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

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

Biogeosciences, 12, 1257-1269, 2015

Author(s): L. Keidel, C. Kammann, L. Grünhage, G. Moser, and C. Müller

Soil respiration of terrestrial ecosystems, a major component in the global carbon cycle is affected by elevated atmospheric CO2 concentrations. However, seasonal differences of feedback effects of elevated CO2 have rarely been studied. At the Gießen Free-Air CO2 Enrichment (GiFACE) site, the effects of +20% above ambient CO2 concentration have been investigated since 1998 in a temperate grassland ecosystem. We defined five distinct annual seasons, with respect to management practices and phenological cycles. For a period of 3 years (2008–2010), weekly measurements of soil respiration were carried out with a survey chamber on vegetation-free subplots. The results revealed a pronounced and repeated increase of soil respiration under elevated CO2 during late autumn and winter 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 ambient CO2 plots.

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

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Happy 2nd Anniversary Little Mix!

August 19th, 2011

In two years the girls have accomplished so much. From four strangers, to Rhythmix, to Little Mix, and finally to dominating the world. They were the first girl group to ever advance so far into The X Factor competition, and the first group to ever win it. They have gotten number one singles, along with breaking records. They are the highest album charting girl group in the UK, and let’s not forget them breaking the Spice Girls’ US chart record. The girls are only getting bigger everyday, and I’m so happy to be there every step of the way. All I can say is in two years and counting, the girls have made me a stronger person as well as others. Not only have we, as fans, helped with their success, but they have helped us in an immense way as well. I look forward to what the girls have in store for us. I know that they will only continue to rewrite history and be the inspiring role models we see them as.