Soil microbes and nutrient inputs influence root nodulation and tree performance in Alnus glutinosa Raw sequence reads

In this study we investigate the impact of microbial communities, characteristic of young and mature forests, and available N and P concentrations on F. alni nodulation associated to the roots of A. glutinosa. A mesocosm experiment was established where nodule biomass and tree performance were evaluated by growing trees in the presence or absence of F. alni, after inoculating them with bacteria, fungi and bacteria + fungi, cultured from the soils of young (~10 years old) and mature (>=100 years old) forests. Furthermore, microbes were isolated from the roots of some trees to test individual interactions between isolates, F. alni and A. glutinosa. To investigate the impact of available nutrient concentrations on root nodule density, trees were grown in sterilized soil, across gradients of increasing available N (NH4NO3) or P (KH2PO4) and in the absence or presence of F. alni. We hypothesized that community cultures of bacteria + fungi from mature forests would decrease nodulation and plant performance. We also expected that an increase in available N would lead to a decrease in nodule biomass, while an increase in available P will stimulate nodulation. Finally, we expect that adding high P to high N will potentially stimulate nodule biomass growth through a reduction in the soil N/P ratio compared to fertilizing with just high N.