Soil aggregate-size diversity determines the resilience of soil organic carbon to experimental warming

Muhammad Saleem, Biological Science, Alabama State University, Montgomery, AL and Zahida H. Pervaiz, Biological Science, Auburn University, Auburn, AL

Background/Question/Methods
Soils are highly heterogeneous and diverse systems in terms of their biological, physical, and chemical components. Similar to soil biodiversity, its physical component also displays a tremendous diversity in its structure in the form of different aggregate-size classes, which may determine its functioning. Previously studies have reported positive effects of soil biological diversity on its vital functions such as productivity, organic carbon storage, and resilience under climate change. However, we know very little about the role of soil aggregate size classes, their composition, and diversity in vital soil functions, for instance, organic carbon retention under warming. Nevertheless, recent studies have predicted the negative impacts of anthropogenic activities on soil structure. Using dry sieving, we prepared mono-aggregated soils representing four different aggregate-size classes. We developed 13 different soils that varied in their aggregate-size diversity. These soils comprised mono- (large-macro>2000μ), small-macro (<2000-500μ), meso (<500-250 μ), and micro-aggregated (<250 μ) to bi-, tri-, and tetra-aggregated ones. We incubated these soils at 15, 25, and 35oC for 30days. Using 120 soil microcosms, we tested the impact of an experimental warming gradient on soil organic carbon contents at the end of our experiment.
Results/Conclusions
At low and high temperatures, both micro-and small-aggregated soils showed relatively higher organic carbon contents, respectively. Interestingly, mono- than mixture-aggregated soils were more sensitive to warming. Therefore, mixture- than mono-aggregated soils retain more organic carbon, thus implying the significance of soil aggregate-size diversity in determining the resilience of organic carbon to warming. Our study might have potential limitations, but this is the first study to empirically test the role of soil physical diversity in influencing the resilience of soil organic carbon to warming. Our research provides a new avenue in soil resilience research, while these results might help in developing climate-resilient soil systems. Our results suggest that preserving soil physical diversity or increasing soil aggregate diversity may increase the resilience of soils to climate warming. Finally, these results also suggest that, similar to biological diversity, the diversity in the physical structure of the soil is critical for its resilience and vital functions, such as organic carbon storage.