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In geology and particularly in sedimentology, a nodule is a small, irregularly rounded knot, mass, or lump of a mineral or mineral aggregate that typically has a contrasting composition from the enclosing sediment or sedimentary rock. Examples include pyrite nodules in coal, a chert nodule in limestone, or a phosphorite nodule in marine shale.
nodule, rounded mineral concretion that is distinct from, and may be separated from, the formation in which it occurs. Nodules commonly are elongate with a knobby irregular surface; they usually are oriented parallel to the bedding.
- The Editors of Encyclopaedia Britannica
- Root Nodule Types
- Root Nodule Formation Steps
- Factors Affecting Nodule Formation
There are mainly two types of root nodules: 1. Indeterminate Root nodulesThey are characterized by persistent nodule meristem. They are elongated due to cell division in nodules. Indeterminate root nodules show development gradient. It shows different zones, which are due to different stages of development, these are:Zone I – Active meristem, where...
Root nodule formation is initiated, when the soil contains a low level of nitrogen. The two symbiotic partners use cell signalling for the association and developing nodules. Steps of nodulation are: 1. Roots of legumes secrete flavonoids, which attracts rhizobia towards the root. Rhizobia congregate around root hairs. 2. Rhizobia secrete nod facto...
Nodulation is affected by both external and internal factors. 1. External factors include heat, acidity, nitrate content of the soil, etc. 2. If soil is rich in nitrogen content, it interferes with the nodule formation and symbiotic association as plants already have enough nitrogen and they do not need more. 3. Nitrogen fixation is an oxygen-sensi...
Nov 8, 2022 · Septarian nodules are a type of concretion where mudstone of some kind is interspersed with calcite or another carbonate-rich mineral. The calcite portions follow the pattern of radiating cracks, which occur during the unique creation of these formations. Septarian nodules consist of at least two minerals in every case.
Nodules grow around the root, forming a collar-like structure. In these nodules and in the peanut type the central infected tissue is uniform, lacking the uninfected ells seen in nodules of soybean and many indeterminate types such as peas and clovers.
Root nodules differ in shape and size based on the bacteroid population and can be classified into two groups, indeterminate (Fig. 3) or determinate nodules (Sprent et al., 2013). Indeterminate nodules contain a heterogeneous population of bacteroids.
Jun 11, 2004 · This article will review the critical biogeochemical processes occurring at the plant root-soil interface.
