Carbon Balance of Peperomia Obtusifolia Plants During Acclimatization to Low PPFD

Abstract. The COL exchange rates of Peperornin obtusijolia A. Dietr. plants (tops and roots) were measured for 12-
hour light and 12-hour dark cycles during 5 weeks of acclimatization at 30 pE ~ - ' m - ~A. c arbon balance analysis of
the data indicated that the growth conversion eniciency (Yg) remained constant (0.73 + 0.1 and 0.77 + 0.04 before
and after acclimatization, respectively). The daily rate of substrate production from photosynthesis (ASIAt) remained
constant at 18 2 2 mg C plant-I 24 hr-', at the acclimatization photosynthetic photon flux density (PPFD), but the
daily rate of synthesis of carbon into new material (AWIAt) increased by 55% within the first week. The maintenance
coenicient (m) decreased from 13.0 ? 0.9 to 7.4 -t 0.4 mg g-' 24 hr-', and change in m may be a criterion for
selection of plants that can be adapted for use at low PPFD. The light con~pensationp oint (LCP) was reduced during
acclimatization, but its use underestimated the PPFD required for 24-hour plant maintenance because of failure to
account for night-time respiratory losses. It is suggested that the PPFD at which AWiAt is zero or slightly above is
more reliable than the light compensation point for determining PPFD required for plant maintenance.