## 2 Materials and Methods  
### Peat Harvest and Water Table Treatments  
Thirty-two cores of peat (\(\sim\)30 cm depth \(\times\) 20 cm diameter) were collected from a _Sphagnum_-dominated oligotrophic peatland in Nestoria, MI (46\({}^{\circ}\)34\({}^{\prime}\)22.66\({}^{\prime\prime}\) N, 088\({}^{\circ}\)16\({}^{\prime}\)44.85\({}^{\prime\prime}\) W) previously described by [31]. Briefly, the overstory consisted of _Larix laricina_ and _Picea mariana_ and the understory consisted of mixed sedge and ericoid shrubs. Peat cores were obtained using a sharpened PVC corer and serrated knives. Cores were collected from two peatland landforms: elevated mounds (hummocks) and lower, flat microforms (hollows/lawns, hereafter 'hollows') in a relatively open, homogeneous area within the peatland. Each peat core was placed in two 3.8 L plastic bags left open at the top and arranged in 35 cm tall \(\times\) 20 cm diameter PVC tubes. The full dynamic range of \"mire breathing\" for hummock/hollow microtopography can range between 20-60 cm depth [32], with the majority of changes in water storativity occurring in the top 40 cm [27]. As such, the top 30 cm measured in this study is likely reflective of this range but does not necessarily capture dynamics occurring within denser peat. Cores were then transported to the Houghton Mesocosm Facility at the USDA Forest Service Northern Research Station, where they were subjected to experimental treatments modeled after a larger mesocosm experiment [33]. Prior to initiating treatments, to allow the samples to acclimate to the new environment, each core was kept saturated for approximately two weeks in the outdoor mesocosm facility. All vascular plants were then clipped, leaving only _Sphagnum_ mosses and a low cover (<5% area) of _Polytrichum strictum_ moss. Each sample (hereafter referred to as'sphagnocosm') was randomly assigned a treatment of either a high or low water table depth coupled with an average or droughted rainfall. The experiment was thus a fully crossed design with water table depth \(\times\) rainfall \(\times\) landform, with 4 replicates per treatment level (Figure 1).  
Water table treatments were implemented by first measuring the average surface height of the _Sphagnum_ in each bin. A collar with a wire grid was placed on each bin, and a ruler was dropped gently from four points formed by the grid until it rested on the surface of the moss. The point where the ruler lined up with the top of the collar was recorded (cm), and the height of the collar was then subtracted from the recorded height. One drainage hole was drilled in each sphagnocosm 5 cm below the average surface height for that sample, and for the low water table treatment an additional hole was drilled at 25 cm below the average surface height. Water was allowed to drain freely from each hole, and small tubes were inserted in each hole to help with drainage. Rainfall treatments were initiated at the same time as water table depth treatments. Sphagnocosms were kept under clear plastic rainout shelters to ensure that all inputs of water were accounted for. Half of the sphagnocosms received a rainfall treatment representing an average monthly summer rainfall of 163 mm while half received a droughted rainfall reduced by -50% from the average: converting the average rainfall this to units of mL/bin and then dividing by the number of rainfall events resulted in a volume of 400 mL/rain event in the \"average\" rainfall treatment, and 200 mL/rain event in the \"droughted\" rain event. Sphagnocosms were watered three times a week over the 25 day duration of the experiment using artificial rainwater (See [PERSON] et al. 2015 [33] for rainfall chemistry).