Seed–Habitat Thermal Interactions Contribute to the Mosaic Distribution Patterns of Invasive <i>Chromolaena odorata</i> and <i>Ageratina adenophora</i> in South Yunnan, China

ABSTRACT Chromolaena odorata and Ageratina adenophora are invasive species in Southern Yunnan, China, where they demonstrate mosaic distribution patterns. Chromolaena odorata , a tropical species, grows primarily at low latitudes and/or low altitudes, whereas Ageratina adenophora is a temperate species and occurs at higher latitudes and/or higher altitudes. We hypothesised that the thermal interactions between these plants and their habitats contribute to their distribution patterns. To explore this, we investigated how temperature affects various seed traits and performance, including seed viability, high‐temperature tolerance, seed longevity under heat stress, and temperature requirements for germination. Our seed ecology study used seeds of both species collected from three of four provenances: Menglun (ML: low latitude and low altitude in Xishuangbanna), Kongmingshan (KMS: low latitude and high altitude in Xishuangbanna), Pu'er (PE: middle latitude and high altitude), and Kunming (KM: high latitude and high altitude). Laboratory experiments were conducted to investigate changes in seed viability after heating at 40°C for 1–10 days and after heating at temperatures between 30°C and 95°C for 30 min. We also investigated seed germination under constant temperatures ranging from 10°C to 40°C, under daily alternative temperatures with warm periods of up to 21 h at 40°C and under water and NaCl stress up to −1.5 MPa. Our results revealed inter‐ and intraspecific variations in seed high‐temperature tolerance of these two invasive species. Chromolaena odorata seeds exhibited greater tolerance to high temperatures, water, and NaCl stress compared to Ageratina adenophora seeds. Additionally, Chromolaena odorata seeds from low latitudes and/or low altitudes performed better than those from high latitudes and/or high altitudes. Conversely, Ageratina adenophora seeds from high latitudes and/or high altitudes performed better than those from low latitudes and/or altitudes. We conclude that high temperatures might influence the distribution of Chromolaena odorata and Ageratina adenophora by affecting seed development, ageing, and germination in the field, suggesting that the thermal adaptation of these invaders to their habitats plays a key role in their spread.