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Radial diffusion, vertical transport, and refixation of labeled bicarbonate in scots pine stems

Konferensbidrag (offentliggjort, men ej förlagsutgivet)
Författare John Marshall
Lasse Tarvainen
Göran Wallin
Publicerad i AGU Fall meeting, 12-16 December 2016, San Francisco, California, USA.
Förlagsort San Francisco
Publiceringsår 2016
Publicerad vid Institutionen för biologi och miljövetenskap
Språk en
Ämneskategorier Skogsvetenskap, Terrestrisk ekologi, Botanik

Sammanfattning

The CO2 produced by a respiring stem provides an index of metabolic activity in the stem and a quantitative estimate of an important component of the forest carbon budget. Production of CO2 by a given stem volume is lost by three competing processes. First, some diffuses radially outward through the bark. Second, some is dissolved and vertically transported upward out of the control volume by the xylem stream. Third, some is refixed by photosynthesis under the bark. The relative balance among these pathways was quantified in 17-m Scots pine trees by 13C-bicarbonate labeling of the xylem stream and monitoring of the 13CO2 in the xylem water, along with continuous monitoring of the radial diffusive flux at four canopy heights and in transpiration from leaves. Most of the label diffused out radially, as 13CO2, immediately above the labeling site, over about a week. The pulse was weakly and briefly detected 4 m above that height. Further up the stem it was not detected at all. We detected significant refixation of CO2 in the stems at all heights above 4 m, where the bark becomes papery and thin, but the label was so weak at this height that refixation had little influence on the pulse chase. We conclude that the vertical flux is negligible in Scots pine, but that the refixation flux must be accounted for in estimates of whole-stem CO2 efflux.

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