Establishment and effectiveness of inoculated arbuscular mycorrhizal fungi in agricultural soils

Abstract

Arbuscular mycorrhizal fungi (AMF) are promoted as biofertilizers for sustainable agriculture. So far, most researchers have investigated the effects of AMF on plant growth under highly controlled conditions with sterilized soil, soil substrates or soils with low available P or low inoculum potential. However, it is still poorly documented whether inoculated AMF can successfully establish in field soils with native AMF communities and enhance plant growth. We inoculated grassland microcosms planted with a grass-clover mixture (Lolium multiflorum and Trifolium pratense) with the arbuscular mycorrhizal fungus Rhizoglomus irregulare. The microcosms were filled with eight different unsterilized field soils that varied greatly in soil type and chemical characteristics and indigenous AMF communities. We tested whether inoculation with AMF enhanced plant biomass and R. irregulare abundance using a species specific qPCR. Inoculation increased the abundance of R. irregulare in all soils, irrespective of soil P availability, the initial abundance of R. irregulare or the abundance of native AM fungal communities. AMF inoculation had no effect on the grass but significantly enhanced clover yield in five out of eight field soils. The results demonstrate that AMF inoculation can be successful, even when soil P availability is high and native AMF communities are abundant.

Inoculation effects on root-colonizing arbuscular mycorrhizal fungal communities spread beyond directly inoculated plants

“…This suggests, alternatively, that the inoculant imposed high initial carbon costs on the host plant prior to starting supplying it with nutrients [64–65], which is consistent with the effect of pre-inoculation on seedling growth in the pre-cultivation stage. Altogether, plant growth did not indicate any inoculation-induced changes in the symbiotic efficiency of the AMF community, reported in some previous studies [17, 66]. However, our data suggest that pre-inoculation is more suitable to immediately promote plant growth than inoculation in-situ, possibly also because it suppresses interactions among the inoculant and native AMF during the root colonization process.…”

Little evidence that farmers should consider abundance or diversity of arbuscular mycorrhizal fungi when managing crops

“…For instance, Köhl et al . () inoculated microcosms of a grass–clover mixture ( Lolium multiflorum and Trifolium pratense ) grown in a glasshouse with nonindigenous Rhizoglomus irregulare . The microcosms contained eight nonsterilised field soils varying in soil type, chemical characteristics and indigenous mycorrhizal fungal community.…”

“…However, Köhl et al . () noted that the amount of inoculum applied was large (corresponding to 1.4 × 10 5 l ha −1 ), expensive and possibly commercially unrealistic.…”

Fungal inoculants in the field: Is the reward greater than the risk?

“…Again, studies using this approach have shown variable outcomes (Farmer et al, 2007;Symanczik, Courty, Boller, Wiemken, & Al-Yahya'ei, 2015). While Köhl, Lukasiewicz, and Van der Heijden (2016) showed Rhizophagus irregularis establishment in a field soil microcosm, they did not measure persistence past 8 weeks. Earlier studies have shown persistence up to two (Pellegrino et al, 2012) and 3 years (Sykorova et al 2015), but these studies also reported inconsistent establishment.…”