Graduate Thesis Or Dissertation
 

Soluble carbon and respiration of forest humus

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/n296x300t

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  • Humus is one of the important factors controlling the soil formation process. The nutrients released from it during the decomposition process also affect the growth and reproduction of the forest. The type of humus formed is influenced by the nature of the forest litter and the environment in which it is decomposed. The whole complex of processes by which plant residues are transformed and finally converted into humus is the result of the combined activity of associations of microbes exhibiting diverse biochemical functions. The respiratory activity in the forest floor decreases with progressive stages of decomposition and humification. This reflects the chemical composition and availability of the remaining carbon compounds as energy source material. It appeared that the content of total soluble carbon might serve as an index of the stage of decomposition and humification. As a mild oxidizing reagent, potassium persulfate oxidizes only the water soluble materials in the temperature range of 70°C to 75°C. A water extraction-potassium persulfate oxidation technique was used for the estimation of total soluble carbon content of forest floor materials. Extraction time and the efficiency of the persulfate oxidation of the extract were also investigated. Continuous aeration and electrolytic respirometer techniques were used for the respiration study and for comparison with the persulfate oxidation technique. A variety of representative forest floor materials from different forest types in Eastern North America and the Coast Range of Oregon were studied both for respiratory activity and for water soluble carbon content. A highly significant positive correlation was found between levels of water soluble carbon and CO₂ evolution in these samples. In the areas sampled in the eastern United States and Canada, a majority of the well humified layers (H) gave respiratory carbon/soluble carbon ratios of 1. Most of the less humified samples showed ratios near 1.4. Materials from Douglas-fir forests having low soluble carbon levels had considerably greater respiratory carbon/soluble carbon ratios than the low soluble carbon materials from eastern forests. The advantages of the persulfate oxidation method over the respiration method are that it is less time consuming, few materials are required and better control can be exercised. Since the water soluble carbon as determined by the persulfate oxidation test may be expressed in terms of respiration, where good correlations are established, it appears that either the soluble carbon value itself or the correlated respiratory activity may be used as an indicator of the stage of humification. Thus a much more rapid, less tedious means of evaluating the status of forest floor materials is available.
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