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To determine the effective cell density of P23 to promote duckweed growth under non-sterile conditions, we grew L. minor in pond water at various densities of P23 cells. Although there was no significant effect on growth at a cell density of 0.025 mg/mL, the effect of P23 became significant (P < 0.05) at higher cell densities (Figure 7, Table 3). The increased frond number and biomass production were increased 2.0- and 1.4-fold, respectively, in the presence of P23 cells at 0.05 mg/mL, and 4.3- and 1.8-fold at 0.15 mg/mL. Thus, the initial inoculation density of P23 cells would be important for the significant promotion of duckweed growth in this system.
Table 3

Effects of different cell densities of P23 on the growth of L. minor in non-sterile pond water

Cell density of P23 (mg dry weight/L)Increase in number of fronds per flask during 12 daysa (and ratio of P23 to control)Biomass production (increase in dry weight; mg) of plants per flask during 12 daysa (and ratio of P23 to control)
0 (control) 22 ± 2.5 4.5 ± 0.4 
0.025 24 ± 9.6 (1.1) 5.0 ± 1.3 (1.1) 
0.05 45 ± 4.8 (2.0)* 6.2 ± 0.4 (1.4)* 
0.15 94 ± 6.7 (4.3)* 8.0 ± 0.1 (1.8)* 
Cell density of P23 (mg dry weight/L)Increase in number of fronds per flask during 12 daysa (and ratio of P23 to control)Biomass production (increase in dry weight; mg) of plants per flask during 12 daysa (and ratio of P23 to control)
0 (control) 22 ± 2.5 4.5 ± 0.4 
0.025 24 ± 9.6 (1.1) 5.0 ± 1.3 (1.1) 
0.05 45 ± 4.8 (2.0)* 6.2 ± 0.4 (1.4)* 
0.15 94 ± 6.7 (4.3)* 8.0 ± 0.1 (1.8)* 

Values are means ± SD. Values in parentheses are the ratio of the P23 value to the control (no P23) value.

aFinal value minus initial value.

*Significant difference (P < 0.05) between values with and without P23 within a treatment.

Figure 7

Effects of P23 on the growth of L. minor in non-sterile pond water for 12 days. (a) Changes in the number of fronds growing with P23 cells at densities of 0 (□, control), 0.025 (○), 0.05 (Δ), or 0.15 (◇) mg dry weight/mL. (b) Biomass production (final minus initial dry weight) of L. minor in pond water with P23 cell densities of 0 (control), 0.025, 0.05, or 0.15 mg dry weight/mL during 12 days. Values are mean ± SD (n = 3). *Significant difference (P < 0.05) from control.

Figure 7

Effects of P23 on the growth of L. minor in non-sterile pond water for 12 days. (a) Changes in the number of fronds growing with P23 cells at densities of 0 (□, control), 0.025 (○), 0.05 (Δ), or 0.15 (◇) mg dry weight/mL. (b) Biomass production (final minus initial dry weight) of L. minor in pond water with P23 cell densities of 0 (control), 0.025, 0.05, or 0.15 mg dry weight/mL during 12 days. Values are mean ± SD (n = 3). *Significant difference (P < 0.05) from control.

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