Rhizosphere Microbial Function Overrides Diversity in Enhancing Aromatic Rice Yield and Quality Under Organic...

Non-Basmati aromatic rice varieties of Indian landrace are preferred for their distinctive aroma and superior grain quality, yet they generally exhibit lower yield potential. Rhizosphere microbial activities play a crucial role in plant performance under organic nutrient management. A 3-year field experiment was conducted in Indo-Gangetic alluvial soil to evaluate whether microbial ecological diversity or functional attributes exert a stronger impact on the yield and aroma of six indigenous non-basmati aromatic rice varieties, along with one non-aromatic check. A total of 140 bacterial cultures, 20 from the rhizosphere of each variety, were characterized for carbon source utilization, stress resistance, and antibiotic resistance, and grouped by hierarchical clustering to estimate diversity. The correlation between the diversity indices and grain yield and aroma score was weak or negative. In contrast, microbial population size, nitrogen fixation, and nutrient-solubilizing capacity showed strong and positive correlation with grain yield and aroma intensity. Principal component analysis clearly distinguished functional traits from ecological diversity indices. Among the tested varieties, Kalojeera rhizosphere had the highest microbial functional activity (57%, 105%, 26%, and 33% higher N fixation and P, K, and Zn solubilization, respectively, than Dudheswar) and grain yield, while Dudheswar had comparatively lower functional capacities. The results clearly demonstrate that microbial functional capacity, rather than species diversity, is the primary determining factor for crop productivity and grain quality under organic farming. Strategies for the selection of aromatic rice varieties harboring rhizosphere microbial functional activities and promoting efficient nutrient cycling could help sustainable aromatic rice production.