bluuebunny/crossref_metadata_2025 huggingface dataset:
Fungal infestation of seeds from seven populations of wild oats (Avena fatuaL.) with different dormancy and viability characteristics
Authors: MORTENSEN K. , HSIAO A. I.
Published: July 2006

Seeds from seven genetically inbred pure lines of wild oats (Avena fatuaL.) with different levels of dormancy and viability were analysed for seed‐borne fungi. All lines had fungi on the seeds. The predominating fungi wereAlternaria alternataandCladosporium herbarum, of which the latter was non‐pathogenic and the former only weakly pathogenic on seedlings of wild oats.Drechslera avenacea, Cochliobulus sativusandFusariumspp., frequently isolated, were pathogenic onA. fatua.OnlyD. avenaceawas host specific toA. fatuaand cultivated oatsAvena sativa. Cochliobolus sativusandFusariumspp, were equal or more pathogenic on seedlings of wheat (Triticum aestivumL.), barley (Hordeum vulgareL.), oats and rye (Secale cerealeL.) than on seedlings ofA. fatua. Drechslera avenaceaoccurred on a significantly higher percentage of seeds fromA. fatualines, AN 51 and AN 474, than from the other lines. Other fungi isolated occurred randomly on allA. fatualines. There was no relationship between low viability of seeds and fungi carried on the seeds.
Untersuchungen zur Keimungsbiologie von sechs tropischen Segetalarten
Authors: SAUERBORN J. , KOCH W.
Published: July 2006

Für die 6 untersuchten tropischen Segetalarten Ageratum conyzoides, Blechum brownei, Crassocephalum crepidioides, Mikania micrantha, Paspalum conjugatum und P. paniculatum lag die untere Temperaturgrenze bei der Keimung im Bereich von 10 bis 15(20)°C, die maximale bei ≤ 40°C, das Optimum zwischen 20 und 35°C. Ageratum conyzoides und C. crepidioides hatten etwas geringere Ansprüche an die Keimtemperatur als die übrigen Arten, was ihre vergleichsweise stärkere Verbreitung in Höhenlagen erklärt. Die Keim‐temperaturen der beiden Vertreter aus den gemässigten Breiten, Alopecurus myosuroides und Chenopodium album, lagen bei 5 (Minimum), 15–25 (Optimum) bzw. 40°C (Maximum). Die Keimung von A. conyzoides, C. crepidioides und M. micrantha wurde bereits ab einem osmotischen Potential von ‐ 1 bar negativ beeinflusst. Bei ‐ 4,7 bar keimte von den 6 tropischen Arten nur noch P. paniculatum in geringem Umfang, während AL myosuroides und Ch. album bis ‐4,7 bar nicht beeinträchtigt wurden. Nach einjähriger trockener Lagerung keimten alle 6 tropischen Arten nur unter Lichteinfluss. Nach 20 Monaten keimten C. crepidioides und P. paniculatum auch in Dunkeln.
Spread of proso millet (Panicum miliaceum L.) in Ontario, Canada. II. Dispersal by combines
Authors: McCANNY S. J. , CAVERS P. B.
Published: July 2006

Seeds of proso millet (Panicum miliaceum L.) are moved between and within fields on combine harvesters. The dispersal of seeds of two biotypes of P. miliaceum by combine harvesters was quantified. The golden‐seeded biotype of this weedy annual grass was known to have larger seeds and to experience less seed shattering than the black‐seeded biotype. An average of 3·3% of the seeds on the plants of the black‐seeded biotype was carried more than 50 m by combines, while 0·9% of the golden seeds were carried the same distance. The densities of the seed rain within 50 m of the weedy patches were 3·7 seeds m−2 for the black‐seeded biotype and 9·7 seeds m−2 for the golden‐seeded biotype. This difference was proportional to the difference in the number of seeds in the respective source patches. The numbers of seeds deposited at various points within 50 m of source patches were close to uniform for both biotypes. There was, however, a significant difference (P < 0·05) in the distributions of the seeds of the two biotypes.
Mathematical modelling in agricultural science
Authors: FRANCE J.
Published: July 2006

A simple initial classification of types of models is given and the essential role of models in science, especially in agricultural science, is reviewed. Empirical models are contrasted with mechanistic models, and these are related to the levels of aggregation considered, and crucially, to the difference between description and understanding. Examples of mechanistic models to simulate aggregated biochemical systems and to interpret experimental data, with reference to nutrition and metabolism in animals, are presented. Requirements for successful modelling in an agricultural context are discussed, followed by consideration of the problems and promise of linking the modelling viewpoint into a biological research programme. Finally, the ranges of possible objectives and potential contributions of mathematical modelling in agricultural science are explored.
Veränderungen der Vegetation durch experimentelle Erdgasbehandlung
Authors: PYŠEK PETR , PYŠEK ANTONÍN
Published: July 2006

Die Veränderungen der Vegetation, die durch experimentelle Erdgasbehandlung hervorgerufen wurden, sind in den Jahren 1978–84 in Mittelböhmen untersucht worden. Das verwendete Erdgas enthielt 93,8% Methan, 3,6%Äthan, 0,8% Propan, 0,25% Butan, 0,3% Kohlendioxid. Die getesteten Kulturpflanzen wurden auf Parzellen von 60·5 m angebaut, bei denen das Erdgas durch unterirdische Sonden in den Boden eingebracht wurde. Darüber hinaus wurden die Reaktionen der Unkrautarten untersucht.

Die Wirkungen auf der Populationsebene bestanden in Wachstumshemmung und Verminderung der Individuenzahl bei den meisten Arten. BeiMedicago sativa, Brassica oleraceavar.acephala, Secale cereale, Lolium multiflorum, Beta vulgarisundZea mayswurden Farbveränderungen beobachtet. Auffällige phänologische Veränderungen wurden beiSolanum tuberasum, Helianthus annuusandZea maysfestgestellt (Verzögerung des Austreibens und des Blühbeginns), Für einen typischen Effekt des Erdgases kann eingeschränkte oder sogar fehlende Reprodutionsfähigkeit angesehen werden, was besonders fürAllium cepa, Triticum aestirum, Hordeum distichon, Trifoliumsp. div.,Medicago sativaund die meisten Unkrautarten gilt. Oftentstanden verschiedene Organdeformationen (Solanum tuberosum, Beta vulgaris).

Einzelpflanzen vonChenopodium albumundMedicago sativa, die in der Umgebung der Erdgas‐ausströmung wuchsen, hatten eine erhöhte Stomatazahl. Es wurden auch Veränderungen im Verlauf der Reflektionskurven beiTrifolium pratensesubsp.sativumbeobachtet. Am Ort der stärksten Erdgaswirkung kam es im Vergleich mit der Kontrolle zu auffälligem Abfall der Reflektion im infraroten Bereich des Spektrums. Der Unterschied entstand und verstärkte sich allmählich im Verlauf der Vegetationsperiode mit steigendem Einfluss des Gases.

Die Deckungsgrad‐ und Dichtereduktion und Veränderungen in der Artenzusammensetzung (Rückgang der empfindlichen Arten) können für cine allgemeine Folge der Erdgaswirkung auf Gesellschaftsebene gehalten werden. Die ersten Wirkungen wurden etwa 15–30 Tage nach Versuchsbeginn beobachtet, was etwa einer Menge von 80–150 m3Gas pro Parzelle entspricht.
Germination responses of buried seeds of Capsella bursa‐pastoris exposed to seasonal temperature changes
Authors: BASKIN J. M. , BASKIN Carol C.
Published: July 2006

Buried seeds of Capsella bursa‐pastoris exhibit an annual conditional dormancy/non‐dormancy cycle. Seeds after‐ripen during summer and remain non‐dormant during autumn and winter. Seeds enter conditional dormancy in early spring, first showing marked decreases in ability to germinate at high (35/20°C) and then at lower (30/15, 25/15°C) temperatures. Seeds do not lose the ability to germinate to high percentages at March (15/6°C) and April (20/10°C) temperatures in March and April. Thus, C. bursa‐pastoris is a facultative winter annual, germinating in both autumn and spring if seeds are exposed to light. However, because some seeds retain the ability to germinate at 30/15 and 25/15°C, they could do so throughout the growing season in regions with cool, moist summers. Conditional dormancy developed in all seeds given 12 weeks at 5°C and subsequently kept for 4 weeks each at March (15/6°C), April (20/10°C) and May (25/15°C) temperatures. Thus, seeds of C. bursa‐pastoris enter conditional dormancy as temperatures increase in spring.
Changes of weed seed bank parameters according to species, time and environment
Authors: CHAUVEL B. , GASQUEZ J. , DARMENCY H.
Published: July 2006

The soil seed bank of weeds was studied in two fields, The first was not treated with herbicides for nine years and had a high weed seed density. The second was treated every year and had a low weed seed density. A study of the probability distributions of the weed seed populations in the soil showed that they were aggregated and appeared to have the negative binomial distribution. Transformations were therefore used to normalize the original values in order to compare the distributions and amounts of different species at different times and locations. However, normalizations were possible only with species having an average of at least two seeds per core. With the normalized values, it was observed that some species had similar statistical distributions in the same field. However, the distribution of a species may vary throughout the field, in time, and according to herbicide and culture rotations.
Effects of flooding on rooting and sprouting of isolated stem segments and on plant growth of Paspalum distichum L.
Authors: HSIAO A. I. , HUANG W. Z.
Published: July 2006

Summary. Bud sprouting, shoot height, and fresh and dry weights of plants arising from single‐node stem segments of Paspalum distichum L. decreased as the depth of burial in the soil increased. Sprouting, rooting and shoot growth of single‐node segments submerged in 5–15 cm of water were reduced significantly in the dark. Light alleviated this water‐induced reduction in 1‐, 3‐ and 7‐node segments. Submergence actually promoted sprouting of the proximal bud and shoot growth from the distal bud in 3‐node segments, and shoot growth of the first two buds from the distal end in 7‐node segments, Flooding the roots of 3‐week ‐old plants for one month had no effect, but markedly reduced tiller production and dry weights after 2 and 3 months. Treatment at 100% relative humidity promoted new shoot production in 4‐month old plants only if all shoots were decapitated (clipped) but not in plants with 6 shoots left intact. Submergence of the whole plant in water drastically reduced new shoot production regardless of clipping treatment. Effects of flooding varied with its duration. It is concluded that though P. distichum, a wetland perennial weed, survives root flooding and submergence conditions, these conditions do not support maximum growth of the plants.
Soil catalysed hydrolysis of fluroxypyr‐methylheptyl ester
Authors: LEHMANN R. G. , MILLER J. R.
Published: July 2006

Summary. Fluroxypyr‐MHE (methylheptyl ester) was hydrolysed to fluroxypyr in soil/water suspensions at rates several thousand times that in distilled, deionized water at similar pH and temperature: the pH 7, 25°C half‐life in water was 454days, compared to 2, 5, and 5·5 hours in 1 : 100 soil/water suspensions of a Barnes loam, Catlin silt loam, and Mhoon clay. The catalysed hydrolysis did not occur in decanted, aqueous supernatants of centrifuged Barnes soil suspensions, nor in Barnes soil/water suspensions which had been autoclaved. In soils incubated (26·1°C) at field moist conditions, only 1 to 2% of the fluroxypyr‐MHE had not hydrolysed after three days. An extracellular enzyme was suggested as the catalyst.
Influence of thiobencarb on nitrate reductase, nitrite reductase and DCPIP photoreduction in rice and Echinochloa crus‐galli (L.) (barnyardgrass)
Authors: PRAKASH T. RAJENDRA , MURTHY R. S. , SWAMY P. M.
Published: July 2006

Summary. The influence of thiobencarb at 1500 ppm on levels of nitrate reductase, nitrite reductase and on 2,6‐dichlorophenolindophenol (DCPIP) photoreduction was studied in rice (Oryza sativa L.) and Echinochloa crus‐galli (L.) (barnyardgrass) to understand the different sensitivities of these two plants to the herbicide. The herbicide treatment did not cause appreciable inhibition of nitrate reductase and nitrite reductase in rice leaf sections. In barnyard grass, the treatment strongly lowered nitrite reductase activity. DCPIP photoreduction by isolated chloroplasts of the treated rice leaves was not greatly affected. On the other hand DCPIP photoreduction by both mesophyll and bundle sheath chloroplasts from treated barnyardgrass was inhibited by 70%. Herbicide caused accumulation of nitrite in treated barnyard grass leaves when compared to rice. Thiobencarb phytotoxicity to barnyard grass may be due to impairment of the Hill reaction that in turn caused accumulation of nitrite in the leaf tissue.
A method for controlling Hakea sericea Schrad. seedlings using the fungus Colletotrichum gloeosporioides (Penz.) Sacc
Authors: Morris M. J.
Published: July 2006

Summary. The shrub Hakea sericea Schrad. is a major weed in the southern and south‐western Cape Province of South Africa. A dried formulation on wheat bran of the fungus Colletotrichum gloeosporioides (Penz.) Sacc. was sprinkled onto plots of young H. sericea seedlings at three sites in the southwestern Cape Province. Following periods of rain, the fungus sporulated profusely on the bran and rain‐splash dispersal of conidia from the bran resulted in infection of seedlings which consequently died back from the stem tips. Applications of bran inoculum during early winter when seedlings were in the cotyledonary to 20‐leaf stage were more effective (93–98% mortality) than later applications (30–36% mortality).
Uptake and metabolism of hexazinone in Rubus hispidus L. and Pyrus melanocarpa (Michx.) Willd
Authors: JENSEN K. I. N. , KIMBALL E. R.
Published: July 2006

Rooted cuttings of Pyrus melanocarpa (Michx.) Willd. had a 3.5‐fold greater tolerance to soil‐applied hexazinone than those of Rubus hispidus L. in a greenhouse trial. R. hispidus accumulated four times more 14C‐label in the foliage following root uptake of 14C‐hexazinone than P. melano‐carpa. Here, the greater uptake and susceptibility of R. hispidus was related to its greater root:fol‐iage (weight) ratio compared to the tolerant P. melanocarpa. However, in whole plant metabolism studies employing younger plants there were no differences in 14C accumulation in the leaves. Here 14Chexazinone was converted to a number of hydroxylated and/or demethylated triazinone metabolites in both species following vacuum infiltration into leaf disks and root sections, or following root uptake in whole plants. A major difference in metabolism between the two species was the greater formation of the mono demethylated metabolite, B, [3‐cyclohexyl‐6‐methylamino‐l‐methyl‐l,3,5‐triazine‐2,4‐dione] in P. melanocarpa which may also contribute to its greater tolerance. A loss of total 14Clabel from all plant parts with time may reflect cleavage of the 14C‐ring‐labelled herbicide.
Effects of N, P and K on Striga asiatica (L.) Kuntze seed germination and infestation of sorghum
Authors: RAJU P. S. , OSMAN M. A. , SOMAN P. , PEACOCK J. M.
Published: July 2006

Sorghum (Sorghum bicolor (L.) Moench) plants were grown in pots with 12.5 and 50 mg applied N kg−1 soil. With an increase of soil N, the Striga asiatica (L.) Kuntze infestation, as well as the sorghum shoot dry matter losses due to infestation, decreased. The relative differences in stimulant capacity to induce Striga seed germination among the four sorghum genotypes were not consistent over the 0 to 150 mg N 1−1 range. The sorghum root exudate was considerably more active at 0 mg N 1−1, than at 30 mg N 1−1, and the stimulant produced at 150 mg N 1−1 failed to induce Striga seed germination. Presence of N in the growth medium considerably reduced the effectiveness of the stimulating substance produced by sorghum roots, whereas K promoted stimulant activity only in the absence of N. The presence or absence of P in the growth medium did not affect Striga seed germinability, probably due to the inability of this element to interfere with the production or activity of the stimulating substance from the host plants. It can be concluded, therefore, that sorghum plants seem to produce active root exudate only in conditions of N deficiency.
Competition between Silene vulgaris (Moench) Garcke and alfalfa (Medicago sativa L.)
Authors: WALL D. A. , MORRISON I. N.
Published: July 2006

Growth indices describing the nature of the competitive relationship between Silene vulgaris and alfalfa during crop establishment were determined from experiments conducted outdoors in southem Manitoba in 1986 and 1987. The results of the experiments indicated that alfalfa dry matter yields were influenced more by intra‐ than interspecific competition. In comparison S. vulgaris was affected more by interspecific competition. Replacement diagrams and aggressivity indices both demonstrated that alfalfa and S. vulgaris were the aggressor and sub‐ordinate species, respectively. Relative replacement rates for alfalfa versus S. vulgaris were significantly greater than unity, indicating that alfalfa exerted a greater replacement pressure on S. vulgaris than did S. vulgaris on alfalfa. Over time alfalfa could be expected to replace S. vulgaris as the dominant species within a population. Barley was more competitive than alfalfa with S. vulgaris. Not only was S. vulgaris shoot dry weight reduced more by barley than by alfalfa during the establishment year, but fewer S. vulgaris seedlings emerged the following year in plots that had been seeded to barley than in those that had been seeded to alfalfa.
Environmental factors affecting the herbicidal activity of DPX‐A7881
Authors: BUCHANAN F. S. , GILLESPIE T. J. , SWANTON C. J.
Published: July 2006

DPX‐A7881, methyl 2‐[(4‐ethoxy‐6‐methyl‐amino‐1, 3, 5‐triazin‐2‐yl)carbamoylsulphanoyl] benzoate, is a sulfonylurea herbicide being developed in Canada and Europe for post‐emergence broadleaf weed control in spring and winter rapeseed. Growth room studies were conducted to determine the environmental factors affecting the herbicidal activity of DPX‐A7881 applied post‐emergence on winter rapeseed (Brassica napusu L. ‘Tandem’) and on a closely related weed species, Sinapis arvensis L. (wild mustard).

Laboratory tests were carried out at tempera tures ranging from 2–26°C, at relative humidities from near 40% to >95%, with rain‐free periods from 0.25–8 h after herbicide application, at soil moisture contents from 50–200% of field capacity, and with irradiances from 23–450 μEm−2s−1 Significant control of S. arvensis was demonstrated for all treatments except under poor growing conditions at the lowest temperatures and irradiances tested. After two weeks' exposure to each of the tem perature treatments, the herbicide maintained control of S. arvensis during a subsequent week of favourable growing conditions. Relative humidity, soil moisture or simulated rainfall did not significantly alter the herbicidal activity of DPX‐A7881 on S. arvensis. DPX‐A7881 showed a high degree of crop safety on B. napus. The herbicide did not significantly reduce the dry weights of B. napus grown under any of the environmental conditions tested.
A simple model of crop loss by weed competition from early observations on relative leaf area of the weeds
Authors: KROPFF M. J. , SPITTERS C. J. T.
Published: July 2006

A new simple empirical model for early prediction of crop losses by weed competition was introduced. This model relates yield loss to relative leaf area of the weeds shortly after crop emergence using the relative damage coefficient q as the single model parameter. The model is derived from the hyperbolic yield density relationship and therefore accounts for the effects of weed density. It is shown that the model also accounts for the effect of different relative times of weed emergence. A strong advantage of the approach is that it can be used when weeds emerge in separate flushes.

The regression model described experimental data on sugar‐beet – lambsquarters (Beta vulgaris L. –Chenopodium album L.) and maize‐barnyard grass (Zea mays L. –Echinochloa crus‐galli L.) competition precisely. The model describes a single relationship between crop yield loss and relative leaf area of the weeds over a wide range of weed densities and relative times of weed emergence. Possibilities for scientific and practical application of the model are discussed.
Attempts to transfer paraquat resistance from barley grass (Hordeum glaucum Steud.) to barley and wheat
Authors: ISLAM A.K.M.R. , POWLES S.B.
Published: July 2006

A paraquat‐resistant biotype of barley grass (Hordeum glaucum Steud.) was hybridized with barley and wheat in an attempt to transfer paraquat resistance to these crops. Although hybridizations with barley did not result in the production of a plant, cytological evidence of chromosome elimination of one parent, presumably of H. glaucum, was obtained from squash preparations of young F1 embryos. Hybridizations of wheat with both diploid and tetraploid H. glaucum resulted in the production of wheat haploids. These results indicate that it may not be possible to transfer paraquat resistance to barley and wheat using conventional hybridization techniques.
The activity and mobility of triasulfuron in soil as influenced by organic matter, duration, amount and frequency of rain
Authors: OPPONG F. K. , SAGAR G.R.
Published: July 2006

Summary: Résumé: Zusammenfassung

The influence of different levels of organic matter and of the duration, amount and frequency of rainfall on the biological activity and mobility of triasulfuron were investigated. Biological activity was inversely related to the organic matter content of the soil. Movement of the herbicide down the soil profile, assessed by bioassay, was inversely related to the organic matter content of the soil, and the amount and frequency of rain directly influenced the extent of leaching of the herbicide. Triasulfuron was moved to a depth of at least 22.5 cm when soil columns were exposed to a total of 528 mm of natural rainfall over a period of 6 months. The presence of phytotoxic levels of the herbicide in the surface layers of soil columns 6 months after exposure to outdoor temperatures and natural rainfall suggested that triasulfuron may persist in soils for relatively long periods.

Influence de la matiére organique, et de la durée, niveau et fréquence des précipitations sur l'activité et la mobilité du triasulfuron dans le sol

L'influence de différentes teneurs en matière organique et de la durée, quantité et fréquence des pluies sur l'activité biologique et la mobilité du triasulfuron a étéétudiée. L'activité biologique est inversement liée avec la teneur enmatière organique du sol. Le mouvement descendant de l'herbicide dans le profil du sol, estimé par bio essai, est inversement lié avec la teneur en matière organique du sol, et la quantité et la fréquence des pluies influencent directement l'importance de la lixiviation de l'herbicide. Le triasulfuron s'est déplacé jusqu'à une profondeur d'au moins 22,5 cm quand les colonnes de sols ont été exposées à un total de 52,8 cm de pluies naturelles sur une période de 6 mois. La présence de taux phytotoxiques d'herbicide dans les couches superficielles des colonnes de sol 6 mois après l'exposition aux températures extérieures et aux précipitations naturelles montre que le triasulfuron peut persister dans 1s sols pendant des périodes relativement longues.

Einfluβ der organischen Substanz des Bodens sowie der Niederschlagsdauer, ‐menge und ‐frequenz auf Persistenz und Mobilität von Triasulfuron im Boden

Die biologische Aktivität sowie die Verlagerung von Triasulfuron im Boden, mit Biotests bestimmt, waren umgekehrt proportional zum Gehalt an organischer Substanz. Die Regenmenge sowie ‐frequenz beeinflußten die Einwaschung des Herbizids direkt. Bei insgesamt 528 mm natürlichem Niederschlag innerhalb 6 Monaten wurde Triasulfuron in Bodensäulen mindestens 22,5 cm tief eingewaschen. Aus dem Vorhandensein phytotoxischer Mengen des Wirkstoffs in den oberen Schichten der Bodensäulen nach 6 Monaten unter Freilandbedingungen wurde auf relativ hohe Persistenz im Boden geschlossen.
Effect of hypoxia on buried weed seed germination
Authors: BENVENUTI S. , MACCHIA M.
Published: July 2006

Trials were carried out in order to investigate the effect of hypoxia on seed germination of Datura stramonium L. in Petri dishes and when buried at various depths in soil. Hypoxia was found to cause a decrease in germination capacity and germination rate. This inhibition was partially alleviated by daily exchange of hypoxic gas surrounding the seeds during incubation. Similarly, seed scarification allowed maintenance of a higher germination capacity under conditions of low oxygen availability, showing that the seed coat was only partially gas permeable. Oxygen deficiency led to a decrease in respiratory capacity. However, this was probably compensated for by induction of fermentation metabolism. The possibility of removing the final products of fermentation exerts a decisive influence on seed germination, especially in an environment such as soil, where their diffusion into the surrounding environment is restricted. Thus daily nitrogen flushing partially eliminated this inhibition, even under conditions of low external oxygen availability. It was therefore postulated that the main depth–derived inhibition was not caused directly by oxygen deficiency but by the increasing difficulty in eliminating toxic fermentation products, which was found to be proportional to the degree of hypoxia. Finally, incubation for several days under completely anaerobic conditions induced secondary dormancy. This was probably due to an ecological adaptation mechanism that prevents germination under conditions that are unfavourable for survival.
The effect of temperature on sprouting and early establishment of Cynodon dactylon
Authors: SATORRE E. H. , RIZZO F. A. , ARIAS S. P.
Published: July 2006

Bud‐sprouting dynamics, sprouting base temperature and reserve mobilization of rhizomes and stolons of Cynodon dactylon (L.) Pers. were characterized in a laboratory experiment under dark conditions. In addition, the dynamics of sprout emergence were determined during 2 years under field conditions. In the laboratory experiment, buds from the vegetative structures did not sprout at temperatures below 7^C. The rate of sprouting increased with temperature within the range 11–33^C, and a base temperature of 7.71^C was determined for bud sprouting of rhizome and stolons of the weed. An exponential model is proposed relating the percentage of sprout emergence in the field to accumulated thermal units, calculated as the sum of the daily mean air temperature above the base temperature of bud sprouting. This model satisfactorily predicted the dynamics of C. dactylon sprout emergence in sunflower (Helianthus annuus L.) crop fields. The efficiency of carbohydrate reserve use during sprout growth was highly dependent on temperature and type of vegetative structure The efficiency was maximum at 20^C and was higher for rhizomes than for stolons. The main factors influencing bud sprouting and early weed establishment are discussed.
The potential for selecting wheat varieties strongly competitive against weeds
Authors: LEMERLE D. , VERBEEK B. , COUSENS R.D. , COOMBES N E
Published: July 2006

The competitive abilities of a wide range of genotypes of wheat (Trilicvm aestivum L.) and durum wheat (Triticum durum Desf.) against Lolium rigidum Gaud, (annual ryegrass) were examined 1o determine the potential for breeders to select strongly competitive varieties, Considerable potential within the wheat genome to breed varieties with greater competitive ability was demonstrated. In 1993, 250 genotypes from around the world were screened and in 1994 a subset of 45 (mainly Australian) genotypes were further examined. A uniform density of L. rigidum reduced grain yield of wheat by up to about 80% in 1993 and to 50% in 1994, depending on wheat genotype. Reduction in grain yield was correlated with L. rigidum dry matter. Wheats varied in competitive ability with source, and durum wheats were less competitive than T. aestivum. The ‘old’ standard wheat varieties (released between 1880 and 1950) suppressed the weed more than all the current varieties, with the exception of eight F1 hybrids. A doubling of the crop seeding rate of 10 of the genotypes in 1994 reduced the biomass of L. rigidum by an average of 25% compared with the standard seeding rate. Ranking of competitive ability of varieties at high density was consistent at both seeding rates. The strongly competitive genotypes had high early biomass accumulation, large numbers of tillers, and were tall with extensive leaf display. The potential for breeding enhanced competitive ability in wheat is discussed.
Precision of soil seedbank sampling: how many soil cores?
Authors: DESSAINT F. , BARRALIS G. , CAIXINHAS M.L. , MAYOR J.‐P. , RECASENS J. , ZANIN G.
Published: July 2006

A prerequisite for a precise estimate of the abundance of weed seeds in sou is prior knowledge of sampling variability, Based on an analysis of EWRS working group trials, it is shown that the sampling variance (s2) of seed counts increases with the sampling mean (S2) and can be predicted with the logarithmic form of Taylor's power law: log10(sz)=a+b log10(x̄). This relationship is constant over time for means greater than 0.1 seeds per core within each of the five different sites studied (temporal variability) but differs slightly among sites (geographical variability). An attempt is made to use a general s2 : x̄ relationship to predict the number of samples as a function of precision and density.
Prediction of Heteranthera reniformis competition with flooded rice using day–degrees
Authors: FERRERO A.
Published: July 2006

In field studies carried out in 1992 and 1993, several durations of growth of Heteranthera reniformis Ruitz et Pavon were established in flooded rice (Oryza sativa L.) to evaluate weed influence on crop yield using day‐degree predictive models for weed growth. H. reniformis was allowed to emerge at 7‐day intervals from rice emergence until 49 days later. Weeds that emerged with the rice accumulated 403 day‐degrees during the first 49 days. Weeds allowed to utilize 308 day‐degrees had a dry weight reduction of 20% compared with plants that emerged with the rice. With the loss of all 403 day‐degrees dry weight was reduced by about 95%. Maximum leaf area index (LAI) was 2.8, reached at 308 day‐degrees. Weed density ranged from 48 to 5 plants m‐2 when all 403 day‐degrees were accumulated or lost by the plant respectively. When the weed lost only 95 day‐degrees out of the possible 403 (1 week's delay in emergence) rice yield was 34% and 39% lower in 1992 and 1993 respectively. When the weed was allowed to accumulate ail 403 day‐degrees yield reduction reached 62% in 1992 and 68% in 1993, very similar to the control plot, which were maintained weedy throughout (64% and 70.5%). After an accumulation of 403 day‐degrees the weed reduced the number of rice panicles by 45% in 1992 and 38% in 1993.
Basal cell carcinoma in outdoor versus indoor workers in Turkey
Authors: Dogan Gursoy
Published: July 2006

Background  Basal cell carcinoma remains a significant health problem, and is most common in people of Caucasian origin with significant sun exposure. This study investigated differences between two groups of Turkish patients with basal cell carcinoma: indoor workers versus outdoor workers.

Methods  One hundred and twenty‐one patients with primary basal cell carcinoma were categorized as outdoor (Group OW) or indoor workers (Group IW), according to sun exposure at work. Findings for age, sex, skin type, tumor location, and histologic subtype/aggression were compared.

Results  The mean age of Group IW was lower than that of Group OW (57.3 ± 9.2 vs. 65.8 ± 12.2 years, respectively). Group OW comprised more men than women (63.4% vs. 36.6%, respectively), whereas women predominated in Group IW (62% vs. 38%, respectively). The facial cheek was a more frequent tumor site in Group IW than in Group OW (20% vs. 7.0%, respectively). There were no statistical differences with respect to skin types or histological subtypes; however, Group OW had a higher proportion of aggressive subtypes than Group IW (25.4% vs. 10%, respectively).

Conclusions  The results in the Turkish population of the study suggest that basal cell carcinoma may develop in indoor workers (intermittent sun exposure) earlier than in outdoor workers with chronic sun‐exposure, but more aggressive subtypes are more likely to be linked with chronic sun‐exposure.
Temporal structure of an ant community in semi‐arid Australia
Authors: BRIESE D. T. , MACAULEY B. J.
Published: July 2006

The activity of five seed‐harvesting and ten non‐harvesting species of ants was examined over a 2‐year period. The ant community appeared to be stable in the long term, but there was considerable variability in the numbers and species of ants active at any one time, both on a seasonal and diel basis. Only four species were active throughout the year, with activity reduced in winter. Two species were consistently nocturnal, nine were mainly diurnal, and the remaining four species switched from diurnal to more nocturnal activity with increasing temperatures.

The changes in the diurnal pattern and intensity of foraging activity were shown to be controlled by several climatic and biotic variables. These were classed as either ‘stimulatory‐inhibitory’ which determined whether activity would occur or not, or ‘regulatory’, which set the physical limits to activity and controlled foraging intensity. Factors such as forage availability and colony satiation were placed in the first category, and soil temperature, moisture stress and light intensity were placed in the second.

There was no simple response to the combination of variables, and individual species responded differently to the various factors. The resulting temporal separation probably reduces competitive interactions between species.
The functional response of a predatory mite and the nature of the attack rate
Authors: LONGSTAFF BARRY C.
Published: July 2006

The assumptions of the Random Predator equation are discussed and the problems associated with parameter estimation and prediction are pointed out.

Experiments are described in which the functional response characteristics of a mesostigmatid mite Pergamasus crassipes, preying upon a collembolan, Onycbiurus armatus, were observed over four successive time intervals. In a series of separate experiments the handling‐time, Th, was estimated directly.

A modification of the random predator equation is proposed in which a searching time sub‐model is incorporated. Predictions from this model suggest that the attack rate is not a constant but is a function of prey density. An attack rate sub model is formulated and the resultant functional response model is shown to be more accurate and more readily usable for prediction than the random predator equation.
An appraisal of techniques for the study of litter decomposition in eucalypt forests
Authors: WOODS P. V. , RAISON R. J.
Published: July 2006

The merits of methods which have been or could be used to estimate the rate of decomposition of litter in eucalypt forests are discussed, and recommendations are given for their improved application. Since each method has serious limitations, several approaches need to be combined in most studies for conclusions to be drawn with confidence.

Suitable methods for studying the loss of weight of litter as it decays include the use of mesh bags, the tethering of leaves, the measurement of respiration rate, and the temporal comparison of inputs of litter with changes in accumulated litter. Where the litter can be aged with some confidence (e.g. after afire) and where grazing by litter invertebrates is low, the loss of weight per unit of leaf area is a useful index of the decomposition rate of leaves in situ. For study of the pattern of nutrient release from litter the most promising method is the collection and analysis of litter leachate. Fresh, naturally shed litter should usually be used in studies which require measurements on a selected sample. Green foliage picked from branches normally has a much higher nutrient content and decomposes more rapidly than leaves which are naturally abscissed.

Difficulty in identifying and thus measuring the weight of the incorporated component (mull‐type humus) of accumulated litter, and the likely absence of steady‐state quantities of accumulated litter because of widespread fires, seriously hinder both the estimation and application of decomposition constants (k) in Australian eucalypt forests.

Based on limited available evidence, initial rates of litter decomposition (e.g. as measured in litterbags over a 12–18 month period) should not be extrapolated to predict long‐term rates of decomposition.

In several eucalypt forests, the major release of organically bound nutrients does not occur until litter has undergone several years of decay, and probably occurs after some fragmentation and incorporation of litter into the surface soil. Much more information is needed on these processes, including the role of C: element ratio, litter fauna, changed microclimate as litter is incorporated, and the influence of plant roots on mineralization processes.
Relationship of litterfall to basal area and climatic variables in cool temperate forests of southern Tasmania
Authors: TURNBULL C. R. A. , MADDEN J. L.
Published: July 2006

Components of litter accession were measured for 2 years in two re growth eucalypt stands, a Nothofagus mixed forest, and a tall shrubland in the temperate forests of southern Tasmania. Total annual litterfall (t ha‐1) ranged from 4.77 to 5.64 in the regrowth eucalypt stands and 4.06 to 4.94 and 1.95 to 2.17 in the Nothofagus mixed forest and tall shrubland, respectively.

Significant correlations were found between annual litterfall of individual tree species and their respective basal area measured at 1.3 m height.

The seasonal patterns of litterfall were most closely related to mean maximum temperatures. However, fall of non‐leaf material was also related to gale force winds associated with the spring equinox.
Vegetation and nesting preferences of black noddies at Masthead Island, Great Barrier Reef. I Patterns at the macro‐scale
Authors: DALE P. , HULSMAN K. , JAHNKE B. R. , DALE M.
Published: July 2006

Vegetation types on Masthead Island. Great Barrier Reef were analysed and related to the distribution and abundance of nests of black noddies, Anous minutus. Vegetation attributes used in the analysis were tree species in height classes for each replicated sample. A classification program based on information statistics was used to group the vegetation into four main types. These were the coastal Casuarina forest, low Pisonia forest. medium Pisonia forests and the tall Pisonia forest. The Casuarina forest was characterized by Casuarina trees in all height classes and by the paucity of other tree species. The Pisonia forests were dominated by Pisonia trees and were differentiated by the height of these and by the associated species and their heights. We suggest that the variety of species and heights associated with each type is related to stages in a succession process. The uneven distribution in time and space of disturbance is reflected in the patchy distribution of each of the Pisonia forests. Disturbances are probably initiated by wind damage to the vegetation.

Noddies prefer to nest in specific vegetation types. Highest nest densities occurred in the medium Pisonia forests, especially where Pisonia trees were only > 6–8 m tall and were associated with Ficus, Celtis and Pipturus. Taller Pisonia forests in which Ficus and Celtis occurred also had fairly high nest densities. Since these Pisonia forests appear to be regenerating following damage, we suggest that noddy nesting is also related to disturbance. The paucity of nests in the low Pisonia forest implies that noddies avoid areas of recent disturbance, probably because suitable nest sites are scarce.
Biomass and nutrient changes in the herbaceous layer of two central Australian mulga shrublands after unusually high rainfall
Authors: FRIEDEL M. H.
Published: July 2006

The amount of standing plant material in the ground storey and its botanical composition are compared for two central Australian mulga communities, one with a predominantly annual understorey and the other with a predominantly perennial understorey. Amounts of litter and nutrient levels in standing plant material, litter and soils are also compared.

The number of species, particularly forbs, was greater in the annual community and differences in botanical composition are unlikely to have been caused by cattle grazing. The differences may be attributable in part to the greater proximity of the annual community to sources of alluvial material, and thus to better supplies of nutrients.

For the 13 1/2 month study period following exceptional summer rain, the weight of herbage in the perennial community generally exceeded that in the annual community, whereas the weight of litter was less in the perennial community. Of a large number of plant and soil nutrients, phosphorus, calcium and magnesium were lower in the perennial community; these three nutrients, together with nitrogen, may be deficient for either plant growth or cattle diet in that community. The amount of sulphur was lower in the annual community but was unlikely to be deficient.
Life table analysis of leaf fall in Tasmanian cool temperate forests
Authors: MADDEN J. L. , TURNBULL C. R. A.
Published: July 2006

The annual leaf fall of three species of cool temperate forest trees was examined for two different consecutive seasons at two localities in Tasmania. The reverse summation of the sequential fall of leaves throughout an annual cycle provided a population biomass that was amenable to life table analyses.

Rates of leaf fall were compared between species at different times, and were related to temperature. The threshold temperature for leaf fall to commence was approximately 11–12°C. Estimates of the probability of leaves remaining on trees at different times through the cycle were also obtained.
Leaf demography of the rainforest shrub Wilkiea macrophylla and its implications for the ecology of foliicolous lichens
Authors: ROGERS R. W. , BARNES A.
Published: July 2006

A population of leaves of the rainforest shrub Wilkiea macrophylla was studied for a period of 3 years. Survival curves for three subsamples were constructed. The estimated proportion of leaves initiated during the study that survived for the length of the study period (1150 days) was 79.7% and, by extrapolating in time, their mean half life was estimated to be 6.8 years. Those leaves present at the inception of the programmes but without lichen cover at that time, showed 80.1% survival over the subsequent 1150 days, whereas only 55.2% of those with lichen cover survived for 1150 days. Leaf growth and fall was concentrated in the period September‐December, suggesting cool temperate affinities. Leaves of W. macrophylla are so long‐lived that it cannot be assumed that foliicolous lichens are ruderals: only comparative studies will establish their nature.
Plant species richness in the mallee region of Western Australia
Authors: VAN DER MOEZEL PAUL G. , BELL DAVID T.
Published: July 2006

Sixteen sites (area 1000 m2) within the mallee region of southern Western Australia were sampled for vascular plant species richness. Species richness ranged from 17 species per 1000m2 in a Halosarcia syncarpa salt‐complex site and a Eucalyptus occidentalis tree mallee site, up to 48 species per 1000 m2 in a Eucalyptus angulosa‐Eucalyptus tetragona shrub mallee site. Woodland, woodland/mallee and mallee sites consisted mainly of perennial species while shrubland sites and salt‐complex sites had a higher percentage of ephemeral species. Sites with the highest species richness occurred on soils with the lowest nutrient content. Sites with lowest species numbers were those with severe habitat conditions or where better nutrient conditions may have provided the dominants with a competitive advantage to suppress associated species.
Soil and litter respiration in rainforests of contrasting nutrient status and physiognomic structure near Lake Eacham, north‐east Queensland
Authors: MAGGS JOHN , HEWETT BOB
Published: July 2006

Soil and litter respiration and nutrient concentrations (N, P, Ca, Mg and K) were measured in two adjacent rainforests near Lake Eacham on the Atherton Tableland in north‐east Queensland. One forest had soil formed on basalt and, in physiognomic‐structural classification of Webb (1968, 1978), was structurally complex. The other had soil formed on metamorphic rock and was structurally simple. Respiration was measured by the alkali trap method on 16 monthly occasions in 1986 and 1987.

Soil and litter nutrient concentrations were higher in the complex forest (with the exception of soil N). The relative differences were greater for soil than litter and more pronounced for P and Ca (and also soil Mg) than other nutrients. Litter polyphenol concentrations were lower in the complex forest.

Rates of litter respiration in the complex forest were, on average, nearly twice those of the simple forest. Soil respiration rates were occasionally slightly lower in the complex forest during the wet season but did not differ between the forests during the dry season. Highest rates of respiration were measured during the wet season although high rates for litter occasionally occurred during the dry season. Cumulative CO2release from the soil and overlying litter did not differ between forests and averaged 5134 ± 96 g CO2m‐2per year (mean ± s.e.m.) (1400 g C m‐2per year). Litter respiration accounted for 14% of the annual release in the complex forest and 11% in the simple forest.

The association between site nutrient status and forest physiognomic structure at Lake Eacham represents a more general pattern in rainforests of north‐east Queensland. Further study is needed to ascertain whether the results from this study apply more generally in both primary and secondary rainforests.
Disturbing hard and soft bottom communities: A comparison of marine and freshwater environments
Authors: LAKE P. S.
Published: July 2006

For communities of intertidal rock surfaces, inshore soft sediments and streams, disturbance is regarded as an important community‐structuring force. Care needs to be taken in defining disturbance to avoid confusion with other processes such as predation. In the environments discussed, there have been many descriptive studies of disturbance and relatively few experimental studies. The latter have yielded interesting insights. Disturbance generates patches and thus may alter the outcome of biotic interactions, especially competition, by providing refuges for poor competitors and beleaguered prey. Between the three environments, colonization and succession differ — a difference no doubt related to the proportion of mobile versus sedentary biota in each environment. In succession on hard intertidal surfaces inhibition appears to be most important, whereas facilitation is dominant on soft sediments and tolerance is the most plausible mechanism of succession in streams. Across the three environments there are some striking similarities in the colonization dynamics of the mobile fauna. Disturbance is a key part of several hypotheses proposed to explain the regulation of community diversity, and for communities in the environments examined none of the hypotheses has been found to have general application.
Species abundance and habitat differences in biomass of subterranean termites (Isoptera) in the wheatbelt of Western Australia
Authors: ABENSPERG‐TRAUN MAX , DE BOER EGBERT S.
Published: July 2006

The distribution and abundance, and habitat differences in biomass of subterranean termites, were assessed through soil trenching for woodland, mallee and heath habitats in the central wheatbelt of Western Australia. Over an 11 month sampling period, there were no significant habitat differences in biomass. Mean dry biomass in the surficial layer of soil (per 5000 cm3) averaged 46 mg in woodland, 28 mg in mallee, and 23 mg in heath. Termite biomass peaked in September, with 141 mg for woodland, 83 mg for mallee and 47 mg for heath (per 5000 cm3). Soil moisture and termite activity near the surface were positively correlated. A total of 36 species of termites, comprising 11 genera, were identified, and species abundance within and across habitats differed significantly.