Using remotely sensed solar radiation data for reference evapotranspiration estimation at a daily time step

International audienceSolar radiation is an important climatic variable for assessing reference evapotranspiration (E0), but it is seldom available in weather station records. Meteosat satellite images processed with the Heliosat-2 method provide the HelioClim-1 database, which displays spatialized solar radiation data at a daily time step for Europe and Africa. The aim of the present work was to investigate the interest of satellite-sensed solar radiation for E0 calculation, where air temperature is the sole local weather data available. There were two study areas in Southern France. One (Southwest, SW) is characterized by Oceanic climate and the other (Southeast, SE) by Mediterranean climate. A data set of daily values for 19 weather stations spanning five years (2000–2004) was used. First, a sensitivity analysis of the Penman–Monteith formula to climate input variables was performed, using the Sobol' method. It shows that E0 is mainly governed by solar radiation during summer, and by wind speed during winter. Uncertainties of HelioClim-1 solar radiation data and their repercussions on E0 formulae were evaluated, using the FAO-56 Penman–Monteith formulae (PM) and radiation-based methods (Turc, TU; Priestley–Taylor, PT and Hargreaves-Radiation, HR). It was shown that HelioClim-1 data slightly underestimate solar radiation and provide relative RMSE (root mean square error) of 20% of the mean annual value for SW and 14% for SE. The propagation of HelioClim-1 data uncertainties is small in PM but considerable in radiation methods. Four estimation methods were then compared to PM data: the 1985 Hargreaves formula (HT) based on air temperature only; TU, PT and HR, based on air temperature and satellite-sensed solar radiation. Radiation methods were more precise and more accurate than HT, with RMSE ranging from 0.52 mm to 0.86 mm against 0.67–0.96 mm. These results suggest that using satellite-sensed solar radiation may improve E0 estimates for areas where air temperature is the only available record at ground level

Estimating spatial and temporal variations in solar radiation within Bordeaux winegrowing region using remotely sensed data

International audienceAims: This paper presents a study solar radiation spatial and temporal variations in Bordeaux winegrowing area, for a 20 year period (1986-2005). Methods and results: Solar radiation data was retrieved from the HelioClim-1 database, elaborated from Meteosat satellite images, using the Heliosat-2 algorithm. Daily data was interpolated using ordinary kriging to produce horizontal solar radiation maps at a 500 m resolution. Using a digital elevation model, high resolution daily solar radiation maps with terrain integration were then produced for the period 2001-2005, at a 50 m resolution. The long term (20 years) analysis of solar radiation at low spatial resolution (500 m) showed a west to east decreasing gradient within Bordeaux vineyards. Mean August-to-September daily irradiation values, on horizontal surface, were used to classify Bordeaux winegrowing areas in three zones: low, medium, and high solar radiation areas. This initial zoning was upscaled at 50 m resolution, applying a local correction ratio, based on 2001-2005 solar radiation on inclined surface analysis. Grapevine development and maturation potential of the different zones of appellation of origin of Bordeaux winegrowing area are discussed in relation with this zoning. 2 Conclusions: Solar radiation variability within Bordeaux winegrowing area is mainly governed by terrain slopes and orientations, which induce considerable variations within the eastern part of Bordeaux vineyards. Significance and impact of the study: Solar radiation has a major impact on vineyard water balance, grapevine development and berry ripening. However, irradiation data is seldom available in weather stations records. This paper underline the interest of high resolution cartography of solar radiation, using satellite sensing and terrain effect integration, for agroclimatic studies in viticulture

Induction of a Carbon-Starvation-Related Proteolysis in Whole Maize Plants Submitted to Light/Dark Cycles and to Extended Darkness

Three-week-old maize (Zea mays L.) plants were submitted to light/dark cycles and to prolonged darkness to investigate the occurrence of sugar-limitation effects in different parts of the whole plant. Soluble sugars fluctuated with light/dark cycles and dropped sharply during extended darkness. Significant decreases in protein level were observed after prolonged darkness in mature roots, root tips, and young leaves. Glutamine and asparagine (Asn) changed in opposite ways, with Asn increasing in the dark. After prolonged darkness the increase in Asn accounted for most of the nitrogen released by protein breakdown. Using polyclonal antibodies against a vacuolar root protease previously described (F. James, R. Brouquisse, C. Suire, A. Pradet, P. Raymond [1996] Biochem J 320: 283–292) or the 20S proteasome, we showed that the increase in proteolytic activities was related to an enrichment of roots in the vacuolar protease, with no change in the amount of 20S proteasome in either roots or leaves. Our results show that no significant net proteolysis is induced in any part of the plant during normal light/dark cycles, although changes in metabolism and growth appear soon after the beginning of the dark period, and starvation-related proteolysis probably appears in prolonged darkness earlier in sink than in mature tissues

Effets des facteurs de l'environnement sur le développement de la vigne. Relations avec l'effet terroir

National audienc

The assessment of vine water uptake conditions by ¹³c/¹²c discrimination in grape sugar

Carbon isotope discrimination in primary products of photosynthesis varies with plant water uptake conditions. This property was used to show that the 13C/12C ratio (called ΔC13) in grape sugars and tartrate measured at ripeness can be a valuable indicator of vine water deficit. Correlation between ΔC13 in grape sugar and minimum pre-dawn leaf water potential is excellent (R2 = 0,81; n = 36). A statistically significant effect of soil and vintage is pointed out. When measured on a great number of plots of an estate, ΔC13 varies with the soil type. This proves ΔC13 can be a valuable tool in « terroir » studies. ΔC13 measured on phenolic compounds in wine is also significantly correlated to minimum pre-dawn leaf water potential as well as to ΔC13 in grape sugar. ΔC13 is actually the only tool capable to assess global vine water uptake conditions between veraison and harvest at a low cost, without the installation of heavy equipment in the vineyard

Effects of ripening conditions on the following season's growth and yield components for Pinot noir and Gewurztraminer grapevines (<em>Vitis vinifera</em> L.) in a controlled environment

Two levels of leaf/area ratio were created for two varieties of grapevine (Vitis vinifera L.) in a glasshouse. Carbohydrate and free amino acids concentrations in the pruning wood were significantly reduced when the leaf/fruit ratio was low. In the following season, growth parameters were affected as well as yield components such as the number of shoots per plant, the number of inflorescences per shoot, the number of flowers per inflorescence and the number of berries per cluster. Fruit set was however not altered. Weight of grapes at fruit set was reduced by 68% for Gewurztraminer and by 46 % for Pinot noir

Long term effects of nitrogen and water supply on confered vigour and yield by SO4 and Riparia gloire de Montpellier rootstocks

Aims: the present study was designed to test the hypothesis according to which rootstock effects on scion growth and yield are related to fundamental physiological traits which are expressed consistently and independently of environmental conditions. Methods and results: Pruning weights and yield components from two independent rootstock experiments are reported. In the first experiment, the effect of two levels (30 and 70 kgN/ha/year) was studied during 15 years on Cabernet-Sauvignon vines grafted onto SO4 and Riparia Gloire de Montpellier (RGM). In the second one, Cabernet-Sauvignon and Merlot vines grafted on SO4 and RGM were submitted to two levels of soil fertility shortly after plantation: control and high (100 kgN/ha/year + irrigation) and data from the plantation to year 6 were recorded. In both experiments, vine vigour and yield were significantly affected by rootstocks and fertilisation/irrigation treatments. No interaction was recorded. The devigorating effect of RGM in comparison to SO4 was observed in both experiments, regardless of other parameters. Cabernet-Sauvignon was more affected by rootstock than Merlot. Conclusion: Rootstock effects on vine vegetative and reproductive development were consistently expressed, indicating that scion-rootstock interactions are governed not only by adaptative, but also by specific physiological traits. Significance and impact of study: This work provides information on scion-rootstock interactions which may be useful in rootstock breeding programs and may help to better choose the rootstock according to the scion and the environment

The assessment of vine water and nitrogen uptake by means of physiological indicators influence on vine development and berry potential (<em>Vitis vinifera</em> L. cv Merlot, 2000, Bordeaux)

Vine water and nitrogen uptake can be assessed by means of physiological indicators in field conditions. In this study, pre-dawn leaf water potential (ψB) and stem water potential (ψT) were used to indicate vine water status of Vitis vinifera L cv. Merlot. Carbon isotope composition of grape sugar (ΔC13) was used as an integrative indicator of vine water deficit during the ripening period. Must assimilable nitrogen and leaf blade colour intensity, were used to assess vine nitrogen status. All of the three indicators of vine water status allowed a clear differentiation of vine water uptake conditions in the ten experimental plots. The indicators of vine nitrogen status showed more ambiguous results. Must assimilable nitrogen content did not only vary with vine nitrogen uptake, but also with yield. Leaf colour was more easy to interpret. Vine development and berry composition were more influenced by water uptake conditions than by vine nitrogen status. In 2000, which was a dry vintage in Bordeaux, water stress induced early growth slackening and a small berry size. Grapes contained more sugar, anthocyanin and total phenolics and less malic acid when water availability was low. On plots where water uptake conditions were similar, low vine nitrogen status increased berry potential