## 2 Materials and Methods
### Gas Exchange Measurements  
From July 2019 to December 2020, we monitored soil autotrophic and heterotrophic respiration. At each plot, we installed four PVC collars, each with 10 cm internal diameter and 10 cm height. Three of those collars were inserted at least 2 cm, directly into the soil, to measure the total soil respiration (Rs). To measure soil heterotrophic respiration, we dug a hole (approximate 30 cm wide and 40 cm deep), and the soil was extracted and separated into its characteristic layers. A bucket with a drainage hole was inserted to provide a barrier \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Plot** &
\begin{tabular}{c} **Elevation** \\ **(m)** \\ \end{tabular} & \(\mathbf{T_{A}}\) & \(\mathbf{T_{min}}\) & \(\mathbf{T_{max}}\) & \(\mathbf{RH_{A}}\) & \(\mathbf{RH_{min}}\) & \(\mathbf{RH_{max}}\) & \(\mathbf{T_{sA}}\) & \(\mathbf{T_{smin}}\) & \(\mathbf{T_{smax}}\) \\ \hline AMAL & 316 & 17.4 & 12.6 & 23.1 & 68.7 & 48.1 & 88.0 & & & & \\ PEV & 213 & 17.3 & 10.6 & 25.4 & 67.2 & 38.5 & 92.6 & & & \\ LML & 166 & 16.6 & 9.2 & 24.7 & 70.8 & 44.8 & 91.5 & & & \\ ACRIL & 261 & 17.3 & 10.8 & 26.9 & 66.6 & 36.8 & 88.9 & & & \\ \hline OLY1 & 350 & 16.5 & 10.3 & 25.8 & 62.5 & 41.5 & 78.7 & 15.8 & 14.3 & 17.6 \\ OLY2 & 450 & 15.7 & 10.5 & 21.8 & 68.5 & 45.7 & 88.1 & 15.4 & 14.6 & 16.2 \\ OLY3 & 550 & 15.4 & 10.4 & 21.6 & 69.6 & 47.1 & 90.0 & 14.9 & 14.1 & 15.7 \\ OLY4 & 650 & 14.2 & 8.8 & 20.5 & 71.8 & 47.4 & 92.5 & 14.3 & 13.5 & 15.2 \\ OLY5 & 750 & 12.6 & 8.5 & 18.3 & 76.0 & 59.5 & 88.1 & 12.3 & 11.6 & 13.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Climatic description of the study plots corresponding to a three-year-long dataset as recorded within each plot. \(\mathrm{T_{A}}\) is the annual average temperature, \(\mathrm{T_{min}}\) and \(\mathrm{T_{max}}\) are the annual average minimum and maximum temperatures, respectively. \(\mathrm{RH_{A}}\) is the annual average relative humidity, \(\mathrm{RH_{min}}\) and \(\mathrm{RH_{max}}\) are the annual average minimum and maximum relative humidities, respectively. Also, \(\mathrm{T_{sA}}\), \(\mathrm{T_{smin}}\) and \(\mathrm{T_{smax}}\) are the annual average, annual average minimum and annual average maximum soil temperatures. Temperatures are in \({}^{\circ}\)C and relative humidities are in percentage (%). for the roots and refilled with the extracted soil layer by layer [49]. Old root fragments were excluded from the bucket. The fourth collar was inserted at least 2 cm into the bucket and left for a month to reach an equilibrium before the first measurement. This method yielded estimates of \(R_{\mathrm{het}}\) and, by combining \(R_{\mathrm{s}}\) and \(R_{\mathrm{het}}\) measurements, we were able to estimate soil autotrophic respiration (\(R_{\mathrm{aut}}\)):  
\[R_{s}=R_{het}+R_{aut} \tag{1}\]  
Soil respiration measurements were carried out using an LI-8100 Automated Soil CO\({}_{2}\) Flux System (LICOR Biosciences Inc., Lincoln, NE, USA) infrared gas analyzer with a 10 cm survey chamber. For each collar, soil respiration was measured from early in the morning until the afternoon of each sampling day (3 to 5 measurements) to account for diurnal temperature and moisture fluctuations, with three replications per measurement. Soil respiration data were processed using the SoilFluxPro 4.2.1 software (LI-COR Biosciences, Inc., NE, USA). During each replicate, a minimum of 80 logs were made (one per second--max 105 logs), with this data used to fit an exponential curve. The slope of the curve was used to estimate \(R_{\mathrm{het}}\) per replicate and the average slope was recorded as the per measurement \(R_{\mathrm{het}}\). At the time of each soil respiration measurement, soil temperature (\(T_{\mathrm{s}i}\)) and water content (\(\theta_{\mathrm{i}}\)) were recorded using the Omega 88311K thermometer (Omega Sensing Solutions ULC, Saint Eustache, QC, Canada) and the ML2x Theta Probe soil moisture sensor (Delta-T Devices Ltd., Burwell, Cambridge, United Kingdom) mounted on the LI-8100.