Do we obtain valid data from climate change incubations using soils of today?

Assessing climate change effects on soils usually involves conducting comparisons of biogeochemical processes under projected future conditions against ambient ones. This is typically achieved through incubation experiments utilizing today’s soils. However, a significant limitation of relying on present-day soils is the oversight of the ongoing evolution of soils in terms of geochemistry and microbiology over several years in response to future climatic conditions.

This study challenges the traditional approach by asking: Can climate change experiments accurately replicate future biogeochemical processes and their outcomes using soils with today's geochemistry and microbiome? To address this question, we collected oxic and anoxic soils from experimental climate studies, exposed to both present-day and concurrently predicted future climate conditions. We reintroduced these soils with varying climate histories to both sets of climatic conditions (ambient/future), employing a crossover design. This unique experimental setup enables us to discern which biogeochemical processes are influenced by the soil’s historical context and which are contingent on the specific incubation conditions imposed.

For the oxic soil, with an eight-year night temperature increase of up to 2°C coupled with altered precipitation patterns (a 10% increase in spring and autumn, a 20% decrease in summer), our findings indicate a notable influence of soil history on soil respiration, surpassing impacts of the incubation climate. This implies that the historical context of the soil wielded a stronger influence than the specific incubation conditions in shaping organic matter pools and turnover within oxic soils. Conversely, iron(III) reduction, as a pivotal indicator of geochemical evolution, was primarily regulated by incubation conditions related to soil moisture rather than being dictated by the soil’s historical background.

In the anoxic soil, with a one-year treatment of temperature increases of 4°C and doubled atmospheric CO₂, a more pronounced reductive iron(III) dissolution occurred in the soil with the future climate history compared to soils with today’s history. This observation suggests that, over the course of soil history, a larger pool of reducible iron became available to microorganisms in soil with a future climate history than in those with today's soil history. Interestingly, the release of arsenic from these ageing iron minerals was higher in soils with a future climate history compared to today’s soils. This indicates that studies investigating arsenic mobility and its impact on crop performances using present-day soils may underestimate the potential environmental consequences of arsenic. Additionally, the history of future soil conditions favoured greater microbial growth than the incubation conditions. However, soil respiration deviated from this pattern, with a predominant increase attributed to the future incubation climate and, to a lesser extent, influenced by soil history.

Complementary data on compositional variations in soil organic matter (LDI-FT-ICR MS) and microbial community (16S rRNA amplicon sequencing) assessing differences based on soil history and short-term experimental conditions will also be presented for both soils.

Our findings indicate that soil history plays a differential role for biogeochemical processes and outcomes of the future with biogeochemical outcomes and temporal trajectories possibly being over- or underinterpreted when studies on climate change utilize present-day soils.