土壤学基本知识-土壤有机质性质及其分解.ppt

* Properties of Soil Organic matter and Its Decay General pattern of element cycle in ecosystems Properties of Soil OM -1: Chemical properties of litter and soil organic matter (OM): Litter (dead leaves, twigs falling on the ground) and soil organic matter contain nutrients be a critical link in nutrient cycles. Decomposition is the process that converts the organic forms of nutrients to inorganic forms available to plants. The nutrient content and the chemical structure of litter/OM, determine the quality of litter/OM affect the decomposition rates. Three general characteristics determine the litter/OM quality: The type of chemical bonds energy released as they decay; The size and spatial complexity of the molecules; Nutrient content. 1 and 2 determine the Carbon Quality of litter/OM, while 3 determines Nutrient Quality of litter/OM Properties of Soil OM -2: Decomposition of OM to inorganic molecules go through a long chain of biochemical processes to gradually degrade complex OM, and many soil organisms and microbes involved (recall detritus food web). These soil organisms and microbes break (decay) the chemical bonds in OM through the enzymes they produced (cost energy). The soil organisms and microbes decay OM to request energy and nutrients for themselves. Therefore, the higher the energy, nutrient content, the simpler the molecule structure the OM is, the easier (faster) it can be decomposed. Both OM quality environment factors affect the biochemical work of the soil organisms/microbes: decomposition is a oxidation process requiring participation of soil organisms/ microbes? factors affect soil organisms/microbes and general aeration condition of soil will influence rates of decomposition. Properties of Soil OM -3: Major Biochemical Constituents of Litter and Their Decay: Simple sugars: mono- and disaccharides: glucose, sucrose.. Starch: polymer of n glucoses linked by 1-4 glucoside bond. Cellulose: polymer of n glucoses linked