Arbuscular mycorrhizal (AM) effects on maize growth and AM colonization of roots under various soil moisture conditions

The effects of arbuscular mycorrhizal (AM) inoculation on growth, P uptake, and AM formation of maize (Zea mays L.) were examined at different soil moisture levels. Arbuscular mycorrhizal inoculum was added to pots filled with sterilized Andosol at concentrations of 0, 10, and 50 g kg(-1) dry soil. From 11 to 75 d after sowing, the soil water potential was adjusted to around -10 (wet: W), -50 (moist: M), or < -63 kPa (dry: D). The effect of inoculation on maize growth and P uptake was distinct in dry soil, in which AM colonization of roots occurred significantly more frequently in inoculated than in non-inoculated soil. The effect, however, was less pronounced with the increase in the soil moisture status, despite wide differences in the AM spore population and AM colonization. The increased AM colonization with the increase in the soil moisture status indicated that a higher soil moisture status improved the efficiency of AM colonization of roots. The increase in the shoot weight of non-inoculated maize with the improvement in the soil moisture status was presumably due to a higher P availability under a higher soil moisture status. Such effects may in turn stimulate P uptake and enhance plant growth, thereby masking the influence of the AM population.