185
reached 80%, when the phosphate concentration was above 1.0  mM.  Thus,
UO 2 (CO 3 ) 3
4−
and UO 2 PO 4
−
were selected as other two different species of uranium
for the hydroponic experiments, and the corresponding pH values in the solutions
were 7; carbonate and phosphate concentrations were 10 and 1 mM, respectively.
2.4 Bioaccumulation Amount and Bioaccumulation Factor
The uranium contents in the Azolla-Anabaena were analyzed after 15 days, and the
bioaccumulation factors (BAFs) were used to assess the capacity of AzollaAnabaena to accumulate and transport uranium, and they were calculated by the
following formula:
BAFs
plant
water
=
C
C
(2)
where C plant is the uranium content in the Azolla-Anabaena (mg  kg
−1
in dry
weight) and C water is the uranium content in the soil (mg kg
−1
).
3 Results and Discussion
3.1 Growth Inhibition Rates on the Azolla-Anabaena
Under Stresses of Different Species of Uranium
The growth inhibition rates on the Azolla-Anabaena under the stresses of five solutions of uranium species with the uranium concentration of 2 mg L
−1
were calculated (Fig. 3). As shown in Fig.  3, the growth of Azolla-Anabaena was inhibited
Fig. 2 Simulated variation of percentages of different species of uranium in deionized water with
the concentration of phosphate or carbonate at pH = 7 (total concentration of U is 2 mg L
−1
).
Influence of Uranium Speciation on Plant Uptake