Promoting early growth in tomato (Solanum lycopersicum L.) by co-application of biochar and beneficial bacteria

The use of biochar and beneficial bacteria as biofertilizers is gaining increasing attention as a means to reduce the reliance on agrochemical inputs in future agriculture. However, the dynamics of introduced bacteria in biochar-amended soils, as well as the additive effects of bacteria and biochar during the early stages of plant growth, are still poorly characterized. First, a synthetic bacterial community was formulated and its ability to survive was assessed in both non-amended and biochar-amended soils. Secondly, both the individual and combined effects of biochar (applied at 10% (w: w)) and a consortium of five bacteria (Bacillus sp. strain B1, Bacillus velezensis strain Bv1, Bacillus pumilus strain Bp1, Bacillus licheniformis sp. strain Bl1 and Priestia megaterium strain Pm1) isolated from a bio-fertilizer were examined on various biometric and physiological traits of young tomato (Solanum lycopersicum L. var. Principe borghese) plants. At the seedling stage, the sole application of bacteria increased hypocotyl length by 25%, but decreased radicle length compared to non-treated soils. At the plantlet stage, bacteria alone further increased both shoot length by and leaf surface area by 13% and 22%, respectively, but decreased leaf chlorophyll content. On the other hand, co-application of biochar and bacteria partially restored leaf chlorophyll content to control levels, and showed additive effects improving the fresh and dry weight of aboveground tissues by ~ 30% compared to untreated soils. Biochar amendment decreased leaf N content both in the presence and absence of bacteria, suggesting a possible N immobilization in biochar particles which could reduce its availability for the plant. These results point biochar as a suitable material for the survival and viability of synthetic bacterial communities, and show that biochar and the tested inoculum can additively improve key attributes in young tomato plants.