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Changes in the Size of the Active Microbial Pool Explain Short-Term Soil Respiratory Responses to Temperature and Moisture.

Salazar-Villegas A, Blagodatskaya E, Dukes JS - Front Microbiol (2016)

Bottom Line: Most current approaches to model microbial control over soil CO2 production relate responses to total microbial biomass (TMB) and do not differentiate between microorganisms in active and dormant physiological states.TMB responded very little to short-term changes in temperature and soil moisture and did not explain differences in SBR among the treatments.These results suggest that decomposition models that explicitly represent microbial carbon pools should take into account the active microbial pool, and researchers should be cautious in comparing modeled microbial pool sizes with measurements of TMB.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Purdue UniversityWest Lafayette, IN, USA; Purdue Climate Change Research Center, Purdue UniversityWest Lafayette, IN, USA.

ABSTRACT
Heterotrophic respiration contributes a substantial fraction of the carbon flux from soil to atmosphere, and responds strongly to environmental conditions. However, the mechanisms through which short-term changes in environmental conditions affect microbial respiration still remain unclear. Microorganisms cope with adverse environmental conditions by transitioning into and out of dormancy, a state in which they minimize rates of metabolism and respiration. These transitions are poorly characterized in soil and are generally omitted from decomposition models. Most current approaches to model microbial control over soil CO2 production relate responses to total microbial biomass (TMB) and do not differentiate between microorganisms in active and dormant physiological states. Indeed, few data for active microbial biomass (AMB) exist with which to compare model output. Here, we tested the hypothesis that differences in soil microbial respiration rates across various environmental conditions are more closely related to differences in AMB (e.g., due to activation of dormant microorganisms) than in TMB. We measured basal respiration (SBR) of soil incubated for a week at two temperatures (24 and 33°C) and two moisture levels (10 and 20% soil dry weight [SDW]), and then determined TMB, AMB, microbial specific growth rate, and the lag time before microbial growth (t lag ) using the Substrate-Induced Growth Response (SIGR) method. As expected, SBR was more strongly correlated with AMB than with TMB. This relationship indicated that each g active biomass C contributed ~0.04 g CO2-C h(-1) of SBR. TMB responded very little to short-term changes in temperature and soil moisture and did not explain differences in SBR among the treatments. Maximum specific growth rate did not respond to environmental conditions, suggesting that the dominant microbial populations remained similar. However, warmer temperatures and increased soil moisture both reduced t lag , indicating that favorable abiotic conditions activated soil microorganisms. We conclude that soil respiratory responses to short-term changes in environmental conditions are better explained by changes in AMB than in TMB. These results suggest that decomposition models that explicitly represent microbial carbon pools should take into account the active microbial pool, and researchers should be cautious in comparing modeled microbial pool sizes with measurements of TMB.

No MeSH data available.


Related in: MedlinePlus

Estimated total microbial biomass (means ± SE; n = 12) at different temperature and soil moisture conditions. SM, Soil moisture.
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Figure 3: Estimated total microbial biomass (means ± SE; n = 12) at different temperature and soil moisture conditions. SM, Soil moisture.

Mentions: Responses of TMB to warming and soil moisture differed from those of SBR (compare Figures 1, 3). The highest TMB occurred in heated, dry soils whereas the lowest occurred in heated, wet soils (i.e., 19% decrease in TMB due to a soil moisture increase in heated soils; Figure 3). Soil moisture level did not significantly affect TMB of unheated soils.


Changes in the Size of the Active Microbial Pool Explain Short-Term Soil Respiratory Responses to Temperature and Moisture.

Salazar-Villegas A, Blagodatskaya E, Dukes JS - Front Microbiol (2016)

Estimated total microbial biomass (means ± SE; n = 12) at different temperature and soil moisture conditions. SM, Soil moisture.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4836035&req=5

Figure 3: Estimated total microbial biomass (means ± SE; n = 12) at different temperature and soil moisture conditions. SM, Soil moisture.
Mentions: Responses of TMB to warming and soil moisture differed from those of SBR (compare Figures 1, 3). The highest TMB occurred in heated, dry soils whereas the lowest occurred in heated, wet soils (i.e., 19% decrease in TMB due to a soil moisture increase in heated soils; Figure 3). Soil moisture level did not significantly affect TMB of unheated soils.

Bottom Line: Most current approaches to model microbial control over soil CO2 production relate responses to total microbial biomass (TMB) and do not differentiate between microorganisms in active and dormant physiological states.TMB responded very little to short-term changes in temperature and soil moisture and did not explain differences in SBR among the treatments.These results suggest that decomposition models that explicitly represent microbial carbon pools should take into account the active microbial pool, and researchers should be cautious in comparing modeled microbial pool sizes with measurements of TMB.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Purdue UniversityWest Lafayette, IN, USA; Purdue Climate Change Research Center, Purdue UniversityWest Lafayette, IN, USA.

ABSTRACT
Heterotrophic respiration contributes a substantial fraction of the carbon flux from soil to atmosphere, and responds strongly to environmental conditions. However, the mechanisms through which short-term changes in environmental conditions affect microbial respiration still remain unclear. Microorganisms cope with adverse environmental conditions by transitioning into and out of dormancy, a state in which they minimize rates of metabolism and respiration. These transitions are poorly characterized in soil and are generally omitted from decomposition models. Most current approaches to model microbial control over soil CO2 production relate responses to total microbial biomass (TMB) and do not differentiate between microorganisms in active and dormant physiological states. Indeed, few data for active microbial biomass (AMB) exist with which to compare model output. Here, we tested the hypothesis that differences in soil microbial respiration rates across various environmental conditions are more closely related to differences in AMB (e.g., due to activation of dormant microorganisms) than in TMB. We measured basal respiration (SBR) of soil incubated for a week at two temperatures (24 and 33°C) and two moisture levels (10 and 20% soil dry weight [SDW]), and then determined TMB, AMB, microbial specific growth rate, and the lag time before microbial growth (t lag ) using the Substrate-Induced Growth Response (SIGR) method. As expected, SBR was more strongly correlated with AMB than with TMB. This relationship indicated that each g active biomass C contributed ~0.04 g CO2-C h(-1) of SBR. TMB responded very little to short-term changes in temperature and soil moisture and did not explain differences in SBR among the treatments. Maximum specific growth rate did not respond to environmental conditions, suggesting that the dominant microbial populations remained similar. However, warmer temperatures and increased soil moisture both reduced t lag , indicating that favorable abiotic conditions activated soil microorganisms. We conclude that soil respiratory responses to short-term changes in environmental conditions are better explained by changes in AMB than in TMB. These results suggest that decomposition models that explicitly represent microbial carbon pools should take into account the active microbial pool, and researchers should be cautious in comparing modeled microbial pool sizes with measurements of TMB.

No MeSH data available.


Related in: MedlinePlus