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6 Plant Form and Function > 37 Soil and Plant Nutrition > Flashcards

37 Soil and Plant Nutrition Flashcards

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1
Q

What are the basic properties of soil?

A

Its texture and its composition.

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2
Q

What are the layers of the solid called?

A

Horizons i.e. the A horizon, B horizon and the C horizon.

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3
Q

What does the ‘A horizon’ of the soil refer to?

A

The top soil.

This layer is made of broken down rocks, decaying organic matter and living organisms like worms. It therefore has the most nutrients for plant growth.

It is frequently weathered by wind and washed away by rain and flood.

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4
Q

What does the ‘B horizon’ of the soil refer to?

A

The layer below the top soil has less organic material than horizon A and is less weathered.

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5
Q

What does the ‘C horizon’ of the soil refer to?

A

The bottom layer of soil

It has little organic material and thus is composed mainly of broken down rocks. Note that some of these rocks migrate up to form the horizon B and horizon C.

While this region has few organic nutrients it may have expansive water tables that can be exploited by the roots of trees etc.

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6
Q

What does ‘hummus’ refer to?

A

Decaying organic material in the solid.

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7
Q

What is the decaying organic material in the soil called?

A

Hummus

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8
Q

What is the most fertile type of topsoil called and what is it composed of?

A

‘Loams’ are topsoils with roughly equal amounts of sand, silt and clay.

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9
Q

Why are ‘loams’ particularly fertile?

A

The small silt and clay particles provide the surface area for the adhesion and retention of minerals and water.

Meanwhile the larger spaces between the san particles allows good diffusion of oxygen to the roots.

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10
Q

Why are sandy soils not good for growth?

A

The large particles have a relatively small surface area and thus less water and minerals are retained.

Sandy soils often have less organic material and are also less firm so do allow the plant to anchor itself in as firmly.

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11
Q

Why are completely clay soils not good for growth?

A

Since they have poor drainage the soil becomes waterlogged and thus oxygen can not reach the roots.

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12
Q

Generally speaking, what properties will soil made of fine particles have?

A

They will be good at retaining water and nutrients as their fine particles provide a high surface area.

This will, however lead to poor drainage and thus the soil will become waterlogged. Therefore the roots will receive little oxygen.

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13
Q

Generally speaking, what properties will soil mad of large particles have?

A

There will be larger spaces between the particles so sufficient oxygen will reach the roots. This also provides good drainage so the soil won’t become waterlogged.

The large particles mean that the soil will have a lower surface are to volume ratio. This means it will be less able to hold onto nutrients and water.

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14
Q

Besides particle size, what factor determines how well the soil will adhere to nutrients?

A

Most soil particles are negatively charged and thus positive ions (cations) bind to them. This makes anions like Ca2+ and K+ easily retained by the soil and thus these minerals are not easily lost through leaching.

Anions like nitrate (NO3-), phosphate (PO4 3-) and sulphate (SO4 2-) are not attracted to the soil particles and thus are lost more easily.

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15
Q

How do root cells absorb minerals form the soil? (not a structural adaptation)

A

They perform ‘cation exchange’ to displace cations that are attracted to the negatively charged soil particles.

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16
Q

How does ‘cation exchange’ work?

A

As the root cell performs respiration it releases CO2 into the surrounding soil. This carbon dioxide reacts with water to form carbonic acid.

The carbonic acid dissociates yielding an H+ ions. These H+ ions neutralise the negative charge of the soil particle and thus cause the bound cations to be released into the water of the soil.

These displaced cations in the soil’s water then diffuse or are actively transported into the root cell.

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17
Q

Why is ‘cation exchange’ important?

A

Otherwise the cations that are attracted to the soil particles would not be free to enter the root cell.

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18
Q

How does soil pH affect nutrient availability?

A

If the soil is already acidic the H+ ions already in the soil will perform cation exchange and thus the nutrients will be freed more easily.

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19
Q

What soil minerals are more prone to be leeched through rain etc?

A

Anions as they are not attracted to the soil particles.

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20
Q

Besides acting as a nutrient source for plants, what is the importance of topsoil?

A

It prevents clay particle from packing together.

It also provides a home for bacteria and other detritivores to recycle the nutrients of the soil.

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21
Q

How do earthworms derive their nutrition?

A

From the bacteria and fungi in the soil.

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22
Q

What roles do worms play in improving the soil?

A

They consume organic material, partly break it down and then return it to the soil through egestion.

This moves organic matter deeper in to the soil. Worms also clump the soil together which provides better air pockets.

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23
Q

What caused the ‘American Dust Bowl?’

A

The destruction of prairie grass and the depletion of soil nutrients combined with a drought made the soil dusty and not held in place by plants.

This lead to giant dust storms.

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24
Q

What are underground water reservoirs called?

A

‘Aquifers’

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25
What does ‘aquifer’ refer to?
An underground water reservoir.
26
What is an increase in soil salinity called?
Salinisation.
27
What is a particularly wasteful form of irrigation and why is it wasteful?
Simply pouring water on a field. Water is lost both by evaporation and by water runoff.
28
What is a less wasteful form of irrigation?
‘Drip irrigation.’ In this method perforated tubes are inserted at the soil layer where the roots are. This minimises evaporation whilst also allowing the water to be slowly added. This reduces run off as water is added at the rate it is lost from the soil. This also prevents oxygen-defiicent water logged soils.
29
What are the main nutrients found in fertilisers?
N,K and P (nitrogen, potassium and phosphorus)
30
In what from is nitrogen added to the soil in fertilisers?
As nitrates or ammonium
31
In what from is potassium added to the soil in fertilisers?
‘Potash'
32
In what from is phosphorus added to the soil in fertilisers?
Phosphate
33
Besides by influence cation exchange, how does soil pH affect nutrient availability?
At pH 8, for instance, plants can absorb calcium, but iron is almost unavailable. At pH 5 or lower, toxic aluminum ions (Al3+) become more soluble and are absorbed by roots. This impairs and the uptake of calcium.
34
How can plants that live in acidic soils with high Al3+ concentration survive?
They release anions that bind to Al3+ and the snake the soil safe.
35
What plowing technique can reduce runoff?
’No till agriculture’ in which the soil is not tilled i.e. turned over. While tilling gets rid of weeds well it also disrupts the roots of the crops and thus makes them less able to anchor the soil in place.
36
How can run off be minimised in farms on hills?
With ‘contour tillage’ in which the farm is planted on flat steps down the side of the hill.
37
What is one way that pollute soils can be remediated?
‘Phytoremediation’ in which specific plants are grown in that soil due to their ability to absorb the particular toxins in the soil. The plants can then be removed, taking the toxins out of the ecosystem.
38
Why is “Thlaspi caerulescens” used in phytoremediation?
It can absorb high levels of zinc.
39
What is ‘phytoremediation’ a type of?
Bioremediation which includes when other organisms i.e. prokaryotes and protists are used to break down or remove pollutants from an environment.
40
What is an ‘essential element’ in terms of plant nutrition?
One that is required of the plant to complete its lifecycle and produce another generation.
41
What is a ‘hydroponic solution’?
A solution containing water and nutrients into which the plant is grown i.e. without soil.
42
What nutrient is a micronutrient in some plants?
C4 and CAM plants need sodium ions to regulate phosphophenolpyruvate the CO2 acceptor in these forms of photosynthesis.
43
What does a magnesium deficiency in plants cause?
‘Chlorosis’, a yellowing in the leaves due to an absence of magnesium which is a component of chlorophyll.
44
What does ‘Chlorosis’ refer to?
A yellowing in the leaves due to an absence of magnesium which is a component of chlorophyll.
45
What mineral deficiency is yellow leaves characteristic of?
The yellowing in the leaves (called chlorosis) is due to an absence of magnesium which is a component of chlorophyll.
46
Besides magnesium, what can cause ‘chlorosis’ and why?
Iron deficient as iron is a co-factor in the enzymatic reactions that form chlorophyll.
47
In what leaves will a nutrient deficiency be first evident?
If the nutrient is highly mobile i.e. transported by phloem the nutrient deficiency will appear first in the old leaves. This is because as the new leaves grow phloem is preferentially routed to them. If the nutrient is not highly mobile then the old leaves will already have a stockpile in them. Therefore it is the new leaves that will show the deficiency first.
48
What are the macronutrients needed by plants? (in order form highest concentration to least)
Carbon. Oxygen, Hydrogen, Nitrogen, Potassium, Calcium. Magnesium, Phosphorus and Sulfur
49
In what form is Carbon primarily absorbed?
CO2
50
In what form is Oxygen primarily absorbed?
CO2
51
In what form is Hydrogen primarily absorbed?
H2O
52
In what form is Nitrogen primarily absorbed?
NO3- and NH4+
53
In what form is Potassium primarily absorbed?
K+
54
In what form is Calcium primarily absorbed?
Ca2+
55
In what form is Magnesium primarily absorbed?
Mg2+
56
In what form is Phosphorus primarily absorbed?
H2PO4- (dihydrogen phosphate) and HPO4 2- (hydrogen phosphate)
57
In what form is Sulphur primarily absorbed?
SO4 2-
58
In a plant, what is the function of Carbon?
Major component of plant’s organic compounds
59
In a plant, what is the function of Oxygen?
Major component of plant’s organic compounds
60
In a plant, what is the function of Hydrogen?
Major component of plant’s organic compounds
61
In a plant, what is the function of Nitrogen?
Component of nucleic acids, proteins, hormones, chlorophyll, coenzymes
62
In a plant, what is the function of Potassium?
Cofactor that functions in protein synthesis; major solute functioning in water bal- ance; operation of stomata
63
In a plant, what is the function of Calcium?
Important in formation and stability of cell walls and in maintenance of membrane structure and permeability; activates some enzymes; regulates many responses of cells to stimuli
64
In a plant, what is the function of Magnesium?
Component of chlorophyll; cofactor and activator of many enzymes
65
In a plant, what is the function of Phosphorus?
Component of nucleic acids, phospholipids, ATP, several coenzymes
66
In a plant, what is the function of Sulphur?
Component of proteins, coenzymes
67
What is the fundamental difference between macronutrients and micronutrients?
Macronutrients are needed in greater amounts than micronutrients. Despite this both are absolutely needed by the plant and thus both are ‘essential nutrients'
68
What are the micronutrients needed by plants? (in order form highest concentration to least)
Chlorine, Iron, Manganese, Boron, Zinc, Copper, Nickel and Molybdenum.
69
In what form do plants typically acquire Chlorine?
Cl-
70
In what form do plants typically acquire Iron?
Fe3+ (ferric), Fe2+ (ferrous)
71
In what form do plants typically acquire Manganese?
Mn2+
72
In what form do plants typically acquire Boron?
H2BO3- (dihydrogen borate)
73
?In what form do plants typically acquire Zinc
Zn2+
74
In what form do plants typically acquire Copper?
Cu+ and Cu2+
75
In what form do plants typically acquire Nickel?
Ni2+
76
In what form do plants typically acquire Molybdenum?
MoO42- (molybdate)
77
How can phosphate deficiency be recognised in plants?
Their leaves, particularly the newer one, develop reddish-purple edges.
78
How can nitrate deficiency be recognised in plants?
They exhibit ‘firing’ (drying) at their tips. A yellowing streak starts at the top and spreads down the ‘main rib’ of the leaf
79
How can potassium deficiency be recognised in plants?
Their older leaves develop hello/orange 'margins' (edges)
80
In what forms can roots absorb nitrogen?
NH4+ and NO3-
81
What is formula of nitrate ion?
NO3-
82
What happens in the nitrogen cycle?
’Nitrogen fixing bacteria’ convert N2 to NH3 (ammonia). ‘Ammonifying bacteria’ convert organic material (humus) to ammonia. This ammonia is converted to NH4+ by the addition of an H+ from the soil. Some of this ammonium is absorbed by the roots. The rest is converted to NO3- by nitrifying bacteria’ This NO3- is absorbed by the plant or converted back to N2 by ‘denitrifying bacteria'
83
What happens when plants absorb NO3-?
Enzymes in the plant convert most of it back to NH4+
84
What is the purpose of ammonifying bacteria?
They act as decomposers to break down organic wastes to NH3. In this way they allow the recycling of nitrogenous nutrients in the soil.
85
What is ’nitrite’?
NO2-
86
What is ’NO2-‘?
Nitrite
87
What is the conversion of NH4+ to NO3- called and how does it occur?
This is called nitrification. It generally involved converting NH4+ to NO2-. A differ type of nitrifying bacteria then converts the NO2- to NO3-
88
How do nitrates travel from the roots to the rest of the plants?
The xylem transports it in the form of nitrates (NO3-) or in the form of nitrogenous compounds produced by the root cells.
89
What is the soil surrounding the plants roots called?
The ‘rhizosphere'
90
What does ‘rhizosphere’ refer to?
The soil that surrounds the roots.
91
What are the soil bacteria that aid in the nitrogen cycle called?
Rhizobacteria
92
Where are rhizobacteria found?
In the rhizosphere i.e. soil around the plants’ roots.
93
How can plants maximise their intake of nitrogenous compounds?
By performing symbiotic relations with rhizobacteria.
94
How do plants maintain the rhizobacteria to form a symbiotic relationship?
They secrete sugars, amino acids and organic acids
95
Besides by releasing nutrients, how do symbiotic rhizobacteria affect plants?
Some called ‘plant-growth-promoting rhizobacteria’ release products that promote the growth and survive of the plant.
96
What are some ways in which ‘plant-growth-promoting rhizobacteria’ affect the plant?
They produce chemicals that stimulate plant growth, produce antibiotics that protect roots from disease, absorb toxic metals or make nutrients more available to roots i.e. when they would not be available due toe soil acidity.
97
Why can’t plants use N2 directly?
Because of the strong triple bond between the two N atoms.
98
What is process of converting atmospheric nitrogen to forms usable by plants called?
Nitrogen fixation.
99
What is the fully equation for the conversion of N2 to NH3?
N2 + 8H+ --> 2 NH3 + H2 (ignoring the redox and ATP bits)
100
Des the conversion of N2 to NH3 release or use ATP? How much
It uses 16 ATP molecules per N2 converted (8 per NH3 formed)
101
In what structure are bacteria in the roots contained?
They are inside ’nodules'
102
What type of rhizobacteria are found in root nodules?
’Nitrogen fixing bacteria’ i.e N2 to NH4+
103
What conditions are needed for the nitrogen fixing bacteria in the root nodules?
It must be anaerobic. To allow this the root nodules has lignified outer layers made of 'sclerenchyma cells' to prevent oxygen from entering. Proteins called ‘leghemoglobin’ bind to any O2 atoms present to further reduce their concentration.
104
Where specifically in the nodules are the bacteria found?
In the cavity of the root nodule are many cells. The bacteria assume a form called a ‘bacteroid’ and enter into the vesicles of these cells in the root nodules.
105
Why is it important that the rhizobacteria are in the vesicles?
This protects the bacteria whilst also making nutrient exchange easier.
106
How do bacteria enter the root?
Roots emit chemical signals that attract Rhizobium bacteria. The bacteria then emit signals that stimulate root hairs to elongate and to form an infection thread by an invagination of the plasma membrane of the root hair cell. Essentially the ‘infection thread’ is a vesicle which carries the bacteria. The infection thread containing the bacteria penetrates the root cortex. Cells of the cortex and pericycle begin dividing, and vesicles containing the bacteria bud into cortical cells from the branching infection thread. Bacteria within the vesicles develop into nitrogen-fixing bacteroids. Growth continues in the affected regions of the cortex and pericycle, and these two masses of dividing cells fuse, forming the enclosed nodule. The nodule develops vascular tissue that supplies nutrients to the nodule and carries nitrogenous compounds into the vascular cylinder for distribution throughout the plant.
107
What class of plants are notable for their association with nitrogen fixing bacteria?
Legumes
108
Why is crop rotation beneficial?
Most crops have nodules to support nitrogen fixing bacteria. Therefore by alternately growing crops and legumes the nitrogen levels of the soil can be maintained without large amounts of fertilisers.
109
How can the nitrogen levels in the solid be maintained?
With ‘crop rotation'
110
Besides nitrogen fixing bacteria, what symbiotic relationship do plants makes to maximise nutrient absorption?
They associate with fungi.
111
What are fungi that are in a symbiotic relationship with roots called?
‘Mycorrhizae'
112
Why are mycorrhizae beneficial?
They massively increase the total surface area and thus increase the surface area for water uptake and the associate minerals, especially ‘phosphate’ The fungi of mycorrhizae also secrete growth fac- tors that stimulate roots to grow and branch, as well as antibiotics to protect the plant.
113
What are mycorrhizae divided into?
Ectomycorrhizae and 'arbuscular mycorrhizae'
114
What are arbuscular mycorrhizae also known as?
Endomycorrhizae
115
What does ‘endomycorrhizae’ refer to?
This is another name for ‘arbuscular mycorrhizae'
116
What form of mycorrhizae is most common?
Arbuscular mycorrhizae
117
What mineral are mycorrhizae most important at absorbing?
Phosphates
118
Describe ‘ectomycorrhizae’?
They form a mantle (fungal sheath) around 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 to increase surface area for nutrient exchange between the fungus and thus plant (note the network of hyphae inside the root is less pronounced then it is in arbuscular mycorrhizae)
119
Describe ‘arbuscular mycorrhizae’?
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 (they don’t pass the Casparian strip) Along the hyphae are bulges called ‘fungal vesicles’ that act as storage structures for the fungus. Note that these aren’t found in ectomycorrhizae.
120
In what types of mycorrhizae are ‘fungal vesicles’ found?
Only arbuscular mycorrhizae
121
How do the hyphae of arbuscular mycorrhizae enter the root and exchange with the cortical cell?
It enter the root simply by winding through the gaps between the epidermal cells. To exchange with the cortical cells it digests a small portion of the cortical cell’s cell wall. The cortical cell then invaginated a region of its plasma membrane so that the hyphae can increase the surface are that is in contact with the plasma membrane of the cortical cell.
122
What does 'phytoremediation' refer to?
The use of plants i.e. those which suck up toxins in bioremediation
123
What are some unusual plant adaptions for nutrition?
Epiphytes, Parasitic Plants and Carnivorous Plants
124
What are epiphytes?
Plants that live on other plants in a non-parasitic way. They often absorb water and minerals from the rain.
125
What are plants that live on others in a non-parasitic way called?
Epiphytes
126
What are parasitic plants?
Those who benefit from the exploitation of other plants i.e. by stealing their nutrients/water
127
Do Carnivorous plants perform photosynthesis?
Yes, they are not heterotrophs. The animals they capture provide extra a minerals to supplement nutrient-poor soils.

6 Plant Form and Function (5 decks)

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