Root structure and arbuscular mycorrhizal colonization of the palm Serenoa repens under field conditions
Root structure and arbuscular mycorrhizal colonization of the palm Serenoa repens under field conditions
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DOI：
10.1023/a:1004576001334
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发表时间：
1999-01-01
期刊：
影响因子：
4.9
通讯作者：
Jayachandran, K
中科院分区：
文献类型：
--
作者：
Fisher, JB;Jayachandran, K
锯齿木Serenoa repens（Bartr.）小是一种原产于美国东南部的棕榈树。它是一种常见的林下植物在松树社区的酸性砂和碱性石灰石。根只有初级生长，厚度从8.0 mm（第一级根）到0.8-2.9 mm（第三级至第五级末级根）不等。最粗的根出现在土壤深度> 20厘米;细根（< 1.2毫米）出现在所有深度（1-60厘米）。一些第二和第三级根是负向地性的，并生长到矿质土壤表面。所有根的表皮都有一个厚的，最终木质化的外壁。除了最薄的根外，所有根都有单层厚壁外皮，首先栓化，然后木质化。根毛从来不存在。由几层脂细胞组成的下皮层（最多8个细胞厚）靠近外皮层，形成外皮层。最细根的外皮层中零星分布着放射状的薄壁、微脂细胞，外皮层中无通道细胞，通道细胞连续。剩余的内皮层由具有通气道的非木质薄壁组织和老根中完全木质化的内皮层组成。在一些最细的根的内皮层中可见传代细胞。丛枝菌根（AM）真菌发生在邻近皮下组织的外三分之一的皮层薄壁组织中。真菌线圈，丛枝和囊泡最常见于最薄的根，但也偶尔发生在所有的根目。离顶端分生组织几毫米的细胞有时被定殖。在附着胞的部位，AM菌丝盘绕在表皮细胞和下面的外胚层和下胚层细胞内。胞间菌丝与胞内分支丛（Arum型）常见于内皮层。有证据表明，在冬季干旱季节，最高级别的根会枯死。土壤剖面和根系剖面AM孢子密度以表层10 cm最高。不同样品中总AM孢子密度为130 ~ 1100个/50 g土壤。球囊霉属其次为巨孢霉属（Gigaspora spp.）这一发现与更普遍的了解生长和AM定植在长寿的热带木本单子叶植物的根。特别是棕榈根，生长缓慢，并受到大量皮下层的保护。
Serenoa repens (Bartr.) Small is a palm native to the southeastern USA. It is a common understory plant in pine communities on both acid sands and alkaline limestone. Roots have only primary growth and range in thickness from 8.0 mm (first order roots from the stem) to 0.8-2.9 mm (ultimate roots of third to fifth order). The thickest roots occur at soil depths > 20 cm; fine roots (< 1.2 mm) occur at all depths (1-60 cm). Some second and third order roots are negatively geotropic and grow up to the mineral soil surface. The epidermis of all roots has a thick, eventually lignified outer wall. Except for the thinnest, all roots have a single-layered, thick-walled exodermis, which is first suberized and later lignified. Root hairs are never present. A hypodermis composed of several layers of lignified cells (up to 8-cells-thick) is next to the exodermis and forms the outer cortex. Radial series of thin walled and slightly lignified cells sporadically occur in the outer cortex of the thinnest roots, but there are no passage cells in the exodermis, which is continuous. The remaining inner cortex is composed of unlignified parenchyma with air canals and a completely lignosuberized endodermis in old roots. Passage cells were seen the the endodermis of the some of the thinnest roots. Arbuscular mycorrhizal (AM) fungi occur in the outer one-third of the cortical parenchyma adjacent to the hypodermis. Fungal coils, arbuscules and vesicles are found most frequently in the thinnest roots, but also occur sporadically in all root orders. Cells a few mm from the apical meristem are sometimes colonized. At sites of appressoria, coils of AM hyphae occur within an epidermal cell and exodermal and hypodermal cells beneath. Intercellular hyphae with intracellular branch arbuscules (Arum-type) are common in the inner cortex. There is evidence of a dieback of the highest order roots during the winter dry season. Profiles of soil and roots have the highest density of AM spores in the surface 10 cm layer. Total AM spore density ranged from 130 to 1100 spores per 50 g soil in different samples. Glomus spp. dominated followed by Gigaspora spp. The findings are related to a more general understanding of growth and AM colonization in long-lived roots of tropical woody monocotyledons. Palm roots, in particular, are slow growing and are protected by massive hypodermal layers.