Abstract. Plant-soil feedback affects performance and competitive ability of individual plants. However, the importance of plant-soil feedback in historical contingency processes and plant community dynamics is largely unknown. In microcosms, we tested how six earlysuccessional plant species of secondary succession on ex-arable land induced plant-specific changes in soil community composition. Following one growth cycle of conditioning the soil community, soil feedback effects were assessed as plant performance in soil of their own as compared to soil from a mixture of the other five early-successional species. Performance was tested in monocultures and in mixed communities with heterospecific competition from midsuccessional species. The role of soil microorganisms was determined by isolating the microbial component from the soil community, re-inoculating microorganisms into sterilized substrate, and analyzing plant biomass responses of the early-and mid-successional species.Plant-soil feedback responses of the early-successional species were negative and significantly increased when the plants were grown in a competitive environment with heterospecifics. In monocultures, three early-successional species experienced negative feedback in soil with a history of conspecifics, while all early-successional species experienced negative feedback when grown with interspecific competition. Interestingly, the nonnative forb Conyza canadensis showed the weakest soil feedback effect. Biomass production of the earlysuccessional plant species was profoundly reduced by the microbial inocula, most strongly when exposed to inocula of conspecific origin. Molecular characterization of the fungal and bacterial rhizosphere communities revealed a relationship between plant biomass production and the composition of the dominant fungal species. Furthermore, our results show that, in early secondary succession, the early-successional plant species induce changes in the soil microbial community composition that cause historical contingency effects in dominance patterns of mid-succession plant communities.We conclude that feedback between early-successional plant species and soil microorganisms can play a crucial role in breaking dominance of early-successional plant communities. Moreover the influences on soil microorganism community composition influenced plant community dynamics in the mid-successional plant communities. These results shed new light on how feedback effects between plants and soil organisms in one successional stage result in a biotic legacy effect, which influences plant community processes in subsequent successional stages.
In apomictic dandelions, Taraxacum officinale, unreduced megaspores are formed via a modified meiotic division (diplospory). The genetic basis of diplospory was investigated in a triploid (3x ϭ 24) mapping population of 61 individuals that segregated 1:1ف for diplospory and meiotic reduction. This population was created by crossing a sexual diploid (2x ϭ 16) with a tetraploid diplosporous pollen donor (4x ϭ 32) that was derived from a triploid apomict. Six different inheritance models for diplospory were tested. The segregation ratio and the tight association with specific alleles at the microsatellite loci MSTA53 and MSTA78 strongly suggest that diplospory is controlled by a dominant allele D on a locus, which we have named DIPLOSPOROUS (DIP). Diplosporous plants have a simplex genotype, Ddd or Dddd. MSTA53 and MSTA78 were weakly linked to the 18S-25S rDNA locus. The D-linked allele of MSTA78 was absent in a hypotriploid (2n ϭ 3x Ϫ 1) that also lacked one of the satellite chromosomes. Together these results suggest that DIP is located on the satellite chromosome. DIP is female specific, as unreduced gametes are not formed during male meiosis. Furthermore, DIP does not affect parthenogenesis, implying that several independently segregating genes control apomixis in dandelions.
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.
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