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Sources of nutrients to terrestrial systems 1 Wet deposition 1. Inputs 2. Recycling 1 Dry deposition 1 OrganicInorganic N-fixation 3. Rates influenced by: Climate Quality of detritus Recycling 1 2* Soil Weathering Parent material Nutrient regeneration in terrestrial systems Breakdown of organic material through decomposition occurs in several different ways Leaching Physical Fragmentation Decomposition Chemical Mineralization (e.g., ammonification) Fungi bacteria Leaching Physical Fragmentation Decomposition Physical Decomposition: Leaching • Rainwater falling on leaf litter and other detritus dissolves inorganic nutrients from surfaces and washes them into the soil • Compounds are not changed during this process (NH4+ on leaf surface becomes NH4+ dissolved in soil water) • These inorganic nutrients (ammonia, nitrate, phosphate, etc.) are immediately available for uptake by plant roots. Physical Decomposition: Fragmentation • Freeze/thaw cycles and animal activities (munching by insects, slugs, nematodes, etc.) break up detritus into smaller pieces • Resulting smaller pieces of detritus have a high surface area to volume ratio, increasing the rate of decomposition Chemical Decomposition: Mineralization • Conversion of organic matter to inorganic compounds (CO2, H2O, NH4+, NO3+, etc.) • Fungi break down the woody components of litter into inorganic molecules (lignin, cellulose) • Bacteria & other microorganisms break down just about anything else Mycorrhizae • Symbiotic association between plant roots and fungi • Endomycorrhizae vs. Ectomycorrhizae • Play a role in decomposition by breaking down proteins into amino acids that are transferred to host plant Decomposition • Mechanisms – Leaching – Fragmentation – Chemical Alteration • Factors influencing decomposition rate – Quality of Detritus – Climate (temperate vs. tropical) – Soil Animals Quality of Detritus • Animal carcasses decompose faster than plants • Leaves decompose faster than wood • In any given climate, there is a 5 to 10fold range in decomposition rates that is attributable to detritus composition Climate: Tropical vs. Temperate What does this tell you about which abiotic factors are most important in terms of controls over rates of decomposition? Soil Animals • Soil animals have effects on soil structure, litter fragmentation, transformation of organic compounds, and composition of microbial community • Microfauna (<0.1mm; protozoans, nematodes) • Mesofauna (0.1mm – 2mm; taxonomically diverse, have the greatest effect on decomposition) • Macrofauna (>2mm; earthworms & termites, called ecosystem engineers because they alter resource availability by modifying physical properties of soils and litter Soils as a compartment Low clay content of soils in the tropics results in nutrients washing out of the soil unless there is quick uptake by plants As a result, most nutrients are found in living biomass rather than soils: important implications of tropical deforestation Vegetation as a compartment Nutrient regeneration in aquatic systems Productivity in aquatic ecosystems Global distribution of chlorophyll in oceans Where is productivity highest? Shallow seas, proximity to bottom sediments Strong upwelling zones Carbon cycle – units = Gt C = 10 15 g C Carbon dioxide 1 2 3 3 Nitrogen Cycle Atmosphere N=N Marine cycling Oceans Leaching Burial Low levels of NH4+, NO3-2 Sediments Soils, Organisms Mineralization Assimilation Nitrification
