Phosphate-Solubilizing Bacteria as a Panacea to Alleviate Stress Effects of High Soil CaCO3 Content in Phaseolus vulgaris with Special Reference to P-Releasing Enzymes

The present study examines the role of leguminous compost (LC), humic acids (HA), and phosphate-solubilizing bacteria (P-SB) in alleviating the stress effects of high soil CaCO3 content in Phaseolus vulgaris. Two pot trials for two consecutive seasons; fall 2019 and summer 2020 were implemented in an open greenhouse. A mixed three-way ANOVA, two independent factors (season and soil treatments) and one within factors (time) were used with four replicates. Residual maximum likelihood (REML) analysis was used for the mixed model of the studied traits. Inoculation of calcareous soil with P-SB (a 1:1 mixture of two Pseudomonas sp.; Ps. mallei and Ps. cepaceae) significantly exceeded LC, HA, or even LC+HA for the positive results obtained. P-SB facilitated nutrient solubility (e.g., N, K, Fe, and Mn), including conversion of insoluble phosphorous into a form available in the tested soil due to increased soil enzymatic activities (e.g., phosphatases and phytases). This mechanism, combined with a decrease in soil calcium carbonate content and an increase in cation exchange capacity (CEC) and organic matter (OM) content, increased the availability of various nutrients to plants, including P, in the soil, which contributed to the increased plant output. Adequate P content in plants led to a marked decrease in plant acid phosphatase activity under high content of CaCO3. The study concluded that the use of P-SB promotes biological activities, nutrient availability, and thus the productivity of calcareous soils, enabling Phaseolus vulgaris plants to withstand stress produced by high CaCO3 content through the development and/or adoption of potentially effective mechanisms. Strong highly significant interactions between the treatments and time were observed using the Wald’s statistics test, which indicates a positive correlation.