2.2 Sampling and sample processing
After 7 weeks of growth, we harvested five microcosms per plant diversity level in the PPI experiment and five microcosms per soil legacy level-planted species combination in the PSI experiment (Appendix Table A1 & A2 ). We separated the shoot and root biomass of one randomly selected plant individual per species and microcosm by cutting the plants with scissors. We washed the roots twice under tap water to remove soil particles, and then dried the samples with paper towels. This process took roughly 30 s. All shoot and root samples were then immediately stored in paper bags on dry ice to stop further metabolism. This resulted in a total of 20 shoot and 20 root samples per species and experiment.
After one additional week of herbivory (see above), we harvested the remaining five microcosms per diversity level in the PPI experiment and five microcosms per soil legacy level-planted species combination in the PSI experiment (Appendix Table A1 & A2 ). We sampled the foliar tissue of one randomly selected control and one randomly selected induced plant individual per species and microcosm by cutting the plants ca. 1 cm above the ground. All samples were then immediately stored in paper bags on dry ice. This resulted in a total of 20 control and 20 induced samples per species and experiment.
In the lab, all samples were stored in a -80°C freezer, and subsequently, freeze-dried (LABCONCO FreeZone Plus 12 Liter, Kansas City, USA) for 72 h. Dried samples were stored in zip-lock bags filled with silica gel at room temperature until we had ground each sample to a fine homogenous powder using a ball mill (Retsch mixer mill MM 400, Haan, Germany).