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991.
During a period of immobilization of nitrate-15N and mineralization of organic N in a sandy-loam, changes were recorded in: (a) the concentration of an added carbon source, glucose-14C: (b) evolution of 14CO2: (c) bacterial populations; (d) distribution and concentration of newly-synthesized, acid-soluble, amino acid-15N; and (e) distribution and activities of several oxidative and hydrolytic enzyme systems.Added glucose-14C was rapidly metabolized by the soil microflora. After 1.5 day's incubation, when only 3.6 per cent of the added glucose was present, 68 per cent of the 14C remained in the soil-microbial system. During this period there was a marked increase in viable bacterial numbers and an almost complete immobilization of nitrate-15N. On continued incubation, microbial metabolites were oxidized at decreasing rates, the more rapid phase corresponding to a period of net decline in the viable bacterial population.Soil was fractionated by a relatively mild procedure into components containing: (a) extractable proteins; (b) extractable amino acids and peptides; (c) particulate material containing microbial cells, cell debris and material bound to larger soil particles; and (d) microbial metabolites mainly bound to soil colloids. Although the total, acid-soluble, amino acid-15N remained relatively constant for about 50 days, there were marked changes in their concentration in different fractions, especially in the extracts and in the fraction containing fine colloidal material. However, the relatively large decline in labelled, acid-soluble, amino acid-15N occurred during the active phase of oxidation of microbial metabolites when little net mineralization of labelled compounds occurred.Increases in enzymic activities generally coincided with increased viable bacterial populations although there were some exceptions, notably casein and benzoyl arginine amide-hydrolysing enzymes. The stabilities of the newly-formed enzymes varied markedly. The greatest relative changes in activity occurred with the casein-hydrolysing enzymes. Their activity reached a maximal value after the main flush of bacterial growth, was short-lived and was to a large extent extractable. The formation and disappearance of this extracellular proteolytic activity coincided approximately with that of a secondary peak of extractable, newly-synthesized, protein-15N. In general however, changes in enzymic activity could not be identified with changes of protein-15N concentrations of the different fractions. 相似文献
992.
A. Warren 《Geoderma》1973,9(1):75-78
The distinction between vegetation arcs and vegetation patterns is discussed. Some patterns are distinguished which are the result of ancient dune-building processes. These occur on an ancient series of aeolian sands. 相似文献
993.
Measurements of downslope rock-creep, of the slow rate of plant establishment on alpine and subalpine road-cuts, and of the reduction in plant cover and plant production in two alpine plant communities, illustrate the degree of disturbance that can occur. The development of large trails or roads should not be permitted in areas of such active downslope rock movement, because of the natural rate of mass-wasting. If more people are to visit and enjoy the alpine communities, asphalt paths to confine their walking are desirable, for trampling experiments showed that plant cover and plant production were rapidly reduced in even one season of light use. Recovery during the following year was, however, quite rapid—especially in the snow-bank community. Different alpine and subalpine habitats have different sensitivities to disturbance, and any plans for increased human use must incorporate this kind of information. 相似文献
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