© 2000 Heron Publishing—Victoria, Canada
Characterization of the photosynthetic induction response in a Populus species with stomata barely responding to light changes
Yanhong Tang (1) and Naishen Liang (1)
1. Global Environmental Research Division, National Institute for Environmental Studies, Onogawa 16-2, Tsukuba 305-0053, Japan / Received November 12, 1999
Summary
The photosynthetic induction response is constrained by stomatal and biochemical limitations. However, leaves in some plants
like Populus koreana × trichocarpa cv. Peace (a hybrid clone) may have little stomatal limitation because their stomata barely respond to changes in photon
flux density (PFD). We examined the induction responses of leaves of well-watered and dehydrated P. koreana × trichocarpa plants grown in a high-light or a low-light regime. With an increase in PFD from 50 to 500 μmol m–2 s–1, steady-state stomatal conductance (gs) increased by only 0.25–8.2%, regardless of the initial gs, but steady-state assimilation rate (A) increased by 550–1810%. Photosynthetic induction times required to reach 50% (IT50) and 90% (IT90) of A at high PFD were 60–90 s and 210–360 s, respectively. Examination of the dynamic relationships between A and gs, and between A and intercellular CO2 concentration, indicated that the induction limitation was imposed completely by the biochemical components within 30–40
s after the PFD increase. Values of IT50 and IT90 were significantly higher in low-light leaves than in high-light leaves, whereas the induction state at 60 s and the induction
efficiency at 60 and 120 s after the increase in PFD were lower in low-light leaves than in high-light leaves. Dehydration
reduced leaf water potential (Ψ) significantly, resulting in a significantly decreased initial gs. Leaf water potential had no significant effects on induction time in high-light leaves, but a low Ψ significantly reduced
the induction time in low-light leaves. We conclude that the photosynthetic induction response was limited almost completely
by biochemical components because the stomata barely responded to light changes. The biochemical limitation appeared to be
higher in low-light leaves than in high-light leaves. Mild water stress may have reduced steady-state A and gs, but it had little effect on the photosynthetic induction response in high-light leaves.
Keywords:
light fluctuation, sunflecks, water stress.
