Temperature and hydrology shape germination strategies of wetland Carex achenes with pericarp manipulation

Under the dual influences of global change and anthropogenic activities, wetland ecosystems are experiencing significant degradation, which directly affect the achenes germination and regeneration strategies of dominant wetland plants such as Carex species. As keystone species in wetlands, Carex achenes possess complex dormancy mechanisms, and their germination responses to environmental cues are crucial for wetland restoration. This study investigated the germination responses of Carex schmidtii and Carex limosa achenes, with and without pericarp removal, under two hydrological status (flooding and non-flooding) and four temperature regimes (5/28 °C, 16/28 °C, 5/35 °C, and 22 °C). Germination percentage, mean germination time (MGT), and germination synchronicity (SYN) were measured. Results showed that germination occurred only under fluctuating temperatures but not at constant temperatures. The pericarp removal treatment i.e. dehulled achenes exhibited higher germination percentages at the fluctuating temperatures under flooding conditions. Hydrological status significantly influenced the final germination percentage of C. limosa, which peaked at 16/28 °C. The C. schmidtii demonstrated a higher germination percentage and a broader temperature range for germination than C. limosa. Both species demonstrated high germination synchronicity under optimal hydrothermal conditions. The hydrothermal conditions in late summer provide an optimal window for sowing dehulled achenes of C. schmidtii and C. limosa to enhance their population establishment and support wetland restoration efforts.