Abstract:Need for regional economic development and global demand for agro‐industrial commodities have resulted in large‐scale conversion of forested landscapes to industrial agriculture across South East Asia. However, net emissions of CO2 from tropical peatland conversions may be significant and remain poorly quantified, resulting in controversy around the magnitude of carbon release following conversion. Here we present long‐term, whole ecosystem monitoring of carbon exchange from two oil palm plantations on convert… Show more
“…In other parts of the world, peatland drainage is still actively happening and studies from these sites show very high rates of peat oxidation during the first 5-10 years of conversion (e.g. McCalmont et al, 2021).…”
Abstract. Peatlands are a significant global carbon (C) store, which can be compromised by drainage and afforestation. Quantifying the rate of C loss from peat soils under forestry is challenging, as soil CO2 efflux includes both CO2 produced from heterotrophic peat decomposition and CO2 produced by tree roots and associated fungal networks (autotrophic respiration). We experimentally terminated autotrophic belowground respiration in replicated forest plots by cutting through all living tree roots (trenching), and measured soil surface CO2 flux, litter input, litter decay rate and soil temperature and moisture over two years. Annual peat decomposition (heterotrophic CO2 flux) was 115 ± 16 g C m−2 y−1, representing c. 40 % of total soil respiration. Decomposition of needle litter is accelerated in the presence of an active rhizosphere, indicating a priming effects by labile C inputs from roots. This suggests that our estimates of peat mineralization in our trenched plots are conservative, and underestimate overall rates of peat C loss. Considering also input of litter from trees, our results indicate that the soils in these 30 year-old drained and afforested peatlands are a net sink for C, since substantially more C enters the soil as organic matter, than is decomposed heterotrophically. However, the C balance for these soils should be taken over the lifespan of the trees, in order to determine if the soils under these drained and afforested peatlands are a sustained sink of C, or become a net source over longer periods of forestry.
“…In other parts of the world, peatland drainage is still actively happening and studies from these sites show very high rates of peat oxidation during the first 5-10 years of conversion (e.g. McCalmont et al, 2021).…”
Abstract. Peatlands are a significant global carbon (C) store, which can be compromised by drainage and afforestation. Quantifying the rate of C loss from peat soils under forestry is challenging, as soil CO2 efflux includes both CO2 produced from heterotrophic peat decomposition and CO2 produced by tree roots and associated fungal networks (autotrophic respiration). We experimentally terminated autotrophic belowground respiration in replicated forest plots by cutting through all living tree roots (trenching), and measured soil surface CO2 flux, litter input, litter decay rate and soil temperature and moisture over two years. Annual peat decomposition (heterotrophic CO2 flux) was 115 ± 16 g C m−2 y−1, representing c. 40 % of total soil respiration. Decomposition of needle litter is accelerated in the presence of an active rhizosphere, indicating a priming effects by labile C inputs from roots. This suggests that our estimates of peat mineralization in our trenched plots are conservative, and underestimate overall rates of peat C loss. Considering also input of litter from trees, our results indicate that the soils in these 30 year-old drained and afforested peatlands are a net sink for C, since substantially more C enters the soil as organic matter, than is decomposed heterotrophically. However, the C balance for these soils should be taken over the lifespan of the trees, in order to determine if the soils under these drained and afforested peatlands are a sustained sink of C, or become a net source over longer periods of forestry.
“…In other parts of the world, peatland drainage is still actively happening, and studies from these sites show very high rates of peat oxidation during the first 5-10 years of conversion (e.g. Cooper et al, 2020;McCalmont et al, 2021;Minkkinen et al, 2018;Prananto et al, 2020). In the UK, forest plantations on deep peat sometimes end in clear felling of the site and restoration of the peat.…”
Abstract. Peatlands are a significant global carbon (C) store, which can be
compromised by drainage and afforestation. Quantifying the rate of C loss
from peat soils under forestry is challenging, as soil CO2 efflux
includes both CO2 produced from heterotrophic peat decomposition and
CO2 produced by tree roots and associated fungal networks (autotrophic
respiration). We experimentally terminated autotrophic below-ground
respiration in replicated forest plots by cutting through all living tree
roots (trenching) and measured soil surface CO2 flux, litter
input, litter decay rate, and soil temperature and moisture over 2 years.
Decomposition of cut roots was measured and CO2 fluxes were corrected
for this, which resulted in a large change in the fraction heterotrophic : autotrophic flux, suggesting that even 2 years after trenching decaying
root biomass makes significant contributions to the CO2 flux. Annual
peat decomposition (heterotrophic CO2 flux) was 115 ± 16 g C m−2 yr−1, representing ca. 40 % of total soil respiration.
Decomposition of needle litter is accelerated in the presence of an active
rhizosphere, indicating a priming effect by labile C inputs from roots. This
suggests that our estimates of peat mineralization in our trenched plots are
conservative and underestimate overall rates of peat C loss. Considering
also input of litter from trees, our results indicate that the soils in
these 30-year-old drained and afforested peatlands are a net sink for C,
since substantially more C enters the soil organic matter than is
decomposed heterotrophically. This study does not account for fluvial C
fluxes, which represent a small flux compared to the CO2 soil efflux;
further, root litter and exudate deposition could be a significant C source
that is only partially sampled by our approach, adding to these plantations
being a potential carbon sink. However, the C balance for these soils should
be taken over the lifespan of the trees, in order to determine if the soils
under these drained and afforested peatlands are a sustained sink of C or
become a net source over longer periods of forestry.
“…Southeast Asia provides a strong set of measurements from drained peatlands, in particular under oil palm plantations. Fluxes from SE Asia are highly variable, with an Rh of 18-56 t CO2 ha-1 yr-1 in drained forest and oil palm in Malaysia (31), 74-111 t CO 2 ha -1 yr -1 from a range of studies on drained oil palm plantations in SE Asia (32), and 24.9 t CO 2 ha -1 yr -1 in a young oil palm plantation in Borneo (33). The Intergovernmental Panel on Climate Change emissions factor for drained cropland and fallow in the tropics is 51 t CO 2 ha -1 yr -1 (34).…”
Our study measured heterotrophic carbon dioxide (CO2) emissions in a drained peatland under potato cultivation in south-western Uganda. Soil carbon losses have not previously been reported for this land use, and our study set out to capture the range and temporal variation in emissions, as well as investigate relationships with key environmental variables. Soil chamber-based emission measurements were taken over five days at four points in time over the year to capture daily and monthly variability, including day and night sampling to capture any diurnal variations in temperatures and soil flux. Differences in soil microtopography from mounding of soils for potato beds and drainage trenches had a significant effect on the rate of soil flux. Diurnal sampling showed no significant difference in emissions or soil temperatures in the raised potato beds between day and night. More significant effects on soil flux from environmental drivers, such as water table depth, were observed between months, rather than hours and days. There were significant differences in the relationships between environmental variables and soil flux, depending on if soils had been recently disturbed or not. Area-weighted emissions based on microtopography gave a mean annual emissions factor of 98.79 ± 1.7 t CO2 ha-1 y-1 (± standard error) from this peatland use.
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