The effect of repeated short-term flooding on mycorrhizal survival in snap bean roots

Abstract

Since arbuscular-mycorrhizal (AM) fungi are aerobic, symbiosis was not considered significant under flooded conditions. However, AM colonization of wetland plants is now believed more common than previously thought. In the humid tropics, storms that result in standing water for 24 hours or less are common. Short-term floods, especially on sandy soils, may leach banded fertilizer, reducing uptake efficiency. Crops planted in flood prone areas are not normally enhanced with mycorrhizal mixes. However, mycorrhizal associations tolerant to wet conditions may improve nutrient uptake as plants recover from short-term flooding. Greenhouse studies were initiated to determine the effects of frequent short-term floods (two to four events) on mycorrhizal colonization and subsequent development in snap bean (Phaseolus vulgaris L.) plants. Flooding produced no obvious long-term physical effects on plant shoots. In the first study, flooding did not affect survival of colonies established before the first flood event. Percent root colonization in flooded vs. nonflooded treatments was not significantly different at either 31 or 50 days after planting (DAP). As root length increased there was a concomitant increase in colonization so that percent colonization remained approximately the same in both flooded and nonflooded treatments. In the second study, three weekly floods beginning 13 DAP (cotyledon leaf open only) did not inhibit initial mycorrhizal colonization. Mycorrhizal associations should form with soap bean under conditions subject to short-term flooding. Additional research is needed to determine the efficacy of different mycorrhizal mixes under short-term flooded conditions in the field.