Lecture 7 - pedogenesis

Question 1

what is pedogenesis?

Answer 1

process of soil formation

Question 2

what 5 factors characterise soil formation?

Answer 2

1) climate
2) organisms
3) relief
4) parent material
5) time

Question 3

what are examples of stochastic factors that can impact soil formation?

Answer 3

fire, flood, humans

Question 4

what is an example demonstrating how soil type is effected by climate?

Answer 4

High rainfall increases soil acidity through element leaching

Question 5

how many soil orders are there?

Answer 5

12

Question 6

what are soil orders linked to?

Answer 6

either vegetation or climate

Question 7

what is the soil formation model?

Answer 7

model explains the development of soil properties and accounts for some of the soil variation in space and time

Question 8

what is the role of organisms in soil formation?

Answer 8

• Plants and associated microbiota can alter soil - making it more or less favourable for their own growth
• Plant-driven effects on soil can drive ecosystem changes with time- driving succession towards ‘climax communities’
• As plants evolved over geological time their interactions with soil have transformed the Earth’s surface and changed biogeochemical cycles of elements into the oceans and atmosphere

Question 9

what is the hypothesis for the evolution of soil and land plants?

Answer 9

As land plants evolved, they increased in size and structural complexity, required more nutrients and water, and invested more photosynthate into supporting their mycorrhizal fungal partners-intensifying soil formation and driving biogeochemical cycles

Question 10

which came first out of 1) trees, 2) mycorrhiza like symbiosis and 3) roots and vascular system?

Answer 10

• First trees - 385ma
• First land and mycorrhiza-like symbiosis - 450ma
• First roots and vascular system - 407ma

Question 11

what forms soil?

Answer 11

• Primary minerals e.g. water, rocks and plant over long periods of time

Question 12

describe the lifecycle of soil?

Answer 12

1) bare rock
2) weathering of parent material and accumulation of mineral grains
3) vegetation accelerates weathering and traps particles
4) soil deepens into a mature profile of fine material enriched in organic matter and clay
5) erosion causes loss of organic matter and clay
6) vegetation is lost via cultivation, landslide, fire etc
7) bare rock exposed - cycle starts again

Question 13

what evidence from chronosequences show how plants drive soil development?

Answer 13

-took rock from eroded mountains - found total nitrogen and carbon content within soils varied depending on the pioneer species / when it reaches a climax community - the ages of the soil has a great effect on the soil conditions

Question 14

what is apatite?

Answer 14

a form of calcium phosphate found in basalt and other rocks

Question 15

what is apatite used for?

Answer 15

the primary source of P in most ecosystems and P fertilizer

Question 16

what can the rate at which rocks get weathered and calcium be released have effect on?

Answer 16

the acidification of the sea and co2 in the atmosphere

Question 17

describe plants roles in weathering

Answer 17

• Plants convert solar energy into chemical energy that can accelerate rates of mineral weathering
• Plants promote chemical weathering on silicate rocks to a greater extent than microbial communities alone

Question 18

what can enhance weathering?

Answer 18

increased:

1) plant productivity
2) rooting depth
3) nutrient demand
4) photsynthate allocation to mycorrhiza
5) mycorrhiza hyphal lengths

Question 19

describe the importance of silica cycling

Answer 19

• The rise of land plants that form biogenic silica from Si in the soil is thought to have increased the soluble Si flux to the oceans, and the increasing importance of diatoms – which now contribute nearly half the ocean primary production

Question 20

what is the effect of plants relationship with mycorrhiza?

Answer 20

enhanced mineral weathering and altered global biogeochemical cycles and atmospheric chemistry e.g. intensifying the weathering process of calcium and silica and removing co2 from the atmosphere

Question 21

why is phosphorus so readily available?

Answer 21

• Phosphorus is readily precipitated out by other elements because it happily binds with many of the elements - apatite is the most readily available

Question 22

what provides over 95% of the primary P source in soils?

Answer 22

-Weathering of the calcium phosphate apatite

Question 23

what happens in the mycorrhizosphere?

Answer 23

• Carbon flows
• Interactions with bacteria etc.
• Uptake and transport of weathering products

Question 24

what did the evolution of deep rooted trees increase?

Answer 24

• The evolution of deep-rooted trees increased biotic weathering rates by more than an order of magnitude compared to liverworts

Question 25

what evidence do we have of trees generating the soils we see?

Answer 25

different clays found from fossil forests

Question 26

what is mycorrhizal symbiosis?

Answer 26

coupling plant energy supply to fungal absorptive networks for mutual benefit

Question 27

what is a mycorrhiza?

Answer 27

plant photosynthate exchanged for fungal-acquired nutrients

Question 28

what is a use of adding rock dust to soils?

Answer 28

can lead to enhanced rates of weathering and release nutrients to replace lost soil

Question 29

what is an additional benefit from adding rock dust to soils other than weathering and release of nutrients?

Answer 29

release silica - adds physical resistance to pests
-Calcium silicate rock dust application to soil pathogen and insect attacks on sugar cane to a greater extent than adding lime or limestone

Question 30

which soils are rich in silica and clay?

Answer 30

forest soils