Agrostis Tennis Research Articles

Gene flow in parapatric plant populations of Agrostis tenuis L.and Festuca rubra L.

The gene flow between populations of <em>Agrostis tennis</em> L. and <em>Festuca rubra</em> L. on a Zn/Pb mine and adjacent areas, which met at a distance of 150 m from the mine boundaries, was studied. It was found that the mine populations exhibit a high index of tolerance to Zn and Pb, elements encountered in the soil. Those outside the mine show relatively high indices of tolerance towards Zn and Pb, despite the fact that these elements are absent from the soil. On the other hand, the index of tolerance towards Cu, absent from the soil, of populations inside and outside the mine, was very low and did not differ from that of the control. Time difference in the flowering of these parapatric populations acts against gene flow thus resulting in a tendency for the neighbouring populations to isolate.

The Growth of White Clover (Trifolium repens) in Five Sown Hill Swards Grazed by Sheep

(1) The growth of white clover (Trifolium repens L.) was studied in five hill swards in mid-Wales, sown 10-39 years before with seed mixtures containing white clover and Lolium perenne L. and grazed by sheep. (2) The biggest reason for the increase in white clover ground cover between February and June (Simpson, Wilman & Adams 1987) was a near-fourfold increase in leaflet size. The peak period for leaflet size was around 21 June. (3) The clover appeared vulnerable to defoliation in early spring, with leaves very close together on the stolon and a lack of branch production. (4) The smallest differences between the five study areas were in rate of leaf emergence and leaflet size and the biggest differences were in the amount of branch stolon extension. (5) More leaves emerged on branches than on the stolon main axis during June, July and August, except on one study area where branching appeared to be inhibited by Agrostis tennis Sibth., acidity and aluminium. (6) Branch production and growth from recorded nodes were greatest where clover ground cover was increasing from a relatively low level. (7) The rate of stolon extension appeared sensitive to moisture supply. (8) Management to encourage vigorous white clover growth, therefore, would include providing both sufficient lime and sufficient moisture, controlling Agrostis, and avoiding both overgrazing in spring and undergrazing in summer. The development of varieties in which a higher proportion of nodes produce branches may be worthwhile.

The Distribution of White Clover (Trifolium repens L.) and Grasses within Six Sown Hill Swards

potassium. (3) White clover was adversely affected by soil acidity and appeared more sensitive to soil aluminium than the grasses. (4) White clover was usually positively associated with Lolium perenne and negatively with Agrostis tennis Sibth. Lolium perenne was usually positively associated with Poa spp. and negatively with Agrostis tennis. (5) White clover appeared to be reduced by shortage of moisture on relatively shallow soils. (6) Molehills which remained raised were largely colonized by species other than white clover and Lolium perenne. (7) Farmers wishing to encourage white clover should therefore apply sufficient lime, grow the clover with Lolium perenne rather than with Agrostis tennis, choose sufficiently deep soils, and control moles.

EFFECTS OF TEMPERATURE, LEVELS OF NITRATE SUPPLY AND DURATION OF LIGHT AND GROWTH ON NITRATE REDUCTASE ACTIVITY IN AGEOSTIS TENUIS AND AGROSTIS STOLONIFERA

SUMMARYNitrate reductase activity (NRA) was assessed at several moments within the day during the early stages of establishment of tiller generated plants and seedling swards of Agrostis tenuis and A. stolonifera grown at different temperatures and levels of nitrate supply. Agrostis tennis consistently exhibited higher NRA values than A. stolonifera at initial developmental stages or low nitrate availability. The reverse situation was found to occur at high nitrate availability or in longer established plants and seedling swards. This emphasizes the difficulties in establishing consistent differences between species in NRA. Both species showed increased NRA with increased nitrate availability, increased night temperature or decreased day temperature. Agrostis stolonifera increased its NRA to a greater extent than A. tenuis as nitrate availability increased. The importance of daily and developmental variation in NRA in establishing differences between these species is discussed.

Erratum: The Use of Metal Tolerant Plant Populations for the Reclamation of Metalliferous Wastes

SUMMARY (1) A survey was made of metalliferous mine wastes in Great Britain. The results suggest that high concentrations of toxic metals are the major cause of sparse vegetation cover, but comparisons of bare and adjacent vegetated areas suggests that phosphorus concentrations are the immediate determinant. (2) Field experiments, using a range of grass species at a large number of mine sites, showed that naturally occurring tolerant populations grew faster and persisted longer than normal commercial varieties. They provide an excellent stabilizing cover, provided adequate fertilizer was given, and have persisted for 9 years with little loss of vigour, even with minimal fertilizer treatment. (3) The most successful populations at each site were those with the highest tolerance to the metals occurring in that waste, provided that the species was appropriately adapted to the other soil conditions occurring there. (4) Three cultivars are now commercially available which are tolerant to: acid lead/zinc wastes (Agrostis tennis, cv. Goginan), calcareous lead/zinc wastes (Festuca rubra, cv Merlin) and copper wastes (Agrostis tennis, cv Parys). These enable stabilization of a wide variety of wastes.

Nitrogen Fixation by Plants Grown on Reclaimed China Clay Waste

(1) Nitrogen fixation rates associated with various plant species growing on china clay waste materials were estimated using the acetylene reduction technique. (2) Rates associated with leguminous species (Lupinus arboreus, Ulex europaeus, Trifolium repens) were at least ten times greater than those of non-leguminous species. (3) Of the swards comprising non-leguminous species, only those with Rumex acetosella or Festuca rubra and Agrostis tennis fixed significant amounts of nitrogen, presumably in their rhizospheres. Low rates were detected in some other species. The estimated rate of atmospheric input of combined nitrogen was greater than the input from any of the non-leguminous species. (4) There was no detectable fixation by free-living micro-organisms, except with an added carbon source. (5) All rates were low, probably because of an exceptionally dry summer. (6) Legumes are therefore recommended as the most valuable method of promoting nitrogen accumulation. Nevertheless up to 50 Kg N ha-' could be applied as fertilizer to Trifolium repens without affecting its fixation rate.

PROBLEMS OF INTERPRETING THE RELATIONSHIP BETWEEN THE AMOUNTS OF LEAD AND ZINC IN PLANTS AND SOIL ON METALLIFEROUS WASTES

SUMMARYThe lead and zinc contents of shoot material of Agrostis tennis, Festuca ovina and Minuartia verna and of the soil in which they were growing at an abandoned lead‐mining area on Grassington Moor, Yorkshire, England were determined. The relationship between the zinc contents of shoot material and soil was broadly linear. There was little increase, however, in the lead content of the shoot material over the range 500‐20000 μg g−1 lead in the soil. Above this value the lead content of the shoot material increased markedly. There were large differences between samples in the metal contents of the shoot material collected from soils having the same metal contents. Possible reasons for this variation are discussed and specific suggestions for future comparative work are made.

A COMPARISON OF NEGATIVE RELATIVE GROWTH RATES IN SHADED SEEDLING

SUMMARYSeedlings of the shade‐tolerant species, Deschampsia flexuosa, were subjected to shade treatments under controlled conditions of daylength, temperature, irradiance, relative humidity and mineral nutrient supply. Dry matter production was compared with that of seedlings of the shade‐intolerant species, Agrostis tennis and Festuca ovina. The three species did not differ markedly with respect to their light intensity compensation points. A more promising explanation for the shade tolerance of Deschampsia flexuosa lies in the extremely low negative relative growth rates which seedlings exhibit at light intensities below the compensation point.

THE ACCUMULATION OF ZINC BY SUBCELLULAR FRACTIONS OF ROOTS OF AGROSTIS TENUIS SIBTH. IN RELATION TO ZINC TOLERANCE

SummaryZinc tolerance in the grass, Agrostis tennis Sibth., was investigated by comparing the uptake of radiozinc by the cell wall and mitochondrial fractions from the roots of sixteen different populations. Large differences in tolerance between populations were found. There was a significant correlation between zinc accumulation by each subcellular fraction and the index of zinc tolerance but the cell wall fraction accumulated a greater quantity of zinc. There was no correlation between the nitrogen content of the cell wall fraction and zinc tolerance. The importance of metal accumulation by the cell wall fraction is discussed and it is suggested that it is a major feature of the mechanism of tolerance to heavy metals in A. tenuis.

Rooting from SOD by Poa Pratensis L. and Agrostis Tennis Sibth.1

The source was examined of roots which “knit” blue and bentgrass sods by emergence from the sod into the soil below. Sod was knit by new adventitious roots which emerged from the sod into the new soil in greater numbers as sod was more thinly cut. Regrowth of old roots was not a factor in knitting of sod. All bluegrass shoots initiated new roots. Only some bentgrass shoots initiated roots the first week, but the percent rooting increased with time.

Trends in Montane Grasslands in Snowdonia, expressed in Terms of “Relative Entropy”

BETWEEN 1957 and 1960 a series of experiments was set up at four sites in Snowdonia, North Wales, to study the influence of sheep grazing on two widely distributed plant communities characterized by the dominance within them of Nardus stricta (on soils of peaty podsol/peaty gley character), and Agrostis tennis and Festuca ovina (on soils of brown earth character), respectively. Some of the experiments were established by M. J. Chadwick1. The experimental sites cover an altitude range of 1,300–3,000 feet O.D. (396–914 m) and, at each site, three treatments are set out in a randomized design incorporating four replicates per treatment. The experimental treatments were: (i) Normal grazing: open to the sheep from the surrounding mountain pastures (most of the breeding ewes and yearling sheep are removed from the mountain in winter); (ii) winter protection from grazing: the plots were protected by fencing from October to April each year; normal grazing took place during the summer; (iii) no grazing; the plots were ungrazed throughout the period of the experiment. (The approximate densities of the sheep populations grazing the experimental plots, expressed in ewe units/acre (hectares), are set out in Tables 1 and 2.)

POPULATION DIFFERENTIATION IN AGROSTIS TENUIS SIBTH

SummaryIn order to investigate the physiological differentiation occurring within a species, samples of sixty tillers of a number of populations of Agrostis tennis were transplanted into experimental plots established in various contrasting natural habitats in the neighbourhood of Aberystwyth in central Wales. Two populations were also grown on lead‐contaminated soil. Their performance under the different environments was examined. It was found that: Populations originating from contrasting habitats differed considerably in their ability to tolerate different extreme conditions. For instance, the growth of lowland populations in the upland plot was seriously affected by winter conditions, and the growth of upland populations in the coastal plot was affected by salt storm spray. The population from a lead mine was able to grow in lead‐contaminated soil, while the population from normal pasture was not. The behaviour of each population could always be related to the environment from which the population originated. These differences were also found, although on a smaller scale, between populations originating from less contrasting environments. Populations originating from habitats only a short distance apart showed considerable differences in performance in those cases where the original habitats were markedly different. Such physiological differentiation was not necessarily accompanied by morphological differentiation. It is likely that this is because the two types of differentiation are in relation to unrelated factors of the environment. It was concluded that the pattern of physiological differentiation was a graded patchwork similar to the pattern of morphological differentiation previously described.

POPULATION DIFFERENTIATION IN AGROSTIS TENUIS SIBTH.

SummaryIn some of thirty‐seven populations of Agrostis tennis and A. stolonifera sampled by tillers and grown as spaced plants, the incidence of infection by the fungal parasite ‘Choke’, Epichloe typhina, has been found to be remarkably high. These populations are from environments in which vegetative growth is important owing to the incidence of heavy grazing, exposure, etc.A comparison of the growth of infected and non‐infected plants shows that infection, in preventing inflorescence production, causes a considerable increase in tiller density, without any other deleterious effects. These effects are of advantage to plants growing under conditions where vegetative growth is important.It is therefore concluded that infection of Agrostis sp. by Epichloe must be considered to be not an example of parasitism but of a curious form of symbiosis.

POPULATION DIFFERENTIATION IN AGROSTIS TENUIS SIBTH

SummaryIn order to investigate the pattern of population differentiation in Agrostis tennis, sixty tillers were collected from each of thirty‐three areas mainly in central Wales. These were grown under garden conditions in Aberystwyth. In a subsequent experiment five of these areas were sampled again by tillers, and at the same time sampled by seed. These samples were grown under garden conditions in Bangor.Numerous differences between these population samples were recorded. The main conclusions are as follows:(i) The environment is the dominating factor in determining population differentiation.(ii) Although the distribution is continuous, distances of about 50 m or less are sufficient to effectively isolate populations from one another.(iii) Thus the species is able to evolve under the influence of natural selection in response to very local variations in environment.(iv) Since the environment is a graded patchwork of different conditions, the pattern of differentiation is similar.(v) It is, therefore, not possible to classify effectively such interspecific variation.(vi) It is likely that this situation is to be found in most other out breeding continuously distributed plant species occupying a wide range of habitats.

NATURAL HYBRIDIZATION OF AGROSTIS TENUIS SIBTH. AND A. STOLONIFERA L.

SummaryThere seems to be little barrier to natural hybridization between Agrostis tennis Sibth. and A. stolonifera L. The F1 hybrid is vigorous: but it is relatively sterile.The analysis of natural mixed populations of these two species from an old grazing meadow by means of a morphological index and by pollen fertilities shows that over a large central area of the meadow, plants indistinguishable from Fl hybrids are very abundant, to the virtual exclusion of the parental species which would be expected in such a habitat. A more elaborate morphological and cytological analysis confirms this, but suggests that there is also a small percentage of plants belonging to F2 and backcross generations.The success of the hybrid is due to its growth habit, which is better adapted to grazing conditions than that of either parent. Under grazing conditions reproductive sterility is no disadvantage.The hybrid populations are made up of a large number of different individual F1 hybrid plants, and cannot be due to the spread of one hybrid plant throughout the meadow, but to the repeated formation of the hybrid. Preliminary examination of other habitats suggests that the hybrid is more common than previously suspected.Discussion from an ecological standpoint suggests that the success of natural sterile hybrids depends on the possession of strong powers of vegetative propagation originally derived from the parental species. For this reason Agrostis tennis stolonifera is particularly successful. There are, however, other contributory factors.Discussion from a genetical standpoint suggests that since the hybrid is sterile and subsequent generations are uncommon, the two species are likely to remain quite distinct, but that gene flow between them cannot be ruled out without further investigation.