Coinoculation of black locust with Rhizobium and Glomus on a desurfaced soil

Abstract

Seedlings of Black locust (Robinia pseudoacacia L.) were co-inoculated with a local effective strain Rhizobium sp. RpI1 and with Glomus deserticola. The effects of both symbioses on plant growth were studied in a greenhouse experiment with four treatments: two single inoculations, one double inoculation, and no inoculation, in a non-sterilized substrate from a desurfaced soil. A synergic effect was observed because double inoculation produced significantly higher shoot biomass, nodule biomass and N2 fixation measured by the acetylene reduction assay (at least 93%, 50% and 192%, respectively), than any single inoculation treatment and than non-inoculated controls which were nodulated by soil-born rhizobia. Mycorrhizal colonization did not improve the growth of control plants, but significantly improved the specific nitrogenase activity of plants inoculated with Rhizobium sp. RpI1 by 77%. We conclude that pre-nodulation of plants is necessary for a better growth on harsh substrates, and that mycorrhizal colonization help nodulated plants to reach their phosphorus demand in P-limited soils.