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PHOTOSYNTHETIC CHARACTERISTICS OF C 3 ‐C 4 INTERMEDIATE FLAVERIA FLORIDANA (ASTERACEAE) IN NATURAL HABITATS: EVIDENCE OF ADVANTAGES TO C 3 ‐C 4 PHOTOSYNTHESIS AT HIGH LEAF TEMPERATURES
Author(s) -
Monson Russell K.,
Jaeger Charles H.
Publication year - 1991
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.1002/j.1537-2197.1991.tb14481.x
Subject(s) - photosynthesis , photorespiration , biology , botany , stomatal conductance , c4 photosynthesis , ecophysiology , water use efficiency , horticulture
Measurements of leaf gas exchange were conducted in situ for the C 3 ‐C 4 intermediate plant Flaveria floridana . Leaves exhibited measurable CO 2 assimilation at atmospheric CO 2 concentrations as low as 20 μ mol/mol. This result demonstrates that the low CO 2 compensation points observed in past studies of greenhouse‐grown C 3 ‐C 4 intermediate plants also exist in plants growing in their natural habitat. Photosynthesis rates in F. floridana were near their maximum at intercellular CO 2 concentrations as low as 112 μ mol/mol. The existence of near‐maximum photosynthesis rates at such low intercellular CO 2 concentrations is interpreted as evidence for the existence of a CO 2 ‐concentrating mechanism in F. floridana . Such a mechanism would also explain the observed lack of response in photosynthesis rates to reductions in stomatal conductance and intercellular CO 2 concentration as the leaf‐to‐air water vapor concentration gradient is increased. Photosynthetic rates were relatively high at leaf temperatures between 35 and 40 C, compared to most C 3 plants. At midday during May, when leaf temperatures were between 35 and 42 C, F. floridana leaves exhibited photosynthesis rates that were four times higher than a sympatric C 3 species ( Eustoma exaltatum ) of similar growth form and ecological habit. The high photosynthesis rates at high leaf temperatures in F. floridana were not due to higher leaf nitrogen contents, but rather to its reduced rate of photorespiration. These results confirm that C 3 ‐C 4 intermediate photosynthesis can provide plants with an advantage at high leaf temperatures, compared to C 3 plants.