Research suggests that weathering by early land plants provided an overall negative feedback on atmospheric CO2 and an overall positive feedback on biologically available inorganic nutrients during the Ordovician. This process is considered to have contributed to global cooling and to the formation of Earth’s first soils. Although there is no known analogue to Earth’s first land plants, mosses possess the most shared spore and sporophyte features with the early cryptophyte fossil, Partitatheca, compared to any known extant group. They therefore present a plausible model organism for examining how the first land plants irreversibly altered Earth's geochemistry. Here we present a microcosm study of biologically induced weathering by two rock dwelling moss species (Imbribryum miniatum and Grimmia leigergii). Moss species were incubated for six months (March-October) on two igneous rock types (andesite and scoria) at natural light and temperatures ranging from 10°-21°C. Microcosms were watered at a constant rate using ultrapure H2O. After six months, tissue was removed and dried at 30°C for 48 hours. Rocks were washed using 50 mL of ultrapure H2O which was then pipetted off and stored at 4°C.
Early ICP-AES results of the washed andesite rocks weathered by Imbribryum miniatum show amplified weathering of K, Ca, P, Si, and metals compared to non-biologically weathered controls. Dry ash tissue analyses also suggest an increased uptake of metals by lithic species compared to generalist species grown separately in the lab. More research is needed to determine the rate at which different lithic moss species weather bare rock and to determine how the interaction of multiple groups, such as lichens and bryophytes, affects weathering rates. The role of lichen weathering in early Earth processes is even more uncertain despite the fact that they are known to have been colonizing the Earth’s surface since the Cambrian. This study lays the groundwork for a future study of lichen and bryophyte weathering. Previous research and our early results raise further questions regarding the physiological drivers of chemical weathering by early plants, specifically in regards to the role of limiting nutrients in plant evolution and the causes and consequences of the increased bioavailability of metals.