Seasonal evolution in leaf and wood δ13C in two co-occurring Mediterranean oaks (Quercus ilex subsp. ballota L. and Quercus faginea Lam.): dynamics of water-use efficiency

Abstract

Aguilera,  M.,  Voltas,  J.,  Ferrio,  J.P.,  Serrano,  L.  2010.Seasonal  evolution  in  leaf  and  wood  δ 13C  in  two  co-occurring Mediterranean  oaks  (Quercus  ilex subsp.  ballota L.  and  Quercus  faginea Lam.):  dynamics  of  water-use  efficiency.
Ecosistemas 19(3):6-13

In the Mediterranean region, the presence of mixed stands of evergreen and deciduous species such as Quercus ilex and Q. faginea is common. In this work we aim to analyze their differential response to seasonal climatic fluctuations using the carbon isotope composition in leaf soluble organic matter (δ13Cl) and in wood α-cellulose (δ13Cw) as indicators of water-use efficiency. We observed different intra-annual patterns in δ13Cl. On the one hand, Q. faginea uses stored starch as carbon source to build new leaves in the beginnings of April, leading to high δ13Cl values. On the other, Q. ilex uses recent assimilates from previous-year, but still functional, leaves. Nevertheless, overall δ13Cl values  in  both  species  were  similar  (-25.4±0.55  and  -25.5±0.89,  for  Q.  faginea  and  Q. ilex, respectively), which translates into similar intrinsic water-use efficiencies. As in leaves, δ13Cw for Q. faginea clearly showed the use of stored carbon for early-wood formation. Both δ13Cl and  δ13Cw recorded  functional  adjustments  in  response  to  seasonal  climatic  variations,  but  the  lower  amplitude  of δ13Cw changes registered in Q. ilex indicates a reduced sensitivity to climate changes as compared with the deciduous oak. This feature may provide this species with a competitive advantage under conditions of steady increase in aridity.