Plant Science Articles

Quantifying turfgrass-available N from returned clippings using anion-exchange membranes

Kelly L. K.opp et al. — Wed, 09 Dec 2009 12:10:43 PST

Returning clippings can provide N to turf, but the amount of plant-available N derived from clippings is not easy to quantify. An accurate estimate of N released by clippings would be useful in guiding turf N fertilizer recommendations. The objective of this study was to determine if anion-exchange membranes (AEMs) could be used to quantify plant-available soil N when clippings are returned. A greenhouse and two field experiments were set out in randomized block designs using a factorial arrangement of 2 clipping practices [removed (CRM) and returned (CRT)] and 4 rates of N fertilization (0 to 392 kg N ha-1 yr-1) on a cool-season lawn turf. Cumulative N uptake in the clippings was determined and correlated to AEM desorbed NO3-N. Returning clippings resulted in greater overall N uptake and AEM desorbed NO3-N. However, the response of N uptake to AEM desorbed NO3-N was not the same for CRM and CRT treatments. Uptake was greater for CRT than CRM at any given AEM desorbed NO3-N level past the minimum values. This suggests that, in addition to NO3-N, other N forms (most likely NH4-N) are being released from the clippings and taken up by the turf. Anion-exchange membranes alone are not adequate to quantify the plant-available N provided by returned clippings. To accurately assess the total pool of plant-available N to turf when clippings are returned with ion-exchange technology, cation- and anion-exchange resins are needed to quantify the total plant-available N pool derived from clippings.

Relationships between soil nitrate desorbed from anion-exchange membranes, canopy reflectance and nitrate leaching losses from cool-season lawn turf.

Thomas J. Barry et al. — Wed, 09 Dec 2009 12:04:35 PST

Nutrient leaching studies are expensive and require expertise in water collection and analyses. Less expensive or easier methods that estimate leaching losses would be desirable. The objective of this study was to determine if anion-exchange membranes (AEMs) and reflectance meters could predict nitrate (NO3-N) leaching losses from a cool-season lawn turf. A two-year field study used an established 90% Kentucky bluegrass (Poa pratensis L.)-10% creeping red fescue (Festuca rubra L.) turf that received 0 to 98 kg N ha-1 month-1, from May through November. Soil monolith lysimeters collected leachate that was analyzed for NO3-N concentration. Soil NO3-N was estimated with AEMs. Spectral reflectance measurements of the turf were obtained with chlorophyll and chroma meters. No significant (p > 0.05) increase in percolate flow-weighted NO3-N concentration (FWC) or mass loss occurred when AEM desorbed soil NO3-N was below 0.84 µg cm-2 d-1. A linear increase in FWC and mass loss (p < 0.0001) occurred, however, when AEM soil NO3-N was above this value. The maximum contaminant level (MCL) for drinking water (10 mg L-1 NO3-N) was reached with an AEM soil NO3-N value of 1.6 µg cm-2 d-1. Maximum meter readings were obtained when AEM soil NO3 N reached or exceeded 2.3 µg cm-2 d-1. As chlorophyll index and hue angle (greenness) increased, there was an increased probability of exceeding the NO3-N MCL. These data suggest that AEMs and reflectance meters can serve as tools to predict NO3-N leaching losses from cool-season lawn turf, and to provide objective guides for N fertilization.

Nitrate leaching from Kentucky bluegrass soil columns predicted with anion exchange membranes

Salvatore S. Mangiafico et al. — Fri, 07 Aug 2009 10:00:34 PDT

Ideal nitrogen (N) management for turfgrass supplies sufficient N for high-quality turf without increasing N leaching losses. A greenhouse study was conducted during two 27-week periods to determine if in situ anion exchange membranes (AEMs) could predict nitrate (NO3-N) leaching from a Kentucky bluegrass (Poa pratensis) turf grown on intact soil columns. Treatments consisted of 16 rates of N fertilizer application, from 0 to 98 kg N ha-1 mo-1. Percolate water was collected weekly and analysed for NO3-N. Mean flow-weighted NO3-N concentration and cumulative mass in percolate were exponentially related (pseudo-R2=0.995 and 0.994, respectively) to AEM desorbed soil NO3-N, with a percolate concentration below 10 mg NO3-N L-1 corresponding to an AEM soil NO3-N value of 2.9 micro g cm-2 d-1. Apparent N recovery by turf ranged from 28 to 40% of applied N, with a maximum corresponding to 4.7 micro g cm-2 d-1 AEM soil NO3-N. Turf colour, growth, and chlorophyll index increased with increasing AEM soil NO3-N, but these increases occurred at the expense of increases in NO3-N leaching losses. These results suggest that AEMs might serve as a tool for predicting NO3-N leaching losses from turf.

Cool-season turfgrass color and growth calibrated to leaf nitrogen

Salvatore S. Mangiafico et al. — Fri, 07 Aug 2009 09:47:29 PDT

Tissue N analysis a tool available for N management of turfgrass. However, peer-reviewed calibration studies to determine optimum tissue N values are lacking. A field experiment with a mixed cool-season species lawn and a greenhouse experiment with Kentucky bluegrass (Poa pratensis L.) were conducted across 2 yr, each with randomized complete block design. Treatments were N application rates between 0 and 587 kg N ha-1 yr-1. In the field experiment, clipping samples were taken monthly from May to September, dried, ground, and analyzed for total N. Clippings samples were collected one to two mowings after plots were fertilized. Linear plateau models comparing relative clipping yield, Commission Internationale de l' Eclairage hue, and CM1000 index to leaf N concentrations were developed. In the greenhouse experiment, clipping samples were taken every 2 wk from May to October and composited across sample dates for leaf N analysis. Color and clipping yields were related to leaf N concentrations using linear plateau models. These models indicated small marginal improvements in growth or color when leaf N exceeded 30 g kg-1, suggesting that a leaf N test can separate turf with optimum leaf N concentrations from turf with below optimum leaf N concentrations. Plateaus in leaf N concentrations with increasing N fertilizer rates suggest, however, that this test may be unable to identify sites with excess available soil N when turf has been mowed before tissue sampling.

A negative regulator mediates quorum-sensing control of exopolysaccharide production in Pantoea stewartii subsp. stewartii.

S B von Bodman et al. — Tue, 16 Sep 2008 06:43:46 PDT

Classical quorum-sensing (autoinduction) regulation, as exemplified by the lux system of Vibrio fischeri, requires N-acyl homoserine lactone (AHL) signals to stimulate cognate transcriptional activators for the cell density-dependent expression of specific target gene systems. For Pantoea stewartii subsp. stewartii, a bacterial pathogen of sweet corn and maize, the extracellular polysaccharide (EPS) stewartan is a major virulence factor, and its production is controlled by quorum sensing in a population density-dependent manner. Two genes, esaI and esaR, encode essential regulatory proteins for quorum sensing. EsaI is the AHL signal synthase, and EsaR is the cognate gene regulator. esaI, DeltaesaR, and DeltaesaI-esaR mutations were constructed to establish the regulatory role of EsaR. We report here that strains containing an esaR mutation produce high levels of EPS independently of cell density and in the absence of the AHL signal. Our data indicate that quorum-sensing regulation in P. s. subsp. stewartii, in contrast to most other described systems, uses EsaR to repress EPS synthesis at low cell density, and that derepression requires micromolar amounts of AHL. In addition, derepressed esaR strains, which synthesize EPS constitutively at low cell densities, were significantly less virulent than the wild-type parent. This finding suggests that quorum sensing in P. s. subsp. stewartii may be a mechanism to delay the expression of EPS during the early stages of infection so that it does not interfere with other mechanisms of pathogenesis.

Structural Basis and Specificity of Acyl-Homoserine Lactone Signal Production in Bacterial Quorum Sensing

William T. Watson et al. — Tue, 16 Sep 2008 06:43:44 PDT

The autoregulatory role of EsaR, a quorum-sensing regulator in Pantoea stewartii ssp. stewartii: evidence for a repressor function.

Timothy D. Minogue et al. — Tue, 16 Sep 2008 06:43:42 PDT

Biofilm Formation in Plant-Microbe Associations

Bronwyn E. Ramey et al. — Tue, 16 Sep 2008 06:43:40 PDT

The Cell Density-Dependent Expression of Stewartan Exopolysaccharide in Pantoea stewartii ssp. stewartii is a Function of EsaR-Mediated Repression of the rcsA Gene.

Timothy D. Minogue et al. — Tue, 16 Sep 2008 06:43:39 PDT

Quorum sensing in plant-pathogenic bacteria

Susanne B. von Bodman et al. — Tue, 16 Sep 2008 06:43:36 PDT

Quorum sensing (QS) allows bacteria to assess their local population density and/or physical confinement via the secretion and detection of small, diffusible signal molecules. This review describes how phytopathogenic bacteria have incorporated QS mechanisms into complex regulatory cascades that control genes for pathogenicity and colonization of host surfaces. Traits regulated by QS include the production of extracellular polysaccharides, degradative enzymes, antibiotics, siderophores, and pigments, as well as Hrp protein secretion, Ti plasmid transfer, motility, biofilm formation, and epiphytic fitness. Since QS regulatory systems are often required for pathogenesis, interference with QS signaling may offer a means of controlling bacterial diseases of plants. Several bacterial pathogens of plants that have been intensively studied and have revealed information of both fundamental and practical importance are reviewed here: Agrobacterium tumefaciens, Pantoea stewartii, Erwinia carotovora, Ralstonia solanacearum, Pseudomonas syringae, Pseudomonas aeruginosa, and Xanthomonas campestris.

Anion exchange membrane soil nitrate predicts turfgrass color and yield.

Salvatore Mangiafico et al. — Wed, 12 Dec 2007 07:07:54 PST

Desirable nitrogen (N) management practices for turfgrass supply sufficient N for high quality turf while limiting excess soil N. Previous studies suggested the potential of anion exchange membranes (AEMs) for predicting turfgrass color, quality, or yield. However, these studies suggested a wide range of critical soil nitrate-nitrogen (NO3-N) values across sample dates. A field experiment, in randomized complete block design with treatments consisting of nine N application rates, was conducted on a mixed species cool-season turfgrass lawn across two growing seasons. Every 2 wk from May to October, turfgrass color was assessed with three different reflectance meters, and soil NO3-N was measured with in situ AEMs. Cate-Nelson models were developed comparing relative reflectance value and yield to AEM desorbed soil NO3-N pooled across all sample dates. These models predicted critical AEM soil NO3-N values from 0. 45 to 1.4 micro g cm-2 d-1. Turf had a low probability of further positive response to AEM soil NO3-N greater than these critical values. These results suggest that soil NO3-N critical values from AEMs may be applicable across sample dates and years and may serve to guide N fertilization to limit excess soil NO3-N.

Fall Fertilization Timing Effects on Nitrate Leaching and Turfgrass Color and Growth

Salvatore Mangiafico et al. — Mon, 12 Nov 2007 11:15:57 PST

Fall season fertilization is a widely recommended practice for turfgrass. Fertilizer applied in the fall, however, may be subject to substantial leaching losses. A field study was conducted in Connecticut to determine the timing effects of fall fertilization on nitrate N (NO3-N) leaching, turf color, shoot density, and root mass of a 90% Kentucky bluegrass (Poa pratensis L.), 10% creeping red fescue (Festuca rubra L.) lawn. Treatments consisted of the date of fall fertilization: 15 September, 15 October, 15 November, 15 December, or control which received no fall fertilizer. Percolate water was collected weekly with soil monolith lysimeters. Mean log10 NO3-N concentrations in percolate were higher for fall fertilized treatments than for the control. Mean NO3-N mass collected in percolate water was linearly related to the date of fertilizer application, with higher NO3-N loss for later application dates. Applying fall fertilizer improved turf color and density but there were no differences in color or density among applications made between 15 October and 15 December. These findings suggest that the current recommendation of applying N in mid- to late November in southern New England may not be compatible with water quality goals.

Bentgrass response to K fertilization and K release rates from eight sand rootzone sources used in putting green construction.

W. M. Dest et al. — Tue, 12 Jun 2007 08:03:55 PDT

There is a lack of plant response to fertilizer K in some sandy soils even though routine soil tests for soil available K are shown to be low. This lack of plant response to K fertilizer application may be explained by K release from nonexchangeable forms. Greenhouse and laboratory experiments were conducted to evaluate (a) response of bentgrass (Agrostis palustris [Agrostis stolonifera var. palustris]) cv. Pencross grown in rootzones with different sand sources to K fertilizer application and (b) K release from nonexchangeable forms from the different sand sources as an index to K availability. Experimental variables in the greenhouse were 2 K levels (0 and 250 mg K/kg soil) and 8 sand rootzone sources. Rootzone soils were sub-irrigated to ensure no K loss from leaching. Two laboratory methods (boiling 1 M HNO3 extraction and continuous leaching with 0.01 M HCl) and total K uptake by the bentgrass were employed to index K release from nonexchangeable forms for each rootzone source. K fertilizer application significantly increased bentgrass yield growing in one rootzone source and root weight in 3 rootzone sources. K uptake by bentgrass and the 2 laboratory methods showed important differences in K release from the sand rootzones. The K removed by the 2 laboratory methods was closely related to leaf tissue K and K uptake, with the 1 M HNO3 extraction method providing the closest fit. The release of K from primary minerals in some rootzones with high sand content is proceeding at rates to satisfy bentgrass requirements for K. The 1 M HNO3 extraction method may provide an alternative to the routine laboratory procedures presently being used to measure the extractable K in sand-based constructed putting greens by measuring K contributed by nonexchangeable forms.

Clipping Contributions To Nitrate Leaching From Creeping Bentgrass Under Varying Irrigation And N Rates

Kelly L. Kopp et al. — Thu, 29 Mar 2007 08:16:42 PDT

The effect of clipping management on nitrate (NO3) leaching beneath creeping bentgrass (Agrostis stolonifera L.) has received little attention. The objective of this experiment was to examine the effects of returning grass clippings to creeping bentgrass in combination with N fertilization and irrigation on NO3 leaching. A 30-week long experiment was conducted using fairway-height creeping bentgrass in large, undisturbed soil columns (20.3-cm diam. x 60.9-cm length) under controlled greenhouse conditions. Treatments were four rates of N fertilization (equivalent to 0, 98, 196, and 392 kg N ha-1 year-1) and two levels of irrigation [standard (25 mm per week) or standard + historical weekly precipitation amounts], with grass clippings either returned or removed. Higher percolate NO3-N concentrations and mass losses were found when clippings were returned, as N rate increased, and with the higher irrigation treatment. Flow-weighted concentrations of NO3-N in percolate ranged from 0.13 to 21.0 mg L-1 and the percent of applied N lost as leachate ranged from 0.9 to 63%. These findings suggest that water quality goals may not be reached if N fertilization rates are not reduced when clippings are returned to bentgrass fairways or in cases of over-watering.

Nitrogen Fertilizer Form and Associated Nitrate Leaching from Cool-Season Lawn Turf

Karl Guillard et al. — Thu, 29 Mar 2007 08:16:40 PDT

Various N fertilizer sources are available for lawn turf. Few field studies, however, have determined the losses of nitrate (NO₃-N) from lawns receiving different formulations of N fertilizers. The objectives of this study were to determine the differences in NO₃-N leaching losses among various N fertilizer sources and to ascertain when losses were most likely to occur. The field experiment was set out in a completely random design on a turf typical of the lawns in southern New England. Treatments consisted of four fertilizer sources with fast- and slow-release N formulations: (i) ammonium nitrate (AN), (ii) polymer-coated sulfur-coated urea (PCSCU), (iii) organic product, and (iv) a nonfertilized control. The experiment was conducted across three years and fertilized to supply a total of 147 kg N ha^-1 yr^-1. Percolate was collected with zero-tension lysimeters. Flow-weighted NO₃-N concentrations were 4.6, 0.57, 0.31, and 0.18 mg L^-1 for AN, PCSCU, organic, and the control, respectively. After correcting for control losses, average annual NO₃-N leaching losses as a percentage of N applied were 16.8% for AN, 1.7% for PCSCU, and 0.6% for organic. Results indicate that NO₃-N leaching losses from lawn turf in southern New England occur primarily during the late fall through the early spring. To reduce the threat of NO₃-N leaching losses, lawn turf fertilizers should be formulated with a larger percentage of slow-release N than soluble N.

Turfgrass Reflectance Measurements, Chlorophyll, and Soil Nitrate Desorbed from Anion Exchange Membranes

Salvatore S. Mangiafico et al. — Thu, 29 Mar 2007 08:16:38 PDT

There is not extensive research on the potential of anion exchange membranes (AEMs) for determining available N in soils of turfgrass systems, nor on the use of reflectance meters for quantifying turfgrass color. The two objectives of this study were to determine relationships between (i) turfgrass color measurements and soil nitrate (NO₃–N) desorbed from AEMs and (ii) reflectance meter measurements and turfgrass chlorophyll concentration. A field experiment was conducted on a 90% Kentucky bluegrass (Poa pratensis L.) stand across 2 yr. Anion exchange membranes were inserted into the soil and exchanged weekly. Desorbed NO₃–N from the AEMs was quantified. Turfgrass color and chlorophyll measurements were taken monthly. Reflectance meter measurements were significantly related to chlorophyll concentration. Linear response plateau models suggested critical levels of AEM soil NO₃–N, above which turfgrass color did not improve, from 0.31 to 0.43 µg cm^–2 d^–1. These models suggest that critical levels of soil NO₃–N could be determined that maximize turfgrass quality without excessive N application. These findings suggest both AEMs and hand-held reflectance meters could be useful tools for N management in turfgrass.

The Effects Of Reinforcement Inclusions On Wear Tolerance, Playing Quality And Physical Properties In A Silt Loam And Sand Rootzone Matrix

William M. Dest et al. — Thu, 29 Mar 2007 07:40:58 PDT

Reinforcement inclusions have been advocated to alleviate wear, compaction, and unstable surfaces in sports fields, but little research on the effects of these materials has been conducted in the USA. Experiments were established on a native silt loam and a sand rootzone matrix, seeded with a Kentucky bluegrass (Poa pratensis L.) blend, at the Joseph Troll Turf Research Center, University of Massachusetts, Amherst, USA to determine the effects of reinforcement inclusions on wear, surface hardness, traction, ball roll, ball bounce resilience, water infiltration rate, soil bulk density, air porosity, total porosity, and root weights. Three types of reinforcement inclusions (Sportgrass, Netlon, Turfgrids) were tested along with a non-reinforced control in a three year study. The treatments were set out in a randomized complete block design with four replications in both soils. No inclusion provided less wear or greater infiltration or air-filled porosity relative to the control. Reinforcement inclusions showed significant differences, however, in surface hardness, traction, and ball roll relative to the control, although this varied with the time of year. Infiltration rates, airfilled porosity, total pore space, bulk density, hardness, traction, ball roll, and ball rebound were greater on the sand rootzone than on the silt loam. Significant correlations were present between soil bulk density, surface hardness, traction, and ball roll. Based on our study, the use of reinforcement inclusions to provide better wear tolerance for sand or native soil athletic fields is not warranted. Certain playing surface characteristics, however, may be slightly improved with the use of reinforcement inclusions. The use of sands for sports surfaces is justified based upon the improvement in playing quality characteristics and soil physical properties important to a good playing surface.

Effects of Cor15a-IPT Gene Expression on Leaf Senescence in Transgenic Petunia x hybrida and Dendranthema x grandiflorum.

Mariya Khodakovskaya et al. — Tue, 27 Mar 2007 08:00:01 PDT

To prevent leaf senescence of young transplants or excised shoots during storage under dark and cold conditions, the cytokinin biosynthetic gene isopentenyl transferase (ipt) was placed under the control of a cold-inducible promoter cor15a from Arabidopsis thaliana and introduced into Petunia x hybrida 'Marco Polo Odyssey' and Dendranthema x grandiflorum (chrysanthemum) 'Iridon'. Transgenic cor15a-ipt petunia and chrysanthemum plants and excised leaves remained green and healthy during prolonged dark storage (4 weeks at 25 degrees C) after an initial exposure to a brief cold-induction period (4 degrees C for 72 h). However, cor15a-ipt chrysanthemum plants and excised leaves that were not exposed to a cold-induction period, senesced under the same dark storage conditions. Regardless of cold-induction treatment, leaves and plants of non-transformed plants senesced under prolonged dark storage. Analysis of ipt expression indicated a marked increase in gene expression in intact transgenic plants as well as in isolated transgenic leaves exposed to a short cold-induction treatment prior to dark storage. These changes correlated with elevated concentrations of cytokinins in transgenic leaves after cold treatment. Cor15a-ipt transgenic plants showed a normal phenotype when grown at 25 degrees C.

Enhanced Cold Tolerance in Transgenic Tobacco Expressing a Chloroplast Omega-3 Fatty Acid Desaturase Gene under the Control of a Cold-inducible Promoter

Mariya Khodakovskaya et al. — Fri, 23 Mar 2007 07:56:26 PDT

A new cold-inducible genetic construct was cloned using a chloroplast-specific omega-3-fatty acid desaturase gene (FAD7) under the control of a cold-inducible promoter (cor15a) from Arabidopsis thaliana. RT-PCR confirmed a marked increase in FAD7 expression, in young Nicotiana tabacum (cv. Havana) plants harboring cor15a-FAD7, after a short-term exposure to cold. When young, cold-induced tobacco seedlings were exposed to low-temperature (0.5, 2 or 3.5 degrees C) for up to 44 days, survival within independent cor15a-FAD7 transgenic lines (40.2-96%) was far superior to the wild type (6.7-10.2%). In addition, the major trienoic fatty acid species remained stable in cold-induced cor15a-FAD7 N. tabacum plants under prolonged cold storage while the levels of hexadecatrienoic acid (16:3) and octadecatrienoic acid (18:3) declined in wild type plants under the same conditions (79 and 20.7% respectively). Electron microscopy showed that chloroplast membrane ultrastructure in cor15a-FAD7 transgenic plants was unaffected by prolonged exposure to cold temperatures. In contrast, wild type plants experienced a loss of granal stacking and disorganization of the thylakoid membrane under the same conditions. Changes in membrane integrity coincided with a precipitous decline in leaf chlorophyll concentration and low survival rates in wild type plants. Cold-induced double transgenic N. alata (cv. Domino Mix) plants, harboring both the cor15a-FAD7 cold-tolerance gene and a cor15a-IPT dark-tolerance gene, exhibited dramatically higher survival rates (89-90%) than wild type plants (2%) under prolonged cold storage under dark conditions (2 degrees C for 50 days).

Expression of ipt Gene Controlled by an Ethylene and Auxin Responsive Fragment of the LEACO1 Promoter Increases Flower Number in Transgenic Nicotiana tabacum

Mariya Khodakovskaya et al. — Wed, 21 Mar 2007 07:43:56 PDT

Cytokinins play important roles in regulating plant growth and development. A new genetic construct for regulating cytokinin content in plant cells was cloned and tested. The gene coding for isopentenyl transferase (ipt) was placed under the control of a 0.821 kb fragment of the 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase gene promoter from Lycopersicon esculentum (LEACO1) and introduced into Nicotiana tabacum (cv. Havana). Some LEACO1(0.821) (kb)-ipt transgenic plant lines displayed normal shoot morphology but with a dramatic increase in the number of flower buds compared to nontransgenic plants. Other transgenic lines produced excessive lateral branch development but no change in flower bud number. Isolated leaves of transgenic tobacco plants showed a significantly prolonged retention of chlorophyll under dark incubation (25 degrees C for 20 days). Leaves of nontransformed plants senesced gradually under the same conditions. Experiments with LEACO1(0.821) (kb)-gus transgenic tobacco plants suggested auxin and ethylene involvement in induction of LEACO1(0.821) (kb) promoter activity. Multiple copies of nucleotide base sequences associated with either ethylene or auxin response elements were identified in the LEACO1(0.821) (kb) promoter fragment. The LEACO1(0.821) (kb)-ipt fusion gene appears to have potential utility for improving certain ornamental and agricultural crop species by increasing flower bud initiation and altering branching habit.