Effect of ultraviolet radiation on alkaline phosphatase activity and planktonic phosphorus acquisition in Canadian boreal shield lakes

Tank, Suzanne E., Marguerite A. Xenopoulos, Len L. Hendzel

Limnol. Oceanogr., 50(5), 2005, 1345-1351 | DOI: 10.4319/lo.2005.50.5.1345

ABSTRACT: We examined how ultraviolet radiation (UVR) affects the activity of alkaline phosphatase (APase), a common extracellular enzyme. APase activity declined up to 57% under UVR exposure and decreased more often under ultraviolet A than ultraviolet B exposure, indicating that most of the observed decrease did not occur through direct enzyme inactivation. Enzyme activity in the particulate fraction (>0.22 µm) was less susceptible to UVR than activity in the total or dissolved fractions, suggesting that attachment to the cell surface may convey some protection against UVR-induced inactivation. Samples that were 0.22-µm filtered before being subjected to radiation treatments often showed increased enzyme activity, especially in the photosynthetically active radiation-only treatment, indicating reactivation of APase in the absence of de novo production of the enzyme. Decreases in APase can be severe near the lake surface, suggesting that UVR-induced variations in APase activity might contribute to microscale variations in nutrient availability and community composition.