Effect of nutrient conditions on root nodule development in <i>Alnus japonica</i>

Abstract

The morphology and structure of nodules on the exotic tree alder Alnus japonica (Thunb.) Steud. inoculated with the North American Frankia strain HFPArI 3 were examined under different nutrient conditions. Seedlings were subjected to a nitrogen, phosphorus, or iron stress treatment using the Ingestad nutrient addition technique which generally produced a decrease in the length of healthy endophytic vesicle cluster zones. External nodule morphology varied according to treatment, with thicker nodules developing under "good" nutrient conditions. Nodule meristems showed apparent apical dominance under conditions of nutrient stress. Increased additions of inorganic nitrogen reduced the levels of nitrogen fixation and increased cortical cell size but reduced the numbers of endopytic vesicles per unit area. High nitrogen fixation levels were accompanied by the formation of numerous large mitochondria in nodule pericycle cells.