南方稀疏马尾松老头林形成的种源供给和种子萌发环境限制分析

Supply of Seed Reserves and Environmental Restrictions of Seed Germination of Sparse and Dwarfish Pinus massoniana Forest in South China

先锋树种马尾松(Pinus massoniana)在南方红壤丘陵区退化生态系统恢复和水土流失治理方面发挥了重要作用。通过南方退化马尾松林种子雨及土壤种子库的调查和光照、水分、温度及酸度的多因子种子萌发试验,分析该地区土壤种子库情况以及各环境因子对马尾松种子萌发的影响。结果表明:于都退化马尾松林土壤种子库密度较低(52.2±10.91粒/m2),马尾松种源缺乏(2.5±1.90粒/m2)。光照对种子萌发没有显著影响(P>0.05)。马尾松种子萌发的最适宜环境因子组合是温度25℃,pH=5.5,种子含水率30%;其次是温度25℃(或15℃),pH=6,种子含水率30%;而多因子极端胁迫环境组合是温度大于35℃,pH<4.5,种子含水率5%;且满足组合中任一单因子条件,种子萌发均会受到显著抑制。适度热激作用(种子置于40℃或45℃的高温环境24 h)可能对马尾松种子萌发有积极影响,但过度的热激作用(处理时间大于36 h或温度高于50℃)则会降低种子萌发率。马尾松对水分胁迫有一定的抗性,但极端干旱时(种子含水率低于5%)种子萌发受到显著抑制。研究证明,马尾松种子萌发需要环境因子的协同作用,任何单方面极端条件都会对种子萌发产生不利影响。

Pinus massoniana,as one of the local pioneer species,plays an important role in restoration of degraded ecosystem and controlling soil erosion in south China. In this study,the authors investigated the conditions of seed rain and soil seed bank of degraded Pinus massoniana forest in South China and described effects of light,temperature,acidity and moisture stress on seed germination features of Pinus massoniana through the multifactor tests of seed germination,with the goal to analyse the condition of soil seed bank and effects of each environmental factor on the seed germination of Pinus massoniana. The results showed that the density of soil seed bank in Yudu experiment site was low（ 52.2 ± 10.91 ind. /m2） and the seed reserve of Pinus massoniana was small（ 2.5 ± 1.90 ind. /m^2）. Light had no significant effect on seed germination（ P〉0.05）. The most suitable environmental factor group for seed germination of Pinus massoniana was temperature（ 25 ℃）- pH= 5. 5- seed moisture content（ 30%）. The next was temperature（ 25 ℃ or 15 ℃）- pH = 6- seed moisture content（ 30%）,while the multi factor group of extreme stress was temperature 〉35 ℃- pH 4. 5- seed moisture content（ 5%）. And when any single condition was met,the seed germination was constrained markedly. It was also found that the effects of moderate heat shock（ seeds were placed in the environment where temperature was 40 ℃ or 45 ℃ for 24 h） might have positive effect on seed germination,whereas excessive heat shock（ treatment time 36 h or temperature〉 50 ℃） would decrease seed germination percentage. Pinus massoniana can endure the drought environment,but its germination was constrained markedly by extreme drought. This study shows that seed germination needs the synergism of each environmental factor,and any unilateral extreme condition would have negative effect on seed germination.