Provide an example of an ecosystem evolving in a manner that preserves or recycles nutrients.
In tropical environments with stable geological topography, there is very little phosphorus in the soil. This is due to the age and stability of the soil. The soil itself is so old that the clays in it have broken down. Because rain is the only input of water, there is no opportunity for the addition of new minerals. The phosphorus necessary to sustain the ecosystem is stored in the vegetation, and is retained phosphorus during growth. When those plants die, the return the phosphorus to the ecosystem in the form of plant litter detritus, and is quickly taken back up into other organisms in the system. The other organisms in the environment have evolved to pull the phosphorus directly out of the litter instead of the soil.
How is it that a nutrient like nitrogen, which is typically qualified as limiting, is present in such excess in many locations?
Nitrogen is historically not easily obtained in natural systems. It exists primarily as N2 gas in the atmosphere and plants are not able to obtain this form directly. Most plants rely on other organisms to fix nitrogen into usable forms like NH4+ and NO3- which they are able to use. This means that the plants are dependent primarily on microorganisms in the soil or in their root structures thus their growth is limited by the productivity of the microorganisms.
Humans have changed this case in three ways. Humans cultivate a variety of plants such as legumes whose root nodules hold anaerobic bacteria which fixes nitrogen. The burning of fossil fuels results in the production of NOx which then re-enters the environment in precipitation. Fertilizer is also a major source of nitrogen that would not occur naturally. By adding these three forms of nitrogen into the system humans actually introduce nitrogen at a faster rate than the plants can assimilate it resulting in vastly increased global deposition of the nutrient. This is particularly true in highly industrialized nations where the amount of nitrogen deposited is often 4 times greater than historical levels.
What is 'occult N'? Do you believe in it?
Some forest readings have found N input readings much higher than would normally be expected and scientists are unsure where this extra N comes from. Some claim that there the forest is somehow gaining additional N through still undiscovered means, while others counter that the studies were simply poorly designed. As for whether you believe or not, well- that's up to you.
Define Nitrogen fixation and provide an example of a nitrogen fixing plant.
Nitrogen fixation is the biological process that converts atmospheric N2 gas into biologically reactive forms of N, usually as ammonia. An example would be soybeans.
What are the key transformations in the nitrogen cycle?
Explain why tropical soils have low fertility.
Tropical soils have low fertility because they are located in a low elevation area that is geologically stable. The soil is very old and the clays have broken down over time. In the absence of clays nutrients are leached from the soil. Also, the high amount of rain in this biome washes away nutrients.
What is humification?
The process by which organic molecules build up. After time this build up becomes harder and harder to decompose. Nitrogen and Carbon often remain in the humus causing the soil to become more fertile over time. This process does not occur in tropical soils where the humus does not build up due to the warmer and wetter climate.
Explain why certain plants may hold their foliage longer.
(Please look up the reason, since I don't know if this is right)
Maybe one reason is that the climate is suitable for a plant to have leaves year-round, that it's the optimum temperature for photosynthesis all year.
Evergreens that live in colder areas have adapted to the climate, having a sort of antifreeze in their small needles that aren't easily harmed by frost.