PARENT SESSION
Oral Session #94: Nutrient Cycling.
Presiding: R. Yanai
Thursday, August 8. 1:00 PM to 3:45 PM. Grand Ballroom East, Radisson.
The fate of phosphorus in a lowland Amazonian forest ecosystem.
McGroddy, Megan*,1, Silver, Whendee1, Cosme de Oliveira, Raimundo2, 1 Environmental Sciences, Policy and Management, Berkeley, CA2 EMBRAPA, Santarem, Para, Brazil
ABSTRACT- Phosphorus is considered the primary limitation to net primary productivity in highly weathered tropical ecosystems. Under limiting conditions the size of the component fractions of the soil P pool can indicate the relative strength of biological and geological processes in soil P cycling. We used natural variations in soil texture and a fertilization treatment to look at the fate of P in a moist tropical forest. On each of two soil types (sands and clays) we examined P sinks and fluxes in root biomass, microbial communities and several soil P pools using ingrowth and exclusion cores. Of all the soil P pools measured only the pool considered of intermediate availability (NaOH + dilute acid extractable) showed a significant increase with fertilization, and this occurred only in clays (+ 18.3 kg ha-1 + 3.2 after 1 year). In contrast, both root and microbial biomass P pools increased more in sands with fertilization suggesting a larger biotic P sink in these soils. Leaching of inorganic P from the surface soils was an unexpectedly significant fate of added P in both soil types (up to 18 % + 3 of added P in the sands and 9 % + 1 in the clays). Patterns in soil P pools and fluxes were strongly seasonal indicating high turnover rates and the dominance of biological mechanisms in short-term P cycling in this ecosystem.
KEY WORDS: phosphorus, Amazon, nutrient cycling, roots