摘要:

Abstract.Juvenile seedlings, micropropagated plantlets, and adult rooted cuttings ofPinus radiata, together with seedlings ofAgathis australisandDacrydium cupressinum, were grown under either high (670/μmol m−2s−1) or low (200 μmol m−2s−1) photosynthetic photon flux density (PPFD) and, at low PPFD, under three red:far‐red (R/FR) conditions, approximately simulating canopy shadelight, daylight and one intermediate value. In all types ofP. radiata, a shade‐intolerant species, stem height and diameter, stem and needle dry weight, and apical dominance were markedly increased by a reduction in R:FR ratio while fascicle density was decreased. In contrast, these increases were considerably less for the shade‐tolerantD. cupressinumand moderately tolerantA. australis.With the exception of theP. radiataseedlings, height growth was greatest in all species under high compared to low PPFD for daylight R:FR ratio conditions. Total shoot (or plant) dry weight was increased approximately two‐fold in all species and types by the higher PPFD. Shoot extension rates were negatively correlated with calculated phytochrome photoequilibrium withP. radiata, the most shade‐intolerant species, having the highest change in rate per unit change in photoequilibrium (i.e. very responsive), andD. cupressinum, the most shade tolerant species evaluated, having the smallest change (i.e. largely unresponsive). Within the spectral quality treatments at low PPFD, it is suggested that higher rates of dry matter accumulation under the low R:FR ratio were the result of reduced mutual shading of adjacent leaves as a consequence of photomorphogenically‐controlled internode lengths rather than of enhanced photosynthesisper se.The significance of the results is discussed in relation to planting stock management in nurseries, the management of forest canopies for understorey seedling growth, and to the construction of representative growth simulation models. Consequences for controlled environment lightin

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01951.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract.The half time (t1/2) of the reduction of P‐700+in the millisecond time frame is known to be limited by the reaction between plastoquinol and the cytochrome cytb6f complex. This is considered to be the rate limiting reaction of thylakoid electron transport and measurements of it provide a means of analysing how thylakoid election transport is regulatedin vivo.The half time for the reduction of photochemically oxidized P‐700 has been measuredin vivousing absorbance changes around 820 nm. The results showed that t1/2is independent of irradiance and decreases as photosynthetic induction progresses. Even with a constant t1/2the quantum efficiency of PSI declined as irradiance increased. The significance of the concept of photosynthetic control of electron transport is discussed in the light of these observati

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01952.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract.The physics of ultrasonic acoustic emissions (AEs) was investigated for AE transmission through wood and transducers. The physical properties measured were velocity, attenuation and frequency composition of AEs produced by two sources: cavitation events in xylem and pencil lead breaks. The authors also measured the relative sensitivity of various combinations of ultrasound transducers and amplifiers to aid in the selection of a measuring system optimized for cavitation detection in woody plants. Some of the authors' conclusions are: (1) Softwoods (Thuja, Pinus) attenuate AEs more rapidly than hardwoods (maple, birch). (2) The velocity of AEs in wood exceeds that measured by others in water so the main medium of AE transmission must be the cellulose. (3) The strongest frequencies of AEs are in the range of 100–300 kHz. (4) Cavitation‐induced AEs tend to shift to higher frequency as wood dehydration progresses. (5) One cannot determine the locus of origin of AEs from its frequency composition. (6) The frequency composition of the acoustic emissions probably cannot be determinedat allwith the sensors used because of their tendency to ‘ring’. The data collected in this paper were used to aid in the design of an improved AE counter having a seven‐fold increase in signal to noise ratio compared to counters previously used in our laboratory. The improved counter, model 4615 Drought Stress Monitor, is now commercially available from Physical Acoustics Corp., Princeton,

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01953.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract.Auxin and ethylene both enhance cell elongation in intact petioles of the semi‐aquatic plantsRegnellidium diphyllumandNymphoides peltata.The authors now show that auxin but not ethylene increases thein vitroextensibility of cell walls. No response to ethylene occurs in auxin‐depleted tissue. Neither hormone regulates cell expansion by direct control of internal osmolality (OS). During growth of segments, OS (and hence turgor) declines rapidly over the first 5–6 h with a net loss of osmotic solutes. Thereafter, an apparent threshold OS is maintained with net gains in osmostic solutes (Nymphoides) or further net losses (Regnellidium). Although wall extensibility determines initial rates of hormone‐induced cell expansion, the primary control of wall loosening appears to differ in the two species.Nymphoidesshows typical ‘acid growth’, and fusicoccin, auxin and ethylene (with auxin) all enhance proton secretion. InRegnellidium, neither low pH nor fusicoccin (FC) alters the rate of cell expansion, although proton secretion is stimulated by FC. Stress relaxation studies using low pH treatment of living or frozen‐thawed segments show increases in the extensibility of wallsin vitroforNymphoidesbut not forRegnellidium.The authors propose that extensibility may be controlled by wall pH inNymphoidesbut the availability of effective wall‐loosening sites determines extensibility

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01954.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract.The only published consideration of product removal from the soybean root nodule hypothesizes that the peripheral xylem circuit of this determinate nodule structure is flushed by the transpiration stream. However, dyes fed to the transpiration stream through a cut root distal to the nodule do not enter the nodule, and the observed movement of radio‐tracers from the root into the nodule can be explained by simple diffusion, Also, there are few xylem elements in the nodule, and these elements are of a small diameter, such that this path can not act as a functional loop of the root system. Further, in this study, nodule vascular strands were never observed to be continuous about the nodule, but were observed to end at the nodule tip in a loop within an intact, closed endodermal sac. Nodule vascular tissue was invested in a pericycle of at least three cell layers. These cells are suggested to be active in the loading of the xylem apoplast with ureides, such that the xylem of the nodule always operates in an export role. Nodule water requirements may be suppliedviathe phloem or the root cortex apoplas

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01955.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract.The present study investigates the relationships between nitrogen uptake, transpiration, and carbon assimilation. Plants growing on nutrient solution were enclosed for 10–16 d in a growth chamber, where temperature, photon flux density, vapour saturation deficit and CO2concentration were controlled. One of these factors was modified every 4 to 5 d. Shoot photosynthesis and root and shoot respiration were recorded every half‐hour. Nitrogen uptake from the root medium and plant transpiration were measured daily. In most cases, an increase in photon flux density led to increases in transpiration, net daily carbon assimilation, and nitrogen uptake. By modifying transpiration rate without changing photosynthesis (varying vapour saturation deficit), or by modifying transpiration and carbon assimilation in opposite ways (varying CO2air concentration), it was shown that nitrogen uptake does not follow transpiration, but is linked to the carbon uptake of the plant. When light was increased from low to intermediate levels, the N uptake/C assimilation ratio remained constant. At higher photon flux density, this ratio declined markedly. It is proposed that in the first case, growth is limited by carbohydrate availability, thus any increase in carbon assimilation leads to a proportional increase in nitrogen uptake, in contrast to the second situation where carbohydrates may accumulate in the plant without further nitrogen requirem

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01956.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract.The effect of nitrate supply upon leaf area development in willow (Salix viminalis) was investigated. Rooted cuttings were grown in culture solution at two different rates of exponentially‐increasing nitrate supply and with free access to other nutrients. During the lag‐phase in attaining stable nutrition, the rate of production of unfolded leaves, in the treatment with poorer N‐supply, decreased. After acclimation to the different N‐availabilities, the rate of dry matter increase per plant nitrogen was constant and the same in both treatments. The ratio of total leaf area to total amount of nitrogen in the plant was slightly higher in the treatment with poorer nitrogen supply. During the exponential (stable) phases of growth, nearly all the increase in total leaf area was attributable to main‐stem leaves; large numbers of leaves on axillary shoots in the treatment with better N‐supply contributed little to the total area. During the stable growth phase, the rate of production of unfolded leaves was the same in both treatments. Higher maximum values of relative rate of increase in area of single leaves were found with a better N‐supply and at higher leaf positions on the main stem. The duration of leaf expansion was not much affected by N‐supply. Final leaf size was greater at higher positions on the main‐stem. Within a treatment (investigated for poorer N‐supply), differences in final leaf size were proportional to differences in numbers of epidermal cells. Final leaf size was greater, at the same node, in the treatment with better N‐supply. Better N‐availability had increased the final size but not the number of epidermal cells. It was concluded that the higher exponential rate of total area increase with a better N‐supply was largely associated with higher rates of exp

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01957.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract.The ability of a plant to survive severe water deficits depends on its ability to restrict water loss through the leaf epidermis after stomata attain minimum aperture. At this stage, the rate of water loss is regulated by the epidermal conductance (gc). Low gcwould be a useful selection criterion to identify genotypes with enhanced survival capability. Consequently, variation in gcamongSorghum bicolor(L.) Moench genotypes was evaluated. Since there is little conclusive evidence linkinggcwith leaf waxiness, alternative hypotheses relatinggcto stomatal trails were also examined. Epidermal conductance varied from 6.3 to 17.6mmol m−2s−1among sorghum genotypes. It was unrelated to stomatal pore length which varied with genotype and to pore depth which was similar for all genotypes measured. However,gc, increased with increasing stomatal density. This indicates that stomatal density plays a direct role in water loss even at very low conductances. The association of low stomatal density with lowgcis consistent with the hypothesis that at the smallest stomata aperture, water loss from the epidermis above guard cell teichodes becomes a significant source of leaf water loss. Since lowgcis directly related to crop survival under severe water deficits, it is recommended that genotypes with lowgc. be selected using the selection criterion of stomatal dens

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01958.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract.Submergence stimulates growth of the petioles ofRumex palustrisandRumex crispusunder field, greenhouse and laboratory conditions. Growth ofRumex acetosapetioles was hardly influenced by submergence. These growth responses under flooded conditions can be partially mimicked by exposing non‐submergedRumexplants to ethylene‐air mixtures. Submergence of intact plants in a solution of AgNO3inhibited the elongation of all petioles ofR. palustrisand the youngest petiole ofR. crispusand stimulated growth of the youngest petiole ofR. acetosa, The ethylene‐air mixture experiments, the effect of AgNO3and observed increase of the endogenous ethylene concentration during submergence suggest that ethylene plays a regulatory role in the growth responses of theseRumexspecies under submerged conditions. The threeRumexspecies showed a gradient in elongation responses to submergence, which correlates with the field distribution of the three species in a flooding gra

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01959.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract.Wall‐yield threshold pressures of growing leaves obtained from field‐grown soybean (Glycine max[L.] Merr.) plants were measured in vapour pressure psychrometers. The plants were grown either under well‐watered or water deficit conditions. Wall‐yield threshold pressures were measured at night when turgor pressure was expected to exceed the wall‐yield threshold pressure both in drought‐stressed and well‐watered growing leaves. Wall‐yield threshold pressure increased as the area of the growing leaves increased in both treatments. After an 8‐d drought, wall‐yield threshold pressure in leaves which had recently emerged from the meristem was 0.50 MPa, while in well‐watered leaves these values ranged from 0.03 to 0.23 MPa. Upon release from drought, wall‐yield threshold pressure rapidly return

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01960.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY