Genotype-Dependent Soil Legacy of Woodland Strawberry (Fragaria vesca L.) on Plant Growth and Herbivore Resistance

Plant genotypes can vary in multiple functional traits due to adaptation to heterogenous environments. However, whether such variation can extrapolate to effects on soils and further on performance of subsequent plants, thus generating a genotypic variation in soil legacy, remains unclear. In this study, we studied how plant genotypic variation impacts soil legacy when exposed to aboveground insect herbivores. We used 11 wild genotypes of woodland strawberry (Fragaria vesca L.) experimentally exposed to leaf beetles (Galerucella tenella) to condition live soil. We then replaced the conditioning plants with naïve plants to examine soil legacy effects on growth and resistance on the subsequent plant genotype (referred to as the focal genotype) against the generalist herbivore Spodoptera littoralis. This allowed us to test the extent to which plant genotypic variation in soil legacy is altered by aboveground herbivory. We found an overall positive soil legacy effect of woodland strawberry, indicated by 69.9% higher belowground biomass of the subsequent focal genotype grown in conditioned soil compared to in unconditioned soil. We also observed a genotype-dependent soil legacy effect on performance of S. littoralis indicated as relative growth rates reduced by 37.9% on the subsequent focal genotype in soil conditioned by the focal genotype itself compared to by other genotypes, though the legacy effect was cancelled out when conditioning genotypes were exposed to G. tenella herbivory. A genotypic variation was further detected in soil legacy on the efficiency of conversion of ingested food by S. littoralis caterpillars feeding on the focal genotype. However, the genotypic variation was only present when the focal genotype was excluded from the conditioning genotypes at the exposure of G. tenella herbivory. Collectively, our study shows a conditional plant genotype-dependent soil legacy effect on herbivore resistance (measured as herbivore performance) rather than on plant growth, and the magnitude of the legacy effects depends on both the identity of the conditioning genotypes and the measures of the herbivore resistance. The findings of this study provide new insights into how plant genotypes or herbivory affects soil feedback on plant growth and herbivore resistance.