The influence of secondary senescence processes within the culm of a pseudoviviparous grass (Poa alpina var. vivipara L.) on the supply of water to propagules

An anatomical investigation of the culm of pseudoviviparous alpine meadow grass (Poa alpina var. vivipara L.) revealed that transpiration flow, as delimited by Lucifer Yellow tracer dye, was maintained despite advanced senescence (as evidenced by loss of chlorophyll and chloroplasts), with leafy spikelets driving transpiration flow. Transpiration flow was not hindered by cavitation or tylosis in older culms, the low frequencies of these senescence processes being bypassed via nodal plexi. Despite this, water content of plantlets declined over time and water stress became apparent, suggesting that water supply via the determinate culm was not sufficient for the increasing transpirational demand of indeterminate plantlets. The implications of declining water content on the biomechanical properties of the culm, and concomitant limitations on the pseudoviviparous reproductive strategy, are discussed. Nomenclature of grass follows Hubbard.     

Pseudoviviparous reproduction of Poa alpina var. vivipara L. (Poaceae) during long-term exposure to elevated atmospheric CO2

Pseudovivipary is an asexual reproductive strategy exhibited by some arctic/alpine grasses in which leafy plantlets are produced in place of seeds, with genetic conservation an advantage for stress tolerators in these nutrient-poor habitats. Photosynthetic metabolism and the development of this reproductive system were investigated under varying nutrient availability and predicted future CO(2) partial pressure (pCO(2)). Poa alpina var. vivipara L., grown at present ambient pCO(2) or ambient plus 340 micro mol mol(-1) CO(2) (elevated pCO(2)), was supplied with either 0.05 mol m(-3) phosphorus and 0.2 mol m(-3) nitrogen, or 0.2 mol m(-3) phosphorus and 1.0 mol m(-3) nitrogen. Gas exchange measurements and determination of total non-structural carbohydrate (TNC), nitrogen and phosphorus contents revealed that parent plant leaf blade tissues experienced acclimatory loss of photosynthetic capacity after long-term growth at elevated pCO(2) (particularly so when nutrient availability was low); there were associated reductions in photosynthetic nitrogen and phosphorus use efficiencies (PNUE and PPUE). In addition, decreased PNUE and PPUE were exhibited by plantlets grown at elevated pCO(2) with low nutrient availability. Decreased reproductive dry matter in this treatment also resulted from a lack of reproductive initiation in daughter tillers, and altered phenology. Pseudoviviparous P. alpina is likely to be at a disadvantage in both vegetative and reproductive phases at predicted future elevated atmospheric CO(2) concentrations, particularly where nutrients are scarce and when in competition with species experiencing less acclimatory loss of photosynthetic capacity.     

Isolation and characterization of microsatellite DNA markers in the grass Poa alpina L.

The important fodder grass Poa alpina L. occurs at several ploidy levels with common aneuploidy. We isolated and characterized five polymorphic microsatellite markers for the study of molecular genetic variation of this species. As first examples of the value of the developed markers for population genetic analyses, we show that plants with more chromosomes have more microsatellite bands and that isolation by distance plays a small role in shaping microsatellite diversity of P. alpina in the Swiss Alps.     

Effect of elevated CO2 and nutrient status on growth, dry matter partitioning and nutrient content of Poa alpina var. vivipara L.

Poa alpina var. vivipara L. was grown in an atmosphere containingeither 340 or 680 µmol CO₂ mol^–1 within controlledenvironment chambers. The available nutrient regime was variedby altering the supply of nitrogen and phosphorus within a completenutrient solution. At a high, but not low, N and P supply regime,elevated CO₂ markedly increased growth. Differences betweennutrient supply, but not atmospheric CO₂ concentration, alteredthe allometric relations between root and shoot. Net photosynthesisof mature leaf blades and leaf N and P concentration were reducedin plants grown at the elevated CO₂ concentration. The question was asked: is it possible to ascribe all of theseeffects to elevated CO₂ or are some due to nutrient deficiencycaused by dilution with excess carbon? Several criteria, includingthe nutrient content of sink tissue, root:shoot allometry andthe use of divalent cations to estimate integrated water flowsare suggested in order to make this distinction. It is concludedthat only at a low supply of N and P₁ and elevated CO₂ concentration,was low leaf N concentration due to induced nutrient deficiency.The data are consistent with a model where the capacity of sinksto use photosynthetically assimilated carbon sets both the rateof import into those sinks (and thus rate of export from sourceleaves) and the rate of photosynthesis of source leaves themselves. Key words: Poa alpina L., growth, photosynthesis, carbohydrate, export, nitrogen, phosphorus     

Microsatellite diversity of the agriculturally important alpine grass Poa alpina in relation to land use and natural environment

BACKGROUND AND AIMS: The Alpine Meadow Grass Poa alpina is common in subalpine and alpine natural sites and agriculturally used land, where it is an important fodder grass. Natural factors and human land use are supposed to have been shaping its genetic diversity for hundreds of years. The species comprises sexually and vegetatively reproducing plants. The aim of this study was to investigate the effects of agricultural land use, environmental factors and the mode of reproduction on the distribution of its microsatellite diversity within and among populations and to analyse whether its genetic diversity is correlated with plant species diversity in grassland parcels. METHODS: Genetic diversity of P. alpina was assessed with five microsatellite markers for 569 plants originating from 20 natural sites and from 54 grassland parcels of different cultural tradition, land use and altitude in the Swiss Alps. Due to polyploidy and frequent aneuploidy of the species, data analyses were based on the presence of microsatellite bands. KEY RESULTS: A low but significant differentiation was found in microsatellite bands among natural sites and agriculturally used parcels, while their microsatellite band diversity within populations did not differ. An increased differentiation was found in microsatellite bands with increasing geographic distance among parcels, and a differentiation among grazed and mown parcels, and among sexually and vegetatively reproducing populations. Band richness of sampled plants per village was higher for villages where parcels represented more different land-use types. Within populations, microsatellite band diversity was higher in grazed than in mown parcels. CONCLUSIONS: The diversity of human land use in the Alps was associated with genetic diversity of P. alpina. Therefore, the ongoing socio-economically motivated land-use changes, which reduce the number of different land-use types, will affect the genetic diversity of P. alpina negatively.     

N uptake and growth responses to sub-lethal freezing in the grass Poa pratensis L.

Background and aims

Climate warming has the potential to increase both the exposure and vulnerability of grass roots to frost in temperate regions by reducing snow cover and altering the timing of cold acclimation. Despite a strong research focus on the direct effects of freezing on grass mortality, the direct sub-lethal effects of freezing on grass performance have not been well-characterized. We examined sub-lethal responses of the grass Poa pratensis to variation in the timing, severity, rate and length of freezing.

Methods

We assessed short term root functional responses (¹⁵N uptake) and longer term plant growth responses to freezing administered both under controlled conditions in a refrigerated incubator, and in the field by manipulating snow and litter cover.

Results

In fall and spring, ¹⁵N uptake declined in response to 1?day of freezing down to ?10?°C or to 3?days of freezing at ?5?°C, whereas in winter, ¹⁵N uptake was insensitive to freezing. Long term growth responses were similar, with reduced growth only occurring for grasses frozen for 3?days at ?5?°C in spring, but not for grasses frozen in fall or winter. Snow and litter removal intensified soil freezing over winter, but did not significantly affect plant growth.

Conclusions

Our results demonstrate that while P. pratensis is relatively tolerant to frost damage over winter, it may be vulnerable to sub-lethal frost effects in fall, and particularly in spring. These sub-lethal effects occur at temperatures approximately 15–20?°C warmer than the published LT₅₀ values for this species.     

Export of carbon from leaf blades of Poa alpina L. at elevated CO2 and two nutrient regimes

The hypothesis was tested that, in plants of the alpine meadow grass (Poa alpina L.) exposed to elevated CO2, net photosynthesis and export from source leaves is reduced as a result of feedback from sinks. Nutrient supply was used as one way of reducing photosynthesis and export. Single plants were grown in sand culture under specified controlled environmental conditions for a period of 50 d at two levels of nitrogen and phosphorus ('low': 0.2 mol m^-3 N, 0.04 mol m^-3 P; 'high': 2.5 mol m^-3 N, 0.5 mol m^-3 P). Compartmentation within, and export of carbon from, individual youngest fully expanded leaves of acclimated plants was determined using ¹⁴C feeding and efflux plus mass balance calculations of carbohydrate export. Independent of treatment, the bulk of soluble carbohydrate (65-75%) was present as fructan, with most of the remainder being sucrose. Depending on nutrient supply, CO2 could alter export from source leaves either by a reduction in the amount of sucrose present in a readily available pool for transport, or by altering the rate constant describing phloem loading.Key words: Poa alpina L., phloem transport, carbohydrate, compartmentation, export, elevated CO2, nutrients.      

Salinity tolerance within the grass speciesAgrostis stolonifera L

Summary Eight populations ofAgrostis stolonifera, collected from maritime and inland habitats, were grown in solution culture and in sand culture at various concentrations of sodium chloride from 0 ppm to 5,000 ppm Na. NaCl had less effect upon the dry weight yield of populations from maritime habitats, with soils of high Na content, than upon populations from inland or maritime habitats with soils of low Na content. The correlation between per cent reduction in dry weight yield and the Na content of the native soil of each population was r=−0.73. Populations from inland or maritime habitats, with soils of low Na content, contained more Na in their shoot materials, and higher Na/K ratios, than did populations from high Na soils, at all Na concentrations. The effect of NaCl upon the root elongation of each population was not correlated with the effect upon dry weight yield, nor with the Na content of their native soil. The effect of Na Cl upon root elongation was highly dependent upon the composition of the culture solution used. It is concluded that the effect of NaCl on root elongation is not an adequate measure of salinity tolerance in this species.     

Diterpenoids and Flavonoids from the Twigs of Cephalotaxus fortunei var. alpina

Three new diterpenoids (a cephalotane, an abietane and a 9(10→20)‐abeo‐abietane) and one new flavonoid, together with 11 known compounds, were isolated from the twigs of Cephalotaxus fortunei var. alpina. The new compounds were identified by comprehensive spectroscopic (including 1D and 2D‐NMR and HR‐ESI‐MS) analysis. Anti‐inflammatory, immunosuppressive and cytotoxic activities of three new compounds were evaluated. 3β,20‐epoxyabieta‐8,11,13‐triene‐3α,12‐diol showed weak cytotoxicity against tumor cell lines NCI?H1975, HepG2, MCF‐7, while fortalpinoid R and 3‐acetonyl‐3,5,7,4′‐tetrahydroxy‐2‐methoxyflavanone were not active at 80 μM. None of these compounds showed anti‐inflammatory and immunosuppressive activities.     

Regeneration of protoplast-derived green plants of Kentucky blue grass (Poa pratensis L.)

Summary Green plants were repeatedly regenerated from suspension-derived protoplasts of Kentucky blue grass (Poa pratensis L.) cv. Geronimo. One suspension was capable of donating competent protoplasts during long-term culture i. e. 10–16 months after its establishment. The plating efficiency of the protoplasts from three different suspension lines varied from 0.004% in the lowest up to 1.5% in the highest responding line, using agarose-bedding in nutrition medium devoid of nurse or feeder cultures. Green plants germinated from polyembryos, which developed from 0.4–2.7% of the protoplast-derived microcolonies. A total of 127 plants were successfully transferred to soil.Abbreviations ABA abscisic acid - BAP 6-benzylaminopurine - 2,4-D 2,4-dichlorophenoxyacetic acid - FW fresh weight - PE plating efficiency     

Frost damage and winter nitrogen uptake by the grass Poa pratensis L.: consequences for vegetative versus reproductive growth

Frost damage can decrease nitrogen uptake by grasses over winter, and it can also decrease biomass production over the following growing season. However, it is not clear to what extent reduced nitrogen uptake over winter decreases grass production, or whether is it merely a symptom of root damage. We examined the growth response of the grass Poa pratensis L. (Kentucky bluegrass) to variation in the timing of freezing and nitrogen availability over winter in London, Ontario, Canada. All tillers were transplanted into untreated soil in early spring, and at peak seed maturation, root, shoot, and reproductive biomass were measured. There was an interaction between freezing and increased winter nitrogen availability, whereby nitrogen addition increased tiller biomass under ambient temperatures, but decreased tiller biomass in combination with a late winter freeze. The nitrogen response of ambient temperature tillers occurred primarily via increased seed production, whereas for frozen tillers seed production was generally absent. Our results support the hypothesis that nitrogen uptake over winter can increase growing season productivity in P. pratensis, but also demonstrate that increased nitrogen availability increases tiller vulnerability to frost. These results have important implications for grass responses to the alteration of soil freezing dynamics with climate change.     

Diversity and varietal classification of Hibiscus syriacus L. with the heterogeneity within retrotransposon-like elements

Retrotransposons are present in multi-copy numbers that are integrated into plant genomes with considerable heterogeneous sequences within a single plant and between plant species, which allows the use of retrotransposons as additional sources of DNA polymorphism. A primer design for the sequence-tagged specific site and cleaved amplified polymorphic sequences (STS-CAPs) that are derived from retrotransposon-like sequences was developed for the molecular marker analysis in Hibiscus syriacus. This method was applied for the detection of sequence variations of intact retrotransposons that exist in plant genomes, which resulted in higher polymorphisms than in the amplified fragment length polymorphism (AFLP). Through STS-CAPs, specific fingerprinting data among H. syriacus varieties can be easily distinguished and generated with reproducible results. It could also be adapted to any species that possess multi-copy retrotransposons for varietal identification as well as the assessment of genetic relationships.     

Sexual dimorphism and sex ratios of two Australian dioecious species of alpine pineapple grass, Astelia alpina var. novaehollandiae and Astelia psychrocharis (Asteliaceae)

Sexual dimorphism and male biased sex ratios have been predicted for dioecious plants experiencing the limited conditions for growth and reproduction found in many alpine environments. To test these predictions, the reproductive ecology of two congeneric, co-occurring, dioecious, clonal, species was examined in the subalpine and alpine zones of Kosciuszko National Park, southeastern Australia. Specifically, plant size (vegetative cover of plants in quadrats), floral display (number of flowers per inflorescence, number of inflorescences per quadrat) and sex ratios (proportion of females in quadrats with flowers) were examined in ten populations of Astelia psychrocharis (Asteliaceae) and nine populations of Astelia alpina var. novae-hollandiae (Asteliaceae). Sexual dimorphism did occur, with males having more flowers per inflorescence (106% more flowers for A.alpina males and 12% more for A.psychrocharis males compared to females) and more inflorescences per quadrat than females (78% more inflorescences for A.alpina males and 46% more inflorescences for A.psychrocharis males compared to females). Plant size did not differ between male and female quadrats of either species, nor were there male biased sex ratios. However, plant size was related to flowering status in A.psychrocharis with the 65 quadrats that did not flower having lower vegetative cover than the 175 flowering quadrats indicating that there may be a minimum size/ cover required prior to flowering in this species. For A.alpina, all but two of the 185 quadrats randomly sampled flowered. There was no effect of altitude on plant size and very little effect of altitude on floral display for either species, apart from a slight increase in the number of inflorescences per quadrat with increasing altitude for A.psychrocharis, and slight decrease in number of flowers per inflorescence with increasing altitude for A.alpina females.     

Assimilation of 14CO2 by the Inflorescence of Poa annua L. and Lolium perenne L.

The relative assimilatory activity of the inflorescence, itsindividual components, and the leaves of flowering tillers ofPoa annua L. and Lolium perenneL. was determined over the periodfrom inflorescence emergence to seed shedding. The pattern of¹⁴CO₂ fixation was similar for both species and the inflorescencewas by far the most important assimilatory organ of the reproductivetiller, particularly over the latter period of seed developmentas leaf senescence progressed. With the exception of the seedsall parts of the inflorescence showed significant assimilatoryactivity and the lemmas and paleas accounted for 40–50per cent of the total ¹⁴C fixed by the inflorescence in bothspecies. The importance of the grass inflorescence as a photosyntheticstructure is discussed in relation to similar studies on cereals. Poa annua, Lolium perenne, carbon dioxide assimilation, inflorescence     

Effect of hexavalent chromium on the growth and physiological and biochemical parameters on Brassica oleracea L. var. acephala DC

In order to determine the toxic effect of chromium Cr(VI) on the seed germination, the root and shoot length, the root-cotyledonary leaves, the fresh and dry weight in eight-day-old seedlings Brassica oleracea L. var. acephala DC (kale) were treated with various concentrations of Cr in the growth medium. The accumulation of chromium in the tissues was determined in the cotyledons and the roots of the kale seedlings. High rate of Cr uptake was observed in the roots. But the organs could not accumulate large amount Cr. The effect of Cr on B. oleracea var. acephala was evaluated by changes in chlorophyll a, b, lipid peroxidation, proline, ascorbate, protein carbonyl groups, non-protein thiols and peroxidase activity. There were significant decreases in chlorophylls a, b content of the plants treated with Cr. Chromium treated kale seedlings had higher lipid peroxidation and the protein carbonyl groups in cotyledonary leaves than the roots. The changes refer to toxic effects of Cr. There were increases in the non-protein thiol, the total ascorbate, and proline content in the cotyledons and the roots of the seedlings grown on the media containing 0.1 and 0.15 mM Cr. The guaiacol peroxidase activity was higher in the roots of the seedlings than their cotyledons.     

Palynological study of Cupressus sempervirens L. var. pyramidalis and var. horizontalis

ABSTRACT

Cupressus sempervirens L. var. pyramidalis and C. sempervirens var. horizontalis were examined for their pollen morphometry and ultrastructure to verify whether, in addition to phenotype, pollen could also show characteristics useful to discriminate the two infraspecific taxa. C. sempervirens var. pyramidalis compared to C. sempervirens var. horizontalis has mainly larger, subcircular pollen with a higher percentage of apolar and germinating grains, and a wall with thicker intine; the cytoplasm has a greater number of callose-containing vesicles. C. sempervirens var. horizontalis has pollen distributed in five classes of shape. In addition it is smaller and shows a higher percentage of ruptured grains, and a lower percentage of germination in vitro. The cytoplasm contains vesicles rich in callose and also a higher amount of osmophilic bodies. Pollen grains in both varietas contain only one cell at dispersal. The reported differences in pollen morphometry, structure and biology, together with the phenotypic characteristics of the tree, support the validity of two infraspecific taxa.     

金瓜和白瓜花叶病毒病病原的初步鉴定

崇明是上海出口蔬菜生产基地之一,也是国家级的绿色食品园区之一,具有生产绿色蔬菜商品的生态环境和资源优势.     

Microbial succession of nitrate-reducing bacteria in the rhizosphere of Poa alpina across a glacier foreland in the Central Alps

Changes in community structure and activity of the dissimilatory nitrate-reducing community were investigated across a glacier foreland in the Central Alps to gain insight into the successional pattern of this functional group and the driving environmental factors. Bulk soil and rhizosphere soil of Poa alpina was sampled in five replicates in August during the flowering stage and in September after the first snowfalls along a gradient from 25 to 129 years after deglaciation and at a reference site outside the glacier foreland (>2000 years deglaciated). In a laboratory-based assay, nitrate reductase activity was determined colorimetrically after 24 h of anaerobic incubation. In selected rhizosphere soil samples, the community structure of nitrate-reducing microorganisms was analysed by restriction fragment length polymorphism (RFLP) analysis using degenerate primers for the narG gene encoding the active site of the membrane-bound nitrate reductase. Clone libraries of the early (25 years) and late (129 years) succession were constructed and representative clones sequenced. The activity of the nitrate-reducing community increased significantly with age mainly due to higher carbon and nitrate availability in the late succession. The community structure, however, only showed a small shift over the 100 years of soil formation with pH explaining a major part (19%) of the observed variance. Clone library analysis of the early and late succession pointed to a trend of declining diversity with progressing age. Presumably, the pressure of competition on the nitrate reducers was relatively low in the early successional stage due to minor densities of microorganisms compared with the late stage; hence, a higher diversity could persist in this sparse environment. These results suggest that the nitrate reductase activity is regulated by environmental factors other than those shaping the genetic structure of the nitrate-reducing community.