Leaching of soils during laboratory incubations does not affect soil organic carbon mineralisation but solubilisation

Abstract

Laboratory soil incubations provide controlled conditions to investigate carbon and nutrient dynamics; however, they are not free of artefacts. As carbon and nitrogen cycles are tightly linked, we aimed at investigating whether the incubation-induced accumulation of mineral nitrogen (Nmin) biases soil organic carbon (SOC) mineralisation. For this, we selected two soils representative of the C:N ratio values found in European temperate forests, and applied two incubation systems: ‘closed’ beakers and ‘open’ microlysimeters. The latter allowed leaching the soil samples during the incubation. By the end of the 121-day experiment, the low C:N soil significantly accumulated more Nmin in beakers (5.12 g kg-1 OC) than in microlysimeters (3.00 g kg-1 OC) but there was not a significant difference in SOC mineralisation at any point of the experiment. On the other hand, Nmin did not accumulate in the high C:N soil but, by the end of the experiment, leaching had promoted 33.9% more SOC solubilisation than beakers. Therefore, we did not find evidence that incubation experiments introduce a bias on SOC mineralisation. This outcome strengthens results from soil incubation studies.

Temperature and moisture are minor drivers of regional-scale soil organic carbon dynamics

“…On days 4, 13, 30, 63, 121, and 181, each microlysimeter was also leached with 30 ml of a nutrient solution 66 without N or P. Subsequently, after equilibration for 30 minutes, a suction of −20 kPa was applied for 25 minutes to the systems. In a previous study, we verified that leaching and the potential accumulation of mineral nitrogen (NO − 2 , NO − 3 , NH + 4 ) during incubation does not bias SOC mineralisation 20 . DOC samples were filtered (1.6 µm MGA glass microfibre, Sartorius) before analysis.…”

“…In February 2015, we incubated fresh soil samples (sieved to ≤2 mm; 40 g equivalent dry mass; adjusted to 0.8 g cm −3 bulk density) in sterilised glass microlysimeters 20 which permitted the flushing of the samples during the incubation to yield soil water extracts. Microlysimeters were placed into 2-litre airtight glass jars that contained 20 ml of distilled water in a separate beaker to ensure the headspace was moist.…”

“…We determined the bulk soil radiocarbon signature by accelerator mass spectrometry 19 on a mixture of material from these three bulk soil composites. Further, we incubated fresh soil samples (sieved ≤2 mm) in microlysimeters, which permitted the flushing of the soils during the incubation to yield water extracts 20 . For 181 days, we repeatedly measured SOC mineralisation as the evolution of CO 2 and the production of dissolved organic carbon (DOC) by determining organic carbon in soil water extracts.…”

Phosphorus and potassium mineralization as affected by phosphorus levels and soil types under laboratory condition

“…Laboratory incubation methods have an advantage over field experiments as drivers of mineralization, such as moisture and easily controlled temperature (González‐Domínguez et al., 2017). Sometimes, it is very hard to find exact processes at the field level, but incubation study gives an initial idea of what can happen in the field scenario (in other words, its mimic or simulation of field experiment).…”