Stomatal regulation in a changing climate: a field study using Free Air Temperature Increase (FATI) and Free Air CO₂ Enrichment (FACE)

Abstract

This study investigates effects of climate warming (+ 2-5 °C above ambient) and elevated CO2 concentration (600 jumo] mol"') on the stomatal functioning and the water relations of Lotiuin perenne, using Free Air Temperature Increase (FATI) and Free Air CO2 Enrichment (FACE). Compared to growth at ambient temperature, whole-season temperature increase reduced leaf stomatal conductance, but only at the top of the canopy (-14-6 and -8-8% at ambient and elevated CO2, respectively). However, because higher canopy temperature raised the leaf-to-air vapour pressure difference, leaf transpiration rate increased (+28% at ambient and +48% at elevated CO2) and instantaneous leaf water use efficiency, derived from short-term measurements of assimilation and transpiration rate, declined (-11% at ambient and -13% at elevated CO2). Nevertheless, at the stand level, growth at + 2-5 °C reduced transpiration due to fewer tillers per plant and a smaller leaf area per tiller. This sparser vegetation was also more closely coupled to the atmosphere and maintained a drier internal microclimate. To assess whether the stomatal behaviour observed in this experiment could be explained by prevailing concepts of stomatal functioning, three models were applied (Cowan 1977; Ball, Woodrow & Berry 1987; Leuning 1995). The latter model accounted for the highest proportion of variability in the data (58%) and was insensitive to CO2 and temperature regime, which suggests that tlie principles of stomatal regulation are not affected by changes in CO2 or climate.

Photosynthesis in a CO2-Rich Atmosphere

“…Studies of crops are inconsistent. Parameters of the Ball et al (1987) model for Lolium perenne (rye grass) did not differ when this species was grown at 350 and 600 ppm CO 2 in a pseudo-replicated FACE study (Nijs et al, 1997). In contrast, Gossypium hirsutum (cotton) grown at 650 compared to 350 ppm CO 2 in controlled environment cabinets exhibited marginally significant stomatal acclimation (Harley et al, 1992b).…”

Post-Fire Seedling Recruitment and Morpho-Ecophysiological Responses to Induced Drought and Salvage Logging in Pinus halepensis Mill. Stands

“…In each one, we carried out instantaneous recordings of gas exchange using a portable system (LI-6400XT; LI-COR, Environmental Division, Lincoln, NE, USA) equipped with a CO2 and H2O infrared gas analyzer (6400-07 Needle Chamber; LI-COR, Environmental Division, Lincoln, NE, USA). To characterize the salvage logging and water stress effects on ecophysiological processes according to [32], we selected the following as target parameters: transpiration ratio (E, mmol m −2 s −1 ); net photosynthetic ratio (A, μmol m −2 s −1 ); stomatal conductance (gs, mol H2O m −2 s −1 ); water use efficiency, defined as the ratio of the carbon assimilation ratio (net photosynthetic ratio); transpiration ratio (WUE = A/E) [33]. Sampling was done under light-saturation conditions for photosynthesis (photosynthetically active radiation (PAR) above 250 μmol m −2 s −1 ), with temperatures ranging from 20 °C to 26 °C , and the CO2 atmosphere concentration within the 380-395 μmol mol −1 CO2 range.…”

Carbon dioxide effects on stomatal responses to the environment and water use by crops under field conditions

“…Equations that summarize environmental responses of conductances of crop plants grown at ambient and elevated [CO 2 ] under field conditions have been published for seven species, alfalfa and orchard grass , perennial rye grass (Nijs et al 1997), wheat and barley (Bunce 2000), and maize and soybean (Wilson et al 1999). For alfalfa and orchard grass, diurnal patterns of canopy conductance were used to develop Jarvis-type multiplicative functions (Jarvis 1976) for responses to PPFD, temperature and water vapor pressure difference .…”