Showing papers on "Growing season published in 1988"

Atmospheric geochemistry of formic and acetic acids at a mid-latitude temperate site

Abstract: Tropospheric concentrations of formic and acetic acids in the gas, the aerosol, and the rainwater phases were determined in samples collected 1-2 m above ground level at an open field site in eastern Virginia. These acids were found to occur principally (98 percent or above) in the gas phase, with a marked annual seasonality, averaging 1890 ppt for formate and 1310 ppt for acetate during the growing season, as compared to 695 ppt and 700 ppt, respectively, over the nongrowing season. The data support the hypothesis that biogenic emissions from vegatation are important sources of atmospheric formic and acetic acid during the local growing season. The same time trends were observed for precipitation, although with less defined seasonality. The relative increase of the acetic acid/formic acid ratio during the nongrowing season points to the dominance of anthropogenic inputs of acetic acid from motor vehicles and biomass combustion in the wintertime.

Effects of fire season on flowering of forbs and shrubs in longleaf pine forests

Abstract: Effects of variation in fire season on flowering of forbs and shrubs were studied experimentally in two longleaf pine forest habitats in northern Florida, USA. Large, replicated plots were burned at different times of the year, and flowering on each plot was measured over the twelve months following fire. While fire season had little effect on the number of species flowering during the year following fire, fires during the growing season decreased average flowering duration per species and increased synchronization of peak flowering times within species relative to fires between growing seasons. Fires during the growing season also increased the dominance of fall flowering forbs and delayed peak fall flowering. Differences in flowering resulting from variation in fire season were related to seasonal changes in the morphology of clonal forbs, especially fall-flowering composites. Community level differences in flowering phenologies indicated that timing of fire relative to environmental cues that induced flowering was important in determining flowering synchrony among species within the ground cover of longleaf pine forests. Differences in fire season produced qualitatively similar effects on flowering phenologies in both habitats, indicating plant responses to variation in the timing of fires were not habitat specific.

Spatial and temporal patterns in the seed bank and vegetation of a desert grassland community

Abstract: SUMMARY (1) Plant and seed temporal and spatial patterns, and the correlation between vegetation and seed bank were examined from 150 samples collected from an 8-ha site in a desert grassland community in north-central New Mexico, U.S.A. (2) Total plant cover increased through the growing season, but relative cover of all species except three annuals remained constant. Spatial pattern of the vegetation was patchy, but species associations within the vegetation patches were weak. (3) Species composition of the seed bank was similar to the vegetation (88 9% concordance) and, like the vegetation, seeds were patchily distributed with little evidence of pattern at the species level. Relative seed densities varied little through the growing season and were positively correlated with cover for the same species. (4) High correlation between the seed bank and vegetation are postulated to be a consequence of frequent and unpredictable disturbance, but may further be promoted by the effects of seed predation on seed bank turnover rates.

The influence of climate and soils on the distribution of four African grasses

Abstract: Around 1900 temperate and semidesert grassland productivity declined, soil erosion increased, and drought destabilized the livestock industry in the northern and southern hemispheres. As government leaders throughout the world began to recognize the importance of grassland productivity and soil conservation, a massive experiment began to evolve. Government and private individuals collected seed from every continent, and planted seed at experimental stations and ranches in their respective countries. Hundreds of individuals who conducted thousands of seeding trials observed that buffelgrass (Cenchrus ciliaris L.), weeping lovegrass [Eragrostis curvula (Schrad.) Nees], kleingrass (Panicum coloratum L.), and Lehmann lovegrass (Eragrostis lehmanniana Nees) plants from seed collected in Africa were easier to establish and persisted longer than other grasses. Between 1930 and 1986 scientists in many countries evaluated the establishment and persistence of these grasses, but no attempt was made to synthesize the data base and determine the effects of climate and soil on plant establishment and persistence. Our objective was to: (1) determine the climatic and edaphic characteristics of areas where the seed of each grass was collected in Africa, and where each grass has been successfully established in both hemispheres, and (2) identify characteristics which influence long-term persistence. Where buffelgrass predominates and spreads, summer rainfall varies from 150 to 550 mm, winter rainfall is less than 400 mm, mean miminum winter temperatures rarely fall below 5? C, and soil texture is loamy. Weeping lovegrass can be established and plants persist when spring, summer, and fall rainfall varies from 400 to 1,000 mm on deep sandy soil and mean minimum winter temperatures rarely fall below -5? C. The invasion of adjacent nonplanted sites occurs only in Africa where growing season rainfall infrequently cycles between 750 and 1,000 mm and soils remain wet in mid-summer. Kleingrass can be established where mean maximum daily summer temperatures are above 30? C, mean minimum daily winter temperatures rarely fall below 0" C, summer growing season rainfall varies from 400 to 990 mm, and soils are clayey or silty. Kleingrass, like weeping lovegrass, spreads to nonplanted sites only in Africa where a mid-summer drought does not occur. Lehmann lovegrass predominates and spreads only in southern Africa, southeastern Arizona, and northern Mexico when summer rainfall in 30 to 40 days exceeds 150 mm, and soil textures are sandy or

The grass plant—its form and function

Abstract: The form of a plant reflects its function. The morphology of grasses is a product of their genetic make-up and the environment they experience, a key component of which is the grazing animal. Forage grasses have evolved to withstand periodic defoliation. Agriculturally important north-temperate grasses remain vegetative throughout most of the year, with the growing points, from which new leaves are produced, held at or near ground level on unelongated stems. Thus, when the leaves are harvested, whether by cutting or grazing, the majority of the growing points escape. Any leaves which are not harvested, entirely or in part, senesce and die. Turnover is rapid. At the height of the growing season, a typical grass shoot may bear three live leaves and produce a new one every 7–10 days (Alberda and Sibma, 1968). The entire leaf canopy can be replaced within as little as 3–4 weeks.

Persistent Differences in Two Forms of Spartina Alterniflora: A Common Garden Experiment

Abstract: Tall- and short-form Spartina alterniflora plants were transplanted from the Delaware marsh to common garden plots during the summer of 1978 and irrigated with saltwater three times a week during that and each subsequent growing season. Nine years later plant biomass, culm height, density, and diameter and flowering frequency remained distinct. Underground regrowth reserves and root profiles likewise remained distinct for the two forms. Since the two growth forms had been living in the same environment for 9 yr and had retained many morphological and physiological differences, some genetic control of the morphology and physiology of the two growth forms is highly probable.

Excessive Soil Water Effects at Various Stages of Development on the Growth and Yield of Corn

Abstract: THE response of corn to naturally fluctuating water tables at five different stages of growth was studied for 3 years. Fifty plots of 15 m x 15 m were established in 1984 on Nicollet soil in an area that is not artificially drained. In the center of each plot, an observation well was installed for water-table measurements. Water-table hydrographs were developed for each plot annually to quantify crop stress factors from excessive wetness (SEW30, a summation of days times the height of the water table above 30 cm). The results of these studies indicate that SEW30 values of as low as 40 cm-days in the early part of the growing season can significantly reduce corn yields. Corn yields decreased linearly with the increase in SEW30 values and the Stress Day Index (SDI). Lower corn yields resulted from both decreased plant population and poor crop growth due to excessive wetness.

Temperature and the distribution of plant species.

Abstract: An understanding of the mechanisms by which temperature influences the distribution of species and vegetation has been attempted by modelling population growth and establishing those stages of the plant life cycle which, when diminished by extremes of temperature, for example, may have the greatest impact on plant survival. This analysis suggests that the heat sum of the growing season, measured as day-degrees, controls the distribution of annual vegetation. For perennial vegetation both the heat sum of the growing season and the annual, absolute minimum temperature are critical. Climatic correlations and experimental analyses indicate that, in northern Europe, the northern latitudinal and upper altitudinal limits of lowland and southern vegetation are directly controlled by climate. In contrast, the southern and lower altitudinal limits of upland and northern vegetation are likely to be controlled by temperature-sensitive competition with southern or lowland species. Many of the temperature-sensitive processes of plant growth and development, such as the non-linearity of extension growth and variations in the threshold temperatures of processes, may increase the realized heat sum at a particular geographical location. However, in more northerly climates, photoperiodic control is crucial in avoiding precocious development in the highly variable climatic conditions of early spring.

Movement rhythms in juvenile Atlantic salmon, Salmo salar L.

Abstract: Nocturnal downstrean migration of juvenile Atlantic salmon is usually interpreted as increased locomotor activity. The frequency of downstream passages of 0–1 + salmon in an endless stream channel was greater by night than by day in both smoking and non-smolting fish in autumn and spring. Movement increased at dusk, and decreased after dawn. Mature male 1 + fish moved slightly less than immatures in October, but significantly more in November. Total movement frequency was lower at full moon than at other moon phases, and movement was reduced when the moon was up. Under turbid conditions by day, the threshold water velocity inducing nett downstream movement was 8.2 cm s−1, and the relative velocity of fish swimming downstream was never more than one third that of fish holding station at the normal maximal flow of 25–30 cm s−1. At the end of their first growing season in October, fish which had been offered food continuously through 24 h did not differ in size from those fed by day only, but the latter were significantly larger than those offered food only at night. We conclude that: (1) the fish fed actively by day, and not by night; (2) station-holding represented activity, and downstream nocturnal movement represented relative inactivity (displacement) which occurred on loss of visual orientation, hence migration resulted from reduced activity; (3) lack of displacement in early autumn has adaptive value for maturing fish, but not for non-spawners.

Growth and Water Relations of Douglas Fir (Pseudotsuga menziesii) Seedlings under Different Weed Control Regimes1

Abstract: Growth of Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) was increased by controlling grasses and broadleaf herbs with eight herbicide regimes during the first 3 yr after planting on a well-drained moist site in the Oregon Coast Range. The greatest growth occurred if weeds were controlled in the same growing season that tree seedlings were transplanted to the field; smaller increments came from second- and third-year weed control. Growth increases attributable to early weed control continued through the fifth year, indicating that conditions during establishment strongly influenced later growth. Plots with no herbaceous vegetation had more available soil water than those with competing vegetation, and tree seedlings on these plots ex- perienced less water stress. Irrigation in the third year in- creased stem diameter of seedlings in that year but had no effect thereafter. Increases in average seedling stem volume at 5 yr after transplanting were linearly related (r2 = 0.77) to the difference in observed xylem potential during the first three growing seasons after transplanting and the xylem potential at which photosynthesis ceased, -2 MPa. Additional index words. Atrazine, weed control, irrigation, phenoxy herbicides, stomatal conductance, water potential, AGSTE.

Temperature as a determinant of plant productivity.

Abstract: Quite small variations in temperature such as those that exist between the north and south of Britain, or on a local scale between north and south aspects of a hill, may cause large variations in plant productivity. An attempt is made to assess the effect of a 1 degree C increase in the mean temperature of the growing season by using published data from various sources. The conclusion reached is that a 1 degree C increase in a north temperate climate may be expected to increase plant productivity by about 10%, providing that other factors like water or nutrients do not become limiting. But, for annual crops, a negative effect of temperature has sometimes been observed. This may be because temperature speeds up the development of the crop and thus reduces the duration of photosynthesis. In the natural environment variations in solar radiation and wind speed may often exert an effect on growth because they influence the energy balance, altering the temperature of meristems and other plant tissues in subtle ways which have a significant impact on the pattern of carbon utilization. A more precise understanding of the relationship between growth and weather variables is unlikely to be achieved unless models are developed which enable integration of component processes of growth with what is known about the spatial and temporal variation in the weather variables.

Submerged aquatic macrophyte biomass in relation to sediment characteristics in ten temperate lakes

Abstract: SUMMARY. 1. This study links maximum biomass from eighteen aquatic macrophyte communities in the Eastern Townships of Quebec, Canada, to sediment characteristics: chemically exchangeable nitrogen, phosphorus and potassium, per cent organic matter, water content and texture, and to biotic variables: number of species and depth of maximum biomass. 2. Total biomass was positively and significantly related to sediment potassium content and to sediment texture. 3. Sediment nitrogen and potassium levels are correlated in the spring but not at the end of the growing season. 4. It appears that sediment potassium is a surrogate variable for the availability of sediment nitrogen which has been shown to limit aquatic macrophyte growth in this area.

Comparative water relations of three successional hardwood species in central Wisconsin.

Abstract: Summary Water relations of co-occuning understory saplings of Quercus ellipsoidalis E.J. Hill, an early successional, xeric species, Populus tremuloides Michx., an early successional, mesic species, and Acer rubrum L., a late successional species that occurs on both wet and dry sites, were evaluated on four dates during the 1986 growing season. The understory was characterized by high soil water content, low irradiance and low vapor pressure deficit throughout the growing season. Stomata1 conductance and calculated transpiration flux were lowest for A. rubrum and highest for P. tremuloides and Q. ellipsoidalis. Except early in the growing season, leaf water potentials were lower in P. tremuloides than in the other species. Populus tremuloides had the highest bulk modulus of elasticity, Q. ellipsoid&is the lowest. Over the growing season, Populus tremuloides and Q. ellipsoidalis, but not A. rubrum, exhibited a decrease in osmotic potential at both full and zero turgor. Of the three species, Populus tremuloides exhibited the sharpest decrease in leaf water potential and turgor pressure with decreasing relative water content.

Empirical models for trophic state in southeastern U.S. lakes and reservoirs

Abstract: A cross-sectional data set of 80 lakes and reservoirs in nine southeastern states was examined to specify and parameterize trophic state relationships. The relationships fitted are based on measurements of several limnological variables taken over the course of a growing season or year in each of the lakes. The trophic state models relate phosphorus and nitrogen loading to inlake phosphorus and nitrogen concentrations, which in turn are related to maximum chlorophyll level, Secchi disk depth, dominant algal species, and hypolimnetic dissolved oxygen status. Due to the empirical nature of the study, causal conclusions are limited; rather, the models are most useful for prediction of average growing season conditions related to trophic state.

Effect of fire on the mycorrhizal ecology of little bluestem (Schizachyrium scoparium)

Abstract: Fire in a prairie significantly affected subsequent vesicular–arbuscular mycorrhizal (VAM) fungal colonization and sporulation, plant aboveground production, and tissue inorganic nutrient concentration. Colonization levels of VAM fungi in little bluestem (Schizachyrium scoparium (Michx.) Nash) roots were significantly (p < 0.05) lower on the burned site than on the unburned site during the first growing season postburn, but there were no significant differences between sites during the 2nd year. On each sampling date during the first growing season postburn, the burned site had significantly higher aboveground production than the unburned site. Significantly higher tissue levels of available K, Ca, and Mg were found on the unburned site than on the burned site; however, when nutrients were expressed in terms of nutrients in tissue per square metre, there were no significant differences between the burned and unburned sites. Spore counts for soil collected from the rhizosphere of little bluestem and random...

Effects of applications of fungicide, phosphorus and nitrogen on the structure and productivity of an annual serpentine plant community

Abstract: Benomyl (a fungicide) and phosphate (as NaH2PO4-H20) were applied to patches of two annual serpentine communities dominated by forbs. After one year neither Benomyl nor phosphate had affected plant productivity (except for legume productivity which was increased by phosphorus application), the abundance of any species or mycorrhizal infection. However, at both research sites Benomyl decreased phosphorus concentration in the shoots whereas added phosphorus increased its concentration. At one site, added phosphorus also increased nitrogen concentration in the shoot. In the following year, nitrogen (as NH4NO3) was added to the experimental design. In that second year, both nitrogen and phosphorus applications decreased the abundance and total above-ground dry weight per unit area of Plantago erecta Morris, a dominant annual forb, and decreased the density of all plants taken together. Additionally, Benomyl increased total plant density. Phosphorus and nitrogen increased productivity of the whole community. The data presented herein support the hypothesis that communities occupying inherently infertile sites are not very responsive to nutrient amendment and that mycorrhizal infection may serve as a controller of community structure. Key-words: Annual grassland, Benomyl, nitrogen, phosphorus, serpentine soils, nutrient limitation, forbs, mycorrhiza, community structure * Address for correspondence: Dr R.T. Koide, Department of Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, USA. t Present address: Dr L.F. Huenneke, Department of Biology, New Mexico State University, Box 3AF, Las Cruces, New Mexico 88003, USA t Present address: Dr S.P. Hamburg, Department of Systematics and Ecology, University of Kansas, Lawrence, Kansas 66045, USA. Introduction Plant productivity in serpentine soils can be limited by a number of factors. These include low levels of macronutrients, high concentrations of nickel or chromium, calcium deficiency or magnesium toxicity (Proctor & Woodell, 1975). It has become clear that no single factor is sufficient to explain growth limitations in all serpentine communities. Indeed, serpentine soils are quite variable chemically and physically (Walker, 1954) and the plant species occupying them appear to reflect this variability (Kruckeberg, 1954). Differential tolerance or preference of species to the particular soil chemical regime may thus influence the structure of the community (Tilman, 1986). Indeed, nutrient availability has been shown to affect species composition of both serpentine (Ferriera & Wormell, 1971) and nonserpentine substrates (le Roux & Mentis, 1986; Tilman, 1986). Turitzin (1982) identified both nitrogen and phosphorus as limiting nutrients in an annual serpentine grassland community in coastal central California (the Jasper Ridge Biological Preserve of Stanford University). He showed that total community productivity increased when either nitrogen or phosphorus were added, that nitrogen had a greater effect than phosphorus, and that annual grasses were more responsive than annual forbs. However, it was not reported how fertilizer application quantitatively altered species composition or other community properties. This same serpentine grassland supports welldeveloped vesicular-arbuscular mycorrhizal infections. As is well documented, infection may enhance plant phosphorus uptake (Smith, 1980), particularly under conditions of soil drought (Fitter, 1985). Because the benefit of infection may differ for each species in the community and because a mycorrhizal fungal mycelial network may mediate the transfer of materials from plant to plant within the community (Grime et al., 1987), mycorrhizal infection may serve as another controller of community structure. This content downloaded from 157.55.39.104 on Mon, 20 Jun 2016 07:32:35 UTC All use subject to http://about.jstor.org/terms 336 In order to document the effects of nutrient R. T. Koide supply and mycorrhizal infection on annual et al. serpentine community characteristics, a study was conducted in two serpentine sites in coastal central California. In the Jasper Ridge Biological Preserve, applications of Benomyl, a fungicide reported to suppress mycorrhizal infection [Menge, 1982]) and of phosphate were made during a single growing season. At another site (referred to as the Kirby Canyon site), applications of Benomyl and of phosphate were made over two growing seasons and nitrogen application was made during a single growing season. Effects on the abundance and shoot productivity of various species, mycorrhizal infection and nitrogen and phosphorus concentrations in the shoots of Plantago erecta Morris, a dominant annual forb, are reported. Materials and methods

High Resolution Characterization of Ozone Data for Sites Located in Forested Areas of the United States

Abstract: Eight years of ambient monitoring data (1978-1985) were used to characterize O3 concentrations in eight forested areas of the United States The analysis focused on the annual number of occurrences of hourly averaged O3 concentrations ≥007, 008, and 010 ppm during the growing season (April-October) as well as during the early (April-June) and late (July-October) portions of the growing season On the average, within those areas studied, elevated O3 concentrations occurred more often in the Piedmont/Mountain/Ridge-Valley and Ohio River Valley areas than elsewhere In the eastern United States, 1978, 1980, and 1983 were generally the years with the most occurrences of elevated O3 concentrations In these years, the later part (July-October) of the growing season experienced more elevated concentrations than the earlier part The results presented in this analysis were used to develop recommendations for future O3 effects research with respect to forested areas and related exposure regimes

Predicting net nitrogen mineralization over a growing season: model verification

Abstract: In a previous study a nitrogen mineralization model was developed by combining the potentially mineralizable nitrogen (No) with functions representing the effect of temperature and soil moisture on the mineralization rate constant (k). The model performed well in predicting the amount of net nitrogen mineralized during a growing season when soil was incubated in plastic bags placed in incubators or buried in the field. In the present study a similar model was used to estimate net nitrogen mineralized in situ from Wood Mountain loam an Orthic Brown soil at Swift Current, Saskatchewan under (a) summerfallow, (b) cropped-dryland and (c) cropped-irrigated conditions. Model output showed good agreement to field measurements especially for the first 45–60 d, but thereafter tended to underestimate the measured data particularly under cropped-dryland conditions. During a growing season the cropped-irrigated system predicted 69 kg ha−1 net nitrogen mineralized, but 81 kg ha−1 was measured; the corresponding values...

Influence of Lake Morphometry on the Response of Submerged Macrophytes to Sediment Fertilization

Abstract: The influence of lake morphometry on the growth of submerged macrophytes in response to sediment fertilization was studied at sites of varying bottom slope (steep to gentle), wave exposure (high to low), and depth (1.0 and 2.5 m) in Lake Memphremagog (Quebec–Vermont). The biomass increases were on average 2.1 times greater for fertilized plants than for the paired controls. The extent of the growth response was greatest at the 1.0-m sites. The smaller response at the 2.5-m sites was further decreased as exposure to waves increased. The smaller response at 2.5 m (depth of maximum biomass) suggests that factors such as light limitation, length of the growing season, and littoral slope, but not sediment nutrient levels, limit submerged biomass there. The importance of the physical factors appears to increase as the biomass increases. "Overwintering" plants showed greater response to fertilization than those growing from seeds. Overall, the extent of the growth response to sediment fertilization depends on th...

The seasonal biomass and productivity of the submerged macrophytes in a polluted Wisconsin stream

Abstract: SUMMARY 1. We measured biomass and light/dark bottle productivity of macrophytes in a Wisconsin stream throughout one growing season. Except for a brief period in early spring when a Cladophora glomerata-filamentous algal community was dominant, Potamogeton pectinatus was the dominant macrophyte species in Badfish Creek. 2. Maximum community biomass was 710 g DW m−2, with a maximum above ground biomass of 620 g DW m−2 and a maximum below ground biomass of 120 g DW m−2. Annual productivity was estimated at 1435 g DW m−2 year−1, with a calculated P/B of 2.01. 3. In situ net production averaged 2.83g C g AFDW−1 h−1 Net positive carbon gain by the P. pectinatus community occurred when water temperatures were above 15°C, and daylength at least 12h. This is correlated to the onset of tuber germination in spring, and the point of maximal biomass decline in autumn.

Succession and fluctuation in Artemisia dominated grassland

Abstract: Vegetation dynamics were studied from 1940 to 1978 in two grazed pastures and associated exclosures in sand sagebrush (Artemisia filifolia) dominated grassland, western Oklahoma, USA. In both pastures and one exclosure, pattern of vegetation change reflected fluctuation rather than succession. In the other exclosure, the grassland exhibited a directional change from annual grasses and forbs to dominance by perennial grasses. Rate of change was consistent during the 39 year period. Cover of grasses increased more in grazed than ungrazed areas. Grass cover was negatively correlated with high air temperatures early in the growing season. Forb cover remained relatively constant over time and shrub cover peaked during the 1960s. Abundance of annuals and cool season species was positively correlated with rainfall early in the growing season. Species diversity and richness were lowest in the ungrazed areas, as a result of increased dominance by perennial grasses such as Schizachyrium scoparium. In pastures and exclosures, richness was positively correlated with growing season precipitation. Cover of the common species differed among sample areas within years and fluctuated between years. Few general patterns emerged from correlations of environmental variables with cover of individual species. In general, vegetation dynamics in these sand sagebrush grasslands reflect a tradeoff in that total cover changes little over time because the loss of some species is compensated for by increased growth of others. Such trade-offs reflect the individualistic response of the component species within each pasture or exclosure. Although changes in growth form composition were related to climatic fluctuation, broad-scale climatic variables could not successfully predict small-scale patterns of change by individual species over time.

Seasonal biomass and nutrient allocation patterns in wild leek (Allium tricoccum Ait.), a spring geophyte

Abstract: NAULT, A. AND D. GAGNON (Dept. Sci. biol., Univ. du Quebec a Montreal, Groupe Rech. Ecol. Forest., Montreal, Quebec H3C 3P8, Canada). Seasonal biomass and nutrient allocation patterns in wild leek (Allium tricoccum Ait.), a spring geophyte. Bull. Torrey Bot. Club 115: 45-54. 1988.-Biomass and nutrient allocation patterns were studied during the growing season in a wild leek (Allium tricoccum Ait.) population in southern Quebec, Canada. Wild leek is a spring geophyte in which the photosynthetic phase precedes and does not overlap the reproductive phase. N, P, K, Mg and Ca allocation to plant structures was studied concurrently with biomass allocation in reproductive plants during the 1983 growing season. Biomass allocation to individuals of all size-classes (divided into two size-classes) of the population was studied in 1984 and 1985. Patterns observed are typical of plants with a spring ephemeral phenology, such as a high investment to leaves during the short photosynthetic period. The large allocation to the bulb suggests a conservative survival strategy, based primarily on vegetative propagation. Nutrient and biomass allocation patterns were largely similar, except for mobile nutrients (N and P) in the scape. Little variation in biomass allocation was seen in large reproductive wild leek plants from year to year; smaller, non-reproductive plants showed higher variability, probably because of higher phenological response to climate.

Factors influencing germination and establishment of Eucalyptus pauciflora near the alpine tree line.

Abstract: Factors affecting seed germination, seedling establishment and growth to reproductive maturity in Eucalyptus pauciflora Sieb. ex Spreng. at the tree line in southeastern Australia were investigated. Timing of germination was determined principally by temperature but could be strongly modified by soil water. Mortality of germinants was heaviest during the first growing season (dependent on soil water) and the first winter (dependent on the depth and duration of snow cover). Neither plant nor soil treatments with insecticide or fungicide had an overriding or consistent effect on germination or seedling establishment. The probability of reaching the sapling stage was greater for planted seedlings than for plants germinated on site, indicating the dependence of survival on accumulated reserves. There was no clear indication of a general decrease in survival with increasing altitude, because of an interplay between elevation and site factors including competing vegetation, snow depth and period of snow cover. Five-year-old saplings planted up to 200 m above the tree line produced reproductive structures and viable seed between the ages of 13 and 18 years. The relevance of the results to an understanding of the location of the present tree line is discussed.

Season of cutting affects biomass production by coppicing browse species of the Brazilian caatinga

Abstract: This paper reports the effect of season of cutting on coppice biomass production by S tree species common in the semiarid caatinga woodlands of northeast Brazil. Trees were cut early and late in the wet and dry seasons and coppice biomass production was monitored for 2 growing seasons after cutting. No mortality occurred as a result of cutting in any season. The effect of season of cutting on subsequent coppice production was most pronounced in the first year but differences persisted into the second year. Production by trees cut late in the wet season lagged behind that of trees cut at any other time. This was true for all species except marmeliero (Croton hemiargyreus Muell. Arg.) during both years. Pau branco (Auxemma oncocalyx Taub.) production was maximized by cutting late in the dry season. Jurema preta (Mimosa acutistipula Benth.) and catingueira (Caesalpinia pyramidalis Tul.) production was maximized by cutting early in the dry season. The season of cutting does not affect marmeliero stem production. Except for the late wet season, no treatment significantly affected sabia Mimosa caesalpinifolia production. Stem biomass production is affected more by season of cut than is leaf biomass production. The different patterns of response among these species could be the basis of a selective cutting scheme to achieve objectives such as browse and wood production.

Primocane (autumn)-fruiting raspberries: a review with particular reference to progress in breeding

Abstract: SummaryThe characteristics of primocane-fruiting (PF) raspberries (developmental cycle, ripening season, yield) and the effects on these of changes in the environment (day-length, length of growing season, temperature, nutrition, growth regulator applications) are described. Economic aspects are discussed in relation to extending the season, reduction in establishment and production costs compared with summer-cropping raspberries, and mechanical harvesting. Progress in breeding new PF varieties in North America and Europe and current and potential future prospects for growing PF raspberries are discussed.

Seasonal variations on water relations of Amygdalus communis L. under drip irrigated and non irrigated conditions

Abstract: Almond plants (Amygdalus communis L.) of the Garrigues variety were grown in the field drip irrigated and rainfed. Leaf water potential (Ψ) and leaf conductance (g1) were determined throughout one growing season. Pre-dawn measurement for Ψ in the irrigated treatment was consistent through the growing season, whereas in the rainfed treatment it decreased gradually. Ψ values at midday (Ψ minimum) was closely dependent on atmospheric evaporative demand, and their recovery was quicker in the wet treatment than in the dry. The g1 values were higher in the wet than dry treatments, decreasing in both cases by leaf ageing. Maximum values for g1 were reached when evaporative demand was highest in the day. The relationship between Ψ and g1 revealed a decrease in the hysteresis throughout the growing season, being most marked in the dry treatment. The results highlight the close dependence of Ψ and g1 on evaporative demand, leaf ageing and irrigtion treatment during the growing season.