1. Mediterranean forest ecosystem under changing precipitation regimes Peressotti A., Cotrufo M.F., Miglietta F., Valentini R., Inglima I., Pecchiari M., Alberti G., Arriga N., Piermatteo D., Zaldei A. Open Science Conference on the GHG Cycle in the Northern Hemisphere Sissi-Lassithi, Crete, 14-18 November 2006

2. Annual precipitation slightly decreased in Central Italy, in the past decade …

3. …and the same is forecasted to the end of the century

4. Conversely, mean surface air temperature increased …

5. … leading to a decrease in soil moisture content

6. The MIND project The EU Mediterranean ecosystems under INcreasing Drought project was designed to:  investigate the potential effects of increasing drought on Mediterranean terrestrial ecosystems;  assess ecosystem vulnerability in response to changes in rainfall patterns;  identify appropriate management strategies to protect the ecosystem from the expected changes in climate

7. The consortium F. Miglietta, CNR IBIMET: WP1_Coordination and experimental manipulation R. Valentini, Università della Tuscia: WP2_Ecosystem fluxes M.F. Cotrufo, Seconda Università di Napoli: WP3_Soil respiration A. Peressotti, Università di Udine: WP4_Transpiration M. Borghetti, Università della Basilicata: WP5_Ecophysiology and growth S. Raddi, Università di Firenze: WP5_Ecophysiology and growth M. Menenti, CNR ISAFOM: WP6_Remote sensing F. Magnani, Università di Bologna: WP7_Modelling

8. Specific questions addressed in this talk:  Do changes in precipitation patterns affect the annual C budget of Mediterranean forest ecosystems?  What are the main controls of soil respiration in Mediterranean ecosystems? To what extent changes in soil water moisture affect soil respiration? … Interactions with temperature??  Will persistent changes in precipitation patterns affect on the long term soil C stocks of Mediterranean forests?

9. Lat.: 42°08’ N Long.: 11°58’ E Area: 6.2 ha Elevation: 220 m a.s.l. Annual precipitation: 650 mm Average air temperature: 15°C Management: coppice Vegetation: non-deciduous broadleaf (Arbutus unedo) A large scale manipulation experiment

10. Wet Dry Con trol Experimental plot layout : Dry Dry = 20% of throughfall displacement, in place since April 2004 Wet Wet = Soil water content maintained above 10%v through irrigation, since April 2004 Control Control = Ambient precipitation regime, in place since April 2005

11. Experimental setup

12. Climate and irrigations in 2004 and 2005 WET PLOT DRY PLOT A: Daily mean air temperature and rainfall B: Soil water content and rainfall + summer irrigation 0% 5% 10% 15% 20% 25% 30% 35% 0100200300400500600700800 Doy % 0 20 40 60 80 100 120 140 160 180 mm 0 5 10 15 20 25 30 35 °C 0 20 40 60 80 100 120 140 160 180 mm A B Rain (mm) Soil water content Rain + irrigations (mm) Mean air temperature (°C)

13. Sap flow cumulative canopy transpiration A B 2004 2005 mm Soil water content Mid summer rains

14. Mean monthly soil respiration 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 456789101112123456789101112 Month SR (  mol m -2 s ) WETDRY * * * * * * * * * * 20042005 Autumn rains

15. Soil respiration  Soil mostrure limits soil respiration at high soil temperature  However, very high SR values can be measured at high temperature, in dry plots An inerpretation: easily decomposable residue accumulation during dry stess realeased at the early rains ?? 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 0510152025 Soil temperature (°C) SR (umol m -2 s ) SRD (umol m-2 s-1) SRW (umol m-2 s-1) DRYmodel WET model

16. Litterfall dynamics Measured Mean Residence Time Leaf litter poduction increases in the wet plots but, due to increased decay rate, annual mean residence time is significanlty higher in dry plots

17. Litter dynamics and long term soil carbon pools LITTER PRODUCTION

18. Ecosystem respiration in 2005 0 1 2 3 4 5 6 7 8 9 10 gC day m -2 0% 5% 10% 15% 20% 25% 30% 35% 050100150200250300350400 DOY % Ecosystem respiration Soil water content gC day -1 m -2 Soil water content

19. First irrigation -600 -400 -200 0 200 400 600 800 1000 1200 1400 1600 050100150200250300350 DOY gC m -2 GPP dry GPP wet Reco dry Reco wet NEE dry NEE wet GPP wet Reco wet GPP dry Reco dry NEE dry NEE wet Fluxes in 2005

20. Conclusions:  Enhanced summer rainfall increases canopy assimilation (GPP). However, ecosystem respiration is also strongly increased and as a result annual Net Ecosystem C sequestration is reduced.  In Mediterranean water limited systems, the expected climatic changes in rainfall regime might not influence or slightly increase ecosystem carbon uptake because is dependent on seasonal distribution of water supply  Soil respiration is controlled by temperature during moist season and by soil moisture during summer drought. Substrate availability controls respiration in warm moist soils. This leads to respiration flashes at the first late summer rains, probably due to easily degradable substrates accumulated in dry soils over summer.  On the long term, persistent summer droughts are predicted to reduce C decay proportionally more than C input, leading to an overall accumulation of soil C in active and slow pools.

21. Thank you for your attention.