© 1995 Heron Publishing—Victoria, Canada
Regulation of photosynthesis in interior spruce during water stress: changes in gas exchange and chlorophyll fluorescence
P. Ann K. Eastman (1) and Edith L. Camm (1, 2)
1. Department of Botany, University of British Columbia, Vancouver, B.C. V6T 1Z4, Canada / 2. Department of Forest Sciences, University of British Columbia, Vancouver, B.C. V6T 1Z4, Canada / Received December 1, 1993
Summary
Photosynthetic response to water stress was analyzed in 1-year-old interior spruce (Picea glauca (Moench) Voss × P. engelmanni Parry hybrid complex) seedlings and emblings produced from somatic embryogenesis. Carbon dioxide uptake, oxygen evolution
and chlorophyll fluorescence at 20 °C were monitored as predawn shoot water potential (Ψ) decreased. Concurrently with stomatal
closure, carbon assimilation declined rapidly as Ψ decreased to –1.0 MPa. Oxygen evolution at 10,000 µl CO2 l–1 declined continuously as Ψ decreased to –1.6 MPa. At photon flux densities (PFD) above 50 µmol m–2 s–1, photochemical efficiency of photosystem (PS) II observed during actinic light exposure (ΦII, calculated as ΔF/Fm′) decreased as Ψ decreased. At the same PFDs, photochemical quenching (qP) declined with decreasing Ψ and nonphotochemical quenching (qN) increased steadily. At PFDs below 50 µmol m–2 s–1, major decreases in qN were not observed until Ψ decreased below –1.6 MPa. We identified three phases of photosynthetic response to progressive
water stress in interior spruce: a pronounced decline in gas exchange, subsequent photoprotective changes in chlorophyll fluorescence
as primary photochemistry was down-regulated, and a decline in photochemical efficiency of dark-adapted needles.
Keywords:
carbon assimilation, gymnosperm, oxygen evolution, photochemical efficiency, shoot water potential, stomatal closure.
