More Gifts of the Glaciers

1. More Gifts of the Glaciers Soils

2. Soil: Foundation of Terrestrial Biomes • Soil is a complex mixture of living and non-living material. • Classification based on vertical layering (soil horizons). • Profile provides a snapshot of soil structure in a constant state of flux.

3. What is Soil? • Unconsolidate cover of the earth • Components • mineral • organic • Function • Medium for plant growth

4. Functions of Soil • Medium for Plant Growth • Anchors plant roots • Supplies water to plant • Provides air for plant roots • Provides minerals for plant nutrition

5. Structure of Soil • Structure of Soil • 4 components • solid particles • water • air • living organisms • relates to erosion resistance • some types less likely to erode • relates to agricultural utility - large peds or clods are not conducive to fine root growth

7. Solid particles • Mineral: classified by particle size • Gravel • Sand • Silt • Clay • Organic • Fresh plant and animal remains • Humus • Most important for plant nutrition: • Clay • Organic matter

8. Soil Profile • Horizons = layers • ID by: • color • texture • composition/chemistry • structure • consistency • porosity

9. Soil Profile • 5 major Horizons • O = organic • A, E, B, C = mineral layers • R = nonsoil (bedrock)

11. Soil Profile • O (organic) Horizon • overlays mineral layers • made up of decaying leaves, twigs, etc. • thick in forests • very thin in prairies

12. Soil profile • A horizon • Topmost mineral horizon (topsoil) • Exposed to surface processes • Most intensively weathered • Contains partially decomposed vegetable matter called humus which helps to hold moisture and provide food for plants to grow • Dark color • Helps to hold moisture • Provides mineral nutrients for plants • Water must percolate through this layer

13. Soil profile • E horizon • Found usually in forest soils • Light-colored • Zone of leaching - water carries away clay and soluble minerals • Iron • Aluminum

14. Soil Profile • B Horizon • contains clay, iron and aluminum leached from E horizon • zone where leached material accumulates (illuviation) • less organic matter • poorly mixed • brown in color.

15. Soil Profile • C Horizon: weathered parent material • directly overlies bedrock • mostly coarse, fragmented rock particles • little if any organic matter • R = unweathered parent material

16. Soil Profile • Soil Classification • Based on • color - reflects mineralogic or elemental composition • texture - describes particle size • sand, silt, clay • influences H2O drainage and retention (infiltration and runoff rates) • important for erosion and flood control

17. Soils are characterized by the differences in the various layers (horizons). O Horizon A Horizon E Horizon B Horizon

19. Soil formation • Complex process • Type of soil formed involves: • Nature of the parent bedrock • Climate • Animals • Vegetation • Slope of the landform • Length of time the soil has been in existence.

20. Soil Formation • Influenced by • Rainfall • Evaporation • Temperature

21. Soil Formation • Type of soil formed depends on • Nature of parent material • Topography of the land • Influences water in soil • Less soil on steep slopes • Time • Climate • Living community of plants, animals, microbes

23. Soil Formation • Arctic, tropic, temperate, and arid regions have different soils. • In the northern midwest the same parent material produces different soils mainly due to different vegetation. • Late winter observations: • light soils indicate former forest • dark soils indicate former prairie

24. Formation of Soils by Weathering • Weathering occurs in place, with no significant transport of material • Mechanical weathering • Physically break large particles of parent material into small particles • Causes a net increase in surface area • Examples • Abrasion by streams and glaciers • Wetting and Drying • Freeze/thaw and Ice Wedging • Plant Growth and Animal Activity

25. Formation of Soils by Weathering • Chemical weathering • Chemical reactions between minerals and • water • gases in water or air • chemicals dissolved in water • Accelerated by acidic conditions • Alkaline materials such as calcium salts are leached away by acidic rain water. • Reactions may completely dissolve rocks or just transform the constituent minerals into new or different minerals.

26. Formation of Soils by Weathering • Chemical weathering • e.g. limestone weathering (dissolves) to produce hard water • soluble minerals made insoluble (transformation of materials) • e.g. silica + aluminum + potassium produce the clay we have in the NE Illinois area

27. Formation of Soils by Weathering • There is a positive feedback between mechanical and chemical weathering • one assists the other • Factors influencing weathering • particle size • climate = precipitation and temperature • organic activity • Mosses and lichens on rocks secrete acids that can etch away and dissolve minerals • Activities of organisms e.g. earthworms

30. Soil Formation • Biotic influences on soil formation • Roots • Help breakup soil structure • Transport water and nutrients • Helps in recycling of mineral nutrients • Add nutrients - decay of dead plants • Animals • Also help breakup soil • Help with soil aeration • Add nutrients - urine, feces, decay of dead animals

31. Soil Formation • Biotic influences (cont) • Microbes • Bacteria and fungi, also protozoa • Agents of decomposition • Important symbionts of plants • Microbial symbionts of plants • Rhizobia • Bacteria • Nitrogen fixers • Mycorrhizal fungi • Help increase surface area of roots • Facilitate nutrient acquisition from soil

32. Rhizobium is a type of bacterium that lives in soil and around and inside of the roots of certain plants (legumes). This is Rhizobiumtrifolii in its free-living state in soil, surrounded by a halo of protective covering called a capsule. The slimy capsule, made of exopolysaccharide, protects Rhizobium from drying out. It also helps the bacterium stick to root hairs during other stages of its life cycle, when rhizobium forms a symbiotic partnership with plants like clover.

34. The large object in the center of this view is the tip of a clover root hair. The cylindrical cells on the top of the root tip are Rhizobium trifolii, bacteria that live in a symbiotic relationship with the clover. The rhizobia shown here are clustered on the surface of the root. Soon they will start to invade the roots and begin a symbiotic partnership that will benefit both organisms.

35. These rhizobia have attached themselves onto a clover root hair. The sticky, web-like tendrils extending from the rhizobia across the root surface are called cellulose microfibrils. The bacteria are beginning to invade the root, where they will form a symbiotic relationship with the clover plants.

38. Mycorrhizae • Symbiotic relationships between fungi and plant roots (the term means literally 'fungus root'). • Perhaps more than 80% of the species of higher plants have these relationships, and so do many pteridophytes (ferns and their allies) and some mosses (especially liverworts). • They are as common on crop plants (cereals, peas, tomatoes, onions, apples, strawberry, etc) as in wild plant communities, and in several cases they have been shown to be important or even essential for plant performance.

39. Mycorrhizae • As the American plant pathologist, Stephen Wilhelm, said: '...in agricultural field conditions, plants do not, strictly speaking, have roots, they have mycorrhizae’. • To a large degree, mycorrhizas seem to be symbiotic (mutualistic) relationships, in which the fungus obtains at least some of its sugars from the plant, while the plant benefits from the efficient uptake of mineral nutrients (or water) by the fungal hyphae. However, there can be circumstances in which the fungus is mildly detrimental, and others in which the plant feeds from the fungus.

40. Mycorrhizae • The fungal hyphae provide the massive surface area for uptake of mineral nutrients. • These hyphae are about 10 micrometers diameter, whereas the fine absorbing roots are about 1 millimetre diameter (100 times wider). • It is a costly process for the plant. Perhaps as much as 30% of the sugars produce by the plant through photosynthesis is used to maintain the mycorrhizal fungi • So, the surface area for absorption of mineral nutrients is vastly greater if the plant supports the fungal network with plant sugars and gains at least some benefit from the mineral nutrients absorbed by this fungal system. TRADE-OFFS!

43. Ladies Tresses prairie orchid

49. Ectomycorrhizae • Fungus grows on the surface of the plant root • Ectomycorrhizal roots are distinct from normal roots • no root hairs • Fungus takes the place of root hairs • fungi = basidiomycetes • critical to many/most forest trees • conifers • beeches • oaks

50. A 15 cm square plant pot with a 3-year-old pine tree. Note the fine roots (each about 1-2 mm diameter), but most of the growth we see is of mycorrhizal fungal hyphae that grow from the roots, thoroughly permeate the soil and absorb mineral nutrients.