FOR2060 1st Edition Lecture 8 Outline of Last Lecture I. Residence TimeII. Nutrient Cycling A. Geochemical CycleB. Biogeochemical CycleC. Biochemical Cycle D. Essential Nutrient E. Nutrient Movement III. MycotrophyA. Ectomycorrhizae B. Arbuscular Mycorrhizae Outline of Current Lecture IV. NitrogenV. The Nitrogen CycleA. Nitrogen FixationB. Nitrogen Mineralization C. Nitrogen Immobilization Current LectureIV. NitrogenNitrogen is the most commonly limiting nutrient in forest ecosystems. Plants require nitrogen in large quantities so it gets used up by all of the plants. 78% of the earth’s atmosphere is nitrogen,but the nitrogen gas has a triple bond, which means it is inert and the plants are unable to use it. The plants have to rely on the nitrogen in the soil. V. The Nitrogen Cycle Nitrogen goes through many transformations during the nitrogen cycle. Nitrogen fixation refers to how nitrogen enters an ecosystem. For this to happen the triple bond between the nitrogen gas must be broken. This can happen in several ways. The Haber-Bosch process breaks the triplebonds with the use of high heat and pressure. Lightning converts nitrogen gas into nitrous oxide, allowing plants to fix small amount of the nitrogen when the nitrous oxide comes down to earth in rain. This was important in early history before the Haber-Bosch process was These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.invented. Nitrogen can also be fixed by the symbiotic association between nitrogen fixing bacteria and higher plants. An example of this is Rhizobium bacteria and legumes. There are also free-living non-symbiotic microorganisms, like certain bacteria and blue-green algae. Nitrogen mineralization is the process in which soil organic matter is decomposed by microbes releasing mineral nitrogen in the process. This frees up nitrogen for plants to use. Heterotrophs use organic molecules as a source of energy; bacteria and fungi break down these organic molecules for the plants to use. Nitrogen is essential for microbial growth, as is carbon. If nitrogen in organic matter exceeds the needs of the microbes (high quality litter, low ratio) the excess nitrogen will be released. Nitrogen immobilization is the conversion of mineral nitrogen to organic nitrogen by microbes. Organisms that decompose organics matter as an energy source require nitrogen. Organic materials with a low carbon content cannot supply the needs of these organisms thus they use the nitrogen in the soil, competing with