Mycorrhizae (VAM) of soybean in soil toposequences and mycorrhizal dependency of corn and soybean cultivars

Abstract

Distribution of vesicular-arbuscular mycorrhizal fungi (VAMF) in relation to soil drainage and toposequences is not well documented. The objective of this study was to determine whether soil drainage and position in the toposequence affects VAMF spore production and colonization of soybean (Glycine max L. Merr.) roots. Plant roots and rhizosphere soils were sampled from four locations each of three paired soils, varying in soil drainage classes, from two toposequences: Clarion-Nicollet-Webster (CNW) and Sharpsburg-Macksburg-Winterset (SMW). Soils were analyzed for chemical properties, and VAMF spores per 50 g soil were determined by a wet-sieving-and-decanting technique. The percentages of root VAMF colonization were determined by the grid-line intersect method. The distribution of spores among locations, series, and series within locations varied significantly (P < 0.001). Soil from the CNW toposequence averaged 417 spores (50 g)' soil, whereas soil from the SMW toposequence averaged 147 spores (50 g)' soil. Within the two toposequences, the poorly to somewhat-poorly drained soils had higher spore counts than the well-drained to moderately-well drained soils. In the CNW toposequence, the mean spore counts of Nicollet and Webster soils (poorer drained) were 137% higher than Clarion soils (better drained). In the SMW toposequence, the mean spore counts of Macksburg and Winterset soils (poorer drained) were 206% higher than Sharpsburg soils (better drained). VAMF colonization of roots ranged from 74 to 88% in the CNW toposequence and from 68 to 86% in the SMW toposequence. No correlation was found between spore count and VAMF colonization. Further research is needed to determine if higher spore counts in poorly drained soils is related to changes in fungal growth patterns or is due to movement and deposition of spores with surface flow of water.