Temperature Sensitivity of Enzyme Kinetics Under Aerobic and Anaerobic Conditions in Wetland Soils Along a P Gradient.

Microbial enzymes play an important role in soil organic matter decomposition. Therefore, their activities have been used as indicators of microbial nutrient availability. Microbial enzyme activities can be affected by several parameters including nutrient concentrations, anaerobic conditions, and temperature changes.

We investigated the effect of temperature and anaerobic conditions on carbon (BGLU, CBH), nitrogen (Lap,NAG), and phosphorus (PHO, BHO) processing enzymes along a phosphorus gradient in soils.  Soil enzyme kinetics (Vmax and Km) in two sites (P-enriched and reference) were determined at four different temperatures under aerobic and anaerobic conditions.

We observed that unlike the P enzymes, Vmax values of C and N enzymes were significantly higher in the P-enriched sites with respect to the reference sites. However, the Km values for all enzymes at the two sites did not appear to be different.

 All enzyme activities (Vmax) were significantly higher than those observed under anaerobic conditions at both P-enriched and reference sites. Bisphosphatase activities at both sites were not significantly different in aerobic and anaerobic conditions. Moreover, we noticed significantly higher Km values for phosphatase and leucine amino peptidase under aerobic condition but in N-acetyl glucosamine we noticed higher efficiency (Km) under anaerobic condition.

Temperature showed a significant (P<0.0001) increase in enzyme activity under both aerobic and anaerobic conditions with a magnitude of temperature response across enzymes from -0.013 to 0.044 °C^-1, which corresponds to Q₁₀ values (0.87 to 2.92).  Bisphosphatase was the exception and did not show an increase.  We noticed significant temperature effect only on phosphatase enzyme efficiency (Km) under both conditions. Among the six enzymes cellobiohydrolase, Leucine amino peptidase, and N acetylglucosaminidase showed different temperature effects in different sites. These results indicate the importance of nutrient variability under aerobic and anaerobic condition and along with temperature, may change enzyme kinetics in wetland soils.