Ecological stoichiometry is increasingly recognized as an important toolkit for ecosystem analysis as it provides a mechanistic link from the cells at one extreme to the biosphere on the other end, based on the realization that all organisms are made of the same essential elements. Plant stoichiometric homeostasis, the ability of a plant to maintain a certain elemental composition despite variation in the elemental composition in the soil, is a key parameter in ecological stoichiometry, and may represent a useful plant trait that is complementary to other plant traits. However, its quantification and application in arctic tundra ecosystems is very poorly understood. In this study, we used two data collection methods (Ion Exchange Membrane incubation method and soil core extraction method) to calculate homeostasis indices based on nitrogen (HN), phosphorus (HP), and nitrogen:phosphorus ratios (HN:P) of leaves for seven common tundra vascular species belonging to three growth forms. We then analyzed how these homeostatic values were related to plant aboveground biomass under various experimental manipulations both at the species and the community levels, after three time-series (one, seven, and thirteen years) manipulations, respectively.
Results/Conclusions
Each set of the H indices derived from the two collection methods was significantly correlated. HP and HN:P indices were positively related to each other, but not to the HN indices, both at the species and the community levels. At the species level, HN indices were highest in the herbaceous species and lowest in the ectomycorrhizal birch, with the ericoid mycorrhizal host species in between. HP and HN:P indices were higher in the evergreen shrub species and the dominant herbaceous species than in the deciduous shrub species. Species HP and HN:P were consistently positively correlated with aboveground biomass within the controls and across all manipulations for all three time series, except for the two manipulations that dramatically increased soil nitrogen and/or phosphorus fertility. Consistent with the species level results, aboveground biomass of the whole community was positively correlated with community HP and HN:P across the experimental manipulations for all three years. This study is the first test of the applicability of the stoichiometric homeostasis theory in the arctic tundra ecosystem, and could feed into biogeochemical models predicting the effects of environmental changes on tundra vegetation dynamics in a changing world.