gas exchange measurements by irga
TRANSCRIPT
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GAS EXCHANGE MEASUREMENTS BY IRGA
Dr. Javier Gulías
University of the Balearic Islands (Spain)
Chania (Greece) June 2008
EFIMED Summer School on Do Mediterranean forests compete for water resources?. A scale approach from leaf to landscape.
1. PRINCIPLES AND FUNDAMENTALS
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1) Light-dependent reactions. PHOTOCHEMISTRY. Light energy is used for the synthesis of ATP and NADPH from ADP and NADP+.
2) Light-independent reactions. BIOCHEMISTRY. ATP and NADPH are used to reduce CO2 and produce sugars through the Calvin cycle.
THE PHOTOSYNTHETIC PROCESSPlants use solar energy to synthesize organic molecules from carbon dioxide (CO2) and water (H2O).
The process can be divided in two parts:
Spectroscopy
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Gas flow (pump)
CLOSED CIRCUIT
OPEN CIRCUIT
Open circuits avoid some problems (i.e., water condensation in the circuit), but requires the use of two IRGAs
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IRGAs position in the system head (close to cuvette), as in the Li-6400, improves accuracy
GAS EXCHANGE MEASUREMENTS BY INFRARED GAS ANALYZER (IRGA): Li-Cor 6400
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Measuring gas exchange
•Measured:
Net photosynthesis (AN)
Transpiration (E)
Air and leaf T, RH, PAR
•Estimated:
Stomatal conductance (gs),
Substomatal CO2 concentration (Ci)
1. E = gH2O x ([H2Oi]- [H2Oa])
2. AN = gCO2 ([Ca]-[Ci])
In (1) E and [H2Oa] are directly measured. Assuming 100% RH in the substomatal cavity and measuring leaf T, [H2Oi] can be
estimated and then solve for gH2O. In (2) AN and [Ca] are directlymeasured. Since gCO2 = gH2O / 1.6, then one can solve for [Ci].
IRGA determines the rates of photosynthesis (AN) and transpiration(E), as:
AN = (Air flux x ΔCO2) / Leaf areaE = (Air flux x ΔH2O) / Leaf area
From Fick’s First Law of diffusion, other parameters are then calculated:
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CO2 O2
H2O
CO2
O2
In the light, photosynthesis and respiration co-occur
FOTOSÍNTESIS
RESPIRACIÓN
RubiscoRubisco
COCO22 OO22
Carboxylation Oxygenation
COCO22OO22
Then, IRGA determines the NET photosynthesis rate:
AN = Gross photosynthesis - Photorespiration –Respiration
And PHOTORESPIRATION
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2. USEFULLNESS AND APPLICATIONS
What can we measure with an IRGA?
•Instantaneous gas fluxe measurements
•Daily courses of gas exchange
•Photosynthesis light response curves
•A/Ci curves
•Feed the models
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Annual Evolution of net photosynthesis and stomatal conductance of Quercus ilexJune 1998-October 2001
Binifaldó (Mallorca)P= 1000 mm
Puigpunyent (Mallorca)P= 600 mm
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How and When to do Instantaneous measurements: Diurnalevolution of Gas Exchange rates
High water availability
Mild water stress
Severe water stress
Mid-morningmeasurements
Sun leaf
Shade leaf
Light response curve
Net
pho
tosy
nthe
sis
Irradiance
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1. Rubisco-limitedphotosynthesis
2. RuBPregeneration capacity
3. Triose phosphate utilisation
Ci (μmol mol-1)0 200 400 600 800 1000
AN ( μ
mol
CO
2 m
-2 s
-1)
0
10
20
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CAREFUL: effect of mesophyll conductance to CO2(Ci NOT EQUAL TO Cc)
With adequate parameterization and a biochemical model(Farquhar et al. 1980), CO2-response curves allow estimates of
metabolic parameters
3. OVERVIEW OF Li-6400: SOME PRACTICAL
ASPECTS
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Li-6400
Li-6400
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Observations:
Date:
Slope:
Orientation:
Altitude:
Longitude:
Latitude:
Tree species:
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ObservationsE (mmolH2O m2s-
1)Ci (mmol CO2
mol air-1)gs (mmol m2s-1)A (μmolCO2 m2s-
1)Tree
nº