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AbstractDelayed and uneven germination of acorns has a negative effect on seedling quality and yield in seedlings. To address this issue, the effects of different mechanical treatments were studied, including a control (CK), removal of cup scar (RS), removal of pericarp (RP), removal of pericarp and 1/2 of the cotyledon (HC) and removal of pericarp and 2/3 cotyledon (TC), on the germination of Quercus variabilis, Q. Wutaishanica and Q. Robur acorns and pericarp thickness. The results showed that (1) RP and HC treatments significantly decreased root and shoot mean germination time, increased rooting and shooting germination percentage, and improved the root and shoot synchronization and vigor indexes of the three species’ acorns; (2) the acorns from the TC treatment significantly reduced root and shoot mean germination time and significantly induced the root and shoot synchronization index for all three species; and (3) the RS treatment significantly reduced the root and shoot mean germination time of the three species.
Therefore, RP and HC treatments can effectively accelerate germination and regular seedling, which are important in the propagation of Q. Variabilis, Q.
Wutaishanica and Q. Robur seedlings. Even and quick germination help reduce acorn predation. IntroductionDue to their richness in proteins and carbohydrates, acorns are very attractive to animals as a food source and suffer heavy predation by a number of consumers.
It is well documented that resistance and tolerance to biotic and abiotic stresses are alternative defense strategies for plants. Tree SpeciesDBH (cm)Plant height (m)Clear bole height (m)Crown width EW/NS (m)Quantity (kg)Acorn maturity timeQ. Variabilis29124.57.5/6.210late AugustQ. Robur268.03.26.0/5.210mid-SeptemberAfter collection, acorns were soaked in water, and all those still floating after 5 min were considered nonviable and removed (, ). The remaining acorns were air dried and stored in 5-ml (0.127 mm) polyethylene bags, which are permeable to carbon dioxide and oxygen, but largely impermeable to moisture , under temperature of 3 ± 1 °C.Prior to storage, 100 acorns were randomly selected so that certain basic acorn morphological characteristics could be measured. Acorn mass (3.93 ± 1.31 g for Q.
Variabilis, 2.07 ± 0.47 g for Q. Wutaishanica and 2.23 ± 0.46 g for Q. Robur) was measured using a 1/1000 electronic balance. Acorn length, package length, diameter, pericarp thickness and diameter of the cup scar were determined by a vernier caliper. The difference in pericarp thickness at the apex, middle, and base of acorns was recorded to determine whether or not pericarp thickness had an effect on acorn germination. Germination testsTo test the effect of pericarp and cotyledon on root and shoot emergence and establishment, the acorns of each species were randomly assigned to one of the following mechanical scarification treatments or categories : (1) the control (CK); (2) removal of the cup scar (RS); (3) removal of the pericarp (RP); (4) removal of the pericarp and half of the cotyledon (HC); (5) removal of the pericarp and 2/3 of the cotyledon (TC). On September 19, 2009, 15 acorns from each category were placed onto three pieces of filter paper moistened with distilled water in petri dishes (11.5 cm diameter) at a constant temperature of 25 °C with 8 hours light in an incubator.
Each category had three replicates. As acorns germinated, root (the length of radicle being longer than acorn length) and shoot emergence were checked every seven days, and the length of all roots and shoots was measured at the end of the experiment (137 days).
Results Effect of different mechanical treatments on acorn emergenceRP, HC and TC treatments all caused a significant increase in the root and shoot final germination rate of Q. Variabilis acorns when compared to control acorns.
Variabilis and Q. Robur from the TC treatment had significantly lower root and shoot germination rates than those from the RP and HC treatments, while those of Q.
Wutaishanica had no significant difference from those from the former treatments. There was no significant difference in root and shoot germination rate between RS and control treatments for all three species. 4 - Percent of germinating, rooting and non-germinating acorns at the end of the 137-day study period for Q.
Variabilis (A), Q. Wutaishanica (B) and Q. Robur (C) acorns. Using the packing diagram area to represent the ratio of germinated acorns, only roots emerged acorns and non-germinated acorns under different mechanical treatments.
(CK): the control; (RS): removal of cup scar; (RP): removal of pericarp; (HC): removal of pericarp and 1/2 of the distal end of cotyledon; (TC): removal of pericarp and 2/3 of the distal end of cotyledon. Effect of pericarp and cotyledon on root and shoot mean germination timeRemoving the pericarp and cutting off the distal end of the cotyledon could give rise to faster root and shoot emergence. The first roots of Q. Variabilis, Q. Wutaishanica and Q.
Robur acorns from the RP, HC and TC treatments emerged 9, 9 and 10 days after incubating, respectively, which amounted to 7, 28 and 21 days earlier than those of the control treatment. The first shoots of RP and HC acorns emerged 4, 3 and 3 weeks faster than those of the control treatment, while the first shoots of TC acorns emerged one week later than those of RP and HC treatments. All RP, HC and TC treatments significantly reduced the root and shoot mean germination time of Q. Variabilis, Q.
Wutaishanica and Q. Robur acorns. The root mean germination time of Q. Wutaishanica and Q. Robur acorns and the shoot mean germination time of Q. Variabilis and Q.
Robur acorns were significantly decreased by RS compared with those under control condition. Effect of the pericarp and cotyledon on root and shoot vigor index and lengthRP and HC treatments significantly improved the root and shoot vigor index of Q.
Variabilis, Q. Wutaishanica and Q. Robur acorns.
The root vigor index of Q. Variabilis and Q. Wutaishanica acorns from the TC treatment was significantly higher than those from the control, but no significant differences were detected among TC, RP and HC treatments.
The shoot vigor index of Q. Variabilis and the root and shoot vigor index of Q.
Robur acorns from the TC treatment were much higher than the control, but significantly lower than those from the RP and HC treatments. The root and shoot vigor index of the three species from RS and the control were not significantly different. The final root emergence of Q. Variabilis, Q. Wutaishanica and Q. Robur acorns from the RS treatment was not significantly different from the control.
A similar result was detected in the final shoot emergence of the three species. The final root length and shoot height of Q. Variabilis and Q. Wutaishanica acorns were not significantly different from the roots and shoots from the RP, HC, TC and RS and the control. Robur acorns from the RP and HC treatments had significant higher root length and shoot height than the control.
The final root length of Q. Robur acorns from the TC treatment was significantly longer than those from the control, but the final shoot height showed no significant different between the oaks subjected to the TC treatment and the control treatment. Effect of pericarp thickness on acorn germinationA significant difference was found in pericarp thickness at the base, middle and apex of Q. Wutaishanica and Q.
Robur acorns, and no significant difference was found for the Q. Variabilis acorns. Pericarp thickness of Q. Wutaishanica and Q. Robur acorns at the base and apex and at the base and medial was significantly lower than that at other sections; however, no difference was observed between the two lower parts. The pericarp thickness of Q.
Wutaishanica acorns was significantly thinner than that of Q. Variabilis and Q. Robur acorns. AcknowledgementsWe are very grateful to Lily van Eeden for various useful suggestions and for correcting the language of this paper. Yan Liu and Longyu Hou have contributed equally to this work. Conceived of and designed the experiments: Qingmei Li, Yan Liu, Longyu Hou.
Conducted the experiments: Yan Liu, Longyu Hou. Analyzed the data: Yan Liu. Contributed reagents / materials / analysis tools: Qingmei Li. Wrote the paper: Yan Liu. The study was carried out at Research Institute of Forestry, Chinese Academy of Forestry, Beijing (China).The work has been funded by the General Financial Grant from China Postdoctoral Science Foundation grant 2014M550886, National Basic Research Program of China (973 Program) grant 2010CB951301-6 and the National Key Project of Scientific and Technical Supporting Programs of China under grants 2006BAD09B06 and 2006BAD 03A0308. First online: May 05, 2015 Publication Date: Dec 01, 2015 Publication Time: 3.40 months Copyright Information© SISEF - The Italian Society of Silviculture and Forest Ecology 2015 Open AccessThis article is distributed under the terms of the Creative Commons Attribution-Non Commercial 4.0 International , which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.Web Metrics.
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