Comparison of photosynthetic induction and transient limitations during the induction phase in young and mature leaves from
three poplar clones
Otmar Urban (1, 2), Mirka Šprtová (1), Martina Košvancová (1, 3), Ivana Tomášková (1), Hartmut K. Lichtenthaler (4) and Michal V. Marek (1, 3)
1. Laboratory of Plants Ecological Physiology, Institute of Systems Biology and Ecology AS CR, Poříčí 3b, CZ-60300 Brno, Czech
Republic / 2. Corresponding author () / 3. Department of Forest Ecology, Mendel University of Agriculture and Forestry in Brno, Zemědělská 3, CZ-61300 Brno, Czech Republic / 4. Botanical Institute (Molecular Biology and Biochemistry of Plants), University of Karlsruhe, Kaiserstrasse 12, D-76133 Karlsruhe,
Germany / Received November 7, 2007; accepted March 19, 2008; published online June 2, 2008
Summary
We tested the hypothesis that leaf age affects photosynthetic induction, because conductance to CO2 diffusion usually decreases with increasing leaf age. Photosynthetic inductions, primarily determined by the light modulation
of Rubisco activity and stomatal opening, were investigated in both young and mature leaves, as defined by leaf plastochron
index (LPI), from three poplar clones: Populus alba L., P. nigra L. and P. × euramericana (Dode) Guinier. In all clones, maximum assimilation rates (Amax), maximum stomatal conductance (GSmax) and dark respiration rates (RD) were higher in young leaves (LPI = 3–5) than in mature leaves (LPI = 10–14), and Amax decreased from P. alba via P. × euramericana to P. nigra. The clones with high photosynthetic capacity had low induction states 60 s after leaf illumination (IS60; indicating a slow initial induction phase), and required less time to reach 90% photosynthetic induction (T90). In contrast, the clone with the lowest photosynthetic capacity (P. nigra) exhibited high IS60 (high initial induction state) but a long induction time (high T90). A comparison of mature leaves with young leaves revealed significantly (P < 0.01) lower IS60 values in mature leaves of P. nigra only, and significantly higher T90 values in mature leaves of P. alba only. In all clones, young leaves exhibited a lower percentage of maximum transient stomatal limitation during photosynthetic
induction (4–9%) compared with mature leaves (16–30%). Transient biochemical limitation, assessed on the basis of the time
constants of Rubisco activation (τ), was significantly higher in mature leaves than in young leaves of P. alba; whereas there were no significant differences in τ between young and mature leaves of the other poplar clones. Thus, our
hypothesis that leaf age affects photosynthetic induction was confirmed at the level of transient stomatal limitation, which
was significantly higher in mature leaves than in young leaves in all clones. For the induction parameters IS60, T90 and τ, photosynthetic induction was more clone-specific and was dependent on leaf age only in some cases, an observation
that may apply to other tree species.
Keywords:
dynamic light environment, gas exchange, LPI, photosynthetic limitations, Populus.
