摘要:

SUMMARYThe amount of organic matter and rate of litter decomposition in relation to vegetation type under mediterranean‐type forests in southern Tuscany was studied. Since existing concepts are largely based on studies of soils on calcareous substrates in this region, particular attention was paid to soils on non‐calcareous materials. The humus type and distribution at five sites on acid metamorphic rocks and at one site on dolomitic limestone with different vegetation types was investigated. The input of above‐ground litter was also determined. On the metamorphic rocks, clear trends in humus profile development could be observed from deciduous through sclerophyllous to coniferous vegetation: there was a decrease in litter nitrogen content (9.3 to 5.8 g N kg−1DM), an increase in the amount of organic matter in ectorganic layers (2.53 to 4.66 kg m−2), a decrease in the decay constantk(0.26 ± 0.02 to 0.17 ± 0.03 a−1), and a decrease in soil faunal activity. The results indicate that, under eu‐mediterranean to sub‐mediterranean forests, decomposition rates are comparable to those under temperate deciduous forests, and that the dominant humus form is a leptomoder. The spatial variation in the amount of organic matter within the plots was considerable, and was related t

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1992.tb00125.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARYThe growth and nitrogenous excretion of a common soil flagellate,Spumellasp., isolated from a Scottish podzol and fed with the common soil bacterium,Pseudomonas fluorescens, were investigated. Video‐enhanced light microscopy and transmission electron microscopy were used to study the digestion process. Ingestion of the bacteria occurred rapidly at the base of the two flagella and involved the formation of a small protrusion, which surrounded the prey. The first signs of digestion appeared a few minutes after ingestion with the degradation of the outer membrane of the bacteria. Digestion was complete within 30–60 min, and the indigestible bacterial residues were then released into the medium. Ammonium nitrogen was the major form of nitrogen excreted. Some apparently intactP. fluorescensbacteria were also egested. For each division 130 bacteria were required. No feeding activities were observed at 5°C. Of the total bacterial protein, 42% was incorporated into biomass of flagell

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1992.tb00126.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARYThe need for a more continuous approach to soil classification is discussed, and methods based on the mathematical constructs known as fuzzy sets are considered most appropriate for this. A centroidal grouping method, fuzzy k‐means with extragrades, which quantifies the intragrading and extragrading of soil individuals is described. An example of the application of this technique to an area of 4800 ha at Wesepe in The Netherlands is presented. The results show that the technique could create a classification that reflects the main pedological features of the area in a continuous way. Although there may be problems in selecting the optimal number of groups and degree of fuzziness, we conclude that the method is most promising and worthy of consideration when any type of quantitative soil classification is require

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1992.tb00127.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARYThe variogram is central in the spatial analysis of soil, yet it is often estimated from few data, and its precision is unknown because confidence limits cannot be determined analytically from a single set of data. Approximate confidence intervals for the variogram of a soil property can be found numerically by simulating a large field of values using a plausible model and then taking many samples from it and computing the observed variogram of each sample. A sampling distribution of the variogram and its percentiles can then be obtained. When this is done for situations typical in soil and environmental surveys it seems that variograms computed on fewer than 50 data are of little value and that at least 100 data are needed. Our experiments suggest that for a normally distributed isotropic variable a variogram computed from a sample of 150 data might often be satisfactory, while one derived from 225 data will usually be reliable.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1992.tb00128.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY