|Blank, Robert - Bob|
Submitted to: Biogeochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2007
Publication Date: 3/2/2007
Citation: Nadeau, J.A., Qualls, R.G., Nowak, R.S., Blank, R.R. 2007. The potential bioavailability of organic C, N, and P through enzyme hydrolysis in soils of the Mojave Desert. Biogeochemistry. 82:305-320. Interpretive Summary: Climate change models suggest increase precipitation in the desert Southwest. The effect of increased precipitation on soil enzymes activities was investigated in shrub and interspace microsites. Increase precipitation did not significantly affect soil enzyme activities and for most enzymes, shrub microsites has greater activities. The effect of short-term watering events may be controlled by diffusion rather than enzyme activity or concentration.
Technical Abstract: Climatic models suggest that global warming will increase monsoonal precipitation in the desert Southwest of the USA. We investigated whether individual precipitation events have an effect on the activities of soil enzymes involved in C, N, and P mineralization in soils of the Mojave Desert. Plots were established in shrub and interspace microsites and watered with a simulated 2 cm precipitation event comparable to the intensity of a spring or summer thunderstorm and compared with unwatered control plots. Soil samples were collected immediately before, and for five days after, the simulated precipitation event and analyzed for the activities of amidase, phenol oxidase, alkaline phosphomonoesterase, and protease. The experiment was repeated three times over two years. In general, there were no significant differences between watered and unwatered plots over the six-day sampling period for any enzyme activities in any sampling period. The ranges of mean enzyme activity measured were: amidase, 0.053 to 0.153 mg NH4+ g-1 soil hr-1; phenol oxidase, 0.024 to 0.052 µmoles 3-dihydroindole-5,6-quinone-2-carboxylate g-1 soil min-1; alkaline phosphomonoesterase, 0.277 to 0.656 µg p-nitrophenol g-1 soil hr-1; and protease, 41.25 to 127.29 µg tyrosine g-1 soil hr-1. Significant differences between microsites for all enzyme activities were found, and all but phenol oxidase had higher enzyme activities in shrub microsites. The lack of response in enzyme activity to soil wetting may indicate the existence of a large stock of extracellular enzymes present in Mojave Desert soils.