β-Glucosaminidase Activity as an Index of Nitrogen Mineralization in Soils

Abstract

N-Acetyl-β-d-glucosaminidase (NAGase, EC 3.2.1.30) is one of three enzymes that catalyze the hydrolysis of chitin. This hydrolysis is important in carbon (C) and nitrogen (N) cycling in soils because it participates in the processes whereby chitin is converted to amino sugars, which are major sources of mineralizable N in soils. This study investigated the relationship between N mineralization indexes and activity of β-glucosaminidase in soils from six agroecological zones of the North Central region of the United States. Nitrogen mineralization was studied by using short-term laboratory incubations under aerobic and anaerobic conditions and by hydrolysis of soil organic N by steam distillation with chemical reagents. Enzyme activity was assayed at its optimal pH value. The amounts of N mineralized by all the biological and chemical methods studied were significantly correlated with β-glucosaminidase activity, with r values of 0.73*** and 0.76*** for the amounts of released by steam distillation with PO4-B4O7 for 4 or 8 min, respectively; of 0.69*** and 0.74*** for the amounts of released with Na2B4O7 for 4 or 8 min, respectively; of 0.47*** for the amounts of inorganic N produced under aerobic incubation; of 0.80*** for amounts of inorganic N produced by incubation under anaerobic conditions of field-moist soils; and of 0.86*** for anaerobic incubation of air-dried soils. There was a significant correlation between β-glucosaminidase activity and organic C (r = 0.56***), total N (r = 0.60***), and fixed of the soils (r = 0.79***). The amounts of inorganic N released by the methods, with the exception of those under aerobic incubation, were significantly (P < 0.001) correlated with organic C and total N contents of the soils, with r values ranging from 0.65*** to 0.78*** and from 0.62*** to 0.80*** for organic C and total N, respectively.