Download Net Primary Production (NPP)

Ben-Gurion University of the Negev"
Vegetation Ecology Course 2015/16
Bertrand Boeken
Net Primary Production (NPP)
•  Measurement
•  Plant growth
•  Global variation
•  Vegetation types
•  Resource limitation
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Measurement
Net primary production
NPP = annual increase in biomass
per unit area [g.m-2.yr -1]
•  Usually only aboveground
•  Though much production is allocated
belowground
Gross primary production
GPP = NPP + R
R = part of GPP used in respiration
Standing mass (crop) = Total (bio-)mass present
including new tissue, old living tissue and dead
material
US Environmental Protection Agency 2
Spatial scale
•  NPP is of interest on the local or regional scale,
•  But carried out by individual plants,
•  While photosynthesis occurs in the leaves at the
molecular level.
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Scaling-up
Summation of single plant or leaf
performance over a whole field,
NPP = f (energy flux, growth conditions)
with random spatial variation in
performance and limited substrate
heterogeneity
or hierarchical
complexity?
NPP = f (energy flux, growth conditions, multiple
species performance)
with significant spatial heterogeneity, species
differences, diversity, and biological interactions
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Resources
For primary production and growth
•  CO2
Air
Light
CO2
•  Light
•  Water
•  Mineral nutrients
•  O2
Soil
O2
Water
Minerals
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Whole plant growth
•  Leaf area index (LAI)
•  Leaf area duration (LAD)
and phenology
Size of photosynthetic surface
Relative to canopy area
per plant or vegetation stand
with layers (LAI can be >1)
Time that photosynthetic
surface is available
LAI and LAD can be combined
by integration of LAI over time
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Life form
•  Annuals invest most photosynthates in new leaves and stems, later in reproduction
•  Ephemeral perennials invest in storage and roots, stems and leaves, only much later in
reproduction
•  Woody perennials also in support and long-term roots, stems and/or leaves
Leaves
Storage
Leaves
Stems
Stems
Roots
RE
Roots
RE
GR=dM/dt
Annual plant
Mass
•  Growth rate
Perennial plant
• Relative growth rate
RGR=∆M/initial M
Time
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Global variation of NPP
Latitudinal gradients
•  Light quality (PAR, angle)
•  Length of growing season
•  Low temperature
•  Aridity
Latitudinal variation in NPP
• 
• 
• 
• 
High near the equator
Intermediate in temperate zones
Low near poles
But very low in the arid zones
ca. 2200 t.km-2.yr-1
1200 t.km-2.yr-1
10-800 t.km-2.yr-1
90 t.km-2.yr-1
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Vegetation types
latitudinal trends
•  Forest
Boreal coniferous forest
Temperate deciduous forest
Tropical rainforest
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•  Grassland
Arctic tundra
Temperate coastal grassland
Tropical savanna
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Vegetation-type effects on NPP
NPP vs Standing mass
NPP/B is greater for
NPP
Grasslands
grasslands, especially if
Forests
dead material is removed
(grazing)
Standing mass (B)
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Vegetation-type effects on NPP
Coniferous forest Deciduous forest
LAD
long
short
LAI
high
low
Chlorophyll content
low
high
Light-use efficiency
low
high
NPP
high
lower
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Water limitation
NPP vs Rainfall
NPP
Limited by transport and stomatal resistance
Drylands
Limited by water deficit, low vegetation cover
3000 mm/yr
Precipitation
However, short-term relative NPP is
very high in deserts: 2.3 g.g-1
Coniferous forest:
1.6
Deciduous forest:
2.2
Temperate grassland: 1.2
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NPP in water-limited systems
High productivity per unit leaf mass,
when and where water is available.
Total biomass (g)
However, growth is limited
•  Temporally, by
low LAD due to short growing season;
R2=0.277, P<0.0001
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20
•  Spatially, by
low LAI due to incomplete ground
cover
Isolated shrub patches
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0
0
50
100
150
200
Total plant density (per 600 cm2)
Widely spaced annuals on biocrust
 Density-independent biomass production
of annuals.
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Spatial patterns in water-limited systems
From closed canopy to contracted vegetation
Humid
Subhumid
Vegetation cover
Semiarid
Arid
“Bare” surface
Lehavim (300 mm/yr)
Makhtesh Ramon (<50 mm/yr)
Park Shaked (150 mm/yr)
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