Spatial and temporal variability of soil N2O and CH4 fluxes along a degradation gradient in a palm swamp peat forest in the Peruvian Amazon
Authors: Hergoualc’h Kristell , Dezzeo Nelda , Verchot Louis , Martius Christopher , van Lent Jeffrey , Del Aguila Pasquel Jhon , Lopez Mariela 
Published: March 2021

&lt;p&gt;Mauritia flexuosa palm swamp, the prevailing Peruvian Amazon peatland ecosystem, is&lt;/p&gt;&lt;p&gt;extensively threatened by degradation. The unsustainable practice of cutting whole&lt;/p&gt;&lt;p&gt;palms for fruit extraction modifies forest's structure and composition and eventually&lt;/p&gt;&lt;p&gt;alters peat-derived greenhouse gas (GHG) emissions. We evaluated the spatio-temporal&lt;/p&gt;&lt;p&gt;variability of soil N&lt;sub&gt;2&lt;/sub&gt;O and CH&lt;sub&gt;4&lt;/sub&gt; fluxes and environmental controls along a palm swamp&lt;/p&gt;&lt;p&gt;degradation gradient formed by one undegraded site (Intact), one moderately degraded&lt;/p&gt;&lt;p&gt;site (mDeg) and one heavily degraded site (hDeg). Microscale variability differentiated&lt;/p&gt;&lt;p&gt;hummocks supporting live or cut palms from surrounding hollows. Macroscale analysis&lt;/p&gt;&lt;p&gt;considered structural changes in vegetation and soil microtopography as impacted&lt;/p&gt;&lt;p&gt;by degradation. Variables were monitored monthly over 3 years to evaluate intra- and&lt;/p&gt;&lt;p&gt;inter-annual variability. Degradation induced microscale changes in N&lt;sub&gt;2&lt;/sub&gt;O and CH&lt;sub&gt;4&lt;/sub&gt; emission&lt;/p&gt;&lt;p&gt;trends and controls. Site-scale average annual CH&lt;sub&gt;4&lt;/sub&gt; emissions were similar along the&lt;/p&gt;&lt;p&gt;degradation gradient (225.6 &amp;#177; 50.7, 160.5 &amp;#177; 65.9 and 169.4 &amp;#177; 20.7 kg C ha&lt;sup&gt;&amp;#8722;1&lt;/sup&gt; year&lt;sup&gt;&amp;#8722;1&lt;/sup&gt; at&lt;/p&gt;&lt;p&gt;the Intact, mDeg and hDeg sites, respectively). Site-scale average annual N&lt;sub&gt;2&lt;/sub&gt;O emissions&lt;/p&gt;&lt;p&gt;(kg N ha&lt;sup&gt;&amp;#8722;1&lt;/sup&gt; year&lt;sup&gt;&amp;#8722;1&lt;/sup&gt;) were lower at the mDeg site (0.5 &amp;#177; 0.1) than at the Intact (1.3 &amp;#177; 0.6) and&lt;/p&gt;&lt;p&gt;hDeg sites (1.1 &amp;#177; 0.4), but the difference seemed linked to heterogeneous fluctuations&lt;/p&gt;&lt;p&gt;in soil water-filled pore space (WFPS) along the forest complex rather than to degradation.&lt;/p&gt;&lt;p&gt;Monthly and annual emissions were mainly controlled by variations in WFPS, water&lt;/p&gt;&lt;p&gt;table level (WT) and net nitrification for N&lt;sub&gt;2&lt;/sub&gt;O; WT, air temperature and net nitrification&lt;/p&gt;&lt;p&gt;for CH&lt;sub&gt;4&lt;/sub&gt;. Site-scale N&lt;sub&gt;2&lt;/sub&gt;O emissions remained steady over years, whereas CH&lt;sub&gt;4&lt;/sub&gt; emissions&lt;/p&gt;&lt;p&gt;rose exponentially with increased precipitation. While the minor impact of degradation&lt;/p&gt;&lt;p&gt;on palm swamp peatland N&lt;sub&gt;2&lt;/sub&gt;O and CH&lt;sub&gt;4&lt;/sub&gt; fluxes should be tested elsewhere, the evidenced&lt;/p&gt;&lt;p&gt;large and variable CH&lt;sub&gt;4&lt;/sub&gt; emissions and significant N&lt;sub&gt;2&lt;/sub&gt;O emissions call for improved modeling&lt;/p&gt;&lt;p&gt;of GHG dynamics in tropical peatlands to test their response to climate changes.&lt;/p&gt;