In a study published in PNAS, researchers from the ISSCAS, the Institute of Natural Resources and Agrobiology of Seville (IRNAS), and the University of Cádiz analyzed 151 ecosystems across six continents, delving into the intricate coexistence network among diverse species including bacteria, fungi, protists, and invertebrates. Through this work, they linked biotic coexistence relationships with global biodiversity maintenance for the first time, thus offering insights into the understanding of soil biodiversity and its ecological networks.

This study challenges traditional views that predominantly focus on competitive interactions in ecological networks by showing that facilitative networks are more common in soil ecosystems than previously thought. This paradigm shift stems from recognizing that soil processes, such as decomposition of organic matter, necessitate cooperation among various species, thus suggesting that facilitation might play a more significant role than researchers had realized. However, empirical evidence supporting this hypothesis has been scarce. 

In addition, this study closes a gap in understanding the basic structures of biotic associations that form complex soil organism communities. While research on plant and animal networks has explored network motifs—i.e., associations among species triads—and their ecological significance, the application of these motifs to soil networks had not been explored. This study thus offers insights into whether soil networks differ significantly from those of other taxa or whether they follow universal ecological principles. 

Moreover, this study demonstrates that soil networks characterized by higher levels of positive facilitation foster richer soil taxa and more stable biotic coexistence patterns, even when accounting for variables like soil properties, climate, and spatial factors. It identifies temperature seasonality as a predictor of the global distribution of positively facilitated soil network modules, offering new perspectives on the widespread nature of facilitative associations among soil organisms and their pivotal role in sustaining global soil biodiversity. 

“This study underlines that positive facilitation is predominant in soil microbial associations and is vital for the diversity and stability of soil biological networks. This globally consistent pattern underscores the role of cooperative interactions in complex soil networks,” said Prof. Haiyan Chu, one of the authors of this study. 

Prof. Manuel, another author, pointed out that the complexity of ecological networks, encompassing both specific and higher-order associations across multiple trophic levels, underscores the need to consider unexplored variables in biodiversity and functioning, and rare species and weak correlations could be included in further soil network studies. 

In conclusion, this study establishes facilitation as a key driver in maintaining diverse and stable soil networks, which is crucial for supporting soil biodiversity and enhancing ecological stability amidst global change.