The influence of physical soil conditions on the formation of root nodules of Melilotus officinalis in the montane zone of Rocky Mountain National Park

Exotic invasion is a key threat to native biological diversity, second only to habitat degradation. Melilotus officinalis is an exotic species that thrives in areas of anthropogenic disturbances and low nutrient availability. Typically, natural disturbance facilitates native species establishment and maintains species diversity; however, anthropogenic disturbance facilitates exotic species establishment. M. officinalis functions as a competitor in the montane communities because of its symbiosis with Rhizobium bacteria, a symbiosis that allows the plant to acquire nitrogen. Although the ability to fix nitrogen permits M. officinalis to grow in nitrogen depleted soils, the soil must have a microclimate that is favorable to symbiosis and nodulation. We analyzed abiotic soil characteristics in Rocky Mountain National Park to determine if nodulation was related to soil texture, as well as in the mid-range level of soil and temperatures. We found that nodules on plant specimens showed a positive correlation with soil moisture and temperature, and occurred in a specific range of moderate moisture and temperature. Soil texture was not correlated to nodule formation.