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Biotic plant-soil interactions and land-use intensity are known to affect plant individual fitness as well as competitiveness and therefore plant-species abundances in communities. Therefore, a link between soil biota and land-use intensity on local abundance of plant species in grasslands can be expected. In two greenhouse experiments, we investigated the effects of soil biota from grassland sites differing in land-use intensity on three grass species that vary in local abundances along this land-use gradient. We were interested in those soil-biota effects that are associated with land-use intensity, and whether these effects act directly or indirectly. Therefore, we grew the three plant species in two separate experiments as single individuals and in mixtures and compared their performance. As single plants, all three grasses showed a similar performance with and without soil biota. In contrast, in mixtures growth of the species in response to the presence or absence of soil biota differed. This resulted in different soil-biota effects that tend to correspond with patterns of species-specific abundances in the field for two of the three species tested. Our results highlight the importance of indirect interactions between plants and soil microorganisms and suggest that combined effects of soil biota and plant-plant interactions are involved in structuring plant communities. In conclusion, our experiments suggest that soil biota may have the potential to alter effects of plant-plant interactions and therefore influence plant-species abundances and diversity in grasslands.
Sphagnum magellanicum Brid. is a worldwide distributed peat moss and an ecosystem-engineer in temperate and boreal bog ecosystems suggesting a great adaptive potential to different environmental conditions. Phenotypes of S. magellanicum have been described as one species so far, although this has been questioned by the detection of several genetic groups in a recent global study. Concordant with morphological uniformity, our analyses of Mid-to Northern European plants revealed only minimal variation in nuclear nrITS and plastid rps4 sequences. However, we detected two distinct genetic groups within Europe by analyzing microsatellite data of 298 individuals from 27 populations. Plants formed an Eastern and a Western European cluster, with overlapping areas in northern Germany and southern Sweden where plants of both clusters coexist within populations but show no signs of admixture. These two cryptic taxa seem therefore to be reproductively isolated. Bayesian analyses indicated that reproductive isolation occurred before the end of the late Pleistocene glaciations. After the meltdown of the glaciers, both clusters colonized northern and central Europe from glacial refugia in the West and possibly from Euro-Siberian populations. To test for divergent adaptation to environmental conditions, we exposed plants of both clusters to experimental climate warming treatments at two different plant-diversity levels (monocultures vs. mixtures) for two years. Despite their different evolutionary history, plants of both genetic clusters responded equally to climate treatments in our southern common garden near Potsdam, Germany. However, only eastern cluster populations benefited from plant-community diversity and increased their biomass in mixtures. These differences in their ecological niche match the diverging microhabitat preferences observed in situ and may effectively hamper genetic exchange if distances between microhabitats are too large for Sphagnum sperm movement. (C) 2017 Elsevier GmbH. All rights reserved.