PARENT SESSION
Oral Session #35: Carbon and Nitrogen Cycling.
Presiding: D. Rothstein
Tuesday, August 6. 8:00 AM to 11:30 AM. Palo Verde Room, Radisson.

Nitrogen transformations along a rainfall gradient in Patagonia, Argentina: role of carbon-nutrient interactions.

AUSTIN, AMY^*,1, SALA, OSVALDO¹, ¹ University of Buenos Aires and IFEVA-CONICET, Buenos Aires, ARGENTINA

ABSTRACT- In water-limited ecosystems, the correlation of changes in net primary production with water availability is well documented, while the interactive effects of precipitation on nitrogen turnover and carbon-nitrogen interactions are less clear. We documented patterns of N availability, natural abundance of ¹⁵N in plants and soil, and nitrogen release from decomposing litter in Patagonian ecosystems along a natural rainfall gradient from 100 to 800 mm mean annual precipitation (MAP). Most indices of N transformations were correlated with MAP, including in situ net N mineralization, which increased with rainfall (Nmin = 0.0002*MAP-0.0005, r²=0.81, p=0.04), nitrogen release from decomposing litter which decreased with increasing rainfall (%Nremaining = 0.001*MAP+0.3482, r²=0.88, p=0.017), and plant and soil ¹⁵N which became more depleted with increasing precipitation (Foliar ¹⁵N=3.77-0.0092*MAP, r²=0.69, p<0.0001). Potential net nitrogen mineralization in soils increased as function of increasing site rainfall. At the same time, indices of carbon dynamics such as net primary production (ANPP=-39.4+0.56*MAP, r²=0.76, p=0.05), litter quality (Lignin:N=0.0059*MAP+8.84, r²=0.81, p=0.01) and soil C:N ratios (Soil C/N=0.0098*MAP+11.113, r²=0.96, p<0.001) also correlated significantly with MAP. These data suggest that both carbon quality (in determining nutrient release) and carbon quantity (in determining pool size and C:N ratios) play critical roles in determining nitrogen turnover and retention, and may ultimately be more important than the direct effect of precipitation on rates of nitrogen cycling in determining nitrogen availability.

KEY WORDS: Precipitation, Carbon cycling, Nitrogen cycling, 15N natural abundance