From Cradle to Grave: the Stoichiometry of Northern Peatlands

English Abstract:

Ecological stoichiometry has been successfully applied to aquatic ecosystems, but with less success to terrestrial ones. Here we examine the stoichiometry of C, N, P and K in northern peatlands, ranging from plants, their response to fertilization and the changes as plants senesce, decompose and transform into peat, based on results from the Mer Bleue peatland and a peat survey in Ontario.

Most plant functional types show few seasonal variations in stoichiometry, apart from forbs and deciduous species at Mer Bleue, most suggesting co-limitation of N and P. N mineralization rates are slow in peatlands, and resin-exchangeable NH₄ and NO₃ is sparse: in porewater N is dominated by organic forms (> 85%), over NH₄ and NO₃. There is evidence that peatland plants can take up significant quantities of organic N, as amines. A long-term fertilization experiment showed that the addition of N, P+K increased foliar concentrations, though increased N concentration did not lead to a pronounced increase in photosynthesis. The response to increased nutrient loading varied, with homeostasis varying by plant functional type and nutrient. During senescence, nutrients are resorbed by the plants, both shrubs and mosses, decreasing the ‘quality’ of litter for decomposition. As litter transforms into peat, C:N ratio decreases (generally from 50:1 to 25:1), whereas the C:P ratio rises from < 1000:1 to 1500-2000:1: much of the hard-won N is buried in peat, whereas P is retained or recycled efficiently in the surface layers of the peat. The C:K ratio also increases down the peat profile, while there are smaller changes in the C:Ca and C:Mg ratios. Most of these stoichiometric changes occur in the early stages of decomposition (Von Post Index of < 4).