Effect of plant allelochemicals on seed germination and its ecological significance

As a form of plant interaction, allelopathy plays a critical role in agriculture and forestry production, including biological invasion, continuous cropping obstacle and weed suppression. Consequently, it is important to guide production if we take advantage of plant allelopathy in crop production. Seed germination is a key stage of a plant and the regulatory mechanism of this physiological process by allelopathy has been paid more and more attention. Numerous studies demonstrated that allelochemicals could promote or inhibit seed germination of different plant species, which had an important influence on the plant growth and development, the composition and distribution of plant communities and the balance within the ecosystem. In this review, the effect of allelochemicals on seed germination and its ecological significance were summarized. On the one hand, the physiological and biochemical mechanisms underlying the inhibition effect of allelochemicals on seed germination were summarized. For example, allelochemicals restrained seed germination through inhibition of radicle and hypocotyl elongation. Allelochemicals also hindered seed germination by damaging subcellular structures, disturbed the synthesis and metabolism of both phytohormones and reactive oxygen species (ROS). Furthermore, allelochemicals delayed seed germination by mediating metabolism of protein, oil and starch, which provide energy during seed germination. On the other hand, we discussed the ecological significance of allelochemicals to seed germination from two perspectives, weeds control of farmland and ecosystem stabilization. Here, we summarized the effects of allelochemicals on weed suppression in natural settings, autotoxicity in agriculture and forestry, and biological invasion caused by allelopathy. Finally, based on current research progresses, future research directions in the field of allelopathy and autotoxicity were proposed and discussed.