种子散布位置对格氏栲幼苗根系形态及生长特征的影响

Effect of seeds dispersal position on the root morphology and growth characteristics of Castanopsis kawakamii seedlings

种子从母株掉落于地面萌发后,其根系在不同散布位置(凋落物上层、土壤表层和凋落物下层)的生长形态影响幼苗定居及建成,而目前对其根系形态及生长特征的了解并不充分,限制了对幼苗根系在不同散布下适应策略的理解。为此,以格氏栲(Castanopsis kawakamii)为研究对象,通过模拟种子在凋落物中位置,设置凋落物上层(种子下层铺垫2 cm和4 cm凋落物,U2和U4处理)、土壤表层与凋落物下层(种子上层覆盖0、2、4、6 cm和8 cm凋落物,CK、D2、D4、D6和D8处理)等3种散布,探讨不同散布位置对格氏栲幼苗根系9个生长指标的影响。结果表明:(1)种子散布位置对幼苗根干物质质量具有显著影响,D2处理达最大值。(2)D2处理的幼苗根长、根表面积、根尖数、分枝数和比根长高于其它处理;根系平均直径在D6处理达最大值。(3)相关分析表明根长、根表面积、根尖数、分枝数和比根长与根系平均直径呈显著负相关关系。(4)对根系9个生长指标提取主成分后聚类为4个类群,D2与D4处理各划分一类;U2与U4处理划分一类,其余三个处理划分一类。综上所述,凋落物浅层覆盖(D2处理)适宜格氏栲根系生长;凋落物上层(U2和U4处理)种子萌生根根系受凋落物阻隔作用阻止其与土壤接触,而一旦根系与土壤接触,生长速度加快;土壤表层(CK处理)受地表光照及水分条件限制及凋落物深层覆盖(D6和D8处理)的幼苗受深层凋落物产生的机械阻碍力影响,通过调整对根干物质质量的投入和根系形态可塑性来适应种子散布。因此,在幼苗根系快速生长阶段,通过人为干扰方式,适当调节森林凋落物厚度,以促进格氏栲幼苗在林内更新。

The seeds of Castanopsis kawakamii fallen from the mother trees on the forest floor, after germination its root morphology under different dispersal positions(seeds on top of litter, seeds without litter, and beneath litter) may affect the seedlings settlement and establishment. Unfortunately, how the seed dispersal positions affect the seedlings root systems, especially for the morphology and growth characteristics, remains insufficiently understood. The lack of information limits the understanding of root adaptive strategy in different dispersal positions. Hence, we took C. kawakamii as research object by simulating the seeds position in litter, and set up three seeds dispersal positions including seeds on top of litter(2 cm and 4 cm litter under seeds, U2 and U4 treatments), soil surface(without litter, CK treatment), and seeds beneath litter(seeds were covered by 2, 4, 6, 8 cm litter, D2, D4, D6 and D8 treatments), aiming to explore the effect of seed dispersal positions on nine growth indices of root for C. kawakamii seedlings. The results showed that(1) there was a significant difference in root dry mass of C. kawakamii seedlings among different seed dispersal positions. Root dry mass of D2 treatment was higher than other treatments, whereas of U4 treatment was the lowest.(2) The root length, root surface area, root tips number, root forks number and specific root length of D2 treatment were higher than those of other treatments;whereas the root average diameter reached the maximum under D6 treatment.(3) Correlation analysis showed that root length, root surface area, root tips number, root forks number and specific root length had significantly negative correlation with root average diameter.(4) We extracted principal components from nine root growth indices and then clustered them into 4 groups. D2 and D4 treatments were separately divided into two groups;U2 and U4 treatments were divided into one group, and the other three treatments were divided into one group. We concluded that seeds beneath litter(D2 treatment) was the most suitable growth pattern for root growth of C. kawakamii. The U2 and U4 treatments of seeds on top of litter mainly prevented roots from contacting with soil via litter barrier;whereas when it contacted with the soil, the root growth rate was accelerated. Seedlings grew in the soil surface(CK treatment) with the restricted light and water conditions, and its root grew in D6 and D8 treatments was inhibited due to mechanical hindrance of deep litter. These factors led the seedlings to regulate the investment of root dry mass and root morphological plasticity to adapt the seed dispersal positions. Therefore, we should properly remove litter by human interference during root rapid growth stage to promote the regeneration of C. kawakamii seedlings in the natural forest.