Assessing the effect of genetic diversity on the early establishment of the threatened seagrass Posidonia australis using a reciprocal-transplant experiment

Two common goals for restoration are rapid plant establishment and long-term plant persistence. The success of transplanted populations may be jeopardized if the donor transplants are not genetically diverse, and/or poorly matched to their new environment. Here, we test the effects of local adaptation and plot-level genetic diversity on the early establishment phase of a threatened seagrass species, Posidonia australis, by performing a reciprocal transplant experiment across two genetically and geographically distinct populations in southeastern Australia. Posidonia australis is a long-lived, slow-growing species that has no seed bank, and the successful transplantation of live shoots and seedlings is the only available restoration method. Our results show a strong effect of local adaptation and genetic diversity on P. australis survivorship and performance over the first 6 months following transplantation. High-genetic diversity plots displayed higher survival rates and exhibited reduced productivity and increased carbohydrate reserves within the rhizome. This suggests that high-diversity plots included shoots that were conserving energy stores by actively reducing growth rates during the early stages of transplantation. The lowest diversity plots exhibited high leaf and root productivity and corresponding low carbohydrate reserves. This may be a sign of stress in the low-diversity transplants, potentially explaining the very low survival rate. We suggest that future restoration efforts source donor transplants from multiple local sources to ensure both local adaptation and sufficient genetic diversity to increase the likelihood of early establishment success