Water Sources and Water‐Use Efficiency in Mediterranean Coastal Dune Vegetation

Abstract

In coastal environments plants have to cope with various water sources: rainwater, water table, seawater, and mixtures. These are usually characterized by different isotopic signatures ( (18)O/ (16)O and D/H ratios). Xylem water reflects the isotopic compositions of the water sources. Additionally, water-use efficiency (WUE) can be assessed with carbon isotope discrimination (Delta) analyses. Gas exchange, Delta of leaf dry matter, and isotopic composition (delta (18)O) of xylem water were measured from June to August 2001 in herbaceous perennials of mobile dunes (Ammophila littoralis, Elymus farctus) and sclerophyllous shrubs and climbers (Arbutus unedo, Pistacia lentiscus, Phillyrea angustifolia, Qercus ilex, Juniperus oxycedrus, Smilax aspera) of consolidated dunes. Assimilation rates were rather low and did not show clear seasonal patterns, possibly due to limited precipitation and generally low values of stomatal conductance. The lowest values were shown in S. aspera. Different physiological patterns were found, on the basis of delta (18)O and Delta analyses. Values of delta (18)O of xylem water of phanerophytes were remarkably constant and matched those of the water table, indicating dependence on a reliable water source; values of Delta were relatively high, indicating low intrinsic WUE, with the exception of J. oxycedrus. Surprisingly, very high delta (18)O values were found for the xylem water from S. aspera in August. This suggests retrodiffusion of leaf water to xylem sap in the stem or direct uptake of water by leaves or stems, owing to dew or fog occurrence. Low Delta values indicated high WUE in S. aspera. Contrasting strategies were shown by the species of mobile dunes: E. farctus relied on superficial water and exhibited low WUE, accordingly to its therophyte-like vegetative cycle; on the contrary, A. littoralis used deeper water sources, showing higher WUE in relation to its long-lasting vegetative habit.

The ACCENT-VOCBAS field campaign on biosphere-atmosphere interactions in a Mediterranean ecosystem of Castelporziano (Rome): site characteristics, climatic and meteorological conditions, and eco-physiology of vegetation

“…A detailed study on water use under drought stress for the most representative species of the dune vegetation is proposed by Mereu et al, 2009. A strong physiological dependence of schlerophyllous plants on the freshwater table level was also observed, in our same experimental site, with a study of isotopic fractionation in xylematic water (Alessio et al, 2004). In particular, the shrubs examined in our study, and particularly A. unedo, P. latifolia and, Q. ilex, showed negative values of 18 O 2 values of xylematic water that are associated with high discrimination ( ) values, even under very dry conditions.…”

“…The weak emission of monoterpenes by Arbutus unedo (0.29 µg(C) g −1 DW h −1 ), was also observed by Owen et al (1997), and Pio et al (1993). Alessio et al (2004) also reported inconspicuous emissions of isoprenoids by Arbutus unedo and Phillyrea latifolia. It is therefore confirmed that these plants do not have the capacity to produce and emit relevant amounts of isoprenoids.…”

“…Smilax aspera). Interestingly, no species of the coastal dune system used marine water or mixtures of marine and freshwater (Alessio et al, 2004), indicating that in this site marine intrusion was absent.…”

Influence of water and terpenes on flammability in some dominant Mediterranean species

“…Water status depends on water availability, and on the extension of plant root systems to reach water available in deeper soil layers when shallow reserves dry out during the summer season. Those species that keep their levels of foliar hydration and suffer less water stress (Alessio et al 2004) are certainly less prone to fire.…”

Analysis on Features of Soil-River-Ground-Plants Water Based on Stable Oxygen Isotope in Poyang Lake Wetland

“…The oxygen isotope value of surface soil water corresponding to plants root system depth at different sampling points of two sections shown as Table 3. Only at sampling point 3 of section I the oxygen isotope value of soil water was similar with corresponding oxygen isotope value of plants leaf water, at others sampling points the oxygen isotope values of soil water were less than corresponding oxygen isotope values of plants leaf water, the reasons shown as: (1) the isotope fractionation was not occurred when water absorbed by plants root system and conveyed to leaves [25,26] , but when the leaf water directly contacted with the air, heavy isotope in leaf water will enriched with plant transpiration [27] . (2) …”