Mycorrhizal dependency and growth responses of Acacia nilotica and Albizzia lebbeck to inoculation by indigenous AM fungi as influenced by available soil P levels in a semi-arid soil.

SHARMA, MAHAVEER P¹, N.P BHATIA¹, RKS CHAUHAN², & ALOK ADHOLEYA¹.

Microbial Biotechnology, Tata Energy Res Inst, Habitat Place, Lodi Rd, New Delhi 110003, INDIA, School of studies in Botany, Jiwaji University, Gwalior, MP, INDIA.

A gradient of available phosphorus (Olsen) levels ranging from 10 to 40 ppm was achieved in a semi- arid soil. The influence of the levels of phosphorus on the symbiotic interaction between two subtropical tree species, namely A.nilotica and A.lebbeck, and a mixed inoculum of indigenous arbuscular mycorrhizal (AM) fungi was evaluated in a greenhouse study. The extent to which the plant species depended on AM fungi for dry matter production decreased as the levels of soil P increased, but the degree of this decrease differed in the two species tested. A.nilotica colonised by AM fungi showed a significant increase in shoot P and dry matter at a soil P level of 10 ppm where as in A.lebbeck , such increase occurred at 20 ppm.Levels of soil P greater than 25 ppm suppressed AM fungus colonization in both the species. Soil P levels of 30 and 40 ppm and 40 ppm showed negative mycorrhizal dependencies (MD) in A.nilotica and A.lebbeck respectively.Based on the MD values, regression equations were developed to predict MD under a given set of edapho-climatic conditions.

Key words: Soil P levels, mycorrhizal dependency, indigenous arbuscular mycorrhizae