Organic and commercial PHOSPHORUS fertilizers are used in today's agriculture to maintain a high level production of agricultural crops, while in most watersheds controlling of PHOSPHORUS is a very important issue. Because of the contribution of PHOSPHORUS to water quality deterioration, the environmental scientists are very concerned about the increasing of PHOSPHORUS concentration in standing waters. The blossom of the algae and other aquatic plants is related to different nutrient concentration e.g. PHOSPHORUS in their media, however, the role of PHOSPHORUS as a key element in eutrophication of the surface water and lakes is well documented. Four soil groups and sediment samples from the St. Esprit watershed of Quebec, Canada were amended with 50, 100, and 500 mg P kg-1soil as KH2PO4.The relationship between water-extractable P, WEP, (soluble PHOSPHORUS) and available P, MHШ, (Mehlich #3) was determined for water-soil ratios of 100:1, 200:1, and 500:1. Soluble P for these water-soil ratios were measured by method of Murphy and Riley after 4 hours shaking. The 4 hours shaking of the samples were based on the laboratory experience that more than 90% of the water-extracted PHOSPHORUS was released after 3 hours shaking for all the samples. Therefore, the shaking time for release of soluble P was set at 4 hours. Mehlich#3 extractable P was also determined in soil and sediment samples. There was a linear relationship (linear isotherm) between the logarithm of soluble and Mehlich#3 extractable P at different water:soil ratios for all soil and sediment samples from the watershed. Therefore, the equation of these isotherms could be used in mathematical models such as ANSWERS, an event based model, for prediction of soluble P TRANSPORT from this watershed.

Background: Waste stabilization ponds are simplest systems applied by human to treat the biological degradable materials. Today, computerized tools and special mathematical MODELING is used to manage environmental systems problems. System Dynamics is a system for problems analys is when time is a significant factor. It includes the way action and reaction of system is encountered by external thistles.Methods: After sampling and testing, PHOSPHORUS was modeled by using mathematical relationships and system Dynamics method. After making the initial model and its testing, the model was calibrated using three months data from facultative pond in Yazd city in Iran.Results: Algal growth rate, PHOSPHORUS settling rate and losses due to algal respiration and excretion were from important agents. Respiration rate of herbivorous zooplankton, non living carbon hydrolysis rate and phosphorous to chlorophyll ratio were from low important agents.Respiration rate of carnivorous zooplankton and phosphorous to carbon ratio were from unimportant agents.Conclusion: In comparison with other models, our System Dynamics Model needs low data. This is also a cheap model and we perceived good operation of it. In sensitive analysis, algal growth rate and PHOSPHORUS settling rate were important in PHOSPHORUS removal. So, we can manage facultative pond better with increasing retention time in pond. Phosphorous to chlorophyll ratio had low important role in this model. Thus, system can tolerate phosphorous variations in inlet wastewater with sufficient algal growth. Respiration rate of carnivorous zooplankton and phosphorous to carbon ratio do not limit system equilibrium. Ability of the model increases with sufficient retention time and further data. System Dynamics ecological models give useful information for facultative ponds. It is recommended this model be used for management affairs and overall assessment of facultative ponds. For more precise assessment, it is apposite to use two or three dimensions models substitute zero dimensions models.

Shahrood aquifer in Semnan province is affected by nitrate pollution sources such as domestic wells, agricultural return flow and industrial activities. These factors caused an increase of about 5.5 to 140 mg/L in groundwater nitrate concentration. In this research the TRANSPORT and fate of nitrate in Shahrood aquifer was studied. Groundwater flow was firstly was simulated using MODFLOW code and the model was calibrated under steady and unsteady states and was verified for a period of 3-years. Then TRANSPORT of nitrate was simulated by MT3DMS code. Initial and boundary conditions and TRANSPORT mechanisms (advection, dispersion, diffusion and chemical reactions) of nitrate were considered and the model was calibrated based on the concentration changes in urban area during a period of 2-years. The results show that nitrate TRANSPORT in Shahrood aquifer is greatly affected by groundwater flow direction and hydraulic conductivity. A zone of low hydraulic conductivity in the west and depression cones due to pumping wells concentration in the south of urban area, prevent nitrate spreading to the aquifer downstream. Denitrification process which decreases the nitrate concentration is probably not involved, because the urban area is located near the aquifer recharge zone where the oxidation conditions are prevailed. Based on the MODELING results, nitrate concentration in urban waste waters recharging Shahrood aquifer varies from 70 to 450 mg/L. The risk zone of nitrate contamination in urban area was also investigated. Nitrate concentration in return flow from agricultural areas was calibrated at about 200 mg/L. Regarding volume of the return flows, about 152 kg nitrate is annually leached from Shahrood agricultural areas. In general, wastewaters recharge from Shahrood urban areas have the highest impact on the nitrate contamination of the groundwater resources.

Objective Root structure modification is associated with the efficient water uptake and the nutrient utilization. It also provides structural support for the anchoring in soil. Genetic engineering for the improvement of plant root structure may help to maintain higher yields under drought conditions. The aim of this study was to modify the root structure of rice in order to improve drought tolerance and the efficiency of nutrient uptake. For this purpose, simultaneous transformation of Deeper Rooting1 or OsDRO1 gene, which is involved in the regulation of growth angle of the root in order to adapt to drought conditions, and PHOSPHORUS-Starvation Tolerance1 or OsPSTOL1 gene, which is effective in increasing PHOSPHORUS uptake and improving root structure, were considered for rice root structure modification. Materials and methods The OsDRO1 and OsPSTOL1 genes derived from the wild rice cultivars were cloned together in a single construct under the control of the root specific and the ubiquitin promoters, respectively. The resulting construct, pUhrDroPstol is transformed into the Agrobacterium tumefactions strain EHA105 and used for the gene transformation into Hashemi cultivar. Putative transgenic plants, survived on 50 mg/L Hygromycin during tissue culture steps, are transplanted into the Yoshida solution and then into the pots until they set seeds. Construct specific and gene specific PCR analysis are used to confirm the transgenic plants. Results In this study, 12 putative transgenic rice events were obtained, of which 10 showed the presence of both OsDRO1 and OsPSTOL1 genes in the PCR analysis. Transgenic plants show stronger root structure compared to the non-transgenic ones. Molecular analysis in the T1 and T2 generations determined the homozygous events. Conclusions In this study, two candidate genes affecting root structure, nutrient uptake and drought tolerance were transferred to the Hashemi rice using genetic engineering. So far, simultaneous transfer of these two candidate genes have not been reported. Transgenic plants present better root system compared to the control plants. The mentioned construct can be used for the transformation of other crops to improve their root structure, nutrient uptake and their drought tolerance. It is hoped that the production of the transgenic rice with modified root structure and efficient PHOSPHORUS uptake increases its drought tolerance and reduce water consumption in rice cultivation.

Background and Objectives: The many advantages of establishing symbiosis between arbuscular mycorrhizal (AM) fungi and most plants, including agricultural and horticultural plants, especially in terms of the growth and nutritional components of the host plant, have given special importance to this symbiosis. Increasing CO2 fixation by the host plants, they participate in the global carbon cycle, and as a result, they increase the organic carbon stock of the soil and in a way participate in the control of global temperature increase. It is now well documented that AM fungi improve mineral nutrition, particularly PHOSPHORUS (P) nutrition of the host plant. This beneficial effect of AM symbiosis is due primarily to enhanced P uptake by mycorrhizal roots. Mycorrhizal colonization can also improve the PHOSPHORUS nutrition of the host plant under abiotic and biotic stresses such as drought, salinity, oil pollutants, heavy metals and plant diseases. The synergistic effects between mycorrhizal fungi and a special group of useful soil microorganisms such as nitrogen fixing bacteria and phosphate solubilizing bacteria will lead to the improvement of plant PHOSPHORUS nutrition and ultimately lead to an increase in plant growth components. The basis of this symbiosis is the two-way exchange of nutrients that takes place in a unit consisting of the arbuscule and the host plant cell as "the central unit of symbiosis or the heart of symbiosis". Although the results of studies show the beneficial role of these fungi, due to the specific complexities of symbiotic relationships, there is still no complete understanding of the mechanisms of this symbiosis. Thus, extensive studies have been conducted with physiological, biochemical and molecular approaches. However, our understanding of the mechanism of this transfer, the exact route of this transfer and the TRANSPORTers involved in transferring P to the host plant are not well known. The objective of this article is to review the new findings of P uptake and TRANSPORT mechanisms in AM plants. It is focused particularly on the routes of P transfer, the contribution of each of these two symbionts in P uptake and transfer it and the mechanisms involved. With the advancement of this knowledge and a complete understanding of the hidden concepts of the fungus-plant relationship, it is possible to develop strategies for plant products by increasing the productivity of this symbiosis, especially in areas facing abiotic and biotic stresses.Materials and Methods: The materials and methods used in the studies of mycorrhizal symbiosis including the mechanisms of PHOSPHORUS uptake and transfer and other related topics, are very diverse, and only a few of them are mentioned here. The use of labelled PHOSPHORUS and a compartment culture system has been used to determine the contribution of each of the two symbionts in the uptake and transfer of P. In genomic studies (Gene expression analysis), quantitative PCR have been used to determine DNA and RNA. Fluorescence microscope and 4,6-diamidino-2-phenylindole (DAPI) staining method are used to visible polyphosphates in arbuscules (young arbuscules, mature arbuscules and degenerated arbuscules) and intraradical hyphae of AM fungi.Results: The findings of this review show that the P uptake and TRANSPORT in AM plants takes place through two different pathways, one directly through the plant root and the other indirectly through the external hyphae of the fungus. These two paths interact with each other in a complex and sometimes unknown way. Physiological approaches using labelled PHOSPHORUS to trace the relative contribution of direct and fungal pathways in plant P nutrition show that the contribution of the fungal pathway varies from negligible to almost all plant PHOSPHORUS. The reported results indicate that not only the percentage of root colonization, but also the total length of external hyphae and PHOSPHORUS concentration are very important in determining the contribution of direct and indirect pathways. TRANSPORTers involved in P uptake and TRANSPORT belong to several families. The PHT family with 5 subfamilies (PHT1, PHT2, PHT3, PHT4, and PHT5) based on their sequence and location has a vital role in P TRANSPORT. Among these TRANSPORTers, the PHT1 TRANSPORTers play an important role in P uptake from the rhizosphere, its distribution and homeostasis. The results of molecular studies show that when Arabidopsis thaliana receives enough P, at least 4 TRANSPORTers (PHT1,1-4) are involved in P uptake. Among these four TRANSPORTers, PHT1,1 is the TRANSPORTer that contributes the most to the uptake and transfer of P from the roots to the leaves of the plant. Most of the P absorbed in the tonoplast is polymerized and a linear chain of polyphosphate with high-energy bonds that can reach the number of 3 to thousands of units is formed inside the vacuole. Polyphosphates are TRANSPORTed mainly through a cytoplasmic stream along a tubular vacuole system towards the intraradical hyphae. How and by what molecular mechanism P is delivered to the host plant is not well known. However, three hypothetical pathways for P delivery to the plant have been proposed.Conclusion: A set of plant and fungal TRANSPORTers are responsible for absorbing, translocation, distributing, accumulating and redistributing P (P homeostasis) in a mycorrhizal plant in an interconnected, precise, complex and sometimes unknown process. However, the mechanism of this transfer, the interaction of plant and fungal TRANSPORTers in the absorption and transfer of P and its delivery to the host plant not well known. Much work conducted focusing on biomolecular and physiological studies to better understand these mechanisms. Although many advances have been made to elucidate the complex mechanisms for the integrated roles of nutrient TRANSPORT in AM symbiosis, much research work needs to be done to improve our understanding of these mechanisms and to answer the key questions. With the progress of this knowledge and a complete understanding of the complex relationships between fungi and plants, it is possible to develop plant product strategies by increasing the efficiency of this symbiosis, especially in areas facing biotic and abiotic stresses.