Plant stoichiometry and its temporal variation in an ombrotrophic peatland

Background/Question/Methods

Ecological stoichiometry provides an integrative framework linking the biogeochemical patterns at a global scale to physiological constraints that operate at cellular or organismal levels. Our understanding of C, N, P and K stoichiometric relationships in terrestrial ecosystems is less well developed than aquatic ecosystems. In boreal peatlands plant growth is considered to be N limited. However, under high levels of atmospheric N deposition and global warming, N limitation can be shifted to P-, or N, P-co-limitation. This questions what the predominant limiting nutrient in boreal peatland ecosystems is and what is the temporal variation? To determine nutrient limitation, 14 plant species belonging to five functional types in an ombrotrophic peatland (Mer Bleue) were sampled monthly from July 2010 to March 2012. Leaf-level C, N, P and K concentrations were measured and applied to the N:P:K ternary diagram.

Results/Conclusions

The average N:P:K stoichiometric ratios (14.8:1:8.4) of all species in peak growing season (June-August) indicated the plant growth in Mer Bleue was co-limited by N and P. A strong N-limitation was only observed in the early season (May) following snow-melt, especially for the deciduous species. The Sphagnum mosses showed weak temporal variations with a constrained stoichiometry. In contrast, a pulse of nutrient concentration in deciduous species in the early and late seasons (September-October) was observed. These data supported the argument that boreal peatlands are vulnerable to the shift from N to P or N, P –co-limitations. The high level of N deposition (0.8 g m^-2 yr^-1) could be a driver of N, P co-limitation in Mer Bleue peatland. The pulse of nutrient concentration in leaves is probably related to nutrient resorption when new leaves develop and old leaves senesce, and this process is more significant in deciduous species than evergreens.