Raoul Lemeur

Effects of sucrose on starch accumulation and rate of photosynthesis in Rosa cultured in vitro

Shootlets of Rosa multiflora L. cv. Montse were cultured in vitro with four different levels of sucrose (0, 1, 3 and 5%). Chloroplasts of shootlets grown in a medium without sucrose contained numerous, large plastoglobuli and were lacking in starch granules. The size and number of starch granules increased with the level of sucrose in the culture medium. Starch content in leaves of shootlets grown with 5% sucrose was higher (ca 1, 3%) than those grown with 3% (ca 0, 45%) and 1% sucrose (ca 0, 27%). Starch might be used by the in vitro shootlets during the acclimation period.

A method for simulating the direct solar radiation regime in sunflower, jerusalem artichoke, corn and soybean canopies using actual stand structure data

Abstract A method has been developed to incorporate actual canopy architecture in radiation models. The mathematical procedure involved, introduces a leaf angle and azimuthal distribution function, and yields an integrated extinction coefficient which can be substituted into basic light extinction formulae. Leaf angle and azimuthal distribution functions were determined for sunflower ( Helianthus annuus ), Jerusalem artichoke ( Helianthus tuberosus ), corn ( Zea mays ) and soybean ( Glycine max var. Amsoy). A special computer program was written to calculate the extinction coefficients for each canopy at a number of solar elevations. Applying these coefficients in the extinction formulae for direct solar radiation, the influence of the four stand structures on penetration, interception, absorption and sunlit leaf area index was evaluated. The variation of these variables with time of the day is influenced by the leaf angle distribution function, while the non-random azimuthal distribution is reflected in an upper and lower limit for each variable. The span of this variation increases with low solar elevations and with higher ratios of maximum and minimum azimuthal density. Although the four crops displayed an almost equal daily absorption of direct solar radiation, it was shown that erectophile plant stands are more efficient in their light intercepting capacity than planophile canopies. An error analysis indicates considerable deviation on the prediction of the radiation regime, when calculations are based on a uniform leaf inclination. Deviations on extinction coefficient, interception and sunlit leaf area index are expected to be 10 to 20% at low solar elevations.

Evaluation of daily evapotranspiration estimates from instantaneous measurements

Abstract Evapotranspiration on a regional scale is useful information for agricultural and hydrological practice and can be determined by combining remote sensing data with ground-based measurements. However, estimates of evapotranspiration using remote sensing data are usually instantaneous values and to obtain daily evapotranspiration at a regional scale, it is necessary to convert these values into daily totals. By using the data obtained during the HAPEX-MOBILHY experiment in southwestern France, two different methods of converting instantaneous evapotranspiration into daily totals were evaluated. The first method is based on the assumption that the diurnal course of evapotranspiration is similar to that of solar irradiance and can be approximated by a sine function. As a result, daily evapotranspiration can be obtained from one instantaneous measurement. The second method assumes that the evaporative fraction, defined as the ratio of the latent heat flux and the available energy flux, is constant during the daytime period. Hence daily evapotranspiration can be determined from the evaporative fraction and daily total available energy. Comparisons of estimated and measured daily evapotranspiration indicated that both the methods are accurate for cloud-free days. However, the first method is preferable for the purpose of estimating regional evapotranspiration using remote sensing data.

An experimental system for analysis of the dynamic sap-flow characteristics in young trees: results of a beech tree

This paper describes an experimental system designed for analysis of the dynamic water flow through young trees, complemented with test results of a 2-year-old beech tree (Fagus sylvatica L.). The system allows automatic and simultaneous measurements of a complex set of plant physiological processes at leaf, branch, stem and root levels [transpiration (E), sap flow (F) and diameter fluctuations (Δd)], in combination with the micrometeorological variables that control these processes [soil and air temperature (Ts and Ta), vapour pressure deficit of the air (D) and photosynthetically active radiation (PAR)]. A 2-d experimental period was used to study the whole-tree water transport dynamics of the young beech tree. Good correspondence between E of the leaves and F in the supporting branch was found. An increased time lag between the F measurements along the hydraulic pathway down towards the root system was observed, indicating the non-steady-state nature of the water flow. The daytime Δd of stem and branch revealed the depletion and the replenishment of internal water reserves. The daily amount of water withdrawn from internal storage was 5% of the total daily transpiration. A good linear relationship was found between the rate of change in internal water storage and the rate of change in stem diameter, having no time lag. We conclude that the data obtained with this system will allow experimental assessment of hydraulic properties in young trees and facilitate calibration of models for non-steady-state conditions of water flow in young trees.

Stem respiration and carbon dioxide efflux of young Populus deltoides trees in relation to temperature and xylem carbon dioxide concentration

Oxidative respiration is strongly temperature driven. However, in woody stems, efflux of CO2 to the atmosphere (EA), commonly used to estimate the rate of respiration (RS), and stem temperature (Tst) have often been poorly correlated, which we hypothesized was due to transport of respired CO2 in xylem sap, especially under high rates of sap flow (fs). To test this, we measured EA, Tst, fs and xylem sap CO2 concentrations ([CO2*]) in 3-year-old Populus deltoides trees under different weather conditions (sunny and rainy days) in autumn. We also calculated RS by mass balance as the sum of both outward and internal CO2 fluxes and hypothesized that RS would correlate better with Tst than EA. We found that EA sometimes correlated well with Tst, but not on sunny mornings and afternoons or on rainy days. When the temperature effect on EA was accounted for, a clear positive relationship between EA and xylem [CO2*] was found. [CO2*] varied diurnally and increased substantially at night and during periods of rain. Changes in [CO2*] were related to changes in fs but not Tst. We conclude that changes in both respiration and internal CO2 transport altered EA. The dominant component flux of RS was EA. However, on a 24-h basis, the internal transport flux represented 9–18% and 3–7% of RS on sunny and rainy days, respectively, indicating that the contribution of stem respiration to forest C balance may be larger than previously estimated based on EA measurements. Unexpectedly, the relationship between RS and Tst was sometimes weak in two of the three trees. We conclude that in addition to temperature, other factors such as water deficits or substrate availability exert control on the rate of stem respiration so that simple temperature functions are not sufficient to predict stem respiration.

Resistance to radial CO2 diffusion contributes to between-tree variation in CO2 efflux of Populus deltoides stems

Rates of CO2 efflux of stems and branches are highly variable among and within trees and across stands. Scaling factors have only partially succeeded in accounting for the observed variations. In this study, the resistance to radial CO2 diffusion was quantified for tree stems of an eastern cottonwood (Populus deltoides Bartr. ex Marsh.) clone by direct manipulation of the CO2 concentration ([CO2]) of xylem sap under controlled conditions. Tree-specific linear relationships between rates of stem CO2 efflux (JO) and xylem [CO2] were found. The resistance to radial CO2 diffusion differed 6-fold among the trees and influenced the balance between the amount of CO2 retained in the xylem v. that which diffused to the atmosphere. Therefore, we hypothesised that variability in the resistance to radial CO2 diffusion might be an overlooked cause for the inconsistencies and large variations in woody tissue CO2 efflux. It was found that transition from light to dark conditions caused a rapid increase in JO and xylem [CO2], both in manipulated trees and in an intact tree with no sap manipulation. This resulted in an increased resistance to radial CO2 diffusion during the dark, at least for trees with smaller daytime resistances. Stem diameter changes measured in the intact tree supported the idea that higher actual respiration rates occurred at night owing to higher metabolism in relation to an improved water status and higher turgor pressure.

Ecophysiological Analysis Of Drought And Salinity Stress Of Quinoa (Chenopodium Quinoawilld.)

We assessed the relative influence of drought or salinity stress with similar soil water potentials on growth, plant water relations, and photosynthesis rate of Chenopodium quinoaWilld., as well as the suitability of common techniques used in stress physiology studies. Our results from greenhouse pot experiments showed that salt stress induced better absolute and relative growth rates, and that the plant developed adaptation mechanisms to drought through high water use efficiency and high root shoot ratios. The stomatal resistance and the leaf water potential increased with an increased stress level. Variable to maximal chlorophyll fluorescence (Fv/Fm) and quenching analysis (qP and qN) showed that dehydrated plants are less protected from photoinhibition. The dynamic diffusion porometer is of limited use in leaves with salt glands. #Master of Science thesis. Article submitted to the First International Workshop of Quinoa. 10-14 May, 1999. Lima, Peru.

A ONE-LAYER RESISTANCE MODEL FOR ESTIMATING REGIONAL EVAPOTRANSPIRATION USING REMOTE-SENSING DATA.

Abstract A methodology has been developed for estimating regional evapotranspiration using remote sensing data. The transfer of sensible and latent heat is described by an aerodynamic resistance and a surface resistance. The aerodynamic resistance is formulated on the basis of the Monin-Obukhov similarity theory and the surface resistance is determined from the energy balance equation using remotely sensed surface temperature. The regional evapotranspiration is then calculated with a one-layer resistance model. The overall surface transfer characteristics at regional scale are characterized by an effective roughness length and this parameter was determined from local roughness length with the aid of remote sensing measurements. The model was validated by using the data obtained during the HAPEX-MOBILHY (Hydrologic Atmospheric Pilot Experiment and Modelisation du Bilan Hydrique) experiment. At local scale with homogeneous surface conditions, good agreement ( r = 0.90, RMSE = 50 W m −2 ) was obtained between model estimates and the measurements at ground stations. The regional evapotranspiration from the agricultural part of the HAPEX-MOBILHY was also calculated with the one-layer resistance model by combining the NOAA-AVHRR with ground-based meteorological data. The calculated regional evapotranspiration was compared with the area averages of the evapotranspiration measured by the ground-based stations. The two techniques agreed fairly well and the average difference was only 28 W m −2 .

Effects of drought stress induced by polyethylene glycol on pigment content and photosynthetic gas exchange of Pistacia khinjuk and P-mutica.

The effects of drought stress induced by polyethylene glycol, PEG (molecular mass 6000) on some ecophysiological characteristics of two wild pistachio species, Mastic and Khinjuk (P. mutica and P. khinjuk) selected as root stocks for production of edible pistachio trees (P. vera) in Iran and Turkey, were studied. Net photosynthetic rate (PN), stomatal conductance (gs), chlorophyll (Chl) fluorescence parameters, leaf water potential (Ψ1), leaf osmotic potential (Ψπ), leaf osmotic adjustment (ΔΨπ), and Chl a and b were measured. All parameters were influenced by increase in concentra-tion of PEG in the nutrient solutions. PN, gs, and Chl a were significantly higher in P. mutica than in P. khinjuk but, compared to the control treatment, P. khinjuk showed a higher resistance to drought stress than P. mutica.

Effects of Osmotic Drought Stress Induced by a Combination of NaCl and Polyethylene Glycol on Leaf Water Status, Photosynthetic Gas Exchange, and Water Use Efficiency of Pistacia khinjuk and P. mutica

Leaf water potential, leaf osmotic potential, chlorophyll a and b contents, stomatal conductance, net photosynthetic rate, and water use efficiency were determined in two pistachio species (Pistacia khinjuk L. and P. mutica L.) grown under osmotic drought stress induced by a combination of NaCl and polyethylene glycol 6000. A decrease in values for all mentioned variables was observed as the osmotic potential of the nutrient solution (Ψs) decreased. The osmotic adjustment (ΔΨπ) of the species increased by decreasing Ψs. Thus P. khinjuk had a higher osmotic drought stress tolerance than P. mutica.