Quiz 19 :
Nutrient Cycling and Retention
One of the most important aspects of the functions of ecosystem is the exchange of nutrients between the organisms and their environment. Nutrients move through an ecosystem in biogeochemical cycles. A biogeochemical cycle is a pathway in which chemical elements move through the biotic and the abiotic factors of an ecosystem. Because of physiological importance of nutrients, their relative scarcity and their influence on rates of primary production, nutrient cycles are important ecological functions. Carbon, nitrogen and phosphorous along with hydrogen and oxygen are the basic elements of all life forms. Carbon is required for building of all organic compounds. Nitrogen and phosphorous are essential components of proteins and nucleic acids. Hence, all the three nutrients are critical for the existence of life on earth. Their availability to organisms is determined by nutrient cycles. Most importantly, nitrogen and phosphorous are essential nutrients for plant growth and their availability significantly affects primary production. These nutrients become available to plants through nutrient cycles. Since primary production is crucial to the maintenance of life on earth, carbon, nitrogen and phosphorous cycles are extremely important and hence, ecologists have extensively studied these nutrient cycles.
The t -test is a statistical test that assesses whether; the means of two groups are statistically different from each other. Therefore, the test can be used when one wants to compare the means of two groups. The t -test is more appropriate to be used in some situations, while it is not appropriate to use the test in some other situations. The situations in which the test gives reliable results include: 1. The two populations being compared to have equal variance. 2. Each of the samples is drawn from a population with a normal distribution. However, the test can be used even if the fit of measurement to a normal distribution is not exact. That is the test provides reliable results even in situations in which the distribution of measurements is fairly symmetrical around the mean. Also, the t -test gives reliable results even with some differences in variances, when the sizes of samples being compared are similar. In contrast, when the two populations are being compared, they have normal distributions for a characteristic. But the characteristic is much more variable in one of the populations compared to the other. Therefore, it would be appropriate to compare the two populations using the t -test. The test gives reliable results even if the fit of measurements to a normal distribution is not exact. Also, the test can be used if the sample sizes of the two populations are similar, because t -test can be used reliably to know the differences in the variances of the two populations.
Parmenter and Lammara (1991) investigated the vertebrate carrion (carcasses of fish and waterfowl) as a potentially important source of inorganic nutrients such as nitrogen and phosphorous in the aquatic systems. The results of their investigation suggest that decay constants (rate of decomposition) are significantly larger than those of plants tissues. The carbon to nitrogen ratio is an important factor of a substrate that determines the rate of its decomposition by microbes. Plant tissue is mainly composed of cellulose, lignocellulose, and lignin and is low in nitrogen. Lignin is a complex polymer of phenyl propane units which are cross-linked to each other through a variety of chemical bonds. Lignin is particularly difficult to decompose and it also substantially reduces the bioavailability of other cell wall components. On the other hand, animal tissues have a higher content of nitrogen and hence a lower carbon to nitrogen ratio as compared to plant tissue. This makes it more readily biodegradable. Hence, it is expected to be decomposed at a faster rate than plant tissue.