Mineral Nitrogen and Phosphorus Pools Affected by Water Table Lowering and Warming in a Boreal Forested Peatland

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Abstract: Changes in atmospheric temperature and lowering in water‐table (WT) are expected to affect peatland nutrient dynamics. To understand the response of peatland nitrogen (N) and phosphorus (P) dynamics to warming and drainage in a continental wooded‐bog of hummock–hollow microtopography, we compared three sites: (a) control, (b) recently drained (2–3 years; experimental), and (c) older drained (12–13 years; drained), during 2013. The WT was lowered at experimental and drained sites to 74 and 120 cm, respectively, whereas a warming of ~1 °C was created at one half of the microforms using open‐top chambers. Responses of peat total inorganic nitrogen (TIN = nitrate nitrogen [NO3−‐N] + ammonium nitrogen [NH4+‐N]) and phosphate‐P (PO43−‐P) pools and vegetation C:N ratio, δ13C and δ15N to the experimental treatments were investigated across sites/microforms and over time. Peat TIN available and extractable pools increased with deepening of WT and over time and were greater at hummocks relative to hollows. In contrast, the PO4 pools increased with short‐term drainage but reverted to very close to their original (control) nutrient values in the longer term. The WT and warming driven change in the peat TIN pool was strongly reflected in the vascular vegetation C:N ratio and shrub δ13C and δ15N, whereas moss nutrient dynamics did not vary between sites. Therefore, we suggest that atmospheric warming combined with WT deepening can increase availability of mineral N and P, which then can be reflected in vascular vegetation and hence modify the productivity and ecosystem functioning of the northern midlatitude continental wooded bogs in the long term.