## 3 Results
### Sphagnum and Peat Physical Structure in Response to Treatments  
Capitula density was most significantly affected by whether moss was a hummock or hollow (_p_-value= 7.69 \(\times\) 10\({}^{-5}\)). Capitula density in hummocks exposed to low water tables was significantly greater than hummocks exposed to high water tables (_p_-value adj = 0.0373) and capitula density in hollows across both WT treatment levels (_p_-value adj = 0.0001). There was no significant difference in capitula density between hummocks and hollows treated with high water tables (_p_-value adj = 0.5128). Hollow capitula density did not show any significant difference between high and low water table treatments (_p_-value adj = 0.9794). Increased capitula density was associated with higher resistance of GPP to lowered water tables, such that this resistance was higher in hummocks compared to hollows.  
Figure 2: Boxplots of fluxes in response to experimental treatments. The treatment labels are “H” = high water tables, “L” = low water tables, “A” = average rainfall, “D” = droughted rainfall. Green boxes are hollows, brown boxes are hummocks. Box intervals represent the first and third interquartile range, whiskers represent the minimum and maximum after removing outliers, and the horizontal bold line represents the median.  
Water table depth was found to have the greatest effect on peat surface height (\(p\)-value = 3.70 \(\times\) 10\({}^{-7}\), see Supplementary File S1 for time series of the change in peat surface height). Whether a bin was a hummock or hollow did not significantly affect surface height (\(p\)-value = 0.09193). However, the interaction between _Sphagnum_ type and water table depth did significantly impact surface heights (\(p\)-value = 0.00304). A mean significant difference of 3.57 cm in surface height was recorded between hollows subjected to low water table treatments and hollows subjected to high water table treatments (\(p\)-value = 7 \(\times\) 10\({}^{-7}\)). A mean difference of only 1.18 cm was recorded between hummocks with high water table treatments and hummocks with low water table treatments (\(p\)-value = 0.134483). It was observed that hummocks tended to compress inwards, rather than subsiding towards the lowered water table as significantly as hollows (Figure 3). Lower peat height was linearly associated with reduced GPP in response to lowered water tables, indicating that peat subsidence did not significantly enhance the resistance of GPP to lower water tables. Conversely, _Sphagnum_/peat inward compression was found to stabilize GPP under lowered water tables (Figure 3).  
Figure 3: The relationship between water tables, peat structure and GPP. The images show Sphagnocosm monoliths removed from the PVC collars and cut into cross sections, representing hollows (**a**,**b**) and hummocks (**c**,**d**), under high (**left**) and low (**right**) water tables. The shape of the monolith was reconstructed based on the measured decrease in peat height and increased density (inward compression) of capitula measured in situ, the pictured change shows the mean decrease in peat height or increased density from a high water table—average rainfall treatment to a low water table drought treatment, with the red arrows representing the primary axis of change in each image. The figures on the right show GPP in relation to e. capitula density and f. surface subsidence (\(\Delta\) peat height). Error bars represent standard error. In the upper right graph, dashed arrows connect the the high and low water table treatments at average rainfall, while solid arrows connect the high and low water table treatments at drought, with colors representing the respective landforms. The line in the lower right figure represents significant linear fit across treatments.