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Lecture 18

Lecture 18 – Water and Nutrient Absorption 2

2 Pages

Course Code
Biology 2601A/B
Graeme Taylor

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LECTURE 18 – WATER AND NUTRIENT ABSORPTION 2: ROOT STRUCTURE AND FUNCTION What is an Essential Nutrient?  A plant can’t complete its life cycle in the absence of that element  The element is part of an essential molecule or constituent  Essential elements required by most plants – hydrogen, carbon, oxygen, micronutrients such as chlorine, iron, boron, sodium, zinc, etc.  How much is enough? o Standardized curve (5.4) o Deficiency zone – do not have enough essential nutrients to get to maximum growth rate/yield o Adequate zone – once nutrients increase, growth of the plant also increases but then enters a zone where the plant stops being responsive to increases in the amount of nutrients being supplied  Does not harm the plant in any way o Toxic zone – high levels of any nutrient produces a toxicity effect, poisons plant with too much of the nutrient leading to a decline in productivity o Critical concentration – shows turnover from increase in deficiency zone to adequate zone  But for a non-essential nutrient, it is different o No deficiency zone o However, toxic effects are still possible from elements that are non-essential nutrients Mobile Nutrients  Mobile nutrients can be re-translocated in the phloem  Deficiency symptoms occur in old tissues first, as nutrients are supplied to new growth  Examples – nitrogen, potassium, magnesium, chlorine, sodium, etc.  Immobile nutrients cannot be re-translocated  Deficiency symptoms occur in new tissues first  Examples – calcium, sulfur, iron, boron, copper Nutrients in Soil  Nutrients must be in solution in the soil  Nutrients reach roots via diffusion and bulk flow  As roots absorb nutrients, the concentration near the root drops – this drives diffusion of nutrients to the depleted zone  Movement of water down the water potential gradient also moves nutrients by bulk flow Plants can Alter Nutrient Availability  Soil particles tend to have negatively-charged surfaces  Extruding H+ ions (via proton pumping) can displace nutrient cations from colloids  As a plant, if protons can be pumped out, positively charged cations can be displaced – can be done in two different ways: o Direct proton extrusion – will go into solution and displace absorbed cations o Emit CO 2hrough respiration, which will react with water in the soil, forming bicarbonate that in turn produces hydrogen ions – release of cations from negatively charged soil surface  Some nutrients are more soluble in acidic solutions
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