Stress responses of terrestrial vegetation and their manifestation in fluorescence and GPP Jaume Flexas

Stress responses of terrestrial vegetation and their manifestation in fluorescence and GPP Jaume Flexas New Methods to Measure Photosynthesis from Space Workshop August,26-31, 2012

Stress responses of terrestrial vegetation and their manifestation in fluorescence and GPP DEFINITION: Environmental factor that reduces the rate of some physiological process below the maximum rate that the plant could otherwise sustain. EXAMPLES: Drought, chilling, pathogens, heat wave, virus. TYPICAL TARGETS: At the PLANT: photosynthesis and growth At the ECOSYSTEM: GPP Lambers et al. 2008 Plant Physiological Ecology 2nd Ed. Springer

Under drought..

A N ( mol CO 2 m -2 s -1 ) 20 15 10 5 0 0,5 0,4 0,3 0,2 0,1 g s (mol H 2 O m -2 s -1 ) Rhamnus (evergreen).. stomata get closed and photosynthesis is reduced. 20 0,0 0,5 A N ( mol CO 2 m -2 s -1 ) 15 10 5 0 0,4 0,3 0,2 0,1 0,0 g s (mol H 2 O m -2 s -1 ) Grapevine (deciduous).. and plant growth is severely restricted 20 0,5 A N ( mol CO 2 m -2 s -1 ) 15 10 5 0 0,4 0,3 0,2 0,1 0,0 0 2 4 6 8 10 12 14 g s (mol H 2 O m -2 s -1 ) Tobacco (annual) Time (days) Bota et al. 2004 New Phytol. 162, 671-681

ETR ( mol electrons m -2 s -1 ) 220 200 180 160 140 120 100 80 60 40 20 0 A Changes occur at the pigment bed and photochemical apparatus, although only at a later stage of drought 7 B NPQ (relative units) 6 5 4 3 2 1 0 0,0 0,1 0,2 0,3 0,4 Stomatal conductance (mol H 2 O m -2 s -1 ) Flexas et al. 2002 Fun.Pl.Biol. 29, 461-471

Annual patterns of photosynthesis reflect the importance of drought Chilling Drought Galmés et al. 2012 In: Terrestrial Photosynthesis in a Changing Environment, Cambridge

as do patterns of GPP Galmés et al. 2012 In: Terrestrial Photosynthesis in a Changing Environment, Cambridge

But still plants can respond in many different ways Stress avoidance Stress tolerance Lost chlorophyll Retained chlorophyll Lost chlorophyll Retained chlorophyll Mundree et al. 2002 Afr. J. Biotech.. 1, 28-38

Stress responses of terrestrial vegetation and their manifestation in fluorescence and GPP FOCUS: Chlorophyll fluorescence.

Early casual observations (PAM) 0,40 0,38 0,36 0,34 Irrigated Fs (relative units) 0,32 0,30 0,28 0,26 0,24 0,22 Drought 0,20 6 8 10 12 14 16 18 20 22 Time (h) Flexas et al. 1999. Plant Cell Environ 73, 283-297.

Parallel response Unclear Anti-parallel response Flexas et al. 2000 Rem. Sens. Environ. 73, 283-297

Same paterns obtained using PASSIVE fluorescence O 2 -A band at 760 nm Moya et al. 2004 Rem. Sens. Environ. 91, 186-197

Differences in the fluorimeter settings? Differences in chlorophyll content? Differences in permanent photodamage? All together? 0,40 0,38 0,36 0,34 Irrigated Fs (relative units) 0,32 0,30 0,28 0,26 0,24 0,22 Drought 0,20 6 8 10 12 14 16 18 20 22 What s this??? Time (h) Flexas et al. 1999. Plant Cell Environ 73, 283-297.

Is this the reason for higher Fs in summer than in winter at mid latitudes????? Or is it mostly due to different light intensities????? Frankenberg et al. 2011. Geophys. Res. Lett. 38, L17706

SOLUTION: Fs normalized to Fo (Fs/Fo) 1,50 1,40 1,30 Fs/Fo (relative units) 1,20 1,10 1,00 0,90 0,80 0,70 6 8 10 12 14 16 18 20 22 Time (h) Flexas et al. 1999. Plant Cell Environ 73, 283-297.

Fs/Fo correlates with photosynthesis: WHY??? 1,8 1,6 A r 2 = 0.71 B r 2 = 0.77 1,8 1,6 Fs/Fo (relative units) 1,4 1,2 1,0 1,4 1,2 1,0 Fs/Fo (relative units) 0,8 0,8 0,6 0 5 10 15 20 A ( mol CO 2 m -2 s -1 ) 0,6 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 g (mol H 2 O m -2 s -1 ) 1,8 1,8 Fs/Fo (relative units) 1,6 1,4 1,2 1,0 C r 2 = 0.81 D r 2 = 0.69 1,6 1,4 1,2 1,0 Fs/Fo (relative units) 0,8 0,8 0,6 0 1 2 3 4 5 6 7 NPQ (relative units) 0 50 100 150 200 250 ETR ( mol e - m -2 s -1 ) 0,6 5 different C 3 species pooled Flexas et al., 2002. Physiol. Plantarum 114, 231-240.

Fs/Fo correlates XANTHOPHYLLS and PRI Peguero-Pina et al. 2008 Oecologia 156, 1-11

although the correlation varies with light intensity Evain et al. 2004 Rem. Sens. Environ. 91, 175-185

And its down-regulation is blocked by DTT 1000 2,4 PPFD ( mol photon m -2 s -1 ) 800 600 400 200 0 2,2 2,0 1,8 1,6 1,4 1,2 1,0 Fs/Fo (relative units) Treated with DTT Normal leaf 0 10 20 30 40 50 60 70 Time (min) All together, the data suggest that Fs/Fo inversely reflects NPQ

ETR ( mol electrons m -2 s -1 ) 220 200 180 160 140 120 100 80 60 40 20 0 A And because NPQ and thylakoid electron transport follow tight anti-paralell responses Fs may somehow be related to photosynthesis 7 B NPQ (relative units) 6 5 4 3 2 1 0 0,0 0,1 0,2 0,3 0,4 Stomatal conductance (mol H 2 O m -2 s -1 ) Flexas et al. 2002 Fun.Pl.Biol. 29, 461-471

So YES: Fs/Fo reflects photosynthesis!!!! Fs/Fo (relative units) 1,8 1,6 1,4 1,2 1,0 0,8 A r 2 = 0.71 B r 2 = 0.77 BUT 1,8 1,6 1,4 1,2 1,0 0,8 Fs/Fo (relative units) Fs/Fo (relative units) 0,6 1,8 1,6 1,4 1,2 1,0 0,8 0 5 10 15 20 A ( mol CO 2 m -2 s -1 ) C D Fr o 2 = cannot 0.81 r 2 = 0.69 be determined passively (i.e. satellite)! 0,6 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 g (mol H 2 O m -2 s -1 ) 1,8 1,6 1,4 1,2 1,0 0,8 Fs/Fo (relative units) 0,6 0 1 2 3 4 5 6 7 NPQ (relative units) 0 50 100 150 200 250 ETR ( mol e - m -2 s -1 ) 0,6 5 different C 3 species pooled Flexas et al., 2002. Physiol. Plantarum 114, 231-240.

Fs/Fo responses to LIGHT differ depending on STRESS severity Fs/Fo (relative units) 1,50 1,40 1,30 1,20 1,10 1,00 g= 150 g=80 g=62 g=55 g=39 g=10 Possible with geostationary satellite At a given light ( sun-synch satellite) 0,90 0,80 0 300 600 900 1200 1500 PPFD ( mol photon m -2 s -1 ) Flexas et al., 2002. Physiol. Plantarum 114, 231-240.

it correlates with stomatal conductance, photosynthesis. Fs/Fo (relative units) 1,5 1,4 1,3 1,2 1,1 1,0 0,9 0,8 (750 mol photon m -2 s -1 ) 0 50 100 150 g (mmol CO 2 m -2 s -1 ) BUT THE CORRELATION IS DIFFERNT AT ANY GIVEN LIGHT!!! Better information from sun-synch or geostationary??? Flexas et al., 2002. Physiol. Plantarum 114, 231-240.

The correlation is independent of the velocity of drought imposition 2,0 1,8 Laser-PAM Fs/Fo 1,6 1,4 1,2 1,0 0,8 0,6 Gradual drought (weeks) 0 50 100 150 200 Stomatal conductance (mmol H 2 O m -2 s -1 ) Ounis et al. 2001 Photos. Res. 68, 113-120

The correlation is independent of the velocity of drought imposition 2.0 1.8 Laser-PAM Fs/Fo 1.6 1.4 1.2 1.0 0.8 0.6 Cut petiole (minutes) 0 50 100 150 200 Conductancia estomática (mmol H 2 O m -2 s -1 ) Ounis et al. 2001 Photos. Res. 68, 113-120

and it is similar during drought imposition and recovery after re-watering 1.4 1.2 Fs/Fo 1.0 0.8 0.6 0.4 Peciolo cortado (minutos) 0.0 0.1 0.2 0.3 0.4 Stomatal conductance (mol H 2 O m -2 s -1 ) Cifre et al. 2005. Agr. Ecosyst. Environ. 106, 159-160

BUT still it ONLY responds BELOW SOME THRESHOLD 2,0 1.4 Laser-PAM Fs/Fo 1,8 1,6 1,4 1,2 1,0 Fs/Fo 1.2 1.0 0.8 0,8 0.6 0,6 0 50 100 150 200 Stomatal conductance (mmol H 2 O m -2 s -1 ) 0.4 0.0 0.1 0.2 0.3 0.4 Stomatal conductance (mol H 2 O m -2 s -1 )

Take-home messages PHOTOSYNTHESIS generally declines under stress, but CHLOROPHYLL CONTENT often does not: but current GOSAT Fs retrieval largely reflects greenness!!! Fs/Fo but not Fs alone reflects photosynthesis: how to get a proxy for Fo using passive fluorescence?: possible at low light (geostationary satellite) At LOW LIGHT Fs/Fo is governed by photochemistry, while at HIGH LIGHT it is governed by THERMAL DISSIPATION. Assessing INCIDENT LIGHT on the canopy is required, measuring at varying light would even be better! (again geostationary) In some cases or above given thresholds Fs/Fo does not reflect photosynthesis properly (even if all the above is fixed, we still have some difficulties )