Autotoxicity of root exudates varies with species identity and soil phosphorus

Root exudate autotoxicity (i.e. root exudates from a given plant have toxic effects on itself) has been recognized to be widespread. Here we examined how plant species identity and soil phosphorus (P) availability influenced this autotoxicity and the possible stoichiometric mechanisms. We conducted an experiment with three species (Luctuca sativa, Sesbania cannabina, and Solidago canadensis), which were subject to four treatments consisting of activated carbon (AC) and soil P. AC addition increased the whole-plant biomass of each species under high P conditions and this AC effect varied strongly with species identity. For Solidago, the relative increase in whole-plant biomass due to AC addition was larger in the low P than in the high P. Root exudate autotoxicity differed between roots and shoots. AC addition decreased root N:P ratios but failed to influence shoot N:P ratios in three species. These findings suggest that soil P enrichment might mediate root exudate autotoxicity and that this P-mediated autotoxicity might be related to root N and P stoichiometry. These patterns and their implications need to be addressed in the context of plant communities.