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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 mm) 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. (C)1995 Academic Press Limited