Genomic signatures of local adaptation in marram grass highlight the importance of provenance in dune restoration

Coastal sand dunes serve as vital flood defenses and habitats for various endangered species. Marram grass (Calamagrostis arenaria) plays a crucial role in stabilizing shifting sands, particularly in Europe. Despite its ecological significance and popularity in dune restoration, little is known about the genomic factors that enabled its colonization of coastal areas, the extent of local adaptation in existing populations, or the genetic repercussions of restoration efforts.

In a recent study, researchers utilized a chromosome-scale reference genome to shed light on these aspects. The findings reveal that C. arenaria exhibits significant expansions in several gene families associated with coastal adaptation, such as those linked to salinity, drought, and nutrient limitation. By analyzing ddRAD-Seq data from over 200 individuals across ten European populations, scientists discovered strong genetic differentiation between northern and southern populations, a pattern corresponding to known subspecies.

Within the northern European populations, genetic structure predominantly stems from isolation-by-distance. However, the study also detected evidence of non-local planting in a restored Swedish dune system. The introduced plants exhibited genetic distinctiveness from the native population, and both groups showcased reduced genetic diversity.

Furthermore, genome-wide scans for local adaptation in northern European marram grass individuals unearthed outlying genomic regions enriched for genes with functions related to nutrient deficiency, drought, pathogen defense, and other environmental stressors characteristic of coastal dunes. These outlying regions might also encompass genes associated with lignin biosynthesis and culm mechanical strength, potentially reflecting selection on structural properties necessary to endure varying burial and wind exposure regimes.

In summary, these findings underscore the presence of widespread local adaptation in C. arenaria and support the utilization of local provenance in dune restoration and conservation efforts.