The saprotrofic food chain in terrestrial ecosystems : Soil Soil colloid particle kow/nT//'/,\ + ® The saprotrofic food chain in terrestrial ecosystems : Soil Soil Buffer Capacity / Pufrovaci kapacita půdy (půdní ústojčivost) Buffer Zone Soil pH pufrovaci zóna (systém) pH půdy Carbonate (Lime) karbonátová Silicate silikátová 6.2-8.6 5.0-6.2 Cation Exchange Capacity 4.2 - 5.0 kationtové výměnné kapacity Aluminium Iron železa 3.0-4.2 3.0-3.5 Chemical Reactions chemické reakce CaC03 + H2C03—► Ca(HC03)2 CaC03 + H2S04—► Ca2+ + S042" + C02 + H20 [(-Si04)AI]- + 4 H+ + 6 H20 — (-SiOH)4 + [AI(H20)6P+ K+ H+ <—H+ OH- Ca2H [AI6(OH)15]3++15H+ + 21 H20 — 6[AI(H20)6p FeOOH + 3 H+ + 4 H20 — [Fe(H20)6]3+ 59 The saprotrofic food chain in terrestrial ecosystems : Soil Tropical ecosystems - tropical soils Very high primary production, lush vegetation (rain forests) Climate: -very high precipitation, - high temperature Original notion (since Alexander von Humboldt): Optimal conditions for plant growth -agricultural production?! Why have efforts to turn rain forests into farmland been so little successful? High precipitation levels - leaching of nutrients The saprotrofic food chain in terrestrial ecosystems : Soil Zonal soil types in West Africa The saprotrofic food chain in terrestrial ecosystems : Soil Tropical soil types ■H Ferralsol (Oxisol) Vertisol) The saprotrofic food chain in terrestrial ecosystems : Soil Clays: -Microcrystals forming in the process of weathering of parent material (rock) - crystals consist of sheet cristalls made of octaheders of aluminiumhydroxide and tetraheders of silicium oxide. Different types of clay minerals differ amongst others their in crystal structure: Three sheets: Two sheets AI-OH Si-0 Si-0 AI-OH y chlorites, illites, vermiculites, montmorillonites Si-0 (outside the tropics) kaolinites (in the tropics) Montmorillonite The saorotrofic food chain ir i terrestrial ecosystems : Soil Characteristic composition of the weathered layer above parent rock outside of and in the tropics Great Britain Medditerranean Westghats compound rock Weathered rock Weathered rock Weathered % material % % material % % material % Si02 49,3 47,0 44,7 35,7 50,4 0,7 AUOo 17,4 18,5 15,5 34,9 22,2 50,5 Fe90q 2,7 14,6 7,5 7,9 9,9 23,4 FeO 8,3 — 3,7 0,7 3,6 — MgO 4,7 5,2 7,9 3,6 1,5 — CaO 8,7 1,5 15,3 4,9 8,4 — Na20 4,0 0,3 1,1 0,9 0,9 — K20 1,8 2,5 1,4 3,1 1,8 — P90. 1,7 2,8 í 0 H20 2,9 7,2 0,9 5,8 0,9 25,0 The saprotrofic food chain in terrestrial ecosystems : Soil • High precipitation levels - leaching of nutrients What prevents nutrient leaching from soils? Cation exchange capacity - given by content (amount, type) of clay minerals and humus Leaching in the tropics affects also silicium (Si; making up for up to 90 % of soil mineral particles). Result: - reduced Si-content in soil - formation of fersialitic and feralitic soils. The saprotrofic food chain in terrestrial ecosystems : Soil Number of exchange units per 100 g clay or humus: Montmorillonites 80 - 150 Chlorites, vermicullites 15 - 40 Kaolinites 3-15 Humus 150-500 In the tropics, humus substances are limited to upper 20-30 cm to soil; humus content is low (fast mineralization): 1-2 (max. 3) % Temperature of topsoil in the tropics: 28-30 °C Decomposition rate increases fourfold when temperature rises from 20 to 30 °C Complete decomposition of organic matter in 9 month (in the temperate zone years) Despite of this, highest CEC in the upper soil layer of tropical soils: 2 g / cm3 specific mass 40 % kaolinite, 2 % humus - humus contributes 2:1 to total CEC! The saprotrofic food chain in terrestrial ecosystems : Soil Effect of slash and burn agriculture: Nutrients are mobilized from the ash 1 _____. Part of humus destroyed by burning J ' "► Nutrient loss by leaching By the 2nd harvest the rest of soil humus has been decomposed, little input, no humus regeneration. If fertilizer is added it runs through the soil (low CEC) The saprotrofic food chain in terrestrial ecosystems : Soil The saprotrofic food chain in terrestrial ecosystems : Soil The saprotrofic food chain in terrestrial ecosystems : Soil Relation between!vegetation type and soil erosion within the natural range of the tropical rainforest WiWwftfeíé)»^^ The saprotrofic food chain in terrestrial ecosystems : Soil The saprotrofic food chain in terrestrial ecosystems : Soil Natural vegetation in Amazonia: only fertile land in Varzea floodplains The saprotrofic food chain in terrestrial ecosystems : Soil Why is there such a lush vegetation in the tropics, then?! • Almost all nutrients in the live biomass (some in SOM) • Direct mineral cycling • The vegetation functions as a filter: several storeys, epiphytes, concentration of roots in the upper 30 cm of soil • Micorrhiza: nutrient traps, closing link (shortcut in the nutrient cycle!) • Nutrients have accumulated over hundreds of years (100-200 years) without forest fires (humidity!), also due to weathering. • The poorer the parent rock the longer the regenetration time. The saprotrofic food chain in terrestrial ecosystems : Soil