Ecology Lecture 3

1. Ecology Lecture 3 Ralph Kirby

2. What is soil • Before life invaded the land from the sea, there was probably little that looked like soil today • Dust like Mars • Little organic matter • A few microorganisms perhaps • However, soil is the basis of all terrestrial life and without soil, there would be no plants, no soil microorganism and no land animals • Plants obtain many of their water and nutrients from soil and it provides an place to attach to.

3. Definition of soil • Soil is hard to define because it is so complex • Soil is a natural product formed by the weathering of rocks and the action of living organism • Does it include the ability to support life • Soil is a collection of mineral and organic matter than can support plant growth • Does this include soil like material that does not support life • What if the climate at present does not support life • The stratum below vegetation and above hard rock • What if there is no vegetation

4. Three dimensional matrix • Soil is a living system made up of a matrix of minerals and organic matter that includes • plants, both roots and stems • Bacteria • Fungi • Protozoa • Algae • Small animals • Larger animals • A unit of soil large enough to define is called • Pedon

5. Formation of soil • Proposed that five factors are involved in the formation of soil • Parent Material • Igneous rock • Sedimentary rock • Metamorphic rock • Climate • Temperature • Rainfall • Elevation • Latitude • Biotic Factors • Input factors from living organisms • Degradation by living organisms • Topography • Water runoff • Draining • Erosion • Time • Weathering, accumulation, decomposition and mineralization take time • Initial differentiation can be within 30 years • Formation of true soil, 2000 to 20000 years • Soil can age

6. Mechanical and Chemical Weathering • Starting Point • Mechanical • Water • Wind • Temperature • Creates loose material • Sorted and moved • Chemical • Acids produced by lichens and mosses • Addition of organic matter • Oxidization • etc

7. Living Organisms • Without living organism there would be no soil • Mars does not have soil as we know it • When plants colonized the land, they changed it by producing soil • Plants introduce organic matter to soil • Microorganisms and small animals recycle the organic matter to humus • Humus can be on top of soil in some acidic environments • Humus is usually mixed with the soil and changes it composition • Many microorganisms have evolved to fill this niche • Actinomycetales • Lignin degrading fungi

8. Soil has many layers • O • Organic layer • Fluctuates with season • A • Upper layer of mineralized soil • Large amount of organic matter • E • Eluvial zone • Maximum leaching • B • Illuvial zone • Accumates leached material such as clays, silicates, etc • C • Unweathered starting material • R • Rock or parent material

9. Soils show a great deal of variation • Color • No direct effect on how soil function • Allows classification • Red • Possibly oxides • Black • Possible high organic content • Texture • Variation in size and shape of soil particles • Gravel • >2mm • Sand • 0.05mm to 2mm • Silt • 0.002mm to 0.05mm • Clay • <0.002mm

10. Structure • Space for roots etc • Pore space • Amount of water held • Rate of water movement • Aeration • Compaction • Aggregation • Aggegates or peds • Depth • Depends on • Slope • Weathering • Parent material • Vegetation • Grasslands are deep • Forests are shallow

11. Water is essential for soils • See lack (?) of water on Mars • Soil can become saturated if all pores filled • Normally at field capacity • Capillary water is usually present • Extracted by plants • Available water capacity • Hygroscopic water unavailable • Drainage • Low drainage results in low aeration • All affected by soil texture • Sand • Lower capacity • Clays • Higher capacity

12. Plants need minerals in the form of ions • Cationic exchange resin type structure • Change in pH affects binding capacity for ions • Immovable • Hydrogen • Aluminium • Removable in order • Calcium • Magnesium • Potassium • Ammonium • Sodium

13. Soils vary with climate and vegetation

16. Entrisol Mountains Where soil making process has been interupted by flooding etc Inceptisol Mineral rich mountain soil Forests and pasture Aridisol Arid regions Low in humus Salinization due to low rainfall Andisol Volcanic in origin Can be very fertile Mollisol Dark organic rich A layer Deep fertile Spodosol Acidic Coniferous forest soil Alfisol Temperate forest Organically rich Ultisol Warm climate soil Redish or yellowish Low nutriant content Oxisol Wet subtropical/tropical soil\ Lots of water movement through soil Low nutrients Histosol High water table Poor drainage Peatlands Gelisol Permafrost Vertisol High % clay No B horizon Swell and shrink Pasture

17. Soil forms a biotic ecosystem on its own

18. Biotic System in soil • Needs • Living space • Varies with soil type • Oxygen • Varies with water saturation • Food • Varies with plant cover • Water • Can vary with climate • Environment is relatively constant • Water can change dramatically • Mechanisms to survive drought • Spores etc • Only upper layer is really available • Diversity is very very large • The ecosystem is largely not understood in detail • Particularly the microorganisms

19. Man has an effect on soil • Changes in plant cover • England • 1000 BC • Forest • 2004 • Cities, towns, villages, farm land, monoculture forests • Erosion • Deforestation in Africa • Climate change • Dams • Roads and storm drains