Examining Total Belowground Carbon Allocation (TBCA) Using the PnET-CN Model Kathryn Berger UNH Department of Natural Resources Research and Discover Fellow.

Examining Total Belowground Examining Total Belowground Carbon Allocation (TBCA) Using Carbon Allocation (TBCA) Using

the PnET-CN Modelthe PnET-CN Model Kathryn BergerKathryn Berger

UNH Department of Natural ResourcesUNH Department of Natural Resources

Research and Discover FellowResearch and Discover Fellow

Advisor: Scott OllingerAdvisor: Scott Ollinger

Committee: Christy Goodale, Andrew Richardson, Committee: Christy Goodale, Andrew Richardson,

& Mary Martin& Mary Martin

Outline Outline

Significance of TBCASignificance of TBCA Current UnderstandingCurrent Understanding Environmental Factors Influencing Carbon AllocationEnvironmental Factors Influencing Carbon Allocation

Elevated COElevated CO22

Nitrogen Limited Systems & N DepositionNitrogen Limited Systems & N Deposition The PnET ModelThe PnET Model Thesis Focus & ResearchThesis Focus & Research

PnET-CN & FACEPnET-CN & FACE Carbon and Nitrogen Availability DatabaseCarbon and Nitrogen Availability Database

SummarySummary

SignificanceSignificance Anthropogenic sources have Anthropogenic sources have

increased COincreased CO22 by 35% since by 35% since the Industrial Revolution the Industrial Revolution

Only 45% of all carbon Only 45% of all carbon released remains in released remains in atmosphereatmosphere

Need for identification of Need for identification of missing carbon sinkmissing carbon sink

Terrestrial ecosystems:Terrestrial ecosystems: Large carbon pool in soilsLarge carbon pool in soils Slow turnover ratesSlow turnover rates

Implications for Implications for environmental policyenvironmental policy http://www.whrc.org/resources/online_publications/warming_earth/scientific_evidence.htm

Current UnderstandingCurrent Understanding Terrestrial ecosystems carbon neutral until 1990sTerrestrial ecosystems carbon neutral until 1990s Crossover to carbon sink suspected result of land use changes in North Crossover to carbon sink suspected result of land use changes in North

America and EuropeAmerica and Europe ReforestationReforestation Increased fire prevention Increased fire prevention Changes in environment (longer growing seasons, fertilizing effects of air Changes in environment (longer growing seasons, fertilizing effects of air

pollution) pollution) Current net flux estimation: -1.4 (+/-) -0.7 Pg C yCurrent net flux estimation: -1.4 (+/-) -0.7 Pg C y-1-1 (IPCC, 2001) (IPCC, 2001) Uncertainty as to how forests will react to increased levels of atmospheric Uncertainty as to how forests will react to increased levels of atmospheric

CO2: CO2: Increased storage, orIncreased storage, or More rapid processing of resources More rapid processing of resources

Knowledge limited because of magnitude and duration of studies needed to Knowledge limited because of magnitude and duration of studies needed to draw conclusionsdraw conclusions

Current UnderstandingCurrent Understanding

When carbon is allocated belowground it can: When carbon is allocated belowground it can: Become immediately lost via soil respirationBecome immediately lost via soil respiration Increase growth of root systems that undergo fast turnover rates & Increase growth of root systems that undergo fast turnover rates &

decompose quicklydecompose quickly Exude from root systems and used by microorganisms in the soilExude from root systems and used by microorganisms in the soil Enter into woody portions of long-lived roots that promote carbon Enter into woody portions of long-lived roots that promote carbon

storagestorage

(http://csp.unl.edu/public/G_carbon.htm)

Environmental Factors Influencing Environmental Factors Influencing Carbon Allocation Carbon Allocation

Elevated COElevated CO22

Nitrogen Limited SystemsNitrogen Limited Systems Tropospheric OTropospheric O33

http://www.tva.gov/environment/air/ontheair/nitrogen.htm http://aspenface.mtu.edu/

Elevated COElevated CO22

Increased COIncreased CO2 2 causes fertilization causes fertilization effecteffect

Can alter chemistry of plant Can alter chemistry of plant tissues; litter input into soil pooltissues; litter input into soil pool

Mediated by feedback related to Mediated by feedback related to microbial processes microbial processes

C:N ratios, rates of litter C:N ratios, rates of litter decomposition, availability of N decomposition, availability of N in soilin soil

For C sequestration: nutrient For C sequestration: nutrient availability must not deter plant availability must not deter plant growth growth

Organic C must be allocated to Organic C must be allocated to stable soil pools with low stable soil pools with low turnover periodsturnover periodshttp://www.ehponline.org/docs/1996/104-1/forum.html

Elevated COElevated CO22

Free-air COFree-air CO2 2 enrichment (FACE) experiments enrichment (FACE) experiments Opportunity to make long-term observations of forests Opportunity to make long-term observations of forests

under elevated COunder elevated CO2 2 in realistic forest stand conditionsin realistic forest stand conditions

http://www.dukemagazine.duke.edu/dukemag/issues/111205/depgaz17.html

Elevated COElevated CO22

http://cdiac.ornl.gov/programs/FACE/whereisface.html

Elevated COElevated CO22

Oak Ridge National Laboratory (ORNL) FACE sweet gum Oak Ridge National Laboratory (ORNL) FACE sweet gum plantation: COplantation: CO2 2 enrichment increased fine-root production enrichment increased fine-root production (Norby (Norby et al.et al., 2004), 2004)

Highest increase in root production under elevated COHighest increase in root production under elevated CO2 2 occurs occurs in deeper layers of soil where sequestration suspected more in deeper layers of soil where sequestration suspected more likely (Norby likely (Norby et al.et al., 2004), 2004)

Additional studies have reported that over half of carbon Additional studies have reported that over half of carbon allocated belowground (in both elevated & ambient plots) is allocated belowground (in both elevated & ambient plots) is found in microaggregates protected from decay (Jastrow found in microaggregates protected from decay (Jastrow et al.et al., , 2005)2005)

Demonstrated very little saturation in this protection Demonstrated very little saturation in this protection mechanism after 5 years (Jastrow mechanism after 5 years (Jastrow et al.et al., 2005), 2005)

Nitrogen Limited SystemsNitrogen Limited Systems

Nitrogen most limiting nutrient in Nitrogen most limiting nutrient in temperate forest ecosystemstemperate forest ecosystems

Potential to down-regulate Potential to down-regulate positive feedback loops caused by positive feedback loops caused by elevated atmospheric COelevated atmospheric CO2 2

Progressive Nitrogen Limitation Progressive Nitrogen Limitation (PNL) caused by the rapid rate of (PNL) caused by the rapid rate of N immobilization by plants and N immobilization by plants and microorganismsmicroorganisms

Scientists also hypothesize Scientists also hypothesize increased N could ameliorate the increased N could ameliorate the effects of rising COeffects of rising CO2 2 by aiding N-by aiding N-limited systemslimited systems

However, if growth is in nutrient However, if growth is in nutrient rich (low C:N) with faster rich (low C:N) with faster turnover, carbon sequestration turnover, carbon sequestration may be minimalmay be minimal

http://www.physicalgeography.net/fundamentals/8h.html

Nitrogen Limited SystemsNitrogen Limited Systems

Additional studies have suggested Additional studies have suggested alternative reasons for lack of growth:alternative reasons for lack of growth:

1515N-tracer studies in 9 forests suggest N-tracer studies in 9 forests suggest N deposition will play only minor N deposition will play only minor role in C sequestration (Nadelhoffer role in C sequestration (Nadelhoffer et al.et al., 1999), 1999)

Current N deposition accounts for Current N deposition accounts for less than 20% of annual 1.5-1.9 Pg less than 20% of annual 1.5-1.9 Pg COCO2 2 carbon uptake credited to forest carbon uptake credited to forest growth (Nadelhoffer growth (Nadelhoffer et al.et al., 1999), 1999)

KKörner et al., (2005) suggests soil örner et al., (2005) suggests soil microbial feedback mechanisms or microbial feedback mechanisms or ambient Oambient O33 to explain the lack of to explain the lack of growth at a Swiss FACE experimental growth at a Swiss FACE experimental forestforest

Quantifying amount of carbon in Quantifying amount of carbon in terrestrial ecosystems as a result of terrestrial ecosystems as a result of anthropogenic N sources will have anthropogenic N sources will have significant implications on the global significant implications on the global carbon cycle and missing carbon sinkcarbon cycle and missing carbon sink

http://harvardforest.fas.harvard.edu/research/nitrogensat.html

The PnET ModelThe PnET Model Developed at UNH (Aber and Developed at UNH (Aber and

Federer, 1992)Federer, 1992) A simple, daily-to-monthly time-A simple, daily-to-monthly time-

step model of carbon and water step model of carbon and water fluxes fluxes

Uses a select number of Uses a select number of parameters to portray essential parameters to portray essential interactions between nitrogen interactions between nitrogen availability and leaf physiology as availability and leaf physiology as they influence photosynthesis and they influence photosynthesis and transpirationtranspiration

Currently three grouped computer Currently three grouped computer models that make up PnET: models that make up PnET:

PnET-DAYPnET-DAY PnET-IIPnET-II PnET-CNPnET-CN

http://biology.usgs.gov/luhna/harvardforest.html

The PnET ModelThe PnET Model The model estimates productivity in the plant pool by allocating biomass The model estimates productivity in the plant pool by allocating biomass

by tissue type: foliage, wood, and/or fine rootsby tissue type: foliage, wood, and/or fine roots PnET equation:PnET equation:

Fine-root carbon = 130 +1.92 * leaf carbon (Aber and Federer, 1992)Fine-root carbon = 130 +1.92 * leaf carbon (Aber and Federer, 1992) PnET model’s mechanism for TBCA is based on the following equations: PnET model’s mechanism for TBCA is based on the following equations:

Raich & Nadelhoffer (1989)Raich & Nadelhoffer (1989) RRss-P-Paa ≈ P≈ Pbb + R + Rr r PPbb + R + Rr r is comparable to fine-root carbonis comparable to fine-root carbon

Davidson Davidson et al.et al. (2002) using IRGA measurements: (2002) using IRGA measurements: (TBCA) = Rsoil – Litterfall-C(TBCA) = Rsoil – Litterfall-C

Both equations based on tentative assumption that carbon pools are at Both equations based on tentative assumption that carbon pools are at steady state steady state

What about implications of global climate change? Environmental What about implications of global climate change? Environmental pollution? FACE experiments?pollution? FACE experiments?

Thesis Focus & ResearchThesis Focus & Research

PnET-CN & FACEPnET-CN & FACE Research Question: Does the PnET-CN model’s TBCA mechanism Research Question: Does the PnET-CN model’s TBCA mechanism

correctly predict carbon allocation in soils under elevated atmospheric correctly predict carbon allocation in soils under elevated atmospheric COCO22 conditions? conditions?

Carbon and Nitrogen Availability DatabaseCarbon and Nitrogen Availability Database Research Question: Is there a trend between TBCA and nitrogen Research Question: Is there a trend between TBCA and nitrogen

availability in terrestrial ecosystems?availability in terrestrial ecosystems?

PnET-CN & FACEPnET-CN & FACE

Duke FACE Forest, Durham, NC (FACTS-I)Duke FACE Forest, Durham, NC (FACTS-I) Loblolly Pine Plantation w/ Sweetgum UnderstoryLoblolly Pine Plantation w/ Sweetgum Understory

Oak Ridge FACE, Oak Ridge TN Oak Ridge FACE, Oak Ridge TN Sweetgum PlantationSweetgum Plantation

Aspen-FACE Aspen-FACE, Rhinelander, WI (FACTS-II)Aspen-FACE Aspen-FACE, Rhinelander, WI (FACTS-II) Aspen PlantationAspen Plantation

http://www.ornl.gov/info/ornlreview/v37_3_04/images/a09_sweetgum_full.jpg

http://www.nicholas.duke.edu/people/faculty/katul/project4.html

http://aspenface.mtu.edu/

Duke FACE ForestDuke FACE Forest

Aspen- FACEAspen- FACE

Oak Ridge FACEOak Ridge FACE

PnET-CN & FACEPnET-CN & FACE

PnET-CN has not yet been used to examine TBCA PnET-CN has not yet been used to examine TBCA mechanisms in FACE experimental sitesmechanisms in FACE experimental sites

Results from the PnET-CN model runs will be Results from the PnET-CN model runs will be compared to published literature for each site to compared to published literature for each site to determine validity of the model’s mechanism for determine validity of the model’s mechanism for TBCA. TBCA.

Each site needs individualized parameter values, Each site needs individualized parameter values, climate and vegetation filesclimate and vegetation files

PnET-DAY will compare unknown values to PnET-DAY will compare unknown values to published results from eddy flux towers at each site published results from eddy flux towers at each site

Carbon and Nitrogen Availability Carbon and Nitrogen Availability DatabaseDatabase

Database will include published values of foliar and Database will include published values of foliar and soil metric measurements in a variety of temperate soil metric measurements in a variety of temperate forestsforests

Potential measurements to include: Potential measurements to include: Soil respiration, litterfall, N mineralization, foliar, N Soil respiration, litterfall, N mineralization, foliar, N

concentrations, carbon-to-nitrogen (C:N) ratiosconcentrations, carbon-to-nitrogen (C:N) ratios Goal: Determine potential correlations between Goal: Determine potential correlations between

TBCA and nitrogen availabilityTBCA and nitrogen availability Potential to contribute useful information on TBCA Potential to contribute useful information on TBCA

and nitrogen availability to PnET-CN modeland nitrogen availability to PnET-CN model Nutrient constraint mechanisms are often not developed or Nutrient constraint mechanisms are often not developed or

absent from most ecological models (Hungate absent from most ecological models (Hungate et al., et al., 2003)2003)

SummarySummary

Increase of COIncrease of CO22 in the atmosphere has created a “missing in the atmosphere has created a “missing carbon sink”carbon sink”

Identifying where this missing carbon sink is of great Identifying where this missing carbon sink is of great importance to COimportance to CO22 mitigation efforts mitigation efforts

Terrestrial ecosystems, belowground soils suspected to be a Terrestrial ecosystems, belowground soils suspected to be a substantial, long-term carbon sinksubstantial, long-term carbon sink

Knowledge of mechanisms related to belowground carbon Knowledge of mechanisms related to belowground carbon allocation are still poorly understoodallocation are still poorly understood

Implications of environmental pollution on soil carbon pools Implications of environmental pollution on soil carbon pools must also be taken into account in carbon modelsmust also be taken into account in carbon models

More conclusive, long-term studies neededMore conclusive, long-term studies needed

SummarySummary

Incorporating knowledge of N availability and TBCA Incorporating knowledge of N availability and TBCA will improve the PnET modelwill improve the PnET model

Including nutrient limitations and elevated levels of Including nutrient limitations and elevated levels of atmospheric CO2 into algorithms for TBCA will help atmospheric CO2 into algorithms for TBCA will help scientists to understand the terrestrial ecosystem’s scientists to understand the terrestrial ecosystem’s impact on climate change in the futureimpact on climate change in the future

Understanding how models like PnET will Understanding how models like PnET will incorporate rising COincorporate rising CO22 into their TBCA mechanism into their TBCA mechanism will be of importance in modeling the effects of will be of importance in modeling the effects of carbon sequestration under future climate change carbon sequestration under future climate change projectionsprojections

AcknowledgmentsAcknowledgments Special thanks to:Special thanks to: My advisor: Scott OllingerMy advisor: Scott Ollinger My thesis committee: My thesis committee:

Christy Goodale, Andrew Christy Goodale, Andrew Richardson, & Mary MartinRichardson, & Mary Martin

Complex Systems Research Complex Systems Research Center: Rita Freuder, Sarah Center: Rita Freuder, Sarah SilverbergSilverberg

UNH-NASA Research and UNH-NASA Research and Discover Fellowship for Discover Fellowship for allowing me to pursue this allowing me to pursue this research for my Masters research for my Masters thesisthesis

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