Net photosynthesis (A) under CO2 enrichment was
found to be highest in week 9, prolonging the enrichment
to 15 weeks recorded comparatively lower than A. The
latter might be due to starch accumulation in the leaves
under prolonged elevated CO2, which could impair net
photosynthesis by disrupting the chlorophyll protein that
reduced net photosynthesis (Bindi et al. 2002). Although A
decreased under prolonged exposure to CO2, it did not
affect growth parameters as plant total biomass and total
leaf area continuously increased and the significant differences
in growth between ambient and elevated CO2
were maintained during the experimental period. Similar
result was observed with sugarcane grown under closed top
chamber where peak A was recorded at the middle of the
experiment and slightly reduced with extended CO2
imposition (Amanda et al. 2008). However, plant height,
leaf biomass and stem biomass of enriched sugarcane were
found to be continuously improved growth as indicated by
the significant positive linear relationship between RGR
and NAR. It was observed that the enhancement of A in oil
palm seedlings under elevated CO2 might be attributed to
increase in leaf thickness or reduced SLA. The latter was
also found to be negatively correlated with A suggesting
that thicker mesophyll layer might contain high photosynthesis
protein especially Rubisco that might up-regulate
several enzymes related to carbon metabolism (Vu et al.
2006).