primary production in terrestrial systems fundamentals of ecosystem ecology class cary institute...
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Primary Production in Terrestrial Systems
Fundamentals of Ecosystem Ecology Class
Cary Institute
January 2013
Gary Lovett
Equations and Definitions1. Net Primary Production = Net C fixation by autotrophs
2. NPP = GPP – Ra
3. NPP = Biomass + Consumption + Detritus + Exudates
CO2GPP
NPP
Detritus and exudates
Not decomposed
Organic C export
Accumulation in sediments or soil
Consumers
Ra
Decomposers
Rh
Accumulation in biomass
NEP
(Re = Ra + Rh)
Oxidation (Fire or UV)
Organic C import
Components of Productivity
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
Normalized Difference Vegetation Index (NDVI) = (NIR – VIS) / (NIR + VIS)
NPP using remote sensing of nitrogen plus a productivity model
From Ollinger and Smith Ecosystems 2005
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
From E.A. Schuur. Ecology 2003.
NP
P (
Mg
C/h
a/y)
Global Patterns of NPP
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
Nutrient Limitation in Forests
•Switch in limitation over time•Liebig’s Law of the Minimum and multiple limitation
0
200
400
600
800
1000
0 500 1000 1500 2000
AN
PP
Precipitation (mm)
Different sites across the Great Plains
Different years at one site in CO
From Lauenroth and Sala 1992.
Variation in ANPP in Grasslands
Equations and Definitions1. Net Primary Production = Net C fixation by autotrophs
2. NPP = GPP – Ra
3. NPP = Biomass + Consumption + Detritus + Exudates
4. Net Ecosystem Production is the net carbon exchange with the atmosphere
5. NEP= GPP - Re = GPP - Ra – Rh = NPP – Rh
6. Re = Ra + Rh
7. NEP= organic C accumulation in ecosystem (biomass, soils/sediments, detritus) + net export of organic C
CO2GPP
NPP
Detritus and exudates
Not decomposed
Organic C export
Accumulation in sediments or soil
Consumers
Ra
Decomposers
Rh
Accumulation in biomass
NEP
(Re = Ra + Rh)
Oxidation (Fire or UV)
Organic C import
Components of Productivity
Eddy Covariance
Requires: homogeneous surface, tower above the canopy, fast response sensors for wind and CO2Measures: Net Ecosystem Exchange (NEE) What does this represent?
Net flux of CO2 = Downward flux – upward flux
LiCor 6400 Portable Photosynthesis System
Measures: Net photosynthesis of leavesHow do you scale up?
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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