Stochastic flowering phenology in Dactylis glomerata populations described by Markov chain modelling

Understanding the relationship between flowering patterns and pollen dispersal is important in climate change modelling, pollen forecasting, forestry and agriculture. Enhanced understanding of this connection can be gained through detailed spatial and temporal flowering observations on a population level, combined with modelling simulating the dynamics. Species with large distribution ranges, long flowering seasons, high pollen production and naturally large populations can be used to illustrate these dynamics. Revealing and simulating species-specific demographic and stochastic elements in the flowering process will likely be important in determining when pollen release is likely to happen in flowering plants. Spatial and temporal dynamics of eight populations of Dactylis glomerata were collected over the course of two years to determine high-resolution demographic elements. Stochastic elements were accounted for using Markov chain approaches in order to evaluate tiller-specific contribution to overall population dynamics. Tiller-specific developmental dynamics were evaluated using three different RV matrix correlation coefficients. We found that the demographic patterns in population development were the same for all populations with key phenological events differing only by a few days over the course of the seasons. Many tillers transitioned very quickly from non-flowering to full flowering, a process that can be replicated with Markov chain modelling. Our novel approach demonstrates the identification and quantification of stochastic elements in the flowering process of D. glomerata, an element likely to be found in many flowering plants. The stochastic modelling approach can be used to develop detailed pollen release models for Dactylis, other grass species and probably other flowering plants.

     

Flowering Competence after Exposure to Naturally Fluctuating Winter Temperatures in a Perennial Grass, Deschampsia caespitosa (L.) Beauv

Tussocks of three clones of the perennial grass Deschampsiacaespitosa were exposed to natural temperatures, for successiveperiods with increments of one week, throughout each seasonin four consecutive autumn/winter seasons. After exposure theywere returned to a warm, illuminated glasshouse and the incidence,intensity and timing of flowering were recorded. The year-to-year variations in exposure time requirement forfull flowering were very highly correlated (r² > 0.98) withmean air temperature in the period between mid-September andearly December. The relationship with the natural logarithmof accumulated air temperature was similarly good. Daily meanair temperature was also demonstrated to be a good indicatorof daily mean tussock temperature (r² = 0.91), in a series ofmeasurements in the autumn of 1976. More prolonged exposure increased the proportion of apices ina tussock which flowered, but the maximum value at the end ofa whole winter was only about 15 per cent. The cumulative vernalizationeffects of naturally fluctuating temperature regimes are analysedand the significance of these findings for the maintenance ofperenniality in clonal grasses is considered. Deschampsia caespitosa (L.) Beauv., tufted hairgrass, flowering, vernalization, temperature, perenniality     

Flowering Responses of Contrasting Ecotypes of Poa annua and their Putative Ancestors Poa infirma andPoa supina

Flowering responses of two Australian and six Norwegian populationsof Poa annua and their putative ancestors P. infirma and P.supina were studied in controlled environments. The two Australianpopulations originating from suburban parks in Canberra hadopposite daylength flowering responses across the range of temperaturestested (9–21 °C), one being a quantitative short-day(SD) plant with no response to vernalization, the other a quantitativelong-day (LD) plant with a quantitative vernalization requirement(winter annual type). Variation in earliness of flowering withinthe former population was shown to be genetically determined,and testing of selfed progenies indicated that the populationis an aggregate of several largely homozygous lines with divergentflowering responses. Two lowland populations from southern Norwaywere both quantitative LD plants with no vernalization response,while two alpine snowbed populations from southern Norway andtwo high-latitude, subarctic populations from northern Norwaywere quantitative SD plants with an obligatory plant vernalizationor SD requirement for flowering. Two populations of P. supinaexhibited the same flowering responses as the alpine and high-latitudepopulations of P. annua with an obligatory plant vernalizationor SD requirement for flowering. A combination of SD and lowtemperature (9–12 °C) for 8–10 weeks was optimalfor induction and inflorescence initiation. On the other hand,P. infirma was found to be an early-flowering quantitative SDplant which flowered freely across the range of temperatures(9–21 °C) as a typical summer annual. The experimentsdemonstrate that virtually any kind of photoperiodic and vernalizationresponses can be found among populations of P. annua. Theseversatile flowering responses reflect the contrasting floweringresponses of P. supina and P. infirma, and add strong supportto the hypothesis that P. annua has originated from these species.Copyright 2001 Annals of Botany Company Adaptation, evolution, flowering, Poa annua, P. infirma, P. supina, photoperiod, vernalization     

Phenotypic variation and performance of diploid subspecies of Dactylis glomerata L.

Dactylis glomerata L. is one of the best known examples of a polyploid complex that includes diploid (2n = 14), tetraploid (2n = 28) and hexaploid (2n = 42) types. The diploids, descending from the ancestors of the genus, are numerous, distinct forms adapted to specific environments and include all the morphological variation and ecological adaptation found in Dactylis. The objective of the present study was to shed more light on the differentiation of diploids and to obtain information for better exploiting the genetic resources of this species. To this end we carried out a discriminant analysis in the most widespread diploid subspecies based on a large number of morpho-physiological traits. We found that some characteristics, such as time to heading, time to flowering, vegetative regrowth, plant height and seed shattering are the most discriminant and enabled us to realize a more exact differentiation of the diploids with respect to the morphological criterion generally adopted. The results demonstrated that diploid taxa offer an interesting combination of relevant agronomical and ecological characteristics which could be useful in breeding programs to promote the use of this species in sustainable agriculture systems. We also performed cytological investigations and defined a general karyotype representative of the diploid Dactylis considered in this study.     

The Effect of Sulphur Dioxide on the Growth of Lolium perenne L., Lolium multiflorum Lam., Dactylis glomerata L., and Phleum pratense L.

Lockyer, D. R. 1985. The effect of sulphur dioxide on the growthof Lolium perenne L., Lolium multiflorum Lam., Dactylis glomerataL., and Phleum pratense L.?J. exp. Bot. 36: 1851-1859. Fouragriculturally important grasses, Lolium perenne L., Loliummultiflorum Lam., Dactylis glomerata L. and Phleum pratenseL. were exposed to sulphur dioxide (SO₂) in a system of exposurechambers. The plants were exposed for a total of 43 d to meanconcentrations of SO₂ in the air of 0,87 or 448 (µg m^–3and herbage was harvested twice. All four grasses showed chloroticlesions after exposure to the highest concentration of SO₂.The effect of SO₂ on the yield of herbage was statisticallysignificant only at the second harvest and at the highest concentration;the dry weights of shoots of D. glomerata and L. perenne werereduced by 33% and 16% respectively. Significant effects ofSO₂ were also found on the 'transpiration coefficients' measuredfor D. glomerata and P. pratense. The grasses differed in theiruptake of sulphur from the atmosphere but this was not relatedto their sensitivity to SO₂. Total–S concentration inthe shoots of L. perenne, L. multiflorum and D. glomerata increasedalmost linearly in response to increasing SO₂ concentration;with P. pratense only the highest SO₂ concentration raised total-Sabove the level in control plants. These increases were almostentirely due to the accumulation of sulphate–S. Key words: Sulphur diozide, Lolium perenne, Lolium multiflorum, Dactylis glomerata, Phleum pratense     

Day length affects the dynamics of leaf expansion and cellular development in Arabidopsis thaliana partially through floral transition timing

Background and Aims: Plant aerial development is well known to be affected by daylength in terms of the timing and developmental stage of floraltransition. Arabidopsis thaliana is a ‘long day’plant in which the time to flower is delayed by short days andleaf number is increased. The aim of the work presented herewas to determine the effects of different day lengths on individualleaf area expansion. The effect of flower emergence per se onthe regulation of leaf expansion was also tested in this study. Methods: Care was taken to ensure that day length was the only sourceof micro-meteorological variation. The dynamics of individualleaf expansion were analysed in Ler and Col-0 plants grown underfive day lengths in five independent experiments. Responsesat cellular level were analysed in Ler plants grown under variousday lengths and treatments to alter the onset of flowering. Key Results: When the same leaf position was compared, the final leaf areaand both the relative and absolute rates of leaf expansion weredecreased by short days, whereas the duration of leaf expansionwas increased. Epidermal cell number and cell area were alsoaltered by day-length treatments and some of these responsescould be mimicked by manipulating the date of flowering. Conclusions: Both the dynamics and cellular bases of leaf development arealtered by differences in day length even when visible phenotypesare absent. To some extent, cell area and its response to daylength are controlled by whole plant control mechanisms associatedwith the onset of flowering.     

Phylogenetic relationships and gene flow between sympatric diploid and tetraploid plants ofDactylis glomerata (Gramineae)

Phylogenetic relationships between sympatric, morphologically indistinguishable diploid and tetraploid plants ofDactylis glomerata L. (Gramineae) in Galicia (Spain) were assessed using allozyme markers for 6 distinct systems. The study exploited recent introduction in Galicia and subsequent hybridization of an alien 4xDactylis subspecies possessing distinct allozymes from those of all the native plants. Opportunities for gene exchanges between the ploidies were estimated from in situ observations of flowering, examination of progenies in 2x/4x natural and experimental crosses, and enzyme analyses. Results show a high genetic similarity between the Galician diploids and tetraploids, which possess peculiar alleles in common. Although the ploidy levels usually have distinct flowering periods, interploidal crosses do occasionally occur. Gene flow is likely much more important from the diploid to the tetraploid level. A good genetic intermixing occurs between the Galician and the alien tetraploid entities which have simultaneous flowering. Autopolyploidization of the diploids followed by various rates of hybridization is proposed as one very probable origin of natural tetraploids inDactylis.     

In Vitro Studies of Floral Induction on Stem Apices of Cuscuta reflexa Roxb. --A Short-day Plant

Stem tips of Cuscuta reflexa, cultured on modified White's medium,were subjected to different light and dark conditions. The culturesflowered when maintained either in continuous darkness or exposedto 14 hours of daily dark period. Thus Cuscuta reflexa behavesas a typically short-day plant. The presence of 5 per cent.sucrose in the medium completely obviates the requirement forhigh-intensity light exposures, otherwise essential for SDP.It appears that the bud itself is sensitive to photoinduction.In spite of the presence of natural tissue-bridge between thehost and the parasite, provided by the haustorial connexions,there is no transportation of flower-forming substance fromone plant to another. The flowering periods of host and parasiteare independent of each other.     

The Influence of Temperature on Photosynthesis and Transpiration in ten Temperate Grass Varieties Grown in four Different Environments

The influence of temperature on photosynthesis and transpirationwas studied in ten varieties of Lolium perenne, L. multiflorum,Dactylis glomerata, and Festuca arundinacea from three climaticorigins grown in three different controlled environments (15?C, 72 W m^-2 visible irradiation, 16-h photoperiod; 25 ?C, 72W m^-2 visible irradiation, 16-h photoperiod; and 25 ?C, 180W m^-2 visible irradiation, 16-h photoperiod) and in the glasshousein July/August. The optimum temperature for photosynthesis was influenced primarilyby growth environment; growth at low temperature (15 ?C) resultedin a low optimum temperature, which differed little from varietyto variety. The maximum CO₂-exchange rate was influenced bygrowth environment and by variety. Within a variety, plantsgrown at higher light intensity or lower temperature had a greaterCO₂-exchange rate. Seven varieties showed a negative correlationbetween the optimum leaf temperature and the maximum CO₂-exchangerate. Activation energies for photosynthesis were influencedby growth environment only. There were marked varietal differences in the values of leafresistances (r_a + r_t) obtained from transpiration data at theoptimum leaf temperature for CO₂ exchange. In Lolium, and Dactylisthe Mediterranean varieties had higher leaf resistances thanthe Northern varieties with the maritime varieties intermediate.In general the Dactylis varieties had higher resistances thanthe corresponding Lolium and Festuca varieties. Only at highgrowth temperatures was (r_a+r_l) insensitive to temperature;otherwise an activation energy of about 10 kcal/mole was observed.A negative correlation was found between mean varietal diffusionresistances (r_a+r_l), and corresponding maximum CO₂-exchangerates.     

Interrelationship Between Plant Developmental Stage, Plant Growth Rate, Nitrate Utilization and Nitrogen Fixation in Hydroponically Grown Soybean

The growth rate of the indeterminate soybean plant [Glycinemax (L.)Merr.] slows as it proceeds from vegetative phase intoreproductive growth. Yet, the well-nodulated plant acquiresmost of its nitrogen during reproductive growth. Thus, the interrelationshipbetween plant developmental stage and nitrogen fixation wasexamined. It is shown that, regardless of the age of the hydroponicallygrown soybean plant at the time of its inoculation with Bradyrhizobiumjaponicum, the highest rate of nitrogen fixation occurs duringthe pod-filling stage (R5). Nevertheless, maximum total nitrogenfixation is generally achieved when inoculation occurs at thefull-bloom stage (R2). It is shown, however, that flower budsand flowering are not responsible for the enhanced nodulationand nitrogen fixation. Rather, the data suggest that the onsetof rapid nodulation occurs soon after the initiation of thedevelopmentally programmed drop in foliar nitrate reductaseactivity. The ensuing increase in nitrogen fixation providesthe plant with much of its needed nitrogen and hence stimulatesplant mass accumulation during pod-fill. It is suggested thatnitrogen fixation enhances growth of the soybean plant by increasingits net photosynthetic efficiency during reproductive growthand by providing the needed nitrogen at the appropriate timefor maximum seed growth. Key words: Glycine max, nitrate, nitrogen fixation, nodulation     

The Immunochemical Relationships of Prolamins of Temperate Meadow Grasses and Cereals

The immunochemical relationships between the aqueous alcohol-solubleprolamin storage proteins of temperate cereals (wheat, barley,rye and oats) and five species of Festucoid meadow grasses (Loliumperenne, Festuca rubra, F. arundinacea, Dactylis glomerata andPhleum pratense) were studied by "Western Blot" analyses usingantisera raised against C hordein of barley, -gliadin of wheatand avenins of oats. In addition, the reaction between the Chordein antiserum and the grass prolamins was studied usinga quantitative laser nephelometer assay. The results confirmedthe previously reported structural relationship between theprolamins of Festuca and Lolium and members of the Triticeae(barley, wheat, rye). They also showed a strong antigenic relationshipbetween the prolamins of Dactylis and Phleum and avenins ofoats, and this is consistent with their molecular weights andamino acid compositions. The results indicate that similar immunochemicalstudies may be of value in clarifying the taxonomic relationshipsof Festucoid meadow grasses. Key words: Cereals, grasses, prolamins, homology, evolution, immunochemistry     

Environmental Control of Flowering in some Northern Carex Species

The environmental control of flowering in some arctic-alpineCarexspecies has been studied in controlled environments.Carex nigra,C. brunnescens, C. atrata, C. norwegica andC. serotina all hada dual induction requirement for flowering. In all exceptC.nigra either low temperature (12 °C or lower) or short days(SD) over a wider range of temperatures were needed for primaryfloral induction and inflorescence formation. InC. nigra primaryfloral induction took place in SD only (9–21 °C),8–10 weeks of exposure being required for a full response.In all these species long days (LD) were required for, or stronglypromoted, culm elongation and inflorescence development (secondaryinduction). Quantitative ecotype differences in both primaryand secondary induction were demonstrated. Unlike the otherspecies,C. bicolor proved to be a regular LD plant which requiredLD only for inflorescence initiation and development. In allspecies leaf growth was strongly promoted by LD, especiallyin the higher temperature range (15–21 °C). In SDand temperatures below 15 °C the leaves became senescentand the plants entered a semi-dormant condition which was immediatelyreversed by LD. The results are discussed in relation to growthform and life history of shoots. Carex ; dual induction; ecotypic diversity; flowering; growth; photoperiod; sedges; temperature     

Plant Growth Analysis: Allometry, Growth and Interference in Orchardgrass and Timothy

A multiple regression procedure was used to evaluate allometricresponses to stand age and species population densities in monoculturesand mixtures of orchardgrass (Dactylis glomerata L., also knownas cocksfoot) and timothy (Phleum pratense L.). In each speciesthe allometry between shoot dry weight and either leaf areaor tiller number per plant was studied. Population density treatmentsaffected allometry by changing allometric exponents expressingthe ratio of relative growth rates of different plant characteristics.Allometric relationships changed as growth proceeded, and thetwo species differed in their allometric responses to treatments. Plant growth analysis, allometry, competition, Dactylis glomerata L., Phleum pratense L.     

Development, growth and egg production of the two copepod species Centropages hamatus and Centropages typicus in the laboratory

Laboratory experiments were set up in order to determine andcompare developmental rates, growth rates, generation timesand egg production rates for the two calanoid copepod speciesCentropages typicus and Centropages hamatus. The nauplii showeda higher developmental rate than the copepodites for both specieswith quite different individual stage durations, which gaveno indication of isochronal development. For C typicus equiproportionaldevelopment was found. The growth rates were exponential andhighest for the largest species C typicus, and for both speciesthe juvenile growth rates were very similar to the egg productionrates of the adults.     

Phenotypic Plasticity of Capitulum Morphogenesis in Microseris pygmaea (Asteraceae: Lactuceae)

Inbred populations of the annual Chilean species Microserispygmaea show phenotypic plasticity in the number of floretsper capitulum. In order to find out how this plastic variationmay arise during development, two inbred lines (A92 and C96)were grown under short day conditions. Groups of plants fromeach strain were transferred to long day conditions at about2 week intervals. In this way we introduced variation for plantsize (number of leaves per plant) at onset of flowering. Thenumber of florets per mature capitulum increased linearly withplant size. After transfer to long day conditions, plants wereharvested daily for light microscopic measurements of meristemwhole mounts. Only the first capitulum of each plant was analysed.All florets were formed after 12 d in strain C96 and after 14d in strain A92. In order to detect the effect of plant sizeon morphogenesis, we performed a multiple regression analysisof developmental parameters on time and number of leaves. Widthand height of the capitulum receptacle increased daily witha growth rate depending on the starting size. Differences inmeristem size were detected already in vegetative plants ofdifferent sizes. In contrast, there was no influence of plantsize on floret primordium size. We combined the multiple regressionmodels in one simple model for prediction of floret numbersfrom numbers of leaves per plant at onset of flowering. Predictionsof this model agree with observed relationships in both inbredlines.Copyright 1994, 1999 Academic Press Asteraceae, capitulum, inflorescence, meristem, meristic character, Microseris pygmaea, morphogenesis, phenotypic plasticity     

Roles of the Af and Tl Genes in Pea Leaf Morphogenesis: Shoot Ontogeny and Leaf Development in the Heterozygotes

The wildtype leaf blade of Pisum sativum possesses proximalleaflets and distal tendrils, which may be altered by two recessivemutations that affect pinna morphology, afila (afaf) and tendrilless(tltl). Using morphological observations and SEM, the variationin leaf forms along the plant axis and leaf development werecharacterized for plants heterozygous at the Af and/or Tl loci.The Af and Tl genes interacted to affect many characteristicsof shoot ontogeny, including rate changes in leaf blade lengthand complexity increases, as well as time to flowering. TheAf gene retarded early vegetative development and acceleratedthe time to flowering. The leaf phenotypes of these heterozygousgenotypes were specified mainly by changes in the timing ofmajor developmental events. The data support the hypothesesthat both genes are heterochronic in nature and that the pealeaf blade consists of three genetically- and developmentally-determined regions: proximal, distal and terminal. Copyright2000 Annals of Botany Company Heterochrony, leaf development, shoot ontogeny, Pisum sativum L., garden pea, afila,tendrilless .     

Growth and flowering of Lemna paucicostata I. General aspects and role of chelating agents in flowering

Lemna paucicostata HEGELM. is normally a short-day plant andflowers only in the presence of a chelating agent (EDTA or EDDHA)in the medium. The plant can be induced to flower even by asingle long night treatment; the flowering percentage, however,increases with further inductive cycles. The length of the criticaldark period depends upon the chelating agent employed in themedium. It is between 10 and 12 hr in the medium containingEDTA and about 8 hr in the EDDHA-supplemented medium. Red lightinterruption in the middle of the dark period—even fora minute—is inhibitory for flowering. Attempts to identify the metal ion(s) chelated reveal that thechelating agents affect flowering by facilitating iron uptake.This is also supported by the fact that the requirement of achelating agent for flowering can be overcome with an excessof iron in the medium. Interestingly, provision of EDDHA andexcess of ferric citrate, together, can bring about floweringeven under long days. ¹Originally HEGELMAIER (1) designated L. paucicostata as a separatespecies; however, THOMPSON (2) and DAUBS (3) have treated itsynonymous to L. perpusilla. More recently, based on physiologicaland chemotaxonomic studies, the distinctiveness of L. paucicostatafrom L. perpusilla has been favoured (4, 5). (Received September 8, 1969; )     

Root and leaf attributes accounting for the performance of fast- and slow-growing grasses at different nutrient supply

Despite their difference in potential growth rate, the slow-growing Brachypodium pinnatum and the fast-growing Dactylis glomerata co-occur in many nutrient-poor calcareous grasslands. They are known to respond differently to increasing levels of N and P. An experiment was designed to measure which characteristics are affected by nutrient supply and contribute to the ecological performance of these species. Nutrient acquisition and root and shoot traits of these grasses were studied in a garden experiment with nine nutrient treatments in a factorial design of 3 N and 3 P levels each. D. glomerata was superior to B. pinnatum in nutrient acquisition and growth in all treatments. B. pinnatum was especially poor in P acquisition. Both species responded to increasing N supply and to a lesser extent to increasing P supply by decreasing their root length and increasing their leaf area per total plant weight. D. glomerata showed a higher plasticity. In most treatments, the root length ratio (RLR) and the leaf area ratio (LAR) were higher for D. glomerata. A factorization of these parameters into components expressing biomass allocation, form (root fineness or leaf thickness) and density (dry matter content) shows that the low density of the biomass of D. glomerata was the main cause for the higher RLR and LAR. The biomass allocation to the roots showed a considerable plasticity but did not differ between the species. B. pinnatum had the highest leaf weight ratio. Root fineness was highly plastic in D. glomerata, the difference with B. pinnatum being mainly due to the thick roots of D. glomerata at high nutrient supply. The leaf area/leaf fresh weight ratio did not show any plasticity and was slightly higher for B. pinnatum. It is concluded, that the low density of the biomass of D. glomerata is the pivotal trait responsible for its faster growth at all nutrient levels. It enables simultaneously a good nutrient acquisition capacity by the roots as well as a superior carbon acquisition by the leaves. The high biomass density of B. pinnatum will then result in a lower nutrient requirement due to a slower turnover, which in the long term is advantageous under nutrient-poor conditions.