Soil feedbacks in northern ecosystems invaded by non-native plants

Abstract

Invasions by non-native plants are a widespread and serious problem throughout temperate regions, but boreal and tundra ecosystems are relatively less invaded. Northern range limits of invaders may be set by environmental or biotic barriers, resulting in poorer plant performance, but these barriers are not well understood. Churchill, Manitoba (58.8°) represents a unique site for northern invasion research, where over a hundred non-native plants have been recorded. Although many have persisted for decades in human-disturbed areas, almost none have spread into nearby boreal forests and tundra ecosystems. Reasons these non-natives have failed to spread remain unclear.

 

An understudied barrier to invasions might lie in the soil. Native plants may be cultivating a soil community that inhibits non-native plants, limiting their potential spread out of human-disturbed areas. To investigate this, we collected soil from sites around Churchill invaded by the non-native Linaria vulgaris, and from uninvaded control sites. We then planted L. vulgaris in soil inoculated with live or sterilized field-collected soil. Serial soil inoculations were performed for a second and third generation, and plant growth, survival, and biomass were compared between soil treatments and generations.

 

Results do not suggest that uninvaded soils are less hospitable for L. vulgaris. Average plant biomass and mortality did not differ between soil treatments, though biomass was reduced in subsequent generations of live soil, while mortality increased. This suggests that non-native plants do not modify soil microbiota or nutrient content to their own benefit, and natives do not cultivate soil that is inhibitory to invaders.