Effects of short-term ecosystem experimental warming on water-extractable organic matter in an ombrotrophic Sphagnum peatland (Le Forbonnet, France)

Abstract

International audienceIn a future warmer world, peatlands may change from a carbon sink function to a carbon source function. This study tracks changes in water-extractable organic matter (WEOM) after one year of in situ experimental warming using open top chambers (OTCs). WEOM was studied in the upper peat layers (0-10 cm) through analysis of water-extractable organic carbon (WEOC), stable C isotopic composition (δ13C), specific UV absorbance at 280 nm and sugar composition of cores taken from an open bog (DRY sites) and a transitional poor fen (WET sites). At the DRY sites, the impact of OTCs was weak with respect to WEOM parameters, whereas at the WET sites, the air warming treatment led to a decrease in peat water content, suggesting that the supply of heat by OTCs was used mainly for evapotranspiration. OTCs at the WET sites also induced a relative enrichment at the surface (0 to 5 cm depth) of aliphatic and/or aromatic compounds with concomitant decrease in WEOC, as a result of decomposition. On the contrary, WEOC and sugar content increased in the deeper peat layer (7.5-10 cm depth) probably as a result of increased leaching of phenolic compounds by roots, which then inhibits microbial activity. The different response to experimental warming at DRY and WET sites suggests that the spatial variability of moisture in is critical for understanding of the impact of global warming on the fate of OM and the carbon cycle in peatlands

Effects of a short-term experimental microclimate warming on the abundance and distribution of branched GDGTs in a French peatland

“…The latter site is hereafter called the "bog site" and the former the "fen site". The terms "fen" and "bog" are used here for simplicity and denote the existence of a trophic and wetness gradient inferred from the vegetation (Delarue et al, 2011). In 2009 and 2010, the average water table level was at 16.5 cm depth at the bog site and at 14 cm depth at the fen site.…”

“…The experimental design was described in detail in previous studies (Delarue et al, 2011;Jassey et al, 2011). Briefly, in each of the two sampling sites, six randomised plots have been chosen.…”

“…Indeed, as recently explained by , higher air temperatures can induce higher evapotranspiration, resulting in lower soil moisture. Higher evapotranspiration may also lead to lower soil temperature by heat loss towards atmosphere and reduction of soil thermal conductivity (Delarue et al, 2011;Jassey et al, 2011): as soil moisture decreases and the air content in soil increases, the resistance to the transfer of heat increases, since heat diffuses faster in water than in air (Rosenberg et al, 1983;Hollister, 1998).…”

“…Concomitant and continuous measurements of air and soil moisture would be necessary to (i) fully understand the phenomenons of heat exchange and evapotranspiration between air and peat (Aerts et al, 2006;Delarue et al, 2011) and (ii) to explain the complex effects of the OTC treatment on environmental parameters (temperature, humidity) in heterogeneous systems such as the fen and bog sites investigated in this study. Even though such measurements have not been performed in Frasne peatland, we can assume that the increase in air temperature induced by in OTC plots at 0-3 cm depth) and lower at the bog site (ca.…”

“…80-90% Sphagnum water content in control plots vs. 75% in OTC plots at 0-3 cm depth). In addition, Delarue et al (2011) measured the ratio of dry to wet matter in peat samples at 0-10 cm depth collected from each plot on June 2009. This ratio was higher for OTCs than for control plots at the fen site, whereas no specific effect of the OTCs was observed at the bog site.…”