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The Nitrogen Cycle The nitrogen cycle • Living things need nitrogen to make protein. • They can not use the nitrogen that is 78% of the air • The nitrogen in the air must be changed to before plants can use it. The nitrogen cycle • Animals get their nitrogen by eating plants. The nitrogen cycle (page 70) Nitrogen fixation • N2 (gas)NH3(ammonia) • Cyanobacteria and Nitrogen-fixing bacteria living in these nodules on plant roots can do this conversion. Nitrogen cycle… • Assimilation – Producers take up nitrogen – Process in which consumers get nitrogen from producers • Ammonium NH4+ or nitrate NO3- The nitrogen cycle • The nitrogen-fixing bacteria are essential to maintain the fertility of the soil. • Without them food yields would rapidly fall. • Considered limiting factor Nitrogen cycle… • Ammonification – Decomposers in soil and water break down the biological nitrogen back into NH4+ Nitrogen Cycle… • Nitrification – Nitrifying bacteria convert ammonium, NH4+, to nitrite, NO2- and then into nitrate, NO3- Nitrogen cycle… • Denitrification – Denitrifying bacteria convert nitrate into nitrous oxide and then nitrogen gas Perhaps catchy way to remember… fix NAAD ANPAN Process • Fix-nitrogen fixation • Nitrification • Assimilation • Ammonification • Denitrification Product • Ammonia NH3 • • • • Nitrates Proteins Ammonia (nitrites) Nitrogen Phosphorus Cycle • Very slow cycle. • Almost all found in the ground. • Cycle impacted by fertilizer and laundry soap form 1940-90, dish soap ‘til 2010 • Limiting agent in most ecosystemstherefor increase has big impact excess can cause algal bloom Phosphorus Cycle Algal Bloom • Algal blooms are the result of an excess of nutrients, particularly phosphorus and nitrogen. • The excess of nutrients may originate from fertilizers, these nutrients can then enter watersheds through water runoff. • Creates hypoxic (low oxygen conditions) Algal bloom Succession (Chapter 6) • How ecosystems change over time. – Change and replacement of species • Gradual process (100-1000s of years) • 2 Types – Primary- occurs where no ecosystem existed before. – Secondary- occurs where ecosystem previously existed. More common Primary Succession • Occur by – Volcanic eruptions creating new islands – Areas exposed when glaciers retreat – Any area that did not have life prior • Slower (several thousand years) • First species present (pioneer) will be bacteria and lichens How it gets started • Bacteria and lichens can start on bare rocks and break them down. • Water than enters rock to freeze and thaw which breaks it further. • Mosses decay and add to soil…more life can start Secondary Succession • Created by –Natural disaster wipes out existing ecosystem and new one is started. –Fire-manmade or lightening. Some ecosystems depend on lightening. –Old field succession is process where abandoned farmland grows back to forest. Process of secondary succession • First you have grasses • Then small bushes, they choke out some of the grasses • Small trees start to grow and they choke out some of the bushes • Then trees get larger…. Ecosystems respond to disturbance • Disturbance- An event caused by physical, chemical or biological agents that results in changes in population size or community composition. The Intermediate Disturbance Hypothesis • The intermediate disturbance hypothesisstates that ecosystems experiencing intermediate levels of disturbance are more diverse than those with high or low disturbance levels. Resistance versus Resilience • Resistance- A measure of how much a disturbance can affect its flows of energy and matter. • Resilience- The rate at which an ecosystem returns to its original state after a disturbance. • Restoration ecology- A new scientific discipline that is interested in restoring damaged ecosystems.