Fungal diversity and plant roots.

Philippe Vandenkoornhuyse et al. (“Extensive fungal diversity in plant roots,” Brevia, 15 March, p. [2051][1]) report on various new and unusual fungi from roots of the grass plant Arrhenatherum elatius . I won't quibble about the putative identification and taxonomic grouping of the fungi involved, but the authors strongly suggest a necessary relationship between the fungi recovered and the plants themselves. I contend that it is just as likely that these fungi were associated with the plants simply by accident. Root sampling and cleaning techniques were not well described, but plant roots commonly have wounds associated with them even before sampling. Many organisms may become passively associated with such wounds or may even be drawn up into the nonliving root xylem if this is exposed to soil and soil water. Polymerase chain reaction techniques are so powerful that even traces of accidental associations would be detected. Thus, I contend that many of the novel organisms detected by the authors could simply be passive associations of soil organisms that have no necessary involvement directly with the roots of these plants. On the basis of DNA extractions from soil directly, we are all aware that most soil microorganisms have yet to be identified because they fail to culture easily on common growth media. The ones described by Vandenkoornhuyse et al. could simply be from that great array. # Response {#article-title-2} In our Brevia, we characterize fungal diversity in a mundane ecological niche, the roots of a plant. Sequences from roots of Arrhenatherum elatius revealed an unexpected diversity, with all known fungal phyla represented. The diversity within these phyla is very high, with a large proportion of fungi that could not be related to any known SSU rRNA gene sequence. The cleaning procedure of the root surface was designed to remove the mineral and organic particles. With this strategy, it is impossible to clean the inner root structures such as xylem. However, observations of stained roots under microscope showed only arbuscular mycorrhiza (Glomales) and septate endophytic fungal structures within or between the root cortical cells and a network of septate fungal filaments on the root surface. These external hyphae did not form the typical structures of ectomycorrhiza, nor did we observe any symptoms of plant pathology. Crowe addresses, in part, the question of the ecological functions of these fungi associated with roots. One fungal group that we certainly did expect to find represented in roots was the arbuscular mycorrhizal (AM) fungi ([1][2], [2][3]). These ubiquitous biotrophic zygomycetes in the order Glomales form symbioses with more than 80% of land plants ([3][4]). The co-occurrence of different symbiotic AM fungal phylotypes within the roots of a plant species is in agreement with previous work ([1][2], [2][3]). However, our results show clearly that the Glomales correspond only to a small fraction of the fungal diversity in these roots. We can only speculate on the possible roles of the other 94% of the root fungal diversity found here. Further studies are required to know which part of root fungal diversity interacts actively with host plant. A better knowledge of the diversity of the fungal world and a better understanding of fungal ecological functions in ecological niches and ecosystems are likely to become important issues. 1. [↵][5]1. T. Helgason, 2. T. J. Daniell, 3. R. Husband, 4. A. H. Fitter, 5. J. P. W. Young , Nature 394, 431 (1998). [OpenUrl][6][CrossRef][7][PubMed][8] 2. [↵][9]1. T. Helgason, 2. A. H. Fitter, 3. J. P. W. Young , Mol. Ecol. 8, 659 (1999). [OpenUrl][10][CrossRef][11][Web of Science][12] 3. [↵][13]1. S. E. Smith, 2. D. J. Read , Mycorrhizal Symbiosis (Academic Press, San Diego, CA, ed. 2, 1997). [1]: /lookup/doi/10.1126/science.295.5562.2051 [2]: #ref-1 [3]: #ref-2 [4]: #ref-3 [5]: #xref-ref-1-1 "View reference 1 in text" [6]: {openurl}?query=rft.jtitle%253DNature%253B%2BPhysical%2BScience%2B%2528London%2529%26rft.stitle%253DNature%253B%2BPhysical%2BScience%2B%2528London%2529%26rft.aulast%253DHelgason%26rft.auinit1%253DT.%26rft.volume%253D394%26rft.issue%253D6692%26rft.spage%253D431%26rft.epage%253D431%26rft.atitle%253DPloughing%2Bup%2Bthe%2Bwood-wide%2Bweb%253F%26rft_id%253Dinfo%253Adoi%252F10.1038%252F28764%26rft_id%253Dinfo%253Apmid%252F9697763%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [7]: /lookup/external-ref?access_num=10.1038/28764&link_type=DOI [8]: /lookup/external-ref?access_num=9697763&link_type=MED&atom=%2Fsci%2F296%2F5575%2F1969.1.atom [9]: #xref-ref-2-1 "View reference 2 in text" [10]: {openurl}?query=rft.jtitle%253DMol.%2BEcol.%26rft.volume%253D8%26rft.spage%253D659%26rft_id%253Dinfo%253Adoi%252F10.1046%252Fj.1365-294x.1999.00604.x%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [11]: /lookup/external-ref?access_num=10.1046/j.1365-294x.1999.00604.x&link_type=DOI [12]: /lookup/external-ref?access_num=000080177700013&link_type=ISI [13]: #xref-ref-3-1 "View reference 3 in text"