PARENT SESSION
Poster Session #75: Nutrient Cycling II.
Friday, August 9. Presentation from 8:00 AM to 9:30 AM. Exhibit Hall B & C, TCC

Phosphomonoesterase activity in violets (Viola rotundifolia) found in watersheds exhibiting varying levels of nitrogen availability.

GRESS, STEPHEN^*,1, PETERJOHN, WILLIAM¹, ¹ West Virginia University, Morgantown, WV

ABSTRACT- Forests receiving high amounts of N deposition often exhibit various degrees of N saturation. As N availability increases during N saturation, P may become increasingly limiting. To examine this hypothesis, we measured root phosphomonoesterase activity and leaf N concentrations of Viola rotundifolia growing in Watersheds 3, 4, 10 and 13 of the Fernow Experimental Forest, WV. These watersheds exhibit various degrees of N availability. Watershed 3 is fertilized with NH4SO4 and has high stream-water nitrate concentrations (152 uM). Watershed’s 4, 10 &13 are unfertilized and have stream-water nitrate concentrations of 54, 15 &37 uM. Since phosphatase activity is often negatively associated with soil P availability, we expected a positive relationship between N availability and phosphomonoesterase activity. At several spatial scales, we found significant log-linear relationships between indices of N availability and phosphomonoesterase activity. For entire watersheds, stream-water nitrate concentrations were positively related with phosphomonoesterase activities (R² = 0.98). For small plots, phosphomonoesterase activities were positively associated with nitrate capture on anion exchange membranes (R² = 0.51). For individual plants, the phosphomonoesterase activities were positively associated with leaf N concentrations (R² = 0.30). Our results support the hypothesis that as N availability increases, P becomes increasingly limiting. Understanding how nutrient limitations change during N saturation should improve models of this process, and offer a way to reduce its effects through the addition of limiting nutrients to affected areas.

KEY WORDS: N-saturation, P-limitation, forests , Viola rotundifolia