The effects of soil biota and fertilization on the success of Sapium sebiferum.
Soil organisms can have important impacts on the structure, diversity, and invasion potential of plant communities. In particular, the short co-evolutionary history of non-native plants with soil biota could confer unusual benefits or costs to hosts in the introduced range with consequences for invasion success. We used parallel pot and field studies to examine how soil biota (active or sterilized soil) and fungicide (addition or control) affected the growth and survival of the invasive, non-native tree, Sapium sebiferum, and three co-occurring native tree species Liquidambar styraciflua, Nyssa sylvatica, and Quercus nigra in the Big Thicket National Preserve in east Texas, USA. In addition, because plant interactions with soil microbes vary with abiotic factors, we also included a fertilization treatment. The aboveground and belowground biomass of all species were higher in the presence of an active soil biotic community than in sterilized soil. Sapium alone showed more than additive growth increases under the combination of both field active and fertilized soils. It was also the only species to maintain high aboveground biomass and high aboveground nitrogen levels under those conditions. The high levels of arbuscular mycorrhizal colonization found on Sapium compared to natives suggest that arbuscular mycorrhizas may be involved in this phenomenon. These results indicate that belowground soil organisms provide unusual positive benefits to the invader that are not experienced by native species. This benefit may increase Sapium growth rates compared to natives in the forest understorey and therefore facilitate Sapium invasion into mesic temperate forests currently experiencing high levels of anthropogenic nutrient inputs.