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Global Potential Net Primary Productivity

Global Potential Net Primary Productivity. Mg C ha -1 yr -1. Variation in NPP. What would Michael Huston say?. Biome Differences in NPP (Terrestrial). Length of the growing season is the major factor that explains biome differences in NPP.

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Global Potential Net Primary Productivity

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  1. Global Potential Net Primary Productivity Mg C ha -1 yr-1

  2. Variation in NPP What would Michael Huston say?

  3. Biome Differences in NPP (Terrestrial) • Length of the growing season is the major factor that explains biome differences in NPP • Differences in leaf area account for most of the variation in biome NPP when growing season length is taken into account. • Leaf area, in turn, is determined by climate, soil resources, and time since disturbance

  4. 25 ¡ 20 Mg C ha-1 yr -1 ¡ ¡ ¡ 15 ¡ ú ¡ ¡ ¡ ¡ ú ú ¡ ú ¡ ú ¡ ¡ ¡ ¡ ú ¡ ¡ 10 ¡ ¡ l ú l ¡ ¡ ¡ ¡ ¡ ¡ l ú ¡ ¡ l ú ú ú ¡ ¡ ú ú ú ¡ ú ¡ ¡ ¡ ú ú l ú ú ¡ ú ú ¡ ú ú ¡ ú ú ú 5 ú ú ¡ ú ú ú ú ú ú l ú ú ú ú ú ú ¡ ú ú ú ¡ ú ú ú ú ú ú ú ú 0 0 2000 4000 6000 8000 Mean Annual Precipitation (mm) Climate controls over NPP • At a global scale, NPP is strongly correlated with ppt and T • Water increases plant growth in drier ecosystems. Also increases decomposition and nutrient cycling. • In very wet ecosystems, ppt can limit NPP by decreasing light or nutrient availability

  5. Climate controls over NPP 25 ¡ 20 Mg C ha-1 yr -1 ¡ ¡ ¡ 15 ¡ ¡ ¡ ¡ ú ¡ ú ¡ ú ú ¡ ¡ ú ¡ ¡ ¡ 10 ¡ ¡ ú l l ¡ ¡ ¡ ¡ ¡ l ú ¡ ¡ l ú ú ú ú ¡ ¡ ú ú ¡ ¡ ¡ ¡ ú ú ú l ú ú ¡ ú ú ¡ 5 ú ú ú ú ú ¡ ú ú ú ú ú ú ú l ú ú ú ú ¡ ú ú ¡ ú ú 0 -15 -10 -5 0 5 10 15 20 25 30 Mean Annual Temperature (ºC) • Temperature is related to growing season length • Temperature stimulates decomposition and nutrient cycling.

  6. NPP co-varies with many factors: • Climate is important at big scales, but what would you do to determine the proximal control over NPP in a site?

  7. What really controls NPP? • Proximate control over NPP is availability of resouces • Light, CO2,H2O, nutrients (N,P,K,Mg,Ca,…) • Many ecosystems increase NPP when N or P fertilizer is added. • Some ecosystems increase NPP when CO2 or H2O is added. • Where T has been manipulated, NPP doesn’t respond directly.

  8. Acronyms to be wary of: GPP = Gross Primary Production NPP = Net Primary Production NEP = Net Ecosystem Production NEE = Net Ecosystem Exchange NECB = Net Ecosystem Carbon Balance NBP = Net Biome Productivity

  9. Ecosystem Carbon Balance Recosys= Resp. of plants, animals, and soil microbes Net Ecosystem Production (NEP) = GPP - Recosys Net Ecosystem Exchange (NEE) is fairly similar… Remember to check the sign convention! Sensu Chapin et al. 2006

  10. NEP is the balance between two large fluxes: GPP and ecosystem respiration To ecosystem To atmosphere

  11. Always ask: Is + NEP (or NEE) accumulation of C in the ecosystem, or in the atmosphere?

  12. Always ask: Is + NEP (or NEE) accumulation of C in the ecosystem, or in the atmosphere?

  13. Ecosystem accumulating C-sink Ecosystem loosing C-source Flux to ecosystem Always ask: Is + NEP (or NEE) accumulation of C in the ecosystem, or in the atmosphere? Flux to atmosphere Valentini et al. 1998

  14. GPP is invariant across latitudes As a result, NEE decreases with latitude While Re decreases as latitude (T proxy) increases Valentini et al. 1998

  15. Eddy Covariance (NEE/NEP)

  16. Eddy Covariance Network

  17. Net Ecosystem Exchange Tower network observations show that most ecosystems that have been measured are net sinks for CO2 1. Ecosystems may be typically net sinks of C in between disturbance (no steady state) 2. Recent environmental changes such as increased atm. CO2 or N deposition may be stimulating GPP more than Recosystem 3. C loss through leaching and other transfers may be an important component of regional C balance 4. Mid-successional ecosystems with high NPP may be over represented in the network

  18. Ecosystem Carbon Balance Net Ecosystem Carbon Balance (NECB) = Net rate of C accumulation or loss dC/dt Sensu Chapin et al. 2006

  19. Ecosystem Carbon Balance Net Ecosystem Carbon Balance (NECB) = GPP - Recosys  other C transfers Recosys= Resp. of plants, animals, and soil microbes • NECB = NPP  Flateral • Rheterotrophic • -Fdisturb • -Fleach • -Femiss

  20. Ecosystem Carbon Balance • Positive NECB; GPP > Recosys + other C losses; • ecosystem is removing C from the atmosphere = C sink • Negative NECB; GPP < Recosys + other C losses; • ecosystem is releasing C to the atmosphere = C source • Factors that affect GPP and C losses differentially will change NECB • Increased CO2 and N deposition have greater direct effect on GPP. Reduction in soil moisture in a wetland may have a greater effect on Rheterotroph and fire

  21. Ecosystem Carbon Balance Steady state = NEP near zero Inputs = outputs Ecosystem + 0 - NEP (a very long) time Atmosphere

  22. Ecosystem Carbon Balance + 0 - NEP time Ecosystem Atmosphere Net Biome Production (NBP) = NECB, integrated over large spatial scales to include removal of C by fire and harvest Sensu Schultze et al. 1997

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