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INTRODUCTION. Nitrogen (N) fertilization in agroecosystems can lead to non-desirable environmental impacts such as water pollution by nitrate leaching and the emission to the atmosphere of the greenhouse gas nitrous oxide. The application of nitrification inhibitors (NIs) such as dimethylpyrazole phosphate (DMPP) and dimethylpyrazole succinic acid (DMPSA) has been proven to be an efficient management option to avoid N2O losses when applied together with an ammonium-based fertilizer (Huérfano et al., 2018). Both DMPP and DMPSA have shown that they can induce some changes in non-target microbial populations different from nitrifiers in a single crop-cycle (Corrochano-Monsalve et al., 2021). Nitrification is a process known to be greatly inhibited by low pH conditions, thus the performance of NIs regarding both their effect on nitrifiers and on non-target microbial populations may not be the same depending on soil pH level. On the other hand, liming is a usual management in agricultural soils. Consequently, the objective of this work was to determine by means of a metabarcoding approach the performance of both NIs on soil microbial diversity under a slightly acidic pH condition in comparison with a neutral pH one.
MATERIALS, METHODS. A three-year experiment with Italian ryegrass (L. multiflorum Lam. var. Trinova) crop was carried out in Zamudio (Northern Spain) where two different pH level conditions of 5.5 (“low pH”) and 7.0 (“high pH”) were maintained, adjusting the pH by means of calcined dolomite application. Within each pH level condition, three fertilizer treatments were assayed: ammonium sulphate (AS), AS+DMPP and AS+DMPSA. NIs were applied at a rate of 0.8% of the ammonium-N of AS. Each year, ryegrass was sown and then cut and fertilized three times, a total amount of 600 kg N ha-1 were applied. At the end of the experiment soil samples were taken and soil microbial diversity was analyzed through bacterial 16S rRNA and fungal ITS massive amplicon sequencing using lllumina technology. Sequence quality control, taxonomical and diversity analyses were conducted using QIIME2 2023.9.
RESULTS. Alpha-diversity analysis showed that soil pH did not alter soil microbiota richness, while under low pH, AS application induced a decrease in their relative abundance, this decrease not being observed when NIs were applied. On the other hand, beta-diversity analysis signaled that neither pH nor the application of AS had any impact on the variations detected among treatments, while the application of NIs was responsible for 30% of the variation of the bacterial composition and 13% in the fungal composition of soils (p<0.05).
DISCUSSION. Most studies showing an effect of pH on soil microbiota have stablished comparisons of wide pH-ranges, between either different soils or same soils for an amount of time from twenty to a hundred years (Zhalnina et al., 2015). So, probably pH may have a more evident pivotal effect on microbial diversity when either long-term treatments or a wider range of pH to the one we have assayed are considered. Regarding the impact of NIs, provided that their target microorganisms are ammonia oxidizing bacteria, our results on beta diversity are of special interest because they indicate that DMPP and DMPSA can affect non-target microorganisms, both bacteria and fungi. This points to the need of future investigations on this topic.
REFERENCES.
Corrochano-Monsalve, M., González-Murua, C., Estavillo, J.M, Estonba, A., Zarraonaindia, I. 2021. Impact of dimethylpyrazole-based nitrification inhibitors on soil-borne bacteria. Science of The Total Environment 792: 148374
Huérfano, X., Estavillo, J.M., Fuertes-Mendizábal, T., Torralbo, F., González-Murua, C., Menéndez, S. 2018. DMPSA and DMPP equally reduce N2O emissions from a maize-ryegrass forage rotation under Atlantic climate conditions. Atmospheric Environment 187:255-265
Zhalnina, K., Dias, R., de Quadros, P.D., Davis-Richardson, A., Camargo, F.A., Clark, I.M., McGrath, S.P., Hirsch, P.R., Triplett, EW. 2015. Soil pH determines microbial diversity and composition in the park grass experiment. Microbial Ecology 69:395-406
ACKNOWLEDGEMENTS.
Spanish Government (Grant PID2021-128273OB-I00 funded by MCIN/AEI/10.13039/501100011033 and “ERDF A way of making Europe”), Basque Government (IT1560-22) and EuroChem Agro Iberia S.L M.M. is holder of an IKERTALENT2022 Fellowship funded by the Basque Government and M.J.M. is holder of the contract PRE2022-102053 funded by MCIN/AEI/10.13039/501100011033 and FSE+. Z.S.S. received a grant co-financed by the European NextGenerationEU.
| Keywords | Microbial diversity; Metabarcoding; N fertilization; Alpha-diversity; Beta-diversity |
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