Title : Use of phosphate-solubilizing bacteria to foster P availability and promote maize growth in P-deficient soils
The agricultural sector is facing several challenges related to climate change and decrease of soil fertility, which is impacting the production of staple food crops. To meet the global food demand and overcome the nutrient deficiency in soils, farmers usually apply high doses of chemical fertilizers. However, this practice brings several environmental and human health concerns, while do not solve the low bioavailability of some nutrients, namely phosphorous (P). Moreover, P resources in nature are finite being of utmost importance to turn available P from all possible sources. Soil microorganisms, namely the phosphate solubilizing bacteria (PSB) can solubilize and/or mineralize insoluble P forms turning them available to plants, increasing their growth under P-deficient conditions.This presentation comprises the results obtained in two different works aiming: (i) to evaluate the ability of PSB to solubilize hydroxyapatite (a naturally occurring calcium phosphate) extracted from the scales of tilapia (Coptodon rendalli) and (ii) to assess the effects of PSB inoculation on Zea mays growth in an agricultural P-deficient soil. In the first work, several different PSB strains were tested for their ability to solubilize tricalcium phosphate (TCP) and hydroxyapatite from fish scale (FSHA). The strain Acidovorax oryzae ZS 1–7 was the best performing bacterial strain, by solubilizing 325 mg/L of P after 10 days, >60 times higher than the negative control. Such solubilisation was related to a decrease of the pH to more acidic values of about 4. This strain also showed higher P solubilisation efficiency with FSHA than with commercial TCP. In the second work, three P-solubilizing strains, Rhodococcus sp. EC35 (B1), Pseudomonas sp. EAV (B2) and Arthrobacter nicotinovorans EAPAA (B3), were singly and mixed (BM) inoculated in maize plants growing in P-deficient soils. Three P-treatments were applied to the soils: control – without P fertilization, soluble P (KH2PO4) and TCP (sparingly soluble P). Overall, PSB inoculation fostered maize growth in all treatments. In soils without P fertilization, bacterial inoculation enhanced P accumulation in roots and shoots, as well as plant dry biomass (ca. 20%). Strain B2 was the bacteria that best performed in soils amended with soluble P, improving root and shoot biomass by 102% and 63%, respectively. In soils amended with TCP, maize biomass and P accumulation were also enhanced by PSB inoculation (strain B3 and BM). The results obtained clearly indicate that the use of residues from the fishing industry, namely tilapia scales, can constitute an alternative source of P when associated with PSB. In addition, PSB inoculation proved to be effective in promoting maize biomass, being an attractive alternative to reduce the rate of application of chemical P-fertilizers.