White lupin (Lupinus albus L.) exposed to elevated atmospheric CO2 requires additional phosphorus for N2 fixation
James B. O’Sullivan, Jian Jin, Caixian Tang
Abstract
Abstract Purpose The steady rise of atmospheric CO 2 concentrations enhances symbiotic N 2 fixation and plant growth. However, it is largely unknown whether more P is required to enhance N 2 fixation under elevated CO 2 . We examined if plants under elevated CO 2 require more P to support enhanced N 2 fixation. Methods White lupin ( Lupinus albus L. cv. Kiev) was grown in nutrient solution under ambient (380 ppm) and elevated (700 ppm) CO 2 levels at 0, 2, 5, 12, 25 and 50 µM P. Nodulation, nodule function, N 2 fixation and plant growth were assessed at 4 and 6 weeks post inoculation. Excess cation uptake and proton release were also analysed due to its importance in P acquisition. Results Elevated CO 2 increased the critical P concentration in nutrient solution for N 2 fixation, indicating plants under elevated CO 2 need to acquire additional P to support greater N 2 fixation. Elevated CO 2 improved N 2 fixation in P-deficient plants by increasing specific nitrogenase activity. Elevated CO 2 also enhanced excess cation uptake which increased proton release by roots. Conclusions As elevated CO 2 increased the plant demand for P, it increased the critical P concentration in nutrient solution for N 2 fixation, thereby plants require more P to mitigate the effect of P deficiency on N 2 fixation. Despite this, elevated CO 2 could enhance N 2 fixation in P-limiting environments.