Soils

Question 1

What is soil?

Answer 1

the uppermost layer of the lithosphere (earth’s crust)

Question 2

Pedology

Answer 2

the study of soils

Question 3

4 components of soil

Answer 3

1) minerals (solid)
2) organic matter (solid)
3) soil air/gases (pore space)
4) soil water (pore space)

Question 4

Tell me about soil minerals

Answer 4

They are classified according to changes in physical or chemical composition over time, determine texture/structure

Soil texture is important for soil water and nutrient availability and refers to the particle size distribution (gravel, sand, silt, clay, colloids, etc.)

Primary minerals are relatively large, unaltered compounds similar to bedrock, whereas secondary minerals are relatively small and result from chemical weathering or mineral alteration

Question 5

Tell me about organic matter

Answer 5

the partially decayed remains of plants and animals, including humus (very fine organic matter that is a source of nutrients)

Soil colour is determined by composition and chemistry… black indicates organic content, white/pale indicates silica/aluminum oxides, and red/yellow indicates iron oxides/minerals

Question 6

Tell me about soil moisture

Answer 6

global circulation patterns, global radiation patterns, and regional patterns control precipitation

Question 7

Define soil moisture availability

Answer 7

dependent on gravitational water (removed by gravity when soil is saturated) and capillary water (resists gravity by clinging to soil particles via capillary tension)

Question 8

Define storage capacity

Answer 8

amount of capillary water available for plant use, depending on soil texture and organic matter (highest storage capacity in fine textured soil with abundant organic matter)

Question 9

Define wilting point

Answer 9

the critical water storage level for plants (high capillary tension and unavailability of water = below the wilting point)

Question 10

What is the soil texture trade-off

Answer 10

fine-textured soils have high storage capacity, high capillary tension, high wilting point, and low water availability

coarse-textured soils have low storage capacity, low capillary tension, high water drainage, and low water availability

Question 11

Explain stomata: plant transpiration and respiration

Answer 11

guard cells respond to light, CO2, and water stress and transpiration occurs through this opening and closing of stomata

Question 12

Adaptations to drought

Answer 12

rooting patterns in the desert/root segregation, efficiency of the stomata valve, waxy leaves, sunken stomata reduces water loss, photosynthesis and water use in C3, C4, and CAM plants

Question 13

C3 plants

Answer 13

survive solely on C3 fixation (Calvin cycle) and tend to thrive in areas where sunlight intensity is moderate, temperatures are moderate, carbon dioxide concentrations are around 200 ppm or higher, and ground water is plentiful

Question 14

C4 plants

Answer 14

have a competitive advantage over C3 plants under conditions of drought, high temperatures and nitrogen limitation

Question 15

CAM plants

Answer 15

open stomata at night, when temperature is low, thus water vapour diffuses out of the leaf more slowly, CO2 is stored overnight, and then converted to carbohydrates the following day using light energy

Question 16

Define water conservation for plants adapting to drought

Answer 16

palisade tissue in expandable stems of desert succulents (photosynthetic stems enlarged to store water, leaves reduced to hard thorns to protect against sun and herbivores)

Question 17

Adaptations to water logging/anoxic environments

Answer 17

O absorbed through pores in bark called lenticels, then diffuses to tissues with low O2 concentration (submerged trunk or roots in saturated soil), aerenchyma move oxygen from emergent shoots to submerged roots (wetland trees have specialized above ground roots like mangroves)

Question 18

Plant nutrition

Answer 18

soil is a source of bioelements, plants require macro/micronutrients through the N cycle, N fixation, P and K, local energy, etc.

Question 19

Factors affecting toxicity

Answer 19

pH, heavy metals, salinity, tolerance mechanisms, etc.

Question 20

What is N fixation?

Answer 20

mediated by bacteria that infect root hairs of higher plants and initiate a symbiotic interaction, supply nitrogen from soil atmosphere in return for carbohydrates, plants build nodule structures that house bacterial colonies

Question 21

What are N-fixers?

Answer 21

colonizers of inhospitable nitrogen-deficient substrates (ex. vetch on sand dunes, mequite on desert alluvial fans, BUT Rhizobium inhibited by acidic soil)

Question 22

Environmental controls on the rate of N cycling

Answer 22

excess or deficient O2, pH, H2O, or heat… these can all affect N-cycle microorganisms

Question 23

What does mycorrhizal symbioses do?

Answer 23

increases the absorption of P and K