无瓣海桑(Sonneratia apetala Buch.Ham)是中国沿海地区常用的红树林造林树种.然而,目前对其根系的空间分布特征仍知之甚少,以下基础性问题仍急待回答:无瓣海桑地表根系和地下根系的空间分布特征如何?这些特征随林龄如何变化?这些根系空间分布特征能为理解无瓣海桑促淤保滩、防风消浪等功能提供哪些启示?选择北部湾13 a、8 a、5 a、3 a 4种龄期的无瓣海桑人工纯林,采用地表根系网格法和壕沟挖掘法,调查了4种林龄下无瓣海桑的水平根系分布幅度、根系深度、地表根密度、高度与基径、地下根系的垂直分布,研究了无瓣海桑植株根系空间分布特征及随树龄的变化规律.研究结果表明:(1)无瓣海桑植株地表根系水平分布范围随树龄增加而不断扩大,13 a、8 a、5 a、3 a无瓣海桑植株地表根系水平分布范围分别是79.20、45.80、18.40、14.64 m,分别是其冠幅的14.46、8.90、5.62、5.52倍;(2)4种林龄的无瓣海桑植株地表呼吸根系的密度、高度、基径在水平方向上由冠幅向外逐渐减小;(3)无瓣海桑植株地下垂直根系分布的深度十分有限,13 a与8 a无瓣海桑根系垂直分布深度为0~60 cm,5 a和3 a为0~40 cm;另外0~20 cm土壤深度为根系主要分布深度,13 a、8 a、5 a、3 a无瓣海桑在0~20 cm分别分布着79.3%、87.6%、93.0%、94.1%的根系.研究结果不仅有助于加强对无瓣海桑根系时空分布特性的理解,而且能从根系角度为进一步理解无瓣海桑促淤保滩、防风消浪等功能提供新解释.%Sonneratia apetala is listed as a pioneer species for mangrove restoration in mainland China,whereas little is known about its temporal-spatial distribution of root system, there is an urgent need to answer the following questions: (1) What is the temporal-spatial distribution traits of Sonneratia apetala Buch. Ham root system? (2) Will these traits change with an increasing planting age? (3) What implications can be provided for further understanding on sediments trapping and wave attenuation based on these root distribution traits of S. apetala? For this purpose, we selected S. apetala monoculture forests with four planting ages [13-yr-old S.apetala community(13 Sa),8-yr-old S.apetala community(8 Sa),5-yr-old S.apetala community(5 Sa)and 3-yr-old S. apetala community (3Sa)] in the Beibu Gulf, China. We used horizontal plane and digging trench methods to measure the distribution range of aerial root, depth of root system, density of aerial root, height of aerial root, basal diameter of aerial root, and the vertical distribution of root system, and then the temporal-spatial distribution traits of root system and its dynamic with an increasing planting age were analyzed. Our results showed that, (1) the horizontal range of pneumatophore distribution increased with an increasing planting age, the horizontal range of pneumatophore distribution was 79.20 m for 13 Sa (14.46 times of its crown size), 45.80 m for 8 Sa (8.90 times of its crown size), 18.40 m for 5 Sa (5.62 times of its crown size), 14.46 m for 3 Sa (5.52 times of its crown size). (2) The density, height and stem basal diameter for pneumatophore decreased outward from position of stem to the crown edge. (3) The underground root was shallow depth. The vertical distribution of underground root depth was 60 cm for 13-yr-old and 8-yr-old S.apetala,and 40 cm for 5-yr-old and 3-yr-old S.apetala.In addition,the majority of underground roots were distributed on the top soil (0~20 cm in depth) regardless of planting age, where 79.3% root for 13 Sa, 87.6% root for 8 Sa, 93.0% root for 5 Sa, 94.1% root for 3 Sa were distributed in this top soil, respectively. These results could advance our knowledge regarding the temporal-spatial distribution of S.apetala root,which could provide implications to understand the sediment trapping and wave attenuation from root perspective.
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