The effects of light availability on plant-soil interactions and salinity tolerance of invasive tree species, Triadica sebifera

Exotic plant species experience conditions in their introduced ranges that differ from those in their native range. These novel biotic and abiotic environments in the introduced range may force exotic plant species to change their strategies for coping with multiple stresses but empirical evidence about such trend is sparse. Here we conducted a pot experiment in the native range to investigate how the combination of light reduction, soil salinity and soil communities determine the performance of Triadica sebifera populations from native (China) and invasive (US) range. Results indicated that in general salinity reduced seedling survival but reductions were larger in sterilized soils than in active soils. Triadica seedling survival under full light conditions was lower when soil was sterilized or salinity levels were increased while soil sterilization and salinity did not have significant influence on plant survival under shade. The origin of seeds had no influence on the survival of Triadica seedlings but plants from invasive populations produced more biomass than plants from native populations when grown under full light availability while population origin did not influence plant growth in shade. Salinity decreased seedling growth rate and total biomass in full light availability but not in shade. Root:shoot ratio was decreased under shaded conditions but salinity treatments increased root:shoot ratio. Arbuscular mycorrhizal fungi (AMF) colonization was greater for seedlings from invasive populations than for those from native populations, in treatments with increased salinity compared to natural conditions and in full light availability compared to shade. Our results suggest that soil organisms, specifically AMF, can increase plant resistance to salinity. Also, plants from the populations from the invasive range seem to be better adjusted for growing under full light availability than plants from native range. Together our results demonstrate that concerning the complex interactions between plant and abiotic/biotic factors at ecological and evolutionary time scales is essential for understanding the role of these factors in successful species invasions.