Plants nutrient uptake

T. Roose, Mathematical model of plant nutrient uptake. D.Phil transfer dissertation. Mathematical Institute, University of Oxford, Oxford. U.K., 1998. 

T. Roose, A. C. Fowler, and P. R. Darrah, A mathematical model of plant nutrient uptake. J. Math. Biol. Submitted. 

The quantities of nutrients in microbes are large compared with the annual plant nutrient uptake, suggesting that even relatively limited dieback of the microbial populations can lead to release of an appreciable proportion of the plants annual nutrient requirement. Indeed, it is known that the annual uptake of P by wet tundra vegetation can be almost entirely accounted for by P released through nutrient flushes from the microbial biomass (Chapin et al, 1978). It is possible, therefore, that the supply rate of nutrients to the soil inorganic pool varies depending on the conditions for microbial population growth or decline and that plant nutrient availability fluctuates inversely to microbial nutrient demand. 

Soil anaerobiosis also affects plant nutrient uptake in wetland environments. Anaerobiosis in the rhizosphere, a dominant factor in wetland areas, causes physiological stresses that can limit active nptake of essential elements snch as nitrogen. The nitrogen status, in turn, can affect photosynthetic activity in plants. In addition to effects on plant growth, both intensity and capacity of reduction... 

Additional removal of BOD5 and T-N could be obtained at the anaerobic/anoxic tank of the constructed wetland. About 57 % of the ranaining BOD5 was removed at the anaerobic/anoxic tank. More than 74 % of the remaining T-N was denitrified, and the average concentration of T-N at the final effluent was 6.9 mg/L. The maximum available capacity for nutrient uptake in plants was far less (of the order of 5 %) than the loading rate of nutrients to the constructed wetland. 

As mentioned before and in Chaps. 4 and 6, the concentration of rhizode-position decreases as the distance from the rhizoplane increases, whereas the opposite generally occurs for the concentration of any plant nutrient in soil. In this context, the role of rhizospheric soil, rather than that of the bulk soil, is crucial for plant nutrition. It has also to be considered that very different situations can occur depending on the type of nutrient (24) and the nutritional status of plants (see Chap. 3) furthermore, different portions of the root system are characterized by differential nutrient-specific rates of uptake (25). All the above statements point to the necessity of reconsidering the concept of plant nutrient availability giving more importance to the situation occurring in the soil surrounding the root. 

This chapter focuses on the effects of humic substances present at the rhizo-sphere on plant growth and nutrient uptake. The main structural features of humic substances, their nutritional function, and the capacity to interact with plant metabolism are also presented. 

D. T. Clarkson, Factors affecting mineral nutrient uptake by plants. Amw. Rev. Plain Physiol. 36 77 (1984). 

As stated earlier, mycorrhizae enhance nutrient absorption. Greater soil exploitation by mycorrhizal roots as a means of increasing phosphate uptake is well established. The normal phosphate depletion zone around non-mycorrhizal roots is 1-2 mm, but an endomycorrhizal root symbiont increased this zone to 7 cm (140). This ability to increase the nutritional level (particularly with regard to phosphorus), and subsequently the overall better growth dynamics of the mycorrhizal plant has been suggested as the reason for the salt (43) and drought (44-46) tolerance and increased nodulation (47) observed in mycorrhizal associations. Another interesting aspect of this enhanced nutrient uptake is the possible effect of mycorrhizae on competitive ability between two plant species. Under some conditions, mycorrhizal... 

Nutrient concentration has a marked seasonal variation in the middle Ebro. Nutrient loads transported by the river are relevant during the high flow season (December-April), while nitrate inputs from agriculture can also be relevant. In this period, crop fertilization is carried out, precipitation is higher, and plant nitrogen uptake is lower [37], Although nutrient loads are high, dilution causes NO3 and... 

Marti HR, Mills HA (1991) Nutrient uptake and yield of sweet pepper as affected by stage of development and N form. J Plant Nutr 14 1165-1175 Mccann E, Sullivan S, Ericson D, Deyoung R (1997) Environmental awareness, economic orientation, and farming practices comparison of organic and conventional farmers. Environ Manage 21 747-758... 

Tarkalson DD, Jolly VD, Robbins CW, Terry RE (1998) Mycorrhizal colonization and nutrient uptake of dry bean in manure and compost manure treated subsoil and untreated top and subsoil. J Plant Nutr 21 1867-1878... 

Galvez L, Douds DD, Drinkwater LE, Wagoner P (2001) Effect of tillage and farming system upon VAM fungus populations and mycorrhizas and nutrient uptake of maize. Plant Soil... 

Weathering is a major H+ consuming process and pH-buffering mechanism, not only globally and regionally but it also plays a major role in local watersheds in soil processes, in nutrient uptake by plants and in epidiagenetic reactions in sediments. 

This chapter has shown the complexity of the chemical and biological processes around wetland plant roots and the effects of the extreme electrochemical gradient between the root surface and surrounding soil. Models of nutrient uptake by plants in aerobic soil, which treat the root as a simple sink to which nutrients are delivered by mass flow and diffusion but the root not otherwise influencing the surrounding soil, work reasonably well for the more soluble nutrient ions. However, the complexity of the wetland root environment is such that such models are inadequate and more elaborate treatments are necessary. Many of the mechanisms involved are still poorly defined and speculative, but their potential significance is clear. 

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