The temperature dependence of Ecosystem Respiration (ER) is often assessed based on the temperature of one specific layer. Air temperature or temperatures in the first ten centimetres of the soil profile are the most frequently used temperatures in models. However, previous studies showed that the relationship between ER and temperature is depth dependent, making depth selection for temperature measurements an important issue, especially at short timescales. The present study explores one possible way to assess this relationship by synchronising the ER and temperature signals and to test if the relationship between ER and temperature differs between daytime and nighttime. To do so, ER measurements were undertaken in 2013 in four Sphagnum-peatlands across France using the closed chamber method. The ER fluxes were measured hourly during 72 hours in each of four replicates in each site. Synchronisations between ER and T signal were determined for each depth (from surface to 30 cm depth) by selecting the time-delay leading to the best correlation between ER and soil temperatures and ER was then modelled. Our results showed that: (i) the delay between ER and soil temperature is greater in peat than in mineral soils; (ii) at a daily timescale synchronisation can improve the model representation using soil temperatures.
Peatlands are a highly effective natural carbon sink. However, the future of the carbon stored in these ecosystems is still uncertain because of the pressure they undergo. As estimation of the peatland carbon balance shows whether the system functions as carbon sink or source. La Guette peatland is a temperate Sphagnum-dominated peatland invaded by vascular plants, mainly Molinia caerulea. The studied site was hydrologically disturbed for years by a road crossing its southern part and draining water out of the system. Our aim was to estimate the main carbon fluxes and to calculate the carbon balance at the ecosystem scale. To reach this goal, CO 2 and CH 4 fluxes, DOC content as well as environmental variables were measured monthly for 2 years on 20 plots spread across the site to taking into account spatial variability. The peatland carbon balance was estimated using empirical models. Results showed that the CO2 fluxes were above 1000 gC m -2 yr -1 . In 2013 and 2014 the peatland was a net C source to the atmosphere with an emission of 220±33 gC m -2 yr -1 . These results provided evidence that restoration should be performed in order to reduce the water losses and favour the Sphagnum-dominance of this peatland.
To cite this version:Benoît D'angelo, Ary Bruand, Jiangtao Qin, Xihnua Peng, Christian Hartmann, et al.. Origin of the high sensitivity of Chinese red clay soils to drought: significance of the clay characteristics. Geoderma, Elsevier, 2014, 223-225, pp.46-53. 10 AbstractThe red clay soils which are widespread in China are known to be highly sensitive to drought during the dry season but the origin of this high sensitivity to drought remains unclear.Several red clay soils were selected in the Hunan province for study. We studied their basic physico-chemical properties and clay mineralogy, their structure and shrinkage properties, as well as their water retention properties. Results show that the amount of water available between -330 and -15 000 hPa water potential is consistent with that recorded in many other clay soils from different parts of the world and thus cannot explain the high sensitivity of the red clay soils to drought. This high sensitivity to drought might be related to the high proportion of poorly available water which was characterized by the amount of available water between -3300 and -15 000 hPa water potential. Comparison with clay soils located in different parts of the world and for which the sensitivity to drought was not identified, showed that this proportion of poorly available water is indeed much higher in the red clay soils 2 studied than in clay soils representing a large range of both clay content and mineralogy. This specific behaviour of the red clay soils studied is thought to be related to the history of their parent materials: these materials are continental sediments which may have been submitted to great hydric stress, thus leading to strongly consolidated soils with consequences such as a high proportion of poorly available water, strong aggregation and weak shrinkage properties.
Mitigating and adapting to global changes requires a better understanding of the response of the Biosphere to these environmental variations. Human disturbances and their effects act in the long term (decades to centuries) and consequently, a similar time frame is needed to fully understand the hydrological and biogeochemical functioning of a natural system. To this end, the ‘Centre National de la Recherche Scientifique’ (CNRS) promotes and certifies long‐term monitoring tools called national observation services or ‘Service National d'Observation’ (SNO) in a large range of hydrological and biogeochemical systems (e.g., cryosphere, catchments, aquifers). The SNO investigating peatlands, the SNO ‘Tourbières’, was certified in 2011 (https://www.sno-tourbieres.cnrs.fr/). Peatlands are mostly found in the high latitudes of the northern hemisphere and French peatlands are located in the southern part of this area. Thus, they are located in environmental conditions that will occur in northern peatlands in coming decades or centuries and can be considered as sentinels. The SNO Tourbières is composed of four peatlands: La Guette (lowland central France), Landemarais (lowland oceanic western France), Frasne (upland continental eastern France) and Bernadouze (upland southern France). Thirty target variables are monitored to study the hydrological and biogeochemical functioning of the sites. They are grouped into four datasets: hydrology, fluvial export of organic matter, greenhouse gas fluxes and meteorology/soil physics. The data from all sites follow a common processing chain from the sensors to the public repository. The raw data are stored on an FTP server. After operator or automatic processing, data are stored in a database, from which a web application extracts the data to make them available (https://data-snot.cnrs.fr/data-access/). Each year at least, an archive of each dataset is stored in Zenodo, with a digital object identifier (DOI) attribution (https://zenodo.org/communities/sno_tourbieres_data/).
<p>Natural peatlands represent 1/3 of the world C soils and contribute significantly to sequestration of atmospheric CO<sub>2</sub> by assimilation and storage of non-well decomposed organic C, due to their specific predominant vegetation such as <em>Sphagnum</em> species. However, they are encountering anthropogenic-induced pressures that disturb their structure (implying shift of vegetation), with potential consequences on their carbon sink function. In an attempt to mitigate this effect, restoration experiments were undertaken at La Guette peatland, a hydrologically disturbed temperate <em>Sphagnum</em>-peatland invaded by vascular plants, which is now a carbon source. Hydrological restoration was performed by blocking drains with dams and vegetation restoration was undertaken by either i) removing first 5 cm of peat (bare plots) or ii) removing first 5 cm of peat and transferring<em> Sphagnum</em> mosses (<em>Sphagnum</em> plots). To study the effect of these experiments, CO<sub>2 </sub>and CH<sub>4</sub> fluxes together with environmental variables and vegetation indices were monitored from 2014 to 2017 in 24 2mx2m plots. The annual carbon budget for each plot was estimated using empirical models. Preliminary results show that the hydrological restored site presented lower annual mean CO<sub>2</sub> emissions than the undisturbed site. In addition, <em>Sphagnum</em> plots had the lowest annual mean CO<sub>2</sub> emissions followed by bare peat plots then by intact plots. Hence, the results of these models provide evidence that hydrological and vegetation restorations favour the return to the C sink function of the peatland. However, there is still a need for larger-scale studies to better estimate the effect of restoration activities on peatland greenhouse carbon budgets.</p>
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