Key Technical Points for Raising 2-Year-Old Container Seedlings of Phoebe bournei and Phoebe zhennan
Key Technical Points for Raising 2-Year-Old Container Seedlings of Phoebe bournei and Phoebe zhennan
To increase the variety of Lauraceae tree species in Anhui Province, protect and increase forest plant germplasm resources, enhance biodiversity, and promote sustainable forest development, from 2013 to 2015 we purchased seeds of Phoebe bournei and Phoebe zhennan from Fujian and carried out introduction and domestication trial research at the nursery of the Chawan Forest Industry Harvesting and Cultivation Farm in Qimen County. The trial was successful, and 2-year-old container seedlings of Phoebe bournei and Phoebe zhennan were successfully planted on suitable forest land.
1 Natural Conditions of the Introduction Site
Qimen County is located at 117°37′25"E, 29°51′47"N; the landform is mountainous and hilly, with an altitude of 160-220 m and relatively flat terrain; the climate is a subtropical monsoon climate, with an annual average temperature of 15.7°C, an extreme maximum temperature of 41.5°C in July, an extreme minimum temperature of -13.2°C in January, an annual average relative humidity of 81%, an annual average daily actual sunshine duration of 1 809.7 h, a frost-free period of 239 d, and an annual average precipitation of 1 790.3 mm; the soils are mainly yellow earth and yellow-brown earth developed from phyllite and granite, with medium to slightly high organic matter content and a pH value of 5.5-6.5.
2 Tree Species Introduction and Experimental Methods
2.1 Tree Species Introduction
Phoebe bournei (P. bournei) and Phoebe zhennan (P. zhennan) belong to the genus Phoebe in the Lauraceae family and are precious tree species, both being valuable timber for construction, furniture, and crafts.
2.1.1 Phoebe bournei
Phoebe bournei is an evergreen large tree of the genus Phoebe in the Lauraceae family. It is endemic to China and is a national Class II key wild plant [1]. It is distributed in evergreen broad-leaved forests at altitudes of 200-1 000 m in Zhejiang, Fujian, Jiangxi, Guangdong, Guangxi, Hunan, Hubei, Guizhou and other provinces, and has been listed in the "List of Rare and Endangered Plants of China" and the "Red Book of Precious Plants of China" [2]. Its wood is fragrant and durable, with beautiful grain, and is an excellent material for superior construction, furniture, craft carving, and shipbuilding.
1 kg of Phoebe bournei seeds was purchased on February 26, 2015, from the Qingyuan Forest Farm in Zhejiang. Before purchase, the seeds had already undergone peeling and cleaning treatment. The thousand-seed weight was 305 g, belonging to medium-sized seeds, with a purity of 95%.
2.1.2 Phoebe zhennan
Phoebe zhennan is an evergreen large tree of the genus Phoebe in the Lauraceae family. It is a national Class II key wild plant, distributed in broad-leaved forests of low mountains and hills below 800 m altitude in Hubei, Jiangxi, Zhejiang, Guizhou and other provinces, often mixed with Castanopsis tibetana, C. fargesii, C. sclerophylla, Choerospondias axillaris, Machilus thunbergii, etc. [2]. Its wood has interlocking grain, is smooth and beautiful, and easy to process. It is a superior material for furniture, construction, flooring, interior decoration, carving, precision instruments, plywood face veneer, and shipbuilding.
1 kg of Phoebe zhennan seeds was purchased on February 26, 2015, from the Qingyuan Forest Farm in Zhejiang. Before purchase, the seeds had already undergone peeling and cleaning treatment. The thousand-seed weight was 278 g, belonging to medium-sized seeds, with a purity of 96%.
After the Phoebe bournei and Phoebe zhennan seeds were purchased, they were stored in wet sand and germinated. Before sowing, the river sand was sifted out with a sieve, larger stones were picked out, and then the seeds were disinfected with 50% carbendazim wettable powder before sowing.
2.2 Experimental Methods
2.2.1 Seedling Raising Experiment
The experimental site was at the nursery of the Chawan Forest Industry Harvesting and Cultivation Farm in Qimen County. The nursery site is sheltered from wind and faces the sun, with loose soil of medium thickness, average fertilizer and water retention, and good drainage and irrigation. The previous crop was a medium sandy loam dryland used for raising Chinese sweetgum (Liquidambar formosana) seedlings. Each 667 sq m of nursery land was applied with 500 kg of organic fertilizer, 50 kg of compound fertilizer, and 40 kg of slaked lime. After plowing and harrowing level, seedbeds were prepared with a width of 120 cm and a height of 30 cm for later use.
For each tree species, three plots were set up with 20 seeds/row, 30 seeds/row, and 40 seeds/row respectively. The plot area was 1 sq m, with 3 replications. Five rows were sown per plot. After the first 5 rows were sown, they were covered with 1.5 cm thick dawn redwood (Metasequoia glyptostroboides) leaves; the second 5 rows were covered with 2 cm thick wet soil; the third 5 rows were covered with a substrate of perlite and vermiculite (mixed at 1:1) (hereinafter referred to as "substrate"); the fourth 5 rows were covered with dawn redwood leaves; the fifth 5 rows were covered with wet soil, and so on. Sowing and covering were completed on March 26, 2015. On March 30, 24% oxyfluorfen (Goal emulsifiable concentrate) herbicide was sprayed on the seedbeds to control weeds during the emergence period in the nursery.
During the seedling stage, weeding, fertilization, drainage and irrigation, and pest and disease control were carried out according to the management measures for broad-leaved tree species such as Chinese sweetgum. Phoebe bournei and Phoebe zhennan are tropical evergreen broad-leaved tree species. When raising 1- to 2-year-old seedlings in Qimen County, the seedlings may face the problem of overwintering freeze damage. To reduce the direct attack of cold wind on seedling leaves and tender shoots, in mid-October we covered the experimental seedlings around the nursery with double-layer "two-needle" shade netting for freeze protection.
2.2.2 Observation of Seedling Growth Indicators
To understand the phenology and growth and development patterns of the seedlings, observation and recording began after seed germination. Phenological observations were made on seedling germination, leaf expansion, and shoot growth. In each plot, 30 robust seedlings were randomly selected as fixed standard plants. On the 30th (or 31st) of each month, a steel tape measure was used to measure shoot growth (leaf expansion) and seedling height, and a vernier caliper was used to measure ground diameter. A final measurement was made after the seedlings set terminal buds. The observed data were then organized and analyzed.
3 Experimental Results
3.1 Seed Germination Rate and Seedling Preservation Rate
The seed coats of Phoebe bournei and Phoebe zhennan are dense, and wet sand storage treatment can effectively break their dormancy. For both Phoebe species, the emergence period runs from seed germination and seedling emergence until the seedlings have basically all emerged. The level of seed germination rate is affected by the mast year of the mother trees, seed collection time, treatment and storage and sowing methods, thickness of cover material, weather and temperature after sowing, microenvironment of the nursery plot, and human management measures. As shown in Table 1, under suitable temperature and soil moisture and proper post-sowing management, the nursery germination rate and seedling preservation rate of Phoebe bournei and Phoebe zhennan seeds can remain at relatively high levels, at 87.2%, 85% and 75.8%, 73.2%, respectively.
The results showed that the three cover materials of dawn redwood leaves, wet soil, and substrate had no obvious effect on seed germination rate, but they posed a certain obstacle to seedlings emerging through the cover. Dawn redwood leaves and wet soil become compacted after rain, affecting seedling shoots emerging from the ground, and at the same time easily absorb a large amount of heat, which can easily cause sunscald to seedlings at noon. Therefore, after sowing Phoebe bournei and Phoebe zhennan, using substrate as cover gave the best effect.
Table 1 Statistics of Seed Germination Rate and Seedling Preservation Rate of Phoebe bournei and Phoebe zhennan
3.2 Seedling Stage Phenology
After sowing the seeds of Phoebe bournei and Phoebe zhennan, the seeds began to emerge on April 18. From April 25 to May 21 was the peak emergence period, during which 85% of the seeds germinated. Emergence basically ended on May 28. It can be seen that the emergence period of Phoebe bournei and Phoebe zhennan seeds is basically consistent with the emergence period of Phoebe nanmu seeds sown in early March 2013 at the Shuanghekou Nursery in Qimen County [3].
The height growth of Phoebe bournei and Phoebe zhennan seedlings begins when the seedlings emerge and continues until late October. After late October, as the temperature gradually decreases, aboveground height growth stops, the stems gradually complete lignification, and the plants enter dormancy, while underground root growth can continue until the end of December [3].
3.3 Seedling Growth
3.3.1 Height Growth
The height growth process of 1-year-old Phoebe bournei and Phoebe zhennan seedlings can be roughly divided into 3 periods: before the end of May is the initial growth period, June to September is the rapid growth period, and October is the seedling hardening period. The height growth indicators of the seedlings in each period are shown in Table 2.
Table 2 Statistics of Average Height Growth of 1-Year-Old Phoebe bournei and Phoebe zhennan Seedlings in Different Periods
As shown in Table 2, the height growth of 1-year-old Phoebe bournei and Phoebe zhennan seedlings is slow. The annual height growth of Phoebe bournei was 17.7 cm, and the height growth in the initial growth period, rapid growth period, and seedling hardening period accounted for 23.7%, 57.1%, and 19.2% of the annual total growth, respectively. Phoebe zhennan grew even more slowly than Phoebe bournei, with an annual height growth of 17.2 cm, which was 97.2% of the total growth of Phoebe bournei. Its height growth in the initial growth period, rapid growth period, and seedling hardening period accounted for 22.7%, 59.3%, and 18.0% of the annual total growth, respectively. The slow height growth of both may be related to factors such as the relatively low summer temperature at the Chawan Harvesting and Cultivation Farm, the large diurnal temperature difference, the previous crop of the nursery land being Chinese sweetgum seedlings, and poor soil fertility. This requires further study.
3.3.2 Diameter Growth
The ground diameter growth process of 1-year-old Phoebe bournei and Phoebe zhennan seedlings can also be broadly divided into 3 periods: the initial period, the rapid growth period, and the late growth period (diameter growth extending to the end of November). The annual ground diameter growth was 0.29 cm. The diameter growth indicators of the seedlings in each period are shown in Table 3.
Throughout the growing season, the ground diameter growth of 1-year-old Phoebe bournei and Phoebe zhennan seedlings was relatively small. In addition to being related to the site conditions and temperature of the nursery land, this is also closely related to the small height growth of the seedlings.
Table 3 Statistics of Average Diameter Growth of 1-Year-Old Phoebe bournei and Phoebe zhennan Seedlings in Different Periods
3.4 Cold Resistance of Seedlings
Around the time of Frost's Descent in October-November, a notable feature of Phoebe bournei and Phoebe zhennan is that seedlings in exposed ground are prone to freeze damage from cold waves. The degree of freeze damage is related to the nursery location, soil fertility, water and fertilizer management during the seedling stage, and whether freeze protection measures are taken before and after Frost's Descent. As shown in Table 4, for 1-year-old Phoebe bournei and Phoebe zhennan seedlings covered with double-layer "two-needle" shade netting, a small number of seedlings in the experimental site (9 sq m) suffered varying degrees of freeze damage to upper leaves and a small number of non-lignified young stems. The number of plants with frozen leaves accounted for 3.5% of the total number of plants, among which the number of plants with frozen young stems accounted for 27.8-31.6% of the number of plants with leaf freeze damage. It can be seen that, under the premise of adopting protective measures, 1-year-old Phoebe bournei and Phoebe zhennan seedlings can overwinter safely.
4 Summary and Discussion
Table 4 Statistics of Freeze Damage to Leaves and Tender Stems of 1-Year-Old Phoebe bournei and Phoebe zhennan Seedlings
Phoebe bournei and Phoebe zhennan are precious evergreen tree species of the central subtropics, with excellent wood quality, wide uses, and huge development potential. To alleviate the contradiction between the supply and shortage of precious tree species for greening, landscaping, and timber in China, in recent years Qimen County has carried out introduction, domestication, seedling raising, and afforestation experimental research on 6 Phoebe species including Phoebe chekiangensis, Phoebe bournei, Phoebe zhennan, and Phoebe sheareri, with initial results.
(1) Under the premise of suitable seed treatment and storage conditions, good nursery soil site conditions, temperature and humidity, and good seedling stage management, the nursery germination rate and seedling preservation rate of Phoebe bournei and Phoebe zhennan seeds can reach relatively high levels. Therefore, Qimen can introduce and cultivate 1-year-old seedlings of Phoebe bournei, Phoebe zhennan, etc., and plant them in forest land after thinning of Chinese fir.
(2) Phoebe bournei and Phoebe zhennan begin to germinate 60 d after sowing. From late April to May 21 is the peak emergence period, and emergence basically ends in late May. After June, they enter the height growth period. During the emergence period, intensive and meticulous management should be strengthened.
From emergence to the end of May is the initial height growth period of Phoebe bournei and Phoebe zhennan, June to September is the rapid growth period, and October is the seedling hardening period. The annual height growth of Phoebe bournei was 17.7 cm, and the annual height growth of Phoebe zhennan was 17.2 cm. The diameter growth of 1-year-old Phoebe bournei and Phoebe zhennan seedlings is also divided into the initial growth period, rapid growth period, and late growth period, with an annual ground diameter growth of 0.29 cm. The slow height and ground diameter growth of both may be related to the relatively low summer temperature at the nursery, the large diurnal temperature difference, the thin soil layer, the poor soil water and fertilizer retention capacity, and the degree of intensive management during the seedling stage. Strengthening early nursery management, increasing the application of organic fertilizer, promoting early height and diameter growth of seedlings, and ensuring timely lignification of seedlings are crucial.
(3) Before Frost's Descent, covering 1-year-old Phoebe bournei and Phoebe zhennan seedlings with double-layer shade netting for protection can effectively reduce freeze damage to the seedlings and ensure their safe overwintering.
(4) In the middle and late stages of the rapid growth period of 1-year-old Phoebe bournei and Phoebe zhennan seedlings, spraying potassium fertilizer and special antifreeze solution for seedlings to harden the seedlings against cold, promote the lignification process, improve their cold resistance and freeze protection ability, and ensure safer overwintering of the seedlings still requires further study.