Litter thickness limits the seed germination and seedling growth of Rhododendron plants

Litter is considered a major constraint that affects the sexual reproduction and regeneration of populations of Rhododendron seedlings. In this study, we analyzed the effects of litter accumulation and its allelopathy on the regeneration potential of four Rhododendron species, and investigated the impacts of different litter amounts and coverage methods on Rhododendron seed germination through indoor pot experiments. The results showed that low amounts of litter promoted the rate of emergence of seedlings, while high amounts of litter inhibited this process. The rate of emergence of Rhododendron reached its maximum value when the amount of litter was between 200 and 400 g/m² . The seeds of four species of Rhododendron began to germinate between days 7 and 8 of the experiment. The duration of germination for the four Rhododendron species ranged from 8 to 11 days. Extracts from different decomposition layers of litter had a "suppressive" effect or a "low promotion and high inhibition" effect on the germination rates of four species of Rhododendron. The litter extract inhibited the germination of Rhododendron decorum and Rhododendron delavayi at 2 mg/mL of extract, while it promoted the germination of Rhododendron irroratum and Rhododendron agastum seeds. Therefore, the presence of litter under Rhododendron shrubs in Northwest Guizhou Province, China, likely reduces the germination of the populations of Rhododendron and may limit their renewal through sexual reproduction. Thus, this study suggests that the presence of litter under Rhododendron shrubs in Northwest Guizhou Province may significantly limit their reproduction by seeds.