| Oaks (Quercus L), the temperate-zone forest tree species and the most commercially important hardwood genus, are widely distributed across Asia, Europe, North America and Africa. However, over several decades, numerous scientists have observed a failure in natural regeneration of oaks. 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 usually exhibit delayed germination. In order to show biological characteristics in oak seed developmental process, find the reasons for delayed and uneven germination and the effecial methods, using Q. variabilis, Q. wutaishanica, Q.×fangshanensis, Q.mongolica, Q. aliena var. acuteserrata, Q. fabri, Q. palustris, Q, aliena and Q.robur as the materials, the changes among different morphological indices and nutrient indices of seeds in development process, the effects of different mechanical treatments on seed germination and growth, and the effects of methanol extracts, at the concentration level1.0and0.5g·ml-1methanol, of embryo, cotyledon and pericarp and five extraction phases on germination of Beassica campestris L. seeds and its growing were studied. The results were showed as followed.(1) The changes among different morphological indices of Q.×fangshanensis, Q. aliena var. acuteserrata, Q. acutissima, Q. wutaishanica and Q. aliena seeds in developmental process showed that the seed mass and volume increased sharply before the end of August; seed length and diameter rapidly grew until the middle of September, then the indices tended towaeds stability. The pericarp thickness decreased continurously with the seed development process, and differences were existed in three parts of pericarp.(2) The moisture content of five oak seeds decresed in the seed developmental process, however, when seed matured, the moisture contents were still high. The moisture contents of Q.×fangshanensis, Q. aliena var. acuteserrata, Q. wutaishanica, Q. acutissima and Q. dentate seeds were39.0%、33.8%、38.0%、37.7%and31.1%, respectively, which illustrates that the oak seeds do not experience dehydration process, which is the property of recalcitrant seed. According to the changes of dry weight, physiologica] maturities were determined:physiological maturity of Q. aliena var. acuteserrata and Q. acutissima was the end of September, that of Q. Xfangshanensis was the end of August to the first third of September, and that of Q. wutaishanica and Q. dentate was the middle of September.(3) Soluble protein, soluble sugar and starch contents in embtyo and cotyledon of Q. X fangshanensis seeds increased first then decreaed, and were up to maximum at the first third of August, the middle of August and the end of August, respectively. Soluble protein contents in embtyo and cotyledon of Q. aliena var. acuteserrata gradually decreaed, while soluble sugar contents in embtyo and cotyledon first increased then decreased and finally increased, and were up to maximum at the middle of September. Starch contents in embtyo and cotyledon of Q. aliena var. acuteserrata increased first then decreaed, and were up to maximum at the end of August.(4) Effects of different mechanical treatments on seeds were studied. These included:a control (CK), removal of cup scar (RS), removal of pericarp (RP), removal of pericarp and1/2of the cotyledon (HC) and removal of pericarp and2/3cotyledon (TC) on acorn germination of Q. variabilis, Q. wutaishanica and Q.robur acorns and pericarp thickness. The results showed that①RP and HC treatments significantly decreased root and shoot mean germination time, increased rooting and shooting germination percentage, improved root and shoot synchronization and vigor indices of the three species acorns, and improved root and shoot length of Q.robur acorns;②the acorns from TC treatment had significantly shorter root and shoot mean germination time, the highest root and shoot synchronization index for all three species, higher rooting and shooting percentage of Q. variabilis and Q.robur acorns and greater root and shoot vigor of Q.robur acorns than those from CK. However, no significant difference was detected in shooting percentage of Q. wutaishanica, root and shoot vigor index of Q. variabilis and Q. wutaishanica acorns, root length and shoot height of Q. variabilis and Q. wutaishanica oak acorns between TC and CK;③RS significantly reduced root and shoot mean germination time of the three species, but root and shoot synchronization and vigor indices, rooting and shooting germination percentage, and root and shoot length of acorns from RS had no significant difference compared with those from CK(5) The effects of methanol extracts, at the concentration level1.0and0.5g·ml-1methanol, of embryo, cotyledon and pericarp and five extraction phases on germination of Beassica campestris L. seeds and its growing were studied bu using the systematic solvent extraction and bioassay method. The results showed that①the germination percentage, shoot and root length of B. campestris seeds watered by1.0g·ml-1methanol extracts from embryo, cotyledon and pericarp of Q. variabilis, Q. aliena var.acuteserrata, Q.mongolica, Q. palustris and Q. acutissima seeds were significantly lower than those from control, and the inhibitory effect of germination rates gradually decreased, and0.5g·ml-1methanol extracts from embryo, cotyledon of Q. variabilis acorns reduced the germination percentage of B. campestris seeds, while no significant difference was detected in germination percentage of B. campestris seeds between those from pericarp of all tree species acorns and the control;②Methanol extracts from embryo, cotyledon and pericarp of Q.robur and Q. Xfangshanensis remarkably reduced shoot and root length of B. campestris seeds, but little response in germination percentage;③The inhibitory effect of methanol extracts from embryo, cotyledon and pericarp declined in turn, with higher concentration of methanol extract having stronger inhibitory intension for each section of seeds;④The inhibitory strengthen of extraction phase of methanol among5extraction phases, was larger than that of extraction phase of ethyl acetate, resulting in the lowest germination rate, shoot or root length of B. campestris seeds, meanwhile, negative effects was observed in other extraction phases. The fact of extracted substances having stronger inhibitiory effect on the length of root and shoot than on the germination percentage of B. campestris, indicating that the inhibitors of oak seeds mainly restrict germination of root and shoot themselves, which could be the cause of the irregular germination.Our studies show that the mechanical restrain of pericarp and cotyledon, embryo, and pericarp having inhibitors are both the reasons for delayed and uneven germination of oak seeds. And removing pericarp and cutting off1/2of cotyledon can effectively accelerate germination and regular seedling, which have an important actual significance in oak seedling. |
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