Elevated Ozone Negatively Affects the Community Characteristics and Productivity of Subtropical Grassland in India

Abstract

Tropospheric ozone (O3) is found to be a severe threat to agriculture and natural vegetation. The present study was conducted to investigate the structural and functional changes in an intact seminatural grassland community when exposed to elevated O3 (EO3; ambient + 20 parts per billion) compared to ambient O3 (AO3) for 3 years using open-top chambers. Parameters such as species richness (SR), evenness (E), Shannon index (H′), β-diversity (BD), concentration of dominance (Cd), similarity index (SI), biomass in canopy layers, and community productivity were evaluated. Species like Cynodon dactylon, Dichanthium annulatum, Parthenium hysterophorus, Digitaria sanguinalis, Cyperus killinga, Oplismenus burmannii, and Commelina benghalensis showed higher importance value index (IVI), whereas Trifolium resupinatum, Desmodium triflorum, Melilotus officinalis, Oxalis corniculata, Eleusine indica, Cyperus rotundus, Malvestrum coromandelianum, and Lindernia anagallis showed lower IVI under EO3 treatment compared to AO3. EO3 enhanced BD and Cd, whereas SR, E, and H′ in the community reduced. Biomass accumulation reduced maximally in top layer compared to bottom and middle canopy layers in both forbs and grasses fraction under EO3 treatment. Higher reduction in total biomass compared to aboveground biomass indicates less carbon allocation toward root system. The results of the present study clearly indicates that 3 years of exposure at EO3 level caused deleterious impact on grassland community by increasing O3-tolerant and decreasing sensitive species, thus resulting in a shift in species composition and community productivity.