鳄梨根系的几点知识

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概要

鳄梨原产于中南美洲、墨西哥和**海的厚密的高地雨林里。鳄梨的根系需要温暖的土壤、良好的透水性（以便在根系生长区域能进行频繁的氧气交换）、丰富的有机质、预防疾风的措施。疾风会将鳄梨树连根拔起。

规模

鳄梨的根系相对比较浅，即便是伸展到树冠边缘也不会伸展到离树冠很远的地方。鳄梨的根主要是稀疏的、纤维状的吸收根，没有浓密的起固定作用的主根。可能是因为对生长地的热带雨林气候的适应结果。那里有浅浅一层肥沃土壤，森林茂密，缺乏疾风，根系不需要担负固定树体的重任。

土壤

由于鳄梨喜好肥沃的土壤，顶部覆盖能分解的护根物和有机物会促进吸收根的生长。再者，这也是模拟它们的生长环境。根据《鳄梨：植物学、生产和应用》的论述，健康的鳄梨吸收根在任何正在分解的枯枝落叶层里面都能茁壮成长。另外，土壤的排水性要很好，因为鳄梨的根系特别容易因为土壤积水而感染很多不同的土传疾病。

疫病

根腐病，是一种鳄梨根系中最常见也是最危险的疾病。饱和的土壤、频繁的降雨或者过于频繁的浇水都会磨损根系的自然防御机制，为此病提供了完美的滋生环境。缺氧的根系开始死去，疾病在腐烂的根部传播，很快传播到整个健康的根部系统。把鳄梨种在厚厚的有机物覆盖层上的做法能明显抑制腐病。

根毛和菌根

鳄梨的吸收根上根毛很少甚至没有根毛。根毛是将根系周围的水分和营养物质传导到树体的组织。取而代之的是，鳄梨树根和一种称为“菌根”的微小的根部真菌形成一种共生关系。这种有机体覆盖在树根上，然后在土壤里伸展出一个广阔的吸收网，为树根吸收营养并和树体交换糖分。

耐寒性

墨西哥系鳄梨的根部和上方的树体比其他种类的鳄梨的耐寒性都要好：最低可以耐零下8摄氏度的低温。其他砧木在冰点以上就受到损害，但很少死亡。用厚厚的覆盖物护根，在冰冻之前正确浇水有助于降低冻害，但树体的上部分也需要做好保护。

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Facts on Avocado Tree Roots

Overview

Avocados (Persea americana) are native to Central and South America, as well as Mexico and the Caribbean, where they grow in dense highland rain forests. Avocado roots need warm soils, good drainage for constant oxygen exchange in the root zone, rich organic matter, and protection from high winds that might uproot the tree.

Size

The root system is relatively shallow, and does not extend far beyond the tree canopy, if it even reaches the edge of the canopy. The roots are primarily thin, fibrous feeder roots. They have no thick, anchoring taproot. These are likely adaptations to the shallow layer of rich soils in their native rain forest climates, as well as the absence of high winds in the dense forest growth that would necessitate better anchorage.

Soil

While they prefer rich soils, a top layer of decomposing mulch and organic material will also encourage feeder root growth. Again, this mimics their natural environment. According to "The Avocado: Botany, Production, and Uses," healthy avocado feeder roots thrive in any decomposing litter layer. Soil should drain readily, as avocado tree roots are susceptible to many different soil-borne diseases that thrive in soggy soils.

Disease

Pytophthora cinnamomi, or cinnamon root rot, is one of the most common and dangerous root diseases of the avocado tree. Saturated soils, frequent rains or too-frequent watering simultaneously provide the perfect breeding ground for the disease while wearing down the root's natural defenses. The oxygen-starved roots start to die, and the disease breeds in the decaying root, quickly spreading to the rest of the healthy root system. Growing avocado with a thick layer of organic mulch has been shown to suppress phytophthora.

Root Hairs and Mycorrhiza

Avocado have very few to no root hairs on their feeder roots. Root hairs are the structures commonly associated with nutrient and water uptake in the root zone. Instead, avocado tree roots have a symbiotic relationship with a microscopic root fungus called mycorrhiza. This organism coats the roots, then forms a vast web out into the soil, where it absorbs nutrients for the roots in exchange for plant sugars.

Hardiness

The roots and upper vegetation of Mexican avocado tree varieties can withstand cold much better than most other varieties: down to minus 8 degrees Celsius. Other rootstocks sustain damage even in above-freezing temperatures, but rarely die from such exposure. Protecting the roots with heavy mulch and watering right before a freeze may help reduce damage, but the upper parts of the tree may also need protection.

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