Abstract
We reported the results of an isotopic study aimed at evaluating the medium to long-term effects of different water qualities and
deficit irrigation strategies on the ecophysiology of grapefruit in a 7-year-old plantation in SE Spain. For a better understanding
of the interaction between nitrogen and salts from reclaimed water, RW, an experiment using natural abundance (δ) of 15N was
conducted. This study showed that in grapefruit crop irrigated with RW leaf δ15N value increased. We concluded that: (i) causal
links exist between leaf δ15N isotope and salt stress: positive correlation between values of this isotope and leaf salt content was
showed; (ii) excess of nitrates provided by the reclaimed irrigation water were lost in the ecosystem through leaching,
denitrification, etc., enriching the medium with δ15N and increasing δ15N values in plants. Therefore, the results of this study
highlight the key role that salt content from RW can play in N uptake by plants and, hence, isotopic discrimination of leaf N.
Consequently, it has been demonstrated the usefulness of isotopic discrimination measure to predict crop sustainability in the
medium to long term when using water sources of different quality combined with deficit irrigation strategies.