Nitrogen in the Terrestrial Environment November 15 th, 2006 General Ecology lecture

Outline General overview of the global nitrogen cycle Focus on soil processes Talk about plant available forms, how N becomes available to plants Environmental context Invasive species context Case study: Russian olive Designing an experiment

Organic Nitrogen- Nitrogen enters the soil in organic forms such as plant roots, leaves, and other plant materials, in addition to dead animals, insects, and microorganisms, manure, compost, and sewage sludge. As these decompose, the once recognizable plant and animal materials are transformed into soil organic matter called humus which contains organic nitrogen. Living plants cannot use these organic forms of N. This is why microbes living in the soil are so valuable, because they can convert organic N into inorganic forms of N that plants can then use.

Mineralization- when an element, such as N, is converted from an organic form to an inorganic form by microbes. Plants can then use this inorganic N to grow.

Nitrosomonas and Nitrobacter specialize in breaking down organic N into inorganic N compounds, making nitrogen available to plants.

Decomposition is metabolism for soil organisms.

Inorganic Nitrogen- Inorganic forms of N are usually added to the soil by rain or snowfall, or as fertilizers. Microorganisms in the soil convert organic forms of N into inorganic forms, a process known as biological N fixation, that are then usable by plants.

Plants that can “fix” nitrogen from the air have a substantial advantage.

Microscopic view of nitrogen-fixing nodules (arbuscule) and fungal roots (hyphae) on a plant root.

Nitrogen is the limiting resource in most ecosystems

Russian olive (Elaeagnus angustifolia)

 Altered flow regimes  altered ecosystem processes.  Increased soil nitrogen may favor other weeds.  presence of exotic invader- changes native plant community.  changes in plant community  changes in faunal diversity and ecosystem services. Russian olive: Why do we care?

Current Research General Question: How does Russian olive change a site, and therefore affect native species regeneration (restoration success)? Assumption: Russian olive chemically alters the soil environment. Why? Nitrogen-fixer, high leaf lignin concentrations, allelopathic (Llinares 1994, Orr 2005).  If soil N augmentation is the result, will favor exotic annual herbaceous cover over native perennials.  After initial invasion, rate of Russian olive dominance will increase (self-promoting).

Methods General Question: How does Russian olive change a site, and therefore affect native species regeneration (restoration success)? How can I get to the heart of this question?  Find a research area  Control as many variables as possible  Experimental design  Sample size  Feasibility  Analysis