Feldspars as a source of nutrients for microorganisms

Phosphorus and nitrogen are essential macronutrients necessary for the surv ival of virtually all living organisms. In groundwater systems, these nutri ents can be quite scarce and can represent limiting elements for growth of subsurface microorganisms. In this study we examined silicate sources of th ese elements by characterizing the colonization and weathering of feldspars in situ using field microcosms. We found that in carbon-rich anoxic ground waters where P and N are scarce, feldspars that contain inclusions of P-min erals such as apatite are preferentially colonized over similar feldspars w ithout P. A microcline from S. Dakota, which contains 0.24% P2O5 but <1 mu mol/ g NH4+, was heavily colonized and deeply weathered. A similar microcli ne from Ontario, which has no detectable P or NH4+, was barren of attached organisms and completely unweathered after one year. An-orthoclase (0.28% P 2O5, similar to 1 mu mol/g NH:) was very heavily colonized and weathered, w hereas plagioclase specimens (<0.01% P, <1 mu mmol/g NH4+) were uncolonized and unweathered. In addition, the observed weathering rates are faster tha n expected based on laboratory rates. We propose that this system is partic ularly sensitive to the availability of P, and the native subsurface microo rganisms have developed biochemical strategies to aggressively scavenge P ( or some other essential nutrient such as Fe3+) from resistant feldspars. Th e result of this interaction is that only minerals containing P will be sig nificantly colonized, and these feldspars will be preferentially destroyed, as the subsurface microbial community scavenges a limiting nutrient.