Does bacterial weathering play a significant role in rock weathering?

Bacterial weathering plays a significant role in rock weathering, yet only a limited number of studies was conducted on this topic. The recent rapid developments in geomicrobiology are expected to increase the pace of research in this area. The extent and duration of the biological weathering processes on mineral and rock samples and minerals preferred by bacteria are still not fully understood due to the wide variety of both bacterial species and rock types. Biological weathering of rock types found in Turkey has also not been studied before. Here, we investigated the effects of two species of bacteria actively contributing to rock weathering on three rock types commonly used as building stone materials in Turkey. Granite, andesite, and limestone samples could interact with Bacillus species (B. subtilis and B. pumilus) in closed system reactors. Samples obtained from these reactors were analysed via Scanning Electron Microscopy (SEM) monitoring to identify morphological features and chemical composition changes. Chemical elements consumed most by bacteria were identified. Changes in the colour index were determined via RGB measurements. The effects of experimental conditions on bacterial growth were monitored via daily optical density measurements. The effects of bacteria on the physical properties of rock samples were also evaluated. B. subtilis and B. pumilus were found to be more aggressive on limestone/andesite and granite, respectively.

Use of Mineral Weathering Bacteria to Enhance Nutrient Availability in Crops: A Review

Rock powders are low-cost potential sources of most of the nutrients required by higher plants for growth and development. However, slow dissolution rates of minerals represent an obstacle to the widespread use of rock powders in agriculture. Rhizosphere processes and biological weathering may further enhance mineral dissolution since the interaction between minerals, plants, and bacteria results in the release of macro- and micronutrients into the soil solution. Plants are important agents in this process acting directly in the mineral dissolution or sustaining a wide diversity of weathering microorganisms in the root environment. Meanwhile, root microorganisms promote mineral dissolution by producing complexing ligands (siderophores and organic acids), affecting the pH (via organic or inorganic acid production), or performing redox reactions. Besides that, a wide variety of rhizosphere bacteria and fungi could also promote plant development directly, synergistically contributing to the weathering activity performed by plants. The inoculation of weathering bacteria in soil or plants, especially combined with the use of crushed rocks, can increase soil fertility and improve crop production. This approach is more sustainable than conventional fertilization practices, which may contribute to reducing climate change linked to agricultural activity. Besides, it could decrease the dependency of developing countries on imported fertilizers, thus improving local development.

Biological weathering by the Devonian trees

<p class="western" lang="en-US"><span>We applied the biogeomorphic ecosystem engineers concept to the Devonian Plant Hypotheses. By linking these two ideas we want to explore how recent discoveries on the role of trees in weathering processes could support the explanation of global environmental changes in the Devonian period. The occurrence of first land plants, vascular plants, trees, and complex forest ecosystems likely changed the nature and pace of many geomorphic and pedogenic processes. For instance, intensification of biological weathering driven by vascular plants might have influenced the global climate through consumption and accumulation of a large volume of atmospheric CO2. Innovation in the form and function of trees likely strongly influenced these processes, including soil stabilization via deep root systems. Mycorrhizal relationships further influenced weathering via chemical processes. While the lack of solid evidence in the fossil record still pose a problem, the progress in our understanding of soil-weathering processes induced by trees and root systems has expanded greatly in recent years, especially in terms of their biogeomorphic functions (e.g. tree uprooting, pedoturbations, biomechanical weathering, etc.), and can provide insights and testable hypotheses regarding the role of trees in the Late Devonian.</span></p>

Mineralogical Analysis of Mortars in the Walls of Ávila (Spain) and Its Surroundings

The present article evaluated the mineralogical composition of 85 mortar samples from some emblematic monuments of Ávila city (Spain), which were collected during the restoration of the monuments. The aim of this article is to try to extract the relationship between the composition and the origin of the raw materials, as well as to identify possible alterations in the samples. The study of the samples was carried out using visual and petrographic techniques such as stereoscopic microscope, XRD, and SEM/EDX analysis. The main components of the mortars were calcite, feldspar and quartz, although small amounts of phyllosilicates were also identified. The minerals of the mortars came from the surroundings of the city, and some of the samples presented evident alteration of the original materials due to humidity, salt concentration, and biological weathering, possibly inducted by unfortunate effects of the restoration. Finally, a study of the salts present in some mortars showed that most samples display contamination of soluble salts such as halite, thenardite, hexaedrite, and carnalite. This investigation offers fresh insight into historic building activity and related techniques, and should provide knowledge useful for restoration and conservation processes.