Spatial and temporal variability of soil N2O and CH4 fluxes along a degradation gradient in a palm swamp peat forest in the Peruvian Amazon

Mauritia flexuosa palm swamp, the prevailing Peruvian Amazon peatland ecosystem, is

extensively threatened by degradation. The unsustainable practice of cutting whole

palms for fruit extraction modifies forest's structure and composition and eventually

alters peat-derived greenhouse gas (GHG) emissions. We evaluated the spatio-temporal

variability of soil N₂O and CH₄ fluxes and environmental controls along a palm swamp

degradation gradient formed by one undegraded site (Intact), one moderately degraded

site (mDeg) and one heavily degraded site (hDeg). Microscale variability differentiated

hummocks supporting live or cut palms from surrounding hollows. Macroscale analysis

considered structural changes in vegetation and soil microtopography as impacted

by degradation. Variables were monitored monthly over 3 years to evaluate intra- and

inter-annual variability. Degradation induced microscale changes in N₂O and CH₄ emission

trends and controls. Site-scale average annual CH₄ emissions were similar along the

degradation gradient (225.6 ± 50.7, 160.5 ± 65.9 and 169.4 ± 20.7 kg C ha⁻¹ year⁻¹ at

the Intact, mDeg and hDeg sites, respectively). Site-scale average annual N₂O emissions

(kg N ha⁻¹ year⁻¹) were lower at the mDeg site (0.5 ± 0.1) than at the Intact (1.3 ± 0.6) and

hDeg sites (1.1 ± 0.4), but the difference seemed linked to heterogeneous fluctuations

in soil water-filled pore space (WFPS) along the forest complex rather than to degradation.

Monthly and annual emissions were mainly controlled by variations in WFPS, water

table level (WT) and net nitrification for N₂O; WT, air temperature and net nitrification

for CH₄. Site-scale N₂O emissions remained steady over years, whereas CH₄ emissions

rose exponentially with increased precipitation. While the minor impact of degradation

on palm swamp peatland N₂O and CH₄ fluxes should be tested elsewhere, the evidenced

large and variable CH₄ emissions and significant N₂O emissions call for improved modeling

of GHG dynamics in tropical peatlands to test their response to climate changes.