Plant-plant interactions like competition or facilitation between seedlings can have profound implications on their establishment and posterior development. These interactions are variable and depend upon the presence of neighbouring plants and environmental factors. In this work, we studied the effects of the interaction by the roots of Eucalyptus urophylla seedlings from a population under various environmental stressful conditions: water deficit, nutrient deficit, low light, low temperature, and high temperature. To evaluate it, we measured some growth and morphological parameters. We demonstrated that shoot parameters such as the number of leaves, leaf area, and dry weight of the leaves were the most affected parameters due to the belowground plant-plant interaction under various environmental conditions. We did not find evidence for competition among the plants, especially under restrictive conditions. Therefore, the study corroborates the stress-gradient hypothesis, which states that plants' differences under stressful conditions lead to facilitative interactions. It has implications for plant ecology and forestry techniques.
Keywords: Eucalyptus; Plant-plant interaction; ecology; facilitation; forestry; plant cognition; self/nonself discrimination; split-root.