Carbon balance of a maize canopy: different gap filling strategies

Irene Lehner, Eva van Gorsel, Vanessa Haverd, Roland Vogt

INTERREG IIIa Project Nr. 3c.10 Impacts of climate change

on vegetation in the Upper Rhine Valley

Gap Filling Comparison WorkshopJena, Germany, September 18-20, 2006

Outline

Site & Set-up

Gap filling methods

Results

Conclusions

Site

Air photograph July 16th 2004

Set-up

Sonic (Campbell CSAT3)

IRGA (Li-Cor Li7500)

Radiation (Kipp&Zonen CNR1)

PPFD (Li-Cor Li190SB)

Ventilated Psychrometer

Soil Heat Flux Plate (Rimco HP3)

Soil Temperature (Campbell CS107B)

Soil Moisture (Campbell CS616)

*Michaelis & Menten (1913) in Falge et al. (2001), Agric.For.Meteorol. 107, 43-69

Method I - Parameterisation

day

sat

sat RPPFDaNEE

NEEPPFDaNEE

'

' *

periods of assimilation

a‘ ecosystem quantum yieldPPFD photosynthetic photon flux densityNEEsat net ecosystem exchange at

„optimum“ lightRday ecosystem respiration during daytimeTs soil temperature

Method I - Parameterisation

* van‘t Hoff (1898) in Lloyd & Taylor (1994), Funct. Ecol. 8, 315-323

Rnight ecosystem respiration at nighta,b parameterTs soil temperature

b

TEXPaR S

night

*

periods of respiration

NEURAL NETWORK OUTPUTINPUT

Method II – Neural Network

PAR

vegetation height

air temperature

soil temperature

absolute humidity

CO2-flux

-2

-1.5

-1

-0.5

0

0.5

-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0

measured CO2-flux (mg m-2 s-1)

"ne

uro

nal

" C

O2-

flux

(mg

m-2

s-1

)

Method II – Neural Network

y = 0.8092x + 0.0074R2 = 0.80

Method II – Neural Network

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

24.07.2005 25.07.2005 26.07.2005 27.07.2005 28.07.2005 29.07.2005 30.07.2005 31.07.2005

CO

2-flu

x (m

g m

-2 s

-1)

measured NN

Method II – Neural Network

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

04.06.2005 07.06.2005 10.06.2005 13.06.2005 16.06.2005 19.06.2005 22.06.2005

CO

2-flu

x (m

g m

-2 s

-1)

measured NN

Method III - SVAT

Leaf-level modelStomatal conductance

photosynthesis (Collatz et al., 1992)energy partitioning

Radiation sub-modelRates of absorption by

sunlit/shaded leaves and soil (Goudrian&van Laar, 1994)

Soil sub-modelmoisture

temperatureevaporation

Optimisation by Levenberg-Marquard algorithm

Multi-layered canopy model (Leuning et al., 1995; Wang&Leuning, 1998)

y = 0.987xR2 = 0.76

Method III - SVAT

Results I – comparison

-2.00

-1.50

-1.00

-0.50

0.00

0.50

1.00

24.07.2005 25.07.2005 26.07.2005 27.07.2005 28.07.2005 29.07.2005 30.07.2005 31.07.2005

CO

2-flu

x (m

g m

-2 s

-1)

measured NN SVAT parameterisation

Results II – fallow

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

01.09.04 22.09.04 13.10.04 03.11.04 24.11.04 15.12.04 05.01.05 26.01.05 16.02.05 09.03.05 30.03.05 20.04.05

CO

2 flu

x (m

g m

-2 s

-1)

measurement NN based on hourly values NN based on daily values

Conclusions

parameterisation fails during fallow

NN based on hourly values doesn‘t capture medium size gaps

to aggregate monthly and yearly NEE values NN can be driven on a daily basis

statistical and process orientated models lead to comparable results

Thank you for your attention!

This study would not be feasible without the assistance of many people in the field and in the office as well as without the financing by the seco and the EU. Thanks!

Thanks