Primary Production in Terrestrial Systems
Fundamentals of Ecosystem Ecology Class
Cary Institute
January 2013
Gary Lovett
Equations and Definitions
1. Net Primary Production = Net C fixation by autotrophs
2. NPP = GPP – Ra
3. NPP = D Biomass + Consumption + Detritus + Exudates
Components of Productivity
NEP
Oxidation
(Fire or UV)
CO2
GPP
Ra
NPP
Rh
(Re = Ra + Rh)
Consumers
Accumulation
Detritus and
in biomass
exudates
Decomposers
Accumulation in
sediments or soil
Organic C
export
Not
decomposed
Organic C
import
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
Grassland, shrubland
Temperate forest
Tropical forest
Wetland, sugar cane, rice
0-100
100-350
300-800
600-1000
>1000
Note: Sometimes expressed in biomass units (g dry mass), equal to roughly
carbon x 2
NPP (Mg C/ha/y)
Global Patterns of NPP
From E.A. Schuur.
Ecology 2003.
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
Variation in ANPP in Grasslands
1000
ANPP
800
Different sites across the
Great Plains
600
400
Different years at
one site in CO
200
0
0
500
1000
1500
Precipitation (mm)
From Lauenroth and Sala 1992.
2000
Equations and Definitions
1. Net Primary Production = Net C fixation by autotrophs
2. NPP = GPP – Ra
3. NPP = D 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
Components of Productivity
NEP
Oxidation
(Fire or UV)
CO2
GPP
Ra
NPP
Rh
(Re = Ra + Rh)
Consumers
Accumulation
Detritus and
in biomass
exudates
Decomposers
Accumulation in
sediments or soil
Organic C
export
Not
decomposed
Organic C
import
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?
LiCor 6400 Portable Photosynthesis System
Measures: Net photosynthesis of leaves
How 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.