Relative contribution of delaying senescence to growth compensation after defoliation

Delaying senescence as a response to tissue losses has been reported in some studies, but there is no information about its influence in growth compensation. We performed a first test of the relative contribution of delaying senescence after defoliation to growth compensation in Dactylis glomerata L. by means of an iterative growth analysis modified to estimate tissue losses to senescent leaves. We show that Dactylis glomerata overcompensated for relative growth rate after defoliation, mainly by slowing down senescence, and to a lesser extent by increasing the newly assimilated mass allocated to leaves.     

Competition between Australian native and introduced grasses along a nutrient gradient

Abstract Seven grass species were grown in monocultures and in multispecies mixtures along a gradient of total nutrient levels that ranged from 1/64 to 16× the normal level of nutrient solution. The seven grasses represented three ecological groups: (i) three perennial species native to Australia (Themeda triandra, Poa labillardieri and Danthonia carphoides); (ii) two introduced annuals (Vulpia bromoides and Hordeum leporinum); and (iii) two introduced perennials (Lolium perenne and Dactylis glomerata). We hypothesized that the native grasses would prove less competitive when grown at increased nutrient levels than those introduced from Europe. Results supported the hypothesis. The native species were unable to compete in mixtures even at the lowest nutrient level, where T. triandra was the most productive species in monoculture. Lolium perenne and Dactylis glomerata dominated mixtures at intermediate nutrient levels. The responses of the annual introduced grasses differed in that Vulpia bromoides showed an optimum at intermediate nutrient levels in both monoculture and in mixtures, whereas Hordeum leporinum dominated at the highest nutrient levels in mixture but was suppressed by V. bromoides, L. perenne and D. glomerata at intermediate levels. The results are discussed in terms of predicting species responses in mixtures from their performance in monocultures as well as in terms of previous observations on the sequential changes in botanical composition of south‐eastern Australian grasslands after 150 years of continuous grazing by sheep.     

Orchardgrass (<Emphasis Type="Italic">Dactylis glomerata</Emphasis> L.) EST and SSR marker development,annotation, and transferability

Orchardgrass, or cocksfoot [Dactylis glomerata (L.)], has been naturalized on nearly every continent and is a commonly used species for forage and hay production. All major cultivated varieties of orchardgrass are autotetraploid, and few tools or information are available for functional and comparative genetic analyses and improvement of the species. To improve the genetic resources for orchardgrass, we have developed an EST library and SSR markers from salt, drought, and cold stressed tissues. The ESTs were bi-directionally sequenced from clones and combined into 17,373 unigenes. Unigenes were annotated based on putative orthology to genes from rice, Triticeae grasses, other Poaceae, Arabidopsis, and the non-redundant database of the NCBI. Of 1,162 SSR markers developed, approximately 80% showed amplification products across a set of orchardgrass germplasm, and 40% across related Festuca and Lolium species. When orchardgrass subspecies were genotyped using 33 SSR markers their within-accession similarity values ranged from 0.44 to 0.71, with Mediterranean accessions having a higher similarity. The total number of genotyped bands was greater for tetraploid accessions compared to diploid accessions. Clustering analysis indicated grouping of Mediterranean subspecies and central Asian subspecies, while the D. glomerata ssp. aschersoniana was closest related to three cultivated varieties.     

Dry matter allocation and nitrogen productivity explain growth responses to photoperiod and temperature in forage grasses

The mechanisms responsible for fluctuations in species composition of semi-natural grassland are not well understood. To identify plant traits that determine the poor competitive ability of Festuca pratensis compared to Dactylis glomerata especially during summer, the growth of both grasses was monitored over time and at different temperatures and photoperiods. Plants of both grasses were grown from seed with non-limiting nutrient supply at three day/night temperatures (11/6, 18/13 and 25/20°C) and two photoperiods (16 and 12 h). F. pratensis had a significantly lower relative growth rate than D. glomerata, mainly due to its lower specific leaf area and reduced nitrogen productivity. At high temperature, F. pratensis had a considerably lower root weight ratio than D. glomerata leading to substantially slower root growth. F. pratensis responded to a shorter photoperiod with an increase in the net assimilation rate, whereas D. glomerata responded with an increase in specific leaf area. The low competitive ability of F. pratensis compared to D. glomerata was mainly associated with its lower specific leaf area and nitrogen productivity. The stronger decline of its competitive ability during summer was probably related to the decreased allocation of dry matter to the roots at higher temperatures which leads to slower root growth compared to D. glomerata. Received: 7 September 1998 / Accepted: 29 July 1999     

Plant resource-use strategies: the importance of phenotypic plasticity in response to a productivity gradient for two subalpine species

Background and Aims

Functional traits are indicators of plant interactions with their environment and the resource-use strategies of species can be defined through some key functional traits. The importance of genetic variability and phenotypic plasticity in trait variations in response to a common environmental change was investigated in two subalpine species.

Methods

Two species with contrasted resource-use strategies, Dactylis glomerata and Festuca paniculata, were grown along a productivity gradient in a greenhouse experiment. Functional traits of different genotypes were measured to estimate the relative roles of phenotypic plasticity and genetic variability, and to compare their levels of phenotypic plasticity.

Key Results

Trait variability in the field for the two species is more likely to be the result of phenotypic plasticity rather than of genetic differentiation between populations. The exploitative species D. glomerata expressed an overall higher level of phenotypic plasticity compared with the conservative species F. paniculata. In addition to different amplitudes of phenotypic plasticity, the two species differed in their pattern of response for three functional traits relevant to resource use (specific leaf area, leaf dry matter content and leaf nitrogen content).

Conclusions

Functional trait variability was mainly the result of phenotypic plasticity, with the exploitative species showing greater variability. In addition to average trait values, two species with different resource-use strategies differed in their plastic responses to productivity.     

Untersuchungen zur physiologischen Spezialisierung von Erysiphe graminis DC

Zusammenfassung In den vorliegenden Untersuchungen wurde der Wirtspflanzenbereich einer Mehltaupopulation von Dactylis glomerata L., Sorte Motterwitzer, überprüft. Von 460 infizierten Grasarten blieben 420 befallsfrei, 40 erwiesen sich als anfällig. Am stärksten befallen wurden die drei Arten Dactylis aschersoniana Graebner, Dactylis glomerata L. und Dactylis polygama Horvat sowie die Subspecies D. glomerata L. spp. aschersoniana (Graebn.) Thell., die aber insgesamt in ihrem Verhalten sehr unausgeglichen waren. Eine unerwartet geringe Anfälligkeit von Dactylis woronowii Ovcz. müßte nochmals überprüft werden. Als sehr anfällig erwiesen sich die drei Grasarten Bouteloua hirsuta Lag., Danthonia provinzialis DC. und Sesleria latifolia (Adam) Degen. Geringer Befall konnte auch an einigen Wildgräsern der Gattungen Agropyron, Bromus, Festuca, Mibora, Poa und Sesleria nachgewiesen werden. Vom Getreide wird nur die Gerste vom Knaulgras-Mehltau befallen. Da sowohl bei der Wildform als auch bei der Zuchtsorte Motterwitzer von Dactylis glomerata L. über 10% befallsfreie Pflanzen gefunden wurden, erscheint die Züchtung mehltauresistenter Sorten von Dactylis glomerata L. nicht ohne Aussicht auf Erfolg.

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Studies on the physiological specialization of Erysiphe graminis DCIV. The host plants of cocksfoot mildew

Summary In the described experiments the interaction of 460 grass species with a mildew population obtained from Dactylis glomerata L. Motterwitzer was examined. 420 species remained free of symptoms, while 40 species were susceptible. The most susceptible ones were Dactylis aschersoniana Graebner, Dactylis glomerata L., Dactylis glomerata spp. aschersoniana (Graebn.) Thell., and Dactylis polygama Horvat, but all showed differences in their behaviour. The unexpectedly low susceptibility of Dactylis woronowii Ovcz. should be examined again. Three grass species Bouteloua hirsuta Lag., Danthonia provinzialis DC., and Sesleria latifolia (Adam) Degen were also highly susceptible to cocksfoot mildew, while on wild grasses of the species Agropyron, Bromus, Festuca, Mibora, Poa, and Sesleria only few symptoms could be seen. Among cereals only barley could be infected by cocksfoot mildew. Not only in the wild form of Dactylis glomerata L. but also in the cultivated variety Motterwitzer, above 10% were found to be free from infection. Therefore the breeding of resistant varieties of Dactylis glomerata L. seems to be feasible.

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Für die freundliche Unterstützung der Arbeiten möchten wir den Botanischen Gärten der Deutschen Demokratischen Republik sowie der Deutschen Bundesrepublik unseren herzlichen Dank aussprechen.

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Angenommen durch H. Stubbe     

Studies on the horizontal migration of dipterous stem borers (Oscinella spp.) in direct drilled Italian ryegrass

The distance stem boring dipterous larvae e.g. Oscinella frit L. migrate in direct drilled Italian ryegrass (Lolium multiflorum) was investigated. First, adjacent contrasting swards of Italian ryegrass or Cocksfoot (Dactylis glomerata) were grown which were, respectively, expected to be either infected with large populations of larvae or likely to be free of larvae. Sampling revealed that these expectations were realised. Swards were then desiccated by herbicide, and subsequently direct drilled with Italian ryegrass. Over 50% of the larvae in original, infested part of the sward migrated to infest tillers of the newly sown ares. The distance larvae migrated was gauged by assessing how far they were found from the perimeter of a previously uninfested area which had been reseeded. Most larvae migrated 20 cm or less, but a small proportion appeared to migrate several metres, apparently passing many suitable host tillers as they did so.deceased September 1989     

Persistence and production of perennial grasses under water deficits and extreme temperatures: importance of intraspecific vs. interspecific variability

Extreme climatic events are expected to increase in frequency and magnitude as a consequence of global warming. Grasslands cover a large proportion of the European continent and contribute to both agricultural production and ecosystem services through inter and intraspecific genetic variability. This study analysed the effects of summer droughts and heat waves on the persistence and production of perennial forage grasses. Mediterranean and temperate populations of Dactylis glomerata L. and Festuca arundinacea (Schreb.) were compared at both Mediterranean and temperate sites in France. By manipulating canopy temperatures and water availability, grass swards in the field were subjected to cumulative summer and spring water deficits (CSSWD) ranging from 329 to 707 mm to test different projected climatic conditions and extreme summer events. Under controlled summer heat waves (6–21 days at a mean daily canopy temperature higher than 30–35 °C), there was no increase in membrane damage to surviving aerial tissues. Plant stress was thus mainly generated through greater soil water deficit. Under the greatest CSSWD, annual biomass production was reduced on average by 60% and 30% with temperate and Mediterranean populations, respectively. Thresholds for a significant increase in summer tiller mortality were seen at CSSWD higher than 450 mm for temperate populations and 550 mm for Mediterranean populations. The latter displayed lower predawn leaf water potentials in summer and recovered through intense tillering in the subsequent seasons. Under the most extreme CSSWD, fewer than 20% of tillers of temperate populations survived and their nitrogen uptake ability was drastically altered. The higher potential productivity of Mediterranean populations in winter was associated with greater frost sensitivity. The identification of thresholds for vulnerability and the determination of the role of genetic diversity will improve the management of plant resilience and the design of new plant material to cope with climate change.     

The germination of grass seeds after storage at different temperatures in aluminium foil and manilla paper packets

The germination of seeds of three species of forage grasses, Lolium perenne, Festuca pratensis and Dactylis glomerata, was studied after storage for 3–5 years under five different storage conditions: in aluminium foil packets at —25°C, 0°C and laboratory temperature (c. 18°C), and in manilla paper packets at 0°C and laboratory temperature. With Lolium perenne and Festuca pratensis high germination values at 3 and 7 days were obtained from seed stored at — 25 °C and 0°C in foil packets (5% moisture), but at laboratory temperatures, seed from foil packets gave lower germination values than those from manilla paper packets. At all three temperatures Dactylis glomerata germination after 7 and 14 days was higher in seed stored in foil than in manilla packages. With all three species stored in manilla packets, germination was higher after laboratory than cold storage.     

Comparative physiological effects of three allelochemicals and two herbicides on <Emphasis Type="Italic">Dactylis glomerata</Emphasis>

Effects of three allelochemicals (2-benzoxazolinone (BOA), p-hydroxybenzoic, and ferulic acid) and two herbicides (linuron and fluometuron) on chlorophyll fluorescence, photosynthesis, accumulation of free proline and polyamines, and total content of soluble proteins were measured to assess herbicidal activity on Dactylis glomerata. The application of chemicals generally reduced Fv/Fm (more than 25 % with p-hydroxybenzoic acid, BOA, or linuron). BOA decreased the quantum efficiency of PSII temporarily, but it did not affect photosynthesis. Polyamine content was very low, while proline content was markedly affected by some of the chemicals, thus producing some osmotic adjustment. Ferulic acid did not cause any physiological effect at all. BOA and p-hydroxybenzoic acid caused significant changes in various physiological traits of Dactylis glomerata, specially interfering with the quantum efficiency of the PSII.     

Regrowth by Swards of Subterranean Clover after Defoliation. 1. Growth, Non-structural Carbohydrate and Nitrogen Content

Swards of subterranean clover (Trifolium subterraneum L.) atLAl 6 grown in N-free nutrient solution were subjected to threedefoliation treatments which removed 30, 70 and 80% of shootdry weight. Subsequent regrowth and changes in the concentrationsof carbohydrate and nitrogen in plant components were measuredat 0, 1, 5, 9 and 13 d after defoliation and compared with thosein uncut swards. The rate of shoot regrowth declined with increasing severilyof defoliation. In all defoliation treatments, growth was confinedto leaves for up to 5 d. Root growth ceased in all treatmentsfor a longer period. Reestablishment of the leaf area in severely-defoliatedswards was facilitated by the rapid opening of developing leavesand by changes in the allocation of carbon which favoured leafover branch and root, and lamina over petiole growth. Loss of carbohydrate and nitrogen from roots and branches lasting5–9 d was observed in the more severe defoliation treatments.Loss of protein (N x 6.25) exceeded that of total non-structuralcarbohydrate, and could have accounted for the nitrogen contentof new leaf during this period. Branches lost 62% of their initialcarbohydrate content compared with 25% from roots in the 80%cut swards. In contrast, roots, by virtue of their greater mass,were the principle source of mobilized nitrogen. Nitrogen accumulationceased in 80% cut swards for 9 d. However, carbohydrate levelsin the crown nodules were not severely depleted. It was concluded that partitioning of growth to lamina and themobilization of carbohydrates and nitrogen were important forrecovery from defoliation. Carbohydrates, carbon partitioning, defoliation, nitrogen, mobilization, regrowth, subterranean clover, Trifolium subterraneum L     

Growth responses of arctic graminoids following grazing by captive lesser snow geese

The effects of grazing by captive goslings of the Lesser Snow Goose on coastal vegetation at La Pérouse By. Manitoba were investigated. Swards of Carex subspathacea, Festuca rubra and Calamagrostis deschampsioides were grazed once for different periods (0–180 min) and regrowth of vegetation determined, based on measurements of standing crop, net above-ground primary production (NAPP) and forage quality (leaf nitrogen content). The amounts of foliage removed from swards of Carex subspathacea increased with the length of the grazing period, but after 44 days of regrowth there were no significant differences in above-ground biomass between control and grazed plots. While the amount of foliage removed by goslings from swards of Festuca rubra increased with the length of the grazing period (except after 150 min of grazing), the increase in biomass following defoliation was similar among treatments. Goslings removed little biomass from swards of Calamagrostis deschampsioides, even when the opportunity for grazing was 180 min. No significant differences in standing-crop or NAPP between grazed and ungrazed plots were detected by the end of summer. Grazing had no significant effect on amounts of nitrogen in leaf tissue of all species, suggesting that faecal nitrogen was not rapidly incorporated into plant biomass within the growing season. Patterns of regrowth of these species are compared to that of Puccinellia phryganodes. An increase in goose numbers in recent years has led to birds foraging on less preferred species, such as Calamagrostis deschampsiodes and Festuca rubra. Their poor nutritional quality and a lack of a rapid growth response following defoliation may explain, in part, the decline in the weight of wild goslings recorded over the last decade.     

Long-term responsiveness to free air CO2 enrichment of functional types, species and genotypes of plants from fertile permanent grassland

To test inter- and intraspecific variability in the responsiveness to elevated CO₂, 9–14 different genotypes of each of 12 perennial species from fertile permanent grassland were grown in Lolium perenne swards under ambient (35 Pa) and elevated (60 Pa) atmospheric partial pressure of CO₂ (pCO₂) for 3 years in a free air carbon dioxide enrichment (FACE) experiment. The plant species were grouped according to their functional types: grasses (L. perenne, L. multiflorum, Arrhenatherum elatius, Dactylis glomerata, Festuca pratensis, Holcus lanatus, Trisetum flavescens), non-legume dicots (Rumex obtusifolius, R. acetosa, Ranunculus friesianus), and legumes (Trifolium repens, T. pratense). Yield (above a cutting height of 4.5 cm) was measured three times per year. The results were as follow. (1) There were highly significant differences in the responsiveness to elevated pCO₂ between the three functional types; legumes showed the strongest and grasses the weakest yield increase at elevated pCO₂. (2) There were differences in the temporal development of responsiveness to elevated pCO₂ among the functional types. The responsiveness of the legumes declined from the first to the second year, while the responsiveness of the non-legume dicots increased over the 3 years. During the growing season, the grasses and the non-legume dicots showed the strongest response to elevated pCO₂ during reproductive growth in the spring. (3) There were no significant genotypic differences in responsiveness to elevated pCO₂. Our results suggest that, due to interspecific differences in the responsiveness to elevated pCO₂, the species proportion within fertile temperate grassland may change if the increase in pCO₂ continues. Due to the temporal differences in the responsiveness to elevated pCO₂ among species, complex effects of elevated pCO₂ on competitive interactions in mixed swards must be expected. The existence of genotypic variability in the responsiveness to elevated pCO₂, on which selection could act, was not found under our experimental conditions. Received: 11 May 1997 / Accepted: 11 August 1997     

A fungal endophyte of a palatable grass affects preference of large herbivores

Temperate grasses frequently acquire resistance to herbivores through a symbiosis with epichloid fungi that produces alkaloids of variable deterrent effects. However, in those cases without apparent endophyte negative effects on domestic herbivores, it is not clear whether plant consumption or preference is affected or not. We performed three experiments with 1‐year‐old steers (Bos taurus, Aberdeen Angus) and the annual grass Lolium multiflorum, infected or not by Epichloë occultans to evaluate preference and to identify the underlying tolerance mechanisms. The first experiment evaluated steer preference for L. multiflorum cultivated in plots with three endophyte infection frequencies (low, medium and high), and investigated the role of canopy structure and plant nutritional traits on preference. The second experiment evaluated preference for chopped grass, offered in individual trays with contrasting infection frequencies (low and high), to discard possible effects associated with canopy structure and to focus on nutritional traits. The third experiment was performed with a tray + basket design that separated visual and olfactory stimuli from nutritional traits. High endophyte infection frequencies reduced consistently animal preference, even after short (~10 min) feeding events. However, we did not find significant evidence of plant structural, nutritional, visual or olfactory traits. Our results discarded several potential mechanisms; therefore, the dissuasive effect of fungal endophytes on animal consumption might be related to other mechanisms, including, likely, alkaloids and changes on grass metabolome.     

Pollen allergens from different Dactylis glomerata varieties harvested between 1986 and 1988

Pollen was collected from different cultivated varieties of Dactylis glomerata in 1986, 1987 and 1988 and compared with an undifferentiated stock of Dactylis glomerata pollen harvested and stored dry at +4°C since 1981. The allergen content of the crude pollen extracts was established on the basis of the IgE antibodies from the sera of three different patients allergic to grass pollen, using the nitrocellulose immunoprint technique following isoelectric focusing (IEF) and separation in agarose gels. Coomassie blue and silver staining patterns were also compared. They showed some marked differences in the isoelectric points of the constituants of these extracts. Using this major allergen recognition by patient sera as a selection criteria we were able to delimit 8 Dactylis varieties with low or undetectable Dac g IV allergen amounts and 7 varieties which contained this allergen. Two other allergens used as markers enabled us to suggest a kind of taxonomy, based upon the allergen presence, of these 15 varieties. The effect of the storage temperature was studied for 8 different varieties kept at +4°C, -20°C and -40°C. The allergen recognition and silver staining patterns after IEF separation of the crude pollen extracts revealed a selective persistance of some constituants and the disappearance of others at +4°C. The effect of freeze-drying was also analysed in the same way. Finally the pollen constituants of one Dactylis glomerata variety, harvested in 1986 and 1987 and kept at different temperatures were compared using the same techniques.     

Regrowth by Swards of Subterranean Clover after Defoliation. 2. Carbon Exchange in Shoot, Root and Nodule

The carbon economy of subterranean clover swards subjected tothree defoliation treatments (removal of 30, 70 and 80% of shootdry weight) was compared with that of uncut swards. Carbon dioxideexchange in shoots and roots was measured independently 0, 4,8 and 12 d after defoliation. The respiration linked to nitrogenaseactivity was estimated by comparing root respiration measuredin an atmosphere containing 3% oxygen with the respiration in21% oxygen. Net photosynthesis fell by up to 100% immediately after defoliation.There was a decline of over 60percnt; in root respiration bythe end of the first light period, composed of a rapid declineof 70% in nitrogenase-linked respiration in all treatments anda slower decline of nearly 40% in root plus nodule growth andmaintenance respiration in the more severe treatments. Recoveryof net photosynthesis to rates achieved by uncut swards occurredover 4 d in the 30% cut treatment and at least 12 d in moresevere treatments. Whilst recovery of photosynthesis was theprinciple determinant of recovery of net positive carbon balance,the early reduction in respiration facilitated this outcome.After the immediate decline in nitrogenase-linked respiration,recovery in this component of respiration appeared to be linkedwith the recovery in net photosynthesis (approximately 10% ofnet photosynthesis). Carbon budgets revealed priorities in allocation towards leafin the first 5 d and later also towards root growth in severelydefoliated swards. Root respiration comprised a large respiratorycost (up to 75% of net photosynthesis) during early regrowth. Carbon budget, defoliation, N₂ fixation, photosynthesis, regrowth, respiration, subterranean clover, Trifolium subterraneum L     

Comparative responses of the Savanna grasses Cenchrus ciliaris and Themeda triandra to defoliation

Summary Two perennial tussock grasses of savannas were compared in a glasshouse study to determine why they differed in their ability to withstand frequent, heavy grazing; Cenchrus ciliaris is tolerant and Themeda triandra is intolerant of heavy grazing. Frequent defoliation at weekly intervals for six weeks reduced shoot biomass production over a subsequent 42 day regrowth period compared with previously undefoliated plants (infrequent) in T. triandra, but not in C. ciliaris. Leaf area of T. triandra expanded rapidly following defoliation but high initial relative growth rates of shoots were not sustained after 14 days of regrowth because of reducing light utilising efficiency of leaves. Frequently defoliated plants were slower in rate of leaf area expansion and this was associated with reduced photosynthetic capacity of newly formed leaves, lower allocation of photosynthate to leaves but not lower tiller numbers. T. triandra appears well adapted to a regime where defoliation is sufficiently infrequent to allow carbon to be fixed to replace that used in initial leaf area expansion. In contrast, C. ciliaris is better adapted to frequent defoliation than is T. triandra, because horizontally orientated nodal tillers are produced below the defoliation level. This morphological adaptation resulted in a 10-fold higher leaf area remaining after defoliation compared with similarly defoliated T. triandra, which together with the maintenance of moderate levels of light utilising efficiency, contributed to the higher leaf area and shoot weight throughout the regrowth period.     

Inter-clonal difference in sodium uptake within the speciesphleum pratense andfestuca pratensis

Summary A study was made of intra-species differences in sodium uptake by timothy (Phleum pratense) and meadow fescue (Festuca pratensis), two pasture grasses that are generally known as being low in Na-content compared with perennical ryegrass (Lolium perenne) and cocksfoot (Dactylis glomerata). Na²² was used with NaNO₃ as a tracer in a fertilizer experiment on seedlings grown on trays placed on benches in the greenhouse. With timothy significant clonal differences in Na-uptake varied from one half to the double, but the Na-contents were still appreciably lower than in ryegrass or cocksfoot.