Identification of Salt Stress Biomarkers in Romanian Carpathian Populations of Picea abies (L.) Karst.

Abstract

The Norway spruce (Picea abies), the most important tree species in European forests, is relatively sensitive to salt and does not grow in natural saline environments. Yet many trees are actually exposed to salt stress due to the common practice of de-icing of mountain roads in winter, using large amounts of NaCl. To help develop strategies for an appropriate use of reproductive seed material on reforestation sites, ensuring better chances of seedling survival in salt-affected areas, we have studied the responses of young spruce seedlings to salt treatments. The specific aim of the work was to identify the optimal salt stress biomarkers in Picea abies, using as experimental material seedlings obtained by germination of seeds with origin in seven populations from the Romanian Carpathian Mountains. These responses included general, conserved reactions such as the accumulation of ions and different osmolytes in the seedlings needles, reduction in photosynthetic pigments levels, or activation of antioxidant systems. Although changes in the contents of different compounds involved in these reactions can be associated to the degree of stress affecting the plants, we propose that the (decreasing) levels of total phenolics or total carotenoids and the (increasing) levels of Na+ or K+ ions in Picea abies needles, should be considered as the most reliable and useful biomarkers for salt stress in this species. They all show very high correlation with the intensity of salt stress, independently of the genetic background of the seeds parental population, and relatively easy, quantitative assays are available to determine their concentrations, requiring simple equipment and little amount of plant material.

Effects of Drought and Salinity on European Larch (Larix decidua Mill.) Seedlings

“…Similar behaviour has been reported in Larix laricina [50] and Picea abies [27], highlighting the importance of maintaining relatively high K + concentrations in the needles, as a mechanism to withstand, to a certain degree, the deleterious effects of salt stress in trees of the Pinaceae family.…”

“…A decrease in chlorophylls a and b, and in total carotenoids as well, has been reported in different coniferous species subjected to salt and drought treatments [27,[52][53][54]. We have also detected a reduction in the mean values of the needle contents of these pigments, but the differences with the control were only statistically significant for the salt stress treatment, indicating that under the experimental conditions used, European larch is more sensitive to salinity than to drought.…”

“…Nevertheless, in (relatively) salt-resistant genotypes of some crop species, Na + compartmentalisation in leaf vacuoles may also contribute to salinity tolerance [59]. Salinity caused the accumulation of high concentrations of Na + and Cl − in L. decidua roots and needles, as reported for other coniferous species [27,60,61]. When comparing ion levels between roots and needles, no differences were observed in Na + contents (in terms of DW), neither in control nor in salt-stressed seedlings; regarding Cl − , its concentration was slightly (but significantly) higher in needles than in roots, again in both non-stressed and salt-stressed seedlings.…”

“…Control plants were watered twice a week with 125 mL of water per plant, whereas for the salt treatment, the same volume of a 150 mM NaCl solution was used. This concentration was selected according to our previous experience on coniferous species [27] and some preliminary experiments on L. decidua seedlings, as a non-lethal salt treatment causing measurable inhibitory effects on seedling growth. Before watering, for removing the salt that may accumulate on the bottom of the trays, these were washed and dried.…”

“…Measurement of morphological parameters to estimate the degree of stress-induced growth inhibition is, therefore, the most straightforward and convenient approach to quantitatively assess the effect on plants of abiotic stress conditions, including water deficit or high soil salinity. In species of very slow growth, such as conifers and many other woody species, lengthy treatments are required to detect the effects of the applied stress [27]. However, among Pinaceae, Larix decidua is considered as a fast-growing tree [7].…”