Soil and Plant

NutritionCh. 37

study of necessary elements for plant

growth

Plants…Critical role in energy flow and chemical

cycling of ecosystems

• Transform light energy chemical energy

• Transform inorganic compounds organic compounds

Dry weight

• 95% organic

• 5% minerals

The uptake of nutrients by a plant: a review

CO2, the sourceof carbon for

Photosynthesis,diffuses into

leaves from theair through

stomata.

Throughstomata, leavesexpel H2O andO2.

H2O

O2

CO2

Roots take inO2 and expelCO2. The plantuses O2 for cellularrespiration but is a net O2 producer.

O2

CO2

H2O

Roots absorbH2O and

minerals fromthe soil.

Minerals

Table 37.1 Essential Elements in Plants

Nutritional RequirementsEssential nutrient• required to develop from a seed

through its life cycleSunlightCarbon dioxideWater• Supplies most of H and O2 for

photosynthesis; 80-85% of plant

• 90% lost during transpiration

Soil TextureMajor factors in what kind of plants will growTexture depends upon particle size• sand 20 - 200 mm; silt 2 - 20 mm;

clay < 2 mmHorizons• distinct soil layers

Topsoil

• Horizon A

• decomposed rock, living organisms, humus

Humus

• decomposing organic matter

• prevents clay from packing together

• crumbly soil

• reservoir of mineral nutrientsLoams• most fertile, mixture of sand, silt, clay• fine particles retain water & minerals• coarse particles provide air spaces

Texture and Composition of Soil

Living organisms• Worms aerate the soil

• Bacteria alter soil mineral composition

• Fungi, algae, protists, insects, nematodes, plant roots

Topsoil Composition

Surface charges of soil particles determine binding ability

Positively charged adhere…• Not likely to leach away• Potassium, calcium, magnesium

Mineral cations enter by absorption from soil solution

• Cation exchange

Negatively charged ions are easily released and leached away

The availability of soil water and mineralsSoil particle surrounded byfilm of water

Root hair

Water available to plant

Air space

H2O + CO2 H2CO3 HCO3– +

Root hair

Soil particle

K+

Cu2+Ca2+

Mg2+K+

K+

H+

H+

–

–– –

– – –––

(a) Soil water. A plant cannot extract all the water in the soil because some of it is tightly held by hydrophilic soil particles. Water bound less tightly to soil particles can be absorbed by the root.

(b) Cation exchange in soil. Hydrogen ions (H+) help make nutrients available by displacing positively charged minerals (cations such as Ca2+) that were bound tightly to the surface of negatively charged soil particles. Plants contribute H+ by secreting it from root hairs and also by cellular respiration, which releases CO2 into the soil solution, where it reacts with H2O to form carbonic acid (H2CO3). Dissociation of this acid adds H+ to the soil solution.

Soil Conservation & Sustainable AgricultureIrrigation

• causes huge drain on water resources; main source is aquifers

• gradually makes soil salty (hypertonic) and infertile salinization

• Solutions – Drip irrigation

– Develop plant varieties that require less water or can tolerate more salinity

Fertilizers

• Way to reverse nutrient depletion

• N, P, K

• mined, chemically produced, organic

• soil pH important

• organic

– Manure, fishmeal, compost

Soil Conservation & Sustainable AgricultureAdjusting soil pH• Influences mineral availability• Most prefer slightly acidic soils

Controlling Erosion• Water and wind are the main causes• Plant rows of trees, terrace hillside crops, contour

pattern• No till agriculture

– Special plowing technique

Phytoremediation• Nondestructive biotechnology• Harnesses the ability of some plants to extract

pollutants and concentration them in portions of the plant that can be easily removed

Macro and MicronutrientsSoil, water, and air all contribute to plant growth• 80-90% of fresh mass is water

Essential Elements• Required for a plant to complete its life cycle• Determined by hydroponic culture

Variety of inorganic, mineral ions in the soil• macronutrients (9) • micronutrients (8)

– Mostly cofactors

Deficiencies depend on• role of nutrient in the plant• its mobility within the plant• K, N, P

Phosphate-deficient

Healthy

Potassium-deficient

Nitrogen-deficient

Genetic Modification - Improving Plant NutritionResistance to Aluminum Toxicity• Introduction of the citrate synthase gene from bacteria

Flood Tolerance• Flood resistant rice (submergence gene)

Smart Plants• Signal when a mineral deficiency is imminent

Soil Bacteria and Plant NutritionRhizobacteria• Soil bacteria with especially large populations in the

rhizosphere– Soil layer that surrounds plant roots

• Produce chemicals to stimulate plant growth• Produce antibiotics to prevent root diseases

Bacteria and the Nitrogen Cycle

Figure 37.10 Root nodules on legumes

(a) Pea plant root. The bumps on this pea plant root are nodules containing Rhizobium bacteria. The bacteria fix nitrogen and obtain photosynthetic products supplied by the plant.

(b) Bacteroids in a soybean root nodule. In this TEM, a cell from a root nodule of soybean is filled with bacteroids in vesicles. The cells on the left are uninfected.

5 m

Bacteroidswithinvesicle

Nodules

Roots

Development of a soybean root nodule

Nitrogen Fixing BacteriaRoot nodules• Legumes

– Roots secrete chemicals to attract nearby bacteria

– Bacteria emit chemicals to cause root hairs to elongate and curl to prepare for infection within the root cortex

• Mutualistic relationship– Bacteria supplies nitrogen and legumes

supply the carbs• Crop rotation

– Legumes planted in off years to restore nitrogen in the soil

– If not harvested, plowed under

Mycorrhizae1 Ectomycorrhizae. The mantle

of the fungal mycelium ensheathes the root. Fungal hyphae extend from the mantle into the soil, absorbing water and minerals, especially phosphate. Hyphae also extend into the extracellular spaces of the root cortex, providing extensive surface area for nutrient exchange between the fungus and its host plant.

2 Endomycorrhizae. No mantle forms around the root, but microscopic fungal hyphae extend into the root. Within the root cortex, the fungus makes extensive contact with the plant through branching of hyphae that form arbuscules, providing an enormous surface area for nutrient swapping. The hyphae penetrate the cell walls, but not the plasma membranes, of cells within the cortex.

Mantle(fungal sheath)

Epidermis Cortex Mantle(fungalsheath)

Endodermis

Fungalhyphaebetweencorticalcells (colorized SEM)

100 m

Epidermis Cortex

Fungalhyphae

Roothair

10 m

(LM, stained specimen)

Cortical cells

Endodermis

Vesicle

Casparianstrip

Arbuscules

Nutritional AdaptationsParasitism• Photosynthetic but supplement diet from the host - mistletoe• If lose photosynthetic ability then get all nutrition from

phloem sap – dodder• Indian Pipe – nonphotosynthetic parasite of mycorrhizae

Nutritional AdaptationsEpiphytes• live on other plants but not parasites• anchored by roots and nourish themselves from

water and minerals absorption• ferns, mosses, orchids

Carnivorous plants: Venus fly trap (left), pitcher plant (right)

Nutritional AdaptationsCarnivorous plants

• supplemental diets because of living in poor soil conditions

• Venus fly trap, Pitcher plants, Sundew

Mangroves – Root, Stems, and Reproductive adaptations