FEMS Microbiology Ecology 86 (1992)303-310 © 1992Federationof European Microbiological Societies 0168-6496/92/$05.00 Publishedby Elsevier 303 FEMSEC 00376 Huge increase in bacterivores on freshly killed barley roots S. Christensen t, BS. Griffiths 2, F. Ekelund m and R. Ronn t i Copenhagen University, Department of Population Biology, KObenhavn, Denmark, and z Scottish Crop Research Institute, Inve~owrie, Scotland, UK Received14 September1991 Revisionreceived13 November1991 Accepted14 November1991 Key words: Barley root; Bacterivore; Microbial activity; Microfaunal activity 1. SUMMARY Adding fresh roots to intact soil cores resulted in marked increases in microbial and microfaunal activity at the resource islands. Microbial activity increased in two phases following root addition. Respiratory activity and concentration of respira- tory enzyme (dehydrogenase) in soil adhering to the roots was very high during the first three weeks resulting in anaerobic conditions in the soil. After a period of low respiratory activity and enzyme content, these quantities increased from 6 to 20 weeks, but not enough to maintain anaer- obic conditions. Numbers of protozoa peaked earlier than the nematodes. Based on yield coeffi- cients of microbes and bacterivores, the increase in bacterivores was in accordance with root-in- duced respiration activity. In soil adhering to roots, numbers of bacterial grazers (protozoa and nematodes) were up to 80 and 30 times higher, respectively, than in the surrounding soil. This Correspondence to: S. Christensen, Copenhagen University, Department of Population Biology, Universitetsparken 15, DK-2100 KcbenhavnO, Denmark. effect is up to 20 times higher than observed around live root systems, which may suggest that the rhizosphere effect on mierobivores could for the major part result from the decomposition of dead segments of the root system. 2. INTRODUCTION Soil is a highly dynamic medium, where or- ganic matter inputs to terrestrial ecosystems are decomposed. Since the resource units are usually very small (a root fragment, a small soil animal etc.), steep gradients in decomposition activity occur over mm distances. A local increase in available carbon in undisturbed soil following plant root decay [1] or addition of dead bacterial cells [2] will lead to the formation of an anaerobic soil volume, as measured by denitrification under conditions of no NO~" limitation. To understand the dynamics of in situ decomposition activity and population changes requires measurement of soil respiration geometry and decomposer popula- tions at the organic resource islands, where the limiting factors operate. Adding pieces of wood to forest soil allowed the study of successional Downloaded from https://academic.oup.com/femsle/article-abstract/86/4/303/435671 by guest on 30 May 2020