Print PageThis past summer, the National Science Foundation funded a 10-week Research Experience for Undergraduates program “Environmental and Earth Systems Research at Biosphere 2". Undergraduates had the opportunity to conduct guided research in environmental and Earth systems science which has resulted in this work.
The goal of this study was to observe plant-mediated weathering of granular basalt under two temperature conditions. Two grass species were studied, one native to Arizona: Tanglehead, Heteropogan contortus, and one exotic to Arizona: Buffelgrass, Pennisetum ciliar.
The grasses were grown in pots located in the Desert and the Savannah Biomes in the Biosphere 2 to take advantage of a 4° C temperature difference. Understanding differences in how these grasses weather soil and take up nutrients may explain the mechanism behind current invasion of Sonoran Desert by exotic species and help predict response of the vegetation to expected increases in temperatures.
Each biome also contained three replicate “control” pots without vegetation, and mixtures of the two grass species.
Three factors were compared in this study:
1. Temperature: the same species of grass under two different temperature conditions
2. Species: Native Arizonan species vs. a species exotic to Arizona
3. Temporal: How the grasses use resources differently as they grow
Leachate samples were collected and analyzed for pH, electrical conductivity, total organic carbon, total nitrogen, inorganic carbon by high temperature combustion coupled with infrared gas analysis; F-, Cl-, Br-, NO3-, NO2-, SO42-, and PO43- by ion chromatography; and cations and metals by ICP-MS.
Results/Conclusions
The data trends indicate that plants enhanced basalt weathering. All of the leachate samples showed higher pH than the input water, and the pH was elevated in treatments that contained grass. This indicated that in the presence of vegetation there was more proton absorption. The trends in total nitrogen concentrations indicate a dependence on temperature. Both organic and inorganic carbon concentrations were found to be higher in grass treatments than in control treatments. Because both dissolved CO2 and soluble organic exudates encourage mineral dissolution, this could be causative of the weathering enhancements observed.
Denudation of nutrient elements differed between plant species and between temperatures, possibly relating to plant uptake and secondary mineral formation. This study gives unique insight into plant-mineral interactions as a function of plant species and temperature that is essential for understanding Earth systems under changing climate.
