Oxidative Enzymes, the Ultimate Regulator: Implications for Factors Affecting Their Efficiency

Soil enzymes influence the distribution of organic matter (OM) and play a decisive role in the retention of OM in soil ecosystems. The present study was conducted to assess the role of oxidative and hydrolytic enzymes in OM decomposition under dry and submerged moisture conditions and to examine factors affecting their activity in Red and Brown soils. An incubation experiment of 6 mo duration was performed in a randomized complete block design with 10 treatments in triplicates. Rice straw (RS) and green manure (GM) were used at three rates (0, 5, and 25 mg g(-1) soil, expressed as control [CK], RS1, RS2, GM1, and GM2, respectively). The soils were maintained at two water levels: 25% (W1) and 200% (W2). All soil chemical properties and enzymatic activities were measured by standard methods. We found that the activities of soil phenol oxidase and catalase in the Brown soil were 2- and 1.5-fold higher than in the Red soil, respectively. This led to high OM decomposition, resulting in 1.23- and 1.2-fold higher carbon (C) and nitrogen (N) mineralization and 1.23- and 1.21-fold more dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) in the Brown soil. In contrast, low oxidative enzyme activities in the Red soil decreased C and N mineralization, DOC, DON, reducing sugars (2.58-fold), and amino acids (2.22-fold) but increased the phenolic compounds (1.36-fold). The hydrolytic enzymes (i.e., urease and neutral phosphatase) showed significant correlation (p < 0.01) to amino acids and reducing sugars but showed no correlation to phenolic compounds and soil organic matter (SOM). Conversely, oxidative enzymes (i.e., phenol oxidase and catalase) showed significant correlation (p < 0.01) to phenolic compounds, amino acids, reducing sugars, and SOM. Our results suggest that oxidative enzymes are key components of the pathways involved in the breakdown of organic compounds and OM in soils and consequently act as an "enzymatic latch." We observed that soil water and pH have significant (P < 0.01) effects on soil enzyme activity.