Deterioration of rhizospheric soil health due to elevated ultraviolet-B

Abstract

Enhancements in ultraviolet-B radiation (UV-B) due to stratospheric ozone depletion affect biological forms directly and indirectly. To investigate how belowground processes are affected under increased UV-B, a field experiment with mung bean cultivars (HUM-1 and HUM-12) was conducted. The responses of selected soil enzymes (β-glucosidase, cellobiohydrolase, polyphenol oxidase, glycine aminopeptidase, and phosphatase), microbial biomass C and N were assessed in rhizospheric and non-rhizospheric zones, along with measurements of phenol and flavanoid contents in roots and leaves. Test plants were exposed to two UV-B levels: (1) UVB, simulating 20% stratospheric O₃ depletion; and (2) UV0, the ambient UV-B. Elevated UV-B depressed shoot biomass by 24.8 and 15.9% and root biomass by 43.7 and 38.4% in cv. HUM-1 and HUM-12 compared with UV0. Although elevated UV-B caused an increase in phenol and flavonoid contents in leaves and roots, a reduction in the number of root nodules (32.4 and 24% in HUM-1 and HUM-2, respectively) and their fresh weight (27 and 23% in HUM-1 and HUM-2, respectively) was observed. Elevated UV-B caused microbial activity to shift from the rhizosphere to non-rhizosphere as indicated by increased microbial biomass N and soil enzyme activities in this zone.

Keywords:

• UV-B
• soil enzymes
• rhizosphere
• non-rhizosphere
• phenol
• flavonoids

Acknowledgements

Authors are grateful to the Head, Department of Botany, Banaras Hindu University for providing all the necessary laboratory facilities and to U.G.C., Government of India, New Delhi for financial support.