Abstract1. Most studies on plant-soil feedback (PSF) and plant competition measure the feedback response at one moment only. However, PSFs and competition may both change over time, and how PSF and competition interact over time is unclear.2. We tested the temporal dynamics of PSF and interspecific competition for the forb Jacobaea vulgaris and the grass Holcus lanatus. We grew both species individually and in interspecific competition in soil that was first conditioned in the greenhouse by J. vulgaris, by H. lanatus or without plant growth. For a period of 11 weeks, we harvested plants twice a week and analysed the fungal and chemical composition of the different soils at the end of the first and second growth phase.3. During the second growth phase, when grown in isolation, both species produced more biomass in heterospecific conditioned soil than in conspecific conditioned soil. Young J. vulgaris exhibited a strong negative conspecific feedback, but this effect diminished over time and became neutral in older plants. In contrast, when grown in competition, the negative conspecific feedback of J. vulgaris exacerbated over time. Older H. lanatus plants benefited more from heterospecific conditioning when competing with J. vulgaris, then when grown isolated.4. Fungal community composition and soil chemistry differed significantly between soils but this was mainly driven by differences between plant-conditioned and unconditioned soils. Remarkably, at the end of the second growth phase, fungal community composition was not explained by the legacy of the species that had been grown in the soil most recently, but still reflected the legacy of the first growth phase. We reexamined plant growth during a third growth phase. Biomass of J. vulgaris was still influenced by the treatments imposed during the first phase, while H. lanatus responded only to the plant growth treatments imposed during the second phase. 5. Synthesis. Our study shows that the direction and magnitude of PSF depends on plant age and competition, and also on soil legacy effects of earlier plant growth.These results highlight the need to incorporate dynamic PSFs in research on plant populations and communities.This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

Summary1. Many studies that provided evidence for a positive relationship between plant diversity and productivity have proposed that this effect may be explained by complementarity among species in resources utilization, or selection of particularly productive species in high-diversity plant communities. Recent studies have related the higher productivity in diverse plant communities to suppression of pathogenic soil biota. If soil biota plays a role in diversity-productivity relationships, the question remains about how they may influence complementarity and selection effects. 2. Here we examine how complementarity and selection effects may depend on soil biota using a plant-soil feedback approach. We used monocultures and mixtures of early successional plant species, which are known to have mostly negative plant-soil feedback effects, and mid-successional plant species, which generally have neutral plant-soil feedback. 3. We found that plant-soil feedback effects differed between monocultures and mixed plant communities, as well as between early and mid-successional plants. This resulted in a significant interaction effect between diversity and successional stage. In monocultures, plant-soil feedback tended to be negative for early and positive for mid-successional plant species. Interestingly, the community feedback responses of the mixed communities were opposite, being positive for early and negative for mid-successional community. 4. Plant-soil feedback differentially affected complementarity and selection effects of early and midsuccessional plant communities: it enhanced complementarity effects of early and decreased selection effects of mid-successional species. 5. Synthesis. Soil biota that drive plant-soil feedback effects can influence the diversity-productivity relationship not only through decreased biomass production in monocultures compared to mixtures, but also through influencing complementarity and selection effects among species in mixed plant communities. Our results reveal that biodiversity-productivity relationships depend on plant-soil feedback interactions, which depend on the successional position of the plant. We propose that including successional position and trait-based analyses of plant-soil feedback in diversity-functioning studies will enhance understanding consequences of biodiversity loss for productivity and other ecosystem processes.

Please cite this article as: Jing, J., Bezemer, T. M., and van der Putten, W. H.,Interspecific competition of early successional plant species in ex-arable fields as influenced by plant-soil feedback, Basic and Applied Ecology (2015), http://dx.Abstract 14 Plant-soil feedback can affect plants that belong to the same (intraspecific feedback) or 15 different species (interspecific feedback). However, little is known about how intra-and 16 interspecific plant-soil feedbacks influence interspecific plant competition. Here, we used 17 plants and soil from early-stage ex-arable fields to examine how intra-and interspecific plant-18 soil feedbacks affect the performance of ten conditioning species and the focal species, 19 Jacobaea vulgaris. Plants were grown alone and in competition in both conditioned and 20 control soils. Overall, plant-soil feedback of the ten plant species influenced the 21 competitiveness of J. vulgaris more strongly than their own competitiveness. However, 22 effects depended on species combination: competitiveness of J. vulgaris was significantly 23 enhanced by interspecific plant-soil feedback from Anthoxanthum odoratum, Agrostis 24 capillaris, and Trifolium dubium, and significantly decreased by interspecific feedback from 25 Achillea millefolium. Intraspecific feedback from Taraxacum officinale and A. odoratum 26 decreased their competitiveness with J. vulgaris. There was a positive relationship between 27 the strength of interspecific feedback and competitiveness of J. vulgaris in conditioned soil. 28 Multiple linear regression showed that the competitiveness of J. vulgaris in conditioned soil 29 was determined by interspecific feedback and competitiveness of neighbour plants. The 30 positive relationship between interspecific feedback and competitiveness in control soil 31 suggests that the soil feedback effect of the competing species on J. vulgaris can build up 32 quickly during competition. We conclude that the effect of plant-soil feedback on interspecific 33 competition may be due to either legacy effects of plant species previously colonizing the soil, 34 or immediate interspecific feedback of the competing plant species via the soil. Therefore, our 35 results suggest that plant-soil feedback can influence interspecific plant competition through a 36 multitude of intra-and interspecific plant-soil interactions both from predecessors, and from A c c e p t e d M a n u s c r i p t

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