Journal of Arid Environments (1995) 31:383-399 Decomposition of root fitter and related microbial population dynamics of a Negev Desert shrub, Zygophyllum dumosurn Y. Steinberger, R. Degani & G. Bamess Department of Life Sciences, Bar-Ilan University, Ramat Gan 52900, Israel (Received 14 February 1994, accepted 6 April 1994) Decomposition of root litter was studied using roots of the perennial shrub Zygophyllum dumosum, located at three depths (10, 20 and 30 cm). There were three diameter classes (1-3; 4-8; 9-16 ram) used during two consecutive years in the Negev Highland Desert, Israel. No significant differences in decomposition rates in root mass losses between the two treatments and years were found. In both treatments there was an annual mass loss of 15.5%, calculated kinetics (k) of 0-18 year -1, with a turnover time of approximately 17 years. Rates of mass losses of root litter in the Negev Desert were found to be different than those reported for two evergreen shrubs from the Chihuahuan Desert but were found to be comparable to the data reported on Scots pine roots from the SECON research site in Sweden. These results suggest that linkage exists between rainfall (events, amount) events, root diameter, lignin and nitrogen concentration, and biotic activity where water availability is one of the most important regulators of decomposition in the Negev Desert. @1995 Academic Press Limited Keywords: decomposition; roots; desert; microbial population Introduction The release of nutrients from different organic sources is a fundamental process in the biogeochemical cycle of an ecosystem (Berg, 1984). The importance of below-ground parts of perennial and annual plants in nutrient cycling has been overlooked. As a result, there are relatively little quantitative data available on this subsystem. The organic material of roots has great value as a nutrient pool, especially in desert ecosystems where nutrient release resulting in 'local availability' may immediately effect the regulation of above-ground production. Litter from an above-ground source is mechanically fragmented and redistributed to new locations (Parker et al., 1984). Some of this litter is then physically buried by animal activity (Steinberger & Whitford, 1983). Just after burial of the litter, a more intensive decomposition process takes place (Santos & Whifford, 1981; Whifford et al., 1981; Steinberger & Whifford, 1988). Therefore, root-originated litter already located in the soil at different depths and 0140-1963/95/010383 + 17 $12.00/0 © 1995 Academic Press Limited