Record ID No. |
5978 |
Author(s) |
Bunn R. A.*, Simpson D. T., Bullington L.S., Lekberg Y. and Janos D. P. , 2019 |
Affiliation |
*Department of Environmental Sciences, Western Washington University, 516 High St., MS-9181, Bellingham, WA, 98225, USA. |
Title |
Revisiting the 'direct mineral cycling' hypothesis: arbuscular mycorrhizal fungi colonize leaf litter, but why? |
Source. Vol.(no):Page |
The ISME journal. 13: 1891-1898. |
Categories |
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Subjects |
Ecology |
Host |
NA |
Organism |
NA |
Country |
USA |
Abstracts |
Half a century ago in an Amazonian rainforest, Went and Stark observed ‘endotrophic mycorrhizal’ hyphae proliferating in leaf litter adjacent to mycorrhizal roots. They inferred the fungi were accessing, and subsequently transferring, litter-bound mineral nutrients to host plants in a phenomenon they called ‘direct mineral cycling.’ This hypothesis was consistent with acceptance of fungi as primary decomposers in forest ecosystems and mycorrhizal fungi as symbionts that transfer mineral nutrients (hereafter, ‘nutrients’) to host plants. ‘Endotrophic mycorrhizas,’ as used by those authors, were later termed ‘arbuscular mycorrhizas’ and involve a phylogenetically distinct group of fungi from the phylum Glomeromycota. Early observations of arbuscular mycorrhizal (AM) fungi proliferating in organic matter led researchers to surmise saprotrophic capabilities. However, attempts to culture AM fungi independent of host plants were unsuccessful, and researchers now understand AM fungi as obligate symbionts entirely dependent on host plant roots for carbon. In fact, AM fungi appear incapable of producing the lytic enzymes necessary to cleave organic molecules and evidence still largely, but not universally, suggests these fungi are limited to assimilating inorganic forms of nutrients (nitrogen reviewed by Hodge and Storer; phosphorus by Smith et al.). Thus, AM fungi alone are unlikely to access litter-bound nutrients as Went and Stark originally envisioned, and ‘direct mineral cycling’ has languished in the bin of unsupported hypotheses.
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