• Strong site effects observed for specific leaf area • Little variation between sites for stomatal density • Confirmation of potentially adaptive SNPs Heat and drought are increasingly affecting forest ecosystems. Also, European beech ( Fagus sylvatica L.) showed growth decline in large parts of its distribution area. Therefore, a better understanding of drought-related traits as well as the identification of suitable provenances for future environmental conditions is necessary. In this study, we investigated specific leaf area (SLA), stomatal density, phenological traits, and growth (diameter at breast height (dbh)) in a trial comprising multiple German and Belgian European beech provenances replicated at two different sites in Germany. We combined trait measurements (ca. 1,900 trees), climatic data, SNP genotyping (41 markers, some of them previously identified as candidate markers in an independent GWAS) and environmental association analysis, to assess differences in the mentioned traits as well as to identify SNPs potentially involved in adaptation. SLA differed markedly between the two sites, indicating strong local effects under our test conditions. Stomatal density varied little between sites. Bud burst timing showed moderate differentiation among provenances, whereas leaf senescence and growing season length showed weak provenance effects. Climatic transfer effects (i.e., trait responses to the difference between climate at provenance origin and climate at the trial site) were detected for bud burst, dbh, and leaf senescence. Moreover, bud burst in 2022 was consistently delayed in provenances originating from warmer climates (higher mean annual temperature) at both trial sites. SNP-trait associations revealed two significant loci that were significant after multiple-testing correction, including an intronic SNP in a gene potentially related to electron transport. This SNP was previously significant in an environmental association study in European beech. Our results showed substantial trait variability, which could contribute to short-term acclimation, but require confirmation in multi-site trials. Maintaining genetic diversity is an important management strategy to promote long-term adaptation under environmental change.
Müller et al. (Sun,) studied this question.