Direct Effects on Seed Germination of 17 Tree Species Under Elevated Temperature and CO₂ Conditions

Effects on seed germination characteristics of 17 tree species were investigated under elevated temperature and CO₂. Seeds of 5 needle-leaf and 12 broad-leaf species were germinated under four conditions: 24°C + 400 μmol CO₂ mol air^-1, 24°C + 750 μmol CO₂ mol air^-1, 27°C + 400 μmol CO₂ mol air^-1, and 27°C + 750 μmol CO₂ mol air^-1. The elevated temperature and CO₂ affected germination percent (GP) of 7 tree species seeds.GPs of Pinus densiflora, P. thunbergii, Betula ermanii, and Maackia amurensisseeds were affected by the elevated temperature, while only that of P.jezoensis seed was influenced by the elevated CO₂. GPs of Malus baccata and Zelkova serrataseeds were influenced by both the elevated temperature and CO₂. In addition, the elevated temperature and CO₂also affected mean germination time (MGT) of 12 tree species seeds. Particularly, MGTs of P. thunbergii and Rhododendron tschonoskii seeds were influenced by both factors. In conclusion, elevated temperature and CO₂ affected seed germination characteristics, which were reflected by significant differences among tree species. Specifically, these two factors exerted stronger influence on germination pattern such as MGT rather than seed germination percent.