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.

Norway spruce is a native European coniferous species distributed from the Carpathian Mountains and the Alps to northern Scandinavia. In the coming decades, spruce forests will need to cope with increasing climate changes which are already threatening their natural habitats. European forest policy should adapt to the changing climate by deploying drought-tolerant genotypes in regions expected to experience increased stress in the future. To identify reliable water stress biomarkers in this species, which may be eventually used to select populations responding better to forecasted drought events, we studied the physiological responses to severe water stress treatments of spruce seedlings originating from several locations in the Romanian Carpathian Mountains. Oneyear old seedlings were denied irrigation for six weeks in order to generate severe water stress in controlled conditions. Variations in the levels of the studied photosynthetic pigments, osmolytes, and non-enzymatic antioxidants were detected across the spruce populations. Several of the determined parameters in seedling needles, such as the decrease in water content (nearly 40% decrement in the most sensitive studied populations), the degradation of chlorophylls, or a low increase of proline levels (up to seven-fold increment in the most sensitive populations in comparison to no change in the most tolerant ones), could be employed as biomarkers for an early assessment of water stress at this stage. Furthermore, seedlings from two of the populations under study (Sudrigiu and Gioristea-Calimanut) apparently responded better to water stress than the other populations, as shown by their lower reduction in needle water content, no degradation of chlorophyll a and carotenoids, and less proline accumulation, suggesting a relatively higher 2 resistance to drought. These populations also seemed to be the least affected by osmotic stress at the seed germination stage. Therefore, we consider that the use of biochemical markers of stress at early seedling stages could represent a useful tool for the initial screening of populations that have relatively high tolerance to drought, warranting further research for potential use in reforestation.