Positive feedback of elevated CO2 on soil respiration in late autumn and winter

[摘要] Soil respiration of terrestrial ecosystems, a major component in the globalcarbon cycle is affected by elevated atmospheric CO₂ concentrations.However, seasonal differences of feedback effects of elevated CO₂ haverarely been studied. At the Gießen Free-Air CO₂ Enrichment (GiFACE)site, the effects of +20% above ambient CO₂ concentration havebeen investigated since 1998 in a temperate grassland ecosystem. We definedfive distinct annual seasons, with respect to management practices andphenological cycles. For a period of 3 years (2008–2010), weeklymeasurements of soil respiration were carried out with a survey chamber onvegetation-free subplots. The results revealed a pronounced and repeatedincrease of soil respiration under elevated CO₂ during late autumn andwinter dormancy. Increased CO₂ losses during the autumn season(September–October) were 15.7% higher and during the winter season(November–March) were 17.4% higher compared to respiration from ambientCO₂ plots.

However, during spring time and summer, which are characterized by strongabove- and below-ground plant growth, no significant change in soilrespiration was observed at the GiFACE site under elevated CO₂. Thissuggests (1) that soil respiration measurements, carried out only during thegrowing season under elevated CO₂ may underestimate the truesoil-respiratory CO₂ loss (i.e. overestimate the C sequestered), and(2) that additional C assimilated by plants during the growing season andtransferred below-ground will quickly be lost via enhanced heterotrophicrespiration outside the main growing season.

[学科分类] 地球化学与岩石