Methodology for soil respirometric assays: Step by step and guidelines to measure fluxes of trace gases using microcosms

Abstract

This methodology is proposed to measure the fluxes of trace gases among microcosms and the atmosphere. As microcosm respiration we include both aerobic and anaerobic respiration, which may results in CO₂, CH₄, NO, N₂O, N₂, H₂S and H₂ fluxes. Its applicability includes the assessment of products biodegradability and toxicity, the effect of treatments and products on greenhouse gases fluxes, and the mineralization of organic fertilizers. A step by step procedure; the complementary parameters and good practices that might be taken into account to perform a microcosm experiment; and the tools nowadays available that could be useful in this respirometric methodology are presented. We included a spreadsheet with calculus examples. Samples were taken at 1; 30; 60 and 90 min after closing the microcosms to determine the gases fluxes. The dilution effect was negligible, as we present. Besides CO₂, we have successfully quantified the fluxes of CH₄ and N₂O from the microcosms in a broad range of concentrations. This method is useful in technical and scientific studies, for instances to test new products and improve the understanding of microbial processes, respectively. •Simple materials are required to set up the microcosm.•Examples of (pre) treatments are given regarding water availability, fertilizer doses, pH adjustment and nutrients amendments.•The method was suitable to directly measure multiple trace gases fluxes, either produced or consumed during microcosm respiration.

Keywords: Carbon dioxide; Methane; Mineralization; Nitrous oxide; Respiration; Respirometry.

Graphical abstract

Fig. 1

A non-scaled illustration representing an incubation flask. In (a) a 4-way stopcock valve with 2 female luer locks and male luer with spin lock (QOSINA, NY, USA); in (b) a Bev-A-Line^® tube (1/8″ ID × 1/4″ OD × 1/16″ Wall Bev-A-Line IV Tubing) inserted in the reagent flask tip used to couple the flask (c) and the valve; and in (d) the incubated soil. The cap was looped using a drill and the tube could be perfectly fitted without any additional treatment.

Fig. 2

Models fitted to study CO₂ (a) and N₂O (b and c) fluxes from the microcosms. Blue lines indicate the 95% confidence interval while the red lines represent the 95% prediction interval. In “b”, the scale at the right corresponds to the “Treatment A” data.

Fig. 3

Fluxes of CH₄ (a), CO₂ (b) and N₂O (c) during the pre-incubation period performed to provide the fluxes stabilization.

Fig. 4

Samples analyzed in house (B) and overseas (A) collect after 60 min the same microcosm was closed with (B) and without (A) the previous sampling times. Blue lines indicate the 95% confidence interval while the red lines represent the 95% prediction interval.

Fig. 5

Fluxes of C−CO₂ from the microcosm after addition of different biopolymers in the soil.

Fig. 6

Fluxes of CH₄ (a), CO₂ (b) and N₂O (c) after addition (A and B) of inorganic fertilizer and straw (A and C) on the soil. In (d) the illustration of covariance between fluxes of CO₂ and N₂O from the treatment B.