Litter thickness limits the seed germination and seedling growth of <i>Rhododendron</i> plants

Litter is considered a major constraint that affects the sexual reproduction and regeneration of populations of <i>Rhododendron</i> seedlings. In this study, we analyzed the effects of litter accumulation and its allelopathy on the regeneration potential of four <i>Rhododendron</i> species, and investigated the impacts of different litter amounts and coverage methods on <i>Rhododendron</i> 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 <i>Rhododendron</i> reached its maximum value when the amount of litter was between 200 and 400 g/m² . The seeds of four species of <i>Rhododendron</i> began to germinate between days 7 and 8 of the experiment. The duration of germination for the four <i>Rhododendron</i> 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 <i>Rhododendron</i>. The litter extract inhibited the germination of <i>Rhododendron decorum</i> and <i>Rhododendron delavayi</i> at 2 mg/mL of extract, while it promoted the germination of <i>Rhododendron irroratum</i> and <i>Rhododendron agastum</i> seeds. Therefore, the presence of litter under <i>Rhododendron</i> shrubs in Northwest Guizhou Province, China, likely reduces the germination of the populations of <i>Rhododendron</i> and may limit their renewal through sexual reproduction. Thus, this study suggests that the presence of litter under <i>Rhododendron</i> shrubs in Northwest Guizhou Province may significantly limit their reproduction by seeds.