Trees, Timber, and Trade Winter 2002

Forest Ecology Study Questions #2

FE Ch 17. These are due Monday, Jan 28th at the beginning of class. Write your answers neatly and legibly on a separate piece of paper that you will turn in. Be prepared to discuss your answers with your study group. You may need to access outside resources to completely answer these questions.

  1. If a free-living diazotroph consumes about 35 g of carbon to fix 1 g of N, how much carbon would have to be supplied to fix 45 kg (about 100 pounds) of nitrogen? Give your answer in kilograms and pounds.
  2. The carbon/nitrogen (C/N) ratio of protozoa is about 20/1 and the C/N ratio of bacteria is about 5/1. The average protozoan weighs 10-8 g and an average soil bacterium weighs about 10-12 g and half of both their weights is carbon.
  1. Calculate the mass of carbon and nitrogen in a single protozoan and in a single bacterium.
  2. Assuming that a protozoan needs to eat its body mass of carbon daily, how many grams of bacteria does a single protozoan need in one day? How much nitrogen would this release?
  3. If a protozoan eats about 10,000 bacteria/day, how many grams of nitrogen will be released by a single protozoan in a day?
  1. Due to the heat from a forest fire, the trees in a nearby stand drop their needles onto the forest floor. Warm moist conditions lead to rapid decomposition of the needles (85% C, 10% N). Assume that the soil microbial biomass has an average C/N ratio of 8/1 and a microbial yield efficiency of 0.4 (40%) in converting the carbon into biomass. Will net ammonification or immobilization of nitrogen occur? Show your calculations and explain your reasoning.
  2. Compare and contrast the processes of nonsymbiotic and symbiotic N2 fixation.
  3. Agroforestry consists of rows of nitrogen-fixing trees with annual crops, such as sorghum and maize, grown in between the trees. How might this affect the overall rate of N2 fixation by the trees? Explain.
  4. Explain how acid rain has caused the loss of cations from the soil in the eastern hardwood forests (hint there are two mechanisms involved).
  5. Describe the optimum soil conditions for nitrogen fixation.
  6. Outline the pattern of nutrient loss from the forest soil following a clearcut. How could this be altered?