Water deficits at anthesis reduce CO(2) assimilation and yield of lychee (Litchi chinensis Sonn.) trees     

Menzel CM  Oosthuizen JH  Roe DJ  Doogan VJ 《Tree physiology》1995,15(9):611-617

Ten-year-old 'Tai So' lychee (Litchi chinensis Sonn.) trees growing on a sandy loam soil in subtropical South Africa (latitude 25 degrees S) were watered weekly (well-watered treatment) or droughted from late July until January (drought treatment). After 16 weeks, at which time the trees obtained most of their water from below 150 cm, average soil water content at 0 to 150 cm depth was 14.5 +/- 0.1% in the well-watered treatment and reached a minimum of 7.6% in the drought treatment. At Week 7, minimum leaf water potential (Psi(L)) in the morning and early afternoon declined to -2.6 and -2.8 MPa, respectively, in droughted trees compared with -1.5 and -2.2 MPa, respectively, in well-watered trees. From Week 9, stomatal conductance and net CO(2) assimilation rate ranged from 70 to 300 mmol m(-2) s(-1) and 3 to 13 micro mol CO(2) m(-2) s(-1), respectively, in well-watered trees. The corresponding values for droughted trees were 50 to 180 mmol m(-2) s(-1) and 2 to 6 micro mol CO(2) m(-2) s(-1). Five weeks after rewatering the droughted trees, gas exchange had not recovered to the rate in well-watered trees, although tree water status recovered within a week of rewatering. In the well-watered trees, water use (E(t)) was 26 +/- 1 mm week(-1) with evaporation (E(p)) of 20 to 70 mm week(-1) indicating a crop factor (k(c) = E(t)/E(p)) of 0.4 to 1.2. Before anthesis, tree water status did not affect extension growth of floral panicles or leafy shoots. In contrast, no vegetative shoots were initiated after fruit set in the droughted trees when Psi(L) in the morning declined to -2.5 MPa. Water deficits reduced initial fruit set by 30% and final fruit set by 70% as a result of fruit splitting (41.2 +/- 4.0% versus 10.0 +/- 1.3%). Water deficits did not alter the sigmoidal pattern of fruit growth, but reduced yield from 51.4 +/- 5.5 kg tree(-1) in well-watered trees to 7.4 +/- 3.3 kg tree(-1) in droughted trees.  相似文献   

Shoot development,chlorophyll, gas exchange and carbohydrates in lychee seedlings (Litchi chinensis)     

Hieke S  Menzel CM  Lüdders P 《Tree physiology》2002,22(13):947-953

Shoot growth, chlorophyll concentrations, gas exchange and starch concentrations were studied in lychee (Litchi chinensis Sonn.) seedlings of cultivar "Wai Chee" grown in a heated greenhouse at Nambour in subtropical Australia (27 degrees S). We also examined the effects of shoot defoliation and root pruning on leaf expansion. Shoot growth showed a rhythmic cycle under constant greenhouse conditions, with a mean duration of flushing of 20 days and an interval of 10 days over three cycles. Shoots and leaves expanded in a sigmoidal pattern to about 80 mm and 500 cm(2), respectively, for each flush. Starch concentrations of the lower stem and roots decreased as the young red leaves expanded, and increased as the fully expanded leaves turned dark green. Chlorophyll concentrations and net CO(2) assimilation rate were highest in the fully expanded dark green leaves. Removing 50% of the area of each fully expanded leaf had little effect on the expansion of younger leaves, but total biomass of defoliated plants was only 60% of that of controls. In contrast, removing half the roots just before bud swelling reduced final leaf area by 80%. We conclude that the young shoot has relatively low rates of photoassimilation until the leaves are fully expanded and dark green, and depends on assimilates from elsewhere in the plant. During leaf expansion, translocation of assimilates to the shoot occurred at the expense of the roots.  相似文献   

Selection of Food by Size in the Chimpanzee,and Comparison with Human Judgments     

Menzel EW 《Science (New York, N.Y.)》1960,131(3412):1527-1528

Adult chimpanzees, given access to an array of pieces of banana, select the pieces in order of size, larger pieces being taken first. Selection is mediated by perceived sizes, and the responses correspond closely to human visual judgment of size.  相似文献   

EPA air pollution standard     

Menzel DB 《Science (New York, N.Y.)》1979,203(4380):500-501

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Giant Friedel Oscillations on the Beryllium(0001) Surface     

PT Sprunger  L Petersen  EW Plummer  E Laegsgaard  F Besenbacher 《Science (New York, N.Y.)》1997,275(5307):1764-1767

Large-amplitude electron density oscillations were observed on a Be(0001) surface by means of variable-temperature scanning tunneling microscopy. Fourier transforms of the images showed a ring of radius 2kF, where kF is the Fermi wave vector of the Be(0001) surface state. This wavelength was expected from Friedel oscillations caused by electronic screening of surface defects, but the amplitude of the waves for energies near the Fermi energy was anomalously large and inconsistent with the Friedel concept of screening. The enhanced amplitude of the waves must be a many-body effect, either in the electron gas (possibly an incipient charge density wave) or in the response of the lattice (electron-phonon coupling).  相似文献   

Homing in the ant Cataglyphis bicolor     

R Wehner  R Menzel 《Science (New York, N.Y.)》1969,164(876):192-194

Cataglyphis bicolor, an ant widely distributed in North Africa and the Near East, orient to the sun as well as to visual patterns of the environment. These two mechanisms can be separated. Foraging ants (hunters) orient to terrestrial cues as long as possible, and only after these have become ineffective do they switch over to the menotactical sun orientation. In the digging individuals, however, the visual knowledge of locality is significantly inferior to that of the hunters. Diggers vary considerably in size, but hunters belong to the largest size group. In addition, the largest and smallest individuals orient differently toward black and white areas and stripe patterns.  相似文献   

The Trouble with Medical Journals - by Richard Smith     

Richard EW Halliwell 《Veterinary dermatology》2008,19(4):240-241

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Selenium values in animal feeds. I. Methods and normal values     

E Wiesner  F Berschneider  K Neuffer  M Menzel 《Archives of Animal Nutrition》1974,24(7-8):601-610

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Not the one,but the only one: about <Emphasis Type="Italic">Cannabis cryptic virus</Emphasis> in plants showing ‘hemp streak’ disease symptoms     

Laura Righetti  Roberta Paris  Claudio Ratti  Matteo Calassanzio  Chiara Onofri  Davide Calzolari  Wulf Menzel  Dennis Knierim  Gianmaria Magagnini  Daniela Pacifico  Gianpaolo Grassi 《European journal of plant pathology / European Foundation for Plant Pathology》2018,150(3):575-588

Interveinal chlorosis and leaf margin wrinkling are widespread symptoms of Cannabis sativa. They are traditionally attributed to the so-called hemp streak virus (HSV), but its existence has not been demonstrated yet. To our knowledge, no molecular investigation has so far been performed in order to identify the causal agent of this symptomatology, we therefore decided to use traditional and molecular virology techniques to better characterize symptoms and pursue the etiological agent. No pathogenic virus was found by using targeted PCR reactions and by RNA sequencing, whereas we were able to detect the Cannabis cryptic virus (CanCV) with both techniques. We, therefore, developed an RT-qPCR assay based on a CanCV-specific TaqMan probe and applied it to a wide range of symptomatic and symptomless plants, using a two-step (for quantification), or a one-step (for fast detection) protocol. Both symptoms and the virus were only shown to be transmitted vertically and did not pass via mechanical inoculation or grafting, though we could not find any cause-effect correlation between them. In fact, the virus was found in all the tested hemp samples, and its abundance varied greatly between different accessions and individuals, independently from the presence and severity of symptoms. The suggestion that hemp streak is caused by a virus is therefore questioned. Some abiotic stresses seem to play a role in triggering the symptoms but this aspect needs further investigation. For breeding purposes, a selection of parental plants based on the absence of symptoms proved to be efficient in containment of the disease.  相似文献   

Elevational response in leaf and xylem phenology reveals different prolongation of growing period of common beech and Norway spruce under warming conditions in the Bavarian Alps     

Christina Kraus  Christian Zang  Annette Menzel 《European Journal of Forest Research》2016,135(6):1011-1023

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