Phosphorus addition severely exacerbates the inhibitory effect of the increased diurnal temperature range on the invasive plant Solidago canadensis.

This study investigates how variations in diurnal temperature and phosphorus concentration affect the growth of native Artemisia argyi and invasive Solidago canadensis under intraspecific and interspecific competition. We conducted factorial experiments to assess the impacts of warming, including an increased diurnal temperature range (DTRinc), a symmetric increase in diurnal temperature range (DTRsys), a decreased diurnal temperature range (DTRdec) and phosphorus application (5 g and 10 g P m² yr^-1) on both intra- and inter-specific competition among plants. The results indicated that (1) the DTRsys for A. argyi was -48.95% and for S. canadensis, it was -31.49% and overall had a more pronounced inhibitory effect on the biomass of both plant species than other warming treatments after comprehensive analysis. (2) Under intraspecific competition, phosphorus promoted the growth of A. argyi and S. canadensis on plant height, root length, and biomass. The biomass of A. argyi (22.75% and 53.61%) and S. canadensis (11.49% and 27.76%) increased under low and high phosphorus, respectively. Under interspecific competition, the plant height and biomass of the two plant species showed different response trends to phosphorus. Still, the competitiveness of S. canadensis increased compared with the untreated group. (3) Plant adaptability in biomass was more sensitive to warming than phosphorus treatments, and warming reduced the promoting effect of phosphorus, indicating that warming and phosphorus have interactive effects on plants. Phosphorus exacerbated the inhibitory effect of DTRinc on the biomass of S. canadensis, which was more pronounced than other warming methods. The different responses of the two plants mention the species to warming and phosphorus treatments under different competition scenarios reflect the differences in their ecological strategies for adapting to the environment.