Assessing Tropospheric Ozone Influence on Garlic (Allium sativum L.) Rhizosphere Microbial Activity

The study conducted at the Climate Change Observatory, Woodhouse Farm, HRS, Ooty, during 2018-2019 focused on investigating the impact of ozone and ozone protectants on rhizosphere microbial activity in garlic cultivation. Specifically, the experiment evaluated the response of the commercial local variety Ooty-1 garlic to varying ozone levels and ozone protectants. Results from the study demonstrated notable variations in microbial activity, including bacteria, fungi, and actinomycetes, within the rhizosphere of garlic plants under different experimental conditions. Notably, the highest increase in bacterial activity was observed under ambient conditions with panchagavya spray, recording a significant log10 cfu/g of 8.9. Similarly, fungal and actinomycetes activity exhibited higher levels under ambient conditions, with respective log10 cfu/g values of 4.8 and 4.7. Conversely, elevated ozone levels at 150 ppb and 200 ppb led to a decline in bacterial, fungal, and actinomycetes activity within the rhizosphere. The reductions were substantial, with bacterial activity dropping to 2.5 log10 cfu/g and 1.9 log10 cfu/g, fungal activity to 1.1 log10 cfu/g and 0.9 log10 cfu/g, and actinomycetes activity to 2.4 log10 cfu/g and 2.1 log10 cfu/g at the respective ozone levels. However, the application of ozone protectants, including 3% panchagavya, 3% neem oil, and 0.1% ascorbic acid, demonstrated a mitigating effect on the negative impacts of tropospheric ozone on rhizosphere microbial diversity. This finding suggests that escalating concentrations of tropospheric ozone have a detrimental effect on the soil microbial activity of garlic. Still, the use of ozone protectants can significantly alleviate these effects by promoting microbial growth. Overall, the study underscores the importance of understanding the complex interactions between ozone levels, ozone protectants, and rhizosphere microbial activity in garlic cultivation, offering valuable insights for sustainable agricultural practices in the face of climate change challenges.