Journal Article

Seasonal root distribution and soil surface carbon fluxes for one-year-old <i>Pinus radiata</i> trees growing at ambient and elevated carbon dioxide concentration

Stephen M. Thomas, David Whitehead, John A. Adams, Jeff B. Reid, Robert R. Sherlock and Alan C. Leckie

in Tree Physiology

Volume 16, issue 11-12, pages 1015-1021
Published in print November 1996 | ISSN: 0829-318X
e-ISSN: 1758-4469 | DOI: http://dx.doi.org/10.1093/treephys/16.11-12.1015
Seasonal root distribution and soil surface carbon fluxes for one-year-old Pinus radiata trees growing at ambient and elevated carbon dioxide concentration

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The increase in number of fine (< 0.5 mm diameter) roots of one-year-old clonal Pinus radiata D. Don trees grown in large open-top field chambers at ambient (362 μmol mol−1) or elevated (654 μmol mol−1) CO2 concentration was estimated using minirhizotron tubes placed horizontally at a depth of 0.3 m. The trees were well supplied with water and nutrients. Destructive harvesting of roots along an additional tube showed that there was a linear relationship between root number estimated from the minirhizotron and both root length density, Lv, and root carbon density, Cv, in the surrounding soil.

Root distribution decreased with horizontal distance from the tree. At a depth of 0.3 m, 88% of the total Cv was concentrated within a 0.15-m radius from tree stems in the elevated CO2 treatment, compared with 35% for trees in the ambient CO2 treatment. Mean Cv along the tubes ranged up to 5 × 10−2 μg mm−3 and tended to be greater for trees grown at elevated CO2 concentration, although the differences between CO2 treatments were not significant. Root growth started in spring and continued until late summer. There was no significant difference in seasonal rates of increase in Cv between treatments, but roots were observed four weeks earlier in the elevated CO2 treatment. No root turnover occurred at a depth of 0.3 m during the first year after planting.

Mean values of carbon dioxide flux density at the soil surface, F, increased from 0.02 to 0.13 g m−2 h−1 during the year, and F was 30% greater for trees grown at elevated CO2 concentration than at ambient CO2. Diurnal changes in F were related to air temperature. The seasonal increase in F continued through the summer and early autumn, well after air temperature had begun to decline, suggesting that the increase was partly caused by increase in Cv as the roots colonized the soil profile.

Keywords: fine roots; minirhizotron; root carbon density; root length density

Journal Article.  0 words. 

Subjects: Plant Sciences and Forestry

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