Effects of mechanical treatments on seed germination of Quercus fabri Hance

Oaks germinate asynchronously under natural conditions and the difference between first and last germinating acorns can be up to a few weeks. In addition, acorns of the subgenus Erythrobalanus usually exhibit delayed germination. The epicotyls germinate 20 days later than the roots. Thick tap roots of Quercus aliena seed grow down several centimeters into the soil instead of a green shoot in the fall. These characters of acorns negatively affect the quality of seedlings. In the past several decades, some feasible practices and associated mechanisms have been published for some oak species in Europe, North America and Asia. And the researches advanced that removing pericarp or cutting parts of cotyledons increased germination percentage and accelerated germination. Although, the previous studies dealt with acorn germination and seedling emergence, the root and seedling development were little understood, especially root development. To solve the problems of delayed and irregular germination of Q. fabri seeds, acorns were mechanically treated in five ways: CK (without any mechanical treatment), cup scar removal (RS), pericarp removal (RP), pericarp removal and half cotyledon cutting (RHC), pericarp removal and 2/3 cotyledon cutting (RPC). Treated acorns were placed onto petri dishes (11.5 cm diameter) with filter paper moistened by distilled water under 25 ℃ and 8 hours light. As acorns germinated (when the length of radicle was longer than acorn length), root and shoot emergence were investigated every seven days. The length of all roots and shoots were measured at the end of the experiment (137 days). Germination percentage, vigor index, mean germination time and synchronization index of roots and shoots were calculated to probe delay and irregular germination of Q. fabri seeds. The results showed that: (1) The mean root germination time of RP and RHC were respectively 39 d and 36 d shorter, while the mean shoot mean germination time of the two treatments were 52 d and 51 d shorter than that of CK, respectively. The root synchronization indices of RP and RHC were respectively 0.3 and 0.2 higher, and the shoot synchronization indices of the two treatments were all 0.4 greater than that of CK. RP and RHC significantly increased rooting percentage (both 57.8% higher) and sprouting percentage (both 33.3% higher). RP improved root length (3.0 cm longer). (2) Compared with CK, RP and RPC treatments significantly decreased mean root and shoot germination time of Q. fabri seeds by 36 d and 50 d, respectively. Both treatments significantly increased root and shoot synchronization indices by 0.2 and 0.4, and rooting percentage by 26.7% over CK. However, the srpouting percentage, root length and shoot height had no significant difference from those of CK. (3) RS significantly reduced the mean root and shoot germination time by 16 d and 21 d, respectively, compared with CK. No significant differences were detected in root and shoot synchronization indices, rooting and sprouting percentage, root length and shoot height between RS and CK treatments. Therefore, RP and RHC treatments effectively accelerated germination and regulated seedling growth, which had an important actual significance in Q. fabri seedling growing.