Mary Ann Bruns | Geology Reports

USGS2019

Manipulating wild and tamed phytobiomes: Challenges and opportunities

This white paper presents a series of perspectives on current and future phytobiome management, discussed at the Wild and Tamed Phytobiomes Symposium in University Park, PA, USA, in June 2018. To enhance plant productivity and health, and to translate lab- and greenhouse-based phytobiome research to field applications, the academic community and end-users need to address a variety of scientific, practical, and social challenges. Prior discussion of phytobiomes has focused heavily on plant-associated bacterial and fungal assemblages, but the phytobiomes concept covers all factors that influence plant function. Here we discuss various management considerations, including abiotic conditions (e.g. soil, nutrient applications), microorganisms (e.g. bacterial and fungal assemblages, bacterial and fungal inoculants, viruses), macroorganisms (e.g. arthropods, plant genetics), and societal factors (e.g. communication approaches, technology diffusion). An important near-term goal for this field should be to estimate the potential relative contribution of different components of the phytobiome to plant health, as well as the potential and risk of modifying each in the near-future.

Phytobiomes Journal↗

USGS2011

Halloysite nanotubes and bacteria at the saprolite-bedrock interface, Rio Icacos watershed, Puerto Rico

Quartz diorite bedrock underlying the Luquillo Mountains of eastern Puerto Rico undergoes weathering at one of the fastest documented rates for granitic rocks in the world. Although tropical temperatures and precipitation promote rapid weathering in this location, increased bacterial densities in the regolith immediately above the bedrock suggest that microorganisms contribute to mineral weathering as well. Deep saprolite and saprock samples were obtained at the bedrock interface in an upland location (Guaba Ridge) in the Rio Icacos watershed for examination by environmental scanning electron microscopy (ESEM). In ESEM images, mineral nanotubes were observed to occur frequently in association with coccus- and rod-shaped structures resembling bacteria. These nanotubes (50–140-nm width and 150–2700-nm length) were identified as halloysite using transmission electron microscopy. Observations of multiple nanotubes on the surfaces of an individual cell are consistent with the cell's exterior functional groups interacting with Si in pore water to facilitate halloysite nucleation. We propose that one mechanism by which bacteria contribute to the rapid weathering of quartz diorite minerals in this regolith is by lowering the free energy for secondary mineral formation. The presence of bacterial surfaces may result in more rapid removal of Si from solution, thereby increasing the dissolution rates of primary minerals.

Puerto Rico↗