We report a space-for-time substitution study predicting the impacts of climate change on vegetated maritime Antarctic soils. Analyses of soils from under Deschampsia antarctica sampled from three islands along a 2200 km climatic gradient indicated that those from sub-Antarctica had higher moisture, organic matter and carbon (C) concentrations, more depleted δ13C values, lower concentrations of the fungal biomarker ergosterol and higher concentrations of bacterial PLFA biomarkers and plant wax n-alkane biomarkers than those from maritime Antarctica. Shallow soils (2 cm depth) were wetter, and had higher concentrations of organic matter, ergosterol and bacterial PLFAs, than deeper soils (4 cm and 8 cm depths). Correlative analyses indicated that factors associated with climate change (increased soil moisture, C and organic matter concentrations, and depleted δ13C contents) are likely to give rise to increases in Gram negative bacteria, and decreases in Gram positive bacteria and fungi, in maritime Antarctic soils. Bomb-14C analyses indicated that sub-Antarctic soils at all depths contained significant amounts of modern 14C (C fixed from the atmosphere post c. 1955), whereas modern 14C was restricted to depths of 2 cm and 4 cm in maritime Antarctica. The oldest C (c. 1745 years BP) was present in the southernmost soil. The higher nitrogen (N) concentrations and δ15N values recorded in the southernmost soil were attributed to N inputs from bird guano. Based on these analyses, we conclude that 5–8 °C rises in air temperature, together with associated increases in precipitation, are likely to have substantial impacts on maritime Antarctic soils, but that, at the rates of climate warming predicted under moderate greenhouse gas emission scenarios, these impacts are likely to take at least a century to manifest themselves.
Abstract The harsh climatic conditions and low levels of human activity in Antarctica, relative to other regions, means few non-native species have established. However, the risk of introductions is becoming greater as human activity increases. Non-native microorganisms can be imported to Antarctica in association with fresh food, cargo and personal clothing, but the likelihood of their establishment is not well understood. In January 2015, a wooden packing crate, heavily contaminated with fungi, was imported by aircraft from Punta Arenas, Chile, to Rothera Research Station, Antarctica. Mucor racemosus Bull. and two strains of Trichoderma viridescens (A.S. Horne & H.S. Will.) Jaklitsch & Samuels were isolated from the wood. Measurements of hyphal extension rates indicated that all three strains were psychrotolerant and capable of growth at 4°C, with M. racemosus growing at 0°C. The imported fungi could grow at rates equivalent to, or faster than, species isolated from Antarctic soils, suggesting that low temperature may not be a limiting factor for establishment. It is recommended that wood heat-treatment standards, equivalent to those described in the International Standards for Phytosanitary Measures No. 15, are employed by national operators importing cargo into Antarctica, and that treated wood is adequately stored to prevent fungal contamination prior to transportation.
In this review, we examine the functional roles of microbial symbionts in plant tolerance to cold and freezing stresses. The impacts of symbionts on antioxidant activity, hormonal signaling and host osmotic balance are described, including the effects of the bacterial endosymbionts Burkholderia, Pseudomonas and Azospirillum on photosynthesis and the accumulation of carbohydrates such as trehalose and raffinose that improve cell osmotic regulation and plasma membrane integrity. The influence of root fungal endophytes and arbuscular mycorrhizal fungi on plant physiology at low temperatures, for example their effects on nutrient acquisition and the accumulation of indole-3-acetic acid and antioxidants in tissues, are also reviewed. Meta-analyses are presented showing that aspects of plant performance (shoot biomass, relative water content, sugar and proline concentrations and Fv /Fm ) are enhanced in symbiotic plants at low (-1 to 15 °C), but not at high (20-26 °C), temperatures. We discuss the implications of microbial symbionts for plant performance at low and sub-zero temperatures in the natural environment and propose future directions for research into the effects of symbionts on the cold and freezing tolerances of plants, concluding that further studies should routinely incorporate symbiotic microbes in their experimental designs.
Mycothalli, symbioses between liverworts and soil fungi, have not previously been recorded in the Arctic. Here, 13 species of leafy liverwort from west Spitsbergen in the High Arctic are examined for the symbiosis using epifluorescence microscopy and sequencing of fungal ribosomal (r)RNA genes amplified from plant tissues. Microscopy showed that intracellular hyphal coils, key indicators of the symbiosis, were frequent (>40% stem length colonized) in nine species of liverwort in the families Anastrophyllaceae, Lophoziaceae, Cephaloziellaceae, Cephaloziaceae and Scapaniaceae, with hyphae occurring frequently (>40% cells occupied) in the rhizoids of 10 species in the same families. Dark septate hyphae, apparently formed by ascomycetes, were frequent on the stems of members of the Anastrophyllaceae, Cephaloziellaceae and Cephaloziaceae, and typically those growing on acidic mine tailings. Sequencing of fungal rRNA genes showed the presence of nine distinct groups (based on a 3% cut-off for ITS sequence divergence) of the basidiomycete Serendipita in the Anastrophyllaceae and Lophoziaceae, with ordinations and correlative analyses showing the presence of the genus to be positively associated with the frequency of hyphal coils, the occurrence of which was positively associated with edaphic factors (soil δ15N value and concentrations of moisture, nitrogen, carbon and organic matter). We propose that the frequency of mycothalli in leafy liverworts on west Spitsbergen, which is an order of magnitude higher than at lower latitudes, may arise from benefits conferred by mycobionts on their hosts in the harsh environment of the High Arctic.
1 We applied the fungicides benomyl and prochloraz to natural populations of the winter annual grass Vulpia ciliata ssp. ambigua at three sites in East Anglia, UK, in an attempt to assess the relative losses and benefits to the plant caused by root pathogenic and arbuscular mycorrhizal fungi in the field, and to explore the possibility that the two groups of fungi interact to determine plant fitness. 2 Prochloraz did not affect fungal colonization of roots or plant performance, but benomyl reduced arbuscular mycorrhizal colonization in the roots of V. ciliata. However, total plant biomass, shoot and root biomass and phosphorus inflows were unaffected in benomyl treated plants. The only direct effect of benomyl on the plants was to increase fecundity (seed number) at one site. 3 These null or positive effects of benomyl on plant performance may be explained by the deleterious effects of the fungicide on the abundance of other root-inhabiting fungi such as Fusarium oxysporum or Embellisia chlamydospora isolated from the roots of V. ciliata. 4 Whilst direct comparisons of plant performance with the abundance of rootinhabiting fungi showed that arbuscular mycorrhizal fungi appeared to play a relatively insignificant role in the ecology of the plant, the abundance of root pathogenic fungi such as F. oxysporum, E. chlamydospora and a species of Phoma was found to be negatively correlated with plant fecundity, even though these fungi produced asymptomatic infections. 5 The poor relationship between plant fecundity and benomyl application contrasted markedly with the clear effects of benomyl on root pathogenic and arbuscular mycorrhizal fungi, and with the clear impact of the root pathogenic fungi on plant fecundity. The most likely explanation for this apparent paradox was that the two groups of fungi were in some way interactive, and that when both groups were reduced in abundance, the resultant effects on the plants were neutral. 6 A generalized linear model applied to the fecundity data appeared to indicate that the arbuscular mycorrhizal fungi interacted directly with the root pathogenic fungi, and improved fecundity by interfering with the negative effects of the pathogens. We concluded that asymptomatic root pathogenic fungi were important determinants of fitness in V. ciliata and that the main benefit supplied by arbuscular mycorrhizal fungi to the plant was apparently in protection from pathogenic attack, not in phosphorus uptake. The implications of the results for plant population dynamics are discussed.
Highly simplified microbial communities colonise rocks and soils of continental Antarctica ice-free deserts. These two habitats impose different selection pressures on organisms, yet the possible filtering effects on the diversity and composition of microbial communities have not hitherto been fully characterised. We hence compared fungal communities in rocks and soils in three localities of inner Victoria Land. We found low fungal diversity in both substrates, with a mean species richness of 28 across all samples, and significantly lower diversity in rocks than in soils. Rock and soil communities were strongly differentiated, with a multinomial species classification method identifying just three out of 328 taxa as generalists with no affinity for either substrate. Rocks were characterised by a higher abundance of lichen-forming fungi (typically Buellia, Carbonea, Pleopsidium, Lecanora, and Lecidea), possibly owing to the more protected environment and the porosity of rocks permitting photosynthetic activity. In contrast, soils were dominated by obligate yeasts (typically Naganishia and Meyerozyma), the abundances of which were correlated with edaphic factors, and the black yeast Cryomyces. Our study suggests that strong differences in selection pressures may account for the wide divergences of fungal communities in rocks and soils of inner Victoria Land.
Abstract We have investigated how the microbially-driven processes of carbon (C) mineralization (respiration) and nitrogen (N) mineralization/immobilization in a soil from the northern Maritime Antarctic respond to differences in water availability (20% and 80% water-holding capacity) and temperature (5°C and 15°C) in the presence and absence of different organic substrates (2 mg C as either glucose, glycine or tryptone soy broth (TSB) powder (a complex microbial growth medium)) in a controlled laboratory experiment over 175 days. Soil respiration and N mineralization/immobilization in the presence of a C-rich substrate (glucose) increased with increases in water and temperature. These factors were influential individually and had an additive effect when applied together. For the N-rich substrates (glycine and TSB), microbial responses to increased water or temperature alone were weak or not significant, but these factors interacted to give significantly positive increases when applied together. These data indicate that under the expected changes in environmental conditions in the Maritime Antarctic, where temperature and the availability of water and organic substrates will probably increase, soil microbial activity will lead to more rapid C and N cycling and have a positive feedback on these biogeochemical processes, particularly where or when these factors increase concurrently.
Tribe Poeae. An annual grass, small, solitary or loosely tufted, 5–30 (–45) cm high. Culms slender, erect, sometimes bent and branched at or near base; 1–2 noded, sheath enclosing scape to base of panicle or higher. Branching intravaginal. Leaves (1–10 cm) green, purplish below, especially in seedling, tightly inrolled or opening out and up to 2 mm wide. Sheaths smooth, rounded on the back; very short membranous ligules. Blades rough on the margins and minutely hairy on the upper surface. Panicles erect or slightly nodding, very slender, linear or lanceolate, one-sided, 3–13 (–20) cm long; green, purplish or reddish. Inflorescence little branched and raceme-like in the upper part or throughout; branches short and erect. Pedicels up to 1 mm, swollen. Spikelets overlapping, wedge-shaped or narrowly oblong, 5–7 mm long excluding awns, 12–18 mm including awns. Florets, 3–7, lower 1–2 (–3) fertile, upper (2–) 3–6 (–7) sterile or male only. Glumes awnless and much shorter than lowest lemma, persistent. Lower glume ovate or oblong, veinless, 0.2–1.0 mm long, sometimes longer on spikelets that are terminal on the inflorescence or on its branches. Upper glume linear to lanceolate, 1-veined, 1.5–3.0 mm long, the fragile, membranous tip often breaking to give a blunted appearance. Florets separated by rhachilla segments, the lowest ± sessile within the glumes. Lemmas narrowly lanceolate in side view, firm, minutely scabrid, overlapping at first and later with the margins incurved, with 3–5 inconspicuous nerves, tapering apically into a fine awn up to 10 mm long. Fertile lemmas 3 (–5) veined, 4–5 mm long excluding awn, 11–17 mm long inclusive of awn. Sterile lemmas up to 6 mm long with shorter awns. Small horseshoe-shaped callus at base of fertile lemmas, 0.1–0.2 mm in longitudinal axis. Paleas of fertile florets almost as long as lemmas, 4.0–4.9 mm with two rough keels. Palea of sterile floret absent or much reduced. Anthers 1 (–3), 0.4–0.6 mm long. Ovary tip glabrous. Caryopsis, linear, slender, 3.5–4.5 mm, enclosed by toughened lemma and palea and firmly attached to the latter, breadth-length quotient c. 1:7 (Cotton & Stace 1977). Short embryo visible at base of dorsal surface. Abaxial surface rounded and inrolled to form groove on adaxial surface. Narrow hilum extends almost entire length of caryopsis. Plants exhibit considerable phenotypic plasticity, varying in height, the amount of tillering and spikelet number. In an unheated glasshouse, exceptional plants have reached a height of 70 cm, but on very poor soils plants may attain only a few cm with one or two spikelets. Growth habit is generally consistent across sites in the British Isles. Populations from Santon Downham in the Breckland and Holme next the Sea in Norfolk at the northern edge of the species range are genetically differentiated in relation to both biomass and seed production (Norton 1996). The plants from Santon Downham grown in a controlled environment facility produced 25% more seeds than those from Holme next the Sea. There were no significant population × environment responses in relation to either temperature or carbon dioxide. There are two subspecies of Vulpia ciliata (Stace & Auquier 1978). Subspecies ambigua (Le Gall) Stace and Auquier (V. ambigua (Le Gall) More), the plant reported here, is devoid of long hairs on the inflorescence, although the lemmas, glumes, rhachis, etc. are scabrid with prickle hairs. In contrast, ssp. ciliata is loosely hairy on the lemmas; the fertile lemmas are pubescent on the dorsal midline and sparsely ciliate on the margin, whereas the sterile lemmas are densely ciliate on the margin. Subspecies ambigua also has a distinctive appearance with a stiffly erect, very narrow inflorescence and a purplish colouring at fruiting. Otherwise, the two taxa differ only by more or less overlapping quantitative characters; ssp. ciliata is generally larger in all its parts with spikelets mostly 7–10.5 mm, fertile lemmas 5–7.5 mm, and sterile lemmas up to 8 mm, all measurements excluding awns. The two subspecies are chiefly allopatric (Fig. 1) with ssp. ambigua restricted to England, Wales and a few localities in Belgium and north-western France (Cotton & Stace 1976). The degree of pubescence in ssp. ciliata is extremely variable (Cotton 1974) and glabrous individuals occur sporadically throughout much of this range and are referred to as V. ciliata var. imberbis (Vis.) Halácsy (Stace & Auquier 1978); these plants can be distinguished from ssp. ambigua by the slightly larger size of their floral parts. The distribution of Vulpia ciliata in Europe. Hatched area is the distribution of V. ciliata ssp. ambigua in the British Isles, Channel Islands, northern France and Belgium. The numbered sites in France are: 1, Le Kernével and Larmor; 2, La Guimorais; 3, Châtelaillon; 4, Brenne; 5, Amboise. Unhatched area is the distribution of V. ciliata ssp. ciliata. Reproduced from Cotton & Stace (1976) as modified by Stace & Auquier (1978). Subspecies ciliata is occasionally found as a casual in England (Hubbard 1984) and was formerly naturalized at railway sidings in Ardingly, East Sussex (Stace & Auquier 1978; Stace 1997). Vulpia ciliata ssp. ambigua is a native species of maritime or submaritime sand and shingle and is also found on roadsides and by tracks in sandy areas inland. All subsequent references to V. ciliata in this paper are to ssp. ambigua. Although formally regarded as ‘scarce’ in a national context (Stewart et al. 1994), the plant may be locally abundant. A key feature in distinguishing ssp. ambigua from other British Vulpia species is the relative length of the two glumes. These are very unequal and the lower is less than one-quarter (0.1–0.25) the length of the upper. Vulpia ciliata belongs to the Mediterranean–Atlantic element of the British flora (Preston & Hill 1997). Distribution in the British Isles centres around the inland, sandy heaths of Norfolk and Suffolk known as the Breckland, and along parts of the southern and eastern coasts extending as far north as the Wash (Fig. 2). In East Anglia, the main range of the species extends from the north Norfolk coast southwards through the eastern counties of Cambridgeshire and Essex. Recent sightings of the species have also been made at Bicester in Oxfordshire and Shoebury in Essex (P.D. Carey & K.J. Adams, personal communication). It is sparsely distributed along the south coast of England, in Devon, Dorset, Hampshire, the Isle of Wight and Sussex, where it occurs on golf links and coastal dunes and inland on sandy roadsides, cinder paths and similar dry places. Vulpia ciliata also occurs in Kent where it is found on maritime and inland shingle. The distribution of Vulpia ciliata ssp. ambigua in the British Isles. Each dot represents at least one record in a 10-km square of the National Grid. Mapped by Mrs J.M. Croft, Biological Records Centre, Institute of Terrestrial Ecology, Monks Wood. (○) pre-1970; (•) 1970 onwards; (+) introductions pre-1970; (×) introductions 1970 onwards. The most northerly occurrence of the species was in north Yorkshire at West Tanfield in 1954. No subsequent records exist of plants at this location. The current two most northerly records are Crosby Warren in north Lincolnshire at the entrance to a quarry and Holme next the Sea in north Norfolk, where there are two small patches of the plant on the edge of a golf course at the back of the dunes. The species’ distribution in western Britain is confined to a few locations in Devon and Somerset and to one site in Gwynedd on the coastal golf course at Aberdyfi. The recorded world distribution of ssp. ambigua is limited to England, Wales, the Channel Islands (Jersey, Guernsey and Alderney) and a few locations on the neighbouring coasts of continental Europe (Fig. 1). There are records of populations along the coast of Belgium and in northern France in the départements Pas de Calais and Somme (Lambinon 1958; Auquier 1977; Stace & Auquier 1978). The subspecies has, however, spread in Belgium in recent years (C.A. Stace, personal communication), and is probably under-recorded in France, where it may well be more widespread in Brittany to the south of the distribution limit shown in Fig. 1; note that the subspecies was first described from Morbihan in southern Brittany within the range of subspecies ciliata (see Section X). Five outlier populations have been recorded within the range of V. ciliata ssp. ciliata (Fig. 1) and both subspecies co-occur on dunes at Châtelaillon in northern France (Stace & Auquier 1978). Subspecies ambigua is a lowland grass in Britain and generally occurs at altitudes between sea level and 60 m (Table 1). In contrast, ssp. ciliata is widespread throughout southern and central Europe (Fig. 1), extending south to North Africa and west at least as far as north-western India (Cotton & Stace 1976). It occurs from sea level to about 2000 m and has a much wider ecological amplitude than subspecies ambigua (Stace & Auquier 1978). Subspecies ciliata is found as a pioneer species on well-drained, open or broken ground, both acidic and calcareous, open grassland, waste places, wood margins or clearings and dunes, usually on sandy or rocky substrata. It is one of the commonest Vulpia species in Europe (Cotton & Stace 1976) and has been introduced into Australia (Willis 1970). The grass is most abundant in the dry eastern counties of England. Throughout its range in the British Isles it is associated with areas of low annual rainfall, typically <900 mm per annum, and at the middle of the species’ range in the Breckland <650 mm per annum (Table 1). The mean annual rainfall across the sites listed in Table 1 is 713 mm and the mean annual minimum and maximum temperatures 6.9 and 13.3 °C, respectively. Norton (1996) has investigated the effect of climate on the survival and fecundity of V. ciliata within and outside its current range by sowing seeds in pots at 22 sites throughout Britain, spanning Orkney in the north to Exeter in the south. The experiment was carried out in 1993–94 and it was found that germination was high at all sites but took longer under the cooler temperatures and shorter days in northern Britain; germination occurred 15 days later in the north. There were no differences in survival between the sites but the long, warm days associated with southerly latitudes shortened the time to seed maturity and increased seed production. Vulpia ciliata produced seeds at all sites in the transplant experiment (Norton 1996), and it was only in Orkney that the finite rate of population increase was less than one, i.e. the number of seeds produced fell below the number of seeds sown. Seed production at a number of sites in the west and north exceeded that within the native range of the plant, and the fundamental climate niche for V. ciliata appears to extend both to the north and west of the present species’ range. The realized climate niche has been modelled by Carey et al. (1995) using multiple regression. They found that the current distribution of the plant could best be modelled in terms of three climatic factors [sunshine hours in March–May; temperatures in winter (December–February) and autumn (September-November)] and concluded that the species is found where there are sunny springs, warm autumns and cold winters. The transplant experiment of Norton (1996) indicates that the requirement for cold temperatures is not absolute, and given that the plant can perform very well outside of its current range, it appears that the present distribution of the plant is more limited by the availability of suitable habitats (Carey et al. 1995). The model produced by Carey et al. (1995) relates primarily to the factors that determine the northern and western limit of the subspecies; different or additional climatic variables may be correlated with the southern edge of its distribution. Vulpia ciliata is often found on small local ridges of slightly elevated ground, for example on banks and track edges, and occasionally on walls. However, the species is not confined to a specific aspect and is also found on flat ground and moderate slopes. At beach locations such as at Snettisham in Norfolk, it can tolerate exposure to high winds, salt spray and occasional inundation by high tide seawater. Vulpia ciliata grows on maritime dunes, especially fixed and semi-fixed dunes, over most of its range (Stace & Auquier 1978), but it also occurs on maritime shingle in Kent and East Anglia and on inland sandy heathlands, especially in the Breckland of East Anglia. Within the Breckland it is found on disturbed sand, on sparsely colonized verges of forest tracks, open areas on heath tracks, on wind-blown low sand-banks under pine belts, open sides of pits, arable headlands in areas of thin crops such as rye, on derelict arable land, in loose sand at the base of wire fences, and in disturbed ground on the sides of furrows (Trist 1979). The locality at Brenne, within the range of ssp. ciliata in France, resembles the Breckland sites in several ways (Stace & Auquier 1978). The subspecies shows a strong preference for dry sands and shingles (Carey et al. 1995) that are well drained with a relatively low organic matter content. Carey et al. (1995) found that within the UK, populations were particularly associated with Brown sands, Brown calcareous sands and Sand-pararendzinas by overlaying the current distribution of the plant with the dominant and subdominant soil types on a 1-km scale for England and Wales. The mean pH of soils on which the plant grows in East Anglia is 6.8, but the species occurs in soils with pH values as low as 3.4 and as high as 7.9 at Santon Downham and Red Lodge, respectively (Table 2). While ssp. ambigua is frequently regarded as a plant of inland, acidic sands, data in Table 2 indicate that it is more characteristic of soils that are neutral to slightly acidic. Soils colonized by V. ciliata are usually nutrient-poor, typically with NH+4-N, NO−3-N, P and K contents of <9.0, <13, <50 and <130 mg kg−1, respectively (Table 2). In west Norfolk and Suffolk, the most extensive populations are found on soils of low moisture content and low organic matter, phosphorus and potassium. Vulpia ciliata is commonly confined to small areas and is seldom found widely dispersed at any location. It may, however, be locally dominant, particularly in disturbed areas, where it is particularly noticeable at the time of fruiting when the infructescence turns its characteristic reddish colour. A list of higher plant species that are commonly associated with V. ciliata in East Anglia is given in Table 3. It is a species of open communities, where perennial cover is typically low and usually includes a range of other annuals, in particular Aira praecox, Anisantha sterilis, Arenaria serpyllifolia, Bromus hordeaceus, Myosotis ramosissima and Vulpia bromoides. Achillea millefolium, Erodium cicutarium, Festuca spp., Koeleria macrantha, Plantago coronopus, P. lanceolata, Poa pratensis, Rumex acetosella, Sedum acre, Taraxacum spp. and Trifolium campestre are also frequently found in association with V. ciliata. In the Breckland, Trist (1979) recorded that V. ciliata was frequently found in association with Arenaria serpyllifolia, Rumex acetosella and Sedum acre. These species are all characteristic of sandy heaths, dunes and shingle. On the last it is also found in association with characteristic shingle species such as Glaucium flavum, Rumex crispus and Silene uniflora. On dunes, it does not grow on such disturbed sand as V. fasciculata, but at Holme next the Sea in Norfolk there is one small patch of dune vegetation at the back of the local golf course where V. bromoides, V. ciliata, V. fasciculata and V. myuros have all been found growing together. In the Breckland, V. bromoides, V. ciliata and V. myuros are occasionally found together. In such vegetation, V. ciliata typically occurs on bare ground in a matrix of perennials dominated by forbs (e.g. Achillea millefolium and Plantago lanceolata), sedges (e.g. Carex arenaria) and grasses (e.g. Festuca rubra and Koeleria macrantha). The species is also commonly found growing with mosses such as Brachythecium albicans, Ceratodon purpureus, Hypnum cupressiforme var. lacunosum, Polytrichum piliferum and Tortula ruralis ssp. ruraliformis (Newsham et al. 1994; 1995). Locally V. ciliata may be found where there is complete moss cover. Germination does not appear to be adversely affected by such cover and may even be facilitated by the improved microclimate within the cushion where the seeds germinate (Newsham et al. 1995). Subsequently the plants root through the moss cushion and leaves rapidly emerge above its surface. Plants are also commonly found growing amongst lichens. For example, at Mildenhall in Suffolk, V. ciliata occurs with Cladonia rangiformis, C. fimbriata, C. squamosa and Diploschistes scruposus (Newsham et al. 1995). It is difficult to place the communities in which V. ciliata is found within the National Vegetation Classification (Rodwell 1992; Rodwell in press) as many of the patches are small, disturbed and influenced by the seed rain from adjacent vegetation. The sample descriptions in Table 1 are, however, consistent with the species being found in Rumex crispus–Glaucium flavum shingle communities (SD1) and communities that are typically transitional between Festuca ovina–Agrostis capillaris–Rumex acetosella grassland (U1), semi-fixed and fixed sand dune types (e.g. SD7 and 8), and disturbed communities of mesotrophic neutral pH conditions (e.g. MG7f, OV23 and OV27). Subspecies ciliata is described by Braun-Blanquet et al. (1952) as a member of the Brachypodietum ramosi association, the richest in species in the French midi. It is one of the characteristic species that splits the western Provence race from the Languedoc race and gives its name to the subassociation Vulpietosum ciliatae. The competitive ability of V. ciliata has been studied by Carey (1991) in a series of experiments in the glasshouse and field. The effects of intraspecific competition on the fecundity of the species was investigated by sowing a monoculture at five densities in trays containing soil from Red Lodge, Suffolk, in an unheated glasshouse. Non-linear regression analysis showed that there was a negative relationship between the mean fecundity (seed number) of individual plants and the density of V. ciliata (fecundity = 1123 [1 + density]−0.849). The effect of local crowding on the grass was also studied using polygon and neighbourhood analysis. Data pooled from all density classes showed that 64% of the variation observed in an individual plant's fecundity in monoculture was related to the number of neighbours surrounding it within an optimal radial distance (the distance over which a plant can influence its neighbour) of 43 mm. The response of V. ciliata to interspecific competition from perennials (Festuca rubra and Plantago lanceolata) and other annuals (Aira praecox, Anisantha sterilis and Vulpia bromoides) was also investigated in an unheated glasshouse by Carey (1991). The mean individual fecundity of V. ciliata within areas bordered by Festuca rubra was reduced by 60–90% when grown within gaps, but no correlation between the density of V. ciliata and its mean fecundity could be discerned in these areas. Further experiments (A.R. Watkinson, L. Forrester & R.P. Freckleton, unpublished data) in an unheated glasshouse have investigated the effects of gap size and gap type on the performance of V. ciliata sown over a range of densities. Gaps were created by planting small bunches of Festuca ovina tillers around square gaps and also by planting mixtures of (i) Hypochaeris radicata and Plantago lanceolata, (ii) F. ovina and Koeleria macrantha and (iii) F. ovina, H. radicata, K. macrantha and P. lanceolata. The competitive pressure exerted on V. ciliata plants grown in 20 × 20 cm gaps in a matrix of F. ovina was equivalent to c. 8000 V. ciliata plants m−2. Competitive pressure exerted by F. ovina increased rapidly as gap size decreased; within 10 × 10 cm gaps, the competitive effect rose to 13 500 plant equivalents m−2. However, decreasing the gap size to 5 × 5 cm had no further measurable effect on the competitive pressure exerted on V. ciliata. The competitive pressure exerted by the three types of gap was approximately equivalent. The implication, in the field, is that the mean plant fecundity of V. ciliata will decline as perennial cover increases (see V (b)). However, at the level of the individual gap in the field, where the gaps are often small and diverse in nature, variation in gap size will have little effect on fecundity as the competitive pressure exerted by the perennials will be relatively constant. Also, variation in the density of V. ciliata can be expected to have little effect on mean individual fecundity as the competitive pressure exerted by the perennials is so large. This accords with the observation that manipulating the densities of V. ciliata in the field has no impact on fecundity (Carey et al. 1995) and with the observation made by Watt (1971) that V. ciliata belongs to a group of small annual plants with low competitive ability. Vulpia ciliata is commonly situated on paths and roadsides and is consequently subjected to trampling by humans and domestic animals. Disturbance can favour the annual by preventing the establishment of perennial species and maintaining an open habitat. Trampling may also aid dispersal through disturbance (Carey & Watkinson 1993); minute upward and forward pointing prickle hairs on the awns of the lemma may also help lodge the diaspores in clothing and fur. Heavy trampling during flowering may damage inflorescences and reduce seed production. Large and small scale disturbances may both destroy and create opportunities for populations. Ant nests, rabbit scrapes and vehicular disturbance have all been observed to create gaps within populations that are then recolonized; for example, seedlings may be found aggregated in depressions in the soil made by tyres. At a larger scale, coastal erosion and the maintenance of sea defences have been observed to destroy populations on shingle, ploughing and tree felling activities have been observed to destroy populations on headlands and forest rides, respectively, while the abandonment of sand and gravel pits has been seen to lead to the establishment of new populations. After the British Museum archaeological dig at High Lodge, Mildenhall in 1970, thousands of V. ciliata had established by 1976 (Trist 1979); a small population still occurred on the site in 1996 in the grazed turf, isolated from other populations by the surrounding pine plantation. No direct evidence of herbivory on V. ciliata has been recorded, even in areas grazed by sheep, deer and rabbits. This is in contrast with the closely related V. fasciculata, which is often found eaten by rabbits during reproductive stages (Watkinson 1978). Grazing of the species may be controlled by the presence of clavicipitaceous fungi, hyphae of which are frequently observed in leaf sections of mature plants. These fungi, which colonize the above-ground plant parts of many grasses, deter feeding by animals and insects by producing alkaloids in leaves (Clay 1990). Some populations, for example at Bodney, Norfolk, and Mildenhall, Suffolk, are mown in late May or early June to tidy up the vegetation close to buildings and along tracks. This rarely has a significant impact on population size in the subsequent year, as a sufficient number of inflorescences escape mowing and/or sufficient seed has generally been set by this time of year. There is generally no production of secondary tillers after mowing. Vulpia ciliata usually forms small, patchy populations, many of which persist over a number of decades (see X). Perennial plants probably limit the size of patches and the density of V. ciliata within them (see IV (a)). Owing to the short seed dispersal distance of the species (see VIII (c)), seedlings are often found aggregated around the remains of inflorescence stalks from the previous year. The largest population in East Anglia extends in a 10-m wide strip intermittently for c. 3 km along an exposed, disturbed shingle beach at Snettisham. More usually, patches tend to range in size from one to a few thousand m2; the distribution of population sizes as measured by area is approximately lognormal, with the area of most populations being c. 100 m2. The area of the four populations studied by Carey et al. (1995) in East Anglia ranged from 184 to 5340 m2, with average densities of plants in the populations ranging from 300 to 878 m−2. The numbers of plants in these populations were estimated to be between 20 000 and 4 700 000. At the edge of its range, and as perennial cover increases, V. ciliata populations occur at densities below 60 plants m−2. Within a population at Mildenhall, where the densities of plants were recorded in contiguous 10 × 10 cm quadrats within four plots of 2 × 1 m, the densities of plants ranged from 0 to 7000 m−2, but most of the densities fell within the range of 500–3500 m−2, with a mode of just under 2000 m−2. An analysis of population performance in the 10 × 10 cm quadrats at Mildenhall showed that density had no effect on mean plant fecundity, but that population growth rate was density-dependent as a consequence of density-dependent recruitment (A.R. Watkinson, R.P. Freckleton & L. Forrester, unpublished data). Population growth rates were reduced by c. 80% as a consequence of density-dependence. Population growth rates were also reduced by 30% as a result of perennial plant cover, but effects could potentially be much higher if the competitive effects of perennials were completely removed (see IV (a)). Analysis of the effects of cover on the growth rate of populations indicated that the effects were not mediated by resource competition, but rather through seed survival through to germination. Vulpia ciliata reproduces freely at all suitable sites throughout its range in the British Isles, and beyond (see II (a)). A study in 1994 examining the relationship between seed number per plant of V. ciliata and soil characteristics at 14 sites in East Anglia indicated that fecundity was higher on soils with relatively low soil moisture (r = −0.73, P < 0.01), organic matter (r = −0.68, P < 0.01) and magnesium (r = −0.70, P < 0.01) content and relatively high nitrogen content (r = 0.55, P < 0.05). There was no evidence to suggest that pH or the concentrations of phosphorus or potassium were associated with plant fecundity. The fecundity of plants also increased with the amount of bare ground (r = 0.74, P < 0.01) in the communities studied. Carey et al. (1995) investigated the population dynamics of V. ciliata at four locations in East Anglia situated along a 75-km transect from the Norfolk coast in the north to Mildenhall, Suffolk, in the south. Plant performance varied both between and within sites. The basic reproductive rate of V. ciliata was higher at the core of the species’ range than at its northern limit. This was attributed to decreased fecundity at more northerly locations, although mortality did also increase to a small extent at these sites. Within sites, high density zones of V. ciliata had earlier seedling emergence and higher survival and fecundity. However, the primary reason for the decline in abundance towards the margin of populations was a decline in the fecundity of individuals, which was strongly correlated with the finite rate of population increase. In a further study of the population dynamics of V. ciliata carried out over 3 years at five contrasting sites (A.R. Watkinson & L. Forrester, unpublished data), it was found that the pattern of population flux was similar although there were significant variations in detail. These sites included coastal dunes, maritime shingle, Breckland heath and the verges of forest tracks. The net rate of population increase varied from 0 to just under 2 in 1993–94 across the five sites; there was local population extinction on the verge of the forest track resulting from forestry operations. In contrast to the findings of Carey et al. (1995), the highest rate of population increase was at the most northern site (Holme next the Sea), while at the other sites the rate of population growth varied from 1 to 1.5. Except on the verge of the forest track, where conditions had changed very substantially as a result of tree felling, the net rate of population increase was < 1 at all the other sites in 1994–95. This was owing to drought in spring 1995, which resulted in higher mortality of vegetative plants than in the previous year. Variation in population density between sites was greater after the dry spring than at any other time. The net rate of population increase across the sites over two years was positively correlated with plant fecundity, supporting the conclusion of Carey et al. (1995) that variations in the finite rate of population increase and abundance between sites are largely a result of variation in the number of seeds produced per plant. At the northern edge of the species’ range at Holme next the Sea, the population was found to have a high population growth rate in one year but negative growth rates in two other years, including the one monitored by Carey et al. (1995). It is clear that the persistence of populations at the northern edge of the species’ range depends critically upon the balance of the finite rate of population increase from year to year. Although disturbance had a major impact on the population by a forest track at Santon Downham, data from Sandringham in Norfolk and a number of other sites indicate that overall population structure is fairly stable with high density patches remaining high and low density patches low over considerable periods of time. Th
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