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

[EN] 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.This work was partly carried out under the frame of the European Social Fund, Human Resources Development Operational Programme 2007-2013, Project No. POSDRU/159/1.5/S/132765.Schiop, ST.; Al Hassan, M.; Sestras, AF.; Boscaiu, M.; Sestras, RE.; Vicente, O. (2017). Biochemical responses to drought, at the seedling stage, of several Romanian Carpathian populations of Norway spruce (Picea abies L. Karst). Trees. 31(5):1479-1490. https://doi.org/10.1007/s00468-017-1563-1S14791490315Abdul-Baki AA, Anderson JD (1973) Relationship between decarboxilation of glutamic acid and vigour in soybean seed. 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Identification of Salt Stress Biomarkers in Romanian Carpathian Populations of Picea abies (L.) Karst

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.Funding: Sorin Schiop is a PhD student at the University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca. This paper was published under the frame of European Social Found, Human Resources Development Operational Programme 2007-2013, project no. POSDRU/159/1.5/S/132765. Mohamad Al Hassan is a recipient of an Erasmus Mundus pre-doctoral scholarship financed by the European Commission (Welcome Consortium).Schiop, ST.; Al Hassan, M.; Sestras, AF.; Boscaiu Neagu, MT.; Sestras, RE.; Vicente Meana, Ó. (2015). Identification of Salt Stress Biomarkers in Romanian Carpathian Populations of Picea abies (L.) Karst. PLoS ONE. 10(8). doi:10.1371/journal.pone.0135419Se013541910

Total phenolic compounds (TP) (a) and total flavonoids (Fv) (b) levels in seedlings from the seven <i>P</i>. <i>abies</i> populations, after 6-week treatments with the indicated NaCl concentrations.

<p>Means with SD (n = 3). For each population, different lowercase letters above the bars indicate significant differences among treatments and capital letters indicate significant differences among populations undergoing the same treatment, according to the Tukey test (α = 0.05).</p

Electric conductivity (EC_1:5, dS m^-1) of substrate samples after 6-week treatments with the indicated NaCl concentrations, for the seven <i>P</i>. <i>abies</i> populations under study.

<p>Means with SD (n = 3). For each population, different lowercase letters above the bars indicate significant differences among treatments and different capital letters indicate significant differences among populations undergoing the same treatment, according to the Tukey test (α = 0.05).</p

Variation of osmolyte content in seedlings from the seven <i>P</i>. <i>abies</i> populations, after 6-week treatments with the indicated NaCl concentrations.

<p>Changes in (a) proline (Pro) and (b) total solube sugars (TSS). Means with SD (n = 3). For each population, different lowercase letters above the bars indicate significant differences among treatments and capital letters indicate significant differences among populations undergoing the same treatment, according to the Tukey test (α = 0.05).</p

Potassium ion (K⁺) levels in seedlings from the seven <i>P</i>. <i>abies</i> populations, after 6-week treatments with the indicated NaCl concentrations.

<p>Changes in (a) needle and (b) root K⁺ contents. Means with SD (n = 3). For each population, different lowercase letters above the bars indicate significant differences among treatments and different capital letters indicate significant differences among populations undergoing the same treatment, according to the Tukey test (α = 0.05).</p

Geographical location of the origin regions for the seven studied <i>P</i>. <i>abies</i> populations.

<p>Populations are identified by numbers, used throughout the text, as follows: 1- Population Gioristea Calimanut, 2- Population Valea Mare, 3- Population Sudrigiu, 4- Population Basca Mica, 5- Population Albac, 6- Population Paraul Turculet, 7- Population Jepi. Figure modified from the U.S. CIA Romania figures (<a href="https://www.cia.gov/library/publications/the-world-factbook/index.html" target="_blank">https://www.cia.gov/library/publications/the-world-factbook/index.html</a>) and is for representative purposes only.</p

Photosynthetic pigments in the needles of seedlings obtained from the seven <i>P</i>. <i>abies</i> populations, after 6-week treatments with the indicated NaCl concentrations.

<p>Variation in (a) total carotenoids, (b) chlorophyll a and (c) chlorophyll b. Means with SD (n = 3). For each population, different lowercase letters above the bars indicate significant differences among treatments and different capital letters indicate significant differences among populations undergoing the same treatment, according to the Tukey test (α = 0.05).</p

PCA of stress markers measured in <i>P</i>. <i>abies</i> seedlings, in correlation to EC of the substrate at the end of treatments and parental populations' altitude and climatic variables.

<p>Abbreviations: proline (Pro), total sugars (TSS), total phenolics (TP), antioxidant flavonoids (Fv), carotenoids (Caro), chlorophyll a and b (Chla and Chlb), water content (WC%), sodium in roots and needles (Na_r and Na_n), potassium in roots and needles (K_r and K_n), altitude (ELEV), mean annual temperature (TEMP), rainfall (RAIN) and evapotranspiration (EVAPO).</p

Average meteorological data of the populations under study (National Meteorological Administration, Romania, reference period 1994–2013).

<p>Average meteorological data of the populations under study (National Meteorological Administration, Romania, reference period 1994–2013).</p