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

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.

The MICE facility - a new tool to study plant-soil C cycling with a holistic approach.

Plant-soil interactions are recognized to play a crucial role in the ecosystem response to climate change. We developed a facility to disentangle the complex interactions behind the plant-soil C feedback mechanisms. The MICE ('Multi-Isotope labelling in a Controlled Environment') facility consists of two climate chambers with independent control of the atmospheric conditions (light, CO2, temperature, humidity) and the soil environment (temperature, moisture). Each chamber holds 15 plant-soil systems with hermetical separation of the shared above ground (shoots) from the individual belowground compartments (roots, rhizosphere, soil). Stable isotopes (e.g. 13C, 15N, 2H, 18O) can be added to either compartment and traced within the whole system. The soil CO2 efflux rate is monitored, and plant material, leached soil water and gas samples are taken frequently. The facility is a powerful tool to improve our mechanistic understanding of plant-soil interactions that drive the C cycle feedback to climate change.