Nutrient availability and management in the rhizosphere: exploiting genotypic differences

Crop nutrition is frequently inadequate as a result of the expansion of cropping into marginal lands, elevated crop yields placing increasing demands on soil nutrient reserves, and environmental and economic concerns about applying fertilizers. Plants exposed to nutrient deficiency activate a range of mechanisms that result in increased nutrient availability in the rhizosphere compared with the bulk soil. Plants may change their root morphology, increase the affinity of nutrient transporters in the plasma membrane and exude organic compounds (carboxylates, phenolics, carbohydrates, enzymes, etc.) and protons. Chemical changes in the rhizosphere result in altered abundance and composition of microbial communities. Nutrient-efficient genotypes are adapted to environments with low nutrient availability. Nutrient efficiency can be enhanced by targeted breeding through pyramiding efficiency mechanisms in a desirable genotype as well as by gene transfer and manipulation. Rhizosphere microorganisms influence nutrient availability; adding beneficial microorganisms may result in enhanced availability of nutrients to crops. Understanding the role of plant-microbe-soil interactions in governing nutrient availability in the rhizosphere will enhance the economic and environmental sustainability of crop production.     

Perception and modification of plant flavonoid signals by rhizosphere microorganisms

Flavonoids are a diverse class of polyphenolic compounds that are produced as a result of plant secondary metabolism. They are known to play a multifunctional role in rhizospheric plant-microbe and plant-plant communication. Most familiar is their function as a signal in initiation of the legume-rhizobia symbiosis, but, flavonoids may also be signals in the establishment of arbuscular mycorrhizal symbiosis and are known agents in plant defence and in allelopathic interactions. Flavonoid perception by, and impact on, their microbial targets (e.g. rhizobia, plant pathogens) is relatively well characterized. However, potential impacts on 'non-target' rhizosphere inhabitants ('non-target' is used to distinguish those microorganisms not conventionally known as targets) have not been thoroughly investigated. Thus, this review first summarizes the conventional roles of flavonoids as nod gene inducers, phytoalexins and allelochemicals before exploring questions concerning 'non-target' impacts. We hypothesize that flavonoids act to shape rhizosphere microbial community structure because they represent a potential source of carbon and toxicity and that they impact on rhizosphere function, for example, by accelerating the biodegradation of xenobiotics. We also examine the reverse question, 'how do rhizosphere microbial communities impact on flavonoid signals?' The presence of microorganisms undoubtedly influences the quality and quantity of flavonoids present in the rhizosphere, both through modification of root exudation patterns and microbial catabolism of exudates. Microbial alteration and attenuation of flavonoid signals may have ecological consequences for below-ground plant-microbe and plant-plant interaction. We have a lack of knowledge concerning the composition, concentration and bioavailability of flavonoids actually experienced by microbes in an intact rhizosphere, but this may be addressed through advances in microspectroscopic and biosensor techniques. Through the use of plant mutants defective in flavonoid biosynthesis, we may also start to address the question of the significance of flavonoids in shaping rhizosphere community structure and function.     

Rhizosphere engineering and management for sustainable agriculture

This paper reviews strategies for manipulating plants and their root-associated microorganisms to improve plant health and productivity. Some strategies directly target plant processes that impact on growth, while others are based on our knowledge of interactions among the components of the rhizosphere (roots, microorganisms and soil). For instance, plants can be engineered to modify the rhizosphere pH or to release compounds that improve nutrient availability, protect against biotic and abiotic stresses, or encourage the proliferation of beneficial microorganisms. Rhizobacteria that promote plant growth have been engineered to interfere with the synthesis of stress-induced hormones such as ethylene, which retards root growth, and to produce antibiotics and lytic enzymes active against soilborne root pathogens. Rhizosphere engineering also can involve the selection by plants of beneficial microbial populations. For example, some crop species or cultivars select for and support populations of antibiotic-producing strains that play a major role in soils naturally suppressive to soil-borne fungal pathogens. The fitness of root-associated bacterial communities also can be enhanced by soil amendment, a process that has allowed the selection of bacterial consortia that can interfere with bacterial pathogens. Plants also can be engineered specifically to influence their associated bacteria, as exemplified by quorum quenching strategies that suppress the virulence of pathogens of the genus Pectobacterium. New molecular tools and powerful biotechnological advances will continue to provide a more complete knowledge of the complex chemical and biological interactions that occur in the rhizosphere, ensuring that strategies to engineer the rhizosphere are safe, beneficial to productivity, and substantially improve the sustainability of agricultural systems.     

Flavonoids and thyroid disease

The most potent natural plant-derived compounds that can affect thyroid function, thyroid hormone secretion and availability to tissues is the group of flavonoids, i.e. plant pigments. They are present in our daily food, such as vegetables, fruits, grains, nuts, wine, and tea. Epidemiological studies suggest beneficial effects on health of flavonoids, which are commonly attributed to their activity as antioxidants. Experimental studies in vitro, however, showed inhibition of organification in thyroid cells and follicles by several flavonoids. Studies in vivo and vitro with synthetic and natural flavonoids showed displacement of T4 from transthyretin leading to disturbances in thyroid hormone availability in tissues. Radioactive labeled flavonoids appeared to be eliminated rapidly from the body mainly through excretion in the feces. In pregnant rats synthetic flavonoids cross the placenta and accumulate in the fetal compartment, including the fetal brain. Therefore, a high intake of flavonoids is contraindicated. In conclusion: flavonoids show strong interference with many aspects of thyroid hormone synthesis and availability.     

Involvement of a soybean ATP-binding cassette-type transporter in the secretion of genistein, a signal flavonoid in legume-Rhizobium symbiosis

Legume plants have an ability to fix atmospheric nitrogen into nutrients via symbiosis with soil microbes. As the initial event of the symbiosis, legume plants secrete flavonoids into the rhizosphere to attract rhizobia. Secretion of flavonoids is indispensable for the establishment of symbiotic nitrogen fixation, but almost nothing is known about the membrane transport mechanism of flavonoid secretion from legume root cells. In this study, we performed biochemical analyses to characterize the transport mechanism of flavonoid secretion using soybean (Glycine max) in which genistein is a signal flavonoid. Plasma membrane vesicles prepared from soybean roots showed clear transport activity of genistein in an ATP-dependent manner. This transport activity was inhibited by sodium orthovanadate, a typical inhibitor of ATP-binding cassette (ABC) transporters, but was hardly affected by various ionophores, such as gramicidin D, nigericin, or valinomycin, suggesting involvement of an ABC transporter in the secretion of flavonoids from soybean roots. The K(m) and V(max) values of this transport were calculated to be 158 mum and 322 pmol mg protein(-1) min(-1), respectively. Competition experiments using various flavonoids of both aglycone and glucoside varieties suggested that this ABC-type transporter recognizes genistein and daidzein, another signaling compound in soybean root exudates, as well as other isoflavonoid aglycones as its substrates. Transport activity was constitutive regardless of the availability of nitrogen nutrition. This is, to our knowledge, the first biochemical characterization of the membrane transport of flavonoid secretion from roots.     

Rhizosphere Properties of Poaceae Genotypes Under P-limiting Conditions

Plant genotypes differ in P efficiency, i.e. their capacity to grow in soil with low P availability. Plant properties such as root and root hair length, release of P mineralising and mobilising compounds by the roots and P requirement for optimal growth are known to influence P efficiency. In order to improve the understanding of the role of rhizosphere properties in plant P uptake, we grew three Poaceae genotypes [two wheat (Triticum aestivum L.) genotypes (the P-efficient Goldmark and the P-inefficient Janz), and the Australian native grass Austrostipa densiflora L.] to maturity in an acidic loamy sand with low P availability. Addition of 120 mg P as FePO₄ kg⁻¹ (P120) improved the growth of all three genotypes. In both P0 and P120, growth and P uptake were smaller in Janz than in Goldmark. During the vegetative phase, growth and P uptake of Austrostipa were smaller than in Goldmark in P0 but greater in P120. These differences can be explained by plant properties such as root growth, specific P uptake, mobilisation of inorganic and organic P by root exudates and P utilisation efficiency. In P120, P availability in the rhizosphere was least in Janz and greatest in Austrostipa. Microbial biomass P in the rhizosphere was least in Janz. Acid phosphatase activity was greatest in the rhizosphere of Austrostipa and least in Janz. Plant growth and P uptake were positively correlated with microbial P, acid phosphatase activity and resin P in the rhizosphere, suggesting that microorganisms contribute to uptake of P by plants in this soil. Microbial community composition in the rhizosphere [analysed by fatty acid methylester (FAME) analysis and denaturing gradient gel electrophoresis (DGGE)] differed among genotypes, changed during plant development and was affected by P addition to the soil. Genotype-specific microbial community composition in the rhizosphere may have contributed to the observed differential capacity of plants to grow at low P availability.     

Rhizosphere processes are quantitatively important components of terrestrial carbon and nutrient cycles

While there is an emerging view that roots and their associated microbes actively alter resource availability and soil organic matter (SOM) decomposition, the ecosystem consequences of such rhizosphere effects have rarely been quantified. Using a meta‐analysis, we show that multiple indices of microbially mediated C and nitrogen (N) cycling, including SOM decomposition, are significantly enhanced in the rhizospheres of diverse vegetation types. Then, using a numerical model that combines rhizosphere effect sizes with fine root morphology and depth distributions, we show that root‐accelerated mineralization and priming can account for up to one‐third of the total C and N mineralized in temperate forest soils. Finally, using a stoichiometrically constrained microbial decomposition model, we show that these effects can be induced by relatively modest fluxes of root‐derived C, on the order of 4% and 6% of gross and net primary production, respectively. Collectively, our results indicate that rhizosphere processes are a widespread, quantitatively important driver of SOM decomposition and nutrient release at the ecosystem scale, with potential consequences for global C stocks and vegetation feedbacks to climate.     

Neuroinflammation: modulation by flavonoids and mechanisms of action

Neuroinflammatory processes are known to contribute to the cascade of events culminating in the neuronal damage that underpins neurodegenerative disorders such as Parkinson's and Alzheimer's disease. Recently, there has been much interest in the potential neuroprotective effects of flavonoids, a group of plant secondary metabolites known to have diverse biological activity in vivo. With respect to the brain, flavonoids, such as those found in cocoa, tea, berries and citrus, have been shown to be highly effective in preventing age-related cognitive decline and neurodegeneration in both animals and humans. Evidence suggests that flavonoids may express such ability through a multitude of physiological functions, including an ability to modulate the brains immune system. This review will highlight the evidence for their potential to inhibit neuroinflammation through an attenuation of microglial activation and associated cytokine release, iNOS expression, nitric oxide production and NADPH oxidase activity. We will also detail the current evidence indicting that their regulation of these immune events appear to be mediated by their actions on intracellular signaling pathways, including the nuclear factor-κB (NF-κB) cascade and mitogen-activated protein kinase (MAPK) pathway. As such, flavonoids represent important precursor molecules in the quest to develop of a new generation of drugs capable of counteracting neuroinflammation and neurodegenerative disease.     

Evidence of a strong coupling between root exudation, C and N availability, and stimulated SOM decomposition caused by rhizosphere priming effects

Increased temperatures and concomitant changes in vegetation patterns are expected to dramatically alter the functioning of northern ecosystems over the next few decades. Predicting the ecosystem response to such a shift in climate and vegetation is complicated by the lack of knowledge about the links between aboveground biota and belowground process rates. Current models suggest that increasing temperatures and rising concentrations of atmospheric CO(2) will be partly mitigated by elevated C sequestration in plant biomass and soil. However, empirical evidence does not always support this assumption, as elevated temperature and CO(2) concentrations also accelerate the belowground C flux, in many cases extending to increased decomposition of soil organic matter (SOM) and ultimately resulting in decreased soil C stocks. The mechanism behind the increase has remained largely unknown, but it has been suggested that priming might be the causative agent. Here, we provide quantitative evidence of a strong coupling between root exudation, SOM decomposition, and release of plant available N caused by rhizosphere priming effects. As plants tend to increase belowground C allocation with increased temperatures and CO(2) concentrations, priming effects need to be considered in our long-term analysis of soil C budgets in a changing environment. The extent of priming seems to be intimately linked to resource availability, as shifts in the stoichiometric nutrient demands of plants and microorganisms will lead to either cooperation (resulting in priming) or competition (no priming will occur). The findings lead us on the way to resolve the varying response of primary production, SOM decomposition, and release of plant available N to elevated temperatures, CO(2) concentrations, and N availability.     

The rhizosphere: complex by design

The rhizosphere represents one of the most complex ecosystems on earth with almost every root on the planet expected to have a chemically, physically and biologically unique rhizosphere. Despite its intrinsic complexity, understanding the rhizosphere is vital if we are to solve some of the world’s most impending environmental crises such as sustainable food, fibre and energy production, preservation of water resources and biodiversity, and mitigation against climate change. One of the key challenges that faces rhizosphere ecologists is how to translate their fundamental research into practical real-world applications. In addition, they need to convince policy makers that consideration of the rhizosphere is vital in the formulation and implementation of any environmental policy relating to plant growth. This is highlighted by the recent biofuel and carbon debt debate whereby rhizosphere processes such as priming were largely ignored leading to destabilization of national policies. Recent advances in our understanding of the tangled web of rhizosphere interactions have been largely driven by technological innovations in analytical, bioinformatic and imaging tools, and this is likely to continue for the foreseeable future. However, there is also a critical need to incorporate this more reductionist information into mathematical models that are capable of incorporating the rhizosphere to allow simulation of plot- or landscape-level processes that are particularly relevant to policymakers. Consequently, as the multidisciplinary rhizosphere science community grows, there will be increasing need to both integrate scientific information and to subsequently convey this in an effective manner to stakeholders. If we can achieve this we will be in a good position to help prevent ongoing global environmental degeneration. These issues were addressed at the RHIZOSPHERE 2 International Conference which was held at Montpellier, France in August 2007. This special issue gathers some of the research presented during this major event.     

The effect of nitrate-nitrogen supply on bacteria and bacterial-feeding fauna in the rhizosphere of different grass species

Summary Microbial growth in the rhizosphere is affected by the release of organic material from roots, so differences in carbon budgets between plants may affect their rhizosphere biology. This was tested by sampling populations of bacteria and bacteriophagous fauna from the rhizosphere of Lolium perenne, Festuca arundinacea, Poa annua, and Poa pratensis, under conditions of high and low nitrate availability. Concentrations of soluble phenolics and lignin varied considerably between the species but were not related to differences in rhizosphere biology. L. perenne and F. arundinacea supported fewer bacteria than the Poa species. There was no significant rhizosphere effect on the groups of protozoa. The major indicators of rhizosphere productivity were the bacterial-feeding nematodes (mainly Acrobeloides spp.), and there was a large positive effect of added nitrate. Nematode biomass was significantly lower in the rhizosphere of the slow-growing P. pratensis compared with the fast-growing P. annua, indicating that the differential allocation of carbon has affects on rhizosphere biology. A large rhizosphere effect on enchytraeid worms was also observed, and their potential importance in the rhizosphere is discussed.     

Soil Nitrogen Availability and Plant Genotype Modify the Nutrition Strategies of M. truncatula and the Associated Rhizosphere Microbial Communities

Plant and soil types are usually considered as the two main drivers of the rhizosphere microbial communities. The aim of this work was to study the effect of both N availability and plant genotype on the plant associated rhizosphere microbial communities, in relation to the nutritional strategies of the plant-microbe interactions, for six contrasted Medicago truncatula genotypes. The plants were provided with two different nutrient solutions varying in their nitrate concentrations (0 mM and 10 mM). First, the influence of both nitrogen availability and Medicago truncatula genotype on the genetic structure of the soil bacterial and fungal communities was determined by DNA fingerprint using Automated Ribosomal Intergenic Spacer Analysis (ARISA). Secondly, the different nutritional strategies of the plant-microbe interactions were evaluated using an ecophysiological framework. We observed that nitrogen availability affected rhizosphere bacterial communities only in presence of the plant. Furthermore, we showed that the influence of nitrogen availability on rhizosphere bacterial communities was dependent on the different genotypes of Medicago truncatula. Finally, the nutritional strategies of the plant varied greatly in response to a modification of nitrogen availability. A new conceptual framework was thus developed to study plant-microbe interactions. This framework led to the identification of three contrasted structural and functional adaptive responses of plant-microbe interactions to nitrogen availability.     

Absorption and metabolism of flavonoids

The benefits of flavonoids as chemopreventive dietary or dietary supplemental agents are still only "potential." Much has been learned about possible mechanisms of action of these agents, but whether they can reach their multiple intended sites of action, particularly in humans, is largely unknown. The biological fate of the flavonoids, including their dietary glycoside forms, is highly complex, dependent on a large number of processes. This review is intended to bring some order into this complex area and deals with the fate of the naturally occurring glycosides, their enzymatic hydrolysis, as well as the resulting aglycones. The impact of membrane transporters as well as metabolic enzymes on the cellular availability of these phytochemicals is examined. A reevaluation of the concept of oral bioavailability applied to the dietary flavonoids is presented.     

The role of flavonoids in root-rhizosphere signalling: opportunities and challenges for improving plant-microbe interactions

The flavonoid pathway produces a diverse array of plant compounds with functions in UV protection, as antioxidants, pigments, auxin transport regulators, defence compounds against pathogens and during signalling in symbiosis. This review highlights some of the known function of flavonoids in the rhizosphere, in particular for the interaction of roots with microorganisms. Depending on their structure, flavonoids have been shown to stimulate or inhibit rhizobial nod gene expression, cause chemoattraction of rhizobia towards the root, inhibit root pathogens, stimulate mycorrhizal spore germination and hyphal branching, mediate allelopathic interactions between plants, affect quorum sensing, and chelate soil nutrients. Therefore, the manipulation of the flavonoid pathway to synthesize specifically certain products has been suggested as an avenue to improve root-rhizosphere interactions. Possible strategies to alter flavonoid exudation to the rhizosphere are discussed. Possible challenges in that endeavour include limited knowledge of the mechanisms that regulate flavonoid transport and exudation, unforeseen effects of altering parts of the flavonoid synthesis pathway on fluxes elsewhere in the pathway, spatial heterogeneity of flavonoid exudation along the root, as well as alteration of flavonoid products by microorganisms in the soil. In addition, the overlapping functions of many flavonoids as stimulators of functions in one organism and inhibitors of another suggests caution in attempts to manipulate flavonoid rhizosphere signals.     

Origins of root-mediated pH changes in the rhizosphere and their responses to environmental constraints: A review

The aim of the present review is to define the various origins of root-mediated changes of pH in the rhizosphere, i.e., the volume of soil around roots that is influenced by root activities. Root-mediated pH changes are of major relevance in an ecological perspective as soil pH is a critical parameter that influences the bioavailability of many nutrients and toxic elements and the physiology of the roots and rhizosphere microorganisms. A major process that contributes root-induced pH changes in the rhizosphere is the release of charges carried by H⁺ or OH^– to compensate for an unbalanced cation–anion uptake at the soil–root interface. In addition to the ions taken up by the plant, all the ions crossing the plasma membrane of root cells (e.g., organic anions exuded by plant roots) should be taken into account, since they all need to be balanced by an exchange of charges, i.e., by a release of either H⁺ or OH^–. Although poorly documented, root exudation and respiration can contribute some proportion of rhizosphere pH decrease as a result of a build-up of the CO₂ concentration. This will form carbonic acid in the rhizosphere that may dissociate in neutral to alkaline soils, and result in some pH decrease. Ultimately, plant roots and associated microorganisms can also alter rhizosphere pH via redox-coupled reactions. These various processes involved in root-mediated pH changes in the rhizosphere also depend on environmental constraints, especially nutritional constraints to which plants can respond. This is briefly addressed, with a special emphasis on the response of plant roots to deficiencies of P and Fe and to Al toxicity. Finally, soil pH itself and pH buffering capacity also have a dramatic influence on root-mediated pH changes.     

Root exudates as mediators of mineral acquisition in low-nutrient environments

Plant developmental processes are controlled by internal signals that depend on the adequate supply of mineral nutrients by soil to roots. Thus, the availability of nutrient elements can be a major constraint to plant growth in many environments of the world, especially the tropics where soils are extremely low in nutrients. Plants take up most mineral nutrients through the rhizosphere where micro-organisms interact with plant products in root exudates. Plant root exudates consist of a complex mixture of organic acid anions, phytosiderophores, sugars, vitamins, amino acids, purines, nucleosides, inorganic ions (e.g. HCO₃ ^–, OH^–, H⁺), gaseous molecules (CO₂, H₂), enzymes and root border cells which have major direct or indirect effects on the acquisition of mineral nutrients required for plant growth. Phenolics and aldonic acids exuded directly by roots of N₂-fixing legumes serve as major signals to Rhizobiaceae bacteria which form root nodules where N₂ is reduced to ammonia. Some of the same compounds affect development of mycorrhizal fungi that are crucial for phosphate uptake. Plants growing in low-nutrient environments also employ root exudates in ways other than as symbiotic signals to soil microbes involved in nutrient procurement. Extracellular enzymes release P from organic compounds, and several types of molecules increase iron availability through chelation. Organic acids from root exudates can solubilize unavailable soil Ca, Fe and Al phosphates. Plants growing on nitrate generally maintain electronic neutrality by releasing an excess of anions, including hydroxyl ions. Legumes, which can grow well without nitrate through the benefits of N₂ reduction in the root nodules, must release a net excess of protons. These protons can markedly lower rhizosphere pH and decrease the availability of some mineral nutrients as well as the effective functioning of some soil bacteria, such as the rhizobial bacteria themselves. Thus, environments which are naturally very acidic can pose a challenge to nutrient acquisition by plant roots, and threaten the survival of many beneficial microbes including the roots themselves. A few plants such as Rooibos tea (Aspalathus linearis L.) actively modify their rhizosphere pH by extruding OH^– and HCO₃ ^– to facilitate growth in low pH soils (pH 3 – 5). Our current understanding of how plants use root exudates to modify rhizosphere pH and the potential benefits associated with such processes are assessed in this review.     

Applying a solute transfer model to phytoextraction: Zinc acquisition by Thlaspi caerulescens

Phytoextraction is the removal of metals from contaminated soils into harvested plant tissues. The rate of phytoextraction is governed by both soil and plant characteristics. Most effort has focused on identifying appropriate plants for phytoextraction, but the benefits from this effort will be marginal unless the metals are in phytoavailable forms in the rhizosphere. The concentration of a metal in the rhizosphere can be estimated using solute transfer models that incorporate: the metal concentration in the bulk soil solution, the buffer power of the soil, diffusion coefficient for the metal, water movement, root size and morphology, and the rate of entry of metal into the roots. Here a solute transfer model is developed to predict the concentration of Zn in the rhizosphere solution ([Zn]_ext) of Thlaspi caerulescens, a hyperaccumulator species that could be exploited for Zn phytoextraction. The model predicts that Zn accumulation by T. caerulescens is sub-optimal when the Zn concentration in the bulk soil solution is <27 M. Such a high [Zn]_ext is rare in contaminated agricultural soils, but is possible in the metalliferous substrates where T. caerulescens is endemic. Sensitivity analyses indicate that Zn diffusion is more important than transpiration-driven mass flow for Zn delivery to the root, implying that management of soil physical and hydrological properties will improve phytoextraction. Sensitivity analyses also imply that strategies to enhance the Zn absorption power of the root will not necessarily be successful for enhancing phytoextraction per se. Thus, research into enhancing Zn availability and mobility in soil will be as important as understanding and manipulating Zn uptake by plants. In general, such models can be used to identify constraints to efficient phytoextraction (whether plant or soil) and to determine whether commercial phytoextraction is feasible.     

Site selection and regulation issues for trout and carp farming in Germany

In most industrialized countries very few natural freshwater habitats are available for the establishment of new fish farms. These limits require regulatory measures, largely depending on local conditions. Regulations on volume and type or water to be extracted from groundwater and/or surface resources exist in Germany on the ‘Linder’ federal level (contained in the ‘Water Acts’ (‘Wasserhaushaltsgesetz’). These regulations also set water quality criteria for effluent discharge into receiving waters. Site selection criteria are largely determined by the type of aquaculture considered: in extensive, conventional pond farming systems, criteria on natural factors include water resource availability, space and geomorphological (e.g. sloe) and geochemical factors (e.g. soils). The appropriate positioning and leveling of ponds will decide on whether excessive energy costs can be avoided. Different site selection criteria will have to be employed for trout and carp culture. For carp, availability of large areas with suitable soil characteristics is essential. Comparably low yields per unit area will be achievable (productivity of the water determines stocking density and yield). Construction costs need to be kept at a minimum, otherwise the operation will never become economically feasible. Exceptions are special ponds for overwintering, or spawning or other special purposes. Trout culture in earthern ponds require different site selection criteria, depending on the volume of water supply, because yield does not depend on area specific productivity of the water body. Water quality management criteria become an overriding issue for this type of culture system. Stocking density will be determined by the permit for extractable water volumes per unit time. (set by the water authorities). Intensification methods for trout farming exist within the range of regulated effluent standards by using specifically designed system components such as concrete ponds, raceways, circular tanks, aeration, oxygenation, etc. The effluents, however, are considered an industrial waste and their release into receiving waters will be under the water management law (57). If standards are not met within the set limits effluents will be charged as the release of any other industrial wastewater.