Effect of salinity on mycorrhizal onion and tomato in soil with and without additional phosphate

Abstract

Vesicular-arbuscular mycorrhizal fungi (VAM) are known to increase plant growth in saline soils. Previous studies, however, have not distinguished whether this growth response is due to enhanced P uptake or a direct mechanism of increased plant salt tolerance by VAM. In a glasshouse experiment onions (Allium cepa L.) were grown in sterilized, low-P sandy loam soil amended with 0, 0.8, 1.6 mmol P kg-1 soil with and without mycorrhizal inoculum. Pots were irrigated with saline waters having conductivities of 1.0, 2.8, 4.3, and 5.9 dS m-1. Onion colonized with Glomus deserticola (Trappe, Bloss, and Menge) increased growth from 394% to 100% over non-inoculated control plants when soil P was low (≤ 0.2 mmol kg-1 NaHCO3-extractable P) at soil saturation extract salinities from 1.1 dS m-1 to 8.8 dS m-1. When 0.8 and 1.6 m M P was added no dry weight differences due to VAM were observed, however, K and P concentrations were higher in VAM plants in saline treatments. Glomus fasciculatum (Gerdeman and Trappe) and Glomus mosseae (Nicol. and Gerd.) isolates increased growth of VAM tomato 44% to 193% in non-sterilized, saline soil (10 dS m-1 saturation extract) despite having little effect on growth in less saline conditions when soil P was low. Higher tomato water potentials, along with improved K nutrition by VAM in onion, indicate mechanisms other than increased P nutrition may be important for VAM plants growing under saline stress. These effects appear to be secondary to the effects of VAM on P uptake. © 1985 Martinus Nijhoff Publishers.