Root Variation in Common Gardens: Divergent Responses in Native and Nonnative Field Sites of an Annual Ruderal Mediterranean Plant

Abstract

Premise of research. Root traits of annual plants are known to vary across environmentally manipulated conditions in controlled settings. Roots absorb nutrients and water, essential for individual function and survival. Yet how ruderal plant populations respond belowground to spatial and temporal variation in field conditions is largely unknown. The present study examines the natural variation of root traits and survival among populations of the annual Arabidopsis thaliana across gardens along a fertility gradient. Methodology. We established common gardens in field settings and in raised beds in the plant’s native and nonnative ranges using populations of A. thaliana from western/central Spain. Survival through the growing season and root traits were investigated for garden and population influences and for the relationship between survival and root biomass. Pivotal results. We demonstrate differences in survival among gardens, populations, and years. Survival was highest in the higher-fertility gardens in the native and nonnative ranges. We detected plasticity (among gardens and between years) of root length, lateral root production, primary root length, and biomass. Roots were substantially larger when grown in the more fertile gardens, where water and nutrients were consistently available. Yet lateral root production was also high in a low-fertility field garden. We detected substantial among-population variation in root traits in the higher-fertility gardens. Conclusions. This study demonstrates among-population variation in root traits in field gardens and substantial root plasticity measured across locations. Evidence of local adaptation was indicated by native local populations showing the highest survival and root growth in the home native garden. Such differences in survival and root functional trait responses inform how plants respond to dramatic changes in environmental conditions, particularly in novel sites. We advocate for additional studies of belowground traits to further uncover the extent of natural variation in root phenotypic responses in the field.