Limits...
Where does the carbon go? A model-data intercomparison of vegetation carbon allocation and turnover processes at two temperate forest free-air CO2 enrichment sites.

De Kauwe MG, Medlyn BE, Zaehle S, Walker AP, Dietze MC, Wang YP, Luo Y, Jain AK, El-Masri B, Hickler T, Wårlind D, Weng E, Parton WJ, Thornton PE, Wang S, Prentice IC, Asao S, Smith B, McCarthy HR, Iversen CM, Hanson PJ, Warren JM, Oren R, Norby RJ - New Phytol. (2014)

Bottom Line: Observed eCO2 effects on allocation were dynamic.Allocation schemes based on constant fractions or resource limitations performed less well, with some models having unintended outcomes.Our recommendations to reduce uncertainty include: use of allocation schemes constrained by biomass fractions; careful testing of allocation schemes; and synthesis of allocation and turnover data in terms of model parameters.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Macquarie University, Sydney, New South Wales, 2109, Australia.

Show MeSH

Related in: MedlinePlus

The effect of CO2 enhancement on vegetation carbon storage at the two sites. Left-handplots show the effect of elevated CO2 on cumulative Net Primary Productivity (NPP; redbars) and biomass increment (blue bars) over the experiment at (a) Duke and (b) Oak Ridge.Right-hand plots show the proportion of additional NPP resulting from the increase in CO2which remains in the plant biomass (foliage, wood and fine roots) at the end of the experiment at(c) Duke and (d) Oak Ridge. Note the bar for TECO in panel (b) has been clipped to 100% forplotting purposes, but extends to 109%. Observations are shown by the abbreviation‘OBS’.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4260117&req=5

fig05: The effect of CO2 enhancement on vegetation carbon storage at the two sites. Left-handplots show the effect of elevated CO2 on cumulative Net Primary Productivity (NPP; redbars) and biomass increment (blue bars) over the experiment at (a) Duke and (b) Oak Ridge.Right-hand plots show the proportion of additional NPP resulting from the increase in CO2which remains in the plant biomass (foliage, wood and fine roots) at the end of the experiment at(c) Duke and (d) Oak Ridge. Note the bar for TECO in panel (b) has been clipped to 100% forplotting purposes, but extends to 109%. Observations are shown by the abbreviation‘OBS’.

Mentions: We compared the CO2 effect on NPP with the CO2 effect on biomass incrementover the duration of the experiment (Fig. 5a,b). Most of themodels predicted that the effect of eCO2 on biomass increment exceeded the effect ofeCO2 on NPP. The difference between the CO2 effect on biomass increment andthat on NPP depends on how far the simulated stand is from steady state, that is, the point wheregains from NPP equal losses to turnover and mortality. In the very early stages of stand growth,before notable turnover or tree mortality commences, the simulated CO2 effect on biomassincrement will be equal to the CO2 effect on NPP. At steady state, by contrast, the rateof biomass increment (at aCO2) is zero, so any stimulation of biomass increment byeCO2 will result in a very high relative response. This stand stage effect accounts forthe large percentage increase in biomass seen in the ISAM model at both the Duke and ORNL FACEsites. A shift in allocation towards long-lived woody components will also increase the percentagebiomass increment response compared to the NPP response, because woody tissue has a long lifespan.This effect can be seen in the TECO simulations, particularly at Oak Ridge where woody allocationincreases by 10% (Fig. 3l), and as a result a36% stimulation of NPP results in a 109% increase in biomass increment over the courseof the experiment.


Where does the carbon go? A model-data intercomparison of vegetation carbon allocation and turnover processes at two temperate forest free-air CO2 enrichment sites.

De Kauwe MG, Medlyn BE, Zaehle S, Walker AP, Dietze MC, Wang YP, Luo Y, Jain AK, El-Masri B, Hickler T, Wårlind D, Weng E, Parton WJ, Thornton PE, Wang S, Prentice IC, Asao S, Smith B, McCarthy HR, Iversen CM, Hanson PJ, Warren JM, Oren R, Norby RJ - New Phytol. (2014)

The effect of CO2 enhancement on vegetation carbon storage at the two sites. Left-handplots show the effect of elevated CO2 on cumulative Net Primary Productivity (NPP; redbars) and biomass increment (blue bars) over the experiment at (a) Duke and (b) Oak Ridge.Right-hand plots show the proportion of additional NPP resulting from the increase in CO2which remains in the plant biomass (foliage, wood and fine roots) at the end of the experiment at(c) Duke and (d) Oak Ridge. Note the bar for TECO in panel (b) has been clipped to 100% forplotting purposes, but extends to 109%. Observations are shown by the abbreviation‘OBS’.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4260117&req=5

fig05: The effect of CO2 enhancement on vegetation carbon storage at the two sites. Left-handplots show the effect of elevated CO2 on cumulative Net Primary Productivity (NPP; redbars) and biomass increment (blue bars) over the experiment at (a) Duke and (b) Oak Ridge.Right-hand plots show the proportion of additional NPP resulting from the increase in CO2which remains in the plant biomass (foliage, wood and fine roots) at the end of the experiment at(c) Duke and (d) Oak Ridge. Note the bar for TECO in panel (b) has been clipped to 100% forplotting purposes, but extends to 109%. Observations are shown by the abbreviation‘OBS’.
Mentions: We compared the CO2 effect on NPP with the CO2 effect on biomass incrementover the duration of the experiment (Fig. 5a,b). Most of themodels predicted that the effect of eCO2 on biomass increment exceeded the effect ofeCO2 on NPP. The difference between the CO2 effect on biomass increment andthat on NPP depends on how far the simulated stand is from steady state, that is, the point wheregains from NPP equal losses to turnover and mortality. In the very early stages of stand growth,before notable turnover or tree mortality commences, the simulated CO2 effect on biomassincrement will be equal to the CO2 effect on NPP. At steady state, by contrast, the rateof biomass increment (at aCO2) is zero, so any stimulation of biomass increment byeCO2 will result in a very high relative response. This stand stage effect accounts forthe large percentage increase in biomass seen in the ISAM model at both the Duke and ORNL FACEsites. A shift in allocation towards long-lived woody components will also increase the percentagebiomass increment response compared to the NPP response, because woody tissue has a long lifespan.This effect can be seen in the TECO simulations, particularly at Oak Ridge where woody allocationincreases by 10% (Fig. 3l), and as a result a36% stimulation of NPP results in a 109% increase in biomass increment over the courseof the experiment.

Bottom Line: Observed eCO2 effects on allocation were dynamic.Allocation schemes based on constant fractions or resource limitations performed less well, with some models having unintended outcomes.Our recommendations to reduce uncertainty include: use of allocation schemes constrained by biomass fractions; careful testing of allocation schemes; and synthesis of allocation and turnover data in terms of model parameters.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Macquarie University, Sydney, New South Wales, 2109, Australia.

Show MeSH
Related in: MedlinePlus