What are the biological characteristics of Angelica sinensis? (Part Two)

(1) Root growth. From sowing to physiological maturity, Angelica sinensis takes three years, overwintering twice, with a total growth period of more than 500 days. After the seed germinates, the radicle elongates rapidly and grows downward in a curved manner, entering the soil. First, one main radicle emerges. When the main radicle extends to 3-4 cm, first-order lateral roots begin to form, and then second-order lateral roots appear on the first-order lateral roots. The main root continues to thicken and elongate and gradually becomes fleshy, forming a typical fleshy taproot system 20-30 cm long and 0.3-0.5 cm in diameter. After transplanting in early to mid-April of the following year, a large amount of nutrients is used for leaf development, and root growth is relatively slow. Because the root tip of the main root is damaged during seedling lifting and transplanting, its development is inhibited, which promotes extensive development of lateral roots. After the rows close in July, the diameter of the main root begins to thicken, new lateral roots are produced, and the first-order lateral roots begin to become fleshy. In early to mid-August, the temperature begins to drop, and leaf expansion reaches its maximum. At this time, the assimilates produced by the leaves are mainly transported to the roots, and the diameters of the main root and lateral roots rapidly thicken and become fleshy. After the temperature turns colder, growth slows down, but the rate of material accumulation in the roots accelerates. By early to mid-October, when the aboveground parts begin to wither, root growth reaches its maximum, with a total length of up to 30-50 cm and a diameter of 3-5 cm. This is the medicinal harvest period for Angelica sinensis. If not harvested in time, plants left in the field to overwinter enter reproductive growth in the third year (some Angelica sinensis plants enter the bolting and flowering stage in the second year). Because bolting, flowering, and seed setting consume a large amount of nutrients, the roots become hard and thin, gradually becoming lignified and hollow, turning into a woody texture and losing their medicinal value.

(2) Stem growth. The stem is the organ connecting the underground root with the aboveground branches, leaves, flowers, and fruits. It plays an important role in transporting and regulating water and nutrients among organs. The stem of Angelica sinensis is divided into a vegetative stem and a flowering stem. The vegetative stem exists only during the vegetative growth period (before bolting). The stem body is extremely shortened, with neither differentiation of stem nodes nor obvious stem stalk extending above the ground. Externally, it appears stemless, with only several leaves emerging from the base, clustered at the top of the vegetative stem in a rosette shape. In mid-to-late March of the third year, Angelica sinensis begins to turn green again, and then the growing point begins to shift from vegetative growth to reproductive growth, forming a reproductive growing point. In mid-to-late May, the aboveground stem begins to emerge and rapidly extends above the ground, that is, bolting, forming an upright, multi-noded (generally 5-8 nodes), much-branched stem stalk that can reach up to 1.5 m in height. At the same time, large compound umbels form at the tops of the main stem and branches.

(3) Leaf growth. Leaves are important vegetative organs of Angelica sinensis, and their main functions are photosynthesis, transpiration, and gas exchange. The leaves of Angelica sinensis are divided into basal leaves and cauline leaves. They are 2-3 times odd-pinnately compound leaves, composed of three parts: leaf blade, petiole, and leaf sheath. The main function of the leaf blade is photosynthesis. Under light conditions, green leaves can synthesize organic substances from water and carbon dioxide absorbed by the plant. Under general conditions, the larger the leaf area per plant, the higher the single root weight. Within a certain range, the larger the leaf area coefficient, the higher the yield per mu. Therefore, improving cultivation and management measures to increase the leaf area coefficient is an important measure for achieving high yields of Angelica sinensis, but at the same time, excessive vegetative growth of the plants must be guarded against. The structure of the leaf blade is divided into three parts: epidermis, mesophyll, and veins. The epidermis is the outermost layer of the leaf and bears trichomes and stomata. The opening and closing of stomata control gas exchange and water transpiration between the inside and outside of the Angelica sinensis plant. Inside the epidermis is the mesophyll, composed of palisade tissue and spongy tissue, containing many chloroplasts. It is an important site for photosynthesis and synthesis of organic nutrients in Angelica sinensis. The main vein of the leaf is located in the middle of the leaf blade, distributed between the palisade tissue and spongy tissue. The leaf veins connect with the vascular systems of the petiole, stem, and root, together forming a complete system for transporting water and nutrients in the Angelica sinensis plant. During the vegetative growth period of the first year, the growing point successively produces leaf primordia, forming 5-7 basal leaves clustered at the top of the vegetative stem in a rosette shape, with relatively large leaf blades and relatively long petioles. After turning green again in the second year, as the temperature rises, growth gradually accelerates, and new cauline leaves are successively produced. Growth is fastest when the average temperature is above 14°C. At this time, not only does the number of leaves increase rapidly, but leaf area also increases rapidly. In June-July, the aboveground parts enter a period of vigorous growth, forming many large compound leaves. The leaf area coefficient reaches 3-4, laying the foundation for obtaining high yields. For plants reserved for seed production, they are not dug up in the second year and are left in the field to overwinter. In mid-to-late March of the third year, they begin to turn green again and send out new leaves, then shift to reproductive growth. The growing point differentiates stem nodes and elongates, forming a flowering stem. At this time, basal leaves stop differentiating, and cauline leaves are produced at the nodes of the flowering stem. They are alternate, with relatively small leaf blades, relatively short petioles, and enlarged sheath-like bases that clasp the stem.