Arbuscular mycorrhizal fungal isolate effectiveness on growth and root colonization of Panicum virgatum in acidic soil

Arbuscular mycorrhizal fungi (AMF) can enhance plant ability to grow and withstand acidic soil induced stresses. Panicum virgatum L. (switchgrass) was grown in pHCa 4 and 5 (soil:10 mM CaCl2, 1:1) soil (typic Hapludult) inoculated with eight isolates of AMF [Glomus (G.) clarum, G. diaphanum, G. etunicatum, G. intraradices, Gigaspora (Gi.) albida, Gi. margarita, Gi. rosea and Acaulospora (A.) morrowiae] to determine the effects of these isolates on plant growth and root colonization. Compared to nonmycorrhizal (nonAMF) plants, mycorrhizal (AMF) plants had as high as 52-fold increases in dry matter (DM) in pHCa 4 soil and as high as 26-fold increases in DM in pHCa 5 soil; G. clarum and G. diaphanum plants had the highest DM and Gi. rosea plants had the lowest DM. The AMF plants grown in pHCa 4 soil had higher DM than in pHCa 5 soil. Root DM decreased more than shoot DM for plants grown in pHCa 5 compared to pHCa 4 soil, which was reflected in shoot-to-root DM ratio changes. Total root length (RL) was similar for plants grown in pHCa 4 and 5 soil and varied considerably depending on AMF isolate. Specific RL was higher for AMF plants grown in pHCa 5 than in pHCa 4 soil. Root colonization [determined as vesicles or arbuscules in root cells (VA), roots with hyphal infections (HI) and total colonization (VA or HI)] varied extensively with AMF isolate. Although percentage root colonization was not directly related to amount of DM, good enhancement of DM did not occur unless total colonization was >20%. Some AMF isolates were highly effective in overcoming acidic soil constraints and good growth of switchgrass in acidic soil may depend on root-AMF symbiosis.