Detailed Explanation of Variable-Temperature Germination Treatment Methods for Korean Pine Seeds

The Korean pine (Pinus koraiensis) is an excellent timber and food forest tree species in Northeast China. Korean pine seeds have a thick, hard seed coat with a waxy layer that is not easily permeable to water and air. The seed coat contains tannins, and other parts contain inhibitors such as abscisic acid. These factors affect the rapid germination of Korean pine seeds, keeping them in a long-term dormant state. To break the long-term dormancy of Korean pine seeds, under natural conditions, after the seeds mature, they must undergo burial through winter--summer--winter, and can only be sown when taken out in the spring of the third year. In recent years, due to the shortage of Korean pine seeds and high market prices, and because the seed bank has no Korean pine seed stock, the traditional overwintering burial method cannot be used to treat Korean pine seeds. In order to better cultivate Korean pine seedlings, from 2003 to the present, the Hebei Forestry Bureau of Heilongjiang Province has used newly collected Korean pine seeds of the same year for variable-temperature germination treatment. Korean pine seeds treated by this method emerge from the soil 3-5 days after sowing, and all emerge completely in about 7 days, with the annual emergence rate reaching over 90%.

I. Preparatory Work

First, lay flooring in the seed treatment room, with the flooring 30 cm above the ground, and ensure proper insulation; second, prepare sufficient river sand, with the volume of river sand being 2 times the volume of the seeds to be treated; third, prepare heating facilities; fourth, fumigate and disinfect the seed treatment room with formaldehyde, and disinfect the river sand with 0.5% potassium permanganate for later use.

II. Specific Methods

1. Properly control water (moisture) conditions: After selecting newly collected naturally matured Korean pine seeds, soak them in clean water, preferably in flowing river water, for 3-5 days, then remove the seeds for further water selection. After water selection, disinfect the seeds (use 0.5 kg potassium permanganate per 500 kg of seeds). After disinfection, mix the seeds with sand at a seed-to-sand volume ratio of 1:2. The moisture of the seed-sand mixture is generally maintained at 40%-50%.

2. Properly control temperature conditions: After mixing with sand, gradually raise the temperature in the seed treatment room. For the first 10 days, control the seed-sand temperature at 10%-12%; for the following 20 days, control the seed-sand temperature at 15%-20%. After 30 days of such treatment, when the embryos of 40%-50% of the seeds turn light yellow, they can be transferred to low-temperature treatment. Gradually lower the temperature in the seed treatment room, controlling the seed-sand temperature at 0°C-5°C. After about 15 days, when the seed-sand temperature drops below 0°C, seal and freeze. The height of the seed-sand mixture should preferably be 40 cm, and must never exceed 60 cm. During the high-temperature treatment stage, turn the mixture over from top to bottom once every 6-8 hours, 3 times per day. Each time you turn it, spray warm water while turning to maintain suitable temperature and moisture of the seed-sand mixture. During low-temperature treatment, turn once per day. This is a necessary measure during seed treatment to ensure uniform temperature throughout the seed-sand mixture from top to bottom.

3. Ensure proper aeration: According to references, when carbon dioxide increases to 17%, it inhibits seed germination and may even poison the seeds and cause death. Therefore, during the variable-temperature germination treatment of Korean pine seeds, open the ventilation windows or doors for timely aeration each time the seed-sand mixture is turned.

In summary, during the variable-temperature germination treatment of Korean pine seeds, in addition to ensuring the use of naturally matured seeds, the temperature and moisture of the seed-sand mixture must be strictly controlled. At the same time, daily observations must be made, recording the temperature of the seed-sand mixture, the room temperature, and the moisture of the seed-sand mixture. Timely cooling and timely aeration are necessary to ensure a short seed treatment time, and the treated seeds have the advantages of rapid, uniform, and even emergence.