Effect of soil storage at 4 °C on the calorespirometric measurements of soil microbial metabolism.

Nieves Barros,Sergio Feijoo,César Pérez-Cruzado,Lee D Hansen

doi:10.3934/microbiol.2017.4.762

Nieves Barros, Sergio Feijoo + Show 2 more

Open Access

https://doi.org/10.3934/microbiol.2017.4.762

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Abstract

Soil samples must usually be stored for a time between collection and measurements of microbial metabolic properties. However, little is known about the influence of storage conditions on microbial metabolism when studied by calorespirometry. Calorespirometry measures the heat rate and the CO2 rate of microbial metabolism, where the ratio of heat and CO2 released, the calorespirometric ratio, informs about the nature of substrates being used by microorganisms. Application to soil microbiology is very recent, and little is known about the influence of the common soil preparation practices between collection and analysis on the calorespirometric measurements. For these reasons, the effect of storage at 4 °C on the microbial metabolism was determined by calorespirometry. Results show CO2 production rate decreases with storage time while the evolution of metabolic heat rate is more stable. The calorespirometric ratio increases with storage time in soil samples with organic matter characterized by lower carbohydrate contribution to the total carbon and higher aromaticity and is unaffected in soil samples with lower carbohydrates in the organic matter and higher aromaticity. Therefore, the calorespirometric ratio values may vary for the same soil sample, such that the soil organic matter properties, as well as the time stored at 4 °C, must be considered in interpreting calorespirometric data on soils.

Highlights

One of the key aspects to study soil microbial metabolism (SMM) is the treatment of soil samples after collection and before measurement in the laboratory
CO2 and heat rates, are normalized to the C content of the soil to evaluate the biological stability the evolution of the soil organic matter (SOM) biological stability among soil samples is not altered by soil storage and keep the same trend reported in previous papers [19,24], showing that samples from mature forest sites (P30 and forest reference (FR) with lower heat and CO2 rate values per unit of soil C than the other samples, P10 and Pasture) have higher biological stability than the young forest site independently of the time of storage along 3 months
Storage at 4 °C does not alter the evolution of the CO2 and heat rates per unit soil C from younger to mature forest soils but affects soil microbial biochemistry, in the soil samples with more labile SOM

Summary

Introduction

One of the key aspects to study soil microbial metabolism (SMM) is the treatment of soil samples after collection and before measurement in the laboratory. Soil microbiology involves many types of measurements to study soil microbial community and soil microbial functions, with different responses to the preliminary sample treatments involving fresh or frozen soil samples [1,2,3]. It is generally accepted that microbial studies on soil must be done with fresh samples, but that can be difficult to achieve due to practical reasons such as a long distance between the sampling places and the laboratory where measurements will be done, sampling restricted to a short period of the year, and so on. The reality is that different features make necessary to store the soil samples before the microbial measurements. One of the main dilemmas arising in this context is how best to store samples between collection and analysis [4]

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