Enhanced Growth Performance of Bauhinia purpurea L. and Rhizosphere Soil Microbial Communities by Inoculation of Beneficial Microbes

Bauhinia purpurea (belonging to Family Fabaceae-Leguminosae) is a small to medium-sized deciduous fast-growing tree that is very important in reforestation and agroforestry, and also used as fodder for livestock. This study investigated the influence of mycorrhizal inoculant with varying nitrogen-fixing bacteria (NFB) amendment levels on the growth performance of B. purpurea, the buildup of microbial communities in its rhizosphere soil, and root colonization in screenhouse conditions with UV plastic roofing, following a two-factor randomized complete block design. Factor 1 was the type of mycorrhizal inoculants applied on containerized seedlings grown in garden soil: AMF1 (MYKOCAP® or MCAP) and AMF2 (MYKORICH® or MRICH). Factor 2 was the rate of NFB (BioNTM) amendment (0 g, 5 g per seedling). At 90 d, MCAP + BioN treated plants were 37% taller than the MRICH + BioN treated ones (34 ± 0.50 cm). Seedlings with MCAP + BioN or MRICH + BioN had higher diameter increment; partitioned biomass from stems, lateral roots, and primary roots; root-shoot ratio; and root colonization than those without BioN and the control. Likewise, the NFB population was 276 and 126%, respectively higher with MCAP + BioN and MRICH + BioN than their counterparts without BioN. Contrarily, partitioned biomass from leaves, roots, and shoots, and the arbuscular mycorrhizal fungi (AMF) spore density were higher with AMF inoculants alone. Spore count was strongly positively correlated with primary root biomass (p = 0.013, r = 0.573), NFB buildup with height increment (p = 0.001, r = 0.708), and root colonization with diameter increment (p = 0.001, r = 0.805), total biomass (p = 0.023, r = 0.532), stem biomass (p = 0.001, r = 0.692), shoot biomass (p = 0.001, r = 0.698), primary root biomass (p = 0.029, r = 0.514), and root biomass (p = 0.005, r = 0.628). AMF and NFB symbiosis was inferred to have been developed, thereby promoting overall plant growth with an increased mycorrhizal root infection and NFB buildup, while the increased spore density contributed to enhanced primary root growth. Field verification trials must be conducted to determine the microbial fertilizer’s efficacy under abiotic and biotic stresses.