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We grew each of the three duckweed species with P23 cells (0.15 mg dry weight/mL) in sterile Hoagland solution at different nutrient concentrations for 7 days. The results are summarized in Figures 25 and Table 1. At all nutrient concentrations, all three duckweed species grew more rapidly in the presence of P23 cells than in the absence. The increase in the number of fronds (final number minus initial 10) was 2.9–3.3-fold in L. aequinoctialis, 2.7–3.8-fold in L. minor, and 1.2–1.4-fold in S. polyrhiza compared with the noninoculated controls (Table 1). Biomass production (increase in dry weight) was similarly increased 3.8–4.3-fold, 2.3–3.3-fold, and 1.4–1.5-fold, respectively (Table 1). The nutrient concentration of the medium did not greatly affect the growth-promoting activity of P23 in any species.
Figure 2

Changes in the number of L. aequinoctialis fronds in culture with P23 (○, 0.15 mg dry weight/mL) and without P23 (●) in Hoagland solution (1× =5.0 mg NO3-N/L + 1.0 mg PO4-P/L) at different nutrient concentrations: (a) 0.25× ; (b) 0.50× ; (c) 1.0× ; (d) 1.5× ; (e) 2.0× . Values are mean ± SD (n = 2).

Figure 2

Changes in the number of L. aequinoctialis fronds in culture with P23 (○, 0.15 mg dry weight/mL) and without P23 (●) in Hoagland solution (1× =5.0 mg NO3-N/L + 1.0 mg PO4-P/L) at different nutrient concentrations: (a) 0.25× ; (b) 0.50× ; (c) 1.0× ; (d) 1.5× ; (e) 2.0× . Values are mean ± SD (n = 2).

Figure 3

Changes in the number of L. minor fronds in culture with P23 (○, 0.15 mg dry weight/mL) and without P23 (●) in Hoagland solution (1× = 5.0 mg NO3-N/L + 1.0 mg PO4-P/L) at different nutrient concentrations: (a) 0.25× ; (b) 0.50× ; (c) 1.0× ; (d) 1.5× ; (e) 2.0× . Values are mean ± SD (n = 2).

Figure 3

Changes in the number of L. minor fronds in culture with P23 (○, 0.15 mg dry weight/mL) and without P23 (●) in Hoagland solution (1× = 5.0 mg NO3-N/L + 1.0 mg PO4-P/L) at different nutrient concentrations: (a) 0.25× ; (b) 0.50× ; (c) 1.0× ; (d) 1.5× ; (e) 2.0× . Values are mean ± SD (n = 2).

Figure 4

Changes in the number of S. polyrhiza fronds in culture with P23 (○, 0.15 mg dry weight/mL) and without P23 (●) in Hoagland solution (1× = 5.0 mg NO3-N/L + 1.0 mg PO4-P/L) at different nutrient concentrations: (a) 0.25× ; (b) 0.50× ; (c) 1.0× ; (d) 1.5× ; (e) 2.0× . Values are mean ± SD (n = 2).

Figure 4

Changes in the number of S. polyrhiza fronds in culture with P23 (○, 0.15 mg dry weight/mL) and without P23 (●) in Hoagland solution (1× = 5.0 mg NO3-N/L + 1.0 mg PO4-P/L) at different nutrient concentrations: (a) 0.25× ; (b) 0.50× ; (c) 1.0× ; (d) 1.5× ; (e) 2.0× . Values are mean ± SD (n = 2).

Figure 5

Dry weight of duckweed biomass after 7 days in culture with P23 (□, 0.15 mg dry weight/mL) and without P23 (▪) in Hoagland solution (1× = 5.0 mg NO3-N/L + 1.0 mg PO4-P/L) at different nutrient concentrations: (A) 0.25× ; (B) 0.50× ; (C) 1.00× ; (D) 1.5× ; (E) 2.0×. Initial dry weights of 10 fronds per flask: L. aequinoctialis, 0.45 ± 0.07 mg; L. minor, 0.85 ± 0.09 mg; S. polyrhiza, 3.4 ± 0.14 mg. Values are mean ± SD (n = 2). *Significant difference (P < 0.05) between values with and without P23 within a treatment.

Figure 5

Dry weight of duckweed biomass after 7 days in culture with P23 (□, 0.15 mg dry weight/mL) and without P23 (▪) in Hoagland solution (1× = 5.0 mg NO3-N/L + 1.0 mg PO4-P/L) at different nutrient concentrations: (A) 0.25× ; (B) 0.50× ; (C) 1.00× ; (D) 1.5× ; (E) 2.0×. Initial dry weights of 10 fronds per flask: L. aequinoctialis, 0.45 ± 0.07 mg; L. minor, 0.85 ± 0.09 mg; S. polyrhiza, 3.4 ± 0.14 mg. Values are mean ± SD (n = 2). *Significant difference (P < 0.05) between values with and without P23 within a treatment.

Table 1

Effects of P23 on the growth of L. aequinoctialis, L. minor, and S. polyrhiza in sterile Hoagland solution at indicated nutrient concentrations

Duckweed speciesHoagland solutionTreatmentIncrease in number of fronds per flask during 7 daysa (and ratio of P23 to control)Biomass production (increase in dry weight; mg) of plants per flask during 7 daysa (and ratio of P23 to control)
L. aequinoctialis 0.25× P23 143 ± 5.0 (3.2)* 9.45 ± 0.71 (4.2)* 
Control 44.5 ± 0.7 2.25 ± 0.28 
0.5× P23 172 ± 4.2 (3.1)* 10.4 ± 0.07 (3.8)* 
Control 55.0 ± 2.8 2.75 ± 0.28 
1.0× P23 134 ± 9.9 (2.9)* 9.20 ± 0.35 (4.1)* 
Control 46.0 ± 1.4 2.25 ± 0 
1.5× P23 130 ± 4.2 (3.3)* 7.95 ± 0.71 (4.3)* 
Control 39.0 ± 2.8 1.85 ± 0.28 
2.0× P23 121 ± 5.7 (3.3)* 7.70 ± 0.35 (4.3)* 
Control 36.5 ± 0.7 1.80 ± 0.35 
L. minor 0.25× P23 65.5 ± 6.3 (3.0)* 9.95 ± 0.85 (3.1)* 
Control 21.5 ± 0.7 3.25 ± 0.28 
0.5× P23 85.5 ± 3.5 (3.5)* 9.80 ± 0.35 (3.0)* 
Control 24.5 ± 3.5 3.30 ± 0.07 
1.0× P23 93.5 ± 6.4 (3.8)* 9.75 ± 0.71 (3.3)* 
Control 24.5 ± 5.0 3.00 ± 0.21 
1.5× P23 86.5 ± 3.5 (3.3)* 8.45 ± 0.28 (2.8)* 
Control 26.5 ± 2.1 3.05 ± 0 
2.0× P23 71.0 ± 2.8 (2.7)* 7.40 ± 0.21 (2.3)* 
Control 26.5 ± 0.7 3.25 ± 0.28 
S. polyrhiza 0.25× P23 34 ± 1.4 (1.4)* 19.0 ± 1.2 (1.5)* 
Control 23.5 ± 3.5 12.4 ± 0.1 
0.5× P23 43.0 ± 1.4 (1.3)* 24.5 ± 0.4 (1.5)* 
Control 32.5 ± 0.7 16.1 ± 0.5 
1.0× P23 46.5 ± 2.1 (1.4)* 26.8 ± 0.8 (1.5)* 
Control 32.5 ± 0.7 17.9 ± 0.6 
1.5× P23 53.5 ± 2.1 (1.2)* 29.1 ± 0.8 (1.4)* 
Control 43.5 ± 2.1 21.5 ± 1.0 
2.0× P23 60.5 ± 2.1 (1.4)* 30.8 ± 0.9 (1.4)* 
Control 44.0 ± 1.4 21.7 ± 0.4 
Duckweed speciesHoagland solutionTreatmentIncrease in number of fronds per flask during 7 daysa (and ratio of P23 to control)Biomass production (increase in dry weight; mg) of plants per flask during 7 daysa (and ratio of P23 to control)
L. aequinoctialis 0.25× P23 143 ± 5.0 (3.2)* 9.45 ± 0.71 (4.2)* 
Control 44.5 ± 0.7 2.25 ± 0.28 
0.5× P23 172 ± 4.2 (3.1)* 10.4 ± 0.07 (3.8)* 
Control 55.0 ± 2.8 2.75 ± 0.28 
1.0× P23 134 ± 9.9 (2.9)* 9.20 ± 0.35 (4.1)* 
Control 46.0 ± 1.4 2.25 ± 0 
1.5× P23 130 ± 4.2 (3.3)* 7.95 ± 0.71 (4.3)* 
Control 39.0 ± 2.8 1.85 ± 0.28 
2.0× P23 121 ± 5.7 (3.3)* 7.70 ± 0.35 (4.3)* 
Control 36.5 ± 0.7 1.80 ± 0.35 
L. minor 0.25× P23 65.5 ± 6.3 (3.0)* 9.95 ± 0.85 (3.1)* 
Control 21.5 ± 0.7 3.25 ± 0.28 
0.5× P23 85.5 ± 3.5 (3.5)* 9.80 ± 0.35 (3.0)* 
Control 24.5 ± 3.5 3.30 ± 0.07 
1.0× P23 93.5 ± 6.4 (3.8)* 9.75 ± 0.71 (3.3)* 
Control 24.5 ± 5.0 3.00 ± 0.21 
1.5× P23 86.5 ± 3.5 (3.3)* 8.45 ± 0.28 (2.8)* 
Control 26.5 ± 2.1 3.05 ± 0 
2.0× P23 71.0 ± 2.8 (2.7)* 7.40 ± 0.21 (2.3)* 
Control 26.5 ± 0.7 3.25 ± 0.28 
S. polyrhiza 0.25× P23 34 ± 1.4 (1.4)* 19.0 ± 1.2 (1.5)* 
Control 23.5 ± 3.5 12.4 ± 0.1 
0.5× P23 43.0 ± 1.4 (1.3)* 24.5 ± 0.4 (1.5)* 
Control 32.5 ± 0.7 16.1 ± 0.5 
1.0× P23 46.5 ± 2.1 (1.4)* 26.8 ± 0.8 (1.5)* 
Control 32.5 ± 0.7 17.9 ± 0.6 
1.5× P23 53.5 ± 2.1 (1.2)* 29.1 ± 0.8 (1.4)* 
Control 43.5 ± 2.1 21.5 ± 1.0 
2.0× P23 60.5 ± 2.1 (1.4)* 30.8 ± 0.9 (1.4)* 
Control 44.0 ± 1.4 21.7 ± 0.4 

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.

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