No abstract

Abstract. Soil moisture is of primary importance for predicting the evolution of soil carbon stocks and fluxes, both because it strongly controls organic matter decomposition and because it is predicted to change at global scales in the following decades. However, the soil functions used to model the heterotrophic respiration response to moisture have limited empirical support and introduce an uncertainty of at least 4% in global soil carbon stock predictions by 2100. The necessity of improving the representation of this relationship in models has been highlighted in recent studies. Here we present a data-driven analysis of soil moisture-respiration relations based on 90 soils. With the use of linear models we show how the relationship between soil heterotrophic respiration and different measures of soil moisture is consistently affected by soil properties. The empirical models derived include main effects and moisture interaction effects of soil texture, organic carbon content and bulk density. When compared to other functions currently used in different soil biogeochemical models, we observe that our results can correct biases and reconcile differences within and between such functions. Ultimately, accurate predictions of the response of soil carbon to future climate scenarios will require the integration of soil-dependent moisture-respiration functions coupled with realistic representations of soil water dynamics.

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J o i~r t i d of General Microbiology (I974), 83, 375-387 Pr.intetl in Greot Britcriti

One hundred and forty-nine strains of nocardiae, freshly isolated from soil samples obtained from a number of countries with either tropical or temperate climates, and from rubber pipe seals, were compared with appropriate marker cultures in a numerical phenetic study using 156 unit characters. Marker strains were chosen to represent the Nocardia asteroides complex, other Nocardia species and related taxa in an effort both to classify the new soil isolates and, possibly, clarify the structure of the heterogeneous N. asteroides complex. The data were examined using the simple matching (SSM) and pattern (DP) coefficients, and clustering was achieved using both single and average linkage algorithms. Cluster composition was not markedly affected by either of the coefficients or clustering methods. The estimated test error of 7.1% was rather high and could account for a few apparently anomalous results. The 16 defined clusters, containing 185 of the 197 strains studied, were divided into seven major and nine minor clusters, four of which were further subdivided into two subclusters. Marker strains allowed four clusters to be designated as N. asteroides, seven as Nocardia species and one each as Nocardia carnea, Nocardia farcinica, Nocardia autotrophica, Mycobacterium farcinogenes and Rhodococcus species. Twelve strains formed single member clusters including the type strains of Nocardia aerocolonigenes, Nocardia amarae, Nocardia fukuyae, Nocardia orientalis and Nocardia otitidis-caviarum. The majority of the soil and rubber isolates were recovered in the major clusters labelled N. asteroides, N. carnea and Nocardia species and clusters of soil isolates without marker strains seem to represent new centres of variation. The study highlights the need for additional reproducible tests to help both define and determine the status of defined clusters within the N. asteroides complex which would considerably benefit both the ecological and epidemiological study of these organisms.