Biogeochemical cycles

Biogeochemical Cycles Elemental cycles that affect ecosystems Time for decomposition Biogeochemical Cycles Carbon – greenhouse gases Nitrogen – acid rain, nutrient Phosphorus - nutrient Sulfur – acid rain Oxygen - ozone C C numbers are billions of metric tons C Carbon dioxide concentrations are lower near trees during midday because trees having been “eating” the CO2 Carbon dioxide concentrations are high near the forest floor, where decomposers work around the clock during the growing season C Carbon dioxide production is highest during the growing season when decomposers are busiest N S Less land in the S hemisphere means both less seasonal difference in CO concentrations Oceans in the S have only a little phytoplankton, which neither uses nor produces much CO2, so there are no seasonal ups and downs Seasonal swings over land in the N are much bigger N N 3.9x106 Gt ~7 Gt ~100 Gt Table of nitrogen cycle processes N Process Fixation Mineralization/ Ammonification Nitrification Denitrification Starts with N2 gas Amino acids Ammonia to nitrite then to Nitrates Ends with Ammonia NH3 Ammonia NH3 Nitrate N2 gas End used by Nitrifying bacteria Nitrifying bacteria Plants Who does it most fixed by nitrogen-fixing bacteria associated with legumes and other plants, as well as free-living bacteria, cyanobacteria some fixed by lightning, cosmic radiation decomposer bacteria and fungi breaking down organic compounds that contain nitrogen (proteins) Nitrifying bacteria: one group of bacteria for each stage (Nitrosomonas, Nitrobacter) Nitrogen-fixing & other bacteria cyanobacteria facultatively anaerobic fungi and bacteria (Pseudomonas) N Nitrogen fixed from the atmosphere and mineralized during decomposition becomes available to living things as ammonia – NH3 or ammonium ion – NH4+ The plants would be happy to take up ammonia, but soil bacteria that don’t want the nitrogen, just the hydrogen ions, usually turn the ammonia into nitrate ions (N03-) by nitrification before the plants can use it The bacteria, being in the soil, are in the right place to grab the ammonia first Plants take up ammonia (if they can get it) and nitrate by assimilation and use it to make proteins, and animals may eat the plants and either use the nitrogen for proteins, or excrete it in urine Nitrogen in nitrate that plants don’t take up can be returned to the atmosphere as N2 gas through denitrification N S S S P P