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Primary Production in Terrestrial Systems

Primary Production in Terrestrial Systems. Fundamentals of Ecosystem Ecology Class Cary Institute January 2013 Gary Lovett. Equations and Definitions. Net Primary Production = Net C fixation by autotrophs NPP = GPP – R a NPP = D Biomass + Consumption + Detritus + Exudates. NEP. CO 2.

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Primary Production in Terrestrial Systems

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  1. Primary Production in Terrestrial Systems Fundamentals of Ecosystem Ecology Class Cary Institute January 2013 Gary Lovett

  2. Equations and Definitions • Net Primary Production = Net C fixation by autotrophs • NPP = GPP – Ra • NPP = D Biomass + Consumption + Detritus + Exudates

  3. NEP CO2 GPP Oxidation (Fire or UV) Ra Rh NPP (Re = Ra + Rh) Consumers Accumulation in biomass Detritus and exudates Decomposers Not decomposed Accumulation in sediments or soil Organic C import Organic C export Components of Productivity

  4. Measurement of Productivity in Terrestrial Ecosystems • Usually by measurement of fates of C • Accumulation in biomass • Diameter growth/ allometric equations in forests (usually over several years) • Harvest in grasslands (usually annually) • Detritus • Herbivory • Other fates of carbon • Aboveground vs. belowground

  5. Normalized Difference Vegetation Index (NDVI) = (NIR – VIS) / (NIR + VIS)

  6. NPP using remote sensing of nitrogen plus a productivity model From Ollinger and Smith Ecosystems 2005

  7. Typical NPP values (g C/m2/y) Desert, poor tundra 0-100 Grassland, shrubland 100-350 Temperate forest 300-800 Tropical forest 600-1000 Wetland, sugar cane, rice >1000 Note: Sometimes expressed in biomass units (g dry mass), equal to roughly carbon x 2

  8. Global Patterns of NPP NPP (Mg C/ha/y) From E.A. Schuur. Ecology 2003.

  9. Nutrient Limitation in Forests From Vitousek 2004 Ky (kiloyears) refers to age of geological substrate on these Hawaiian Islands C = Control, N = N addition, P = P addition, NP = N+P addition • Switch in limitation over time • Liebig’s Law of the Minimum and multiple limitation

  10. Variation in ANPP in Grasslands Different sites across the Great Plains Different years at one site in CO From Lauenroth and Sala 1992.

  11. Equations and Definitions • Net Primary Production = Net C fixation by autotrophs • NPP = GPP – Ra • NPP = D Biomass + Consumption + Detritus + Exudates • Net Ecosystem Production is the net carbon exchange with the atmosphere • NEP= GPP - Re = GPP - Ra – Rh = NPP – Rh • Re = Ra + Rh • NEP= organic C accumulation in ecosystem (biomass, soils/sediments, detritus) + net export of organic C

  12. NEP CO2 GPP Oxidation (Fire or UV) Ra Rh NPP (Re = Ra + Rh) Consumers Accumulation in biomass Detritus and exudates Decomposers Not decomposed Accumulation in sediments or soil Organic C import Organic C export Components of Productivity

  13. Eddy Covariance Net flux of CO2 = Downward flux – upward flux Requires: homogeneous surface, tower above the canopy, fast response sensors for wind and CO2 Measures: Net Ecosystem Exchange (NEE) What does this represent?

  14. LiCor 6400 Portable Photosynthesis System Measures: Net photosynthesis of leaves How do you scale up?

  15. Evolving knowledge: How does increasing N deposition affect C storage in forests? 1990s: Global models assumed N fertilization of tree growth, leading to enhanced C storage (e.g. ~ 2 Pg C/yr, Holland et al. 1997) 1999: Nadelhoffer et al summarized 15N addition studies in Europe and NA, showed most 15N stored in soils (low C:N) rather than in wood (high C:N). Global C sink estimated at 0.25 Pg C/y. 2000s: Multiple papers and reviews showing that N addition increases soil C storage by decreasing decomposition and soil CO2 release 2007: Magnani et al reported eddy covariance /modeling at multiple sites in Europe/NA. Strong relationship between N deposition and tree growth and C storage, dC/dN>200 2007-9: DeVries, Sutton, others: Criticism of Magnani et al in literature. dC/dN too high. 2008: Hyvonen et al, Devries et al: Experimental N additions in European forests show dC/dN of ~ 20-30 for trees and 10-15 for soil. 2010: Thomas et al. show statistical relationship between N deposition and tree growth in Northeastern US, varies by tree species, dC/dN=61, global N-induced C sink = 0.31 Pg C/y.

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