Responses of secondary compounds in plant foliage to feedback effects of selective removal of soil biota

Secondary metabolites are crucial for plant defenses. To explicitly understand plant responses in secondary metabolites to altered soil legacy effects is important for plant-soil feedback interactions. In this study variable groups of soil inocula extracted from soil conditioned by Jacobaea vulgaris were inoculated into sterilized soil, to examine influences of different soil biomes on the composition and concentration of pyrrolizidine alkaloids (PAs). The results showed that legacy of the proceeding J. vulgaris condition greatly altered both composition and concentration of PAs, leading to relatively poor plant performances. Selective removal of soil biota via filtration reduced the total concentration of PAs and changed the composition of PAs in the succeeding conspecifics. By decreasing the complexity of soil biota, it consecutively increased total biomass of succeeding J. vulgaris. However, the increase was offset when soil fungi was sieved out as well as plant root-shoot ratio and specific leaf area which were also decreased by exclusion of soil fungi. In particular, spectral reflectance analysis of succeeding plant leaves also indicated soil fungi may mainly determine chemical distribution of conditioned plant tissues. These results suggested that fungi may be a major group of soil organisms that are responsible for the changes in PA profiles and plant growth. Our study establishes a new approach to studying ecological functions of different groups of soil biota in plant-soil feedback interactions. It also showed that impacts of soil legacy on plant secondary metabolites can be selectively removed via fractionation of soil biota.