ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11579977

出版商:Blackwell Publishing    

年代:1980

数据来源: WILEY

摘要:

Abstract.Alternating temperatures stimulate the germination ofRumex crispusL. andRumex obtusifoliusL. The optimum period spent at the lower temperature in a diurnal cycle is greater than that spent at the higher temperature. Under most conditions the optimum period at the upper temperatures is about 8 h but, as the upper temperature of a cycle is increased, the optimum period at the upper temperature becomes shorter and more critical. Thus when it is 35°C the optimum period is 2.5–4 h in the light, or about 1 h in the dark. The effect of alternating temperatures is much less in the dark than in the light and in general only extreme alternations with short periods at the higher temperature are effective in the dark. In the light any temperature alternation within the range 1–35°C is effective to at least some extent, providing the temperature difference is 5°C or more and providing the alternation includes one temperature which is above approximately 15°C and one which is below approximately 25°C. The optimum temperature difference is about 15°C. In the light, 4 to 10 cycles saturate the response, but in the dark, where the effect is much less, the response may not be saturated even by 16 cycles. KNO3at 10−3M has little effect on the response to alternating temperatures either in the light or the dark. The response to alternating temperature regimes does not appear to vary in quality, i.e., in terms of which particular treatments are best, but it varies in magnitude with site and year of seed collection; and it increases slowly during dry storage, even when stored at a temperature as l

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11580392

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract.Stomatal conductances (gs) were measured on the leaves of 3–4 year old Golden Delicious trees and of seedlings of two other cultivars. Measurements were made on container grown trees in the field with a diffusion porometer in 1975 and 1976, and in controlled conditions in a leaf chamber in the laboratory in 1976. Stomatal densities in the Golden Delicious leaves were assessed from scanning electron micrographs. Stomatal density on extension shoot leaves was higher than on other leaf types after June.The response to irradiance shown by both the porometer and the leaf chamber results could be described by a rectangular hyperbola:wheregmaxis maximum conductance and β indicates the sensitivity of gsto photon influx density (Qp). The values of β were in the range 60–90 μmol m−2s−1.There was no evidence that apple stomata are sensitive to temperature per se, butgswas reduced by increasing leaf to air vapour pressure deficits (D). There was a linear relationship betweengsandDwhich was not attributable to feed‐back to leaf water potential (ψL) as the latter did not affectgsuntil a threshold of about −2.0 to −2.5 MPa was reached. Conductance generally declined with increasing ambient

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11580397

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract.An empirical model of stomatal response to environmental factors was developed from measurements of stomatal conductance (gs) made in a leaf chamber under controlled conditions. Results presented in a companion paper (Warrit, Landsberg&Thorpe, 1980) indicated that the model could be written in terms of only two factors, photon flux density (Qp) and leaf to air vapour pressure gradient (D). The response ofQpwas hyperbolic and that toDlinear; combining these the equation of the model iswheregris a reference conductance, α is the slope of the response toDand β indicates the sensitivity ofgsresponse toQp. Values of α were 0.20 and 0.30 kPa−1in June and August; the corresponding values of β were 59 and 79 μmol m−2s−1.The model was tested against mean values ofgsobtained with a porometer in the field, using environmental measurements as inputs. Correspondence between measured and calculated values was good. Transpiration rates were calculated from the Penman‐Monteith equation, with stomatal resistance values calculated from the model, and compared with gravimetric measurements of tree water use. It was shown that transpiration could be calculated with acceptable accuracy. The effects of variations in stomatal resistance on transpiration rates under a range of conditions were explored using the model and the Penman‐ Mon

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11580508

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract.Transpiration rates from apple leaves are analysed in terms of the ratio of latent heat flux (λE) to leaf net radiation (Q1) and the climatological resistance (ri). Increases in stomatal resistance with increasing leaf to air vapour pressure gradient (D), described by an empirical model, are incorporated in the analysis. This humidity effect causes the proportion of energy dissipated as latent heat to fall asQ1increases, so that leaf transpiration rates in high energy environments are likely to be similar to those in lower energy environments. Boundary layer resistance (ra) exerts an increasingly important effect on transpiration rates asQ1increases. At constantQ1stomatal closure in response to increasingDresults in very small changes in leaf temperature (T1) across a wide range of ambient vapour pressure deficits (δe);rais then the major factor determiningT1. The implications of these results are discusse

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11580512

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract.The tribe Phaseoleae, of the sub‐family Papi‐lionoideae of the Leguminosae shows distinct differences from the tribes Vicieae and Trifolieae in nodule morphology and anatomy. Nodules of the Phaseoleae have determinate growth as, at maturity, the vascular strands fuse at the apex forming, effectively, a closed loop of the root stele. Nodules of the Vicieae and Trifolieae have an apical meristem, hence indeterminate growth; one or more branches of the root stele enter and dichotomise within the nodule, new elements are differentiated in relation to nodule growth, and the fine branches are free at the apical end of the nodule. Nodules of the Vicieae and Trifolieae additionally have vascular transfer cells and vacuolate infected cells, and the rhizobial bacteroids are pleomorphic.The principal export products of nitrogen fixing nodules of the Phaseoleae are the ureides allantoin and allantoic acid, whilst those of the Vicieae and Trifolieae are amides and amino acids, especially glutamine and asparagine. The advantages and disadvantages of these export products are discussed in the light of nodular vascular anatomy and in respect of the tropical/subtropical origin of the Phaseoleae and the temperate origin of the Vicieae and Trifoli

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11580516

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract.A proposal has recently been made (Johnson&Tasker, 1979) that phytochrome acts through the multiplicative effect of two components of the phytochrome system, only one of them beingPfrand the other a product of the photoconversion reactionPr→Pfr. It has been shown previously that HIR action spectra based on this assumption show a good resemblance to the observed responses with the possible exception of the red region of the spectrum. There, a greater response is predicted than is often observed and fluence rate dependency is predicted, on which matter there is disagreement in the literature.The experiments reported here show that, because chlorophyll is formed in red light but not in far‐red, chlorophyll screening lowers theeffectivefluence rate in red light with respect to phytochrome. When such screening is eliminated the observed responses show strong fluence rate dependency, as predicted. Evidence is also presented to support the conclusion that the two proposed effectors must act together multiplicativ

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11580522

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract.The apparent resistance to diffusion of water vapour presented by a set of holes in a calibration plate when measured by a commercial porometer depended on materials previously measured in the sensor head of the instrument. The data reported show the variation in apparent resistance of a set of holes with a specified value of 13.7 s cm−1after a leaf of small resistance, a set of holes with a specified resistance of 3.75 s cm−1, or a hydrophobic membrane had been in the sensor head and the effect of covering the foam seal around the mouth of the cup with aluminium foil. It was concluded that the results were profoundly affected by the history of water vapour accumulation and release from the foam seal which could give rise to biased readings both during calibration and in measurements of leaf resistance and might also explain much of the scatter when calibration data obtained at different times were pooled for the calculation of a calibration equation. Reliable estimates of resistance over the effective range of the instrument cannot be expected unless this transfer of water vapour between the seal and the cup is preven

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11580549

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract.Azetidine 2‐carboxylic acid inhibits ion release to the xylem and exudation from excised barley roots. This inhibition is not accompanied by reduction in hydraulic conductivity showing that the action of azetidine 2‐carboxylic acid is on ion movement across the root to the xy

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11580560

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY