At the heart of our project are biodiversity-driven processes that control soil functions (Fujii et al. 2018, Marín et al. 2017). If the stability of the functional web is challenged by stress, functions might be lost, or perform at another stable level. This means that the function has been stressed beyond its resilience, thus a tipping point of this function has been crossed. Most of the time the consequences are “hidden” or not perceived by human stakeholders. If too many hidden tipping points are crossed the apparent tipping point eventually will be crossed too and ecosystem functioning will relevantly be affected (Scheffer & Carpenter 2003) and is not likely to return to its previous state. Our general hypothesis is that soil ecosystems are less prone to cross a drought-induced tipping point if they can rely on a safety net called functional redundancy provided by soil biodiversity (Girvan et al. 2005, Panizzonet al. 2015, Jurburg & Salles 2015, Grządziel 2017, Yu & Whalen 2020). When many organisms with slightly different functional traits conduct functions, they mutually prevent these related functions to easily cross a tipping point (Allison & Martiny 2008).
In field experiments, we challenge soil systems by “simulating” a real-world problem. Drought has been defined as a globally highly relevant problem, particularly for the wet tropics, and is clearly identified in our trilateral study region as the major threat. Functional diversity of soil microorganisms will be evaluated along gradients of above-ground biodiversity: spanning from highly degraded (pasture) ecosystems into the core areas of protected areas with subsistence farming in the vicinity to baseline-forest sites. Soil type and inclination will be held comparable along these transects so that the assessed variable is belowground biodiversity and its functioning. The establishment of the belowground biodiversity gradient will assume a connection between above- and belowground diversity (Wagg et al. 2014).
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Fujii, K., Shibata, M., Kitajima, K., Ichie, T., Kitayama, K., & Turner, B. L. (2018). Plant–soil interactions maintain biodiversity and functions of tropical forest ecosystems. Ecological Research, 33(1), 149-160. https://doi.org/10.1007/s11284-017-1511-y
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Grządziel, J. (2017). Functional redundancy of soil microbiota–does more always mean better?. Polish Journal of Soil Science, 50(1), 75. http://dx.doi.org/10.17951/pjss.2017.50.1.75
Marín, C., Godoy, R., Valenzuela, E., Schloter, M., Wubet, T., Boy, J., & Gschwendtner, S. (2017). Functional land-use change effects on soil fungal communities in Chilean temperate rainforests. Journal of soil science and plant nutrition, 17(4), 985-1002. http://dx.doi.org/10.4067/S0718-95162017000400011
Panizzon, J.P., Pilz Júnior, H.L., Knaak, et al., 2015. Microbial Diversity: Relevance and Relationship Between Environmental Conservation And Human Health. Brazilian Archives of Biology and Technology, 58,1: 137–145. http://doi.org/10.1590/S1516-8913201502821
Scheffer, M., & Carpenter, S. R. (2003). Catastrophic regime shifts in ecosystems: linking theory to observation. Trends in ecology & evolution, 18(12), 648-656. https://doi.org/10.1016/j.tree.2003.09.002
Wagg, C., Bender, S. F., Widmer, F., & Van Der Heijden, M. G. (2014). Soil biodiversity and soil community composition determine ecosystem multifunctionality. Proceedings of the National Academy of Sciences, 111(14), 5266-5270. https://doi.org/10.1073/pnas.1320054111
Yu, J. I. A., & Whalen, J. K. (2020). A new perspective on functional redundancy and phylogenetic niche conservatism in soil microbial communities. Pedosphere, 30(1), 18-24. https://doi.org/10.1016/S1002-0160(19)60826-X