Photosynthesis and stomatal light responses in snap beans exposed to hydrogen sulfide and ozone
Apparent photosynthesis and leaf stomatal conductance were measured in well watered, field grown snap beans (Phaseolus vulgaris L. cv GV50) fumigated with various levels of H/sub 2/S alone and in the presence of 0.072 ppM ozone. Mean concentrations of H/sub 2/S were 0, 0.74, 3.25, and 5.03 ppM. Plants were fumigated from 1000 to 1400 h (PDT) each day beginning at the first trifoliate leaf stage. The youngest fully expanded leaves were sampled after 18 +- 2 days of fumigation. The plants had 10 to 11 leaves and were flowering with about 80% of the flowers open. Hydrogen sulfide at 0.74 ppM increased maximum (max) stomatal conductance (C/sub max/) by 25% and maximum apparent photosynthesis (P/sub max/) by 10%. Higher concentrations of H/sub 2/S depressed stomatal opening and CO/sub 2/ uptake, and O/sub 3/ plus H/sub 2/S depressed stomatal and photosynthetic response more than H/sub 2/S alone. At the highest H/sub 2/S concentration plus O/sub 3/, C/sub max/ was 41%, and P/sub max/ was 52% of the control. Both C/sub max/ and P/sub max/ responded similarly to the 8 treatments but the difference between maximum and minimum responses was greater for conductance. As pollutant stress increased, photosynthesis ceased to respond linerarly to increasing conductance at lower conductance values indicating that mesophyll resistance to CO/sub 2/ transfer was more limiting than CO/sub 2/ diffusion through the stomata at higher light intensities. The initial slope of the curves of both conductance and photosynthesis as a function of irradiance decreased with increasing stress, suggesting decreased sensitivity to light. This indicates an increased sluggishness in the guard cells, which could be related to induced leaf senescence caused by the pollutants. It also indicates a loss of photochemical conversion efficiency resulting from loss of chlorophyll and development of necrotic areas on the leaves of the more stressed plants.
- Research Organization:
- Univ. of California, Livermore, CA (United States)
- OSTI ID:
- 5818830
- Journal Information:
- J. Air Pollut. Control Assoc.; (United States), Vol. 28:11
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
HYDROGEN SULFIDES
TOXICITY
OZONE
PLANTS
BEANS
CHLOROPHYLL
DOSE-RESPONSE RELATIONSHIPS
LEAVES
PHOTOSYNTHESIS
STOMATA
VISIBLE RADIATION
CARBOXYLIC ACIDS
CHALCOGENIDES
CHEMICAL REACTIONS
ELECTROMAGNETIC RADIATION
FOOD
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HYDROGEN COMPOUNDS
OPENINGS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHYTOCHROMES
PIGMENTS
PORPHYRINS
RADIATIONS
SULFIDES
SULFUR COMPOUNDS
SYNTHESIS
VEGETABLES
560303* - Chemicals Metabolism & Toxicology- Plants- (-1987)