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United States Department of Agriculture

Agricultural Research Service

Title: Effects of Organic Amendments to Soil and Soilless Potting Media on Arbuscular Mycorrhizae and Their Microbial Associates

Authors
item Linderman, Robert
item Davis, E Anne
item Marlow, Joseph

Submitted to: Proceedings of Fourth International Conference on Mycorrhizae
Publication Type: Proceedings
Publication Acceptance Date: March 1, 2003
Publication Date: August 10, 2003
Citation: Linderman, R.G., Davis, E.A., Marlow, J.L. Effects Of Organic Ammendments To Soil And Soilless Potting Media On Arbuscular Mycorrhizae And Their Microbial Associates.

Interpretive Summary: Organic matter is used as a major component of soilless potting mixes (peat, coir, composts, etc.), or is amended to soil in the form of composts, manure, crops residues, etc. It is important to growers who also want to exploit the benefits of mycorrhizal fungi to know how organic matter amendments might affect mycorrhiza formation and function. We investigated the effects of different sources and amounts of peat, coir, and composts on the formation and function of VA mycorrhizal(VAM) fungi and their microbial associates. Some peats inhibited some VAM fungi; coirs did not inhibit VAM fungi; and all composts inhibited VAM fungi when amended to peat-based potting mix. VAM formation and function was not inhibited by composts added to low-organic matter soil, however. All composts and some peats and coirs increased the antagonistic potential of amended potting mix or soil, as well as some functional groups of bacteria, such as acid phosphatase producers. These results indicate that organic amendments can affect VAM fungi and their microbial associates in various ways and to various extents, depending on the nature of the material and the VAM fungal genotype.

Technical Abstract: Organic matter content of soilless potting media is high due to the amendment with peat moss, coir, bark, or composts, and soil may be amended with composts, mulches, manure, crop residues or cover crops. How such organic amendments affect the formation and function of arbuscular mycorrhizae (AM) was investigated. Some peat mosses added to soil inhibited AM formation and host plant growth enhancement under low soil phosphorus (P) conditions, but the effects were source- and AM species-dependent. Coir amendment to a peat-based soilless potting mix did not adversely affect AM formation at any concentration used, from 15% to 60% by volume. Several different composts amended to the potting mix at rates of 5, 10, 15, and 30% by volume depressed AM formation, presumably due to their inherently high P content, but all enhanced growth of marigold plants proportional to the concentration. In contrast, adding composts to low-organic matter soil (10% by volume) did not suppress AM formation or function. Composted grape pomace amendment to soil enhanced onion growth, an effect further increased by inoculation with AM fungi. All composts, and some peats and coirs, increased the antagonistic potential to soilborne fungal pathogens in both potting mix and soil, and also affected different functional groups of bacteria such as producers of acid phosphatase. These results indicate that organic matter can have varied effects on AM fungi, depending on the nature of the material and the AM fungal genotype, as well as on their microbial associates in the mycorrhizosphere.

Last Modified: 12/29/2014
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