Enzymatic activities and microbial communities in an Antarctic dry valley soil: Responses to C and N supplementation

D. W. Hopkins, A. D. Sparrow, L. L. Shillam, L. C. English, P. G. Dennis, P. Novis, B. Elberling, E. G. Gregorich, L. G. Greenfield

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    The soils of the Antarctic dry valleys are exposed to extremely dry and cold conditions. Nevertheless, they contain small communities of micro-organisms that contribute to the biogeochemical transformations of the bioelements, albeit at slow rates. We have determined the dehydrogenase, P-glucosidase, acid and alkaline phosphatase and arylsulphatase activities and the rates of respiration (CO2 production) in laboratory assays of soils collected from a field experiment in an Antarctic dry valley. The objective of the field experiment was to test the responses of the soil microbial community to additions of C and N in simple (glucose and NH4Cl) and complex forms (glycine and lacustrine detritus from the adjacent lake comprising principally cyanobacterial necromass). The soil samples were taken 3 years after the experimental treatments had been applied. In unamended soil, all enzyme activities and respiration were detected indicating that the enzymatic capacity to mineralize organic C, P and S compounds existed in the soil, despite the very low organic matter content. Relative to the control (unamended soil), respiration was significantly increased by all the experimental additions of C and N except the smallest NH4Cl addition (1 mg N g(-1) soil) and the smallest detritus addition (1.5 mg C g(-1) soil and 0.13 mg N g(-1) soil). The activities of all enzymes except dehydrogenase were increased by C and combined large C (10 mg C g-1 soil) and N additions, but either unchanged or diminished by addition of either N only or N (up to 10 mg N g-1 soil) with only small C (1 mg C g-1 soil) additions in the form of glucose and NH4Cl. This suggests that in the presence of a large amount of N, the C supply for enzyme biosynthesis was limited. When normalized with respect to soil respiration, only arylsulphatase per unit of respiration showed a significant increase with C and N additions as glucose and NH4Cl, consistent with S limitation when C and N limitations have been alleviated. Based on the positive responses of enzyme activity, detritus appeared to provide either conditions or resources which led to a larger biological response than a similar amount of C and more N added in the form of defined compounds (glucose, NH4Cl or glycine). Assessment of the soil microbial community by ester-linked fatty acid (ELFA) analysis provided no evidence of changes in the community structure as a result of the C and N supplementation treatments. Thus the respiration and enzyme activity responses to supplementation occurred in an apparently structurally stable or unresponsive microbial community. (C) 2008 Elsevier Ltd. All rights reserved.

    Original languageEnglish
    Pages (from-to)2130-2136
    Number of pages7
    JournalSoil Biology and Biochemistry
    Issue number9
    Publication statusPublished - Sept 2008


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