Nutrient Acquisition by Plants Flashcards
Soil Formation
soil is formed from weathering of rock by mechanical, chemical, and biological processes; all consisting of living and nonliving components:
- Humus
- Rock fragments
- Water + Gasses (air)
Humus
organic matter (living + dead); ~5% of soil volume
- plant roots
- prokaryotic + eukaryotic organisms
- decomposing plants + animals
Rock Fragments
fragments and other inorganic mineral matter from rock, slowly broken down into smaller particles;
~40-45% of soil volume
Water + Gasses (AIR)
dissolved in the soil particles; ~50% of soil volume
Soil Composition
- amount of each major component of soil depends on the amount of vegetation, soil compaction, and water present
- good, healthy soil has sufficient air, water, minerals, and organic material to promote + sustain plant life
Soil Texture
determined by the proportions of differently sized particles in the soil
- affects the ability of roots to penetrate the soil + ability of the soil to hold water
- Gravel > Sand > Silt > Clay > Loam
Influences on Soil Formation
- Parent Material
- Climate
- Topography
- Biological Factors
- Time
Parent Material
the organic + inorganic material in which the soil horizons forms from
- EX: bedrock, sand, glacial drift, river sediment
Climate
temperature, moisture, and wind cause different weathering patterns and therefore affect soil characteristics
- presence of moisture and nutrients from weathering also promote biological activity
Topography
regional surface features can have a major influence on the characteristics + fertility of soil
- affects water runoff - strips away parent material + affects plant growth
- steep soil are more prone to erosion and thinner
Biological Factors
- animals + microorganisms can produce pores and crevices for plant roots to penetrate for more fragmentation
- leaves + other material that fall from plants decompose and contribute to soil composition
Time
important factor in soil formation, since it develops over long periods
- materials are deposited over time, decompose, and transform into materials animal use/deposited into soil surface
- can take 200-1000 years to create 1 inch of soil
Root Hairs
extensions of the root epidermal tissue that increase SA of the root, contributing to the absorption of water and minerals
Soil Property Types
properties of soil can directly influence the availability of specific ions present; THE MOST CRITICAL SOIL PROPERTY THAT INFLEUNCES ION AVAILABILITY IS THE PRESENCE/ABSENCE OF CLAYYY
- Clay Soil
- Sandy Soil
- Organic Matter Soil
CLAY
CLAY IS NEGATIVELY CHARGED - any cations present in clay-rich soils remain tightly bound to clay particles
- tight association prevents cations from being washed away and being absorbed by plant root hairs
- negative anions are easily dissolved in soil water + readily accessible to plant root hairs
Clay Soil
- retains water well (water remains associated with the charged clay surface)
- clay particles pack tightly, meaning there is less air available in the soil , making it difficult for roots to penetrate the dense soil
- clay particles prevent leaching of cations from soil by rainwater, but also prevent absorption of the cations by the plant
Sandy Soil
- consists of loosely packed soil particles - lot of air pockets that facilitate root penetration + respiration
- loose packing means water drains easily - taking nutrients away with it
Organic Matter Soil
- large amount of organic matter provides a near-ideal environment for roots
- high concentration of nutrients, high water retention, loose soil packing with many air pockets
Plant Uptake of Mineral Nuteirnts
rely on proton pumps, cation channels, and anion cotransporter channels present in root hair membranes
Plant Root Proton Pumps
the epidermal tissue is lined with proton pumps that use ATP to pump protons OUT of the cells into the soil (against their ECG)
- create a strong ECG with a high concentration of protons and + charge outside the cell and the opposite inside
- these protons pumped into the soil cause TWO direct outcomes
Proton Pump: OUTCOME ONE
the positive protons bind to negative clay in the soil, releasing the cations from the clay through CATION EXCHANGE
- cations diffuse DOWN their ECG into root hair through cation channels)
- energetically favorable for cations to move into the root hairs from the soil
Proton Pump: OUTCOME TWO
the high concentration of protons in the soil creates a strong ECG that factors transport of protons BACK into the root hairs
- plants use COTRANSPORT of protons down their ECG as an energy source to move anions AGAISNT their CG into the root hairs
- occurs through anion cotransporter channels
- energetically unfavorable for the anions, but favorable for the protons
Limiting Nutrients
- phosphorus, potassium, and NITROGEN
- atmospheric nitrogen is ~80% of the atmosphere, but not biologically available to plants since they lack the enzymes to convert it into biologically useful forms
- plants have ready access to carbon and water, but use soil to get the rest of the nutrients
Nitrogen Sources
there are 2 natural sources of biologically available nitrogen for plants:
1. conversion of N2 into ammonia by specific bacteria species
2. release of nitrogen from biomacromolecules of dead organisms by decomposers like fungi
