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  • Chlorophyll fluorescence  (1)
  • Tallgrass prairie  (1)
  • 1
    ISSN: 1573-5052
    Keywords: Chlorophyll fluorescence ; Drought ; Elevated CO2 ; High temperature ; Larrea tridenata ; Photosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The interaction of extreme temperature events with future atmospheric CO2 concentrations may have strong impacts on physiological performance of desert shrub seedlings, which during the critical establishment phase often endure temperature extremes in conjunction with pronounced drought. To evaluate the interaction of drought and CO2 on photosynthesis during heat stress, one-year-old Larrea tridentata[DC] Cov. seedlings were exposed to nine days of heat with midday air temperature maxima reaching 53 °C under three atmospheric CO2 concentrations (360, 550 and 700 μmol mol−1) and two water regimes (well-watered and droughted). Photosynthetic gas exchange, chlorophyll fluorescence and water potential responses were measured prior to, during and one week following the high temperature stress event. Heat stress markedly decreased net photosynthetic rate (A net), stomatal conductance (g s), and the photochemical efficiency of photosystem II (F v/F m) in all plants except for well-watered L. tridentata grown in 700 μmol mol−1 CO2. A net and g s remained similar to pre-stress levels in these plants. In droughted L. tridentata, A net was ca. 2× (in 550 μmol mol−1 CO2) to 3× (in 700 μmol mol−1 CO2) higher than in ambient-CO2-grown plants, while g s and F v/F m were similar and low in all CO2 treatments. Following heat stress, g s in all well-watered plants rose dramatically, exceeding pre-stress levels by up to 100%. In droughted plants, g s and A net rose only in plants grown at elevated CO2 following release from heat. This recovery response was strongest at 700 μmol mol−1 CO2, which returned to A net and g s values similar to pre-heat following several days of recovery. Extreme heat diminished the photosynthetic down-regulation response to growth at elevated CO2 under well-watered conditions, similar to the action of drought. Ambient-CO2-grown L. tridentata did not show significant recovery of photosynthetic capacity (A \max and CE) after alleviation of temperature stress, especially when exposed to drought, while plants exposed to elevated CO2 appeared to be unaffected. These findings suggest that elevated CO2 could promote photosynthetic activity during critical periods of seedling establishment, and enhance the potential for L. tridentata to survive extreme high temperature events.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-5052
    Keywords: Elevated CO2 ; Growth form ; Stomatal conductance ; Tallgrass prairie ; Water relations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Responses in stomatal conductance (g st ) and leaf xylem pressure potential (ψ leaf ) to elevated CO2 (2x ambient) were compared among 12 tallgrass prairie species that differed in growth form and growth rate. Open-top chambers (OTCs, 4.5 m diameter, 4.0 m in height) were used to expose plants to ambient and elevated CO2 concentrations from April through November in undisturbed tallgrass prairie in NE Kansas (USA). In June and August, ψ leaf was usually higher in all species at elevated CO2 and was lowest in adjacent field plots (without OTCs). During June, when water availability was high, elevated CO2 resulted in decreased g st in 10 of the 12 species measured. Greatest decreases in g st (ca. 50%) occurred in growth forms with the highest potential growth rates (C3 and C4 grasses, and C3 ruderals). In contrast, no significant decrease in g st was measured in the two C3 shrubs. During a dry period in September, reductions in g st at elevated CO2 were measured in only two species (a C3 ruderal and a C4 grass) whereas increased g st at elevated CO2 was measured in the shrubs and a C3 forb. These increases in g st were attributed to enhanced ψ leaf in the elevated CO2 plants resulting from increased soil water availability and/or greater root biomass. During a wet period in September, only reductions in g st were measured in response to elevated CO2. Thus, there was significant interspecific variability in stomatal responses to CO2 that may be related to growth form or growth rate and plant water relations. The effect of growth in the OTCs, relative to field plants, was usually positive for g st and was greatest (〉30%) when water availability was low, but only 6–12% when ψ leaf was high. The results of this study confirm the importance of considering interactions between indirect effects of high CO2 of plant water relations and direct effects of elevated CO2 on g st , particularly in ecosystems such as grasslands where water availability often limits productivity. A product of this interaction is that the potential exists for either positive or negative responses in g st to be measured at elevated levels of CO2.
    Type of Medium: Electronic Resource
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