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

Annual precipitation slightly decreased in Central Italy, in the

past decade …

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

Conversely, mean surface air temperature increased …

… leading to a decrease in soil moisture content

The MIND projectThe EU Mediterranean ecosystems under The EU Mediterranean ecosystems under INcreasing Drought project was designed to: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

The consortiumThe consortium

F. Miglietta, CNR IBIMET: WP1_Coordination and experimental manipulationR. Valentini, Università della Tuscia: WP2_Ecosystem fluxesM.F. Cotrufo, Seconda Università di Napoli: WP3_Soil respiration A. Peressotti, Università di Udine: WP4_TranspirationM. Borghetti, Università della Basilicata: WP5_Ecophysiology and growthS. Raddi, Università di Firenze: WP5_Ecophysiology and growthM. Menenti, CNR ISAFOM: WP6_Remote sensingF. Magnani, Università di Bologna: WP7_Modelling

Specific questions addressed in this talk: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?

• 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

Wet

Dry

Control

Experimental plot layout:

DryDry = 20% of throughfall displacement, in place since April 2004

WetWet = Soil water content maintained above 10%v through irrigation, since April 2004

ControlControl = Ambient precipitation regime, in place since April 2005

Experimental setupExperimental setup

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

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Doy

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mm

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°C

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+ irrig

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s (mm

)

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(°C

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Sap flow cumulative canopy transpiration

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ET WET ET DRY SWC WET SWC DRY

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Soi

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Mid summer rains

Mean monthly soil respiration

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SR

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mo

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-1)

WET DRY

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*

2004 2005

Autumn rains

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 ??

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s-1)

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WET model

Litterfall dynamics

Litterfall

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g litter/m2 WET

DRY

Measured Mean Residence TimeMeasured 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

Litter dynamics and long term soil carbon pools

LITTER PRODUCTION

Ecosystem respiration in 2005

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First irrigation

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NEE wet

Fluxes in 2005

Conclusions: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.

Thank you for your attention.