Influence of cyanobacterial inoculants, elevated carbon dioxide, and temperature on plant and soil nitrogen in soybean

Abstract

Climate change affects nitrogen dynamics in crops and diazotrophic microorganisms with carbon dioxide (CO 2 ) sequestering potential such as cyanobacteria can be promising options. The interactions of three cyanobacterial formulations (Anabaena laxa, Calothrix elenkinii and Anabaena torulosa-Bradyrhizobium japonicum biofilm) on plant and soil nitrogen in soybean, were investigated under elevated CO 2 and temperature conditions. Soybean plants were grown inside Open Top Chambers under ambient and elevated (550 ± 25 ppm) CO 2 concentrations and elevated temperature (+2.5-2.8°C). Interactive effect of elevated CO 2 and cyanobacterial inoculation through A. laxa and Anabaena torulosa-B. japonicum biofilm led to improved growth, yield, nodulation, nitrogen fixation, and seed N in soybean crop.Nitrogenase activity in nodules increased in A. laxa and biofilm treatments, with an increase of 55% and 72%, respectively, over no cyanobacterial inoculation treatment. Although high temperature alone reduced soil microbial biomass carbon, dehydrogenase activity, and soil available N, the combined effect of CO 2 and temperature were stimulatory; cyanobacterial inoculation further led to an increase under all the conditions. The highest seed N uptake (758 mg plant −1 ) was recorded with cyanobacterial biofilm inoculation under elevated CO 2 with control temperature conditions. The positive interactions of elevated CO 2 and cyanobacterial inoculation, particularly through A. laxa and A. torulosa-B. japonicum biofilm inoculation highlights their potential in counteracting the negative impact of changing climate along with enhancing plant and soil N in soybean.