Variation in the Structure and Response to Flooding of Root Aerenchyma in some Wetland Plants

The structure and response to flooding of root cortical aerenchyma(air space tissue) in a variety of wetland (flood-tolerant)species was investigated and compared with some flood-intolerantspecies. In some species aerenchyma consisted of enlarged schizogenousintercellular spaces and in others aerenchyma formation involvedlysigeny. Two types of lysigenous aerenchyma were distinguished.In the first the diaphragms between lacunae were arranged radiallyand consisted of both collapsed and intact cells. In the secondtype, which was confined to the Cyperaceae, the radial diaphragmscontained intact cells, and stretched between them were tangentially-arrangeddiaphragms of collapsed cells. Flooding in sand culture generally increased root porosity (airspace content) although there were exceptions. The flood-intolerantspecies Senecio jacobaea produced aerenchyma but did not survivelong-term flooding. Among the flood-tolerant species, Filipendulaulmaria did not produce extensive aerenchyma even when flooded.Eriophorum angustifolium and E. vaginatum produced extensiveaerenchyma under drained conditions which was not increasedby flooding. In Nardus stricta root porosity was increased bylow nutrient levels as well as by flooding. Aerenchyma, root cortex, wetland plants, waterlogging, flooding-tolerance, Ammophila arenaria, Brachypodium sylvalicum, Caltha palustris, Carex curia, Eriophorum vaginatum, Filipendula ulmaria, Glyceria maxima, Hieracium pilosella, Juncus effusus, Myosotis scorpioides, Nardus stricta, Narthecium ossifragum, Phalaris arundinacea, Senecio jacobaea, Trichophorum cespitosum     

Remains of grasses found with the Neolithic Iceman “Ötzi”

The plant remains from the discovery site of the Iceman include a large quantity of grass, from which parts of his clothing were also made. His cape consists of bundles of Brachypodium pinnatum tied with Tilia bast fibres, and the hay used as insulating material in his shoes consists of several species, such as Avenella flexuosa, Avenula versicolor/pubescens, Festuca spec., Nardus stricta and Brachypodium pinnatum. Most probably, these grasses were collected in subalpine matt-grass communities. Additionally, the birch bark vessel found beside the body contained pieces of Molinia caerulea. Grass fragments were evenly distributed all over his equipment as well as in the ice of the gully in which the Iceman was embedded. This implies that the ice in the gully thawed at least once between 3300 and 800 b.c. and the find assemblage was floating in the melt water.     

Experimental manipulation of succession in heathland ecosystems

An experiment was carried out in two heathland ecosystems, one dominated by Calluna vulgaris and the other by Molinia caerulea, to analyse the effects of soil organic matter accumulation and nutrient mineralization on plant species dynamics during succession. The experiment included one treatment that received nutrient solution and two treatments where the rate of soil organic matter accumulation was reduced by removing litter or accelerated by adding litter. In a fourth treatment the C. vulgaris litter produced in the C. vulgaris-dominated plots was replaced by litter of M. caerulea and vice versa. Treatments were applied over 8 years. Addition of nutrient solution caused C. vulgaris to decline, and grass species to increase sharply, compared to the control plots. Addition of litter enhanced both N mineralization and the biomass of M. caerulea and Deschampsia flexuosa but reduced the biomass of C. vulgaris. The effects of replacing C. vulgaris litter by M. caerulea litter, or vice versa, on N mineralization and species dynamics could not be attributed to differences between the decomposability of the different litter materials that were transferred. The results confirm the hypothesis that increased litter inputs accelerate the rate of species replacement during succession.     

Sixty years of vegetation dynamics in a south boreal coniferous forest in southern Norway

Abstract. Vegetation data from permanent plots were collected in 1931, 1961 and 1991 in a south boreal forest 20 km north of Oslo in southern Norway. Major changes were found in the vegetation composition during those 60 years. The main changes were a reduction in the frequency of species and the frequency of joint occurrences of vascular species such as Andromeda polifolia, Calluna vulgaris, Cornus suecica, Eriophorum vaginatum, Maianthemum bifolium, Melampyrum pratense, Trientalis europaea, Vaccinium uliginosum and V. oxycoccus, and mosses, e.g. Dicranum fuscescens, Hylocomium splendens, Pleurozium schreberi, Ptilidium ciliare and Ptilium crista-castrensis. The observed changes were interpreted as being induced by internal processes e.g. notably a long-term change from paludified forest to mesic forest. In particular the growth of Picea abies seems to be a main driving force. The dominance of Picea abies and Vaccinium myrtillus appears to have rendered the conditions more unfavourable for other species. A doubling of the living stem biomass of P. abies during the last 67 yr shows that this old-growth forest has not yet reached a steady state. It was demonstrated that species such as Deschampsia flexuosa and Molinia caerulea did not increase in frequency in response to nitrogen deposition, as has occurred elsewhere in northern Europe. pH in the humus layer increased with 0.2 unit from 1961 to 1991. The results of this study indicate that protection from logging has initiated the reduction of species in the field layer and bottom layer. This study questions if monitoring of forest vegetation should be restricted to protected forests as is the practice in Scandinavia today. We recommend that also areas with some kind of selective cutting will be used for monitoring of forest vegetation.     

Agamospermous seed production of the invasive tussock grass Nardus stricta L. (Poaceae) in New Zealand – evidence from pollination experiments

The breeding system of the European tussock grass Nardus stricta L. (Poaceae) was investigated with pollination experiments. Plants were sampled from two populations at Lake Pukaki, Canterbury, New Zealand, where the species is recognised as an alien invader. Bagging of flowers with king-sized cigarette paper and hand-pollination were used to test for three modes of reproduction in the greenhouse: (1) agamospermy (apomixis), (2) autogamy and self-compatibility, and (3) allogamy (outcrossing). Two control groups without experimental treatments were further tested for seed set under (1) greenhouse and (2) field conditions. The success or failure of all experimental treatments was assessed with seed set and germination trials. All agamospermy treatments showed high seed set and germination proportions arguing for an apomictic mode of reproduction in Nardus stricta. Cross-pollination treatments were also successful making it difficult to estimate the degree of outcrossing, selfing, and agamospermous seed production in Nardus stricta. Fecundity in field populations was considerably reduced, possibly due to environmental factors acting upon seed development during maturation. The reproductive strategy of Nardus stricta might be particularly beneficial during invasion because single tussocks can form reproducing colonies and high reproductive output is ensured even in the absence of pollination. Genetic studies in combination with pollination experiments would be necessary to gain deeper insights into the breeding strategy of Nardus stricta.     

Use of sod cutting for restoration of wet heathlands: revegetation and establishment of typical species in relation to soil conditions

Abstract. Field observations in sod-cut wet Molinia caerulea dominated heath lands revealed information on the revegetation process in relation to plot age and soil variables. Data on the most common species; Erica tetralix, Molinia caerulea, Drosera intermedia and Rhynchospora fusca show that Molinia tends to dominate again within a few years. Whereas the other species are affected in their development by either groundwater regime, soil acidity, nutrient availability or cut depth, Molinia caerulea is highly competitive in all situations. Soil acidity is the major factor affecting species diversity.     

Grazing-induced effects on soil properties modify plant competitive interactions in semi-natural mountain grasslands

Plant-soil feedbacks are widely recognized as playing a significant role in structuring plant communities through their effects on plant-plant interactions. However, the question of whether plant-soil feedbacks can be indirectly driven by other ecological agents, such as large herbivores, which are known to strongly modify plant community structure and soil properties, remains poorly explored. We tested in a glasshouse experiment how changes in soil properties resulting from long-term sheep grazing affect competitive interactions (intra- and inter-specific) of two graminoid species: Nardus stricta, which is typically abundant under high sheep grazing pressure in British mountain grasslands; and Eriophorum vaginatum, whose abundance is typically diminished under grazing. Both species were grown in monocultures and mixtures at different densities in soils taken from adjacent grazed and ungrazed mountain grassland in the Yorkshire Dales, northern England. Nardus stricta performed better (shoot and root biomass) when grown in grazing-conditioned soil, independent of whether or not it grew under inter-specific competition. Eriophorum vaginatum also grew better when planted in soil from the grazed site, but this occurred only when it did not experience inter-specific competition with N. stricta. This indicates that plant-soil feedback for E. vaginatum is dependent on the presence of an inter-specific competitor. A yield density model showed that indirect effects of grazing increased the intensity of intra-specific competition in both species in comparison with ungrazed-conditioned soil. However, indirect effects of grazing on the intensity of inter-specific competition were species-specific favouring N. stricta. We explain these asymmetric grazing-induced effects on competition on the basis of traits of the superior competitor and grazing effects on soil nutrients. Finally, we discuss the relevance of our findings for plant community dynamics in grazed, semi-natural grasslands.     

<Emphasis Type="Italic">Molinia caerulea</Emphasis> responses to N and P fertilisation in a dry heathland ecosystem (NW-Germany)

In the present study we analysed whether airborne N pollution may constitute one important driver for the encroachment of Molinia caerulea in dry heathland ecosystems. Based on full-factorial field experiments (in 2006 and 2008) and complementary greenhouse experiments (in 2008), we quantified growth responses of Molinia caerulea to N and P fertilisation (50 kg N ha⁻¹ year⁻¹, 20 kg P ha⁻¹ year⁻¹). Aboveground biomass production of Molinia caerulea was limited by P in 2006, but by N in both experiments in 2008. In the greenhouse experiment, N addition caused a sixfold increase of the biomass of vegetative tillers, and in all experiments the biomass and numbers of flowering tillers showed a significant increase due to fertilisation. Our experiments indicated that growth of Molinia caerulea was primarily limited by N, but in dry heaths the kind of nutrient limitation may be mediated by other factors such as water availability during the vegetative period. Shifts in biomass allocation patterns resulting from N fertilisation showed that Molinia caerulea encroachment in dry heaths is not only attributable to increased leaf biomass, but also due to higher investments in reproductive tissue that allow for increased seed production and thus accelerated encroachment of seedlings in places where the dwarf shrub canopy has been opened after disturbance.     

A field assessment of the success of moorland restoration in the rehabilitation of whole plant assemblages

Question: How successful is restoration that is focused on a single dominant plant at enabling the reassembly of the whole vegetation assemblage and what factors affect the relative success of such restoration? Location: Moorlands in England and Scotland, UK. Methods: Vegetation composition was sampled in grassdominated (degraded), restored and long established Calluna vulgaris‐dominated (target) areas within eight moorland restoration sites. Additional soil and biogeographic data were collected. Data were analysed by Canonical Correspondence Analysis, which allowed the impact of moorland management to be examined. Results: All sites showed good restoration success when the dominant managed species (Calluna vulgaris, Molinia caerulea and Nardus stricta) were considered. Restoration success of the remainder of the plant assemblage, disregarding these dominant species, was lower with restored samples at some sites differing little from their respective degraded samples. Moors restored solely by grazing exclusion were more similar to their respective targets than were those restored by more intensive mechanical means. The most important factors in explaining vegetation assemblages were management status (i.e. whether samples represented degraded, restored or target parts of the moor) and latitude. Conclusions: The project demonstrates that, where possible, restoration should be attempted by grazing exclusion alone. Furthermore the importance of applying local restoration targets and of monitoring the whole plant assemblages when assessing the success of moorland restoration is highlighted.     

Evidence from water chemistry as a criterion of ombrotrophy in the mire complexes of Abernethy Forest,Scotland

Question: Can cation analyses of water samples within a peatland site be used to infer solute sources to the samples, and so provide an objective criterion of ombrotrophy? Location: Mire complexes within native Pinus sylvestris forest, in Abernethy Forest, north of the Cairngorm Mountains, Scotland, UK. Methods: Chemical analyses of major cations in 200 water samples, and χ² analysis of contingency tables relating species occurrence in the corresponding quadrat samples to the ombrotrophic‐telluric division. Results and conclusions: The chemical data (especially the ratios Ca²⁺/Mg²⁺ and Na⁺/Mg²⁺) indicated a separation of about 140 essentially ombrotrophic samples from about 60 showing clear telluric influence; these conclusions are consistent with published rainwater analyses. For hydrological and meteorological reasons, a sharp separation cannot be expected, so the limit adopted here (Ca/Mg=1.0) is to some extent arbitrary, but the methods described provide a more objective criterion of ombrotrophy than any other. Contingency tables showed highly significant associations between species occurrence and the ombrotrophic‐telluric division. The strongest associations included: (ombrotrophic) Eriophorum vaginatum, Odontoschisma sphagni and Sphagnum cuspidatum; (telluric) Carex panicea, Potentilla erecta, Carex echinata, Narthecium ossifragum, Sphagnum auriculatum s.l., Agrostis canina, Molinia caerulea, Eriophorum angustifolium, and Sphagnum recurvum s.l. The Abernethy mires are arguably more comparable with mire complexes on base‐poor rocks in southern Scandinavia than with most ombrotrophic sites further south and west in Britain. As in Sweden, Narthecium ossifragum and Eriophorum angustifolium, generally ubiquitous on British and Irish ombrotrophic bogs, are “fen” plants at Abernethy.     

A New Approach to Understanding the Calcifuge Habit of Plants

Growth rate of the calcifuge plants Carex pilulifera, Deschampsiaflexuosa, Holcus mollis, Luzula pilosa, Nardus stricta, andVeronica officinalis, transplanted into an Ordovician limestonesoil of pH 8, increased by two to three times on addition of5 mol m^-3 of CaHPO₄ compared to untreated conditions. For Galiumsaxatile, however, P treatment was lethal and growth was possibleonly in soil supplied with Fe(III) citrate, which had littleor no effect on growth of the other six species. Phosphate treatmentof the limestone soil greatly increased plant uptake of P, whereasP concentration of shoots from untreated soil was very low andprobably highly deficient, compared to plants of field siteorigin. From this and two other recent studies it is now possibleto conclude that the calcifuge habit of plants, at least underclimatic conditions prevailing in northern Europe, is most oftendue to an inability of such plants to render the native phosphateof limestone soils available to plant uptake. Out of ten calcifugespecies tested, only one exception to this rule was identified.Copyright1994, 1999 Academic Press Carex pilulifera, Deschampsia flexuosa, Galium saxatile, Holcus mollis, Luzula pilosa, Nardus stricta, Veronica officinalis, calcifuge plants, phosphorus, iron, limestone soil, limiting factors     

Re-establishment of dominance by dwarf shrubs on grass heaths

Experimental fields were established at three sites on different soil types in Dutch heathlands, where grass species have become dominant, in order to find methods for re-establishment of an ericoid dwarf-shrub heath. Treatments included mowing, mowing and cutting for hay, ploughing, milling, sod cutting and burning.Re-establishment of ericoid dwarf shrubs was only observed after creation of gaps or patches of open soil. The results after nine years for two of the sites and six years for the other site indicate that sod cutting is the most suitable method provided that the mineral top soil is not removed or disturbed. More profound removal of the sod including mineral soil causes a delay in re-establishment of ericoid dwarf shrubs and an increase of grasses.Factors that may explain different responses to gap creation including availability of seeds, soil moisture, soil fertility and plant survival strategies are briefly discussed.Abbreviations Calluna = Calluna vulgaris - Deschampsia = Deschampsia flexuosa - Erica = Erica tetralix - Molinia = Molinia caerulea - Sarothammus = Sarothammus scoparius     

Differential responses of UK upland plants to nitrogen deposition

Native upland species, Nardus stricta , Eriophorum vaginatum , Erica cinerea and Vaccinium vitis-idaea were given 3 or 60 kg N ha⁻¹ yr⁻¹, over 2 yr, applied as a mist (NH₄NO₃). The high N treatment increased above-ground biomass in all four species, but only significantly in E. cinerea , E. vaginatum and N. stricta . Biomass increases in E. vaginatum and N. stricta resulted from enhanced tiller production rather than shoot elongation. Root growth increased in N. stricta , so that root:shoot ratio in this species was unchanged by N. Root growth in E. vaginatum , E. cinerea and V. vitis-idaea did not respond to N and their root:shoot ratios decreased. Tissue N concentrations increased in both shoots and roots of all species in response to N. The accumulated foliar N did not increase the proportion of N allocated to Rubisco and the photosynthetic capacities of N. stricta , E. vaginatum and V. vitis-idaea were unchanged. Thus growth responses to N were due to altered allocation rather than increased rate of photosynthesis per unit leaf area. The high N treatment increased flower production significantly in E. cinerea but not in the other species. Although in this experiment dwarf shrubs were more responsive than graminoids to N, in the field at current N inputs the enhanced tillering of the graminoids may be more competitively advantageous, especially where gaps develop in the canopy. Thus increasing N deposition may lead to increased grassiness of upland heath, and in particular, a spread of N. stricta .     

The feeding behaviour of Carterocephalus palaemon (Lepidoptera: Hesperiidae) caterpillars: does it avoid host defences or maximize nutrient intake?

Abstract.

• 1 The larvae of the chequered skipper butterfly Carterocephalus palaemon notch the blades of purple moor-grass Molinia caerulea before feeding.
• 2 The nutrient concentrations above and below these notches were measured and the nutrient concentrations of undamaged blades of the host plant.
• 3 Nutrient concentrations above the notches remained similar to undamaged blades for a short period, whilst concentrations below declined, especially nitrogen, calcium and magnesium.
• 4 The feeding behaviour of C.palaemon larvae is discussed in relation to declining levels of nutrients in the food plant over the larval season and to other possible reasons for this behaviour, such as avoidance of host defences initiated in response to attack.

     

Sputtering,a New Method for Coating Pollen Grains in Scanning Electron Microscopy

Sputtering is an easy, rapid and effective method for metal coating of pollen grains for examination in the scanning electron microscope. A very thin, regular and stable metal layer is obtained by bombarding a metal target with ions under a low vacuum, so that it ejects atoms on to the specimen. This allows of the observation of exine sculpturing which would be completely masked by a coating resulting from evaporation of carbon and metal. The sputtering method was tested on pollen of Deschampsia flexuosa, Molinia caerulea and Betula pubescens. Very narrow perforations could be discerned in the exine, similar to those seen in the images of carbon replicas obtained by many authors with the transmission electron microscope.     

An attempt to restore a central European species‐rich mountain grassland through grazing

Abstract. This paper describes the effects of re‐establishing seasonal cattle grazing by 0.7 animal.ha^‐1 on vegetation in a long‐term abandoned, and partly degraded, semi‐natural mountain pasture in the ?umava National Park, Czech Republic. There was very uneven grazing intensity inside the locality, and grazing preference changed during the season: cattle grazed most of the time in productive but species‐poor Deschampsia cespitosa swards, but changed to a species‐rich Violion caninae stand in the middle of the summer. A species‐rich Carex rostrata community was only grazed at the end of the season. Species‐poor swards dominated by Nardus stricta and Carex brizoides were mainly used as resting areas. Both grazing and excluding from grazing had a negative effect on species diversity of the Deschampsia cespitosa swards. The soil seed bank contained only few species that are characteristic of mountain grassland communities, and seed dispersal of the target species by cattle dung was also found to be very limited. Thus both grazing and exclusion from grazing are probably of limited value for the restoration of species‐rich grasslands from species‐poor Deschampsia cespitosa swards in this case.     

Control of Molinia caerulea by cutting management on sub-alpine grassland

There has been a considerable expansion of Moliniacaerulea after the cessation of cutting management of Nardus stricta sub-alpine grasslands in the Giant Mts. (Krkonoše/Karkonosze/Riesengebirge, the Czech Republic) in the last 50 years. The aim of this study was to investigate whether the reestablishment of traditional management (one cut per year in late July) could reverse Molinia encroachment and help to restore the original Nardus grassland.     

Contrasted Responses of Two Understorey Species to Direct and Indirect Effects of a Canopy Gap

Positive associations between adult trees and understorey species have been explained either by direct or indirect facilitation. We tested both models by comparing the performance of two understorey species with contrasted stress-tolerance abilities Galium odoratum and Deschampsia flexuosa. Individuals of both species were transplanted in the four combinations of two treatments (gap and removal of an herbaceous competitor, Molinia caerulea). Our experiment demonstrated that direct facilitation of adult trees may explain the restricted occurrence of the shade-demanding Galium within closed forest communities. In contrast, the shade-tolerant Deschampsia was subjected to additional competition within the forest, likely because adult trees had a higher negative effect on light availability and a similar negative effect on nitrogen availability within the forest than did Molinia in the gaps.     

Inter-Specific Competition,but Not Different Soil Microbial Communities,Affects N Chemical Forms Uptake by Competing Graminoids of Upland Grasslands

Evidence that plants differ in their ability to take up both organic (ON) and inorganic (IN) forms of nitrogen (N) has increased ecologists’ interest on resource-based plant competition. However, whether plant uptake of IN and ON responds to differences in soil microbial community composition and/or functioning has not yet been explored, despite soil microbes playing a key role in N cycling. Here, we report results from a competition experiment testing the hypothesis that soil microbial communities differing in metabolic activity as a result of long-term differences to grazing exposure could modify N uptake of Eriophorum vaginatum L. and Nardus stricta L. These graminoids co-occur on nutrient-poor, mountain grasslands where E. vaginatum decreases and N. stricta increases in response to long-term grazing. We inoculated sterilised soil with soil microbial communities from continuously grazed and ungrazed grasslands and planted soils with both E. vaginatum and N. stricta, and then tracked uptake of isotopically labelled NH₄ ⁺ (IN) and glycine (ON) into plant tissues. The metabolically different microbial communities had no effect on N uptake by either of the graminoids, which might suggest functional equivalence of soil microbes in their impacts on plant N uptake. Consistent with its dominance in soils with greater concentrations of ON relative to IN in the soluble N pool, Eriophorum vaginatum took up more glycine than N. stricta. Nardus stricta reduced the glycine proportion taken up by E. vaginatum, thus increasing niche overlap in N usage between these species. Local abundances of these species in mountain grasslands are principally controlled by grazing and soil moisture, although our results suggest that changes in the relative availability of ON to IN can also play a role. Our results also suggest that coexistence of these species in mountain grasslands is likely based on non-equilibrium mechanisms such as disturbance and/or soil heterogeneity.     

A laboratory assessment of the relative susceptibility of Molinia caerulea (L.) Moench and Calluna vulgaris (L.) Hull to a range of herbicides

There is a concern that Molinia caerulea (L.) Moench may be increasing in upland moorland communities at the expense of Calluna vulgaris (L.) Hull and other ericaceous species. In order to develop a strategy for the control of Molinia, laboratory studies were carried out to determine the dose-response relationships of seven graminicides and glyphosate on both Molinia caerulea and Calluna vulgaris. Plants were grown under laboratory conditions and sprayed with increasing doses of herbicide using a precision sprayer. Results were highly variable, indicating the great morphological plasticity of these two species, making determination of the ED₅₀ difficult. Glyphosate, quizalofop-ethyl and sethoxydim successfully reduced various measures of Molinia growth to 50% of control levels (ED₅₀ estimates ranged from 0.41–0.67 kg a.i. ha^-1, 0.18–1.20 kg a.i. ha^-1and 0.37–0.49 kg a.i. ha^-1respectively). In contrast, only glyphosate reduced Calluna growth significantly (ED₅₀s ranged from 0.025–0.45 kg a.i. ha^-1), whilst selective herbicides left it undamaged. A comparison of the results for Molinia and Calluna suggests that there is no application rate of glyphosate which will reduce Molinia effectively whilst leaving Calluna undamaged. Recommendations for field testing of selective herbicides are discussed.