Differential associations between nucleotide polymorphisms and physiological traits in Norway spruce (Picea abies Karst.) plants under contrasting water regimes

Norway spruce is an ecologically and commercially important species, which currently suffers from climate change and is expected to decline because of heat and drought stress. A manipulative experiment with drought-stressed and well-watered (control) seedlings was established, comprising five populations of Norway spruce coming from a small territory but distributed along a steep elevational transect from 550 to 1280 m.a.s.l. Plants were phenotyped at physiological traits (content of phytohormones and monoterpenes, chlorophyll a fluorescence, gas exchange and hyperspectral indices) and genotyped using ddRAD sequencing. After filtering, 34 127 polymorphisms (SNPs) were retained and used for analysis. Association tests revealed 42 SNP-variable pairs located across 29 scaffolds exhibiting significant associations, among them 20 were found for drought-stressed seedlings and 22 for control (watered) plants. However, there was no consistency between drought-stressed and control plants, no SNP-trait pair was common for both treatments. The study demonstrated that the identified genotype-phenotype associations can only be interpreted in the context of environmental setup preceding the assessment of phenotypic traits.