Background and Aims
Changes in root-zone Ca2+ concentration affect a plant's performance under high salinity, an issue poorly investigated for Mediterranean xerophytes, which may suffer from transient root-zone salinity stress in calcareous soils. It was hypothesized that high-Ca2+ supply may affect differentially the response to salinity stress of species differing in their strategy of Na+ allocation at organ level. Phillyrea latifolia and Pistacia lentiscus, which have been reported to greatly differ for Na+ uptake and transport rates to the leaves, were studied.
In plants exposed to 0 mm or 200 mm NaCl and supplied with 2·0 mm or 8·0 mm Ca2+, under 100 % solar irradiance, measurements were conducted of (a) gas exchange, PSII photochemistry and plant growth; (b) water and ionic relations; (c) the activity of superoxide dismutase and the lipid peroxidation; and (d) the concentration of individual polyphenols. Gas exchange and plant growth were also estimated during a period of relief from salinity stress.
The performance of Pistacia lentiscus decreased to a significantly smaller degree than that of Phillyrea latifolia because of high salinity. Ameliorative effects of high-Ca2+ supply were more evident in Phillyrea latifolia than in Pistacia lentiscus. High-Ca2+ reduced steeply the Na+ transport to the leaves in salt-treated Phillyrea latifolia, and allowed a faster recovery of gas exchange and growth rates as compared with low-Ca2+ plants, during the period of relief from salinity. Salt-induced biochemical adjustments, mostly devoted to counter salt-induced oxidative damage, were greater in Phillyrea latifolia than in Pistacia lentiscus.
An increased Ca2+ : Na+ ratio may be of greater benefit for Phillyrea latifolia than for Pistacia lentiscus, as in the former, adaptive mechanisms to high root-zone salinity are primarily devoted to restrict the accumulation of potentially toxic ions in sensitive shoot organs.