Arbuscular mycorrhizal fungi alleviate iron deficient chlorosis in Poncirus trifoliata L. Raf under calcium bicarbonate stress

The effect of the arbuscular mycorrhizal (AM) fungus Glomus versiforme on chlorosis due to iron deficiency in trifoliate orange (Poncirus trifoliata L. Raf) was studied under calcium bicarbonate stress in sand culture. Seeds were sown in a mixed substrate [1:l (v/v), perlite:sand] with or without mycorrhizal inoculum. The test was carried out with four treatments: Hoagland and Arnon nutrient solution with normal, no added iron, or 50% normal iron at two levels of calcium bicarbonate. The results showed that the proportion of the total root length infected by the AM fungus was >= 83%, and was depressed under Fe deficiency. No root colonisation was found with no added AM fungus (NM plants). Colonisation by AM fungus resulted in higher dry weights of both shoots and roots compared to NM treatments, suggesting that the AM fungus accelerated plant growth. The activities of peroxidase and catalase in NM plants were lower than in AM fungus-inoculated plants. The results indicate that AM fungus alleviated calcium bicarbonate stress on the cell membranes of host plants. The results also showed that AM fungus increased chlorophyll concentrations, iron contents, and the Fe:P ratios of whole plants, and decreased 50(10P+K):Fe ratios, which implied that the uptake and translocation of iron was strengthened. Therefore, AM fungus had a positive effect on ameliorating chlorosis due to iron deficiency in P. trifoliata L. Raf.