Poa Nemoralis Research Articles

What Is the Impact of Impatiens parviflora on Diversity and Composition of Herbal Layer Communities of Temperate Forests?

The aim was to estimate the impacts of invasive Impatiens parviflora on forests’ herbal layer communities. A replicated Before-After-Control-Impact field experiment and comparisons with adjacent uninvaded plots were used. The alien’s impact on species richness was tested using hierarchical generalized mixed effect models with Poisson error structure. Impact on species composition was tested using multivariate models (DCA, CCA, RDA) and Monte-Carlo permutation tests. Removal plots did not differ in native species richness from neither invaded nor adjacent uninvaded plots, both when the treatment’s main effect or its interaction with sampling time was tested (Chi2 = 0.4757, DF = 2, p = 0.7883; Chi2 = 7.229, DF = 8, p = 0.5121 respectively). On the contrary, ordination models revealed differences in the development of plots following the treatments (p = 0.034) with the invaded plots differing from the adjacent uninvaded (p = 0.002). Impatiens parviflora is highly unlikely to impact native species richness of invaded communities, which may be associated with its limited ability to create a dense canopy, a modest root system or the fact the I. parviflora does not represent a novel and distinctive dominant to the invaded communities. Concerning its potential impacts on species composition, the presence of native clonal species (Athyrium filix-femina, Dryopteris filix-mas, Fragaria moschata, Luzula luzuloides, Poa nemoralis) on the adjacent uninvaded plots likely makes them different from the invaded plots. However, these competitive and strong species are more likely to prevent the invasion of I. parviflora on the adjacent uninvaded plots rather than being themselves eliminated from the invaded communities.

环境因子对巴山冷杉-糙皮桦混交林物种分布及多样性的影响

Environmental factors have a full impact on species distribution and diversity of forest community.The relationship between environmental factors and species patterns suggests important implications for developing optimal strategies for conservation of species diversity,sustainable managing and utilizing plant resources.Various types of plant communities have been documented in regard to the relationship of environmental factors to species distribution and diversity;however,little attention has been paid to Abies fargesii-Betula utilis mixed forest,the typical plant community functioning critically in soil and water conservation.We investigated characteristics and environmental factors of the Abies fargesii-Betula utilis mixed forest located within an elevation of 2700-3100 m in Taibai Mountain,China from July through September 2009 and July through August 2010.We established 3 transects along elevation gradient,and set up 10 plots(20m×20m,for trees) in each transect.In the corner of each plot,we set up one subplot(10m×10m) for shrubs and herb.We recorded the community characteristics including species name,number,cover,height,tree basal diameter and diameter at breast height(DBH1cm) as well as the environmental factors including elevation,slope,stone cover,soil pH,organic matter,total nitrogen and total phosphorus.Three analysis procedures were carried out: canonical correspondence analysis(CCA) to examine relationship between species distribution and environmental factors,partial CCA to assess the respective importance of environmental factors on species distribution,and generalized additive model(GAM) to fit response of species richness to various environmental factors.The results showed that soil pH,elevation and stone cover had significant effect on species distribution(P 0.05) with the impact intensity being elevation stone cover pH.Nevertheless,the other environmental factors(soil organic matter,total nitrogen,total phosphorus content and slope) had no significant effect(P 0.05).Some species,such as Ribes glaciale,Lonicera webbiana,Rubus amabilis,Chrysosplenium pilosum var.valdepilosum,and Kobresia myosuroides,were associated with low stone cover,acidic and total phosphorus poor-soil;otherwise,Betula utilis,Sabina pingii var.wilsonii,Potentilla glabra,Ajuga ciliate and Ajania variifolia were more prominent in high stone cover,low acidic and total phosphorus rich-soil.Besides,Spiraea mongolica,Pleurospermum heterosciadium,Carex filamentosa,Poa nemoralis and Draba ladyginii var.trichocarpa occurred at a high elevation.However,Lonicera szechuanica,Rubus pileatus,Fragaria gracilis,Viola biflora and Carex capilliformis var.major were found in all plots since all environmental factors had little effects on their distribution.GAM analysis indicated that the major environmental factors associated with species richness were soil pH,stone cover,elevation and total nitrogen content(P 0.01).Species richness increased with increasing pH and decreasing stone cover and elevation,and richness changed intricately with changes of total nitrogen content;in contrast,there were no significant effects on species richness(P 0.05) from soil organic matter,total phosphorus content and slope.Thus,species distribution and richness pattern of Abies fargesii-Betula utilis mixed forest were influenced by a variety of environmental factors in which elevation,stone cover and soil pH played the most important role.

Prevalence of an intraspecific Neotyphodium hybrid in natural populations of stout wood reed (Cinna arundinacea L.) from eastern North America

Members of genus Neotyphodium are asexual derivatives of sexual Epichloë species and maintain endophytic relationships with many cool-season grasses. Most Neotyphodium species analyzed so far are interspecific hybrids with combined or partial genomes of two or three ancestral species. In this study we characterized Neotyphodium isolates from Cinna arundinacea, a perennial cool-season grass from eastern North America. A total of 23 isolates grouping into two distinct morphotypes were obtained from five local populations of C. arundinacea. PCR amplification and cloning of translation-elongation factor 1-α (tefA) and β-tubulin (tubB) genes of 10 isolates comprising both morphotypes (two isolates per location) revealed that all 10 contain two copies of tefA and tubB genes. Surprisingly phylogenetic analysis of mainly non-coding sequence from these genes revealed that both copies in each isolate were inherited from Epichloë typhina ancestors, indicating that the C. arundinacea endophytes arose through intraspecific hybridization between two E. typhina progenitors with extant relatives infecting hosts Poa nemoralis and Poa pratensis. Furthermore the tefA sequences were identical between isolates, as were tubB sequences, despite obvious morphological differences. Profiling of alkaloid biosynthetic genes from these isolates indicated the presence of the peramine biosynthetic gene (perA) and the absence of genes required for biosynthesis of lolines, indole-diterpenes and ergot alkaloids. Thus this endophyte is potentially capable of producing peramine in planta and providing protection to its host from insect pests. The absence of genes for indole-diterpenes and ergot alkaloid biosynthesis makes this endophyte a candidate for agricultural applications. Based on our phylogenetic analysis, alkaloid profiling and description of morphological characteristics, we propose the name Neotyphodium schardlii for these isolates from C. arundinacea, a new member of genus Neotyphodium and the first described to have arisen through intraspecific hybridization.

OVERCOMING IRON DEFICIENCY CHLOROSIS IN CITRUS THROUGH INTERCROPPING WITH PERENNIAL GRASS SPECIES

The objective of this experiment was to investigate the influence of intercropping with three different perennial grass species (Festuca ovina L., Festuca rubra subsp. tricophylla L. and Poa nemoralis L.) on the Fe nutritional status of citrumelo 'Swingle' (Citrus paradisi Macf. × Poncirus trifoliata), a highly Fe chlorosis susceptible citrus rootstock. One-year old citrumelo plants were grown in pots on calcareous soil-sand mixture under greenhouse conditions and treated as follows: 1) citrumelo plants grown in a monoculture system (without a companion crop); 2) citrumelo plants fertilized with 18.6 mg Fe per plant in form of FeEDDHA; 3) citrumelo plants separately intercropped with the three perennial grass species. These grasses were sown at a rate of 3 seeds cm -2 , mowed only one time and allowed to re-grow. The experiment lasted five months. Chlorophyll measurements were performed on the youngest fully expanded leaves in terms of SPAD index and at the end of the experiment leaf chlorophyll content (μg cm -2 ), leaf length and width and dry weight of young shoots were determined. Intercropping citrumelo plants with F. rubra was effective almost as FeEDDHA in preventing the development of leaf chlorosis and improving their growth compared to the control plants, while those intercropped with F. ovina overcame Fe deficiency symptoms only after mowing/clipping this grass species. The Poa nemoralis did not demonstrate any potential to prevent leaf chlorosis or improve the growth of citrumelo plants. These results indicate that only Fe-efficient perennial grass species can be utilized as an effective ecological orchard floor management practice to improve the Fe nutrition of fruit trees grown on calcareous soils.

Repatriation of lost old grass varieties to the germplasm collection of the Czech Republic

 In former Czechoslovakia, grass breeding was located in the three distinct regions of Southern Bohemia and Northern Moravia during the 1920’s; and later in Slovakia in the 1940’s. This resulted in the development of 45 cultivars of 17 grass species which originated from local ecotypes and were named after the place of their breeding (<I>e.g. </I>Táborský, Větrovský, Rožnovský, and Levočský). Most of these historical cultivars were not preserved in any national germplasm collection, and the number of missing accessions amounted to 27 of the 34 deleted varieties. Using the findings about unpreserved materials of Czechoslovak origin in the European Central Crop Databases, as well as the EURISCO web catalogue, it was possible to repatriate 7 historical cultivars (<I>Arrhenatherum elatius </I>Větrovský, <I>Festuca pratensis </I>Větrovská, <I>Festuca rubra </I>Rožnovská, <I>Lolium perenne </I>Táborský, <I>Phleum pratense </I>Větrovský, <I>Poa nemoralis </I>Rožnovská, and <I>Poa pratensis </I>Levočská) from the gene banks of the neighbouring European countries. The accessions were regenerated, and their seed has been stored <I>ex situ </I>in the Gene Bank of the Crop Research Institute in Prague.  

Genetic adaptation to soil acidification: experimental evidence from four grass species

Anthropogenic acidification has reduced soil pH and released potentially toxic aluminium (Al) ions in many regions. This investigation examines whether increased acidity has caused genetic adaptation to acidic conditions within the grass species Elymus caninus, Poa nemoralis, Deschampsia cespitosa and D. flexuosa. We sampled tussocks (genets) of each species in two regions of southern Sweden, differing in their exposure to acidifying deposition. The tolerance of the genets was tested in a solution experiment with different pH and Al concentrations. Our data suggest that species found at lower pH field locations have a greater tolerance to low pH and high Al levels than species found on less acidic soils. Analysis of variance showed a significant average effect of population and (or) genet in most species; however, we found little evidence of genetic adaptation to acidic conditions at the regional, population and micro-site level. In fact, there was no consistent change in the ranking of populations or genets with varying pH or Al concentration. Based on these results, we hypothesize that phenotypic plasticity rather than genetic adaptation has been favoured as the predominant mechanism to cope with soil acidity in the four grass species.

Colonisation by arbuscular mycorrhizal and fine endophytic fungi in four woodland grasses – variation in relation to pH and aluminium

Acidic soils are harsh environments for plants. One of the major problems is the potential toxicity of aluminium (Al) and hydrogen ions at a pH below 5; another is the shortage of nutrients usually accompanying soil acidity. The aim of this study was to elucidate the relationship between arbuscular mycorrhizal (AM) colonisation and soil acidity (measured by pH and Al concentration) in order to evaluate the possibility that AM fungi facilitate the existence of plants on acidic soils. We sampled tussocks of four grass species, Elymus caninus, Poa nemoralis, Deschampsia cespitosa and Deschampsia flexuosa, together with samples of the surrounding soil, in oak forests of varying soil pH in southern Sweden. We determined pH, easily reacting Al (Al r), extractable Al (Al BaCl2) and phosphate in the soil samples, analysed the shoots for Al and phosphorous and quantified the degree of AM and fine endophyte (FE) colonisation in the roots. E. caninus was found on the least acidic soils and had the highest AM colonisation of all the species studied, while D. flexuosa, which was found on the most acidic soils, had the lowest AM colonisation. P. nemoralis and D. cespitosa were intermediate with respect to pH and AM colonisation. The colonisation of AM fungi exceeded FE colonisation for E. caninus and P. nemoralis, while the opposite was true for the two Deschampsia species. Our results indicated a negative relationship between Al r and the degree of AM colonisation at the within-species level. The low colonisation of AM fungi on acidic soils may to some extent be explained by a sensitivity of AM fungi to Al r: this parameter showed a stronger negative association with AM colonisation than did pH and Al BaCl2. We hypothesize that Al toxicity is a critical factor for plant nutrition in forest soils through the impact on symbiotic fungi.

Seed dispersal from a forest into adjacent cropland

Seed banks in seven fields adjacent to deciduous forests were investigated for the potential input of seeds from forest into cropland. The influence of proximity of a forest stand was qualitative rather than quantitative and limited to a 3 m zone from the field/forest margin. Density and species richness of the seed bank were significantly higher there, and declined sharply with distance into the field. A comparison of the composition of forest vegetation and the crop seed bank showed that most species in the latter presumably dispersed from the forest and forest edge vegetation. Seeds occurred however at very low densities in the field and the most abundant species in the seed bank, Juncus bufonius, did not originate from the nearby forest. Dispersal of individual species into the field was very limited, the ranking of decreasing dispersal distance into the cropland being Stellaria media > Urtica dioica > Rumex obtusifolius and Sonchus oleraceus > Juncus effusus > Hypericum humifusum, Poa nemoralis and Rubus spp. The forest edge cannot be regarded as an important source of weed infestation in the adjacent cropland, whereas there was evidence for the reverse dispersal of seeds from the field into the forest edge.

Scree forests (Mercuriali-Tilietum) of the Börzsöny Mountains, Hungary

Scree forest communities Mercuriali-Tilietum Zolyomi et Jakucs 1958 of Borzsony Mts were not processed until the present. These lime-dominated forests develop on andesite base-rock, mainly on periglacial scree surfaces. Using the Braun-Blanquet-Soo method 15 sampling spots were studied and analysed based on floristical composition, cenological aspects and habitat characteristics. The stand's species stock consists of tree species like Acer platanoides, Carpinus betulus, Fraxinus excelsior, Tilia platyphyllos, shrubs like Cornus mas, Corylus avellana, Euonymus verrucosus, Ribes uva-crispa and herbs like Cystopteris fragilis, Dryopteris filix-mas, Galeobdolon luteum, Galium schultesii, G. odoratum, Hedera helix, Melica uniflora, Mercurialis perennis, Mycelis muralis, Poa nemoralis, Waldsteinia geoides. Rare Tilio-Acerion species are Adoxa moschatellina, Gagea minima, Geranium lucidum. Cenological categories, life forms, geoelement distribution, and Borhidi's Social Behaviour Types were studied on the basis ...

Plant nitrate use in deciduous woodland: the relationship between leaf N, 15N natural abundance of forbs and soil N mineralisation

Our aim was to study whether the in situ natural abundance 15N (δ15N)-values and N concentration of understory plants were correlated with the form and amount of mineral N available in the soil. Also to determine whether such differences were related to earlier demonstrations of differences in biomass increase in the same species exposed to nutrient solutions with both NO3− and NH4+ or to NH4+ alone. Several studies show that the δ15N of NO3− in soil solution generally is isotopically lighter than the δ15N of NH4+ due to fractionation during nitrification. Hence, it is reasonable to assume that plant species benefiting from NO3− in ecosystems without significant NO3− leaching or denitrification have lower δ15N-values in their tissues than species growing equally well, or better, on NH4+. We studied the δ15N of six understory species in oak woodlands in southern Sweden at 12 sites which varied fivefold in potential net N mineralisation rate (minNH4++NO3−). The species decreased in benefit from NO3− in the following order: Geum urbanum, Aegopodium podagraria, Milium effusum, Convallaria majalis, Deschampsia flexuosa and Poa nemoralis. Four or five species demonstrated a negative correlation between minNO3− and leaf δ15N and a positive correlation between minNO3− and leaf N concentration. In wide contrast, only D. flexuosa, which grows on soils with little nitrification, showed a positive correlation between minNH4+ and the leaf N concentration and δ15N-value. Furthermore, δ15N of plants from the field and previously obtained indices of hydroponic growth on NH4+ relative to NH4++NO3− were closely correlated at the species level. We conclude that δ15N may serve as a comparative index of uptake of NO3− among understory species, preferably in combination with other indices of N availability. The use of δ15N needs careful consideration of known restrictions of method, soils and plants.

The evolutionary origins of three new Neotyphodium endophyte species from grasses indigenous to the Southern Hemisphere

Members of the genus Neotyphodium are asexual, seedborne, protective fungal endophytes of cool season grasses that have likely evolved either directly from sexual Epichloë; species, or by the interspecific hybridization of distinct lineages of Epichloë; and Neotyphodium. We investigated the evolutionary origins of Neotyphodium endophytes from several grasses that are indigenous to the Southern Hemisphere using a multiple-gene phylogenetic approach. Intron regions of the genes encoding β-tubulin (tub2), translation elongation factor 1-α (tef1) and actin (act1) were amplified by polymerase chain reaction and sequenced. Phylogenetic analyses of these sequences, aligned with homologous sequences from Epichloë; spp., revealed the evolutionary origins of the Southern Hemisphere endophytes, where one lineage of apparently non-hybrid origin, and three lineages of unique interspecific hybrid origin were identified. On the basis of morphology, host range and evolutionary history, we propose three new species of Neotyphodium. Neotyphodium aotearoae was isolated from Echinopogon ovatus populations from New Zealand and Australia, and comprised a unique, apparently non-hybrid lineage within the Epichloë; species phylogeny. In contrast, an interspecific hybrid lineage was identified from two Australian Ec. ovatus populations, whose ancestry apparently involved lineages closely related to extant E. festucae and an E. typhina genotype similar to that of isolates from Poa pratensis. Endophytes infecting South African Melica racemosa and M. decumbens (dronkgras) appeared to be hybrids of E. festucae and N. aotearoae or close relatives. The names N. australiense and N. melicicola are proposed for these two hybrid lineages, respectively. The origin of N. tembladerae, an established endophyte species from South American Poa and Festuca spp., was also investigated. Neotyphodium tembladerae appeared to be of hybrid origin, involving E. festucae and an E. typhina genotype similar to that of isolates from Poa nemoralis. The results of this study highlight the widespread occurrence of interspecific hybrid Neotyphodium lineages on a global scale, and the extent of endophyte gene-flow between the Northern and Southern Hemispheres.

Host specialization of different populations of ergot fungus (Claviceps purpurea)

In our previous study of Claviceps purpurea three populations were found: G1 on open localities, G2 from shady or wet habitats and G3 on Spartina stands of coastal salt marshes. The latter two are also chemoraces. In the Czech Republic, isolates of G1 and G2 were found. The ability of four isolates representing these populations to infect and develop sclerotia on different host species (Holcus lanatus, Helictotrichon pubescens, Phalaris arundinacea, Dactylis glomerata, Arrhenatherum elatius, Bromus inermis, Bromus erectus, Elytrigia repens, Avenella flexuosa, Lolium perenne, Poa nemoralis, Poa annua, and different cultivars of Poa pratensis) was studied along with their alkaloid production. P. pratensis and D. glomerata were infected by all the isolates and sclerotia were formed by isolates 207 (G1) and 434 (G2), and on two P. pratensis cultivars even by 481 (G3). Infection ability (formation of sphacelial stage and honeydew) was less host-restricted than formation of mature sclerotia. G2 and G3 strains infected A. flexuosa without sclerotia formation. L. perenne was infected only once by strain 207 (G1) without sclerotia formation. P. annua (natural host of G2), was infected by all isolates, but no sclerotia were formed even with G2 strains. From the two G2 isolates, strain 434 from Dactylis formed sclerotia on five host species, whereas isolate 475 originating from Phragmites stand formed only sphacelia. Composition of alkaloid mixture produced in sclerotia of the same strain from various hosts confirmed that host plant does not influence the type of alkaloids produced, only their ratio.

Effects of soil acidification and liming on ground flora establishment after clear-felling of Norway spruce in Sweden

We used 2 long-term field experiments with Norway spruce Picea abies (L.) Karst. to investigate the influence of lime, acid sulphur compounds, or nitrogen (1 site) on the rate of recruitment of new vascular species after clear-fellings. On the study sites, Farabol in southern Sweden and Fäxboda in south–central Sweden, the chemical treatments had been applied before clear-felling and whole-tree harvesting. An additional, post-harvest experiment was conducted at Farabol in which lime, hardened wood-ash, or logging residues were applied. A germination experiment including seven species was carried out in a greenhouse using sifted humus from Fäxboda that was sampled 2 years before clear-felling. The clear-fellings resulted in establishment of many ephemeral species. The number of newly established species was greater than the number of disappeared species. There was an overall positive correlation with pH in the humus layer and the number of newly established species. The treatment effects differed between the sites, probably reflecting differences in total dose and initial soil conditions. Farabol is characterised by more acid soils and greater atmospheric deposition of S and N than Fäxboda. At Farabol, liming (in total 6000 kg limestone ha −1 distributed over 12 years) resulted in about 20 new species established after clear-felling, four times more species than in untreated, sulphur-treated, or nitrogen-fertilised plots. At Fäxboda, where lime (2000 kg dolomite ha −1), sulphuric acid, and elementary S had been applied 16 years before clear-felling, the number of newly established species was about 15, and no effect of the treatments was revealed. The post-harvest treatments at Farabol showed that wood-ash and logging residues had similar effects as lime on the establishment of new species. The pot experiment showed that liming or acidification can affect the germination of seeds. Compared with untreated soil, a greater proportion of seeds of Primula veris ( P. veris) and Senecio sylvaticus ( S. sylvaticus) germinated in limed soil and the germination of P. veris was lower in acid- or sulphur-treated soils. The germination of Vaccinium myrtillus ( V. myrtillus) seeds was negatively affected by liming. No effects of the treatments were discovered on the germination of Deschampsia flexuosa, Calamagrostis arundinacea, Galeopsis bifida ( G. bifida), or Poa nemoralis. The soil water in the pot experiment had higher pH, higher concentrations of Ca and Mg, and higher NO 3 −/NH 4 + ratios in limed soil compared with other treatments. Nomenclature of plants follows Lid (1985).

TESTING NATIVE GRASSES FOR SURVIVAL AND GROWTH IN LOW pH MINE OVERBURDEN

Overburden piles at the Molycorp molybdenum mine in north central New Mexico contain neutral rock types as well as mixed volcanic rocks, which are highly weathered materials with low pH and high salinity from pyrite oxidation. The mixing of rock types during overburden pile construction has resulted in heterogeneous substrates with a range of pH and soluble salt levels. An experiment to determine grass species more likely to survive and grow in these low pH overburden materials used substrate treatments consisting of an unadulterated acid rock, an acid:neutral overburden mixture ratio of 9: I, and an acid:neutral overburden mixture ratio of 3:1. Containerized grass seedlings of 54 species/ecotypes, primarily cool-season natives of the western U.S, were transplanted into these substrates. Species grown from seed collected at the Mo\ycorp site having superior performance included Muhlenbergia montana (2 ecotypes), Blepharoneuron trieholepis, Festuea species (3 ecotypes), and a Poa species. A number of commercially available grass varieties had good survival and growth in these substrates: Deschampsia caespitosa 'Peru Creek Festuea ari:::onica 'Redondo', Festuca ovina 'Covar Festuea ovina 'MX-86', Festllea sp. 'Shorty', Poa compressa 'Reubens', Paseopyrum smith;; 'Arriba, Barton, and Rosana and Elymus traehycaulus 'San Luis'. Other native grass species that showed superior survival and growth in these acid rock substrates included Elymus canadensis, Danthonia interrnedia, Sporobolus wrightii, Poa nemoralis, and Hesperostipa cornata. Additional

The evolutionary origins of Epichloë endophytes from annual ryegrasses

The annual Lolium (ryegrass) species were surveyed for seedborne, asexual Epichloë endophytes (i.e., Neotyphodium spp.). Endophytes that were extremely slow growing in culture were identified from all seven annual ryegrass spp. Sequences of β-tubulin gene (tub2) introns and the internal transcribed spacers of the nuclear ribosomal RNA (rDNA-ITS) were determined, as were profiles based on five microsatellite loci. Two taxonomic groups of annual ryegrass endophytes were distinguishable by morphology, culturability and genotypes. One group, for which the name Neotyphodium, occultans is proposed, comprised only isolates that could not be subcultured on potato dextrose agar medium. These isolates contained multiple tub2 genes and multiple alleles at microsatellite loci, suggestive of an interspecific hybrid origin. The results of phylogenetic analysis implied that the ancestors of N. occultans included Epichloë baconii and E. bromicola, or close relatives. The second taxonomic group of annual ryegrass endophytes, exemplified by isolate Lc4, was found only in L. canariense. This taxon had a single tub2 sequence and microsatellite genotype that was nearly identical to those of extant Epichloë typhina isolates that infect Poa nemoralis. Therefore, it is proposed that Lc4 is an asexual derivative of an E. typhina genotype closely related to extant strains from P. nemoralis. We propose the name Neotyphodium typhinum var. canariense for this taxon. These two new endophyte taxa from the annual ryegrasses are further examples of asexual Neotyphodium species that have arisen from sexual Epichloë spp. either directly by loss of the sexual state, or by interspecific hybridization events.

Potential Nitrification as an Indicator of Preferential Uptake of Ammonium or Nitrate by Plants in an Oak Woodland Understorey

The preferences of some woodland understorey species for ammonium and nitrate were investigated by measuring the potential nitrification (conversion of ammonium to nitrate) in the rhizosphere compared with the bulk soil. Less acid-tolerant species, which usually prefer nitrate or a mixture of ammonium and nitrate in hydroponic culture, should have a higher potential nitrification in the rhizosphere compared to the bulk soil due to a low uptake of ammonium (since ammonium is relatively immobile). Acid-tolerant species should have a high uptake of ammonium and thereby lower or equal potential nitrification in the rhizosphere compared to the bulk soil. The hypothesis was tested in a field investigation of five understorey herb species, Deschampsia flexuosa, Convallaria majalis, Poa nemoralis, Geum urbanum andAegopodium podagraria performed in oak forests in southern Sweden. Overall, the two less acid-tolerant species, Geum urbanum and Aegopodium podagraria, had high potential nitrification in the rhizosphere compared to the bulk soil (indicating a relatively low uptake of ammonium), whilst the acid tolerant species, Deschampsia flexuosa andConvallaria majalis , had approximately equal potential nitrification in the rhizosphere compared to the bulk soil (indicating a relatively high uptake of ammonium). In the case of Poa nemoralis, a species which grows in both acid and less acid soils, we found the potential nitrification in the rhizosphere and in the bulk soil to be similar at low inorganic nitrogen concentrations, but the difference (rhizosphere>bulk) increased when nitrification in the bulk soil was enhanced (i.e. when the nitrogen availability increased). The potential nitrification in the bulk soil varied between 0 and 16nmol g−1h−1and was positively correlated with pH. When species occurred at the same site, the potential nitrification in the bulk soil tended to be lower for the acid tolerant species. Despite a large variation in potential nitrification, the method offers a possibility of measuring the preference of plants for ammonium/nitrate in a soil system, under natural conditions.

Megasporocyte Callose in Apomictic Buffelgrass, Kentucky Bluegrass, Pennisetum squamulatum Fresen, Tripsacum L., and Weeping Lovegrass

Callose, a β‐l,3‐glucan, is synthesized and deposited in the walls of megaspore mother cells (MMCs) of angiosperms that produce either normal monosporic (>90% of all angiosperm species) or bisporic embryo sacs. Such deposits are absent in angiosperms that produce tetrasporic embryo sacs and were recently shown to be absent in diplosporous Elymus rectisetus (Nees in Lehm.) A. Löve & Connor, Tripsacum L. spp., and Poa nemoralis L. We determined the extent of callose deposits in MMCs of diplosporous weeping lovegrass (Eragrostis curvula Schrad.), several additional diplosporous Tripsacum accessions and aposporous buffelgrass (Pennisetum ciliare (L.) Link), Kentucky bluegrass (Poa pratensis L.), and Pennisetum squamulatum Fresen. Callose deposition was studied in pistils cleared in an aqueous aniline blue clearing medium and observed by means of UV microscopy. Pistils cleared with conventional clearing media were studied by means of interference contrast microscopy. Some pistils were cleared and analyzed in one clearing medium and recleared and reanalyzed in the other. A callosic MMC was observed in only one of 376 appropriately staged pistils taken from diplosporous species. This pistil, one of 89 weeping lovegrass pistils studied, was probably facultatively sexual. An absence of callose during megasporogenesis may be characteristic of most types of diplospory. Though present, the distributions and quantities of callose observed in MMC walls of aposporous apomicts were erratically reduced, possibly as a result of early MMC abortion or early activation of nucellar initials. Callose deficiencies and vacuolization patterns support the following hypotheses: (i) apospory is caused by a moderately precocious gametophytization of nucellar cells, and (ii) bispory, tetraspory, and diplospory are caused by a moderately to extremely precocious gametophytization of the MMC that is nearly complete in the latter case and variably incomplete in the former two cases. Understanding how these precocious gametophytizations evolved and are regulated may be crucial to the eventual transfer of apomixis to major crop species and to its successful manipulation by breeders.

Reversibility of damages to forest floor plants by episodes of elevated hydrogen- and aluminium-ion concentrations in the soil solution

Herbs and grasses may episodically be exposed to elevated concentrations of potentially toxic elements as H+ and Al3+ due to considerable temporal variability in the chemical composition of soil solutions in the uppermost layer of the soil profile. Greenhouse experiments were performed to test the effect of episodes of different length (1 and 2 weeks) and concentrations of H+ and Al3+ (pH 3.8, 4.0, 4.2 and 4.5; 0, 20 and 70 μM Al) on root and shoot growth, designed to elucidiate the reversibility of growth inhibition. Three forest floor species were studied-Galium odoratum and Lamium galeobdolon, having similar pH distribution ranges in the field and Poa nemoralis which also occurs at slightly lower pH. The plants were grown for 5 weeks (episode and recovering time) in a synthetic soil solution in a flowing solution system without recirculation. The species reacted in three different ways. Galium odoratum was the most sensitive species and seemed to be irreversibly damaged (ceased growth) by 2 week episodes of pH≤4.0 and Al≥20 μM at pH≤4.2. Lamium galeobdolon was about equally sensitive during the episodes but it had a much greater ability to recover. Poa nemoralis was rather insensitive to the episode treatments tested. It is concluded that episodes of elevated H+ and Al3+ concentrations may be decisive for plant performance. It is therefore important to consider the extreme environmental conditions which plants may be exposed to in the field, in addition to long-term averages of e.g. soil solution concentration of potentially toxic elements, when studying species distribution and performance in relation to soil chemical properties.

Interspecies differences in the preference of ammonium and nitrate in vascular plants.

Three solution experiments were performed to test the importance of NH 4+ versus NO 3- +NH 4+ to growth of 23 wild-forest and open-land species, using field-relevant soil solution concentrations at pH 4.5. At N concentrations of 1-200 μM growth increased with increasing N supply in Carex pilulifera, Deschampsia flexuosa, Elymus caninus and Bromus benekenii. Geum urbanum was the most N demanding species and had little growth below 200 μM. The preference for NH 4+ or NO 3- +NH 4+ was tested also at pH 4.0; no antagonism was found between NH 4+ and H+, as indicated by similar relative growth in both of the N treatments at both pH levels. Growth in solution with NH 4+ relative to NO 3- +NH 4+ , 200 μM, was negatively related to the mean pH of the field occurrence of the species tested; acid-tolerant species grew equally well with only NH 4+ as with NO 3- +NH 4+ (Oxalis acetosella, Carex pilulifera, Festuca gigantea, Poa nemoralis, Deschampsia flexuosa, Stellaria holostea, Rumex acetosella), while species of less acid soils were favoured by NO 3- +NH 4+ (Urtica dioica, Ficaria verna, Melandrium rubrum, Aegopodium podagraria, Geum urbanum, Bromus benekenii, Sanguisorba minor, Melica ciliata, Silene rupestris, Viscaria vulgaris, Plantago lanceolata). Intermediate species were Convallaria majalis, Elymus caninus, Hordelymus europaeus and Milium effusum. No antagonism between NH 4+ and Ca2+, Mg2+ and K+ was indicated by the total uptake of the elements during the experiment.

Control of flowering and reproduction in temperate grasses.

Temperate grasses of the subfamily Festucioideae can be grouped into two main categories according to their environmental control of flowering, species with regular long day (LD) induction, and those with dual induction requirements. The former group includes the temperate annual crosses and a few perennial species such as Phleum pratense and Poa nemoralis. These species base no winter requirement and require only LD to flower. Most temperature perennial grasses have a dual induction requirement for flowering, a primary induction which is brought about by low temperature (vernalization) and/or short days (SD), and a secondary induction which requires a transition to long days and is enhanced by moderately high temperatures. In most dual induction species SD and low temperature are interchangeable and independently able to fulfil the primary induction requirement. Yet, they are highly interactive in this process. Commonly the plants become day neutral at low temperature (0-6 °C) and primary induction takes place in both SD and LD. Primary induction is then identical with the common vernalization response. At higher temperatures induction becomes increasingly dependent on SD. until a critical temperature is reached, usually c. 12-18 °C, at which primary induction cannot take place regardless of the photoperiod. In a few species, e.g, Bromus inermts, Phalaris arundinacea and to some extent Dactylis glomeratca, the SD response predominates while low temperature induction is weak or absent. Critical temperatures and photoperiods for primary induction vary greatly among species and, within the species, among ecotypes of different geographical origin. Critical exposure time may vary from 3-4 wk in arctic-alpine Poa species to 20 wk in some Festuca species. Generally, ecotypes from high latitudes and especially arctic-alpine ones, have wider temperature and daylength limits and require fewer inductive cycles for primary induction than their low-latitude counterparts. In some grasses, especially- arctic-alpine species, initiation of inflorescence primordia takes place during SD primary induction, in others it requires a transition to LD. In the former group, primordia are initiated in the autumn, an important adaptation to arctic-alpine conditions. Critical photoperiods for secondary induction vary from 9-10 h in Mediterranean ecotypes to more than 16 h, and the critical number of LD cycles from four to eight, whereas 12-16 LD cycles are needed for the full saturated response. Generally, high-latitude ecotypes have longer critical photoperiods and require more LD cycles for secondary induction than do those from lower latitudes. Culm elongation, heading and inflorescence development are all promoted by LD. The more inductive cycles given and the more favourable their daylength, the greater is the response. Grasses also have efficient vegetative means of reproduction which are also environmentally controlled. Vegetative proliferation of inflorescences or 'vivipary' is readily induced in habitually seminiferous grasses of both LD and dual induction types, by marginal LD induction of flowering. On the other hand, a high proportion of normal flowering can be obtained in habitually viviparous species and ecotypes by optimal primary and secondary Moral induction. Thus, sexuality is by no means entirely suppressed in viviparous species but is under environmental control. In the high-latitude environment the primary induction requirements are met: by the decreasing daylength and temperature of autumn and winter, while the increasing daylength and temperature of spring and early summer fulfil the secondary induction requirements. Thus, the dual Horal induction control system of the temperate perennial grasses provides an efficient and important mechanism for fitting their life cycles to the dramatic seasonal changes of the high-latitude environment in which they live.