Functional groups in Quercus species derived from the analysis of pressure–volume curves

Abstract

Oaks that occupy Mediterranean phytoclimates share common leaf features (evergreenness, high leaf dry mass per unit area, LMA). Due to this phytoclimatic, morphological, and phenological convergence it has been suggested that they might constitute a coherent functional group. To confirm this hypothesis, some physiological parameters were determined after calculating pressure-volume curves (P-V curves) using the free-transpiration method. Seventeen Quercus species from contrasting phytoclimates were studied: six Mediterranean evergreen species (Q. agrifolia, Q. chrysolepis, Q. coccifera, Q. ilex ssp. ballota, Q. ilex ssp. ilex, and Q. suber); seven nemoral deciduous species (Q. alba, Q. laurifolia, Q. nigra, Q. petraea, Q. robur, Q. rubra and Q. velutina), and four nemoro-Mediterranean deciduous species (Q. cerris, Q. faginea, Q. frainetto, and Q. pyrenaica). Two-year-old seedlings growing under homogeneous environmental conditions (no water restrictions, uniform light, and nutrient supply) were used. The statistical analyses (correlation, mean-value comparisons, principal component analysis) of leaf features and parameters derived from the P-V curves confirmed the functional homogeneity of the three phytoclimatic groups, which were characterized by their contrasting ecophysiological response to water stress. The Mediterranean oak species developed mechanisms to avoid an excessive loss of cell water (e.g. high cell-wall rigidity). Conversely, the nemoral oaks showed the opposite. The nemoro-Mediterranean oaks perform better than nemoral oaks under water-stress conditions, but they cannot perform as well as the Mediterranean oaks on relatively dry soils.

Water relations of cork oak (Quercus suber L.) seedlings in response to shading and moderate drought

“…In oak species, drought commonly results in decreases in Ψπ 100 of about 0.6 MPa or less [2,3,6,13,14]. Decreases in osmotic potential near to 0.5 MPa under moderate drought conditions and differences in osmotic adjustment between seedlings grown under low light (LL1 and LL2) and high light (HL1 and HL2) environments of 40% demonstrated an osmotic adjustment capacity in accordance to water conditions in our study.…”

“…The result is a recruitment of seedlings of variable age, not more than 30 cm high, with a deep root system, that in most cases are not able to perform adequately, as long as favourable conditions for growth do not occur [29,54]. Thus, although mature cork oak is a shade-intolerant evergreen species, which shows a water-saver strategy under water stress [14,34,45], some canopy protection during the seedling state favours its establishment and early growth.…”

Rank reversals in tree growth along tree size, competition and climatic gradients for four forest canopy dominant species in Central Spain

“…Q. ilex is a sclerophyllous Mediterranean oak more drought tolerant than Q. pyrenaica which has been classified as a nemoro-Mediterranean oak (Corcuera et al, 2002). P. pinaster is considered more drought tolerant than P. sylvestris.…”

A conceptual dynamic vegetation-soil model for arid and semiarid zones

“…Parameters as A n,mx , B pot , T mx , k, ψ * , ψ w and I mx depend on the specie selected to be modelled. For vegetation in semiarid and arid environment, Corcuera et al (2002) reported 3.2 MPa wilting water potential ψ w as a point of turgor-loss, whereas used 3 MPa. The last one was used for the HORAS simulations.…”