ISHS Acta Horticulturae 705: V International Walnut Symposium
USING OXYGEN STABLE ISOTOPES TO INVESTIGATE THE SOIL-PLANT-ATMOSPHERE HYDRAULIC CONTINUUM IN COMPLEX STANDS OF WALNUT |
| Authors: | M. Lauteri, G.A. Alessio, P. Paris |
| Keywords: | Juglans regia, mixed plantations, oxygen stable isotopes, soil-plant-atmosphere continuum, water sources, root competition |
| DOI: | 10.17660/ActaHortic.2005.705.27 |
| Abstract:
Oxygen stable isotopes can be used as natural tracers for studying the sources of water and processes of water use by plants. Soil water is usually characterized by complex patterns of isotopic composition (  18O) along the soil profile.
Both climate and hydrology influence the 18O values of different water pools so the water table and the waters in the shallow, medium and deep soil layers usually differ in their isotopic composition.
No isotopic effects occur during water uptake by roots or during xylem transport, so that xylem water 18O reflects a weighed average of the different water sources used by the plant.
In contrast, leaf water 18O is enriched by evaporative effects that occur during transpiration.
Our study was aimed at elucidating the strategies of plant water use in pure and mixed walnut (Juglans regia) plantations based on quantifying the variation in oxygen isotope composition of soil and plant tissue water.
We tested the hypothesis that walnut trees may benefit from associations with other species (e.g., Eleagnus umbellata, Corylus avellana, Alnus cordata) if they exploit different water pools that in turn modifies the overall canopy microclimate that changes overall stand water use.
Our data show that these three species, in particular A. cordata, used a higher proportion of shallow water sources than walnut, thus reducing competition for water in mixed stands.
In addition, the hypothesis is discussed that the more complex stratification of the canopy when walnut trees grew in association with other species might affect the canopy-to-atmosphere interactions with differential effects on 18O values in leaf water from walnut trees in mixed compared to pure plantations.
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