An assessment of growth, floral morphology, and metabolites of a medicinal plant Sida cordifolia L. under the influence of elevated ozone.

Tropospheric ozone (O3) is a major secondary air pollutant and greenhouse gas, and its impact on growth, yield, and its quality is well established in the case of crop plants. However, the effects of tropospheric O3 have not been comprehensively studied on medicinal plants. Therefore, a field study was planned on a medicinally important Sida cordifolia L. plant (commonly known as country mallow or Bala) to assess the expected changes on the morphology, growth, and leaf injury under elevated O3 (ambient + 20 ppb) by using open-top chambers (OTCs) at 30, 60, and 90 days after treatment (DAT), while leaf and root metabolites were observed at 60 DAT. At all the growth stages, significant leaf damage was recorded as foliar injury symptoms. Most of the growth parameters also showed significant reductions at all the growth stages. Plants under elevated O3 showed a significant negative impact on most of the reproductive parts of the plant. Leaf weight ratio (LWR) showed significant increment at early stages while reduced at 90 DAT; however, root shoot ratio (RSR) showed a significant reduction at 60 DAT. The majority of the steroid metabolites showed an increase in root and leaves under elevated O3, while terpenes showed variable response. Due to O3 stress, most of the major metabolites showed an increase possibly due to their role in defense and other metabolic activities. Based on the outcomes, it is concluded that the future increase in the levels of tropospheric O3 will impact a significant effect on important metabolites of medicinal plants growing in tropical countries like India.