PARENT SESSION
Oral Session # 98: Biogeochemistry V: Forests; Nitrogen.
Presiding: RL Sanford
Friday, August 8. 8:30 AM to 12:00 PM, SITCC Meeting Room 204.

Scaling of C:N:P ratios in forest ecosystems world-wide.

McGroddy, Megan^*,1, Hedin, Lars¹, Daufresne, Tanguy¹, ¹ Department of Ecology and Evolutionary Biology, Princeton, NJ, USA

ABSTRACT- The relative constancy of carbon:nitrogen:phosphorus (C:N:P) ratios has been key to understanding the role of limitation and biotic-abiotic interactions in shaping nutrient cycles and ecosystem function in marine ecosystems for decades. In contrast, research on stoichiometry in terrestrial ecosystems has primarily focused on variations at the individual and stand level and fluxes and stocks within individual sites, although there has been interesting work at larger scales looking at ratios as indices of nutrient limitation. Using the marine ecologists' approach we looked for 'Redfield-type' ratios in terrestrial forests on a global scale. While we were more interested in the relative constancy of the C:N:P ratios than their numerical value we did note that the atomic ratios calculated for foliage (1100:29:1) and litter (3400:47:1) reflect the increased proportion of C-rich structural material characteristic of terrestrial vegetation. We found that the global forest C:N:P ratios in both foliage and litter were more variable than those of marine particulate matter, biome level (temperate broadleaf, temperate coniferous and tropical) ratios were as constrained as marine ratios and statistically distinct from one another. These results led us to ask if the biome scale patterns are generated by physiological constraints of foliar tissue or are they the result of constraints imposed by community or ecosystem structure. Nitrogen:P ratios held constant across the range of biomass stocks and productivity in all forests suggesting that physiological constraints are effective at all scales. Coniferous forests showed a shift to lower C:N and C:P ratios at higher foliar biomass. Litter C:N and C:P ratios in tropical forests and C:N ratios in temperate broadleaf forests also decreased at higher productivity. We suggest that these diagnostic differences between biomes with respect to ratios and their scaling patterns may lead to further understanding of strategies of forest nutrient cycles on global scales.

Key words: litter, stoichiometry, foliage