## 4 Discussion
### Mire-Breathing  
We investigated changes in peat height and capitula density throughout the study in each sphagnocosm, and witnessed not only the standard subsidence \"mire-breathing\" we had expected [25; 41] but also an inwardly compressive \"mire-breathing\". We found that hollow masses tended to track the water table downwards, exhibiting a subsidence mire-breathing strategy which has been well documented [25; 42]. However, we also found that hummocks exhibited a compressive mire-breathing technique wherein capitula density increased as the mosses compressed into each other (Figure 3). This compression was associated with sustained GPP in response to lower water tables in the hummocks but not hollows.  
There are many studies that mention mire-breathing as the swelling and subsidence of peat moss in response to fluctuating water tables [25; 42; 43]. However, to our knowledge there is very little information on the compressive mire-breathing response that we observed and found to act as a stabilizing factor for GPP.  
Some studies have questioned whether \"mire-breathing\" is a passive reaction simply associated with lowered water tables, or an adaptive mechanism that has evolved over time [25]. Although our study did not investigate evolutionary relationships in _Sphagnum_ traits, we found that hummocks exhibited a different, more successful \"mire-breathing\" strategy than hollow species, arguing that mire-breathing may not be passive, but rather an evolutionary species-specific response. Hummock species did not exhibit vertical subsidence as expected, yet were able to more successfully regulate GPP than the hollow species that did, suggesting a species-specific beneficial trait that may have been preserved through natural selection. Previous studies have concluded that traits related to litter decomposition rates and the niche descriptor height-above-water table are phylogenetically conserved [18]. Therefore, it may not be too far of a stretch to question whether the \"mire-breathing\" response of hummock species is also phylogenetically conserved.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Response** & **Factors** &
\begin{tabular}{c} **Standardized** \\ **Effect** \\ \end{tabular} & **Z-Value** & **P \textgreater{} \textgreater  
[PERSON] et al. (2021) [18] mapped several species of hummock and hollow forming _Sphagnum_ along a height-above-water table decay constant gradient. The two dominant species in our study--_Sphagnum fuscum_ (hummock) and _Sphagnum fallax_ (hollow)--were located on opposite ends of the gradient as _Sphagnum fuscum_ was located high above the water table and had low decomposability while _Sphagnum fallax_ was located closer to the water table and had a much higher decomposability. We already know that hummocks form higher above the water table than hollows in part due to slower litter decomposition [18; 44], but it is possible that slow decomposition is also linked to greater stability under water stress, and could possibly be a contributing factor behind the inwardly compressive \"mirebreathing\" that we witnessed in hummocks. As the litter layer in hummocks accumulates, capillary action is most efficient as the live moss pushes closer together, rather than subside towards the water table, which is impeded by the thick litter layer (Figure 3). Whereas in hollows, a thinner litter layer may allow the live moss to simply subside with the water table as we witnessed (Figure 3). Our findings, when grouped with the [PERSON] et al. (2021) gradient, suggest that _Sphagnum_ species on the far end of the gradient that grow higher above the water table and decompose more slowly, may be more prone to compressive \"mire-breathing\" and therefore more resilient to water stress than species on the opposite end of the gradient. This supports the idea that evolution in _Sphagnum_ dominated peatlands may be favoring slower resource acquisition.