Responses of a semi-natural grassland community of tropical region to elevated ozone: An assessment of soil dynamics and biomass accumulation

摘要

Despite knowing the phytotoxic effects of tropospheric ozone (O_3), which is of global concern, there is no study so far reported about its impacts on grassland community of tropical regions. Therefore, we assessed the responses of a semi-natural grassland community of Indo-Gangetic plains to elevated O_3 exposure (Ambient + 20 ppb) compared to ambient after three years of exposure using open-top chambers. Percent decreases were found in above (26%; p ≤ 0.002) and belowground (30%; p ≤ 0.003) biomass under elevated compared to ambient O_3 exposure. Percent decrements in total organic carbon (TOC; 24%; p ≤ 0.001), total nitrogen (29%; p ≤ 0.001) and available phosphorus (11%; p ≤ 0.002) in the soil were also observed under elevated O_3 exposure. Exposure at elevated O_3 reduced soil microbial biomass and activities of β-glucosidase, amylase, urease and phos-phatase, while polyphenol oxidase and peroxidase showed enhancement in their activities, showing negative effects on belowground soil health. Percent reduction in root shoot ratio (10%; p ≤ 0.05) depicts that less C-allocation towards root system led to a reduction in TOC in the soil, which could affect C-sequestration under elevated O_3 condition in the semi-natural grasslands. Elevated O_3 also affected enzymes participating in N and P-cycles, causing reductions in total nitrogen and phosphorus. The study concludes that projected O_3 concentrations have serious implications for aboveground biomass as well as belowground soil health in tropical areas, identified as hotspots of O_3 in the world.