Root physiological responses can explain the effects of short-term plant-plant interactions on growth of two subalpine coniferous species

The functional traits of roots play an important role in nutrient acquisition in plants, which affects the outcome of plant-plant interactions. However, few studies have comprehensively investigated the plastic responses of plant root traits to plant-plant interactions. A pot experiment was conducted to quantify the effects of intraspecific and interspecific interactions on seedling growth and on multiple root traits of two coniferous species, Picea asperata Mast. and Abies faxoniana Rehd. et Wils. The results showed that plant-plant interactions changed the root physiology of these two species but had no effect on the morphological, architectural, and biotic traits of their root system. Intraspecific interaction resulted in lower root nitrogen content and stronger resource competition than interspecific interaction. Under intraspecific interaction, P. asperata had lower root vigor and nitrate reductase activity, which impeded the acquisition and utilization of the limited resources, and thus resulted in marginally decreased total biomass, where the total biomass for A. faxoniana was not significantly affected. Under interspecific interaction, the high total biomass of A. faxoniana could be explained by rhizosphere interactive effects and reduced metabolic (carbon and nitrogen) costs due to lower root exudative outputs. Our results demonstrate that root physiological responses can explain the effects of short-term plant-plant interactions on plant growth.