Nodulation of Snowbrush Ceanothus in Three Soilless Substrates1

Snowbrush ceanothus (Ceanothus velutinus Dougl. Ex Hook.) is a broadleaf evergreen shrub. It fixes nitrogen in symbiosis with nitrogen-fixing actinobacteria and plays a crucial role in soil-building. However, the effective induction of nodules in snowbrush ceanothus using soil containing Frankia sp. remains unclear. Therefore, the growth and nodulation of snowbrush ceanothus were investigated in three soilless substrates: calcined clay, peat-based mix, and perlite. Snowbrush ceanothus seedlings were transplanted into containers with calcined clay, peat-based mix, or perlite, and inoculated with 30 mL of native soil. Seedlings were grown for establishment in the first month and then harvested every two weeks to check for nodules. The results showed that nodules formed on seedlings’ roots approximately four months after the inoculation of native soil. Interestingly, nodulation was more pronounced in seedlings grown in calcined clay compared to those in a peat-based mix and perlite. Notably, the substrates exhibited impacts on shoot dry weight, root dry weight, and leaf area. Seedlings grown in a peat-based mix had significantly greater shoot dry weight, root dry weight, and leaf area than those grown in calcined clay or perlite. Further investigation is necessary to explore the role of substrate composition on the nodulation and growth of snowbrush ceanothus. Species used in this study: Ceanothus velutinus Dougl. Ex Hook., Frankia sp.