Microalgae-based biofertilizers improve fertility and microbial community structures in the soil of potted tomato

Continuous cropping decreases soil nutrients and destroys microbial community structure, so the development of eco-friendly and effective biofertilizers is necessary under present conditions. In this study, the preserving microalgal strain <i>Tribonema</i> sp. (H) was firstly selected to be combined with agroforestry waste (shell powder, straw fermentation liquid) and the agroforestry microorganism <i>Bacillus</i> sp. to form microalgae-based fertilizers for the continuous cropping soil of potted tomato. Compared to the control (CK), microalgae-based fertilizers (concentration: 4.45 × 10⁶ cells/ml, dosage: 20 ml/day) improved soil nutrients and salinization indicators. Specifically, the combination of <i>Tribonema</i> sp. and shell powder (HB) reduced electrical conductivity (EC) by 33.7% and significantly increased the Ca²⁺ content by 59.4%; <i>Tribonema</i> sp. and <i>Bacillus</i> sp. (HY) improved the effects of available phosphorous (AP), DOC, DON, NH₄ ⁺-N, NO₃ ^--N, and Mg²⁺ in the soil by 27.4%, 231.3%, 403.4%, 125.2%, 215.6%, and 73.4%, respectively. Microalgae-based fertilizers alter the abundance of soil bacteria and fungi, causing beneficial bacteria such as <i>Thermonaerobaculia</i>, <i>Subgroup_10</i>, <i>Sordariomycetes</i>, and <i>Microascaceae</i> to increase, while pathogenic bacteria like <i>Pseudomonas</i>, <i>Togniniaceae</i>, and <i>Phaeoacremonium</i> decreased. Combining microalgae with agroforestry wastes as a biofertilizer is promising to improve the microbial community structure of the soil with continuous cropping, which will aid in the increase of tomato production and promote green agricultural development.