Arbuscular mycorrhizal fungi effect on the hydrological regime in vegetated soil

Arbuscular mycorrhizal fungi (AMF) are increasingly used as biofertilisers in agriculture and being implemented in geotechnical engineering to establish vegetation on slopes. It is therefore crucial to understand the geotechnical consequences of AMF inoculation on water removal and retention and, hence, on the stability of embankments and cut slopes. A first series of laboratory experiments involved planting Medicago sativa or Lolium perenne in mini-lysimeters, either inoculated with Rhizophagus irregularis or Funneliformis mosseae, or left uninoculated, and the monitoring of transpiration rates. A second series only involved M. sativa with monitoring of transpiration rates plus pore-water pressure and soil water content. AMF inoculation in M. sativa in the first experiment increased potential transpiration by over 55% due to increased shoot biomass but produced no effect in the second experiment despite similar AMF colonisation. This was attributed to nutrient scarcity in the first experiment that possibly promoted fungal growth to scavenge nutrients in soil pores not accessible to roots. AMF inoculation did not significantly affect L. perenne transpiration, possibly because AMF did not offer competitive advantages compared to the fine fibrous roots. No differences were observed in water-limited transpiration, consistent with no changes in water retention behaviour observed at low degrees of saturation.