how does the nitrogen fixation occur in those plants which do not have root nodules

Under nitrogen - limiting conditions, capable plants form a symbiotic relationship with a host-specific strain of bacteria known as rhizobia. This process has evolved multiple times within the legumes, as well as in other species found within the Rosid clade..... Nitrogen fixation Inthe nodule is very oxygen sensitive.

Under nitrogen-limiting conditions, capable plants form a symbiotic relationship with a host-specific strain of bacteria known as rhizobia. This process has evolved multiple times within the legumes, as well as in other species found within the Rosid clade. Nitrogen fixation in the nodule is very oxygen sensitive.