Biofertilizer and biostimulant properties of the microalga Acutodesmus dimorphus

Abstract

Microalgae represent a potential sustainable alternative for the enhancement and protection of agricultural crops. Cellular extracts and dry biomass of the green alga Acutodesmus dimorphus were applied as a seed primer, foliar spray, and biofertilizer, to evaluate seed germination, plant growth, and fruit production in Roma tomato plants. A. dimorphus culture, culture growth medium, and different concentrations (0, 1, 5, 10, 25, 50, 75, and 100 %) of aqueous cell extracts in distilled water were used as seed primers to determine effects on germination. Seeds treated with A. dimorphus culture and with extract concentrations higher than 50 % (0.75 g mL^-1) triggered faster seed germination-2 days earlier than the control group. The aqueous extracts were also applied as foliar fertilizers at various concentrations (0, 10, 25, 50, 75, and 100 %) on tomato plants. Extract foliar application at 50 % (3.75 g mL^-1) concentration resulted in increased plant height and greater numbers of flowers and branches per plant. Two dry biomass treatments (50 and 100 g) were applied 22 days prior to seedling transplant and at the time of transplant to assess whether the timing of the biofertilizer application influenced the effectiveness of the biofertilizer. Biofertilizer treatments applied 22 days prior to seedling transplant enhanced plant growth, including greater numbers of branches and flowers, compared to the control group and the biofertilizer treatments applied at the time of transplant. The A. dimorphus culture, cellular extract, and dry biomass applied as a biostimulant, foliar spray, and biofertilizer, respectively, were able to trigger faster germination and enhance plant growth and floral production in Roma tomato plants.

Keywords: Acutodesmus dimorphus; Biofertilizer; Biostimulant; Foliar spray; Microalgae; Seed primer.

Fig. 1

Seed germination percentage: seeds treated with Acutodesmus culture (S9), growth medium (S8), and cell extracts: S1 1 % extract concentration, S2 5 % extract concentration, S3 10 % extract concentration, S4 25 % extract concentration, S5 50 % extract concentration, S6 75 % extract concentration, and S7 100 % extract concentration. All extract dilutions were with DI water

Fig. 2

Germination energy of seeds treated with Acutodesmus culture (S9), growth medium (S8), and cell extracts: S1 1 % extract concentration, S2 5 % extract concentration, S3 10 % extract concentration, S4 25 % extract concentration, S5 50 % extract concentration, S6 75 % extract concentration, and S7 100 % extract concentration. All extract dilutions were with DI water

Fig. 3

Effects of Acutodesmus culture (S9), growth medium (S8), and extract concentrations (S1–S7) on lateral root development of tomato seedlings. S1 1 % extract concentration, S2 5 % extract concentration, S3 10 % extract concentration, S4 25 % extract concentration, S5 50 % extract concentration, S6 75 % extract concentration, and S7 100 % extract concentration. All extract dilutions were with DI water. Columns denoted by a different letter are significantly different at P < 0.05. Values represent average (n = 10); bars represent standard error

Fig. 4

a Effects of cell extracts as foliar treatments on flower development, b effects of foliar treatments on average number of branches, c effects of foliar sprays on average shoot length per treatment on tomato plants: T1 10 % extract concentration, T2 25 % extract concentration, T3 50 % concentration, T4 75 % concentration, and T5 100 % extract concentration. All extract dilutions were with DI water. Columns denoted by a different letter are significantly different at P < 0.05. Values represent average (n = 3); bars represent standard error

Fig. 5

Effects of Acutodesmus dimorphus extracts as foliar sprays on total fresh plant weight (one sample per treatment chosen at random)

Fig. 6

a Effects of biofertilizer on branch development—number of branches per plant (P = 0.0002), b effects on number of flowers (P = 0.0001), and c effects on early fruit setting—number of fruits (P = 0.0129): B1 50 g 22 days prior to transplant, B2 100 g 22 days prior to transplant, B3 50 g at the time of transplant, and B4 100 g at the time of transplant. Columns denoted by a different letter are significantly different at P < 0.05. Values represent average (n = 3); bars represent standard error

Fig. 7

Total fresh plant (shoot + root) weight of samples selected at random from treatments: B1 50 g 22 days prior to transplant, B2 100 g 22 days prior to transplant, B3 50 g at the time of transplant, and B4 100 g at the time of transplant