Extracellular enzyme activities in soils and ferromanganese deposits from several New Mexican caves

Background/Question/Methods

Low nutrient availability is one of the main selective pressures within caves due to the lack of photosynthesis and low nutrient input in caves that lack streams or bat populations. Human visitation may increase nutrient availability, which may alter microbial community composition and function. One way to measure microbial responses to nutrient availability is to measure extracellular enzyme activity (EEA), indicators of environmental nutrient availability and microbial metabolism. To assess EAA, samples were collected from above and within caves, including soils and ferromanganese deposits (FMD). Three limestone and four basalt caves were chosen due to their varying temperatures, human visitation frequencies, and geologies. β-1,4-glucosidase (BG), acid phosphatase (AP), and L-alanine aminopeptidase (AAP) activities in soils were measured following published protocols. 

Results/Conclusions

High human visitation caves had the greatest AP activity (54.1 nmol h^-1g^-1), which is a measure of phosphorus demand. Infrequently visited caves had the highest BG and AAP activities (36.3 and 2.3 nmol h^-1g^-1), indicating higher carbon and nitrogen demand. Carbonate caves had higher BG and AP activities (39.5 and 67.3 nmol h^-1g^-1) than basalt caves (0.7 and 0.1 nmol ^-1g^-1). Phosphorus availability may be the principal limitation on microbial activity in caves with current preliminary data. Our results suggest that EEA measurements can be used to assess the impact of human activity, as well as other factors, on cave ecology, which can contribute to our understanding of how to protect rare and unusual cave microbial communities.