Do precipitation changes affect Cork oak water relations?

Kurz-Besson C., Lobo do Vale R., Rodrigues L., Almeida P., Herd A., Chaves M.M., Pereira J.S. (in Press) Do precipitation changes affect
Cork oak water relations. In “Present and Future of Cork Oak in Portugal” (2012). Oliveira MM, Matos JA, Saibo NJ, Gil L (Eds.), Soc.
Portuguesa de Fisiologia Vegetal, Oeiras, Portugal.
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Do precipitation changes affect Cork oak water relations?
Cathy Béatrice Kurz Besson 1, Raquel Lobo do Vale 2, Lucilia Rodrigues 2, Pedro Almeida 2,
Alastair Herd 2, Maria Manuela Chaves 2, João Santos Pereira 2
1. Instituto Dom Luiz, Centro de Geofísica da Universidade de Lisboa Faculdade
de Ciências, Campo Grande, 1749-016 Lisboa, Portugal
2. Instituto Superior de Agronomia, Tapada da Ajuda, 1349-017 Lisboa, Portugal
In Portugal, Cork oak trees cover about 716000 ha and 13.4% of the national territory area [1]. They are mostly cultivated in
savannah-type agro-forestry systems occupying a large part of the most critical region of Portugal regarding water
availability. Though its distribution in the country slightly increased (+12%) over the last 40 years, the mean tree density in
pure and dominating stands dropped 23% over the last decade [1], with higher densities falling in profit to stands with
lower one. Between 1998 and 2011, a period including the extreme drought of 2005 [2], Cork oak mortality rate raised
450%, while stand areas showing fire indices increased 200%. These numbers give a consistent indication of vulnerability
increase and decline of Cork oak in Portugal.
Though recent studies tend to show an increase of annual precipitation in Portugal over the last centuries [3],
climate model simulations predict an increase in drought severity and a decrease in spring precipitation within the end of
st
the 21 century [4]. To understand and quantify the changes in Cork oak water relations under changing precipitation,
water availability was experimentally manipulated from 2003 to 2005 in a Montado area from south Portugal. Three
treatments were applied: Dry, Wet and Ambient with 80, 120 and 100% of the total annual precipitation, respectively.
Twenty-seven trees (3 trees*3 treatments*3 replicates) were monitored during 3 years following Granier sap flow (E), leaf
predawn and midday water potential (Ψ), leaf osmotic water potential (Ψπ) and leaf turgor (Ψp), as well as meteorological
conditions and soil water content (θ) responses to water availability.
Significant effects of the treatments were frequently detected on soil water content at 0.1 and 0.2m depth from
winter until late spring 2004, and in most of the measurements performed in 2005. For lower depths measured in 2005, the
significance appeared mostly in spring and summer periods. In spite of the significant differences in θ and E observed
between the Wet and the other treatments, no significant treatment effect could be detected on Ψ, Ψπ or Ψp, except in
early July 2005 (one week after the last irrigation). In response to increasing drought a marked decline in Ψπ was observed
in 2004 and 2005 accompanied by an increase in the amount of leaf solutes per unit dry mass, indicating that a seasonal
osmotic adjustment had occurred in trees under the three treatments. Significant treatment effects were found in tree E
especially during summer drought periods. E dropped 7% and 13% in summer 2004 and 2005 respectively in the DRY areas,
while it climbed 8% and 33% respectively in the WET areas. There was a huge benefit of the last 13mm irrigation pulse
applied in June 2005 on cork oak overall water status (Fig 1). E showed higher fluxes in spring 2005 than in spring 2004, in
spite of a lower θ (Fig. 1). This could be explained by the lack of competition for water with grasses that did not grow. The
strong benefit of the last single pulse irrigation could be due to a higher root density of trees in the topsoil in 2005 as
compared to 2004 [5].
Aknowledgement: EVK2-CT-2002-00158 (MIND), Pest-OE/CTE/LA0019/2011 - IDL
Key-words: Transpiration, water status, rainfall manipulation
1. AFN, 2010. Relatório Final do 5.º Inventário Florestal Nacional (IFN5), Autoridade Florestal Nacional, Lisboa, Portugal. AFN, 2001. Inventário florestal
nacional: Portugal continental: 3.º revisão, 1995-1998: relatório final. ISBN/ISSN 972-8097-47-6, Lisboa, Portugal.
2. Garcia-Herrera, R., D. Paredes, R. M. Trigo, I. F. Trigo, E. Hernandez, D. Barriopedro and M. A. Mendes. 2007. The outstanding 2004/05 drought in the
Iberian Peninsula: Associated atmospheric circulation. J. Hydrometeor., 8, 483-498
3. Acácio, V., M. Holmgren, F. Rego, F. Moreira, and G. M. J. Mohren. 2009. Are drought and wildfires turning Mediterranean cork oak forests into
persistent shrublands? Agroforestry Systems 76:389-400
4. Miranda, P.M.A., Valente, M.A., Tomé, A.R., Trigo, R., Coelho, M.F., Aguiar, A. and Azevedo E.B., (2006): O Clima de Portugal nos séculos XX e XXI. In
Santos, F.D., Forbes K. and Moita R. (Eds.), Climate Change in Portugal: Scenarios, Impacts and Adaptation Measures - SIAM II Project (pp. 47-113).
Gradiva, Lisbon.
5. D.O. Otienoa, H. Mirzaei, M.Z. Hussain, Y.L. Li c, M.W.T. Schmidt, M. Wartinger, E. Jung, N. Ribeiro, J.S. Pereira, J. Tenhunen. 2011. Herbaceous layer
development during spring does not deplete soil nitrogen in the Portuguese montado. Journal of Arid Environments 75 (2011) 231e238.
Kurz-Besson C., Lobo do Vale R., Rodrigues L., Almeida P., Herd A., Chaves M.M., Pereira J.S. (in Press) Do precipitation changes affect
Cork oak water relations. In “Present and Future of Cork Oak in Portugal” (2012). Oliveira MM, Matos JA, Saibo NJ, Gil L (Eds.), Soc.
Portuguesa de Fisiologia Vegetal, Oeiras, Portugal.
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-1
-1
E (L.m .day )
140
120
Tree sap flux
W
A
D
P<0.05
100
80
60
40
20
3
-3
θ (m .m )
0
0.30
W_Prof.
A_Prof.
D_Prof.
W_Grav.
A_Grav.
D_Grav.
W_Echo
A_Echo
D_Echo
P<0.05
0.25
0.20
0.15
0.10
0.05
Soil water content
W
D
A
-1
***
Ψmd (Mpa)
0.00
0
-2
-3
Leaf midday water potential
ΨΠ (Mpa)
-0.5
-1.0
W
D
A
-1.5
-2.0
-2.5
Leaf Osmotic Potential
2.5
ΨP (Mpa)
2.0
W
D
A
1.5
1.0
0.5
0.0
-0.5
Leaf Turgor
Precipitation
Irrigation
40
30
20
10
Sep-05
Jul-05
Aug-05
Jun-05
May-05
Apr-05
Mar-05
Jan-05
Feb-05
Dec-04
Oct-04
Nov-04
Sep-04
Jul-04
Aug-04
Jun-04
Apr-04
May-04
Feb-04
Mar-04
Jan-04
Dec-03
Oct-03
Nov-03
Sep-03
Jul-03
Aug-03
0
Jun-03
Rainfall,
Irrigation (mm)
-1.0
Figure 1. Evolution of Cork oak water status between 2003 and 2005 in Herdade da Mitra,
Évora, Portugal. Grey background color indicates summer drought periods.