The effect of temperature and moisture on lag phase length of bacterial growth in soil after substrate addition

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Microorganisms in soil are commonly limited by available substrate, and removing the limitation will increase activity and growth, with predictable dynamics in growth. The initial phase with a lag period (λ) will usually be followed by exponential growth (also called log phase, with growth rate μ). These two growth phases may be differently affected by environmental conditions, like temperature and moisture. Using glucose addition as a model of a sudden increase in labile C, we studied the effect of temperature (0 °C–30 °C) and soil moisture (10%–35%) on bacterial growth dynamics (estimated using leucine incorporation). Decreasing temperature resulted in decreased μ and increased λ. The latter increased from a minimum around 6 h at 25 °C to >100 h at 0 °C. The square root of μ increased linearly with temperature below Topt according to the Ratkowsky equation, with an apparent Tmin of −11 °C. The square root of 1/λ also increased linearly with temperature (the inverse Ratkowsky equation), with a Tmin of −10 °C. Thus, there was a close correlation between μ and 1/λ, suggesting that the length of λ at different temperatures was entirely determined by the rate of growth after adding glucose. Increasing soil moisture increased μ and decreased λ (at 20 °C), with the latter decreasing from 14 to 21 h at 15% moisture to 8–14 h at 35% moisture. No exponential growth was found within 71 h at 10% moisture. μ after glucose addition was more affected by moisture than λ. The effects of moisture on 1/λ could therefore not be explained solely by changes in μ. Temperature effects on μ and λ after adding substrate could be estimated, including effects of temperature adaptation of the community, using the Ratkowsky equations. Thus, effects on future changes in temperature on both μ and λ can be predicted.