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Stomatal responses to changes in air humidity are not necessarily linked to nocturnal CO 2 uptake in the CAM plant Plectranthus marrubioides Benth. (Lamiaceae)
Author(s) -
HERPPICH W. B.
Publication year - 1997
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1046/j.1365-3040.1997.d01-74.x
Subject(s) - plectranthus , crassulacean acid metabolism , relative humidity , humidity , stomatal conductance , nocturnal , horticulture , transpiration , botany , chemistry , lamiaceae , photosynthesis , biology , ecology , meteorology , physics
Plants of the crassulacean acid metabolism (CAM) species Plectranthus marrubioides (Lamiaceae) were subjected to short‐ and long‐term changes in air humidity in controlled‐environment experiments. Stomata of well‐watered individuals of this all‐cell leaf‐succulent taxon responded directly, quickly and reversibly to variations of the water vapour gradient between leaf and air (Δ w ). Mean night‐time leaf conductance to water vapour decreased curvilinearly with increasing Δ w but linearly with lowered relative air humidity. Stomatal response was generally independent of the prevailing temperature and was not linked to CO 2 uptake rates. Therefore, net night‐time carbon gain, nocturnal malic acid accumulation and, thus, relative carbon recycling were not influenced by changes in air humidity in the temperature range tested. Mean nocturnal molar water use efficiency, however, decreased with decreasing air humidity because of the increased transpirational water loss. If watering was repeatedly withheld for several days during the experiments, employing a temperature regime of 35/30°C day and night, stomatal conductance became low enough to inhibit CO 2 uptake, but only at the highest Δ w. The results suggest that drought stress was necessary to increase responsiveness of plants to the point where CAM was also inhibited by decreases in air humidity.