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891.
Diagnosis of light leaf spot (Pyrenopeziza brassicae) on winter oilseed rape (Brassica napus) in the UK 总被引:1,自引:0,他引:1
B D L FITT K J DOUGHTY P. GLADDERS J M STEED K G SUTHERLAND 《The Annals of applied biology》1998,133(2):155-166
Light leaf spot lesions were generally first observed as light green areas on leaves of UK winter oilseed rape crops in January or February and later became brittle and bleached. Elongated lesions, which were brown with indistinct edges, developed on stems in the spring and summer, when lesions were also observed on flower buds, pedicels and pods. Development of diagnostic white pustules (spore masses of Pyrenopeziza brassicae, which erupt through surfaces of infected tissues) for confirmation of light leaf spot infection on symptomless plants or plants with indistinct or ambiguous symptoms in the autumn, winter or spring was enhanced by incubating plants in polyethylene bags. In experiments with artificially inoculated plants, glasshouse-grown plants exposed in infected crops and plants sampled from crops, white pustules developed at all incubation temperatures from 2oC to 20oC on infected leaves of different cultivars. The period of incubation required before the appearance of pustules decreased as the time that had already elapsed since the initial infection increased. The longest periods of incubation were required at the lowest temperatures (2oC or 5oC) but leaves senesced and abscised from plants most quickly at the highest temperatures (15oC or 20oC), suggesting that the optimal incubation temperature was between 10oC and 15oC. 相似文献
892.
Rainbow trout were exposed (90 days) in synthetic soft water to sublethal low pH (5.2) and a simulated climate warming scenario (+2°C above the control summer temperature range of 16.5–21° C), alone and in combination, under conditions of limited food (∼4% dry body weight day−1 ). Weight specific oxygen consumption rates ( M o2 ) were ∼55% of M o2(max) , in contrast to ∼75% of M o2(max) found in trout fed an unlimited ration. This is likely due to a reduction in food quantity and thus feeding activity. However, the trout exposed to low pH at control temperatures exhibited higher conversion efficiencies and increased growth. In contrast, trout exposed to +2°C had reduced growth rates. No ionoregulatory disturbance occurred in any treatment, suggesting that this ration was sufficient to provide a replacement salt load in the diet. Energy budgets indicated that the limited ration resulted in a lowered optimum temperature for growth, with a greater proportion of the energy intake dissipated for metabolic expenditure, resulting in reduced conversion efficiencies. A fourfold reduction in faecal and unaccounted energy losses indicated higher absorption efficiencies than in satiation-fed trout. 相似文献
893.
Habitat choice in shoals of roach as a function of water temperature and feeding rate 总被引:2,自引:0,他引:2
Temperature and food availability are two important factors which affect fish growth and therefore are expected to influence habitat choice in fish. In this study, shoals of 16 juvenile roach, Rutilus rutilus , were given a choice between two chambers that differed in temperature by 1·5°C or 3°C whereas food availability was the same in both chambers (ratio 1 : 1) or higher in the colder one (ratio 4 : 1). The number of fish in each chamber was recorded for 10 min each during a pre-feeding, feeding and post-feeding period. Roach generally preferred the warmer over the colder chamber during the pre-feeding periods. Temperature had a significant effect on the distribution of fish during all three time periods whereas food availability was a significant factor only during the feeding period. The important role of temperature was emphasized further by the fact that a relatively small difference in the temperature gradient of 1·5°C had a stronger effect on fish distribution than a four times higher feeding rate during the feeding period. The implications for growth rates of such short-term decision-making of roach are discussed. 相似文献
894.
S. T. Szedlmayer 《Journal of fish biology》1998,53(1):58-65
For wild red snapper Lutjanus campechanus , mean otolith increment deposition rate after marking with oxytetracycline dihydrate (OTC) was daily (0.97 increments day−1 ) when growth rates were fast (0.63 mm fork length, L F day−1 ), but were not daily (0.82 increments day−1 ) when somatic growth was slow (0.2 mm L F day−1 ). For reared larvae ( n =8), increment deposition rates were daily (0.99–1.03 increments day−1 ), and growth rates ranged from 0.6 to 0.9 mm L F day−1 . Growth rate affected increment deposition rate as a threshold function, i.e. when growth rate was <0.3 mm L F day−1 , deposition was less than daily, but above this level increment deposition did not exceed a daily rate. As growth rates increased increment widths increased. Examination of a sub-sample ( n =8) of the otoliths from the slowest growing wild fish by scanning electron microscopy did not increase increment counts. Because L. campechanus are late spring-early summer spawners, young fish can expect maximum growth due to warm summer temperatures. Thus, daily ageing methods should be well suited to this species. 相似文献
895.
The contribution of indigenous arbuscular mycorrhizal fungi (AMF) to growth and phosphorus (P) uptake by oilseed flax (Linum usitatissimum L.) was examined in two field experiments covering soil P levels from 20–86 mg kg-1 NaHCO3-extractable P. The fumigant dazomet was applied to the soil in half of the plots to obtain control plants with reduced mycorrhiza formation. An extensive AMF colonization of up to 48% of the root length was established in untreated soil of both experiments, although P fertilization reduced colonization to 28–39% at the latest harvests. Fumigation markedly decreased or totally prevented AMF colonization throughout the experiments. Root growth responded to fumigation by increased total and specific root length. Shoot P uptake was decreased by fumigation at soil P levels lower than ca. 50 mg kg-1 whereas shoot growth was reduced by fumigation at soil P levels lower than ca. 40 mg kg-1. The effects of fumigation were ascribed to the suppression of mycorrhiza formation. The effect of the AMF increased with decreasing soil P levels. Phosphorus inflow through roots (based on shoot P uptake) was reduced more strongly by fumigation than total P uptake. The P inflow through fungal tissue in roots was estimated to 4 × 10-14 mol P cm-1 s-1. We conclude that AMF are essential to flax growth at soil P levels below ca. 40 mg P kg-1, which is representative of the conditions under which most flax is grown. 相似文献
896.
The response of soil microorganisms and roots to elevated CO2 and temperature in a terrestrial model ecosystem 总被引:11,自引:0,他引:11
Kandeler E. Tscherko D. Bardgett R.D. Hobbs P.J. Kampichler C. Jones T.H. 《Plant and Soil》1998,202(2):251-262
We investigate the response of soil microorganisms to atmospheric CO2 and temperature change within model terrestrial ecosystems in the Ecotron. The model communities consisted of four plant species (Cardamine hirsuta, Poa annua, Senecio vulgaris, Spergula arvensis), four herbivorous insect species (two aphids, a leaf-miner, and a whitefly) and their parasitoids, snails, earthworms, woodlice, soil-dwelling Collembola (springtails), nematodes and soil microorganisms (bacteria, fungi, mycorrhizae and Protista). In two successive experiments, the effects of elevated temperature (ambient plus 2 °C) at both ambient and elevated CO2 conditions (ambient plus 200 ppm) were investigated. A 40:60 sand:Surrey loam mixture with relatively low nutrient levels was used. Each experiment ran for 9 months and soil microbial biomass (Cmic and Nmic), soil microbial community (fungal and bacterial phospholipid fatty acids), basal respiration, and enzymes involved in the carbon cycling (xylanase, trehalase) were measured at depths of 0–2, 0–10 and 10–20 cm. In addition, root biomass and tissue C:N ratio were determined to provide information on the amount and quality of substrates for microbial growth.Elevated temperature under both ambient and elevated CO2 did not show consistent treatment effects. Elevation of air temperature at ambient CO2 induced an increase in Cmic of the 0–10 cm layer, while at elevated CO2 total phospholipid fatty acids (PLFA) increased after the third generation. The metabolic quotient qCO2 decreased at elevated temperature in the ambient CO2 run. Xylanase and trehalase showed no changes in both runs. Root biomass and C:N ratio were not influenced by elevated temperature in ambient CO2. In elevated CO2, however, elevated temperature reduced root biomass in the 0–10 cm and 30–40 cm layers and increased N content of roots in the deeper layers. The different response of root biomass and C:N ratio to elevated temperature may be caused by differences in the dynamics of root decomposition and/or in allocation patterns to coarse or fine roots (i.e. storage vs. resource capture functions). Overall, our data suggests that in soils of low nutrient availability, the effects of climate change on the soil microbial community and processes are likely to be minimal and largely unpredicatable. 相似文献
897.
Two forms of sustained xanthophyll cycle-dependent energy dissipation in overwintering Euonymus kiautschovicus 总被引:6,自引:3,他引:3
Seasonal differences in PSII efficiency (Fv/Fm), the conversion state of the xanthophyll cycle (Z + A)/ (V + A + Z), and leaf adenylate status were investigated in Euonymus kiautschovicus. On very cold days in winter, Fv/Fm assessed directly in the field remained low and Z + A high throughout day and night in both sun and shade leaves. Pre-dawn transfer of leaves from subfreezing temperatures in the field to room temperature revealed that recovery (increases in Fv/Fm and conversion of Z + A to violaxanthin) consisted of one, rapid phase in shade leaves, whereas in sun leaves a rapid phase was followed by a slow phase requiring days. The pre-dawn ATP/ADP ratio, as well as that determined at midday, was similar when comparing overwintering leaves with those sampled in the summer, although pre-dawn levels of ATP + ADP were elevated in all leaves during winter relative to summer. After a natural transition to warmer days during the winter, pre-dawn Fv/Fm and Z + A in shade leaves had returned to values typical for summer, whereas in sun leaves Fv/Fm and Z + A levels remained intermediate between the cold day in winter and the summer day. Thus two distinct forms of sustained (Z + A)-dependent energy dissipation were identified based upon their differing characteristics. The form that was sustained on cold days but relaxed rapidly upon warming occurred in all leaves and may result from maintenance of a low lumenal pH responsible for the nocturnal engagement of (Z + A)-dependent thermal dissipation exclusively on very cold days in the winter. The form that was sustained even upon warming and correlated with slow Z + A to violaxanthin conversion occurred only in sun leaves and may represent a sustained engagement of (Z + A)-dependent energy dissipation associated with an altered PSII protein composition. In the latter, warm-sustained form, uncoupler or cycloheximide infiltration had no effect on the slow phase of recovery, but lincomycin infiltration inhibited the slow increase in Fv/Fm and the conversion of Z + A to violaxanthin. 相似文献
898.
Light and temperature dependence of the emission of cyclic and acyclic monoterpenes from holm oak (Quercus ilex L.) leaves 总被引:4,自引:2,他引:2
In a laboratory study, we investigated the monoterpene emissions from Quercus ilex, an evergreen sclerophyllous Mediterranean oak species whose emissions are light dependent. We examined the light and temperature responses of individual monoterpenes emitted from leaves under various conditions, the effect of heat stress on emissions, and the emission-onset during leaf development. Emission rate increased 10-fold during leaf growth, with slight changes in the composition. At 30 °C and saturating light, the monoterpene emission rate from mature leaves averaged 4·1 nmol m–2 s–1, of which α-pinene, sabinene and β-pinene accounted for 85%. The light dependence of emission was similar for all monoterpenes: it resembled the light saturation curve of CO2 assimilation, although monoterpene emission continued in the dark. Temperature dependence differed among emitted compounds: most of them exhibited an exponential increase up to 35 °C, a maximum at 42 °C, and a slight decline at higher temperatures. However, the two acyclic isomers cis-β-ocimene and trans-β-ocimene were hardly detected below 35 °C, but their emission rates increased above this temperature as the emission rates of other compounds fell, so that total emission of monoterpenes exponentially increased from 5 to 45 °C. The ratio between ocimene isomers and other compounds increased with both absolute temperature and time of heat exposure. The light dependence of emission was insensitive to the temperature at which it was measured, and vice versa the temperature dependence was insensitive to the light regime. The results demonstrated that none of the models currently applied to simulate isoprene or monoterpene emissions correctly predicts the short-term effects of light and temperature on Q. ilex emissions. The percentage of fixed carbon lost immediately as monoterpenes ranged between 0·1 and 6·0% depending on temperature, but rose up to 20% when leaves were continuously exposed to temperatures between 40 and 45 °C. 相似文献
899.
金毛弓背蚁的巢穴结构、头宽频数分布及活动节律 总被引:2,自引:0,他引:2
对金毛弓背蚁Camponotus tonkinus Santschi的巢穴结构、工蚁头宽频数特征及巢外活动节律作了系统的观察和分析。发现金毛弓背蚁地下巢穴极为复杂,有纵横交错的通道系统和众多的小室,蚁后室位于巢穴底部,工蚁的头宽为连续性,范围在1.05-3.85mm,频数分布为不对称的单峰,头宽在1.4~2.Omm的个体最多,占总数的72.7%,晴朗天气里工蚁出入巢活动在上午和下午各有一个高峰,中午随温度升高金毛弓背蚁外出活动进入低谷. 相似文献
900.
Solvent exchange rates and temperature coefficients for Asn/Gln side-chain amide protons have been measured in Escherichia coli HPr. The protons of the eight side-chain amide groups (two Asn and six Gln) exhibit varying exchange rates which are slower than some of the fast exchanging backbone amide protons. Differences in exchange rates of the E and Z protons of the same side-chain amide group are obtained by measuring exchange rates at pH values > 8. An NOE between a side-chain amide proton and a bound water molecule was also observed. 相似文献