lettuce and sugar beets in thefield and injected a mixture of gases (common in geothermal emissions) at various concentrations through the bottom of the chambers (Fig. 1). Each chamber maintained a constant exposure condition for a period of several hours, and during making these measurements in the field. We found that geothermal air carbon dioxide fixed per gram of . emissions actually stimulate leaf tissue per hour) and the resistance of leaf pores (stomata) to photosynthesis at low concentrathe diffusion of gases into the leaf tions (see Fig. 2) because the addition of carbon dioxide and (inverse conductance, i.e., s/cm}. We have pioneered techniques for hydrogensulfide provides elements needed for carbohydrate and amino acid production. Thefirst significant decrease in photosynthesis occurred when the concentration of hydrogen sulfide exceeded about 3 ppm (4200 g/m?) in the mixture. This value is two orders of magnitude that period we measured the rate of photosynthesis (milligrams of ACO, concentration — ppm 25 5 Trt TT Cross photosynthesis 20 ;— sing co 3/9- h)— 15 | photosynthesis MK control 10 — 90 — ~~ 2 Leaf stomatal resistance 5 om Lb ae Control (s/em)} ontro 0 0.3 teppriil Hos 1 4 4 ot 3 concentration — ppm 6 JRA 4 G) Photosynthesis rates (Qi. (mg COz/g-h) and stomatal resistance (s/cm)in lettuce exposed (for 3h at 30°C and high light) to a mixture of gases similar to that emitted by geothermal power plants. Geothermal emissions actually stimulate ra Hes ‘ne aed I Open-topped chambers used to measure the reactions of plants Qiil é to hydrogen sulfide and other gases. Potential air pollutants are injected in various concentrations into the bottom of the chamber. Each chamber maintains a constant exposure condition for a period of several hours, during which researchers make physiological measurements to evaluate effects on the plant's metabolism. ~ Cn cg Ne Oa ay a cm 5 24 photosynthesis at low concentra- tions because the additional carbon dioxide and hydrogen sulfide provide essential elements for carbehydrate and amino acid produc- tion. The first significant decreasein photosynthesis occurs when hydrogen sulfide exceeds about 3ppm in this mixture.