Responses of Nutrient Dynamics to Warming and Water Table Lowering Simulations of Climate Change in a Northern Treed Bog

English Abstract:

In a dry continental treed bog of hummock-hollow microtopography, we compared three sites 1) control, 2) recently drained (2-3 years; experimental), and 3) older drained (12-13 years; drained) with water levels at 38, 74 and 120 cm below the surface, respectively. At each site/microform we quantified nutrient dynamics in response to open-top chamber warming of ~1 °C and the above-mentioned water level gradient. We used ion exchange membrane probes (PRS^TM probes; plant root simulator) to capture available nutrients followed by potassium chloride extraction to quantify the extractable nutrients from peat, and vegetation sampling to determine C:N ratio of above-ground dominant plant functional groups.

Deeper drainage for a longer-term resulted in higher TIN availability with an increase of 28% relatively to the control. TIN availability increased by 18% in response to the shallower drainage over short-term. In contrast to TIN, the increases in available and extractable pools of PO₄ were more in response to the recent drainage (51% and 56%, respectively) compared to no increase at the older drained site. Both the available and extractable pools of TIN, NO₃^- and NH₄⁺ increased the most at the older drained hummocks likely due to the significant increase in productivity at these locations. The OTC warming alone increased the extractable TIN, NO₃^-, NH₄⁺ and PO₄^3- compared to unwarmed controls by 13%, 7%, 32% and 11%, at the drained site, 10%, 4%, 24% and 31% at the experimental site, and 11%, 9%, 12% and 37% at the control site. The strongest response to warming was from drained hummocks for TIN and experimental hummocks for PO₄^3-. The C:N ratios of shrub and tree functional groups decreased along the gradient of decreasing water level indicating increasing N uptake by these plants post-drainage. Available nutrient pools were strong predictors of extractable nutrient pools which in turn were strongly related to the vegetation C:N ratios.

We conclude that the predicted climatic changes will likely enhance nutrient pools in the soils of forested non-permafrost ombrotrophic boreal bogs. These changes in bog nutrient dynamics are likely to shift plant community composition favouring woody plant growth and NPP, and thereby affecting whole ecosystem functioning.