Ch 2Mineral Nutrition — Class 12 Botany, concept-first.

Figure 12.1 shows a simple static hydroponic set-up: a seedling in a pot of nutrient solution, with a funnel for topping up water and nutrients, cotton packed around the stem at the pot mouth to hold…

More Elements Are Absorbed Than Are Needed Plant roots are not fussy about what they take up from the soil — more than 60 of the roughly 105 known chemical elements have been detected inside one plant…

- Absolute requirement: the plant must be unable to complete its life cycle — to grow normally and to produce viable seed — without that element.

- Macronutrients are needed in large amounts — more than 10 millimoles per kilogram of dry matter. They are carbon, hydrogen, oxygen, nitrogen, phosphorus, sulphur, potassium, calcium and magnesium.

- Mobile elements — such as nitrogen, potassium and magnesium — can be broken down out of old tissue and exported to actively growing young tissue.

A Narrow Safe Window Because micronutrients are needed only in tiny amounts, the safe range between too little and too much is narrow: even a moderate fall in supply causes deficiency, while a moderat…

- Stage one — into the apoplast: ions move quickly into the 'free space' or 'outer space' of the cell, called the apoplast, by a passive process that needs no metabolic energy.

Travelling Up With the Water Stream Once a plant's roots have absorbed mineral salts, the minerals do not stay put — they need to be carried to every part of the plant that needs them.

- harbours nitrogen-fixing bacteria and countless other soil microbes that plants depend on, - holds water that the plant's roots can draw on, - supplies air (oxygen) to the roots, which need it for r…

Why Nitrogen Matters So Much After carbon, hydrogen and oxygen, nitrogen is the most abundant element found in living organisms.

- Nitrogen enters the soil pool from the atmosphere through three routes: biological nitrogen fixation (certain bacteria converting N2 to ammonia), industrial nitrogen fixation (man-made fertiliser pr…

- Free-living N2-fixers — including the aerobic bacteria Azotobacter and Beijerinckia, the anaerobic bacterium Rhodospirillum, the bacterium Bacillus, and free-living cyanobacteria such as Anabaena an…