrose, and fructose) in stolon nodes and internodes were found to be increased due to elevated CO 2 in stoloniferous creeping bentgrass. The objectives of this study were to determine the roles of auxin and the underlying mechanism of auxin in regulating elevated CO 2 -induced improvement on stolon growth and carbohydrate accumulation in stolon nodes and internodes of creeping bentgrass. Plants were treated with foliar applications of auxin (1-naphthalene acetic acid, NAA) and auxin transport inhibitor (2,3,5-triiodobenzoic acid, TIBA) at different concentrations to observe their effects on stolon growth. Hence, 10 mg⋅L−1 NAA and 100 mg⋅L−1 TIBA were selected as optimal concentrations to foliarly spray plants grown under either ambient CO 2 (400 µmol⋅mol−1) or elevated CO 2 (800 µmol⋅mol−1). Under water control and NAA treatments, stolon growth (stolon internode number, total stolon length, and stolon biomass) and contents of carbohydrate (glucose, sucrose, and fructose) were significantly increased by elevated CO 2 , but no positive effects were found in TIBA treatments in stolon nodes and internodes of creeping bentgrass. The results confirmed that IAA mediated elevated CO 2 -enhancement in stolon growth and carbohydrates accumulation in stolon nodes and internodes. The increase in IAA level was mainly associated with genes involved in auxin synthesis and transport in stolon nodes and internodes of creeping bentgrass. Our results would provide new insights for the rapid growth of stoloniferous plants under the scenario of continuous rise of the atmosphere CO 2 concentration. [ABSTRACT FROM AUTHOR]

Highlights • Elevated CO 2 stimulated stolon growth and proliferation in stoloniferous grass species exposed to drought stress. • CO 2 -enhanced stolon growth was due to increased formation of stolon nodes. • Enhanced stolon growth was due to metabolite changes for energy reserves, respiratory metabolism, and membrane maintenance. Abstract Stolon growth and proliferation are highly desirable traits for stoloniferous plant species. The objectives of this study were to elucidate the effects of elevated CO 2 on stolon growth in a stoloniferous perennial grass species, creeping bentgrass ( Agrostis stolonifera ), and identify metabolites and associated metabolic pathways for CO 2 -regulation of stolon growth under well-watered and drought conditions. Plants were grown under either ambient CO 2 concentration at 400 μmol mol−1 or elevated CO 2 concentration at 800 μmol mol−1 and subjected to well-watered control or drought stress by withholding irrigation in growth chambers. Elevated CO 2 led to increased number of stolon internodes and stolon length, and mitigated drought damages to creeping bentgrass, as manifested by the increased leaf relative water content and reduced electrolyte leakage. Elevated CO 2 increased stolon content of metabolites involved in carbohydrate reserves, respiratory metabolism, and membrane maintenance, including maltose, mannobiose, galactinol, 5-oxoproline, galacturonic acid, glycolic acid, gluconic acid, isoferulic acid, citric acid, threonic acid, lactic acid, succinic acid, and linolenic acid and linoleic acid. The CO 2 -reponsive metabolites for carbohydrate reserves, respiratory metabolism, and membrane maintenance could contribute to the enhanced stolon growth, thereby potentially facilitating rapid stand establishment and increasing shoot biomass production in perennial grass species. [ABSTRACT FROM AUTHOR]

Pressures on water availability for irrigation of turfgrasses continue in many parts of the United States as climate and weather patterns shift and populations increase. It is essential to understand underlying factors controlling water loss to more precisely predict irrigation requirements and develop new strategies for improving effective use of water. In this study, we investigate two key components of potential water loss from a bentgrass ( Agrostis stolonifera L.) system that have not previously been examined in detail: 1) water loss in darkness, and 2) water loss through evaporation directly from the soil. The experiments were conducted in controlled environment chambers with intact cores from the field. An automated gravimetric system and soil moisture probes allowed precise measurements of water loss over ranges of vapor pressure deficits (VPD). The gravimetric and soil probe results indicated that substantial evapotranspiration occurred in darkness, at rates 40 to 60% of that in the light across VPDs. Simulations using field weather data from dry and humid environments indicated nighttime water loss rates would be expected to be 30 to 40% of that in the light. Using cores treated with a fast-acting, desiccating herbicide that eliminated transpiration but kept core resistances intact, evaporation directly from the soil surface was estimated to account for 40% of total water loss in the light and 60 to 70% in the dark. The results, collectively, indicated that water loss in darkness must be separately accounted for to accurately estimate daily evapotranspiration totals and irrigation requirements. Furthermore, because of the very high potential for evaporative water loss in the light and dark, efforts to improve water use efficiencies in the turfgrass system should include strategies that regulate both transpiration by the plant and evaporation from the soil surface. [ABSTRACT FROM AUTHOR]

Abstract Turf provides an irreplaceable surface for recreational and sport activities in urban landscape. Sand-based rootzone is recommended for turf establishment because of its excellent compaction resistance. It is necessary to improve the water and nutrient retention of sand-based rootzone by soil amendments in maintaining healthy turf. The objective of this research was to evaluate the effects of rice-husk biochar on sand-based rootzone amendment and creeping bentgrass (Agrostsis stolonifera) establishment. The results showed that bulk density was linearly decreased in proportion to rice-husk biochar. Total porosity and capillary porosity, water retention, and saturated hydraulic conductivity were significantly increased in proportion to rice-husk biochar. Sand-based rootzone amended with 10% of rice-husk biochar promoted the seed germination and young seedling growth with the significantly higher growth rate, leaf emergence rate, shoot and root biomass, and turf coverage than the control. These results indicate that rice-husk biochar had superior characteristics to previous reported biochars in the sand-based rootzone amendment and could be used to improve soil physical properties and turf healthy in sports and recreation playgrounds. [ABSTRACT FROM AUTHOR]

Butanediol (BD) is a bacterial volatile compound which can activate induced-systemic resistance to diseases in plants, but its effects on abiotic stress tolerance are not well-known. The objectives of this study were to examine physiological effects of BD on heat tolerance in creeping bentgrass and to identify BD-responsive metabolites and genes contributing to effects of BD on heat tolerance. Creeping bentgrass plants (cv.’ PennA4’ and’ Penncross’) were treated with 2,3 -butanediol or water through foliar spray and were exposed to heat stress (35/30 °C, day/night) or optimal temperature (20/15 °C) in growth chambers. Creeping bentgrass plants treated with BD exhibited improved heat tolerance, demonstrated by higher visual quality and leaf photochemical efficiency when compared with the untreated control plants. Real-time PCR revealed that BD application resulted in up-regulation of genes related to cell elongation, metabolism, and stress responses in plants exposed to heat stress. Metabolite profiling identified a number of organic acids, sugars and sugar acids that accumulated due to BD treatment under heat stress. Results of the current study suggest that BD is effective in improving heat tolerance in creeping bentgrass, mainly through the enhancement of gene expression and metabolite accumulation involved in energy metabolism and stress signaling. [ABSTRACT FROM AUTHOR]

Brown patch, caused by Rhizoctonia solani , is a serious disease in Agrostis stolonifera . 2, 3-butanediol (2, 3-BD) is the major component of volatile organic compounds and was found to initiate induced systemic resistance (ISR). To investigate the induced resistance mechanism of 2, 3-BD, we examined the effects of resistance by area affected, along with changes in the content of phytohormones (Zeatin (ZT), Abscisic Acid (ABA) and Indole-3-Acetic Acid (IAA)), the activities of three phenylpropanoid metabolic enzymes (Phenylalaninammo-Nialyase (PAL), Chalcone Isomerase (CHI) and 4-Coumarate:Coenzyme A Ligase (4CL)) and the level of secondary metabolites (total phenols, flavonoid and lignin). The result showed that 2, 3-BD treatment at 250 μmoL/L had the best induction effect with the area affected decreased from 95% of the control to 55%. Compared to the controls, treatment with 250 μmoL/L 2, 3-BD induced higher levels of PAL, CHI and 4CL activity and increased total phenols, flavonoid and lignin levels. While 2, 3-BD treatment decreased the content of ZT and ABA but increased the content of IAA compared to controls. This study provides a basis for elucidating the mechanism of 2, 3-BD as a new plant disease control agent. [ABSTRACT FROM AUTHOR]

Creeping bentgrass ( Agrostis stolonifera ), an important turfgrass on golf course putting greens can become plagued by bacterial etiolation disease caused by Acidovorax avenae subsp. avenae ( Aaa ). There are no known pesticides that have been shown to be effective in managing this disease. This series of hydroponic growth chamber studies investigated whether pre-treating plants with SA or JA could be effective in reducing disease symptoms of Aaa in creeping bentgrass ‘Penn-A4’ ( Aaa sensitive) and ‘Tyee’ (more tolerant). The treatments included foliar application of 10 μmol/L SA, 20 μmol/L SA, 0.5 mM JA in 0.02% ethanol and 2 mM JA in 0.02% ethanol prior to exposure to heat stress (35 °C) and optimal temperature (23 °C) with or without Aaa inoculation. Physiological measurements included turf quality (TQ), leaf and root electrolyte leakage, chlorophyll content (CHL), photochemical efficiency and root viability. No significant differences were detected in either cultivar due to chemical or heat treatment alone, which indicates chemical treatments had specific effects on plant responses to bacteria and were not confounded by plant heat stress symptoms. SA application reduced Aaa disease symptoms of both cultivars under both optimal and high temperature treatments. At both 23 °C and 35 °C, the severity of disease in plants treated with SA was less than in control plants based on all measurements in our experiment. Creeping bentgrass ‘Tyee’ treated with JA showed significantly higher TQ than control plants at 35 °C. ‘Penn-A4’ treated with JA only showed significantly higher CHL than control at 23 °C. SA and JA treatments could be viable methods to induce creeping bentgrass tolerance of bacterial pathogens; however, field testing of these methods is needed. [ABSTRACT FROM AUTHOR]

Drought stress induces leaf senescence while cytokinins (CK) and melatonin (ME) play roles in regulating leaf senescence. The objectives of this study were to determine whether ME alone or interacting with CK could suppress drought-induced leaf senescence through mediating CK pathways and chlorophyll catabolism in creeping bentgrass ( Agrostis stolonifera ). Plants of wild type (‘WT’) (cv. ‘Penncross’) or a transgenic line (‘S41′) harbouring isopentenyltransferase ( ipt ) gene were foliar sprayed with either 20 μM ME or water and exposed to drought stress for 14 d in growth chambers. Exogenous applied ME increased visual quality, photochemical efficiency, chlorophyll content and relative water content, while it suppressed leaf electrolyte leakage, lipid peroxidation and hydrogen peroxide production in both WT and ipt -transgenic plants. Cytokinin-signaling and synthesis genes were also significantly up-regulated in ME-treated ipt -transgenic plants. Dehydration responsive genes ( JUB1 and DREB2A ) were up-regulated and chlorophyll-degradation genes ( Chlase , PPH and Chl-PRX ) and enzyme activities were significantly down-regulated by ME application. Endogenous melatonin content and ME-biosynthesis genes ( TDC1 , SNAT1 , and COMT ) expression increased in ipt -transgenic plants with ME treatment. ME-alleviation of drought-induced leaf senescence in creeping bentgrass was associated with the down-regulation of chlorophyll catabolism and the synergistically interaction with CK-synthesis gene and signaling pathways. [ABSTRACT FROM AUTHOR]

Simulated golf greens were used to test the growth of creeping bentgrass ( Agrostis stolonifera L. ‘007′) receiving suboptimal chemical fertilization in sand based substrates amended with 15% peat (control), a commercial biochar, a commercial biochar-compost mixture (CarbonizPN-Soil), or seven formulated biochar-compost mixtures. Physical and chemical properties including pH, bulk density, pore space, compaction distance, nutrient content and water/nutrient retention capacity varied among the mixtures. The heights, root lengths, and fresh and dry weights of creeping bentgrass plants grown in polyvinyl chloride tubes containing the different substrate mixtures mimicking a United States Golf Association root zone were evaluated and compared. Forty days after seeding, plants grown in 5% biochar and 10% Metropolitan Water Reclamation District of Greater Chicago biosolids had significantly greater fresh weights, dry weights, and shoot heights than the control. Dry weights and shoot heights were also higher than the control in bentgrass grown in the 15% CarbonizPN-Soil mixture. Based on these results the addition of these two biochar-organic amendment mixtures would improve overall plant growth in sand-based root zones under reduced chemical fertilization. [ABSTRACT FROM AUTHOR]

Maintaining quality golf course turf often requires irrigation and application of fertilizer. The transport of excess nutrients with runoff water from highly managed and fertilized biological systems to surrounding surface waters has been shown to result in enhanced algal blooms and promotion of eutrophication. Environmental stewardship includes looking for new approaches to reduce adverse environmental impacts of current practices. One strategy is to replace traditional turfgrass with low-maintenance turfgrass species. Fescue grasses have been shown to provide characteristics desirable for golf course fairways. Thus side-by-side studies comparing runoff from plots planted in creeping bentgrass (CGB) or fine fescue mixture (FFM), similarly managed as a golf course fairway, were conducted to measure runoff volumes and the amount of ammonium nitrogen (NH 4 -N) and nitrate nitrogen (NO 3 -N) transported off-site with runoff. Greater runoff volumes and mass of applied nutrients were measured in the runoff from the FFM, representing a 38% and 56% median increase in the off-site mass transport of NH 4 -N and NO 3 -N with surface flow. Shoot density, thatch depth and soil moisture were the most important factors related to runoff volume. Results of this research will be useful to grounds superintendents and researchers for selecting and developing management strategies to improve environmental stewardship of managed turf while providing desired turf quality. [ABSTRACT FROM AUTHOR]

Acidovorax avenae subsp. avenae ( Aaa ) is a pathogen that can cause bacterial etiolation of creeping bentgrass ( Agrostis stolonifera ). In vitro and in vivo studies of this pathosystem for phytohormone analysis were performed. Aaa and a non-pathogenic, negative control Pseudomonas aureofaciens ( Pa) were cultured at room temperature (20–22 °C) for 14 days. For in vivo studies, Aaa infected and uninfected creeping bentgrass ‘Tyee’ and ‘Penn-A4’ were grown in hydroponics under optimal 23/20 °C day/night temperatures and heat stress 35/30 °C conditions in growth chambers. Bacterial culture or plant samples were taken for analysis of phytohormones: gibberellic acid isoforms (GA1, GA3, GA4, and GA20), jasmonic acid (JA), salicylic acid (SA), indole-3-acetic acid (IAA), zeatin riboside (ZR), and abscisic acid (ABA). GA1, GA3, GA4 and IAA were detected in some Aaa cultures but not in Pa . ‘Penn-A4’ was more Aaa sensitive under high temperature than ‘Tyee’. ‘Tyee’ infected with Aaa at high temperatures showed higher JA content in all plant tissues, higher SA in stolons and roots, and less GA3 and GA20 in leaf and stolon tissues than ‘Penn-A4’ in the same conditions. Differential GA isoform accumulation produced by Aaa could contribute to disease severity and JA and SA accumulation may contribute to disease tolerance. [ABSTRACT FROM AUTHOR]

Efficacy of foliar applied fungicides following simulated rainfall for the control of dollar spot (caused by Sclerotinia homoeocarpa F.T. Bennett) was assessed in a two-year field study on creeping bentgrass ( Agrostis stolonifera L.) turf maintained as a golf course fairway. The study was conducted as a randomized complete block design with a factorial arrangement. Fluazinam (0.8 kg a.i. ha −1 ), chlorothalonil (3.79 kg a.i. ha −1 ) or iprodione (1.5 kg a.i. ha −1 ) were applied, then subjected to simulated rainfall (2.54-mm) at intervals of 15-, 30-, 60-min post-application, or no simulated rain. In most cases, simulated rainfall occurring ≤60 min post-application had greater disease than no rain plots; however, few differences occurred among rainfall intervals ≤60 min. Fluazinam provided the greatest dollar spot reduction regardless of simulated rainfall interval throughout the study. Chlorothalonil was most susceptible to losses in efficacy due to simulated rainfall, resulting in the greatest disease incidence of those fungicides evaluated. Iprodione was comparable to chlorothalonil during high disease pressure, although during moderate disease pressure it controlled dollar spot for approximately 7 days before disease increased in plots receiving simulated rain compared to those without simulated rain. These data demonstrate that efficacy of fungicides applied for dollar spot control are affected by rain, and differ in their ability to control disease following post-application rain events. Fluazinam, a recently introduced contact fungicide for use on turfgrass, can provide improved control compared to chlorothalonil or iprodione when rain is eminent. [ABSTRACT FROM AUTHOR]

Preventive, watered-in applications of DMI fungicides provide control of several soilborne turfgrass diseases on golf putting greens. The objectives of this two-year field study were to determine the impact of these applications on foliar diseases, and evaluate the impact of application timing of paclobutrazol, a plant growth regulator, on disease severity and turfgrass quality. Triadimefon (1.58 kg a.i. ha −1 ), tebuconazole (0.82 kg a.i. ha −1 ), metconazole (0.43 kg a.i. ha −1 ), and triticonazole (0.64 kg a.i. ha −1 ), were applied twice in late April and May and immediately watered in to the soil profile with 5 mm of post application irrigation. Paclobutrazol (0.28 kg a.i. ha −1 ) was applied alone, in a tank-mix with the fungicide application, 7 days or 14 days after the fungicide application. Overall dollar spot severity, assessed as area under the disease progress curve (AUDPC), was significantly lower in fungicide treated plots than non-treated plots in both trial years. The date of threshold symptom observation (≥5 infection centers per plot), however, was not different between fungicide treated and non-treated plots in 2011. Triadimefon treated plots had lower AUDPC values than other fungicide treatments. Brown patch severity was not significantly different among treatments. Paclobutrazol applied alone did not reduce dollar spot or brown patch severity, however, paclobutrazol + fungicide treatments resulted in lower dollar spot severity than plots treated with fungicide alone. Short-lived phytotoxicity (bronze discoloration) was observed in plots treated with triadimefon or paclobutrazol + fungicide. Spring preventive fungicide applications targeted at soilborne disease control also provided residual control of dollar spot in this study. [ABSTRACT FROM AUTHOR]

Organic amendments such as peat moss and various composts are typically added to sand-based root zones to increase water and nutrient retention. However, these attributes are typically lost within a few years as these amendments decompose. Biochar is a high carbon, porous coproduct produced from the pyrolysis of phytobiomass. Its unique porosity gives it excellent water and nutrient retention properties. Additionally, unlike other organic amendments, biochar is extremely resistant to microbial decomposition. Pure calcareous sand (control) or mixtures of three different biochars and sand at 1, 5 and 10% volume biochar/total volume were tested. Bulk densities decreased while percent pore space increased with the addition of all three biochars at all of the addition rates. Water retention was greater than the control in all but one of the biochar treatments, and several of the biochar mixtures had values for compaction resistance similar to pure sand. Creeping bentgrass ( Agrostis stolonifera L. ‘Pure Distinction’) plant heights, root lengths, and fresh and dry weights were evaluated in mixtures grown hydroponically in polyvinyl chloride tubes (112 mm outside diameter × 99 mm inside diameter) filled 30 cm deep with 1 cm diameter pea gravel, over which 30 cm of either pure sand or sand/biochar mixtures were added to mimic a United States Golf Association root zone. Five weeks after seeding, plants grown in several of the biochar mixtures had significantly greater fresh and dry weights, shoot heights and root lengths than the control. Based on these results it appears that the addition of certain biochars would improve water retention and increase overall plant growth in sand-based root zones. [ABSTRACT FROM AUTHOR]

Bacterial etiolation, caused by Acidovorax avenae and Xanthomonas translucens , has become a widespread problem in turfgrass throughout the U.S. Various management tactics are used in managing this disease and differ among turfgrass managers. The use of biostimulants and trinexapac-ethyl (TE) has become a staple in putting green management and many products have been associated with etiolation outbreaks. Experiments performed in field and controlled environments evaluated the impact of commercial biostimulants and TE on etiolation of creeping bentgrass ( Agrostis stolonifera L. c.v. ‘Penn A-1’) caused by both A. avenae and X. translucens. In the field, a factorial study was arranged as a split-plot randomized complete block design with 4 replications. The main plot consisted of biostimulants (Knife Plus, CytoGro, Astron, Nitrozyme, PerkUp, BioMax, and none) applied at label rates while the subplot treatments consisted of TE application frequency (0.049 kg ha −1 applied at 7 d, 14 d, and none). For controlled environment experiments, biostimulant and TE treatments were arranged in a randomized complete block design with 4 replications. Bacterial etiolation was measured regularly when present using a grid count to determine the percent area exhibiting etiolation in the field while etiolated turfgrass plants were counted individually in controlled environments. Turf quality was also rated using a scale of 1–9 with 1 = completely dead, 9 = best, and 5 = minimum acceptable turf quality for all experiments. Biostimulant treatments did not have a significant effect on etiolation caused by either bacterium. Trinexapac-ethyl decreased etiolation caused by X. translucens and increased etiolation caused by A. avenae. These results support the necessity of identifying bacteria associated with etiolation as variable effects were observed with TE treatments. These factors should be considered when developing plant growth regulator programs if etiolation is problematic. Future research to evaluate phytohormone production in these bacteria may improve our understanding of etiolation development while improving methods for control. [ABSTRACT FROM AUTHOR]

Atmospheric carbon dioxide (CO2) concentration has been increasing and is predicted to further increase in the future along with the climatic changes which may increase evaporative demand on plants. Elevated CO2 concentration has a positive effect on plant growth and tolerance to drought stress with regard to above-ground plant organs but limited information is available describing effects of elevated CO2 concentration on root growth and the subsequent impact on plant responses to drought stress. The specific proteins and metabolic pathways controlling root functions regulated by CO2 that may contribute to improved root growth and drought stress damages are not well understood. In this study with creeping bentgrass (Agrostis stolonifera cv. Penncross), a widely-used perennial grass for forage and turf, elevated CO2 concentration (800 μL L-1) promoted root proliferation compared to the ambient CO2 concentration (400 μL L-1). Under drought stress, roots developed under elevated CO2 concentration were able to maintain improved membrane integrity as demonstrated by lower electrolyte leakage. Proteins were extracted from roots of creeping bentgrass exposed to both elevated and ambient CO2 concentration under well-watered and drought stress conditions. Drought- and CO2-responsive proteins were separated with two-dimensional electrophoresis and identified using mass spectrometry. Root proteins were mainly classified into the following functional categories: cellular growth, energy, metabolism, and defence. The improved root growth and mitigation of drought stress in creeping bentgrass under elevated CO2 could be mainly associated with alteration of proteins governing primary metabolism involving nitrogen metabolism (glutamine synthetase), energy metabolism involving respiration (glyceraldehyde-3-phosphate dehydrogenase), and stress defence by strengthening antioxidant metabolism (ascorbate peroxidase, superoxide dismutase, and catalase) and chaperone protection (HSP81-1). [ABSTRACT FROM AUTHOR]

Abstract: Thatch is a tightly intermingled layer of dead and living organic matter present below the turf aerial shoots and above the soil. Excess thatch can be a major problem on many turfgrass sites, especially golf greens. A greenhouse experiment was conducted on dead potted bentgrass (Agrostis stolonifera L.) to eliminate the confounding effects of continual growth as we attempted to determine the efficacy of a ligninolytic enzyme, laccase, along with mediator guaiacol in reducing organic matter content in thatch layer biomass. Laccase was added bi-weekly at 0, 2.06, and 20.6 units of activity cm−2 with and without guaiacol (2-methoxyphenol) and sampling was performed after two and six months. Parameters investigated included thickness of thatch layer, organic matter, saturated hydraulic conductivity, lignin content, and structural sugars. After two months of treatment application, thatch layer thickness was reduced by 22.1% and extractive-free acid-soluble lignin by 12.3%. Lignin content decreased by 6.5% and saturated hydraulic conductivity improved to 124.7% higher than the non-treated control. No reduction in organic matter and sugar content was observed after two months of treatment application. After six months, thatch layer thickness was reduced by 62.0%, total organic content (0–2.5 cm) by 24.7%, and total sugar content by 29.3%. Extractive-free acid-insoluble lignin and saturated hydraulic conductivity increased by 17.1 and 70.8%, respectively in comparison to the control. These positive responses suggest laccase treatments could expedite organic matter degradation in the thatch layer of creeping bentgrass. [Copyright &y& Elsevier]

Abstract: High summer temperatures often cause damage to bentgrass on putting greens in transition zone regions. One of the most damaging effects is a depression of rooting. Although heat stress effects on plant functions are considered as a main reason for the damage, heat stress also may be related to organic matter (OM) accumulation and poor gas exchange into the rhizosphere. The OM accumulation and the often-observed root dieback suggest that soil microbial processes play a role in summer bentgrass decline. In this study, the impact of high temperature on soil microbial properties and enzyme activities was examined using creeping bentgrass (Agrostis stolonifera) growing in a phytotron controlled environment chamber. The high temperature exposures (34/30°C versus 22/18°C for controls) lasted for four weeks and the bentgrass cultures received mineral N at two rates. Our working hypothesis was that not only did high temperatures stimulate overall soil microbial and enzyme activity but also selectively modified microbial catabolic functions. To test this hypothesis, we compared temperature sensitivities and Q 10 values of microbial substrate utilization patterns using a Biolog plate approach and soil enzyme activities. The results indicated that soil enzyme activities had similar responses to assay temperatures and their Q 10 values averaged ∼2 with changes of laboratory assay temperatures from 12 to 22°C and from 22 to 34°C. Such positive responses of microbial activity to high temperatures were supported by parallel increases in rates of microbial substrate utilization. Total substrate availability in Biolog plates also increased with laboratory assay temperatures. This enhancement could not be explained by the overall stimulation of high temperature on microbial activity, but instead by selective modification of microbial community functions. Nitrogen fertilization significantly changed soil biological activities. Phenol oxidase activity was reduced by the high rate of N fertilization, whereas β-glucosidase and β-glucosaminidase activities were increased. Interactions on soil enzyme activities between growth chamber temperatures and N fertilization rates also occurred. Soil peroxidase activity was ∼three-fold greater for bentgrass subjected to heat stress and the low rate of N fertilization. Our results indicated that summer heat stress and the associated increases in root and OM degradation in bentgrass systems are related with overall temperature stimulations on soil microbial and enzyme activities as well as with modifications in functional components of the microbial community. [Copyright &y& Elsevier]

Abstract: It has been previously reported that either nitrogen (N) or cytokinin (CK) applications can alleviate heat stress injury on creeping bentgrass, with some studies reporting enhanced antioxidant metabolism being related to stress protection. The objective of this research was to investigate the simultaneous effects of CK and N on the antioxidant enzyme activity and isoforms of heat stressed creeping bentgrass. ‘L-93’ creeping bentgrass treated with three rates of CK (trans-zeatin riboside, tZR, 0, 10 and 100μM, designated by CK0, 10, and 100) and two nitrogen rates (2.5 and 7.5kgNha−1 biweekly, low and high N) in a complete factorial arrangement was maintained in a 38/28°C (day/night) growth chamber for 28d and then harvested. Grass grown at high N (averaged across CK rates) had higher O2 − production, H2O2 concentration, and malondialdehyde content in roots. The activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), and guaiacol peroxidase (POD) in roots were enhanced 19%, 22%, and 24%, respectively, by high N relative to low N. Twenty-eight days of heat stress resulted in either the development of new isoforms or enhanced isoform intensities of SOD, APX, and POD in roots compared to plant responses prior to heat stress. However, no apparent differences were observed across treatments. Both SOD and POD showed different isoform patterns between roots and shoots, suggesting the function of these isoforms could be tissue specific. Interestingly, no CK effects on these antioxidant parameters were found in this experiment. These results demonstrate the impacts of N on antioxidant metabolism of creeping bentgrass under heat stress with some differences between roots and shoots, but no simultaneous impacts of CK and N. [Copyright &y& Elsevier]

Abstract: Nitrogen fertilization is a key factor of the aesthetics and playability for golf greens. Nitrogen fertilization management is based on predetermined scheduled applications, set rates, or expected improvement in visual quality and green speed. As a consequence, the objective of this study was to obtain seasonal N application models (algorithms) based on remote sensing, optimizing playability and aesthetic quality. A 3-yr field study under Mediterranean conditions was conducted on an experimental ‘L-93’ creeping bentgrass (Agrostis stolonifera L.) USGA green, to examine effects of seasonal N fertilizer rates on color, clipping yields, and ball roll (green speed). The remote sensors used were a digital camera and reflectance meter (FieldScout CM1000 Chlorophyll Meter). From digital photographs, a dark green color index (DGCI) was calculated. All data were normalized (relative). For all seasons, a third-order polynomial response model was the best when using a CM1000 and a digital camera. Clipping yields and ball roll regressions were linear, increasing and decreasing when the N fertilizer rate increased, respectively. Ball roll and clipping relative values were correlated with both sensors. To fit a seasonal optimum N fertilizer rate model as a function of remote sensors and the other measured parameters, the intersection of models obtained from relative values of CM1000 and digital camera with ball roll and clipping was calculated, but ball roll was considered the most suitable. The model of the digital camera with automatic settings was less accurate and underestimated the optimum N rate. However, because the actual values of digital camera and CM1000 were correlated, converting DGCI values and applying CM1000 models enabled the obtaining of practically the same N fertilizer applications. A practical application procedure of these seasonal models for an entire golf course was also shown. Actual N recommendation applications with a quick remote diagnosis (CM1000) for creeping bentgrass golf green are feasible under similar management practices in Mediterranean environments. A digital camera can also be used successfully, but it should be better when its analysis is based on CM1000 models. [Copyright &y& Elsevier]

Abstract: Protein metabolism and expression play important role in plant adaptation to water stress. The objectives of this study were to examine proteomic responses to water stress induced by polyethylene glycol (PEG) in creeping bentgrass (Agrostis stolonifera L.) leaves and to identify proteins associated with stress tolerance. Plants of two cultivars (‘Penncross’ and ‘Penn-A4’) differing in water stress tolerance were grown in sand irrigated daily with water (control) or PEG solution (osmotic potential of −0.66MPa) to induce water stress, for 28d in growth chambers. Shoot extension rate, relative water content and cell membrane stability were measured to compare drought tolerance between the two cultivars. All parameters maintained at a significantly higher level in ‘Penn-A4’ than in ‘Penncross’ under PEG treatment. After 28d of water stress, proteins were extracted from leaves and separated by difference gel electrophoresis. Among 56 stress-responsive protein spots, 46 were identified using mass spectrometry. Some proteins involved in primary nitrogen and carbon metabolism were down-regulated by PEG-induced water stress in both cultivars. The abundance of antioxidant enzyme proteins (ascorbate peroxidase, catalase and glutathione-S-transferase) increased under water stress, particularly ascorbate peroxidase in ‘Penn-A4’. The abundance levels of actins, UDP-sulfoquinovose synthase and glucan exohydrolase were greater in ‘Penn-A4’ than in ‘Penncross’ under PEG treatment. Our results suggest that proteins involved in membrane synthesis, cell wall loosening, cell turgor maintenance, and antioxidant defense may play roles in perennial grass adaptation to PEG-induced water stress. [ABSTRACT FROM AUTHOR]

Abstract: Temperature and vapor pressure deficit (VPD) effects on turfgrass growth are almost always confounded in experiments because VPD commonly is substantially increased in elevated-temperature treatments. The objective of this study as to examine specifically the influence of VPD on transpiration response of four ‘warm-season’ (C4) and four ‘cool-season’ (C3) turfgrasses to increasing VPD at a stable temperature (29.3±1.5°C). Although transpiration rates were noticeably lower in C4 grasses, transpiration rates increased linearly in response to increasing VPD across the range of 0.8–3.0kPa. In contrast, transpiration rates of C3 increased sharply with increasing VPD across the range of low VPDs, but became constrained at higher VPDs (>1.35kPa). Restricted transpiration rate at elevated VPD was most evident in Agrostis palustris and Lolium perenne. Assuming restricted transpiration rates reflect a limitation on leaf CO2 uptake, these results indicate that the commonly observed decline in growth of C3 (and success of C4) grasses at elevated temperature may include a sensitivity to elevated VPD. [Copyright &y& Elsevier]

Abstract: Single seed origin creeping bentgrass (‘Penncross’) clonal lines were screened to find genetic heterogeneity, which reflected diversity of phenolic production linked to cold stress within a cross-pollinated cultivar. In this study, total soluble phenolic and antioxidant activity varied among 20 creeping bentgrass clonal lines, confirming wide heterogeneity in this cross-pollinated species. Correlations between phenolic content and proline-associated pentose phosphate pathway were also found among the clonal lines. The active metabolic role of proline in cellular metabolic adjustment to cold stress and its support for likely energy synthesis via mitochondrial oxidative phosphorylation was inferred in creeping bentgrass clonal lines based on the activity of proline dehydrogenase. Results of photochemical efficiency of these clonal lines after cold temperature treatment (4°C) also indicated a close association between stress tolerance and proline-associated pentose phosphate pathway regulation for phenolic biosynthesis and antioxidant response. This study provides a sound metabolic based rationale to screen bentgrass clonal lines for enhanced cold stress tolerance. [Copyright &y& Elsevier]

Abstract: In this experiment, three grasses, bermuda grass (Cynodon dactylon), bent grass (Agrostis palustris Huds.), lawn grass (Zoysia japonica), and a shallow-rooted legume, white clover (Trifolium repens L.) were planted into uncontaminated soil and dibenzofuran (DBF)-contaminated soil. The germination rates of all plants were investigated using contaminated soils to evaluate their sensitivities to DBF. During 2 months of growth, the root biomass and heterotrophic microbial numbers were measured in order to evaluate the potential of remediation. Furthermore, the number of DBF-degrading bacteria was counted to evaluate plants that enhance the microbial DBF degradation potential in contaminated soil. The DBF-removal performance of four plant species was also compared. Regardless of the contamination of DBF, white clover had not only the highest root biomass, but also the highest DBF-degrading bacterial numbers compared to those of the other three grasses. Moreover, white clover-planted contaminated soil exhibited the highest rate of DBF removal among all tested plants. These results suggest that microbial populations capable of degrading DBF were selectively increased by the addition of DBF in the rhizosphere, and also indicate that the presence of plants significantly enhances the reduction of DBF in soils. Based upon these results, white clover was selected for the further investigation of the phytoremediation of dioxin-contaminated soil. [Copyright &y& Elsevier]

Abstract: Heat stress is a major factor limiting the growth of cool-season grasses in warm climatic regions by affecting many physiological processes, including protein metabolism. Protein degradation often occurs with increasing temperatures, but certain specific proteins such as heat shock proteins (HSPs) may be induced or enhanced in their expression under supraoptimal temperatures. The objectives of this study were to determine the critical temperature that causes protein induction or degradation in two Agrostis grass species differing in heat tolerance and to compare protein profiles between the two species under different temperature regimes. Plants of heat-tolerant Agrostis scabra and two cultivars of heat-sensitive Agrostis stolonifera (‘L-93’ and ‘Penncross’) were exposed to constant day/night temperatures of 20, 30, 35, 40, or 45°C for 14d. Leaf photochemical efficiency (Fv/Fm), chlorophyll and carotenoid contents, and soluble protein content declined with increasing temperatures. The decreases were the least severe for A. scabra, intermediate for ‘L-93’, and the most severe for ‘Penncross’, indicating interspecific and intraspecific variations in heat tolerance in Agrostis species. Protein degradation was observed at 30–45°C in both cultivars of A. stolonifera, and at 40–45°C in A. scabra. HSPs were induced or enhanced at 35–45°C in ‘L-93’ and A. scabra, and at 40–45°C in ‘Penncross’. Immunoblotting also revealed stronger expressions of HSP60 and HSP70 in A. scabra or ‘L-93’ than in ‘Penncross’ at 35–45°C after 3d. The results suggested the superior heat tolerance of Agrostis grass species and cultivars could be attributed to the early induction of HSPs, particularly small molecular weight (23kDa), at a lower level of heat stress and the maintenance of protein thermostability, particularly high-molecular weight proteins (83kDa and large units of Rubisco). [Copyright &y& Elsevier]

Abstract: Agrobacterium-mediated transformation provides a powerful tool for plant biotechnology. Great efforts have been made to unravel the underlying mechanisms of T-DNA integration. Creeping bentgrass (Agrostis palustris Huds.), an economically important turfgrass species, has been widely studied for genetic transformation. In order to characterize T-DNA integration in this species, we analyzed T-DNA junction sequences in transgenic bentgrass obtained by transformation with A. tumefaciens strain EHA101 carrying a pPZP201-derived plasmid. Using T-DNA specific primers, inverse polymerase chain reaction (IPCR) and standard PCR were performed to identify T-DNA/plant junctions and T-DNA/T-DNA junctions, respectively. Sequence comparisons revealed that T-DNA right border (RB) termini were more intact, represented by a smaller range of border deletions and no backbone integration, compared to T-DNA left border (LB) termini. Multiple T-DNA arrays inserted at a single chromosome locus were detected in various configurations. It was shown that the formation of the multiple T-DNA arrays was governed by illegitimate recombination (IR), with sequence microsimilarities over and/or close to the T-DNA breaking points. It was also demonstrated that the fusion of two T-DNA copies was frequently associated with the formation of filler DNA and significant T-DNA truncation. Compositional analysis over the bentgrass sequences revealed a similar A/T (A + T) content but a polarized distribution of A and T associated with LB flanking sequence tags (FSTs) and RB FSTs, which was further documented in Arabidopsis T-DNA FSTs. DNA folding analysis on T-DNA FSTs suggested that the T-DNA target region had a potential of forming secondary structures, which may designate an active region for T-DNA integration. The results presented in this study shed new light on microsimilarity-based illegitimate recombination and advance our understanding of T-DNA integration. [Copyright &y& Elsevier]

High soil temperature is a critical factor limiting growth of cool-season grasses. This study was designed to examine changes in water, nutritional, and hormonal status in response to high soil temperature for creeping bentgrass (Agrostis stoloniferavar. palustris) and to compare the sensitivity of those parameters to high soil temperatures. Plants of ‘Penncross’ were exposed to 35 °C soil temperature (heat stress) or 20 °C (control) in water baths while air temperature was maintained at 20 °C in growth chambers. Turfgrass quality, shoot growth rate, and root biomass decreased below the control levels at 15, 15, and 10 days of heat stress, respectively, while root mortality increased above the control level at 5 days of heat stress. Relative water content (RWC) of leaves decreased below the control level at 15 days of heat treatment. Root N content increased while P and K content did not change over time at 35 °C. Shoot N, P, and K content decreased below the control level at 15, 15, and 10 days of heat stress, respectively. Root abscisic acid (ABA) content decreased below the control level at 10 days while shoot ABA content increased above the control level at 5 days. The content of cytokinins (zeatin (Z) and zeatin riboside (ZR), dihydrogen zeatin riboside (DHZR), and isopentenyl adenosine (iPA)) decreased below their respective control levels as early as 5 days of heat stress for roots and 10 days for shoots. The decline in cytokinin content was also more dramatic than changes in other parameters. Our results suggested that cytokinin was most sensitive to high soil temperature among parameters examined, suggesting that changes in cytokinins could serve as an early stress indicator for plant responses to high soil temperature; however, decreased water, nutrient (N, P, and K), and cytokinin content, and increased ABA could all contribute to the decline in shoot and root growth for creeping bentgrass exposed to high soil temperatures. [Copyright &y& Elsevier]

The effects of nitrogen nutrition on cell membrane stability (CMS), leaf water potential, N, K, P, Ca, Mg, and glycinebetain concentrations in C3 plant, Agrostis palustris Huds. (creeping bentgrass) were assessed under water-stress conditions. Water-stressed plants showed greater adaptation to water stress at higher nitrogen (N) levels. Cell membrane stability measured by the polyethylene glycol (PEG) technique was increased by increased N application. Osmotic potential decreased and turgor pressure increased with increased N application. Nitrogen, K, Ca, and glycinebetaine concentrations in leaf tissues increased with increased N application under water-stress conditions. Malondialdehyde (MDA) concentration in leaves which is an indicator of lipid peroxidation, was greater in the water-stress treatment than in the control, however, MDA concentration decreased with increased N application in the water-stressed plants. The results suggested that higher levels of N nutrition may have contributed to drought tolerance in creeping bentgrass by preventing cell membrane damage and enhancing osmoregulation. [Copyright &y& Elsevier]

Changes in membrane lipid compositions and saturation levels during high temperature acclimation and heat stress were investigated in leaf and root tissues for three cultivars of creeping bentgrass (Agrostis stolonifera) that differ in heat tolerance. ‘L-93’ (heat tolerant), ‘Penncross’ (heat sensitive) and ‘Crenshaw’ (intermediate) showed differential decreases in grass visual quality (leaf color and shoot density), increases in TBARS (a measure of oxidative damage), increases in membrane leakage and decreases in chlorophyll content of leaves during 28 days of heat stress (35 °C) in a growth chamber study. Total lipid extracts from the leaves of all three cultivars showed that the lipid saturation level increased over time under heat stress, with the change being predominantly due to decreases in linolenic acid and increases in linoleic and palmitic acids. The only significant difference in leaf lipid saturation between the three cultivars was that L-93 extracts contained a higher proportion of saturated lipids prior to heat stress than the other two cultivars. No cultivar differences in lipid composition were detected during heat stress. Penncross plants given a mild heat pre-treatment (30 °C) (heat acclimated) prior to being exposed to heat stress (35 °C) showed increased saturation of leaf lipids at the initiation of heat stress. There were no significant differences in root lipid composition between heat-acclimated and non-acclimated plants. Penncross plants which had acquired thermotolerance through heat acclimation, and heat tolerant L-93 plants showed similar leaf lipid composition at the initiation of heat stress, and similar levels of thermotolerance during heat stress. These results imply that there may be some connection between the degree of saturation of leaf membrane lipids prior to heat stress and the ability of that plant to limit heat-induced damages during the stress period. Root lipid extracts from the three cultivars showed no change in saturation levels during heat stress. However, Penncross root extracts contained a lower proportion of saturated lipids than L-93 or Crenshaw. These results suggest that lipid composition or saturation level of roots could be an important factor in controlling plant tolerance to heat stress. [Copyright &y& Elsevier]

Summary: The objective of this study was to determine effects of elevated CO2 and soil nutrient availability on growth and plant tissue quality in four grass species, Agrostis stolonifera, Anthoxanthum odoratum, Festuca rubra and Poa pratensis, native in Western European calcareous grassland. Plants were grown for 65 days in the greenhouse in pots with untreated soil from calcareous grassland under ambient (350 ppm) and elevated (700 ppm) CO2 either with or without fertilisation. In general, elevated CO2 increased plant height, total biomass, starch and sugar concentrations, and decreased water and nitrogen concentrations. However, the response to CO2-enrichment depended strongly on the grass species investigated. Fertilisation enhanced most effects of elevated CO2. Biomass production in fertilised plants increased more under elevated CO2 than in unfertilised plants whereas leaf nitrogen concentration of fertilised plants decreased more at elevated CO2 than it did in unfertilised plants. Furthermore, a species-specific response to elevated CO2, depending on soil nutrient availability was detected in starch and sugar concentrations (three-way interaction). The data from this study indicate that grass species vary in their response to elevated CO2 in biomass production and tissue quality. Furthermore, increasing nutrient availability can substantially alter effects of elevated CO2. Since the investigated grass species are important larval food-plants of insect herbivores on calcareous grassland, the observed species-specific reactions to CO2-enrichment and high nutrient availability in tissue quantity and quality are discussed with respect to their effects on insect performance and thus abundance and biodiversity of these insects. In der vorliegenden Studie wurde der Effekt von erhöhtem CO2 und dem Nährstoffangebot im Boden auf das Wachstum und die Blattqualität von vier Trockenrasen Grasarten (Agrostis stolonifera, Anthoxanthum odoratum, Festuca rubra und Poa pratensis) untersucht. Die Gräser wurden in einem unbehandelten Boden eines Trockenrasens während 65 Tage im Gewächshaus angezogen. Die Pflanzen wurden unter normalen (350 ppm) und erhöhten (700 ppm) CO2-Bedingungen, mit oder ohne Düngung kultiviert. Im Allgemeinen hatten erhöhte CO2-Bedingungen einen positiven Effekt auf die Pflanzenhöhe und -gewicht, Stärke- und Zuckerkonzentration und einen negativen Effekt auf den Wasser- und Stickstoffgehalt des Blattgewebes. Dieser CO2-Effekt war stark von der Grasart abhängig und wurde durch die Düngung verstärkt. So erhöhte sich die Biomasse von gedüngten Pflanzen unter erhöhten CO2-Bedingungen stärker als bei nicht gedüngten Pflanzen. Hingegen nahm der Stickstoffgehalt der Gräser durch die Düngung unter erhöhten CO2- Bedingungen stärker ab als bei nicht gedüngten Pflanzen. Zusätzlich konnte eine artspezifische Reaktion auf CO2-Erhöhung in Abhängigkeit vom Nährstoffangebot im Boden für den Gehalt von Stärke und Zucker gefunden werden. Die Daten der vorliegenden Studie zeigen, dass der Effekt von erhöhten CO2-Bedingungen auf Wachstum und Blattqualität von der Grasart abhängig ist. Zusätzlich kann der CO2-Effekt durch das Nährstoffangebot im Boden beeinflusst werden. Da die untersuchten Grasarten wichtige Futterpflanzen für pflanzenfressende Insekten sind, könnten diese artspezifischen Reaktionen einen Effekt auf die Entwicklung der Insekten und somit auf deren Vorkommen und Artenvielfalt haben. [Copyright &y& Elsevier]

• Heat-induced leaf senescence was mainly due to acceleration of chlorophyll degradation rather than inhibition of synthesis. • GABA, proline, and nitrogen effectively suppressed heat-induced leaf senescence. • Heat-induced leaf senescence was suppressed by GABA, proline, and N, which reduced chlorophyll-degrading enzyme activities. Heat-induced leaf senescence may be regulated by nitrogen or nitrogen-enriched amino acids. The objectives of the current study were to examine whether exogenous application of у-aminobutyric acid (GABA), proline, and ammonium nitrate (N) could alleviate heat-induced leaf senescence in creeping bentgrass (Agrostis stolonifera L.) and to determine whether the effects of GABA, proline, and N on heat-induced leaf senescence were associated with the alteration of chlorophyll (Chl) metabolism. Plants were exposed to heat stress (35/30 °C, day/night) or non-stress (22/18 °C, day/night) temperature conditions for 35 d in controlled-environment growth chambers. Turf quality, Chl content, and photochemical efficiency declined whereas the activities of Chl-degrading enzymes (chlorophyllase and pheophytinase) increased in response to heat stress. Application of GABA, proline, or N significantly enhanced turf quality, Chl content, and photochemical efficiency, and suppressed Chl-degrading enzyme activities under heat stress. The activity of a Chl-synthesizing enzyme (porphobilinogen deaminase) was not affected by GABA, proline, or N application. These results indicate that heat-induced leaf senescence could be mainly due to heat-accelerated Chl degradation, and GABA, proline, or N could suppress Chl degradation, alleviating heat-induced leaf senescence in creeping bentgrass. [ABSTRACT FROM AUTHOR]