NE: No effect. Data were not significantly different from control. (p<0.05). N D-R: No doses-response. Table 4. Data of EC50 ecotoxicity values to plants with the 95% confidence limits, obtained for the contaminated soils using different chlorophyll fluorescence variables. Data are expressed as concentration of contaminant (  l/kg). NE: No effect. Data were not significantly different from control. (p<0.05). N D-R: No doses-response. Table 3. Data of EC50 ecotoxicity values to photosynthetic pigment content in plant leaves, with the 95% confidence limits, obtained for the contaminated soils using different measure variables. Data are expressed as concentration of contaminant (  l/kg). NE: No effect. Data were not significantly different from control. (p<0.05). N D-R: No doses-response. Table 2. Data of EC50 ecotoxicity values to plants with the 95% confidence limits, obtained for the contaminated soils using different measure variables. Data are expressed as concentration of contaminant (  l/kg). EFFECTS OF PETROLEUM HYDROCARBONS ON PHOTOSYNTHETIC PARAMETERS: CLOROPHYLL FLUORESCENCE AND STOMATAL CONDUCTANCE Alonso-Blázquez N., González A., Del Río C., Fernández M.D. INIA. Ctra. De la Coruña km 7, Madrid (Spain). ACKNOWLEDGEMENTS.- This work was funded by Madrid Community through EIADES Project Zea maysCucumis sativus Growth (Wet weight) Seedling Emergence Stomatal Conductance Growth (Wet weight) Seedling Emergence Stomatal Conductance Transplanted oil NE-ND-RNE- Transplanted diesel 8658 ( ) -ND-R<2000-NE Sown oil ND-RNEND-R ( ) NEND-R Sown diesel ND-RNEND-R<2000> ( ) UNION EUROPEA FONDO SOCIAL EUROPEO Zea mays Wet weight (% inhibition)Cucumis sativus Wet weight (% inhibition) Figure 1. Effects of mineral oil and diesel fuel on Wet Weigh of Zea mays and Cucumis sativus Zea maysCucumis sativus ChlorophyllsCarotenoidsChlorophyllsCarotenoids Transplanted oil NE Transplanted diesel 9065 ( ) >16000<2000 Sown oil >16000NDR 8885 ( ) ( ) Sown diesel >16000 NDRND-R Zea maysCucumis sativus AreaPI (abs)AreaPI (abs) Transplanted oil NE >16000 Transplanted diesel >16000ND-R ( ) <2000 Sown oil NE > ( ) Sown diesel <2000NEND-R Figure 2. Effects of mineral oil and diesel fuel on Stomatal Conductance. Zea mays Stomatal Conductance (% inhibition)Cucumis sativus Stomatal Conductance (% inhibition) Figure 3. Effects of mineral oil and diesel fuel on leaf pigments content of Zea mays and Cucumis sativus Zea mays chlorophyll content (% inhibition)Cucumis sativus chlorophyll content (% inhibition) Zea mays carotenoids content (% inhibition)Cucumis sativus carotenoids content (% inhibition) Zea mays Area (% inhibition)Cucumis sativus Area (% inhibition) Zea mays PI(abs) (% inhibition)Cucumis sativus PI(abs) (% inhibition) Figure 4. Effects of mineral oil and diesel fuel on Area of fluorescence curve and Performer Index (PI abs) of Zea mays and Cucumis sativus. Introduction and objectives Biochemical and physiological changes due to contaminants can be detected earlier than morphological changes. Plant physiological functions such as photosynthesis and stomatal conductance are useful tools to study the effects of environmental stress on plants. Photosynthesis variables evaluated by the Chlorophyll a Fluorescence and Stomatal Conductance are considered very sensitive biomarkers when plants have been exposed to pollutants. These functions have been widely applied to study effects caused by water deficit, temperature, nutrient deficiency, etc. Their use in determining the effects due to chemicals is limited and mainly focused on metals and herbicides. The purpose of this study was to assess the effects of petroleum hydrocarbons (diesel fuel and mineral oil) on the responses of photosynthesis and stomatal conductance and compare with other parameter such plant emergence, fresh weight and chlorophyll content of leaves. The effects caused by hydrocarbon stress were assessed on plants with a fully developed photosynthetic apparatus and plants with a developing photosynthetic apparatus, in order to determine the influence of these contaminants in the development of the photosynthetic apparatus. Materials and Methods Soil (clay 7.8%, silt 18.8%, sand 73.4%, pH 7.3 and OC 3.4%) was taken from the surface layer (0-20 cm) of a field located in Madrid (Spain). Soil was homogeneously mixed with diesel fuel or mineral oil at four concentrations: 2000, 4000,  l kg-1 soil. Effects were determined on two plant species: Cucumis sativus and Zea mays. The plants were sown on the contaminated soil or germinated in a nursery one week before transplanting to the contaminated soil (Table 1). After 28 days, emergence of seedlings and above-ground biomass production, measured as wet mass of shoots were recorded. The content of chlorophylls and total carotenoids in leaves were determined following the method of Lichtenthaler and Wellburn (1983). Before harvesting plants, chlorophyll fluorescence and stomatal conductance were recorded. Chlorophyll fluorescence was measured with the instrument Handy Pea, of Hansatec S.A. Stomatal conductance measurements were performed on the same leaves that the photosynthetic measurements, using the porometer: SC-1 of Decagon, in the units: µm m -2 s -1. The following variables derived from the study of the stationary curve OJIP points were studied: 1.Area between fluorescence curve and Fm. 2.Maximum quantum yield for primary photochemistry:  (Po) 3.Reaction centre density: RC/CSo. 4.Performance index (PI abs): Gives the information about overall photosynthetic performance. It comprises three main processes in PSII: ABS, TR and ET. Table 1. Treatments studied Results and Discussion Conclusions Effects of hydrocarbon contaminated soils on plants depended on contaminant, plant species and germination procedure. However, in most cases, diesel fuel was more toxic than mineral oil for all measured parameters. Hydrocarbons did not cause significant inhibition of seedling emergence, but seeds germinated in contaminated soils showed higher toxic effects than transplanted ones. The sensitivity of wet weight as effect variable was similar to measurements based on plant physiological functions. However, stomatal conductance and chlorophyll fluorescence provided information about how hydrocarbons affect the photosynthesis and has the advantage of being non-invasive methods. Zea mays (C4 plant specie) was the most affected specie on stomatal opening and closing, whereas parameters related to photosynthesis (chlorophyll content, carotenoid content, area, PI(abs)) had the highest response in Cucumis sativus. Leaf pigment contents were a more sensitive parameter than fluorescence measurements, but it has the disadvantage that it is an invasive method.