Abstract: Precipitation seasonal distribution and intensity have been significantly changed according to the forecast on global precipitation pattern. To explore how the precipitation seasonal distribution affects the growth and root morphology of seedlings in a tropical secondary forest, a precipitation simulation experiment with three treatments, delay wet season (DW), wetter wet season (WW), and control (CT, ambient precipitation), was established in Dianbai District, Maoming City of Guangdong Province, to address the responses of root morphological traits of different function-type seedlings (N-fixing and non-N-fixing) to the changes in precipitation seasonal distribution. The results showed that WW treatment significantly increased fine root length, surface area, volume, biomass, and specific root length (SRL) of the seedlings of the five species. WW treatment significantly decreased fine root length and SRL, and coarse root SRL of Cinnamomum camphora. WW treatment significantly increased coarse root length, surface area, volume, and biomass of Syzygium hancei, and significantly increased coarse root volume and average diameter of Acacia auriculiformis. WW treatment significantly increased fine root length, surface area, volume, and biomass of two N-fixing tree species (Cassia siamea and A. auriculiformis), and increased fine root average diameter of C. siamea. Additionally, WW treatment significantly increased fine root length of S. hancei, coarse root volume of S. jambos, and fine root biomass of C. camphora and S. hancei. DW treatment had minor effects on root morphological traits. It significantly decreased coarse root length of C. camphora, coarse root surface area of A. auriculiformis, SRL of C. camphora fine root and S. jambos coarse root; increased the coarse root volume and average diameter of S. hancei, coarse root volume of C. siamea, and coarse average diameter of S. jambos. N-fixing species had higher root biomass and volume under DW and WW treatments than under CT. These results suggest that the roots of five species can be tolerant to drought (delayed wet season) to some extent. Fine roots are more sensitive to WW treatment than coarse roots. WW treatment has greater effects on fine root morphology of N-fixing tree species rather than non-N-fixing tree species, indicating that N-fixing tree species are more adaptable to abnormal rainfall. Root morphology of understory seedlings in tropical secondary forest can well adapt to the changes of seasonal distribution of rainfall, with consequence on community regeneration and stability.

Key words: precipitation pattern, root morphology, seedling regeneration, tropical secondary forest, global change