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E-book Grassland use in Europe

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Penilaian

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Grass seeds include the coleoptile (shoot sheath), the scutellum, the radicula and the coleorrhiza (root sheath) (Figure1.1). The scutellum is homologous to the leaf lamina of the cotyledon and the coleoptile to the leaf sheath of the cotyledon. Co-leoptile and coleorrhiza are membranes that protect shoot and leaf meristems and the radicula, respectively, during the first step of the germination process when these fragile organs have to find their way through the soil. When a seed germinates, it first produces the radicula (the first root) that quickly absorbs water and nutrients. The coleoptile is then pushed upward and elongates to reach the soil surface, where the first leaf emerges from it. Side roots are produced quickly around the primary root. When the first three leaves are deployed, a bulge appears just above the seed and below the soil surface. It is the tillering plateau from which all secondary roots and aerial tillers are produced. Primary roots and seeds disappear afterwards. rass leaves comprise three sections. The first is the upper part of the leaf, the lamina or blade, which is the most visible because it usually detaches from the stem). The second is the lower part of the leaf, the sheath, which encircles the stem (Figures1.2 and 1.3). Finally, at the intersection of the lamina and the sheath, there can be two organs: the auricle and the ligule. Auricles are often claw-like appendages which tend to clasp the sheath. The ligule is an extension of the sheath at the base of the lamina. Its axis is parallel to the stem and thus perpendicular to the lamina. It may prevent water penetration between the sheath and the stem which could cause stem rotting. Tillers are the equivalent of branches in woody species. A tiller appears at the internal base of a leaf sheath. Each tiller can again produce leaves and new tillers at the base of these leaves. Tillering is thus theoretically exponential, but it is limited by light, nutrient and water resource availability. After germination, when four leaves are visible on the main tiller, there is a moment when two secondary tillers appear at the base of the first two leaves. The full tillering phase is then reached.During the vegetative phase described above, all meristems are located just below or just above soil surface, keeping them well protected from herbivore teeth. This gives grasses a unique capacity to regrow quickly after defoliation compared to many dicotyledons. Grass plant species are thus well adapted to herbivore presence and activity. In fact, the two plant and animal species groups co-evolved and depend on each other. Most dicotyledon species are not especially well adapted to grazing because most of their meristem is located well above the soil surface. Because these plants can be easily destroyed by grazing animals, most swards grazed by herbivores are dominated by grasses. In a way, herbivores ‘weed’ herbaceous swards by reducing he proportion of dicotyledon species. In return, grasses produce more nutritious leaves to reward herbivores for this service. Unlike many dicotyledon species, grasses do not try to escape from grazing action by producing toxic compounds or mechanical defence organs; on the contrary, they encourage herbivores to graze them.

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Ketersediaan

Informasi Detail

Judul Seri

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No. Panggil

636 PEE g

Penerbit

France : éditions Quae., 2019

Deskripsi Fisik

267 hlm

Bahasa

English

ISBN/ISSN

9782759231461

Klasifikasi

636

Tipe Isi

text

Tipe Media

computer

Tipe Pembawa

online resource

Edisi

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Subjek

Animal Husbandry

Info Detail Spesifik

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Pernyataan Tanggungjawab

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Versi lain/terkait

Lampiran Berkas

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