Abiotic stress is the negative impact of non-living factors on the living organisms in a specific environment. The non-living variable must influence the environment beyond its normal range of variation to adversely affect the population performance or individual physiology of the organism in a significant way.
Hydroponics is a type of horticulture and a subset of hydroculture which involves growing plants, usually crops or medicinal plants, without soil, by using water-based mineral nutrient solutions in an artificial environment. Terrestrial or aquatic plants may grow freely with their roots exposed to the nutritious liquid or the roots may be mechanically supported by an inert medium such as perlite, gravel, or other substrates.
Nitrate is a polyatomic ion with the chemical formula NO−
3. Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are soluble in water. An example of an insoluble nitrate is bismuth oxynitrate.
A fertilizer or fertiliser is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from liming materials or other non-nutrient soil amendments. Many sources of fertilizer exist, both natural and industrially produced. For most modern agricultural practices, fertilization focuses on three main macro nutrients: nitrogen (N), phosphorus (P), and potassium (K) with occasional addition of supplements like rock flour for micronutrients. Farmers apply these fertilizers in a variety of ways: through dry or pelletized or liquid application processes, using large agricultural equipment or hand-tool methods.
Guttation is the exudation of drops of xylem and phloem sap on the tips or edges of leaves of some vascular plants, such as grasses, and also a number of fungi. Ancient Latin gutta means "a drop of fluid", whence modern botany formed the word guttation to designate that a plant exudes drops of fluid onto the outer surface of the plant, when the source of the fluid is inside the plant. Guttation happens in a variety of plant species.
Plant nutrition is the study of the chemical elements and compounds necessary for plant growth and reproduction, plant metabolism and their external supply. In its absence the plant is unable to complete a normal life cycle, or that the element is part of some essential plant constituent or metabolite. This is in accordance with Justus von Liebig's law of the minimum. The total essential plant nutrients include seventeen different elements: carbon, oxygen and hydrogen which are absorbed from the air, whereas other nutrients including nitrogen are typically obtained from the soil.
Diazotrophs are bacteria and archaea that fix atmospheric nitrogen(N2) in the atmosphere into bioavailable forms such as ammonia.
Nitrogen assimilation is the formation of organic nitrogen compounds like amino acids from inorganic nitrogen compounds present in the environment. Organisms like plants, fungi and certain bacteria that can fix nitrogen gas (N2) depend on the ability to assimilate nitrate or ammonia for their needs. Other organisms, like animals, depend entirely on organic nitrogen from their food.
Water potential is the potential energy of water per unit volume relative to pure water in reference conditions. Water potential quantifies the tendency of water to move from one area to another due to osmosis, gravity, mechanical pressure and matrix effects such as capillary action. The concept of water potential has proved useful in understanding and computing water movement within plants, animals, and soil. Water potential is typically expressed in potential energy per unit volume and very often is represented by the Greek letter ψ.
Soil fertility refers to the ability of soil to sustain agricultural plant growth, i.e. to provide plant habitat and result in sustained and consistent yields of high quality. It also refers to the soil's ability to supply plant/crop nutrients in the right quantities and qualities over a sustained period of time. A fertile soil has the following properties:
Soil acidification is the buildup of hydrogen cations, which reduces the soil pH. Chemically, this happens when a proton donor gets added to the soil. The donor can be an acid, such as nitric acid, sulfuric acid, or carbonic acid. It can also be a compound such as aluminium sulfate, which reacts in the soil to release protons. Acidification also occurs when base cations such as calcium, magnesium, potassium and sodium are leached from the soil.
Fertigation is the injection of fertilizers, used for soil amendments, water amendments and other water-soluble products into an irrigation system.
Soil respiration refers to the production of carbon dioxide when soil organisms respire. This includes respiration of plant roots, the rhizosphere, microbes and fauna.
Soil biodiversity refers to the relationship of soil to biodiversity and to aspects of the soil that can be managed in relative to biodiversity. Soil biodiversity relates to some catchment management considerations.
High salt marsh dieback, or salt marsh browning, is the primary force in salt marsh degradation in the high marsh. The general effect is that the plants in the marsh die off and brown, leaving dead organic matter, and ultimately open sediment. Without strong plant roots holding the sediment, these open areas of land erode, causing the salt marsh to retreat back to the mainland. Dieback zones lack their main producers, such as the salt marsh cord grass, or Spartina alterniflora, and ultimately become completely unproductive.
Osmoregulation is the active regulation of the osmotic pressure of an organism's body fluids, detected by osmoreceptors, to maintain the homeostasis of the organism's water content; that is, it maintains the fluid balance and the concentration of electrolytes to keep the body fluids from becoming too diluted or concentrated. Osmotic pressure is a measure of the tendency of water to move into one solution from another by osmosis. The higher the osmotic pressure of a solution, the more water tends to move into it. Pressure must be exerted on the hypertonic side of a selectively permeable membrane to prevent diffusion of water by osmosis from the side containing pure water.
Leaf scorch is a browning of plant tissues, including leaf margins and tips, and yellowing or darkening of veins which may lead to eventual wilting and abscission of the leaf.
In higher plants water and minerals are absorbed through root hairs which are in contact with soil water and from the root hairs zone a little the root tips.
Biomass partitioning is the process by which plants divide their energy among their leaves, stems, roots, and reproductive parts. These four main components of the plant have important morphological roles: leaves take in CO2 and energy from the sun to create carbon compounds, stems grow above competitors to reach sunlight, roots absorb water and mineral nutrients from the soil while anchoring the plant, and reproductive parts facilitate the continuation of species. Plants partition biomass in response to limits or excesses in resources like sunlight, carbon dioxide, mineral nutrients, and water and growth is regulated by a constant balance between the partitioning of biomass between plant parts. An equilibrium between root and shoot growth occurs because roots need carbon compounds from photosynthesis in the shoot and shoots need nitrogen absorbed from the soil by roots. Allocation of biomass is put towards the limit to growth; a limit below ground will focus biomass to the roots and a limit above ground will favor more growth in the shoot.
Seventeen elements or nutrients are essential for plant growth and reproduction. They are carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), potassium (K), sulfur (S), calcium (Ca), magnesium (Mg), iron (Fe), boron (B), manganese (Mn), copper (Cu), zinc (Zn), molybdenum (Mo), nickel (Ni) and chlorine (Cl). Nutrients required for plants to complete their life cycle are considered essential nutrients. Nutrients that enhance the growth of plants but are not necessary to complete the plant's life cycle are considered non-essential, although some of them, such as silicon (Si), have been shown to improve nutrent availability, hence the use of stinging nettle and horsetail macerations in Biodynamic agriculture. With the exception of carbon, hydrogen and oxygen, which are supplied by carbon dioxide and water, and nitrogen, provided through nitrogen fixation, the nutrients derive originally from the mineral component of the soil. The Law of the Minimum expresses that when the available form of a nutrient is not in enough proportion in the soil solution, then other nutrients cannot be taken up at an optimum rate by a plant. A particular nutrient ratio of the soil solution is thus mandatory for optimizing plant growth, a value which might differ from nutrient ratios calculated from plant composition.
