The 2011 ASHS Annual Conference

Mycorrhizal colonization confers multiple benefits to horticultural crops. Inoculation of plants with arbuscular mycorrhizal fungi often improves the survival and growth of seedlings and cuttings in greenhouse and natural conditions, increases plants’ tolerance to water and salt stress, and resistance to diseases caused by soil-borne pathogens. Mycorrhizal colonization has also been considered a potential tool to decrease nutrient runoff and leaching, because it has been shown that mycorrhizal plants of several species can be produced with a smaller amount of fertilizers than nonmycorrhizal plants. However, the direct effect of mycorrhizal colonization on nitrogen (N) and phosphorus (P) leaching has seldom been quantified. Our objective was to investigate the effects of mycorrhizal colonization on N and P leaching from plants grown in nursery containers. We compared the growth response and the content of nitrate, ammonium, and orthophosphate, in leachates collected from mycorrhizal (AM) and nonmycorrhizal (NonAM) plants of Encelia californica and Rhus integrifolia. Plants were grown with no fertilizer, or with half and full rates of Osmocote controlled release fertilizer, for eight weeks. Mycorrhizal colonization increased the growth and nutrient uptake of E. californica and R. integrifolia, but was more effective at decreasing nutrient leaching from containers with E. californica. Leachates collected from AM plants of E. californica, had significantly lower N and P content than those from NonAM plants, at all fertilizer rates. In contrast, only the leachates from AM plants of R. integrifolia grown without additional fertilizer had generally lower nutrient content than those from NonAM plants. However, mycorrhizal colonization reduced the fertilizer requirement to achieve maximum growth, in both species. AM plants of E. californica and R. integrifolia grown with half rates of Osmocote had greater dry weight than the NonAM ones grown in full rates of Osmocote. Our study shows that mycorrhizal colonization can reduce N and P leaching either by increasing nutrient uptake, or by allowing the use of lower fertilizer rates and increasing nutrient use efficiency.