Starved bacteria retain their size but lose culturability - Lessons from a 5000 years old undisturbed A-horizon     

Mette Vestergård  Flemming Ekelund  Carsten Suhr Jacobsen  Søren Christensen 《Soil biology & biochemistry》2011,43(6):1379-1382

The vast majority of soil bacteria are unable to form visible colonies on agar media. One hypothesis is that unculturable soil bacteria are dwarf cells that may either be small starved forms derived from larger species or represent inherently small species. We test the hypotheses that cells of extremely starved soil bacterial communities are smaller and less culturable than cells of bacterial communities from a richer soil, and that culturability is related to cell size by comparing an extremely starved community from a 5200-year-old A-horizon buried under a burial mound with a community from a modern agricultural A-horizon.We serially filtered cell suspensions through filters with successively smaller pore sizes (0.8 μm, 0.6 μm and 0.4 μm) and assessed total cell number and culturability, i.e. the ability to form colonies on two types of agar media, in each size fraction. Cell size distributions were assessed in unfiltered suspensions. Average cell size was only moderately reduced in the starved community, where culturability was low for all size classes. In contrast, culturability was much higher in the modern community, where culturability decreased dramatically with decreasing cell sizes.  相似文献   

Interaction between a fungal plant disease,fungivorous nematodes and compost suppressiveness     

Jan Lagerlöf  Violeta Insunza  Bengt Lundegårdh  Birgitta Rämert 《Acta Agriculturae Scandinavica, Section B - Plant Soil Science》2013,63(4):372-377

Abstract

We tested the hypothesis that the fungivorous nematodes Aphelenchoides spp. and Aphelenchus avenae can suppress damping-off caused by Rhizoctonia solani in cauliflower seedlings, and enhance the disease-suppressive effect of compost. In greenhouse experiments, we used two different composts mixed with peat (20% + 80%) and pure peat as growth substrates in growing pots. In each substrate, treatments were: (A) with R. solani and nematodes, (B) with R. solani, (C) with nematodes, (D) control without R. solani or nematodes. Treatment effects were measured as percentage of healthy seedlings 7, 10 and 14 days after start of the experiment. We conducted two different experiments with the treatments A–D; one with Aphelenchoides spp. and one with Aphelenchus avenae. Aphelenchoides spp.+R. solani (treatment A) had 85% healthy plants (= control without addition of fungi (D)) compared with 45% in R. solani without nematodes (B). Aphelenchus avenae suppressed damping-off significantly in all substrates, from almost 100% dead plants in peat with R. solani to 65% healthy plants in R. solani+A. avenae. One compost mixture had an intrinsic suppressive effect on damping-off, while plant health in the other compost mixture was not better than in 100% peat as growing substrate. There were no additive suppressive effects (enhancement) between nematode effects and the suppressive compost. The results demonstrate the ability of fungivorous nematodes to suppress plant diseases. The effects of fungivorous nematodes in combination with compost and other control measures on disease suppression need further attention. The usefulness of fungivorous nematodes in agriculture and horticulture is discussed.  相似文献   

Plant development,agronomic performance and nutritive value of forage maize depending on hybrid and marginal site conditions at high latitudes     

Zohaib Mussadiq  Mårten Hetta  Christian Swensson  Anne-Maj Gustavsson 《Acta Agriculturae Scandinavica, Section B - Plant Soil Science》2013,63(5):420-430

Abstract

The objectives of this investigation were to study the effects of marginal site conditions and hybrid on plant development, agronomic performance and nutritive characteristics of forage maize (Zea mays L.) at high latitudes. Field experiments were conducted in 2008 and 2009 at three experimental sites, Kristianstad, Skara and Västerås, at increasing latitudes from 55°–60° N. Experimental design used two replicated randomized complete blocks at each site with three maize hybrids, Avenir (FAO 180), Isberi (FAO 190) and Burli (FAO 210), which were continuously assessed for plant development and harvested at various levels of maturity. The chemical composition and nutritional characteristics of harvested plant materials were analysed and hybrid responses to advancing maturity in terms of yield and nutritional qualities were evaluated. Results showed that maize hybrids required different numbers of accumulated thermal units at sites on varying latitudes to achieve developmental stages. Lowest thermal unit requirements among hybrids were observed for hybrid Avenir, and for sites it was highest for plants grown in the most northern site, Västerås. The most southern site, Kristianstad, was the only site at which all hybrids reached the dent stage (c. 450 g kg^?1 kernel DM), a recommended maturity for ensiling. The DM yields of early maturing hybrid Avenir were consistently lower than those for Isberi and Burli at all the sites. Results also revealed nutritional differences among maize hybrids at a given maturity (DM, g kg^?1), indicating that the effects of maturation should be factored into design of hybrid performance trials. This study highlights the effects of marginal site conditions and hybrids on plant development, agronomic performance and nutritional characteristics of maize hybrids at high latitudes. Further studies on marginal sites are recommended to enlighten the understanding of interaction between environmental and genetic factors on the performance of forage maize.  相似文献   

Root development in potato and carrot crops – influences of soil compaction     

Tor J. Johansen  Mette G. Thomsen  Anne-Kristin Løes  Hugh Riley 《Acta Agriculturae Scandinavica, Section B - Plant Soil Science》2013,63(2):182-192

Row crops such as potatoes (Solanum tuberosum L.) and carrots (Daucus carota L.) are of high economic value in the Nordic countries. Their production is becoming more and more specialized, including continuous arable cropping and heavier farm machinery, with increased risk of soil compaction. The result may be restricted root development and economic losses. Potatoes have widely branched adventitious roots, whereas carrots have taproots with fibrous roots extending from them. Under optimal soil conditions, total root length per surface area may reach more than 10 km m^?2 for both species. Maximal root depth is about 140 cm for potato and more than 200 cm in carrots. Most of the root mass is usually distributed within the upper 100 cm, whereof more than 50% may be deeper than 30 cm. Soil compaction causes a dense soil with few large pores, poor drainage and reduced aeration, especially in wet soils with low organic matter content and high proportions of silt or clay. With compacted subsoil layers, roots will be concentrated more in the upper layers and thus explore a smaller soil volume. This will lead to reduced water and nutrient uptake, reduced yields and low nutrient utilization efficiency. In this review article, we describe the interactions between root development and soil conditions for potatoes and carrots, with special focus on sub-optimal conditions caused by soil compaction. We also discuss the effects of tilling strategies, organic material, irrigation and fertilization strategies and controlled traffic systems on root and yield development. To reduce subsoil compaction there is a need to implement practises such as controlled traffic farming, new techniques for ploughing, better timing of soil operations, crop rotations with more perennial crops and supplements of organic material. Moreover, there is a need for a stronger focus on the impacts of farm machinery dimensions.  相似文献   

Influence of Harvest Time and Stubble Height on Weed Seedling Recruitment in a Green Cereal     

Margareta L. Hansson  Ullalena Boström  Håkan Fogelfors 《Acta Agriculturae Scandinavica, Section B - Plant Soil Science》2013,63(1):2-9

A long-term field experiment was conducted in southern Sweden to evaluate the effect of harvest before crop ripeness on weed infestation. In addition, two stubble heights, 10 cm and 30 cm, were compared. The aim was to determine the potential of the treatments in weed regulation. The harvests were performed on three occasions: milk-ripeness (I), which is the normal harvest time for a green cereal, yellow-ripeness (II) and binder-ripeness (III). In control plots, harvested at full ripeness, herbicides were used in all years. Weed density initially increased exponentially in all treatments except for the control, but had a tendency to level off after 4 years. In all years weed density was higher when harvest was delayed and the stubble was high. Harvest at milk ripeness (I) favoured short-season annuals such as Stellaria media (L) Vill and worked against late-maturing species such as Polygonum tomentosum (Schrank). Weed density differed between the treatment plots during the last year of the experiment. In the treatment harvested at stage I combined with low stubble height, weed density was only slightly higher than in the control. Thus, when harvesting a green cereal, herbicides can be avoided.  相似文献   

Effects of Soil Conditions on the Prevalence of Netted Scab     

Hans Bång 《Acta Agriculturae Scandinavica, Section B - Plant Soil Science》2013,63(4):271-277

Abstract

In two field trial series different planting techniques, used to alter soil conditions at planting time, and rates of seed infection with netted scab were compared regarding their effects on plant development, yield, tuber size distribution and the prevalence of netted scab in the progeny. A greenhouse pot experiment was also carried out to study the influence of soil contamination and infection of seed with the netted scab organism on the prevalence of netted scab in the progeny. Both seed infection and planting technique affected the progeny tuber infection with netted scab. Seed infection also negatively influenced plant development and yield. It is concluded that seed infection affects plant development and yield more than soil contamination does, whereas soil contamination is more an important source of progeny tuber infection.  相似文献   

INFLUENCE OF NITROGEN SUPPLY ON CADMIUM ACCUMULATION IN POTATO TUBERS     

E. Helene Larsson Jönsson  Håkan Asp 《Journal of plant nutrition》2013,36(3):345-360

The effect of different levels and forms of nitrogen (N) fertilizer on cadmium (Cd) concentrations in potato (Solanum tuberosum L.) tubers, a large component of the northern European diet, was investigated with the aim of decreasing the Cd content. A high and a low Cd-accumulating cultivar were used in two field trials and a pot experiment. The N fertilizers tested were balanced N- phosphorus (P)- potassium (K) 11-5-18 + micronutrients, alkaline calcium nitrate and acidic ammonium sulfate at levels of 60, 160, and 240 kg N ha^?1 at planting or (for the higher N doses) split between two or three occasions. The Cd concentration in tubers of both cultivars decreased when increasing the N fertilizer from 60 to 160 or 240 kg N ha^?1, indicating that Cd uptake and translocation are not positively correlated to the growth rate of the potato plant. A strong positive linear correlation was found between the Cd concentration in leaves at 77 days after planting and the Cd concentration in tubers at harvest, irrespective of N treatment, although the Cd concentration was three-fold higher in the leaves. The genetic variation in leaf and tuber Cd accumulation was consistent, regardless of the form of N fertilizer used. Ammonium sulfate decreased soil pH and increased tuber Cd concentration in both cultivars compared with NPK fertilizer, possibly due to increased amounts of plant-available Cd arising from the pH decrease after ammonium sulfate application. The tuber Cd concentration in the low Cd-accumulating cultivar increased when fertilized with calcium nitrate, an effect attributed to Cd availability being influenced by the increased Ca²⁺ concentration.  相似文献   

Predicting spring barley yield from variety-specific yield potential, disease resistance and straw length, and from environment-specific disease loads and weed pressure   总被引：1，自引：1，他引：0  

Hanne ?sterg?rd  Kristian Kristensen  Hans O. Pinnschmidt  Preben Klarskov Hansen  Mogens S. Hovm?ller 《Euphytica》2008,163(3):391-408

For low-input crop production, well-characterised varieties increase the possibilities of managing diseases and weeds. This analysis aims at developing a framework for analyzing grain yield using external varietal information about disease resistance, weed competitiveness and yield potential and quantifying the impact of susceptibility grouping and straw length scores (as a measure for weed competitiveness) for predicting spring barley grain yield under variable biotic stress levels. The study comprised 52 spring barley varieties and 17 environments, i.e., combinations of location, growing system and year. Individual varieties and their interactions with environments were analysed by factorial regression of grain yield on external variety information combined with observed environmental disease loads and weed pressure. The external information was based on the official Danish VCU testing. The most parsimonious models explained about 50% of the yield variation among varieties including genotype-environment interactions. Disease resistance characteristics of varieties, weighted with disease loads of powdery mildew, leaf rust and net blotch, respectively, had a highly significant influence on grain yield. The extend to which increased susceptibility resulted in increased yield losses in environments with high disease loads of the respective diseases was predicted. The effect of externally determined straw length scores, weighted with weed pressure, was weaker although significant for weeds with creeping growth habit. Higher grain yield was thus predicted for taller plants under weed pressure. The results are discussed in relation to the model framework, impact of the considered traits and use of information from conventional variety testing in organic cropping systems.  相似文献   

Developments in breeding cereals for organic agriculture   总被引：7，自引：6，他引：1  

M. S. Wolfe  J. P. Baresel  D. Desclaux  I. Goldringer  S. Hoad  G. Kovacs  F. Löschenberger  T. Miedaner  H. Østergård  E. T. Lammerts van Bueren 《Euphytica》2008,163(3):323-346

The need for increased sustainability of performance in cereal varieties, particularly in organic agriculture (OA), is limited by the lack of varieties adapted to organic conditions. Here, the needs for breeding are reviewed in the context of three major marketing types, global, regional, local, in European OA. Currently, the effort is determined, partly, by the outcomes from trials that compare varieties under OA and CA (conventional agriculture) conditions. The differences are sufficiently large and important to warrant an increase in appropriate breeding. The wide range of environments within OA and between years, underlines the need to try to select for specific adaptation in target environments. The difficulty of doing so can be helped by decentralised breeding with farmer participation and the use of crops buffered by variety mixtures or populations. Varieties for OA need efficient nutrient uptake and use and weed competition. These and other characters need to be considered in relation to the OA cropping system over the whole rotation. Positive interactions are needed, such as early crop vigour for nutrient uptake, weed competition and disease resistance. Incorporation of all characteristics into the crop can be helped by diversification within the crop, allowing complementation and compensation among plants. Although the problems of breeding cereals for organic farming systems are large, there is encouraging progress. This lies in applications of ecology to organic crop production, innovations in plant sciences, and the realisation that such progress is central to both OA and CA, because of climate change and the increasing costs of fossil fuels.  相似文献   

Plant breeding for organic and sustainable,low-input agriculture: dealing with genotype–environment interactions     

Edith T. Lammerts van Bueren  Hanne Østergård  Isabelle Goldringer  Olga Scholten 《Euphytica》2008,163(3):321-322

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