Soil Temperature, Matric Potential, and the Kinetics of Microbial Respiration and Nitrogen Mineralization

Abstract

Soil temperature and matric potential influence the physiological activity of soil microorganisms. Changes in precipitation and temperature can alter microbial activity in soil, rates of organic matter decomposition, and ecosystem C storage. Our objective was to determine the combined influence of soil temperature and matric potential on the kinetics of microbial respiration and net N mineralization. To accomplish this, we collected surface soil (0-10 cm) from two northern hardwood forests in Michigan and incubated samples at a range of temperatures (5,10, and 25°C) and matric potentials (-0.01,-0.15,-0.30,-0.90 and-1.85 MPa) that encompass field conditions. Soils were maintained at each temperature-matric potential combination over a 16-wk laboratory incubation, during which we periodically measured the production of CO, and inorganic N. First-order kinetic models described the accumulation of CO ; and inorganic N and accounted for 96 to 99% of the variation in these processes. First-order rate constants (k) for net N mineralization significantly increased with temperature, but the k for microbial respiration did not increase in a consistent manner; it was 0.107 wk~' at 5°C, 0.123 wk ' at 10°C, and 0.101 \vk ' at 25°C. Matric potential did not significantly influence k for either process. Substrate pools for microbial respiration and net N mineralization declined between-0.01 and-0.30 MPa, and the decline was greatest at the highest soil temperature; this response produced a significant temperature-matric potential interaction. We conclude that high rates of microbial activity at warm soil temperatures (e.g., 25°C) are limited by the diffusion of substrate to metabolically active cells. This limitation apparently lessens as physiological activity and substrate demand decline at relatively cooler soil temperature ., 5°C). P REDICTING THE EXTENT to which climate change might alter ecosystem C balance and rates of organic matter decomposition is, in part, contingent on a better understanding of the physiological response of soil microorganisms to altered temperature and precipitation regimes. On a global basis, soil organic matter contains twice as much C as the earth's atmosphere (Schlesinger, 1977; Post et al., 1982; Jenkinson et al, 1991), and the release of CO 2 from this globally important pool is mediated by the physiological activities of soil microorganisms. Organic substrates entering the soil serve as a source of energy for heterotrophic biosynthesis, during which microbial respiration returns a portion of substrate C to the atmosphere as CO 2. Some have hypothesized that warmer global temperatures will enhance microbial activity, rates of organic matter decomposition, and hence, the global flux of CO 2 from soil (

Effects of temperature change on water discharge, and sediment and nutrient loading in the lower Pearl River basin based on SWAT modelling

“…Higher soil temperatures result in increased N mineralization if the soil water content does not limit microbial activity (Piatek & Allen, 1999;Zak et al, 1999). In the study area, annual precipitation is around 2000 mm and water is not a limiting factor for microbial activity.…”

Temperature sensitivity of soil carbon decomposition and feedbacks to climate change

“…Note the mathematical similarity between this function and the Arrhenius function (Box 1), from which the k i value for each c i in this equation is derived. Just as the variability of the a-term in the Arrhenius function is being debated, a debate has also emerged in the literature as to whether temperature dependence should reside only in the k i -terms or also in the c i -terms [96][97][98][99] . While the k i -term describes the current instantaneous decomposition rate and its temperature sensitivity, the relative sizes of the carbon pools (c i ) of varying degrees of decomposability were determined over longer timescales and may also partially be a consequence of climatic history, including temperature.…”

Warming constrains bacterial community responses to nutrient inputs in a southern, but not northern, maritime Antarctic soil

“…Again, this is unlikely, given the tendency for microbes in soils exposed to wide seasonal fluctuations in temperature, such as those at Mars Oasis, to be psychrotrophs, which have optimum growth temperatures of >15 °C (Russell, 1990). A more plausible explanation is that the elevated soil temperatures within OTCs 375 decreased soil water matrix potential, which limited the diffusion of the substrates to metabolically active cells and decreased bacterial growth rates in soil (Zak et al, 1999).…”