Little was known about the light and temperature requirements for germination of Ficus species that grow in different habitats. On the basis of differences in the gap and understory environment in Xishuangbanna, Dr. Chen Hui of Xishuangbanna Tropical Botanical Garden (XTBG) and his teachers investigated the effects of temperature and red:far-red light (R:FR ratio) on seed germination of two gap-demanding species (Ficus hispida and Ficus racemosa) and two shade-tolerant species (Ficus altissima and Ficus auriculata) in a tropical seasonal rainforest in Xishuangbanna, southwest China.
Daily alternating regimes were selected to simulate the range of daily temperature fluctuations that would occur in the understory versus those in gaps of varying sizes. A R:FR ratio gradient was created by filtering fluorescent light through polyester filters. Four temperature treatments were used to test the effect of temperature on seed germination of the four Ficus tree species across the R:FR gradient.
Their study found that seeds of the four Ficus species were positively photoblastic. Seed germination of F. hispida and F. racemosa was not affected across the R:FR ratio gradient (0.25–1.19) at 25/35°C, but it was inhibited under low R:FR at 22/23°C. By contrast, germination percentages of F. altissima and F. auriculata were not inhibited along the entire light gradient in all temperature treatments.
Their study suggested a new mechanism by which understory temperature could interact with a low R:FR ratio to restrict seed germination of gap-demanding species to gaps. The mechanism could contribute to spatial niche differentiation of species and to their adaptive strategies for habitat preferences in tropical rainforests.