The interactive effects of three levels of N (mM) (low 0.36, medium 2.1 and high 6.4) and two levels of P
(mM) (low 0.10 and high 0.48) on growth and resource allocation of Canna indica Linn. were studied in
wetland microcosms. After 91 days of plant growth, there was a significant interactive effect of N and P on
plant growth, but not on resource allocation (except for allocation of N to leaves and allocation of P to the
stems). The plant growth positively responded to the relatively higher nutrient availability (taller plants
with more stems, leaves and flowers), but the growth performance was not significantly different
between the mediumN-low P and high N-low P treatments. At high P, the total biomass in the high N was
about 51% higher than that in the medium N and about 348% higher than that in the low N. The growth
performance was related to the physiological responses. The photochemical efficiency (F
) increased
from 0.843 to 0.855 with an increase in N additions. The photosynthetic rate increased from 13 to
16
mmol m
2
s
1
in the low P levels and from 14 to 20 mmol m
2
s
1
in the high P levels with an increase
in N applications, but significant difference was only between the low and mediumN levels, regardless of
the P levels. The tissue concentrations of N increased with an increase in N applications and decreased
with an increase in P additions, whereas reverse was true for tissue concentrations of P. The highest
concentrations of N and P in leaves were 30.8 g N kg
1
v
/F
in the high N-low P treatment and 4.9 g P kg
in
the low N-high P treatment. The percent biomass allocation to aboveground tissues in the high N was
nearly twice that in the low N treatments. The N allocation to aboveground tissues was slightly larger in
high N than in low N treatments, whereas the P allocation to aboveground tissues increased with an
increase in the N addition. Although some patterns of biomass allocation were similar to those of nutrient
allocation, they did not totally reflect the nutrient allocation. These results imply that in order to enhance
the treatment performance, appropriately high nutrient availability of N and P are required to stimulate
the growth of C. indica in constructed wetlands.
m
1