Mineral fertilization reduces the drought resistance of soil multifunctionality in a mountain grassland system through plant-soil interactions
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Abstract
Increasing droughts threaten soil microbial communities and the multiple functions they control in agricultural soils. These soils are often fertilized with mineral nutrients, but it remains unclear how this fertilization may alter the capacity of soil multifunctionality (SMF) to be maintained under drought, and how plant-soil interactions shape these effects. In this study, we used a mountain grassland soil to test the interactive effect of mineral nutrient (Nitrogen and Phosphorous) addition and drought on SMF with and without plants ( Lolium perenne ) in a mesocosm experiment. We calculated SMF based on 8 microbial properties associated with the capacity of soil microbes to store carbon (C), nitrogen (N) and phosphorous (P) in their biomass, and to process these elements through organic matter depolymerization, mineralization, nitrification and denitrification processes. To investigate mechanisms underlying the SMF response we characterized the associated changes in soil stoichiometry and microbial community composition using 16S and 18S rRNA amplicon sequencing. Our results showed that fertilization decreased the SMF drought resistance when plants were present, but the opposite was observed in the unplanted mountain grassland soil. Our analysis suggested this was due to the interaction of plants, fertilization and drought in influencing four coupled properties related to high SMF: high soil moisture, low microbial C limitation, high bacterial diversity and low bacteria gram positive:gram negative ratio. Altogether, our results suggested that reducing the use of mineral fertilizer for plant production in mountain grassland could improve the ability of their soils to maintain their multifunctionality during drought period. Finally, our study clearly further demonstrated the importance of plant in the complex responses of SMF to global changes and showed that combining stoichiometric and microbial diversity assessment represents a powerful approach to disentangle the underlying mechanisms.
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The ingredients of this study are classic in soil ecology and in the study of belowground-aboveground interactions: the presence of plants, draught and mineral fertilization (for the experimental treatments) and microbial carbon, microbial nitrogen, microbial phosphorus, substrate-induced respiration, cumulative extracellular enzyme activity, nitrogen mineralization potential, nitrification potential, denitrification potential (as a result of the treatments). It is interesting and useful to have tested all the combinations of the three treatments and the height variables (also in the form of a soil multifunctionality index) in the same study and to have been able to express hypotheses on the underlying mechanisms of interaction.
A key result is that mineral fertilization can reduce the soil ability to withstand draughts in terms of …
The ingredients of this study are classic in soil ecology and in the study of belowground-aboveground interactions: the presence of plants, draught and mineral fertilization (for the experimental treatments) and microbial carbon, microbial nitrogen, microbial phosphorus, substrate-induced respiration, cumulative extracellular enzyme activity, nitrogen mineralization potential, nitrification potential, denitrification potential (as a result of the treatments). It is interesting and useful to have tested all the combinations of the three treatments and the height variables (also in the form of a soil multifunctionality index) in the same study and to have been able to express hypotheses on the underlying mechanisms of interaction.
A key result is that mineral fertilization can reduce the soil ability to withstand draughts in terms of soil multifunctionality. This effect would be due to the increase in plant growth associated with fertilization, which reduces the availability of soil resources. This subsequently affects microbial diversity and soil multifunctionality. This confirms that the interactions between plants and soil microorganisms are complex and relevant for understanding and predicting the impact of climate and fertilization on soil functioning and the sustainability of plant-soil systems.
Although the study is rather fundamental, it has been designed to be relevant to grassland management and points to very general mechanisms that are likely to be relevant to arable land management. It would therefore be useful to repeat this work for interactions between a crop and its soil. Finally, it would be crucial to test the impact of heavy fertilization in intensive cropping systems on the resistance and resilience of soil functions to climate variability and climate changes.
A slightly disturbing fact is that the underlying interactions are probably so complicated that it seems so far impossible to me to make predictions about the ranking of the height combinations of treatments on each soil variable. But this complexity is clearly inherent to ecology and, in particular, plant-soil interactions.
References
Gabin Piton, Arnaud Foulquier, Lionel Bernard, Aurelie Bonin, Thomas Pommier, Sandra Lavorel, Roberto Geremia, Jean Christophe Clement (2025) Mineral fertilization reduces the drought resistance of soil multifunctionality in a mountain grassland system through plant-soil interactions. bioRxiv, ver.2 peer-reviewed and recommended by PCI Ecology https://doi.org/10.1101/2024.09.19.613911
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