?13C and tree-ring width reflect different drought responses in Quercus ilex and Pinus halepensis

Abstract

Holm oak (Quercus ilexL.) and Aleppo pine (Pinus halepensisMill) are representative of two different functional types of trees extensively found in the Mediterranean: evergreen sclerophyllous and drought-adapted conifers. The former is considered a partially drought-tolerant species, whereas the latter is a typically drought-avoiding, water-saving species. We postulated that contrasting strategies in response to water deficits in Q. ilex and P. halepensis would lead to a differential sensitivity to changes in water availability. To test this hypothesis, we compared the response of both species in growth rate (measured as radial increments) and intrinsic water use efficiency WUE(i), as inferred from carbon isotope discrimination (Delta(13)C) in wood samples] among sites from different provenance regions in NE Spain. We found significant differences in Delta(13)C and growth among provenance regions, partly explained by contrasting water availability. Wood Delta(13)C was positively related with precipitation and the ratio between precipitation and potential evapotranspiration (P/ E). However, these relationships were stronger in P. halepensis (for P / E, r(2)=0.67, P <0.001) than in Q. ilex ( r(2)=0.42, P <0.01). In addition, radial growth was positively related with precipitation and Delta(13)C in P. halepensis ( r(2)=0.32 and r(2)=0.35, respectively, P <0.01), but not in Q. ilex. We concluded that P. halepensis was more sensitive than Q. ilex to water availability, showing faster increase in WUE(i) in response to water stress. We also found that the effect of north/south aspect on Delta(13)C and growth was site-specific, and unrelated to climatic variables.

Point processes statistics of stable isotopes: analysing water uptake patterns in a mixed stand of Aleppo pine and Holm oak

“…This points out that long-term growth in Aleppo pine is more strongly affected by competition than it is in the case of Holm oak, in agreement with its greater plasticity in radial growth (Ferrio et al, 2003; interception, as compared to oaks (Zavala et al, 2000). Conversely, the shade-tolerant nature and conservative growth of the evergreen oak would cause a lack of negative response to this sort of dominance.…”

“…Branch evaporation, in turn, would increase the proportion of heavy isotopes in xylem water, due to the faster evaporation of the light isotopes, and thus could explain the higher δ 18 O and δ 2 H observed in trees with close neighbours. This would also explain the stronger neighbour effect in pine as compared to oak, since the former is a water-saving species, with a more sensitive stomatal response (Ferrio et al, 2003;Zavala et al, 2000). However, again certain effect of the presence of oaks over pine isotope composition would have been expected, since the effective water uptake of oaks would also decrease water available for the pine, pushing the reduction of transpiration.…”

Relationships of stable carbon isotopes, plant water potential and growth: an approach to asses water use efficiency and growth strategies of dry land agroforestry species

“…Orwig and Abrams (1997), in their studies of radial growth responses to drought in the tree-ring records of six species growing within two locations of differing land-use history, canopy position and soil moisture characteristics, noted that during moist years, drought-sensitive species show enhanced growth than drought-tolerant species, while they show more reduced growth during drought years. A lower increase in WUE (d 13 C values) under drier conditions by drought tolerant (Quercus ilex) compared to drought sensitive (Pinus halepensis) species has also been reported by Ferrio et al (2003).…”

Leaf δ18O of remaining trees is affected by thinning intensity in a semiarid pine forest

“…2a). P. halepensis is a drought-avoiding species with tight stomatal control of transpiration and photosynthesis under water-limiting conditions (Ferrio et al 2003;Klein et al 2005;Maseyk et al 2008;Voltas et al 2008). Lower foliar d 18 O suggests higher leaf-level gs in stands subjected to heavy thinning than in stands subjected to moderate thinning (Barbour et al 2000;Barbour 2007;Farquhar et al 2007), and this interpretation of isotopic data is well supported by leaf gas exchange data (Fig.…”