Elevated CO along with inoculation of cyanobacterial biofilm or its partners differentially modulates C-N metabolism and quality of tomato beneficially.

Diazotrophic cyanobacteria are known to influence nutrient availability in soil, however, their benefits under elevated CO environment, particularly on fruit quality attributes, is a less investigated aspect. Laboratory developed cyanobacterium-fungal biofilm (An-Tr), composed of (An) as the matrix with the partner as (Tr), along with the individual partners were evaluated under ambient (aCO-400 ± 50 ppm) and elevated (eCO-700 ± 50 ppm) conditions, with and without tomato plants. An-Tr inoculation exhibited distinct and significantly higher values for most of the soil microbiological parameters, plant growth attributes and antioxidant/defense enzyme activities measured at 30 and 60 DAI (days after inoculation). Significant enhancement in soil nutrient availability, leaf chlorophyll, with 45-50% increase in the enzyme activities related to carbon and nitrogen assimilation, higher yields and better-quality parameters of tomato, with An-Tr biofilm or An inoculation, were recorded, particularly under eCO conditions. The fruits from An-Tr treatments under eCO exhibited a higher titrable acidity, along with more ascorbic acid, carotenoids and lycopene content, highlighting the superiority of this inoculant. Multivariate analyses revealed significant (p ≤ 0.05) interactions among cultures, DAI, and CO levels, illustrating that cyanobacterial inoculation can be advocated as a strategy to gainfully sequester eCO. Significant improvement in yield and fruit quality along with 50% N savings, further attest to the promise of cyanobacterial inoculants for tomato crop in the climate change scenario.