Positive feedback of riparian soil microbes on the growth of invasive Solidago canadensis from riparian and non-riparian habitats

Abstract

There is increasing evidence that patterns of local adaptation to abiotic conditions in plants may be mediated by soil microbes. The alien plant Solidago canadensis increasingly invades riparian habitats, where it can even grow in waterlogged areas. However, whether S. canadensis is locally adapted to waterlogging in its non-native range, and whether soil microbes mediate this, has not yet been investigated. We measured the size of S. canadensis plants in riparian and non-riparian habitats at three locations in China. Then we grew offspring of these plants for 52 days in a full factorial greenhouse experiment under waterlogged, drought or intermediate conditions, and with soil microbes that either came from the riparian or non-riparian habitat. In the field, riparian S. canadensis plants grew less tall and had thinner stems than non-riparian ones. In the greenhouse experiment, riparian plants produced on average less biomass than non-riparian plants, and biomass production was on average higher at intermediate water availability than under drought and waterlogged conditions. Moreover, plants produced on average more biomass when grown with riparian instead of non-riparian soil microbes. However, the positive effect of riparian soil microbes was not found for riparian plants in the waterlogging treatment, and for non-riparian plants in the drought treatment. In conclusion, although our results indicate that riparian and non-riparian S. canadensis plants are genetically differentiated with regard to biomass production during the 52 days of our experiment, these data do not provide support for local adaptation to waterlogged conditions. Furthermore, as riparian soil microbes increased biomass production of both the riparian and non-riparian S. canadensis plants, there was also no evidence for local adaptation to the local soil microbes.