Pacific Northwest Research Station

Title: Microbial populations and activities in the rhizoplane of rock-weathering desert plants. I. root colonization and weathering of igneous rocks.

Author: Puente, M.E.; Bashan, Y.; Li, C.Y.; Lebsky, V.K.

Date: 2004

Source: Plant Biology. 6: 629-642

Description: 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 165 rRNA molecular method. Unidentified fungal and actimomycete species were also present. Some of the root-colonizing microorganisms fixed in vitro N₂, 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.

Keywords: Bacillus, cactus, cardon, cholla, desert, Ficus, fig tree, fluorescent psuedomonads, lava degradation, nitrogen fixation, Opuntia, Pachycereus, phosphate solubilization, rock weathering, soil formation, Stenocereus

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Citation

Puente, M.E.; Bashan, Y.; Li, C.Y.; Lebsky, V.K.  2004.  Microbial populations and activities in the rhizoplane of rock-weathering desert plants. I. root colonization and weathering of igneous rocks..   Plant Biology. 6: 629-642.