Low soil temperature reduces the positive effects of high nutrient supply on the growth and biomass of white birch seedlings in ambient and elevated carbon dioxide concentrations

To investigate the interactive effects of soil temperature (T soil ) and nutrient supply on the responses of growth and biomass of white birch ( Betula papyrifera Marsh.) to atmospheric carbon dioxide concentration ([CO 2 ]), seedlings were grown under two [CO 2 ] (360 and 720 µmol·mol –1 ), three T soil (5, 15, and 25 °C initially, increased to 7, 17, and 27 °C one month later), and three nutrient regimes (Low: N–P–K = 4:1.8:3.3 mg·L –1 ; Intermediate: N–P–K = 80:35:66 mg·L –1 ; and High: N–P–K = 160:70:132 mg·L –1 ) for 4 months. Low T soil reduced leaf and total biomass at high nutrient supply and root biomass at intermediate and high nutrient supply. There were significant three-factor interactive effects on root collar diameter (RCD), stem biomass, and leaf mass ratio. Low T soil reduced RCD at high nutrient supply and stem biomass at intermediate and high nutrient supply in elevated [CO 2 ] while intermediate and high T soil enhanced them. Values of leaf mass ratio were lowest at low T soil and low nutrient supply in elevated [CO 2 ]. The effect of T soil was generally insignificant at low nutrient supply, but the responses of growth and biomass remained significantly higher under high than low nutrient supply at all T soil .