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Peat bogs are globally important soil carbon pools, and deep carbon is an important part of
soil carbon pools in peat bogs.
Climate change and human activities have severely degraded peat bogs
.
In degraded peat bogs, the lower water level divides the soil profile of peat bogs into three layers of environmental differences: 1) the surface aerobic layer, which is in an aerobic environment for a long time and contains a large amount of new organic carbon from plant roots and litter; 2) Deep anaerobic layer, which is in an anaerobic environment for a long time and contains almost no new organic carbon from plants; 3) Aerobic anaerobic transition layer, periodically in an aerobic anaerobic alternating state, containing a small amount of organic carbon
from plant roots and litter.
Long-term differences in environment may lead to differences in carbon quality, microbial activity and carbon emission dynamics of the three layers of soil
.
In the past, the study of soil carbon dynamics in peat bogs was based on depth to study soil carbon emission dynamics at different depths, ignoring the differences in hydrological environment along soil profiles (Figure 1).
Fig.
1: Soil profile and the influence of water level fluctuations on soil profile
Professor Chen Huai and team members of Chengdu Institute of Biology, Chinese Academy of Sciences, studied the dynamics and regulation of soil carbon dioxide emission in different layers of soil organic carbon composition, microbial activity and climate change through soil collection and indoor control experiments in different layers, and pointed out that the aerobic anaerobic transition layer is a relatively stable part of the soil carbon pool in peat swamps, which has the effect of
slowing soil carbon emissions.
The main findings of the study are as follows:
(1) Soil carbon quality and microbial activity
Among the three layers of soil with fluctuating water levels, the top soil carbon quality and microbial activity were the highest
.
Transition layer soils contain a large amount of complex organic carbon and mineral protective organic carbon, while transition layer soils have the smallest rapid decomposition carbon pool and the largest slow decomposition carbon pool, and the soil organic carbon composition is complex and of low quality (Figure 2).
Microbial activity and diversity in transition soils were also lowest
among the three soils.
Figure 2: Soil carbon chemical composition (a-d) and different carbon pool sizes (e-f) of different layers
(2) Soil carbon emission potential and response to warming
Among the three layers of soil, the top soil has the highest CO2 rate, followed by the deep anaerobic layer, and the transition layer soil has the lowest
CO2 emission rate.
In the warming state, the CO2 emission rate of surface and deep soil increased significantly, and its increment was significantly higher than that in the transition layer, and the increase in the CO2 emission rate in the transition layer soil was the lowest, indicating the insensitive characteristics of the transition layer soil to warming (Figure 3).
The insensitivity of the transition layer to warming makes it effective in slowing soil carbon loss in peat bogs in the context of climate change
.
Fig.
3: Soil CO2 emission rate and response to warming in different layers
(3) The regulation process of soil carbon emissions
Through the structural equation model, it is found that the CO2 emission of topsoil is mainly affected by the chemical composition of soil carbon, especially the refractory organic carbon pool, and it is found that the contribution of the difficult-to-decompose carbon pool to the CO2 emission of topsoil gradually increases
with the extension of the cultivation time.
Soil CO2 emissions in deep anaerobic layers are mainly affected by decomposers, such as microbial and enzymatic activities
.
Transition layer soil CO2 emissions are mainly limited by nutrient content, such as nitrogen content (Figure 4).
Figure 4: Regulation process of soil carbon dioxide emissions in different layers
This study found that the three layers of soil affected by water level fluctuations have great differences
in organic carbon composition, microbial characteristics and carbon dioxide emission dynamics.
Among them, the surface aerobic layer and the deep anaerobic layer soil carbon dioxide emissions are sensitive to warming, and the carbon dioxide emissions are regulated
by carbon quality and decomposer activity, respectively.
Experienced long-term disturbances in water level fluctuations, the soil in the middle transition layer has the lowest CO2 emissions and is less sensitive to warming than the other two soils
.
The results suggest that previous depth-based carbon dynamics studies may have overestimated carbon loss
in degraded peat bogs due to neglect of stable transition layers.
In future studies of soil carbon dynamics in peat swamps, changes in soil environment along the profile need to be considered, and the importance of
nutrients in soil carbon dynamics needs to be considered.
The research was published in Communication Earth & Environment
.
Professor Chen Huai of the alpine grassland and wetland ecology project team of the Chengdu Institute of Biology, Chinese Academy of Sciences, is the corresponding author
of the paper.
The research was jointly funded by the Category A Strategic Leading Science and Technology Project of the Chinese Academy of Sciences (XDA200500404) and the Second Comprehensive Scientific Expedition to the Qinghai-Tibet Plateau (2019QZKK0304).
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