Changes in growth pattern and rhizospheric soil biochemical properties of a leguminous tree species Leucaena leucocephala under long-term exposure to elevated ozone

Increasing concentrations of ground-level ozone (O₃) exert significant impacts on the plants, but there is limited data for belowground processes. We studied the effects of long-term exposure of elevated O₃ (EO₃) on plant growth parameters (plant height and biomass) and biochemical parameters (nutrients, microbial biomass and enzymatic activities) of rhizospheric soil of leguminous tree species Leucaena leucocephala. L. leucocephala seedlings were grown under ambient O₃ (AO₃) and EO₃ (+20 ppb above ambient) under Free Air Ozone Concentration Enrichment (O₃-FACE) facility and changes in plant growth and their rhizospheric soil properties were studied during 6, 12, 18 and 24 months of EO₃ exposure. L. leucocephala showed significant reductions in shoot length, root biomass, shoot biomass, leaf biomass and total biomass during 12, 18 and 24 months of exposure to EO₃. Total nutrients in rhizospheric soil like carbon and phosphorus were significantly reduced after 24 months of EO₃ exposure. Most of the available nutrients showed significant reduction after 6, 12 and 24 months of EO₃ exposure. A significant decrease was apparent in microbial biomass carbon, nitrogen and phosphorus after 6, 12, 18 and 24 months of EO₃ treatment. Significant reductions were observed in extracellular enzymatic activities (dehydrogenase, alkaline phosphatase, β-glycosidase, fluorescein diacetate, arylsulfatase, cellulase and protease) of soil after 6, 12 and 24 months of EO₃ exposure. These results suggest that increasing O₃ concentrations will directly impact L. leucocephala growth as well as have indirect impact on the nutrient contents (C, N, and P), microbial biomass and extracellular enzymatic activities of rhizospheric soil of L. leucocephala. Our results suggest that continuous increase in O₃ concentrations will have serious implications for aboveground plant growth and belowground soil fertility in this region considered as O₃ hotspot.