Possibilities for soilless cultivation in cut chrysanthemum: Effect of irrigation frequencies and spacing schedules

Three levels of irrigation frequencies, provided by root misting, combined with three plant densities and two spacing treatments were tested to evaluate the optimum conditions during the first crop stages of chrysanthemum in a soilless cultivation system (aeroponics) in an experiment conducted in autumn. The optimum misting frequency was 3¿2’ times ¿ min h-1. A higher frequency (12¿1’) had no additional effect, whereas the lowest frequency (1¿6’) had a negative effect on total shoot dry mass (TDMs). The highest plant densities (172 and 344 plants m-2) could be used until week 2 with hardly any negative effect on TDMs, and resulted in higher light interception and higher total shoot dry mass per m2. During the period between week 2 and 4 after planting, a higher density (172 compared to 86 plants m-2) had a strong negative impact on the TDMs, while a further increase to 344 plants m-2 had only a minor effect. When spacing (week 2) from 344 to 172 plants m-2, TDMs at week 4 was not negatively affected by the high starting density, though spacing from 172 to 86 plants m-2 resulted in a 13% reduced TDMs, as compared to plants grown at 86 plants m-2 continuously. It is concluded that the irrigation frequency until week 4 after planting under these light conditions, should be three times per hour. Furthermore, very high plant densities (e.g., 344 plants m-2) are feasible until week 2 with hardly any negative effects on plant growth, while spacing schemes give several possibilities for a smaller reduction of the TDMs, than that expected by the higher initial densities

Genotypic variation of cut chrysanthemum response to high CO2 concentration: Growth, time to flowering and visual quality

In this study sixteen cut chrysanthemum cultivars were used to evaluate the effects of high CO2 concentration (1500 µmol mol-1) on growth, time to flowering and visual quality as compared to the concentration used in commercial greenhouses (600 µmol mol-1). CO2 enrichment increased light use efficiency (11-41%) and total plant dry mass (TDM) (5-40%) in a cultivar dependent manner. This TDM increase was a result of: (i) higher relative growth rate during the long day period (i.e., 0 to 2 weeks; LD); and (ii) higher absolute growth rate both during the period between 2 to 6 weeks (SD1), and 6 weeks to final harvest (SD2). Cultivar differences in TDM at flowering between the two CO2 concentrations could be explained by differences in growth rate during the LD and SD2 periods. Furthermore, growing at high CO2 regime enhanced the number of flowers and flower buds per plant (NoF, 4-48%). Interestingly, the cultivars that showed the highest percentage of TDM increase, with CO2 enrichment, were not the ones that had the highest increase in the percentage of NoF. In contrast, high CO2 concentration had only a minor or no effect on the number of internodes on the main stem and on the reaction time in all the cultivars examined. From this research it is concluded that there is a large variation in the response of cut chrysanthemum cultivars to CO2 enrichment, in terms of TDM and NoF, which gives possibilities for breeding

Effect of Relative Air Himidity on the Stomatal Functionality in Fully Developed Leaves

Several studies have shown that stomata developed under long-term high relative air humidity (RH =85%) are malfunctional, resulting in a poor control of water loss. Yet, little is known about the dynamics of stomatal adaptation to moderate RH, and the possibilities to improve or reverse the destabilized stomatal responsiveness. In this study, a reciprocal transfer experiment was conducted in climate chambers using Rosa hybrida ‘Prophyta’, grown at moderate RH (60%) or at high RH (90%). The adaptation of fully developed leaves to the new RH environment was assessed at day 0, 4, 8 and 12 after plant transfer by measuring the transpiration rate in detached leaves. Stomata fully developed at high RH had a lower closing capacity in response to a decrease in leaf Relative Water Content (RWC) (i.e. water loss was considerably high at RWC below 20%, whereas in moderate RH stomata the water loss almost ceased at 57% RWC). Furthermore, stomata developed at high RH did not become functional after 12 days of cultivation at moderate RH. Similarly, stomata developed at moderate RH and transferred to high RH for a 12 day period did not loose their ability to close in response to desiccation. This indicates that stomatal functionality is determined during leaf development, while after this period stomata have a limited capacity to adapt to new RH environment. It is concluded that stomata from fully developed rose leaves conserve their behaviour independently of the post-development humidity leve

Stomatal response characteristics as affected by long-term elevated humidity levels

Restriction of leaf water loss, by stomatal closure, is decisive for plant survival, especially under conditions of water deficit. This sensitivity of stomata to low water potential is attenuated by high relative air humidity (RH ≥ 85%) during growth, which impedes the plant’s ability to survive when subsequently exposed to lower humidities due to a negative water balance. This thesis focuses on the extent of the existing variation and the reasons underlying cultivar differences in their tolerance to high RH, as well as the rate and reversibility of stomatal adaptation to elevated RH in the course of leaf ontogeny. Cut rose was used as a model plant. An experiment on the postharvest water relations of three contrasting cultivars in their sensitivity to high RH showed that the sensitive cultivar (i.e. steepest decrease in the cut flower longevity) underwent a higher increase in the water loss compared to the tolerant cultivars. Preventing vascular occlusion considerably extended the time to wilting in the sensitive cultivar grown at high RH, showing that the high rate of water loss, as a result of plant growth at high RH, can only be detrimental for keeping quality under limiting water uptake conditions. Further investigation showed a large genotypic variation in the regulation of water loss, as a result of leaf development at high RH, and stomatal closing capacity was the key element in this process. The degree to which the stomatal anatomical features were affected and the extent that their functionality was impaired were not correlated. However, higher stomatal density, longer pore length and depth contributed to the higher water loss of high RH-grown leaves (16–30% of the effect depending on the cultivar). Reciprocal change in RH showed that stomatal functioning was no longer affected by the RH level after full leaf expansion. However, expanding leaves were always able to partly adapt to the new RH level. For leaves that started expanding at high RH but completed their expansion after transfer to moderate RH, the earlier this switch took place the better the regulation of leaf water loss. This behaviour of expanding leaves experiencing a shift from high to moderate RH was related with the increasing population of stomata exceeding a critical stomatal length. Contrary to this, leaves initially expanding at moderate RH and transferred to high RH exhibited poor stomatal functioning, even when this transfer occurred very late during leaf expansion. This suggests that stomata at various developmental stages were similarly prone to loss of closing ability, when these had been exposed to high RH prior to full leaf expansion. Key words: abscisic acid, cuticular permeability, heterogeneity, hydraulic conductivity, pore aperture, relative air humidity, Rosa hybrida, stomatal anatomy, stomatal conductance, stomatal growth, stomatal initiation, stomatal malfunctioning, stomatal population, stomatal proximity, vase life. </p

Evaluation of the creep coefficients of international concrete creep prediction models

Abstract: Creep of concrete is an important design consideration. National design codes therefore provide empirically based models for the estimation of creep deformation. Such models estimate a creep coefficient (φ) and an elastic modulus (E) of the concrete, both of which are used to predict the creep strain at any age. This paper assesses the accuracy of the creep coefficients (φ) predicted by fourteen “design code-type" models, with a view to ascertain whether the estimated φ or E is responsible for the inaccuracy of some of the models. The models considered are those contained in SANS 10100 (2000)/BS 8110 (1985), SANS 10100 (2000) Modified, ACI 209 (1992), AS 3600 (2001 & 2009), CEB-FIP (1970, 1978 & 1990), the Eurocode EC (2004), Gardener and Lockman (2000 & 2004), Gardener and Zhao (1993) and the RILEM B3 (1995) methods. Laboratory creep tests were conducted on concrete prisms covering a range of mixes. The measured φ values were statistically compared to those predicted by the models considered. The results indicated that, for the range of concretes tested, the CEB-FIP (1990) method yielded the most accurate predictions of creep coefficient, giving the lowest overall coefficient of variation (all) of 27,7 %. The least accurate method was the CEB-FIP (1978) which yielded an overall coefficient of variation (all) of 112,5 %. Furthermore, the accuracy of the predicted φ values correlated highly significantly (P = 0,001 %) with the accuracy of the predicted creep magnitudes. The results of this investigation led to recommending the SANS 10100 (2000)/ BS 8110 (1985) model for predicting creep coefficients for South African conditions

Accurate Estimation of the Trilinear Gauge Couplings Using Optimal Observables Including Detector Effects

This paper describes the definition of maximum likelihood equivalent estimators of the Trilinear Gauge Couplings which include detector effects. The asymptotic properties of these estimators as well as their unbiasedness and efficiency when dealing with finite statistical samples are demonstrated by Monte Carlo experimentation, using simulated events corresponding to the production of q qbar lepton neutrino in e+ e- collisions at 172 GeV. Emphasis is given to the determination of the expected efficiencies in extracting the aWphi, aW and aBphi couplings from LEPII data, which in this particular case found to be close to the maximum possible.Comment: 32 pages, 12 figures, Late

Evaluation of the creep coefficients of the fib 2010 and RILEM B4 concrete creep prediction models

Abstract: Creep of concrete is an important design consideration. National design codes therefore provide empirical based models for the estimation of creep deformation. Such models generally estimate a creep coefficient () and an elastic modulus (E) of the concrete, both of which are used to predict the creep strain at any age. This paper assesses the accuracy of the creep coefficients () predicted by the relatively new international fib Model Code 2010 (MC 2010) and RILEM Model B4 using a laboratory test programme. The measured creep coefficient () values were statistically compared to those predicted by the models considered. The MC 2010 (2012) Model, which yielded an overall coefficient of variation (ωall) of 44.9 %, was found to be more accurate than the RILEM Model B4 (with a (ωall) of 103.3 %). Both the models validated were found to yield less accurate creep coefficients than their respective predecessor models

A Method to include Detector Effects in Estimators sensitive to the Trilinear Gauge Couplings

This paper describes the use of weighted Monte Carlo events to accurately approximate integrals of functions of the experimentally measured kinematical vectors and their dependence on physical parameters. This technique is demonstrated in estimating the evolution of cross sections, efficiencies, measured kinematical distributions and mean values as functions of the Trilinear Gauge Couplings.Comment: 20 pages, 10 figures, Late