PARENT SESSION
Poster Session #19: Nutrient Cycling.
Tuesday, August 7, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall
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Phosphatase activity along an alpine age and nutrient gradient.
Holland, Keri1, Townsend, Alan1, Bowman, William1, 1
ABSTRACT- Variation in the extent of past glaciations has created an apparent soil age gradient on Niwot Ridge and the adjacent Green Lakes Valley that ranges from approximately 10,000 y bp to a minimum 100,000 y bp, and perhaps much older. Prior work has shown that plant available forms of phosphorus (resin + bicarbonate extractable soil P) are moderate in the youngest soil, highest in the 60k y site, and lowest at the oldest site. Based on earlier theoretical models, we hypothesized that soil phosphatase activity would inversely follow the trend in available P, and that microbial extractable C: P ratios would be highest in the most P poor site. Eight soils from each site were sampled and analyzed for phosphatase activity, inorganic P, and chloroform extractable C and P. In contrast to our expectations, phosphatase activity declined over the age gradient, with levels in the oldest soil (18 ± 5.1 umol pnp/gS/h) half that in the younger soil (37 ± 4.7 umol pnp/gS/h), while the chloroform extractable microbial C: P ratio of the oldest soil (12 ± 1.1) was significantly higher than the younger soil (8.8 ± 0.9), which would suggest a stronger P constraint in the oldest site. Chloroform extractable C and P, and inorganic P, were highest at the 60k y site. Phosphatase activity was also measured in a long-term N & P fertilization experiment on the oldest soil. While microbial extractable C: P ratios reflected patterns in inorganic P, ranging from 3 ± 0.9 in the phosphorus fertilization treatments to 11 ± 0.9 in the control treatments, there were no significant differences in phosphatase activity between fertilization treatments nor the oldest age gradient sampling. While phosphatase activity was not inversely related to inorganic P, measured phosphatase activities were quite high relative to other studies.
KEY WORDS: phosphatase, phosphorus availability, soil age gradient, Niwot Ridge