Nostoc, Microcoleus and Leptolyngbya inoculums are detrimental to the growth of wheat (Triticum aestivum L.) under salt stress

This study investigated the effect of cyanobacterial inoculants on salt tolerance in wheat. Unicyanobacterial crusts of Nostoc, Leptolyngbya and Microcoleus were established in sand pots. Salt stress was targeted at 6 and 13 dS m(-1), corresponding to the wheat salt tolerance and 50 % yield reduction thresholds, respectively. Germinated wheat seeds were planted and grown for 14 (0 and 6 dS m(-1)) and 21 (13 dS m(-1)) days by which time seedlings had five emergent leaves. The effects of cyanobacterial inoculation and salinity on wheat growth were quantified using chlorophyll fluorescence, inductively coupled plasma-optical emission spectrometry and biomass measurements. Chlorophyll fluorescence was negatively affected by soil salinity and no change was observed in inoculated wheat. Effective photochemical efficiency correlated with a large range of plant nutrient concentrations primarily in plant roots. Inoculation negatively affected wheat biomass and nutrient concentrations at all salinities, though the effects were fewer as salinity increased. The most likely explanation of these results is the sorption of nutrients to cyanobacterial extracellular polymeric substances, making them unavailable for plant uptake. These results suggest that cyanobacterial inoculation may not be appropriate for establishing wheat in saline soils but that cyanobacteria could be very useful for stabilising soils.