Differences in growth responses of maize to preceding cropping caused by fluctuation in the population of indigenous arbuscular mycorrhizal fungi

Recent studies on crop rotation have suggested that the cultivation of mycorrhizal host crops increases the arbuscular mycorrhizal (AM) colonization of succeeding crops. A pot experiment was conducted to determine whether the positive effect of AM host cropping on the growth of succeeding maize is mainly due to the multiplication of indigenous AM fungi. Maize plants were grown in soils after mustard (non-host) cropping without AM fungal (AMF) inoculum (MD sub(NI)); with inoculum from the soil after sunflower cropping (MD sub(ISF)); with sterilized inoculum (MD sub(SI)); and in the soil after sunflower (host) cropping without inoculum (SF sub(NI)). The growth of maize after mustard cropping (MD sub(NI)) was inferior to that after sunflower cropping (SF sub(NI)). The AMF inoculum from the soil after sunflower cropping (MD sub(ISF)) improved the growth and AM colonization of maize, and shoot weight was increased from 17 to 49% of that in the SF sub(NI) treatment. However, the sterilized inoculum (MD sub(SI)) did not show similar effects. Similar AMF species to those increased by sunflower cropping were dominant in SF sub(NI)-treated or MD sub(ISF)-treated soils following maize cropping, also indicating that the AM colonization of maize was improved by multiplied AM fungi through sunflower cropping. These results suggest that the effects of preceding crops on maize growth are at least partly due to differences in AMF density caused by various preceding crops.