Biochemical responses to drought, at the seedling stage, of several Romanian Carpathian populations of Norway spruce (Picea abies L. Karst)

Norway spruce seedlings apparently showing a relatively higher tolerance to drought can be easily selected using a battery of biomarkers such as water content, chlorophyll, and proline levels in the needles, and could be eventually used as an initial screening method in reforestation programmes. 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. 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 (6-week withholding irrigation in the greenhouse) of 1-year-old spruce seedlings originating from several locations in the Romanian Carpathian Mountains. Variations in the levels of the studied photosynthetic pigments, osmolytes, and non-enzymatic antioxidants were detected across the spruce populations. Several of the parameters determined in seedling needles, such as the decrease in water content (nearly 40% reduction in the most sensitive populations), the degradation of chlorophylls, or a low increase of proline levels (up to sevenfold increment in the most sensitive populations but no change in the most tolerant), could be employed as biomarkers for an early assessment of water stress at this stage. Furthermore, seedlings from two of the populations under study responded better to water stress than the other populations and also seemed to be the least affected by osmotic stress during seed germination. Therefore, the determination of these biochemical markers at early seedling stages could represent a useful tool for the initial screening of populations with relatively high tolerance to drought, warranting further research for their potential use in spruce reforestation programmes.