Nitrogen Use within the Growing Leaf Blade of Tall Fescue

Leaf elongation rate (LER) of grasses depends on N supply and is expressed mostly through cell production, whereas most N in mature leaf tissues is chloroplastic. Our objective was to evaluate a possible competition for N between cell production and chloroplast development processes, utilizing the gradient of cell development along the leaf growth zone of tall fescue (Festuca arundinacea Schreb.). Under the two contrasting N regimes, total N content was highest in the cell production zone, declined sharply as cells elongated, and remained relatively constant in more distal positions, at values close to those measured in mature tissues. A similar pattern was found for N in proteins and nucleic acids that were not soluble in 80% ethanol. Content of N compounds soluble in 80% ethanol was higher in the cell production and elongation zones than in mature parts of the leaf. NO3- N content was low in the cell production zone and increased in the cell elongation zone for high-N plants. The deposition rate of total N in the growth zone was much higher with plants in high N than in those shifted to no N. For both N regimes, most N was deposited during cell production and early cell elongation. Little N was deposited during cell maturation where ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) was being actively synthesized. This suggests that synthesis of Rubisco, and probably other chloroplastic proteins, occurs largely from recycling of N that was previously incorporated into proteins during cell production. Thus, Rubisco content in mature tissues is more closely associated with N deposited during cell production than with N deposited during its biosynthesis.     

Growth Rates and Carbohydrate Fluxes within the Elongation Zone of Tall Fescue Leaf Blades

Investigations were performed to better understand the carbon economy in the elongation zone of tall fescue leaf blades. Plants were grown at constant 21°C and continuous 300 micromoles per square meter per second photosynthetic photon flux density where leaf elongation was steady for several days. Elongation occurred in the basal 20 mm of the blade (0-20 millimeters above the ligule) and was maximum at 9 to 12 millimeters. Eight 3-millimeter long segments were sampled along the length of the elongation zone and analyzed for water-soluble carbohydrates. Sucrose concentration was high in the zone of cell division (0-6 millimeters) whereas monosaccharide concentration was high at and distal to the location where cell elongation terminated (20 millimeters). Fructan concentration increased in the basal part, then remained constant at about 85% of the total mass of water-soluble carbohydrates through the remainder of the elongation zone. Data on spatial distribution of growth velocities and substance contents (e.g. microgram fructan per millimeter leaf length) were used to calculate local net rates of substance deposition (i.e. excess rates of substance synthesis and/or import over substance degradation and/or export) and local rates of sucrose import. Rates of sucrose import and net deposition of fructan were positively associated with local elongation rate, whereas net rates of sucrose deposition were high in the zone of cell division and those of monosaccharide were high near the termination of elongation. At the location of most active elongation imported sucrose (29.5 milligrams per square decimeter per hour) was used largely for synthesis of structural components (52%) and fructan (41%).     

Carbohydrate Metabolism in Leaf Meristems of Tall Fescue : II. Relationship to Leaf Elongation Rates Modified by Nitrogen Fertilization

Our objective was to examine alterations in carbohydrate status of leaf meristems that are associated with nitrogen-induced changes in leaf elongation rates of tall fescue (Festuca arundinacea Schreb.). Dark respiration rates, concentrations of nonstructural carbohydrates, and soluble proteins were measured in leaf intercalary meristems and adjacent segments of elongating leaves. The two genotypes used differed by 43% in leaf elongation rate. Application of high nitrogen (336 kilograms per hectare) resulted in 140% higher leaf elongation rate when compared to plants receiving low nitrogen (22 kilograms per hectare). Leaf meristems of plants receiving high and low nitrogen had dark respiration rates of 5.4 and 2.9 microliters O₂ consumed per milligram structural dry weight per hour, respectively. Concentrations of soluble proteins were lower while concentrations of fructan tended to be slightly higher in leaf meristems of low-nitrogen plants when compared to high-nitrogen plants. Concentrations of reducing sugars, nonreducing sugars, and takadiastase-soluble carbohydrate of leaf meristems were not affected by nitrogen treatment. Total nonstructural carbohydrates of leaf meristems averaged 44 and 39% of dry weight for low- and high-nitrogen plants, respectively. Within the leaf meristem, approximately 74 and 34% of the pool of total nonstructural carbohydrate could be consumed per day in high- and low-nitrogen plants, respectively, assuming no carbohydrate import to the meristem occurred. Plants were able to maintain high concentrations of nonstructural carbohydrates in leaf meristems despite a 3-fold range in leaf elongation rates, suggesting that carbohydrate synthesis and transport to leaf intercalary meristems may not limit leaf growth of these genotypes.     

Specific Leaf Weight in Zones of Cell Division, Elongation and Maturation in Tall Fescue Leaf Blades

Patterns of change in specific leaf weight (SLW), water-solublecarbohydrate (WSC) content and leaf width were used to delineatethe region of secondary cell wall accumulation, and determinethe rate of increase in structural material along a developingleaf blade of tall fescue (Festuca arundinacea Schreb.). Structuralspecific leaf weight (SSLW) was determined by subtracting WSCmass from dry weight to emphasize structural material. Becausemeristematic activity, cell elongation, and cellular maturationare arranged successively in the grass leaf, these patternsrepresent a developmental sequence through which each segmentof the leaf blade passes. Patterns were generally similar fortwo genotypes, one selected for high (HYT) and the other forlow (LYT) yield per tiller, for a single genotype grown at 17or 25 C, and for two field-grown populations which differedin leaf area expansion rate (LAER). In all three studies, the elongation zone of the developingleaf had 31 to 39 per cent WSC on a dry weight basis. The LYTgenotype had a higher SLW at all stages of development whengrown at 17 than at 25 C, due to greater WSC accumulation.At 20 C, the HYT genotype had a higher SLW all along the elongatingleaf blade than the LYT genotype. This difference was due toa difference in SSLW, while WSC content was similar. The LERwas 64 per cent higher in the high population than the low,but elongation zones were similar in WSC. In all cases, SSLWwas high in the meristematic region, lowest near the distalend of the cell elongation zone, then increased linearly astissue matured. Rate of increase in SSLW was 8.5 and 5.2 g m^–2d^–1 for the HYT and LYT genotypes, respectively, and 7.6and 6.7 g m^–2 d^–1 for the high and low LAER populations,respectively. Festuca arundinacea Schreb., tall fescue, specific leaf weight, leaf width, water-soluble carbohydrates, leaf elongation rate     

A Model of the Leaf Extension Rate of Tall Fescue in Response to Nitrogen and Temperature

The leaf extension rate (LER) of tall fescue (Festuca arundinaceaSchreb.) was studied in the field under various nitrogen andtemperature regimes. The LER was closely related to temperaturewhen N was not limiting plant growth. Two distinct relationshipsbetween the LER and the temperature were obtained, one for vegetativegrowth and one for the reproductive period. These relationships,described by a Gompertz function, were exponential at temperaturesbelow 8 °C and linear at temperatures above 8 °C. Theymade possible the calculation of an optimal LER correspondingto non-limiting N conditions for plant growth. The strong influence of the temperature on the LER was stillobserved under N limiting conditions. The N status of the swardswas described by the ratio between the actual N content (N_actual)and the optimal N content (N_optimal). The N_optimal was definedas the N content experienced at a non-limiting level of N nutritionbut without N luxury consumption. The N_optimal, expressed asa function of dry matter yield, declined during growth. Theeffect of the N status of the swards on the LER was analysedby calculating the ratio between the actual LER and the optimalLER, and relating it to the ratio between N_actual and N_optimal.It was shown that these two ratios were highly correlated. Leaf extension, Festuca arundinacea, nitrogen, temperature     

Fructosyltransferase Activities in the Leaf Growth Zone of Tall Fescue

High concentrations of water-soluble carbohydrates, mainly fructan, accumulate in the growth zone of tall fescue (Festuca arundinacea Schreb.) leaf blades. We studied sucrose-hydrolyzing activities in the leaf growth zone because of their importance in carbohydrate partitioning. Sucrose hydrolysis in the basal 1.5 cm was largely due to fructosyltransferases, which had activities up to 10 times higher than in fully developed leaf tissue. Three fructosyltransferases (F1, F2, and F3) were purified from the leaf growth zone. Each synthesized, from either sucrose or 1-kestose, a mixture of trisaccharides and higher-order oligofructans identical with the low-degree of polymerization fructan extracted from similar plant tissue. The highly purified fructosyltransferases retained ability (13%) to transfer fructose from sucrose to water. Time-dependent and substrate-dependent studies, using sucrose as the substrate, showed proportional production of fructose and glucose, indicating that both products are from the same enzyme. Fructosyltransferase was calculated to contribute about half the total transfer of fructose to water in the basal 1.5 cm. Invertase activity increased to near 2.0 cm when fructosyl transfer to sucrose and other oligofructans decreased. Invertase was the major activity for sucrose hydrolysis at positions distal to 3.0 cm.     

Effect of Ploidy on Quality of Tall Fescue, Italian Ryegrass x Tall Fescue and Tall Fescue x Giant Fescue Hybrids

Selected quality parameters were measured for forage leaf tissuefrom a spaced-plant nursery. The genotypes used were Ky 31 tallfescue and hybrids of Italian ryegrass (Lolium multiflorum Lam.)x tall fescue (Festuca arundinacea Schreb.) and tall fescuex giant fescue [Fescue gigantea (L ) Vill.]. Hybrid ploidy rangedfrom 2n = 28 to 84 chromosomes. Forage quality was characterizedby neutral detergent fibre (NDF), acid detergent fibre (ADF),total soluble carbohydrates (TSC) nutritive value index (NVI),hemicellulose, and in vitro dry matter disappearance (DMD). Quality of tall fescue, as measured by increased DMD, was improvedby hybridization with giant fescue. Improved DMD and NVI correlatedwith lower NDF and ADF in the hybrids. A few hybrids of Italianryegrass x tall fescue (2n = 28) were higher in some qualityparameters than Ky 31. Tall fescue x giant fescue hybrids (2n= 80 to 84), as a group, had significant quality improvementover Ky 31 in higher DMD and NVI and lower NDF and ADF. Whilesome individual hybrids within each group were significantlyhigher in quality, only the 2n = 80 to 84 chromosome group wasconsistently higher than Ky 31. Prediction equations for DMD,NDF, and ADF were established based on solvent extraction withnear-infrared reflectance spectroscopy (NIRS). Linear correlationcoefficients between chemical measurement and NIRS for eachquality parameter were 0–95 or higher. Acid detergent fibre, neutral detergent fibre, dry matter disappearance, hemicellulose, nutritive value index, Festuca arundinacea, Festuca gigantea, Lolium multiflorum     

Effects of the Fungal Endophyte Acremonium coenophialum on Nitrogen Accumulation and Metabolism in Tall Fescue

Infection by the fungal endophyte Acremonium coenophialum affected the accumulation of inorganic and organic N in leaf blades and leaf sheaths of KY 31 tall fescue (Festuca arundinacea Schreb.) grown under greenhouse conditions. Total soluble amino acid concentrations were increased in either the blade or sheath of the leaf from infected plants. A number of amino acids were significantly increased in the sheath, but only asparagine increased in the blade. Infection resulted in higher sheath NH₄⁺ concentrations, whereas NO₃⁻ concentrations decreased in both leaf parts. The effects on amino acid, NO₃⁻, and NH₄⁺ concentrations were dependent upon the level of N fertilization and were usually apparent only at the high rate (10 millimolar) of application. Administration of ¹⁴CO₂ to the leaf blades increased the accumulation of ¹⁴C in their amino acid fraction but not in the sheaths of infected plants. This may indicate that infection increased amino acid synthesis in the blade but that translocation to the sheath, which is the site of fungal colonization, was not affected. Glutamine synthetase activity was greater in leaf blades of infected plants at high and low N rates of fertilization, but nitrate reductase activity was not affected in either part of the leaf. Increased activities of glutamine synthetase together with the other observed changes in N accumulation and metabolism in endophyte-infected tall fescue suggest that NH₄⁺ reassimilation could also be affected in the leaf blade.     

Defoliation and Leaf Age Influence on Ergot Alkaloids in Tall Fescue

A controlled environment experiment was conducted to determinethe influence of defoliation on the regrowth and developmentof two tall fescue (Festuca arundinacea Schreb.) host-endophyte(Neotyphodium coenophialum Morgan-Jones and Gams (Glenn, Bacon,Price and Hanlincomb. nov. ) associations (DN2 and DN11), knownto differ in morphology and alkaloid production capacity. Defoliationtreatments included an uncut control, and clipping to a 5- or10-cm residue height. In a separate experiment, leaf age effectswere determined on an uncut plant canopy. Ergot alkaloid concentrationwas greatest in pseudostem and least in harvested leaf. Non-infectedplants were devoid of alkaloid. Alkaloid production (expressedas a function of dry matter) and yield were greater in uncutthan clipped plants, and were greater in DN11 than DN2 plants.Alkaloid production increased with increasing N concentrationin both associations; however, the rate of production was influencedby concentration of non-structural carbohydrate. Leaf age influencedleaf mass and alkaloid concentration and yield. Oldest leaves(>6 weeks after appearance) of DN2 and DN11 had the lowestconcentrations of ergot alkaloid, while leaves that were 2 to4 weeks old had the greatest alkaloid concentration and yield(alkaloid concentrationxleaf mass). Repeated defoliation reducedthe production of alkaloids, but did so as a function of non-structuralcarbohydrate. Our data suggest that alkaloid production canbe modified by defoliation as well as by host-endophyte association. Neotyphodium coenophialum ; Festuca arundinacea ; N; non-structural carbohydrate     

Diurnal Growth of Tall Fescue Leaf Blades : II. Dry Matter Partitioning and Carbohydrate Metabolism in the Elongation Zone and Adjacent Expanded Tissue

The spatial distributions of net deposition rates of water soluble carbohydrate-free dry matter (WSC-free DM) and WSC were evaluated within and above the elongation zone of tall fescue (Festuca arundinacea Schreb.) leaf blades during light and darkness. Imported DM used for WSC-free DM synthesis during darkness (67% of the total in experiment I and 59% in experiment II) was greater than during light (47% in both experiments), suggesting that the 65% higher leaf elongation rate during darkness was accompanied by higher rates of synthesis of cellular structural components. Deposition rates of WSC in the basal and central part of the elongation zone (0-20 mm from the ligule) were similar during light and darkness, but above 20 millimeters WSC deposition occurred during light and WSC loss occurred during darkness. WSC deposition and loss throughout the elongation zone and the recently expanded tissue were mostly due to net synthesis and degradation of fructan. Fructan was predominantly low molecular weight and contributed about 50% of the total osmotic partial pressure of WSC. In the most actively growing region, where fructan synthesis was most rapid, no diurnal change occurred in molecular weight distribution of fructan. WSC solute concentrations were diluted in the most actively growing tissue during darkness because net monosaccharide and fructan deposition were unaltered and sucrose deposition was decreased, but growth-associated water deposition was increased by 77%. Net rates of fructan synthesis and degradation were not related to tissue sucrose concentration, but appeared to respond to the balance between assimilate import and assimilate use in synthesis of cellular structural components (i.e. WSC-free DM) and deposition of monosaccharides. Fructan synthesized in tissue during most active elongation was degraded when the respective tissue reached the distal limit of the elongation zone where assimilate import in darkness was insufficient to maintain synthetic processes associated with further differentiation of cells.     

The Effects of Endophytes on Seed Production and Seed Predation of Tall Fescue and Meadow Fescue

Fungal endophytes of grasses are often included in agricultural management and in ecological studies of natural grass populations. In European agriculture and ecological studies, however, grass endophytes are largely ignored. In this study, we determined endophyte infection frequencies of 13 European cultivars and 49 wild tall fescue (Schedonorus phoenix) populations in Northern Europe. We then examined seed production and seed predation of endophyte-infected (E+) and endophyte-free (E?) tall fescue (in wild grass populations and in a field experiment) and meadow fescue (Schedonorus pratensis; in a field experiment only). Endophytes were detected in only one of the 13 cultivars. In contrast, >90% of wild tall fescue plants harbored endophytes in 45 wild populations but were absent in three inland populations in Estonia. In three wild tall fescue study sites, 17%, 22%, and 56% of the seeds were preyed upon by the cocksfoot moth. Endophyte infection did not affect seed mass of tall fescue in the field experiment. However, seed predation was lower in E+ than E? grasses in the two tall fescue populations with higher predation rates. For meadow fescue, the mean number of seeds from E+ plants was higher than E? plants, but E? and E+ seeds had equal rates of predation by the moth. Our results suggest that the effects of grass endophytes on seed production and cocksfoot moth seed predation vary considerably among grass species, and the effects may depend on herbivore pressure and other environmental conditions.     

Encroachment of Endophyte-infected on Endophyte-free Tall Fescue

Persistence of endophyte-free (E-) tall fescue (Festuca arundinaceaSchreb.)is erratic. Little information exists as to how fast endophyte(Neotyphodium coenophialum)-infected (E+) tall fescue mightencroach on E- tall fescue and whether specific conditions mightinfluence the speed of encroachment. Plots of E+ and E- tallfescue genotypes 7 and 17 were established using a modifiedNelder's design to compare performance of the E+ forms of theplants in pure and mixed communities at different populationdensities. The plots were planted at the USDA Southern PiedmontConservation Research Laboratory in Watkinsville, Georgia, andthe University of Georgia Plant Sciences Farm in Bogart, Georgia.Plants were grown over a 5 year period and dry matter yieldmonitored 1, 3, and 5 years after establishment. Relative crowdingcoefficients were calculated for each to establish trends ofencroachment of the E+ on the E- plants in the mixed communities.Generally, dry matter yields of E+ tall fescue were greaterthan E- tall fescue regardless of whether they were grown inpure or mixed communities. As time progressed, the differencein dry matter yield between E+ and E- tall fescue grown in mixedcommunities was greater than that of the pure communities. Relativecrowding coefficients increased as time progressed. Relativecrowding coefficients at the Watkinsville location were greaterafter 5 years than those at the Plant Sciences Farm. Therefore,site specific conditions exist which affect the competitivenessof E- tall fescue and degree of encroachment by E+ tall fescue.Research is needed to identify which biotic, abiotic and managementvariables exacerbate encroachment of E+ tall fescue to betterdefine the conditions which best suit E- tall fescue.Copyright1998 Annals of Botany Company tall fescue, endophyte,Neotyphodium coenophialum,Festuca arundinacea, competition, population density     

Carbon Balance of Tall Fescue (Festuca arundinacea Schreb.): Effects of Nitrogen Fertilization and the Growing Season

The C balance of a tall fescue sward grown under different ratesof N fertilization in summer, autumn, and spring was calculatedusing models derived from measurements of shoot growth, canopygross photosynthesis, shoot respiration and of C partitioningto the roots. Under the diverse growing conditions associatedwith the seasons and the N fertilization, C utilization forabove- and below-ground biomass accumulation never exceeded39 and 14% of the canopy gross photosynthesis, respectively.Carbon losses attributed to root respiration and exudation,which were estimated by difference between canopy net photosynthesisand total growth, ranged between 3 and 30% of canopy gross photosynthesis.Seasonal differences in shoot growth could be attributed tothe amount of intercepted radiation, the radiation-use efficiencyand the C partitioning to the roots. The effect of N deficiencyon shoot growth can be attributed to its effects on canopy photosynthesis(principally resulting from changes in intercepted photosyntheticallyactive radiation) and C partitioning. In comparison with theeffect on shoot growth, the effect of the N deficiency on thecanopy gross photosynthesis per unit of light intercepted overthe regrowth cycle was limited. It is concluded that most ofthe effect of N fertilization on shoot growth is due to changesin C partitioning which result in faster leaf area developmentand greater light interception.Copyright 1994, 1999 AcademicPress Tall rescue, Festuca arundinacea Schreb., carbon balance, nitrogen, grass, fertilization     

The Effects of Nitrogen Fertilization and the Growing Season on Photosynthesis of Field-grown Tall Fescue (Festuca arundinacea Schreb.) Canopies

Canopy gross photosynthesis of tall fescue receiving three tofour rates of N fertilization was studied under field conditionsduring three contrasting growing seasons. Under non-limitingN growing conditions, the growing seasons did not have a significanteffect on the maximum canopy gross photosynthesis (canopy grossphotosynthesis at saturating PAR) and the maximum light yield(quantum efficiency of the canopy at low PAR). In the absenceof N fertilization and for a similar LAI, the values of themaximum canopy gross photosynthesis were approximately equalto 70% of those obtained under non-limiting N conditions. Thisresponse of the tall fescue canopy to N concentration is muchsmaller than that reported at the leaf level. The reductionin canopy photosynthetic capacity with no N applied comparedto non-limiting N conditions is much less than the reductionobserved previously in above-ground dry matter accumulation.The effect of N fertilization on above-ground dry matter accumulationis due primarily to changes in C partitioning and the resultingfaster leaf area development and greater light interceptionrather than the effect of N on the canopy photosynthetic capacityper se .Copyright 1993, 1999 Academic Press Festuca arundinacea Schreb., photosynthesis, nitrogen, grass, carbon     

Nitrogen Metabolism of the Upper Three Leaf Blades of Wheat at Different Soil Nitrogen Levels

Upper three leaf blades on the mainshoot of wheat cultivar, cv. Pusa Lerma, grown under three soil nitrogen levels (0, 30 and 120 kg ha^-1), were examined for changes in total reduced nitrogen and protease activity at pH 4.0 and 7.0. No net loss of reduced nitrogen takes place prior to and around anthesis. The protease activity is low during this period. At later stages there is rise in the loss of nitrogen which is paralleled by enhancement in protease activity. From amongst the leaf blades, nitrogen concentration is significantly high in the flag and penultimate as compared to the values in the third leaf blade. There were significant differences in protease activity (pH 4.0) amongst the leaf blades. At pH 7.0, however, the differences between the flag and penultimate leaf blades were not significant. Highest enzyme activity was in the flag followed by penultimate and then third leaf blade. Soil N application significantly enhanced the nitrogen content of all the leaf blades. At pH 4.0, the protease activity (g fr. wt.^-1) increased significantly due to soil N application (N₃₀ over N₀). There was, however, decline in the enzyme activity at pH 7.0, though the differences at different soil N levels were not significant. Analysis in terms of μmol N (reduced form) accumulated in the grains (ear)^-1 revealed that two-thirds of N is translocated by 28-day stage and the rest between 28-day and final harvest. The three leaf blades together contributed 22.7, 32.6 and 48.5% of the grain N (ear)^-1 at N₀, N₃₀ and N₁₂₀- respectively. Most of the nitrogen applied to the soil is reduced by these leaf blades.     

The Effects of Nitrogen Fertilization and the Growing Season on Carbon Partitioning in a Sward of Tall Fescue (Festuca arundinacea Schreb)

The effect of N fertilization on the relative carbon partitioningto the roots of tall fescue (Festuca arundinacea Schreb ), grownunder field conditions, was studied with a ¹⁴C-labelling techniqueon three regrowths representing contrasting growing seasonsUnder non-limiting N growing conditions, the relative carbonpartitioning to the roots averaged 17.0, 15 8, and 11 1% inthe summer, autumn, and spring regrowths, respectively The relativecarbon partitioning to the roots increased during the summerand autumn regrowths but decreased during the spring regrowthIn the absence of N fertilization, the relative carbon partitioningto the roots averaged 31 3, 26 5, and 26 7 in the summer, autumn,and spring regrowths, respectively The results were interpretedin terms of a functional equilibrium between the shoots andthe roots It was concluded that, for a dense canopy of a perennialgrass growing under fluctuating conditions of solar radiationand temperature, the relative growth of the roots compared tothe relative growth of the total biomass is primarily a functionof the shoot biomass Festuca arundinacea Schreb, carbon, partitioning, nitrogen, root growth, fertilization, grass     

高羊茅转基因研究进展

高羊茅为很重要的多年生冷季型草坪草,生物技术在其品种改良中具有很大的应用潜力。本文对高羊茅植株再生体系的建立及遗传转化方面的研究进展进行了综述。同时,对高羊茅转基因研究中存在的问题和前景作了讨论。     

多效唑对高羊茅叶片中淀粉酶和转化酶活性的影响（简报）

高羊茅草坪草施用多效唑后,叶片的垂直生长受抑,叶片光合同化物向根系运输增强,叶片和根系中淀粉及可溶性糖含量升高,且叶片中淀粉含量与淀粉增活性正相关（r=0.88),另外,酸性转化酶活性也增加,但中性转化酶活性则降低,叶片中可溶性碳水化合物含量一直维持在较高水平。     

Accumulation of Ergopeptide Alkaloids in Symbiotic Tall Fescue Grown under Deficits of Soil Water and Nitrogen Fertilizer

The fungus Acremonium coenophialum is endophytically associated with tall fescue (Festuca arundinacea Schreber). Within this symbiotum the fungus produces ergopeptide alkaloids, which are associated with livestock toxicoses. Environmental effects on the production of ergot alkaloids within the symbiotum are unknown. We conducted a greenhouse study of the effects of flooding, nitrogen rate during fertilization (11, 73, and 220 mg of N per pot weekly), nitrogen form (3.4 and 34 mg of N as NH₄⁺ or NO₃^- per pot), and drought stress (-0.03, -0.05, and -0.50 MPa) on ergopeptide alkaloid concentrations in one genotype of nonsymbiotic and symbiotic tall fescue grown in plastic pots. It was determined that the concentration of ergovaline, the major type of ergopeptide alkaloid, was increased but was not as high as that in nonflooded controls. Total ergopeptide and ergovaline concentrations in plants receiving high (220 mg of N per pot) and low (11 mg of N per pot) levels of NH₄NO₃ fertilization were not affected by flooding. The form of nitrogen was important since all concentrations of NO₃^--N increased ergopeptide alkaloid content, as opposed to the effects of NH₄⁺-N, which was effective only at high concentrations (34 mg of N per pot). Ergopeptide concentrations were highest in drought-stressed plants grown at -0.50 MPa and fertilized at the moderate or high N rate. The results suggest that within this genotype, ergopeptide alkaloid biosynthesis by the fungus is not appreciably affected by flooding but is greatly increased by high rates of N fertilization and moderate water deficit.     

土施多效唑对高羊茅生长的效应

土施条件下,多效唑用量与高羊茅生长速率存在显著的二次函数关系,其矮化效应随着多效唑用量的增大而增大,剂量超过0.65g·m-2时效应减弱;植株地上部生物量和生长速率有类似关系,剂量超过0.8g·m-2时效应不显著,但地下部生物量随多效唑供给量增加而递减。多效唑低于0.35g·m-2的高羊茅叶色深绿,超过此剂量叶片即枯黄,且随着剂量增大而更加严重。高羊茅叶片总含水量随着多效唑用量增大而减小,但在干旱胁迫条件下,叶中总含水量随着多效唑用量增大而增大;束缚水含量也有上升。高羊茅在严重干旱后的生长恢复能力随着多效唑用量增大而增大,超过0.95g·m-2时即下降。