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Stem respiration and carbon dioxide efflux of young Populus deltoides trees in relation to temperature and xylem carbon dioxide concentration

Oxidative respiration is strongly temperature driven. However, in woody stems, efflux of CO2 to the atmosphere (EA), commonly used to estimate the rate of respiration (RS), and stem temperature (Tst) have often been poorly correlated, which we hypothesized was due to transport of respired CO2 in xylem sap, especially under high rates of sap flow (fs). To test this, we measured EA, Tst, fs and xylem sap CO2 concentrations ([CO2*]) in 3-year-old Populus deltoides trees under different weather conditions (sunny and rainy days) in autumn. We also calculated RS by mass balance as the sum of both outward and internal CO2 fluxes and hypothesized that RS would correlate better with Tst than EA. We found that EA sometimes correlated well with Tst, but not on sunny mornings and afternoons or on rainy days. When the temperature effect on EA was accounted for, a clear positive relationship between EA and xylem [CO2*] was found. [CO2*] varied diurnally and increased substantially at night and during periods of rain. Changes in [CO2*] were related to changes in fs but not Tst. We conclude that changes in both respiration and internal CO2 transport altered EA. The dominant component flux of RS was EA. However, on a 24-h basis, the internal transport flux represented 9–18% and 3–7% of RS on sunny and rainy days, respectively, indicating that the contribution of stem respiration to forest C balance may be larger than previously estimated based on EA measurements. Unexpectedly, the relationship between RS and Tst was sometimes weak in two of the three trees. We conclude that in addition to temperature, other factors such as water deficits or substrate availability exert control on the rate of stem respiration so that simple temperature functions are not sufficient to predict stem respiration.

Resistance to radial CO2 diffusion contributes to between-tree variation in CO2 efflux of Populus deltoides stems

Rates of CO2 efflux of stems and branches are highly variable among and within trees and across stands. Scaling factors have only partially succeeded in accounting for the observed variations. In this study, the resistance to radial CO2 diffusion was quantified for tree stems of an eastern cottonwood (Populus deltoides Bartr. ex Marsh.) clone by direct manipulation of the CO2 concentration ([CO2]) of xylem sap under controlled conditions. Tree-specific linear relationships between rates of stem CO2 efflux (JO) and xylem [CO2] were found. The resistance to radial CO2 diffusion differed 6-fold among the trees and influenced the balance between the amount of CO2 retained in the xylem v. that which diffused to the atmosphere. Therefore, we hypothesised that variability in the resistance to radial CO2 diffusion might be an overlooked cause for the inconsistencies and large variations in woody tissue CO2 efflux. It was found that transition from light to dark conditions caused a rapid increase in JO and xylem [CO2], both in manipulated trees and in an intact tree with no sap manipulation. This resulted in an increased resistance to radial CO2 diffusion during the dark, at least for trees with smaller daytime resistances. Stem diameter changes measured in the intact tree supported the idea that higher actual respiration rates occurred at night owing to higher metabolism in relation to an improved water status and higher turgor pressure.

Report on non-temperature related variations in CO2 efflux rates from young tree stems in the dormant season

Respiration rates are reported to increase exponentially with temperature. Respiration rates of woody tissues are commonly measured as CO2 efflux rates (

Woody tissue photosynthesis and its contribution to trunk growth and bud development in young plants

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Drought and the diurnal patterns of stem CO2 efflux and xylem CO2 concentration in young oak (Quercus robur)

) from that tissue. However, this paper describes clear variations in stem

A comprehensive model for simulating stem diameter fluctuations and radial stem growth

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