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Unformatted text preview: 2-19 Soils and I norganic Nut r ient Absorption by Roots I norganic Nut r ients i n the Soil CO2 is the source of C and O; H 2O is the source of H and O. Everything else comes in to the plant roots from the soil solution. N in the form of NO 3(nitrate)and N H 3 (Ammona), S as SO42- (Sulfate), P as PO43- (Phosphate) Fe as Fe2+, K as K +, etc. Available affected by pH 1. C hemical weathering of rock minerals i n the soil releases salts t hat dissolve in to the water to form these ions that the roots take up. 2. D ecomposition of dead plant and animal matter by fungi and bacteria (decomposers) release excess inorganic nut rients, such as ammonia, to the soil. Uptake of I norganic Nut r ients 1. The ions in the soil must fi rst be absorbed by epidermal or cortex cells of t he young root due to the presence of an endodermis. a. Means that they m ust pass across a cell membrane, which a llows for selectivity as to what gets in and accumulation of the ions from a dilute solution, the soil solution. b. H ow do dissolved substances cross membranes? (1) By p assing th rough the lipid layer (generally, only gases do). (2) By p assing th rough a t ransmembrane protein channel . (3) By being “carried” across by a p rotein car r ier that binds the substance on one side of membrane, releases it to other side. 2. F or the ion accumulation i n epidermal or cortical cells before they move v ia plasmodesmata to the xylem, n eed ATP energy . a. A TP is synthesized i n these cells b y respiration t hat r equires carbohydrates and oxygen (O 2) . b. Severing the phloem above the roots, starves the cells. They cannot respire and produce ATP for survival or nut rient uptake. c. R emoving O 2 f rom the soil w ill cause plants to show nut rient deficiencies (usually yellowing of leaves in various patterns). (1) N o O 2, little ATP production from respiration ; li t tle ATP available for ion accumulation in the cells. d. Plants vary as to how long they can tolerate anaerobic conditions. P lants in f lood plains have very shallow root systems. ...
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- Spring '08