SCALING OF C:N:P STOICHIOMETRY IN FORESTS WORLDWIDE: IMPLICATIONS OF TERRESTRIAL REDFIELD-TYPE RATIOS

TLDR

Inspired by the importance of globally well‑constrained C:N:P ratios in planktonic biomass for understanding marine nutrient cycles, we investigated analogous patterns in forest ecosystems worldwide. The study aimed to determine whether and when forest C:N:P ratios respond to macroscale ecosystem properties such as nutrient availability by examining their scaling with biomass and production. Using literature data, we examined C, N, and P stoichiometry in forest foliage and litter at global and biome levels and assessed how nutrient investments scale with biomass and production. We found that global forest C:N:P ratios are more variable than marine ratios, but biome‑level ratios are as constrained and distinct from one another; across biomass and production they scale isometrically, except that broadleaf litter and coniferous foliage exhibit disproportionate increases in nutrient investment relative to carbon, indicating macroscopic influences.

Abstract

Inspired by the importance of globally well-constrained carbon:nitrogen: phosphorus (C:N:P) ratios in planktonic biomass to the understanding of nutrient cycles and biotic feedbacks in marine ecosystems, we looked for analogous patterns in forest ecosystems worldwide. We used data from the literature to examine the stoichiometry of C, N, and P in forest foliage and litter on both global and biome levels. Additionally, we examined the scaling of nutrient investments with biomass and production both globally and within biomes to determine if and when these ratios respond to macroscale ecosystem properties (such as nutrient availability). We found that, while 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. While we were more interested in the relative constancy of the C:N:P ratios than their numerical value we did note, as have others, that the atomic ratios calculated for foliage (1212:28:1) and litter (3007:45:1) reflect the increased proportion of C-rich structural material characteristic of terrestrial vegetation. Carbon : nutrient ratios in litter were consistently higher than in comparable foliar data sets, suggesting that resorption of nutrients is a globally important mechanism, particularly for P. Litter C:N ratios were globally constant despite biome-level differences in foliar C:N; we speculate that this strong coupling may be caused by the significant contribution of immobile cell wall bound proteins to the total foliar N pool. Most ratios scaled isometrically across the range of biomass stocks and production in all biomes suggesting that ratios arise directly from physiological constraints and are insensitive to factors leading to shifts in biomass and production. There were, however, important exceptions to this pattern: nutrient investment in broadleaf forest litter and coniferous forest foliage increased disproportionately relative to C with increasing biomass and production suggesting a systematic influence of macroscopic factors on ratios.