Role of allelopathy during invasion process by alien invasive plants in terrestrial ecosystems

Biological invasion is causing serious current biodiversity loss in different parts of the world and involves different stages: introduction, establishment, naturalization, and fast dispersion outside the normal ranks. Invasion may cause a reduction in abundance of native species or the elimination of populations of a particular species. Exotic species have to surpass different biological filters to get to be invaded in a new habitat. Importance of allelopathy in the invasion process may include the release of secondary chemical metabolites into the surrounding environment to inhibit the seedling establishment and other ecophysiological attributes of native biota. Temperature, drought, cold, association, and feedback from soil microorganisms can also adversely affect the biological nutrient cycle, and other aspects that can favor the invading capacity of exotic species. Environmental problems generated by invading species can become serious in naturally protected and sensitive areas, where climatic circumstances may evolve in the shape of global warming. The purpose of this chapter is to highlight the role of allelopathy during the invasion process with special emphasis to ecophysiological relationships between exotic and native plants, and soil microorganisms.