Range expanding plant species establishing in the new range: are the effects on native plant communities determined by soil biota?

Current climate warming has brought about range expansion of plants, animals, and microor-ganisms to higher altitudes and latitudes. Range shifts of plant species are well documented, but we still know little about the ecological consequences, for example how the establishment of range-expanding plant species influences native plant communities. Plants are living in close association with aboveground and belowground higher trophic level organisms. Research has shown that soil organisms can have major impact on plant community dynamics, but relatively little is known about their role in community organization following plant range expansion. As plants disperse faster than soil organisms, range-expanding plants may in their new range be released from their natural enemies, but also from symbionts and decomposer organisms. How-ever, with time soil organisms may also disperse over long distances and expand their ranges but so far, no studies have investigated how this may influence plant community dynamics in the new range. We established a greenhouse experiment to examine (i) how the addition of range-expanding plant species affects the performance of native plant species and (ii) how range expansion of soil organisms influences plant community composition in the new range. Eight plant individuals, consisting of plants from distinctive ecological strategies (range-expand-ing plants, native plant species, and their combination), were grown in 7l mesocosms, which were inoculated with different soil communities (sterile soil, soil community from the original range, new range or a mixture of the original and new range). After 14 weeks of growth, plants were harvested, dried and weighed. Our results show that the addition of range-expanding plant species increases the productivity of plant communities in the new range. However, the effect of range-expanding plant species depends on their relativeness to the native plant community: range-expanders that have no closely related plant species in native plant communities sup-press the growth of native plants, whereas range-expanders with closely related species in the native plant community have no negative effect. Interestingly, the effect of soil communities differed also between these two types of range-expanding plants and also between individual species. We will discuss more specific responses in the presentation.