Degradation-driven changes in fine root carbon stocks, productivity, mortality, and decomposition rates in a palm swamp peat forest of the Peruvian Amazon

Abstract

Background Amazon palm swamp peatlands are major carbon (C) sinks and reservoirs. In Peru, this ecosystem is widely threatened owing to the recurrent practice of cutting Mauritia flexuosa palms for fruit harvesting. Such degradation could significantly damage peat deposits by altering C fluxes through fine root productivity, mortality, and decomposition rates which contribute to and regulate peat accumulation. Along a same peat formation, we studied an undegraded site (Intact), a moderately degraded site (mDeg) and a heavily degraded site (hDeg) over 11 months. Fine root C stocks and fluxes were monthly sampled by sequential coring. Concomitantly, fine root decomposition was investigated using litter bags. In the experimental design, fine root stocks and dynamics were assessed separately according to vegetation type (M. flexuosa palm and other tree species) and M. flexuosa age class. Furthermore, results obtained from individual palms and trees were site-scaled by using forest composition and structure. Results At the scale of individuals, fine root C biomass in M. flexuosa adults was higher at the mDeg site than at the Intact and hDeg sites, while in trees it was lowest at the hDeg site. Site-scale fine root biomass (Mg C ha−1) was higher at the mDeg site (0.58 ± 0.05) than at the Intact (0.48 ± 0.05) and hDeg sites (0.32 ± 0.03). Site-scale annual fine root mortality rate was not significantly different between sites (3.4 ± 1.3, 2.0 ± 0.8, 1.5 ± 0.7 Mg C ha−1 yr−1 at the Intact, mDeg, and hDeg sites) while productivity (same unit) was lower at the hDeg site (1.5 ± 0.8) than at the Intact site (3.7 ± 1.2), the mDeg site being intermediate (2.3 ± 0.9). Decomposition was slow with 63.5−74.4% of mass remaining after 300 days and it was similar among sites and vegetation types. Conclusions The significant lower fine root C stock and annual productivity rate at the hDeg site than at the Intact site suggests a potential for strong degradation to disrupt peat accretion. These results stress the need for a sustainable management of these forests to maintain their C sink function.

Major carbon losses from degradation of Mauritia flexuosa peat swamp forests in western Amazonia

“…Leaf litter decomposition rates at the sites (0.77 to 1.17 year −1 ) are in the range of global values estimated for rain forests and swamps (1.3 and 0.9 year −1 , respectively; Zhang et al 2008) but slightly higher than rates measured in peat forests of Panama (0.60-0.83 year −1 ; Hoyos-Santillan et al 2015) or in palm swamp peatlands of Brazil (0.41-0.60 year −1 ; Sales et al 2020). Fine root litter at the sites decomposed twice as slowly as leaf litter, with rates between 0.35 and 0.55 year −1 (Dezzeo et al 2021), confirming the importance of belowground litter relative to aboveground litter inputs for peat accumulation in tropical systems (Chimner and Ewel 2005;Hoyos-Santillan et al 2015).…”

“…Values are average ± standard error # C outputs from heterotrophic respiration (Rh) are from this study, loss as dissolved organic carbon (DOC) is the default IPCC value (Drösler et al 2014). C inputs from litterfall are from this research, inputs from root mortality are also site-specific (Dezzeo et al 2021). The soil CH 4 emission was measured at the sites (Hergoualc'h et al 2020) $ Peat C stock gained/lost per site are presented in SI2 and ABG was measured by Bhomia et al (2019) Peat stock gained/lost (5 year −1 ) − 7.9 ± 3.3 − 6.0 ± 2.9 9.9 ± 2.8 1.9 the Intact site (Fig.…”

“…Soil heterotrophic respiration and litterfall rates were measured as part of this study (see next section). Root mortality rates were measured monthly at the sites by Dezzeo et al (2021) from March 2016 to January 2017. The DOC loss was assigned the default IPCC value for natural flux in undrained tropical peatlands (Drösler et al 2014) as no such data were available for the sites.…”

Spatial Distribution of Degradation and Deforestation of Palm Swamp Peatlands and Associated Carbon Emissions in the Peruvian Amazon

“…Palm swamps are an important source of livelihood for many people throughout the region by providing income from fruit sales, and also deliver critical ecosystem services, such as food, water flux regulation, and hunting grounds (Gilmore et al, 2013;Virapongse et al, 2017;Schultz et al, 2019). The palm M. flexuosa is considered a "hyperkeystone" species (van der Hoek et al, 2019) and contributes to peat formation by producing vegetation litter both above and belowground (Dezzeo et al, 2021). M. flexuosa is dioecious, meaning that individual palms are either males (pollen producers) or females (fruit producers) (Holm et al, 2008).…”

“…As a result, M. flexuosa abundance and density decrease in increasingly degraded sites (Horn et al, 2012;Hidalgo Pizango et al, 2022) and become more male-dominated which reduces the capacity of the species to reproduce (Virapongse et al, 2017;Falen Horna and Honorio Coronado, 2018). Consequences include a reduction in biomass and necromass C stocks and in litter C inputs which build up the peat over time (Hergoualc'h et al, 2017;Bhomia et al, 2019;Dezzeo et al, 2021;Hergoualc'h et al, 2023). Depending on the intensity of degradation the natural C sink capacity of the soil can be reduced, or the soil can turn into a C source (van Lent et al, 2019;Hergoualc'h et al, 2020).…”