## 1 Introduction  
Northern peatlands are globally important carbon sinks, storing more carbon than all of Earth's forests [1, 2, 3, 4] despite taking up only 3% of the global land area [5]. However, the carbon sink status of peatlands is vulnerable because climate warming and land conversion are currently inducing a suite of changes to vegetation and hydrology that will impact peat formation and storage [1]. For instance, as the climate continues to change, it is likely that warmer temperatures will cause drops in water table (WT) position [6]. When water tables are lowered, the oxic zone of peat is expanded, causing increases in decomposition rates [7]. At the same time, water stress caused by lowered water tables is likely to reduce rates of photosynthesis, therefore reducing net primary production (NPP) [8, 9]. If decomposition exceeds production, peatlands will no longer function as carbon sinks. Similarly, large-scale ditching to convert peatlands to agriculture and forestry has caused substantial regional losses of peat [10]. _Sphagnum_ moss is a key player in the formation of peatland ecosystems, and alone is responsible for the storage of around 10% of the world's soil carbon [11]--more than any other plant genus [12]. _Sphagnum_ lacks a vascular system, and relies solely on the capillary transport of water to survive, resulting in potentially high susceptibility to water stress [12, 13] such as more frequent or prolonged droughs that are predicted to occur with climate change [7, 14, 15]. Many northern peatlands contain a diverse microtopographyformed by _Sphagnum_ growing in hummocks and hollows [16], defined primarily by their relative heights with an alternating hummock-hollow microtopographical pattern [17]. Because they grow further above the water table than hollow mosses, hummock mosses have adaptations that allow them to tolerate (and even create) drier conditions than hollow mosses can tolerate [18; 19]. For instance, capitula in hummocks tend to be smaller and denser than those in hollows as more resources are put towards stem growth which in turn increases the efficacy of capillary transport and retention of water from deeper in the peat [11; 19; 20]. For this reason, we hypothesized that hummocks would be more resistant to drought and lowered water tables than hollows, maintaining more stable CO\({}_{2}\) cycles. It has been observed that _Sphagnum_ dominated peatlands often undergo changes in surface height as a result of fluctuating water tables [21; 22; 23; 24]. This following of the water table is often referred to as \"mire-breathing\" and is thought to be a method of self-preservation under water stress [25], which has been documented at scales of entire peatlands, with variations related to the height above water table of different peatland landforms [26]. In the traditional model, the collective peat surface expands as the water table position rises, raising the bog surface and increasing water storage. With a decline in water table position the peat loses volume, and the peat surface drops, which maintains close contact between _Sphagnum_ mosses and the water table--thereby maintaining their productivity. While prior work has shown there to be different water transport and storage characteristics among different peatland microforms [27], it is unknown whether the contrasting _Sphagnum_ landforms (i.e., hummocks and hollows) exhibit similar mechanisms of mire-breathing and how that affects their ability to maintain productivity under drier conditions. Despite the critical influence _Sphagnum_ dominated peatlands have in the global carbon cycle, ecosystem and climate models are only beginning to take _Sphagnum_ moss function in peatlands into account [1; 3; 28; 29; 30]. Additionally, data regarding the role _Sphagnum_ architecture may play in stabilizing peatland carbon storage as the climate warms is lacking [24]. This study aims to identify whether differing _Sphagnum_ types are more resistant to water stress than others, and how carbon cycling may be impacted by that resistance.