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Abstract: A field study was conducted in the Negev Desert over three seasons: June (summer), October (autumn), and April (spring). Cellulose of plant or paper origin was added to the study soils. The concentration of cellulase in the soil was determined by monitoring the rate of solubilization of chromophoric molecules covalently linked to artificial insoluble cellulose (cellulose-azure). The amount of CO2 evolved from the soil was also evaluated at 60-day intervals. In this paper, we demonstrate that significant differences (p<0.01) in the cellulase concentration in desert soils are mainly due to the time period during which organic matter was incorporated into the soil. Data are presented showing changes in cellulase concentrations in the soil as a response to different cellulose sources (plant and paper origin) throughout the year. The results of our field experiments show that the cellulase concentration in the soil surrounding cellulose (paper) is higher during the summer than during the other seasons. The concentration of cellulase associated with fresh organic matter was found to be double that associated with paper. CO2 evolution was higher in soil samples supplemented with organic matter than in control samples. This study demonstrates that the concentration of cellulase in desert soil changes over the year and is influenced by the cellulose source and by the quality of the cellulose incorporated in the soil. [Copyright &y& Elsevier]

The concentration of cellulose in plant material greatly affects the decomposition rate of plant-derived litter and hence carbon availability. The disappearance of pure cellulose in soil was studied as a measure of plant decomposition and carbon turnover. Our objective was to understand the effect of various cellulose concentrations and plant material added to soil and collected during different seasons, on cellulase concentrations under laboratory conditions (e.g. constant soil moisture and incubation temperature). The percentage of recovery of the enzyme in the control soil and in samples amended with known amounts of cellulose powder was estimated. Several methods for estimating soil cellulase concentrations/activity are available, most based on the determination of released reducing sugars. The method used in this study is based on the cleavage of a cellulose-azure substrate by cellulase to spectrophotometrically detectable fragments. Our results showed a significant correlation (p<0.05) between cellulose concentration and cellulase levels in soil, which varied along the study period. When pure cellulose was added to the soil, cellulase was detected after 7 days of incubation, whereas when plant material was added to the soil, cellulase was detected after 14 days. The recovery of cellulase from soil was also found to be seasonally dependent. The method of cellulase determination used in this study was simple, safe and rapid. From the results presented in this study, it can be assumed that there are seasonally dependent factors that affect the existence and concentration of cellulase in soils of the arid Negev Desert, in addition to organic matter, water and temperature. [Copyright &y& Elsevier]