Plants can produce and release allelochemicals to interfere with the establishment and growth of conspecific and interspecific plants. Such allelopathy is an important mediator among plant species in natural and managed ecosystems. This review focuses on allelopathy and allelochemicals in grasslands and forests. Allelopathy drives plant invasion, exacerbates grassland degradation and contributes to natural forest regeneration. Furthermore, autotoxicity (intraspecific allelopathy) frequently occurs in pastures and tree plantations. Various specialized metabolites, including phenolics, terpenoids and nitrogen-containing compounds from herbaceous and woody species are responsible for allelopathy in grasslands and forests. Terpenoids with a diversity of metabolites are qualitative allelochemicals occurring in annual grasslands, while phenolics with a few specialized metabolites are quantitative allelochemicals occurring in perennial forests. Importantly, allelochemicals mediate below-ground ecological interactions and plant–soil feedback, subsequently affecting the biodiversity, productivity and sustainability of grasslands and forests. Interestingly, allelopathic plants can discriminate the identity of neighbors via signaling chemicals, adjusting the production of allelochemicals. Therefore, allelochemicals and signaling chemicals synergistically interact to regulate interspecific and intraspecific interactions in grasslands and forests. Allelopathy and allelochemicals in grasslands and forests have provided fascinating insights into plant–plant interactions and their consequences for biodiversity, productivity and sustainability, contributing to our understanding of terrestrial ecosystems and global changes.

The improvement in yield in cultivar mixtures has been well established. Despite increasing knowledge of the improvement involving within-species diversification and resource use efficiency, little is known about the benefits arising from relatedness-mediated intraspecific interactions in cultivar mixtures. This study used a relatedness gradient of rice cultivars to test whether neighbor relatedness contributes to improvements in grain yields in cultivar mixtures. We experimentally demonstrated the grain yield of rice cultivar mixtures with varying genetic relatedness under both field and controlled conditions. As a result, a closely related cultivar mixture had increased grain yield compared to monoculture and distantly related mixtures by optimizing the root-to-shoot ratio and accelerating flowering. The benefits over monoculture were most pronounced when compared to the significant yield reductions observed in distantly related mixtures. The relatedness-mediated improvement in yields depended on soil volume and nitrogen use level, with effects attenuating under larger soil volumes or nitrogen deficiency. Furthermore, neighbor relatedness enhanced the richness and diversity of both bacterial and fungal communities in the rhizosphere soil, leading to a significant restructuring of the microbial community composition. These findings suggest that neighbor relatedness may improve the grain yield of rice cultivar mixtures. Beneficial plant–plant interactions may be generated by manipulating cultivar kinship within a crop species. A thorough understanding of kinship strategies in cultivar mixtures offers promising prospects for increasing crop production.

Reseeding is widely used to restore degraded grasslands, but the extent to which restoration outcomes depend on grass–legume species combinations remains unclear. We conducted a two-year field experiment in a degraded semi-arid grassland in Inner Mongolia, China, using two grasses (Elytrigia elongata and Bromus inermis) and two legumes (Caragana microphylla and Lespedeza davurica) reseeded as monocultures or grass–legume mixtures. Reseeding resulted in higher vegetation cover than the unseeded control across all treatments, whereas biomass responses depended on species combination, with B. inermis + L. davurica showing the highest mean biomass and cover in both years. Most reseeding treatments reduced Shannon–Wiener and Simpson diversity, whereas E. elongata + C. microphylla maintained both indices at levels comparable to the unseeded control. Legume-containing treatments consistently increased soil total N, ammonium nitrogen, nitrate N, and microbial biomass N, while available P and microbial biomass C increased across all reseeding treatments. Vegetation productivity was positively associated with soil nutrient availability and microbial biomass but negatively associated with plant diversity. Overall, reseeding promoted early vegetation and soil recovery, but grass–legume mixtures were not universally superior to monocultures. These findings suggest that B. inermis + L. davurica may be preferred for rapid vegetation recovery, whereas E. elongata + C. microphylla may be considered when maintaining plant diversity is a priority.