Co-planting vascular and nonvascular boreal species to promote belowground biomass on mine-impacted substrates

Species interactions play a critical role in structuring early revegetation communities and co-planting may help to promote species interactions that facilitate plant establishment. However, further research is needed to predict outcomes from co-planting and to identify the conditions that elicit facilitative interactions among boreal species. We evaluated the influence of co-planting on aboveground and belowground biomass and root:shoot ratios of four boreal vascular plants ( Picea glauca, Salix discolor, Chamerion angustifolium, Calamagrostis canadensis) using two greenhouse trials. The vascular co-planting trial involved vascular species grown in pairs under mean decadal precipitation conditions. The nonvascular co-planting trial consisted of vascular species grown with or without moss mats ( Ceratodon purpureus) under decadal mean maximum or minimum precipitation conditions. In the vascular co-planting trial, P. glauca and Chamerion angustifolium showed variable biomass responses to co-plant identity while S. discolor and Calamagrostis canadensis were unresponsive. In the nonvascular co-planting trial, moss mats were associated with higher volumetric water content 48 and 72 h post-watering and P. glauca exhibited increased belowground biomass under the minimum water regime. Our results suggest that responses to vascular co-planting are species-specific and that soil moisture may mediate belowground biomass responses of P. glauca to nonvascular co-planting.