Jordi Bort Unitat de Fisiologia Vegetal Universitat de Barcelona

1. Past climate and agricultural water management inferred from stable isotopes in archaeological plant remains Jordi BortUnitat de Fisiologia Vegetal Universitat de Barcelona

2. Contents • Carbon isotopes in plant matter • C3 Cereals • Trees • Oxygen isotopes in plant matter • C3 Cereals • Case studies: climate changes and water management in the past

3. Carbon isotopes in plant matter

4. 12CO2 12CO2 12CO2 13CO2 12CO2 12CO2 12CO2 12CO2 RuBisCO RuBisCO 12C(H2O) 12C(H2O) 12C(H2O) 13C and stomatal conductance • STOMATA OPEN (well-watered): • CO2 diffuses into intercellular space • High CO2 concentration • High discrimination against 13CO2 • LOWER WATER DEFICIT • HIGHER 13C Discrimination (D13C) CO2

5. 13C and stomatal conductance X 12CO2 13CO2 13C(H2O) 12C(H2O) • STOMATA CLOSED (water stress): • CO2 flux through stomata is limited • Low CO2 concentration • Low discrimination against 13CO2 • HIGHER WATER DEFICIT • LOWER 13C Discrimination (D13C) CO2

6. 13C vs Water Inputs - Cereals D13C = 1.78Ln(TWI) + 8.50 D13C = 1.52Ln(TWI) + 9.99 • D13C in cereal grains is highly correlated with water inputs during grain filling • D13C is more sensitive under low levels of water inputs (water stress) • Trend lines for Wheat and Barley do not differ significantly

7. 13C vs Annual Precipitation - Trees D13C = 1.91Ln(Prec) + 4.63 D13C = 0.97Ln(Prec) + 11.72 • D13C in wood cores of Aleppo Pine and Holm Oak is highly correlated with annual precipitation • D13C is more sensitive to changes in water inputs under low precipitation • D13C is more sensitive in species with greater stomatalregulation

8. Oxygen isotopes in plant matter

9. Origins of d18O variations in plants • 18O evaporates more slowly and precipitates more readily • Evaporation and condensation involve opposite trends • Both fractionations are temperature dependentHIGHER TEMPERATURE = HIGHER 18O IN RAIN WATER  T 18O  T 18O

10. Origins of d18O variations in plants Plant Uptake • During transpiration, 18O evaporates more slowly • Water vapour is depleted and leaf water is enriched in 18O • Fractionation is proportional to transpiration rateHIGHER TRANSPIRATION = LOWER 18O IN LEAF WATER  ET 18O  T 18O  T 18O

11. Origins of d18O variations in plants Plant Uptake • Oxygen atoms of water exchange with plant organic matter during hydration reactions TEMPERATURE and TRANSPIRATION RATES ARE STORED IN PLANT d18O  ET 18O  T 18O  T 18O

12. 13C and d18O in cereals and climate Over a range of 9 different environments, d180 in wheat grains shows no relationship with total water inputs during the growth season, whereas D13C is strongly correlated with this parameter...

13. 13C and d18O in cereals and climate ... However, d180 in cereal grains is highly correlated with mean temperatures during the growth season, whereas D13C shows no relationship with temperature

14. 13C and d18O in cereals and climate In addition, after removing the effect of temperature, d180 and D13C shows opposite trends respect water deficit (TWI/Eto), due to influence of transpiration rates on d180 and stomatal conductance on D13C

15. Case Studies: estimation of water availability in the past

16. Yield estimations from the analysis of carbon isotope compositions in fossil cereal grains collected in archaeological sites

17. Global changes in Water Inputs • We analysed d13C of charred grains from archaeological sites in North-Eastern and South-Eastern Spain, thenD13C was calculated, including variations in dair • We analysed present-day samplesfrom the same zones

18. Global changes in Water Inputs • We used models calibrated with present-day samples to estimate water inputs during grain filling • We found a steep decrease in water availability during the last millennium, partly explained by climate changes

19. Global changes in Water Inputs • The same procedure was applied to wheat and barley samples from Middle Euphrates (Syria) • We found a significant increase in aridity, further supporting the idea of a global climate change

20. Archaeological Sites TELL HALULA, Middle Eufrates (Syria) Excavations by Catalonian Archaeological Museum

21. Archaeological Sites TELL HALULA, Middle Eufrates (Syria) Excavations by Catalonian Archaeological Museum

22. Archaeological Sites TELL HALULA, Middle Eufrates (Syria) Excavations by Catalonian Archaeological Museum

23. Archaeological Sampling

24. Archaeological Sampling

25. Pre-Ceramic Neolithic (6300 years BP

26. Evidences of water management • Barley and wheatD13C in sites from SE Spain were correlated: • they responded to common (climatic) factors • Faba bean had higherD13C and not related with cereal values, in part due to differences in the time of seed formation • Irrigation of small plots of legumes, combined with rainfedcereals could be usual in the past

27. Evidences of water management • Under the same conditions, wheat has lowerD13C than barley due to its longer cycle • In two sites wheat had higherD13C, suggesting that it was grown under better conditions than barley • Values are closer to irrigated wheat • Nowadays it is a common practice indry areasto plant rainfed barley, while growing wheat under irrigation

28. Conclusions • Carbon isotope discrimination in C3 plants reflects changes in water availability • Oxygen isotope composition in plant tissues reflects changes in mean temperature • Both Carbon and Oxygen isotopes are affected, with opposite trends, by evapotranspirative demand

29. Conclusions • The application of Carbon isotope discrimination to archaeological plant remains can be used to estimate climate changes and water availability in the past • By comparing the results from several species, we can get information about ancient water management and land distribution

30. Acknowledgements • Dr. Ramon Buxó (Archaeological Museum of Catalonia) and Dr. Miquel Molist (Universitat de Barcelona) for providing archaeological samples. • J.P. Ferrio and Dr. Jordi Voltas (Universitat de Lleida) for analysis of samples and bibliographical review.