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Stomatal sensitivity to vapour pressure difference over a subambient to elevated CO 2 gradient in a C 3 /C 4 grassland
Author(s) -
MAHERALI H.,
JOHNSON H. B.,
JACKSON R. B.
Publication year - 2003
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.1365-3040.2003.01054.x
Subject(s) - stomatal conductance , transpiration , guard cell , photosynthesis , vapour pressure deficit , water use efficiency , botany , horticulture , chemistry , zoology , biology
In the present study the response of stomatal conductance ( g s ) to increasing leaf‐to‐air vapour pressure difference ( D ) in early season C 3 ( Bromus japonicus ) and late season C 4 ( Bothriochloa ischaemum ) grasses grown in the field across a range of CO 2 (200–550 µ mol mol −1 ) was examined. Stomatal sensitivity to D was calculated as the slope of the response of g s to the natural log of externally manipulated D (d g s /dln D ). Increasing D and CO 2 significantly reduced g s in both species. Increasing CO 2 caused a significant decrease in stomatal sensitivity to D in Br. japonicus, but not in Bo. ischaemum . The decrease in stomatal sensitivity to D at high CO 2 for Br. japonicus fit theoretical expectations of a hydraulic model of stomatal regulation, in which g s varies to maintain constant transpiration and leaf water potential. The weaker stomatal sensitivity to D in Bo. ischaemum suggested that stomatal regulation of leaf water potential was poor in this species, or that non‐hydraulic signals influenced guard cell behaviour. Photosynthesis ( A ) declined with increasing D in both species, but analyses of the ratio of intercellular to atmospheric CO 2 ( C i / C a ) suggested that stomatal limitation of A occurred only in Br. japonicus . Rising CO 2 had the greatest effect on g s and A in Br. japonicus at low D . In contrast, the strength of stomatal and photosynthetic responses to CO 2 were not affected by D in Bo. ischaemum . Carbon and water dynamics in this grassland are dominated by a seasonal transition from C 3 to C 4 photosynthesis. Interspecific variation in the response of g s to D therefore has implications for predicting seasonal ecosystem responses to CO 2 .