Presence of Bradyrhizobium sp. under continental conditions in Central Europe

Soil samples from different locations with varied cultivation histories of soybeans were taken from arable fields in 2018 in East Germany and Poland (Lower Silesia) to evaluate the specific microsymbionts of the soybean, Bradyrhizobium japonicum, over the years after inoculation. Soybean was grown in the selected farms between 2011 and 2017. The aim of the experiment is to investigate whether there is a difference in rhizobia content in soils in which soybean was grown over a different period of time and whether this might lead to differences in plant growth of soybean. The obtained soil samples were directly transferred into containers, then sterilized soybean seeds were sown into pots in the greenhouse. After 94 days of growth, the plants were harvested and various parameters such as nodular mass, number of nodules and dry matter in the individual plant parts were determined. In addition, the relative abundance of Bradyrhizobium sp. in soil samples was determined identified by sequencing. No major decline in Bradyrhizobia could be observed due to a longer interruption of soybean cultivation. Soil properties such as pH, P and Mg content had no significant influence on the formation of nodule mass and number, but seem to have an influence on the relative abundance of Bradyrhizobium sp. The investigations have shown that Bradyrhizobium japonicum persists longer in arable soils even under the site conditions of Central Europe and forms an effective symbiosis with soybeans.