Nutrient mineralisation and microbial functional diversity in a restored bog approach natural conditions 10 years post restoration

• Rates of N transformations follow trend of harvested > natural > restored bog.
• Microbial functional diversity similar across sites.
• Microbial respiration similar between natural and spontaneously re-vegetated peat.
• Highest microbial respiration (activity) observed at restored site.
• Vegetation functional type may exert control on belowground processes in peat.

Peatland restoration has been implemented on sites exploited for horticultural peat for over a decade in Eastern Canada. However, little is known about nutrient dynamics and microbial processes in this region. Belowground nitrogen (N) and phosphorus (P) transformations and carbon utilisation by microorganisms were examined in a harvested peatland 10 years after restoration measures were implemented to assess whether restoration is returning the peatland to a state that falls within the natural range of variation found in a neighbouring bog. N mineralisation rates were almost 10-fold higher in the surface (0–10 cm) compared to the subsurface (10–20 cm) layers for all sites and were highly variable within sites. P pools were small (<0.02 μg g−1 dry peat) and mineralisation rates of P were low in all sections. In the surface layer, the net mineralisation and ammonification rates appeared to be highest in unrestored sites but lowest in restored sites. In contrast, the capacity of microorganisms in using different carbon (C) sources, also described as microbial functional diversity, was highest at restored sites but lowest at unrestored sites. The preferable C sources varied between sites and were significantly correlated with aboveground vegetation composition. Our study suggests that microbial activity and nutrient transformations differ between natural and unrestored harvested peatlands. Our results indicate that the presence of vegetation regrowth in the unrestored area of a peatland alters belowground processes by stimulating microbial activity and increasing the uptake of nutrients, leading to smaller pools of inorganic N available in the peat. When restoration has been carried out, microbial activity is even higher than in natural conditions, possibly leading to high immobilization of N, and net mineralisation rates are very low. This research indicates that while belowground processes have shifted from unrestored conditions following restoration, they do not appear to be fully re-established to a degree similar to natural conditions 10 years post-restoration.