Physiological mechanism of hypertolerance of cadmium in Kentucky bluegrass and tall fescue: Chemical forms and tissue distribution

Kentucky bluegrass (Poa pratensis) and tall fescue (Festuca arundinacea) are hypertolerant grasses to soil cadmium contamination. Little information is available on their tolerance mechanism. A sand culture and a hydroponic culture experiment were designed to investigate the Cd chemical form changes and its translocation in different tissues. The results showed that Kentucky bluegrass and tall fescue can tolerate 50–200 mg kg⁻¹ of soil Cd stresses and accumulate as high as 4275 and 2559 mg Cd kg⁻¹ DW, respectively, in their shoots without the loss of shoot biomass. Their Cd hypertolerance was correlated with an increase of the undissolved Cd phosphates in the leaves in both grass species, as determined by sequential solvent extraction procedures. The superior Cd tolerance of tall fescue to Kentucky bluegrass was associated with less Cd translocation into the stele of roots and less Cd transported to leaves. The pectate- and protein-integrated Cd forms may be involved in the symplastic translocation of Cd from cortex into stele, and this may lead the higher Cd concentrations in the stele of roots and then above ground leaves via long-distance transport in Kentucky bluegrass.     

Differential metabolic responses of perennial grass Cynodon transvaalensis×Cynodon dactylon (C₄) and Poa Pratensis (C₃) to heat stress

Differential metabolic responses to heat stress may be associated with variations in heat tolerance between cool‐season (C₃) and warm‐season (C₄) perennial grass species. The main objective of this study was to identify metabolites associated with differential heat tolerance between C₄ bermudagrass and C₃ Kentucky bluegrass by performing metabolite profile analysis using gas chromatography‐mass spectrometry. Plants of Kentucky bluegrass (Poa Pratensis‘Midnight’) and hybrid bermudagrass (Cynodon transvaalensis×Cynodon dactylon‘Tifdwarf’) were grown under optimum temperature conditions (20/15°C for Kentucky bluegrass and 30/25°C for bermudagrass) or heat stress (35/30°C for Kentucky bluegrass and 45/40°C for bermudagrass). Physiological responses to heat stress were evaluated by visual rating of grass quality, measuring photochemical efficiency (variable fluorescence to maximal fluorescence) and electrolyte leakage. All of these parameters indicated that bermudagrass exhibited better heat tolerance than Kentucky bluegrass. The metabolite analysis of leaf polar extracts revealed 36 heat‐responsive metabolites identified in both grass species, mainly consisting of organic acids, amino acids, sugars and sugar alcohols. Most metabolites showed higher accumulation in bermudagrass compared with Kentucky bluegrass, especially following long‐term (18 days) heat stress. The differentially accumulated metabolites included seven sugars (sucrose, fructose, galactose, floridoside, melibiose, maltose and xylose), a sugar alcohol (inositol), six organic acids (malic acid, citric acid, threonic acid, galacturonic acid, isocitric acid and methyl malonic acid) and nine amino acids (Asn, Ala, Val, Thr, γ‐Aminobutyric acid, IIe, Gly, Lys and Met). The differential accumulation of those metabolites could be associated with the differential heat tolerance between C₃ Kentucky bluegrass and C₄ bermudagrass.     

Comparison of tall fescue (Cyperales: Gramineae) to other cool-season turfgrasses for tolerance to European chafer (Coleoptera: Scarabaeidae)

Three cultivars of tall fescue, Festuca arundinacea Schreb., were compared with three cultivars each of fine fescue (Festuca spp.), Kentucky bluegrass (Poa pratensis L.), and perennial ryegrass (Lolium perenne L.) to evaluate tolerance to root-feeding by European chafer grubs, Rhizotrogus majalis (Razoumowsky). Potted turfgrasses were infested with initial densities equivalent to 33 or 66 grubs per 0.1 m2 on 19 August 2000. More grubs were added in late September and October, bringing the total to 66 or 143 grubs per 0.1 m2. Plant growth, root loss, weight gain, and survival of grubs were measured. The experiment was repeated in fall of 2001 with an initial density of 66 grubs per 0.1 m2. The proportion of root mass lost as a result of grub feeding was a function of turf species, root growth, grub survival, and grub growth during the test. Grubs gained the most weight and consumed the most roots when feeding on fine fescue. Fine fescue suffered the greatest percentage of root loss in 2000, despite having the most rapid root growth and largest mass in control pots. Cultivars of tall fescue appeared to be the most tolerant of grub feeding, having the smallest reduction in root mass in both years. Data from fine fescue, Kentucky bluegrass, and perennial ryegrass cultivars were not as consistent as tall fescue, because for some cultivars root growth and grub survival were different between years. We also found that grubs increased in mass by 20% when the mass of available roots was doubled.     

Photosynthesis,respiration, and carbon allocation of two cool-season perennial grasses in response to surface soil drying

The study was conducted to investigate carbon metabolic responses to surface soil drying for cool-season grasses. Kentucky bluegrass (Poa pratensis L.) and tall fescue (Festuca arundinaceae Schreb.) were grown in a greenhouse in split tubes consisting of two sections. Plants were subjected to three soil moisture regimes: (1) well-watered control; (2) drying of upper 20-cm soil (upper drying); and (3) drying of whole 40-cm soil profile (full drying). Upper drying for 30 d had no dramatic effects on leaf water potential (Ψ_leaf) and canopy photosynthetic rate (P_n) in either grass species compared to the well-watered control, but it reduced canopy respiration rate (R_canopy) and root respiration rate in the top 20 cm of soil (R_top). For both species in the lower 20 cm of wet soil, root respiration rates (R_bottom) were similar to the control levels, and carbon allocation to roots increased with the upper soil drying, particularly for tall fescue. The proportion of roots decreased in the 0-20 cm drying soil, but increased in the lower 20 cm wet soil for both grass species; the increase was greater for tall fescue. The Ψ_leaf, P_n, R_canopy, R_top, R_bottom, and carbon allocation to roots in both soil layers were all significantly higher for upper dried plants than for fully dried plants of both grass species. The reductions in R_canopy and R_top in surface drying soil and increases in root respiration and carbon allocation to roots in lower wet soil could help these grasses cope with surface-soil drought stress. This revised version was published online in June 2006 with corrections to the Cover Date.     

Festuca campestris density and defoliation regulate abundance of the rhizomatous grass Poa pratensis in a fallow field

Invasion by the rhizomatous grass Kentucky bluegrass (Poa pratensis) is a global phenomenon, including into foothills rough fescue (Festuca campestris) grasslands of southwestern Alberta, Canada. In order to better understand the competitive relationships between these species, we conducted a fallow field study where rough fescue bunchgrass tussocks were transplanted at one of three planting densities (15, 30, or 45 cm spacing), and then subject to various treatments in a factorial design, including one‐time intensive summer defoliation and seeding of bluegrass into adjacent bare soil. Rough fescue plants exhibited marked intraspecific competition, as high planting densities increased tussock mortality, while decreasing plant tiller counts and relative inflorescence production, together with plant and tiller‐specific mass. However, high densities of the bunchgrass also reduced the cover and biomass of encroaching bluegrass, coincidental with reduced resource (soil moisture and light) availability in mid‐summer. Although summer defoliation increased rough fescue tiller counts, this disturbance reduced plant and tiller mass, and also increased Kentucky bluegrass. We conclude that while high densities of nondefoliated stands of rough fescue may increase resistance to bluegrass encroachment, a reduction in either fescue plant density or vigor via defoliation can increase the risk of bluegrass invasion within northern temperate grassland.     

Proteins and Metabolites Regulated by Trinexapac-ethyl in Relation to Drought Tolerance in Kentucky Bluegrass

Plants have developed various mechanisms in adaptation to water deficit stress, including growth retardant to reduce water loss. Previous studies reported that plants treated with a growth inhibitor, trinexapac-ethyl (TE), had improved drought tolerance. The objective of this study was to determine alterations in proteins and metabolite accumulation associated with drought tolerance improvement in a perennial grass species, Kentucky bluegrass (Poa pratensis), induced by TE application. Plants were treated with TE [1.95 ml l⁻¹ (v:v); a.i. TE = 0.113%] through foliar spray for 14 days, and then subjected to drought stress by withholding irrigation for 15 days in growth chambers. TE-treated plants exhibited significantly higher relative water content and photosynthetic capacity and lower membrane leakage than nontreated plants under drought stress, suggesting TE-enhanced drought tolerance in Kentucky bluegrass. Physiological improvement in drought tolerance through TE application was associated with the increased accumulation of various proteins and metabolites, including ferritin, catalase, glutathione-S-transferase, Rubisco, heat shock protein 70, and chaperonin 81, as well as fatty acids (palmitic acid, α-linolenic acid, linoleic acid, and octadecanoic acid). Our results suggest that TE may regulate metabolic processes for antioxidant defense, protective protein synthesis, photorespiration, and fatty acid synthesis, and thereby contribute to better drought tolerance in Kentucky bluegrass.     

Involvement of antioxidants and lipid peroxidation in the adaptation of two cool-season grasses to localized drought stress

In natural environments, drought often occurs in surface soil while water is available for plant uptake deeper in the soil profile. The objective of the study was to examine the involvement of antioxidant metabolism and lipid peroxidation in the responses of two cool-season grasses to surface soil drying. Kentucky bluegrass (Poa pratensis L) and tall fescue (Festuca arundinacea Schreb.) were grown in split tubes, consisting of two sections (each 10 cm in diameter and 20 cm long). Grasses were subjected to three soil moisture regimes: (a) well-watered control: whole soil profile was watered; (b) surface drying: surface 20 cm of soil was dried by withholding irrigation and the lower 20 cm of soil was watered; (c) full drying: whole soil profile was dried. Surface drying had no effects on relative water content (RWC) and chlorophyll content (Chl) for both grasses and only slightly reduced shoot growth for tall fescue. Superoxide dismutase (SOD) activity increased, while catalase (CAT) and peroxidase (POD) activities remained unchanged during most periods of surface drying. Malondialdehyde (MDA) content was unaffected by surface drying for tall fescue, but increased initially and then decreased to the control level for Kentucky bluegrass. Under full drying, RWC, Chl content, and shoot dry weight decreased, but MDA content increased in both grasses; SOD and POD activities initially increased transiently and then decreased; CAT remained unchanged for 25 days and then decreased. These results suggested that both Kentucky bluegrass and tall fescue were capable of surviving surface soil drying. This capability could be related to increases in antioxidant activities, particularly SOD and CAT. However, full drying suppressed antioxidant activities and induced lipid peroxidation.     

Neotyphodium Coenophialum-Infected Tall Fescue and Its Potential Application in the Phytoremediation of Saline Soils

The growth response of endophyte-infected (EI) and endophyte-free (EF) tall fescue to salt stress was investigated under two growing systems (hydroponic and soil in pots). The hydroponic experiment showed that endophyte infection significantly increased tiller and leaf number, which led to an increase in the total biomass of the host grass. Endophyte infection enhanced Na accumulation in the host grass and improved Na transport from the roots to the shoots. With a 15 g l^?1 NaCl treatment, the phytoextraction efficiency of EI tall fescue was 2.34-fold higher than EF plants. When the plants were grown in saline soils, endophyte infection also significantly increased tiller number, shoot height and the total biomass of the host grass. Although EI tall fescue cannot accumulate Na to a level high enough for it to be termed a halophyte, the increased biomass production and stress tolerance suggested that endophyte / plant associations had the potential to be a model for endophyte-assisted phytoextraction in saline soils.     

Endophytic fungus improves growth and metal uptake of Lolium arundinaceum Darbyshire ex. Schreb

The effect of endophyte infection on plant growth, cadmium (Cd) uptake, and Cd translocation was investigated using tall fescue (Lolium arundinaceum) grown in greenhouses in contaminated solution. Endophyte infection significantly increased tiller number and biomass of the host grass under both control and Cd-stress conditions. Endophyte infection not only enhanced Cd accumulation in tall fescue, but also improved Cd transport from the root to the shoot. Under 20 mg L(-1) Cd stress, the phytoextraction efficiency of endophyte-infected (EI) tall fescue was 2.41-fold higher than endophyte-free plants. Although the total Cd accumulation in EI tall fescue was insufficient for practical phytoextraction applications, the observed high biomass production and tolerance of stress from abiotic factors including heavy metals, gives endophyte/plant associations the potential to be a model for endophyte-assisted phytoremediation of metal-polluted soils.     

Use of herbivore‐induced plant volatiles as search cues by Tiphia vernalis and Tiphia popilliavora to locate their below‐ground scarabaeid hosts

Japanese beetle, Popillia japonica Newman, and oriental beetle, Anomala orientalis (Waterhouse) (both Coleoptera: Scarabaeidae) are considered invasive species and have been reported as key pests of urban landscapes in the Northeastern USA. Tiphia vernalis Rohwer and Tiphia popilliavora Rohwer (Hymenoptera: Tiphiidae) were introduced as biocontrol agents against these beetles. These parasitic wasps burrow into the soil and search for grubs. When a host is found, the wasp attaches an egg in a location that is specific for the wasp species. It is unknown if these wasps can detect patches of concealed hosts from a distance above ground and what role, if any, herbivore‐induced plant volatiles play in their host location. This study evaluated the responses of female T. vernalis and T. popilliavora to grub‐infested and healthy plants in Y‐tube olfactometer bioassays. Also the effect of root herbivory on the composition of turfgrass (Poaceae) volatile profiles was investigated by collecting volatiles from healthy and grub‐infested grasses. Tiphia wasps were highly attracted to volatiles emitted by grub‐infested tall fescue (Festuca arundinacea Schreb.) and Kentucky bluegrass (Poa pratensis L.) over healthy grasses. In contrast, wasps did not exhibit a significant preference for grub‐infested perennial ryegrass (Lolium perenne L.) as compared with the control plants. The terpene levels emitted by grub‐infested Kentucky bluegrass and tall fescue were greater than that of control plants. Low levels of terpenes were observed for both test and control perennial ryegrass. The elevated levels of terpenes emitted by grub‐infested Kentucky bluegrass and tall fescue coincided with the attractiveness to the tiphiid wasps. Here, we provide evidence that plant exposure to root‐feeding insects P. japonica and A. orientalis resulted in an increase in terpenoid levels in turfgrasses, which strongly attracts their above‐ground parasitoids.     

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.     

Lipidomic reprogramming associated with drought stress priming‐enhanced heat tolerance in tall fescue (Festuca arundinacea)

Stress priming by exposing plants to a mild or moderate drought could enhance plant tolerance to subsequent heat stress. Lipids play vital roles in stress adaptation, but how lipidomic profiles change, affecting the cross‐stress tolerance, is largely unknown. The objectives of this study were to perform lipidomics, to analyse the content, composition, and saturation levels of lipids in leaves of tall fescue (Festuca arundinacea) following drought priming and subsequent heat stress, and to identify major lipids and molecular species associated with priming‐enhanced heat tolerance. Plants were initially exposed to drought for 8 days by withholding irrigation and subsequently subjected to 25 days of heat stress (38/33°C day/night) in growth chambers. Drought‐primed plants maintained significantly higher leaf relative water content, chlorophyll content, photochemical efficiency, and lower electrolyte leakage than nonprimed plants under heat stress. Drought priming enhanced the accumulation of phospholipids and glycolipids involved in membrane stabilization and stress signalling (phosphatidic acid, phosphatidylcholine, phosphatidylinositol, phosphatidylglycerol, and digalactosyl diacylglycerol) during subsequent exposure to heat stress. The reprogramming of lipid metabolism for membrane stabilization and signalling in response to drought priming and subsequent exposure to heat stress could contribute to drought priming‐enhanced heat tolerance in cool‐season grass species.     

Differential accumulation of proteins in leaves and roots associated with heat tolerance in two Kentucky bluegrass genotypes differing in heat tolerance

To understand the mechanisms of heat stress responses in perennial grasses, differential proteins in leaves and roots of two genotypes of Kentucky bluegrass (Poa pratensis), including heat-tolerant ‘Midnight’ and heat-sensitive ‘Brilliant’, were analyzed with two-dimensional gel electrophoresis (2-DE) and mass spectrometry (MS). Plants were exposed to heat stress for 28 days in growth chambers. Under 7–28 days of heat stress, leaf photochemical efficiency declined significantly while electrolyte leakage increased in leaves and roots, and to a lesser extent for heat-tolerant ‘Midnight’ than for heat-sensitive ‘Brilliant’. Compared with leaves, cell membrane damage due to heat stress was more severe in roots. The 2-DE and MS analysis identified 37 heat-responsive proteins in leaves, 28 heat-responsive proteins in roots; 14 proteins in leaves and 9 proteins in roots exhibited differential expression between the two genotypes. The results indicate that proteins involved in metabolism and energy in leaves and those in antioxidant defense in roots are associated with heat tolerance in Kentucky bluegrass. The differential accumulation of these proteins might be the reason for different heat tolerance in two Kentucky bluegrass genotypes in aerial and underground parts.     

Grass species and their fungal symbionts affect subsequent forage growth

Persistence of forage grasses is enhanced through the deliberate and selective use of symbiotic fungal endophytes that confer benefits, particularly pest resistance. However, they have also been implicated in reduced plant community diversity as a result of directly or indirectly enhancing competitive ability. A relatively underexplored mechanism by which endophytes might influence pasture plant composition is by altering the biotic or abiotic soil conditions. To examine the soil conditioning effects of forage grass species and their fungal symbionts we tested the responses of three pasture plants, perennial ryegrass, prairie grass, and white clover in nine different soils that had been conditioned by monocultures of endophyte-containing (E+), or endophyte-free (E?), perennial ryegrass, tall fescue, or meadow fescue. Conditioning grass species had little effect on the responses of perennial ryegrass and prairie grass regardless of E+ or E? treatments. In contrast, conditioning species had a strong effect on the response of white clover, resulting in reduced biomass when grown in perennial ryegrass conditioned soils. The presence of endophyte also had significant growth consequences for white clover, but was either positive or negative depending on the conditioning grass species. In comparison to their respective E? treatments, E+ tall and meadow fescue conditioned soils resulted in reduced biomass of white clover, whereas E+ perennial ryegrass conditioned soils resulted in increased biomass of white clover. Among the conditioning strains (AR1, AR37, NEA2, WE) of E+ perennial ryegrass, white clover showed significantly different responses, but all responses were positive in comparison to the E? treatment. By examining the effects of several grass species and endophyte strains, we were able to determine the relative importance of grass species vs. fungal symbiont on soil conditioning. Overall, the conditioning effect of grass species was stronger than the effects associated with endophyte, particularly with regard to the response of white clover. We conclude that both grass species and their fungal endophytes can influence pasture plant community composition through plant–soil feedback.     

Turfgrass, crop, and weed hosts of Blissus occiduus (Hemiptera: Lygaeidae)

Blissus occiduus Barber is an important pest of buffalograss, Buchlo? dactyloides (Nuttall) Engelmann, turf. No-choice studies documented the susceptibility of selected turfgrasses, crops, and weeds to B. occiduus feeding. Highly to moderately susceptible grasses included buffalograss; yellow Setaria glauca (L.) and green foxtail Setaria viridis (L.); Kentucky bluegrass, Poa pratensis L.; perennial ryegrass, Lolium perenne L.; brome, Bromus spp. Leyss.; zoysiagrass, Zoysia japonica Steudel; Bermuda grass, Cynodon dactylon (L.) Pers.; sorghum, Sorghum bicolor (L.) Moench; tall fescue, Festuca arundinacea Schreb.; and barley Hordeum vulgare (L.). Slightly to nonsusceptible grasses included fine fescue, Festuca ovina hirtula L.; rye, Secale cereale L.; crabgrass Digitaria sanguinalis (L.); bentgrass, Agrostis palustris Huds.; wheat, Tritium aestivun L.; corn, Zea mays L.; fall panicum Panicum dichotomiflorum Michx.; and St. Augustinegrass, Stenotaphrum secundatum (Walt.) Kuntze. The reproductive potential of B. occiduus was also investigated on these same grasses. B. occiduus produced offspring on 15 of the 18 turfgrass, crop, and weed species evaluated. No reproduction occurred on either Bermuda grass or St. Augustinegrass, and buffalograss plants were killed by B. occiduus feeding before offspring could be produced.     

Effects of endophytic fungi on some drought tolerance mechanisms of tall fescue in a hydroponics culture

Neotyphodium, a seed-transmissible nonpathogenic fungal endophyte (symbiont) is considered beneficial because endophyte-infected grasses are more drought-tolerant, produce more dry matter, utilize soil nitrogen more efficiently, and deter insects. In this study, the effects of endophytes on physiological mechanisms of drought tolerance in tall fescue (Festuca arundinacea Schreb.) were studied in a greenhouse. Two clonally propagated genotypes of tall fescue (F. arundinacea Schreb.), naturally containing endophyte (EI), and their endophyte-free ramets (EF) were tested at three water stress treatments exerted by PEG 6000 in a hydroponics system. Relative water content (RWC), cell membrane stability (CMS), proline and chlorophyll contents in plant leaves were measured during water stress treatments. After harvest, K⁺, Ca²⁺, and Mg²⁺ contents were measured in plant roots and shoots. After 20 days under stress conditions, plants were transferred to basal hydroponics medium, and their survival after stress relief was evaluated. The results showed that endophyte considerably contributes to host grass water stress tolerance. Both genotypes of EI and EF plants did not differ in RWC, but, regardless of the infection status, genotype 75 had the higher RWC than genotype 83. EI clones of both genotypes maintained slightly higher chlorophyll content and membrane stability than EF clones, although these differences were not significant. The EI plants of genotype 83 concentrated significantly more proline than EF plants, but in the genotype 75, differences between EI and EF clones were not significant. Plant mineral absorption was also influenced by the endophyte presence. EI clones had the higher concentrations of K⁺ in the shoots of both genotypes. The Mg²⁺ and Ca²⁺ contents in EF plants of both genotypes were higher than EI plants in the roots, but in the shoots there were no differences between EI and EF clones. EI clones survived longer after stress removal. These results strongly suggest that Neotyphodium endophytes exert their effects on tall fescue drought tolerance through alteration of various physiological mechanisms involved. Published in Russian in Fiziologiya Rastenii, 2009, Vol. 56, No. 4, pp. 563–570. This test was submitted by the authors in English.