9.2: Influence of pH and temperature on enzyme activity

The activity of an enzyme is sensitive to temperature and pH, as discussed in Chapter 6. Variation in temperature and pH affect the structure of enzymes, which in turn affects their ability to bind substrates and catalyze reactions. As such, enzyme activity decreases outside of its optimal temperature and pH (Fig. \(9.3\)).

Enzyme properties help define temperature and pH preferences of individual microbial species, but microbial communities are generally composed of many species, which can vary in their enzyme properties. As a result, microbial activity does not necessarily cease because temperature and/or pH changes. Instead, changes in temperature and/or pH may alter who is growing and at what rates.

With regard to changes in temperature, rates of abiotic reactions tend to increase as temperature increases. The same can also be true of microbial enzymatic reactions. As an example, Craine et al. (2010) demonstrated that rates of microbial organic matter degradation in soil increase with warming, with the largest increases associated with organic matter pools that are difficult to degrade. Their findings imply that, as soils warm in response to climate change, organic matter stored within them can be more rapidly oxidized and returned to the atmosphere as carbon dioxide. Thus, this influence of temperature on degradation rates has the potential to serve as a positive feedback on climate change.

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