摘要:

Summary:Seed dormancy inSorghum halepenseis overcome by exposure to fluctuating temperatures and the effect is determined both by the diurnal amplitude and the maximum temperature. It was found that repeated cycles of particular regimes were additive, each cycle resulting in release from dormancy of a further proportion of the population. The range of regimes having this additive effect was wider in seeds which had after‐ripened in the soil during winter than in those which were freshly dispersed. The temperature‐dependent germination rate of seeds whose dormancy had been removed by the effect of fluctuating temperatures was analysed using a ‘thermal time’ approach, and estimates obtained of base and optimum temperatures and the required ‘thermal time’ for the germination of different fractions of the population. The results provide a basis for developing a model to predict seedling recruitment in the field using soil tempe

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1990.tb01690.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Summary:A mathematical model to predictSorghum hale‐penseseedling recruitment dynamics in relation to soil temperature was derived from the experimen‐tal results obtained in a previous investigation. The model is based on the assumption that soil temperature controls seedling recruitment ofS. halepenseby controlling release from dormancy and germination rate once dormancy breakage has been produced. The previous analysis sup‐plied mathematical functions to describe both the release from dormancy as controlled by tempera‐ture fluctuations, and the response to ‘thermal time’ after dormancy breakage. These relation‐ships were used in the construction of the model. This was tested against experimental field data with two differently aged seedbanks, in two seasons: spring and autumn. In each casein situgermination was monitored in plots with bare soil or soil surface shaded to simulate cover by a canopy. Soil temperature was recorded hourly and was used as an input of the model.A good description of seedling emergence dynamics in the field was obtained with the model, showing that seedling recruitment can be predicted using soil temperature data. The practi‐cal value of the developed mod

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1990.tb01691.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Zusammenfassung:In der vorliegenden Arbeit wurden 140 Ackerfláchen aus 7 Regionen Bayerns auf ihr Samenpotential und ihre Bodeneigenschaften untersucht. Dabei zeigte sich, daß die Samendichte eng mit Faktoren der Bodenökologie korreliert ist. So fanden sich in basischen Substraten zumeist niedrige, in schluffigen und sandigen Böden mit mäßig saurer Reaktion mittlere und in stark sauren Sanden hohe Samengehalte. Sehr hohe Samenkonzentrationen wurden außerdem in saisonal vemäßten Äckern festgestellt. Diese Ergebnisse lassen sich dadurch erklären, daß sich unter bestimmten Bodenverhältnissen charakteristische Artenkombinationen entwickeln. Über eine artspezifische Samenproduktion entsteht somit auch ein für den Standort typisches

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1990.tb01692.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Summary:The effects of concentrated sulphuric acid, dry heat, hot water and NaOCl treatments on the germinability of dormant large and small aerialCommelina benghalensisL. seeds were evaluated. Concentrated sulphuric acid and NaOCl treatments were more effective than the dry heat and hot water treatments in breaking the dormancy ofC. benghalensisaerial seeds. Treatments increased germination of both seed types due to its effect on the seed coat integrity. A scanning electron microscope revealed that changes as a result of scarification occurred in the hilum region of the seed and in the seed coat surface. The large aerial seeds were affected by all treatments more than the small aerial seeds. Difference in germinability between the two seed types was related to the difference in their seed vigour.

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1990.tb01693.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Summary:The effect of glyphosate on leaves and basal bulbs of yellow nutsedge (Cyperus esculentusL.) plants was studied. Treatment with glyphosate did not affect leaf anatomy, although light necrotic spots were seen on the veins. In contrast, basal bulb organization was greatly affected with large necrotic zones and disorganization in the vascular cylinder due to herbicide accumulation. Depletion or disappearance of vacuolar phenols was observed in bulbs of plants treated with the highest doses of glyphosate. The most remarkable effect of glyphosate was the appearance of one layer of sclerenchymatic cells between root and rhizome primordia and the cortical tissues which could play an important role in the inhibition of rhizome and root emergence by the herbicide.

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1990.tb01694.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Summary:The adsorption of atrazine and its transformation products, desisopropylatrazine (2‐chloro‐4‐ethylamino‐6‐amino‐l,3,5‐triazine), desethyl‐atrazine (2‐chloro‐4‐amino‐6‐isopropylamino‐l,3,5‐triazine) and hydroxyatrazine (2‐hydroxy‐4‐ethylamino‐6‐isopropylamino‐l,3,5‐triazine) to four top‐soils was measured. Adsorption coefficients decreased in the order hydroxy atrazine, atrazine, desisopropylatrazine, and desethyl‐atrazine: the distribution coefficient between organic matter and water (KOM) ranged from 40 to 100 dm3kg−1for atrazine, from 30 to 60 dm3kg−1for desisopropylatrazine, from 20 to 50 dm3kg−1for desethylatrazine and from 100 to 590 dm3kg−1for hydroxy atrazine.

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1990.tb01695.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Summary:An investigation was made into the resistance of some biotypes ofStellaria mediato mecoprop. Comparison of the sensitivity of five biotypes to foliar applications of mecoprop salt confirmed the presence of resistant and sensitive types and one of intermediate sensitivity. Applications of mecoprop through the roots of plants growing in nutrient culture were also more active on biotypes sensitive to foliar mecoprop, although the differences were less marked than they were with foliar treatments. Thus, possible differ ences in retention, uptake and translocation do not seem to be important causes of resistance. Consequently, it appears that resistance is associated with detoxification of mecoprop at the site of action. In two further experiments the cytochrome P450 mixed function oxidase inhibitor, 1‐aminobenzotdazole, had only a small effect on the susceptibility of resistantS. mediaplants to mecoprop. The importance of these data in the elucidation of the mechanism of resistance is discusse

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1990.tb01696.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Summary:Sorghum (Sorghum bicolor(L.) Moench) plants were grown in pots with 12.5 and 50 mg applied N kg−1soil. With an increase of soil N, theStriga asiatica(L.) Kuntze infestation, as well as the sorghum shoot dry matter losses due to infestation, decreased. The relative differences in stimulant capacity to induceStrigaseed germination among the four sorghum genotypes were not consistent over the 0 to 150 mg N 1−1range. 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 1−1failed to induceStrigaseed 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 affectStrigaseed 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 d

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1990.tb01697.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Summary:Growth indices describing the nature of the competitive relationship betweenSilene vulgarisand 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 comparisonS. vulgariswas affected more by interspecific competition. Replacement diagrams and aggressivity indices both demonstrated that alfalfa andS. vulgariswere the aggressor and sub‐ordinate species, respectively. Relative replacement rates for alfalfa versusS. vulgariswere significantly greater than unity, indicating that alfalfa exerted a greater replacement pressure onS. vulgaristhan didS. vulgarison alfalfa. Over time alfalfa could be expected to replaceS. vulgarisas the dominant species within a population. Barley was more competitive than alfalfa withS. vulgaris. Not only wasS. vulgarisshoot dry weight reduced more by barley than by alfalfa during the establishment year, but fewerS. vulgarisseedlings emerged the following year in plots that had been seeded to barley than in those that had been seeded to alfa

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1990.tb01698.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY