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.