Genetic legacy in soil seedbanks after grassland conversion to plantation forests: evidence from Potentilla freyniana

Semi-natural grasslands in Japan are becoming increasingly scarce due to land-use change and the discontinuation of traditional management techniques like mowing and burning. The conservation of genetic diversity is crucial for the long-term survival of grassland plants, yet the genetic diversity retained in soil seedbanks after converting grasslands to plantation forests is not well understood.

This study examined the genetic diversity and population structure of both above-ground and soil seedbank populations of Potentilla freyniana, a perennial forb, across three sites in each of three land-use types: burned grasslands, deciduous plantation forests, and evergreen plantation forests (established around 21-62 years ago) on the Kaida Plateau in central Japan.

The soil seedbank samples were derived from soil germination experiments, and genetic analysis was performed using newly developed simple sequence repeat (SSR) markers. Genetic diversity was evaluated through expected heterozygosity, allelic richness, and private allelic richness, while population structure was analyzed using analysis of molecular variance, STRUCTURE analyses, and pairwise FST values.

The findings reveal that soil seedbank populations retained genetic diversity levels similar to those of above-ground populations and showed no significant differences between the two population types. Moreover, soil seedbank populations in evergreen plantation forests, lacking above-ground individuals of P. freyniana, maintained genetic diversity comparable to burned grasslands.

Importantly, AMOVA did not detect significant genetic differentiation between above-ground and soil seedbank populations. These results indicate that high genetic diversity can persist in soil seedbank populations for decades following forest establishment and emphasize the potential significance of soil seedbanks as genetic resources for grassland restoration efforts.