Puente M E, Bashan Y, Li C Y, Lebsky V K
Environmental Microbiology Group, Center for Biological Research of the Northwest (CIB), P.O. Box 128, La Paz, B.C.S. 23000, Mexico.
Plant Biol (Stuttg). 2004 Sep;6(5):629-42. doi: 10.1055/s-2004-821100.
Dense layers of bacteria and fungi in the rhizoplane of three species of cactus (Pachycereus pringlei, Stenocereus thurberi, Opuntia cholla) and a wild fig tree (Ficus palmeri) growing in rocks devoid of soil were revealed by bright-field and fluorescence microscopy and field emission scanning electron microscopy. These desert plants are responsible for rock weathering in an ancient lava flow at La Purisima-San Isidro and in sedimentary rock in the Sierra de La Paz, both in Baja California Sur, Mexico. The dominant bacterial groups colonizing the rhizoplane were fluorescent pseudomonads and bacilli. Seven of these bacterial species were identified by the 16S rRNA molecular method. Unidentified fungal and actimomycete species were also present. Some of the root-colonizing microorganisms fixed in vitro N(2), produced volatile and non-volatile organic acids that subsequently reduced the pH of the rock medium in which the bacteria grew, and significantly dissolved insoluble phosphates, extrusive igneous rock, marble, and limestone. The bacteria were able to release significant amounts of useful minerals, such as P, K, Mg, Mn, Fe, Cu, and Zn from the rocks and were thermo-tolerant, halo-tolerant, and drought-tolerant. The microbial community survived in the rhizoplane of cacti during the annual 10-month dry season. This study indicates that rhizoplane bacteria on cacti roots in rock may be involved in chemical weathering in hot, subtropical deserts.
通过明场和荧光显微镜以及场发射扫描电子显微镜，发现生长在无土壤岩石中的三种仙人掌（普氏强刺球果仙人掌、瑟氏花柱仙人柱、仙人掌属）和一棵野生无花果树（帕尔默榕）的根际存在密集的细菌和真菌层。这些沙漠植物导致了墨西哥南下加利福尼亚州拉普里西马 - 圣伊西德罗一处古老熔岩流以及拉巴斯山脉沉积岩中的岩石风化。定殖在根际的主要细菌类群是荧光假单胞菌和芽孢杆菌。其中七种细菌物种通过16S rRNA分子方法得以鉴定。同时也存在未鉴定的真菌和放线菌物种。一些定殖在根部的微生物在体外固定N₂，产生挥发性和非挥发性有机酸，随后降低了细菌生长所在岩石介质的pH值，并显著溶解了不溶性磷酸盐、喷出火成岩、大理石和石灰石。这些细菌能够从岩石中释放大量有用矿物质，如磷、钾、镁、锰、铁、铜和锌，并且耐热、耐盐且耐旱。在长达10个月的年度旱季中，微生物群落存活于仙人掌的根际。这项研究表明，生长在岩石中的仙人掌根际细菌可能参与了炎热亚热带沙漠中的化学风化作用。
