This document summarizes the results of a study on how nutrient and water availability impact carbon and water fluxes in a semi-arid tree-grass ecosystem. The study involved a large-scale fertilization experiment and analysis of sites along a precipitation gradient. Key findings include: fertilization increased GPP and decreased WUE; lower WUE led to earlier senescence under nitrogen addition; and carbon balance and fluxes were more sensitive to precipitation changes at drier sites. Nutrient additions had differing impacts on carbon fluxes depending on nitrogen to phosphorus ratios.

1. I CO S S CI E NC E CO NF E R E N CE 2 020 | SE PT E MB E R 1 5TH 2 02 0 | S E I TE 1
HOW NUTRIENT AND WATER AVAILABILITY
IMPACT CARBON AND WATER FLUXES IN A
SEMI-ARID TREE-GRASS ECOSYSTEM
Results from a large scale fertilization experiment
and a precipitation gradient analysis
Tarek S. El-Madany, Arnaud Carrara, Gerardo Moreno, M. Pilar Martin, Yunpeng Luo, Richard
Nair, Olaf Kolle, Martin Hertel, Thomas Wutzler, Markus Reichstein, Mirco Migliavacca

2. STOCHIOMETRIC N:P IMBAANCE
TA R EK S. E L - MA D A N Y | EG U 2 02 0 | S E S SIO N BG3. 2 2 | MAY 5TH | HOW N A N D P AVAI LA BI LIT Y C H A N G E W UE | S E I TE 2
Nair et al., 2019 Biogeosciences

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SITE LOCATION
El-Madany et al., 2018 Agriculture and Forest Meteorology

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SITE DESCRIPTION
Winter Spring Summer
Quercus Ilex trees
Tree height 8.7 m
20 % tree canopy fractional cover
MAP 650 mm
MAT 16.7 °C
0.3 cows ha-1

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PRE-TREATMENT
Negligible between sites
differences
• Fluxes
• Tree-grass fraction
• Soil nutrient
• Plant nutrient
Nair et al., 2019 Biogeosciences
El-Madany et al., 2018 Agriculture and Forest Meteorology

6. TREATMENT EFFECT – LEAF NUTRIENTS
TA R EK S. E L - MA D A N Y | EG U 2 02 0 | S E S SIO N BG3. 2 2 | MAY 5TH | HOW N A N D P AVAI LA BI LIT Y C H A N G E W UE | S E I TE 6
El-Madany et al., Submitted

7. TREATMENT EFFECT – HYPERSPECTRAL FLIGHTS
TA R EK S. E L - MA D A N Y | EG U 2 02 0 | S E S SIO N BG3. 2 2 | MAY 5TH | HOW N A N D P AVAI LA BI LIT Y C H A N G E W UE | S E I TE 7
Pacheco Labrador et al., 2020 Biogeosciences Discussions

8. AVERAGE ANNUAL CHANGES IN CARBON AND WATER FLUXES (2015-2019)
NT NPT
NEENEE Reco GPPRecoGPP
-80+50+130 +70-75 +145
Strong increase in GPP
Small increase in Reco
NEE from C-source to C-neutral
ET increase at NT small reduction at NPT
ET
+50
ET
-5
Units:
gC m-2 year-1
kg H2O m-2 year-1

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WATER-USE EFFICIENCY
WUE WUE WUE
Gs Gs Gs
T T T
GPP GPP GPP
El-Madany et al., Submitted

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WATER-USE EFFICIENCY
WUE WUE WUE
Gs Gs Gs
T T T
GPP GPP GPP
El-Madany et al., Submitted

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FUNCTIONAL RELATIONSHIPS WITH LAI
GPPmax: GPP at PAR 2000 µmol m-2 s-1 based on light response curves
Gs: surface conductance of water
El-Madany et al., Submitted

12. WATER AVAILABILITY EFFECTS ON PHENOLOGY
TA R EK S. E L - MA D A N Y | EG U 2 02 0 | S E S SIO N BG3. 2 2 | MAY 5TH | HOW N A N D P AVAI LA BI LIT Y C H A N G E W UE | S E I TE 1 2
Faster
regreening
due to more
Nitrogen
Luo, et al., 2020 Global Change Biology DOI: (10.1111/gcb.15138)
Earliest and fastest
senescence
NT < NPT < CT

13. EARLIER SENESCENCE CAUSED BY HIGHER WATER USE AND
LOWER SOIL MOISTURE IN THE TREATMENTS
PARTICULARLY NITROGEN
TA R EK S. E L - MA D A N Y | EG U 2 02 0 | S E S SIO N BG3. 2 2 | MAY 5TH | HOW N A N D P AVAI LA BI LIT Y C H A N G E W UE | S E I TE 1 3
Luo, et al., 2020 Global Change Biology DOI: (10.1111/gcb.15138)

14. CONCLUSIONS
• N:P imbalance impact fluxes in different ways;
• P-addition lead to an increase of water use efficiency (more efficient
transpiration in the NPT treatment);
• The lower water use efficiency in the N-lower treatment lead to earlier
senescence;
• Effects of changes in species in the herbaceous layers still under evaluation
TA R EK S. E L - MA D A N Y | EG U 2 02 0 | S E S SIO N BG3. 2 2 | MAY 5TH | HOW N A N D P AVAI LA BI LIT Y C H A N G E W UE | S E I TE 1 4

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2018 ICOS INITIATIVE
Majadas de Tietar
Albuera
El-Madany et a, 2020 PTRS-B

16. NOT POSSIBLE WITHOUT
16
Gerardo
Moreno
M. Pilar Martin
Arnaud
Carrara
Rosario
Gonzalez-
Cascon
BAIE group

17. 2 4 / 0 8 / 20 20
Tarek S. El-Madany17
http://1920x1080hdwallpapers.com/image/201505/macro/1516/grass-drop-water-dew-sunrise.jpg
Thank you for your attention

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CARBON BALANCE
• Dry site more sensitive
• Reco dominant at wet site
• Summer period
contributes stronger to
Reco at wet site

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CARBON AND PRECIPITATION
• Dry site stronger
relationship with NEE
• Stronger increase in GPP
and Reco

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Legumes
Forbes
Grasses