Isolate Selection and Phosphorus Interaction of Vesicular‐Arbuscular Mycorrhizal Fungi in Biomass Crops

Abstract

AbstractIndustrial sweet potato [Ipomoea batatas (L.) Lam, cv. White Star] and Napiergrass (Pennisetum americana × P. purpureum hybrid triploid PI 300086) have good potential for biomass energy systems. The objective of this research was to evaluate vesicular‐arbuscular mycorrhizal (vam) fungi for their ability to provide P to these crops across a range of soil P. To select effective vam fungi, cuttings of sweet potato were inoculated with nine isolates of fungi and were grown in soil with no P addition. Plants were evaluated after 3, 7, and 11 wk. To determine the range of soil P where these crops respond to vam fungi, experiments were conducted with sweet potato and Napiergrass, using at least two vam fungi and five P additions ranging from 0 to 198 mg P kg−1 of soil. Plants were evaluated after 4 and 16 wk. Sweet potato response to vam fungi ranged from growth enhancement to growth depression, compared to control plants. Both inter‐ and intraspecific fungal variation was observed. Total biomass production at 11 wk was correlated positively with root colonization at 3 wk, but not at 7 or 11 wk. Mycorrhizal dependency for both biomass plants decreased with P addition; nonetheless, growth was greater for plants inoculated with vam fungi and with up to 23 mg added P kg−1. The apparent ineffectiveness of the indigenous vam fungi, and the responsiveness of these biomass crops to selected vam fungi within a practical range of fertilizer P, may provide an opportunity for inoculation.