Challenges in applying an empirical modelling approach for resilience of soil carbon functioning

Soils function under highly variable weather conditions which can be challenging to capture in models and metrics. A previous metric of soil resilience used an empirical model to characterize a key soil function (substrate induced respiration) and how this changed over repeated stress cycles. Here, we apply this laboratory and modelling approach to soils from a plot experiment in which cover crops (single species monocultures and 4-species polycultures) were grown over the summer in between autumn sown cash crops in a cereal rotation to compare their resilience. Open Top Chambers (OTCs) were also used to warm the soil surface of part of each plot to mimic climate change impact. Soil samples were collected from these experimental plots after harvesting the cereal crop and we assessed barley grass powder substrate induced soil respiration (a measure of soil microbial function) after 0, 1, 2, 4, and 8 wet/dry cycles imposed in the laboratory. In contrast to previous studies, the initial drying and rewetting stress did not markedly decrease or alter the substrate induced respiration profiles, suggesting that the soil was highly resilient to this stress. Warming slightly reduced soil microbial function after 8 repeated wet/dry cycles, relative to microbial function after 0 wet/dry cycles. However, cover crops, and particularly the 4-species cover crop polyculture, increased soil microbial function significantly after 8 repeated wet/dry cycles, relative to microbial function after 0 wet/dry cycles. The modelling approach suggested high resilience of this soil function in all plots, but did not detect any differences in the resilience of soil carbon functioning for soils from the different plots, but it was unclear whether this was due to lack of sensitivity of the approach. This further emphasizes the challenges in quantifying the ‘resilience’ of soil functioning as it is highly dependent on context.