The role of seed provenance in the early development of Arbutus unedo seedlings under contrasting watering conditions

In the last decades, several studies have reported the increase of land degradation and desertification in the Mediterranean Basin. Depending on degradation severity, ecological restoration might be needed in order to promote ecosystem recovery. The ecology of the selected species and intra specific variability should be considered in order to improve restoration options, especially facing climate change.The present study tested the hypothesis that seedlings from drier provenances would be better adapted to low water content conditions. Seeds were germinated under controlled temperature after which seedlings were grown in a phytotron under two contrasting watering regimes. Seedling performance was analysed using morphological and physiological parameters.Low water content had a clear negative effect on the seedlings' aboveground biomass (total dry weight, root collar diameter, leaf dry weight and leaf weight ratio) and a positive effect on belowground biomass (root weight and root:shoot ratio). This response was not unequivocal, since provenances differed in morphological adaptations to low water content. Seedlings from the wettest provenance revealed a higher relative growth rate under high water content but a poor adaptation to limited water availability when compared to the other two provenances. This was observed by the absence of a significant belowground investment in this provenance. Seedlings from the wettest provenance also presented a significant reduction of total leaf area that was not observed in the other two provenances. This can however be hardly considered as a successful adaptation to cope with drought since this provenance produced less sclerophyllous leaves, less belowground biomass and also lower sapwood to leaf area ratio independently from the water content conditions. By contrast, seedlings from the dry provenance with the hottest summer had similar root collar diameter, leaf dry weight and physiological performance under both watering regimes.The observed adaptations to water regimes seem to be related with the climate of the seed source and highlighted the importance of seed provenance in ecological restoration actions using Mediterranean species. This knowledge could improve early establishment success predictions for different plant populations, allowing more reliable and cost-effective management decisions under climate change scenarios.

The authors are grateful to ICNB for the permission to harvest seeds in the Portuguese territory and also to Diana Vieira, Xufeng Shen and Mariana Pedro for their kind help in seed harvesting. We also want to acknowledge the University of Alicante and CEAM for providing the conditions to perform the experiment and Banc Llavors Forestalls (Valencia, Spain) for giving informations related with the germination requirements of A. unedo. Finally, we are especially grateful to Miriam Heredia, Sara Ferrer, Cristina Adam, Francesca Villa, Gara Oriana, Samantha Ruiz, Imre van Hal and Sara Alcañis for their laboratory support and to Juan Bellot for lending the load cells. We would also like to thank the two anonymous reviewers for their comments on the manuscript.

published