The negative effects of soil microorganisms on plant growth only extend to the first weeks

Soil biotic communities can strongly impact plant performance. In this paper, we ask the question: how long-lasting the effect of the soil microbial community on plant growth is. We examined the plant growth rates at three stages: early, mid and late growth. We performed two growth experiments with Jacobaea vulgaris, which lasted 49 and 63 days in sterilized soil or live soil. In a third experiment, we examined the effect of the timing of soil inoculation prior to planting on the relative growth rate of J. vulgaris with four different timing treatments. In all experiments, differences in biomass of plants grown in sterilized soil and live soil increased throughout the experiment. Also, the relative growth rate of plants in the sterilized soil was only significantly higher than that of plants in the live soil in the first two to three weeks. In the third experiment, plant biomass decreased with increasing time between inoculation and planting. Overall, our results showed that plants of J. vulgaris grew less well in live soil than in sterilized soil. The negative effects of soil inoculation on plant mass appeared to extend over the whole growth period but arise from the negative effects on relative growth rates that occurred in the first weeks.