Pyric herbivory decreases soil denitrification despite increased nitrate availability in a temperate grassland

• Published in: Journal of environmental management 2024-08, Vol.365, p.121695, Article 121695
• Main Authors: Múgica, Leire, Le Roux, Xavier, San Emeterio, Leticia, Cantarel, Amélie, Durán, María, Gervaix, Jonathan, Creuzé des Châtelliers, Charline, Canals, Rosa M.
• Format: Article
• Language: English
• Subjects: Animals; Burning severity; Denitrification; Denitrifying enzyme activity; Fire; Grassland; Grazing; Herbivory; Nitrates - analysis; Nitrates - metabolism; Nitrification; Nitrifying enzyme activity; Nitrogen - metabolism; Soil - chemistry; Soil N cycling
• ISSN: 0301-4797; 1095-8630; 1095-8630
• DOI: 10.1016/j.jenvman.2024.121695

Pyric herbivory, the combination of controlled burning and targeted grazing, is an effective strategy for restoring abandoned, shrub-encroached rangelands to open ecosystems. This practice may impact soil nitrogen pools by altering soil nitrification and denitrification rates, and may lead to an increase of nitrogen losses through nitrate leaching and N-gas emissions. This research, located in the south-western Pyrenees, investigated the effects of pyric herbivory on soil nitrification and denitrification potentials and mineral nitrogen content in a gorse-encroached temperate rangeland six months after the burning was implemented. The study included three treatments: high-severity burning plus grazing, low-severity burning plus grazing, and unburned and ungrazed areas (control). We measured soil nitrification and denitrification potentials (net and gross), the limitation of denitrifiers by nitrogen or organic carbon, and the abundance of nitrite- and nitrous oxide-reducing bacteria. Additional soil and vegetation data complemented these measurements. Results showed that pyric herbivory did not significantly affect nitrification potential, which was low and highly variable. However, it decreased gross denitrification potential and nitrous oxide reduction to dinitrogen in high-severely burned areas compared to the control. Denitrification rates directly correlated with microbial biomass nitrogen, soil organic carbon, soil water content and abundance of nirS-harbouring bacteria. Contrary to the expected, soil nitrate availability did not directly influence denitrification despite being highest in burned areas. Overall, the study suggests that pyric herbivory does not significantly affect mid-term nitrification rates in temperate open ecosystems, but may decrease denitrification rates in intensely burned areas. These findings highlight the importance of assessing the potential impacts of land management practices, such as pyric herbivory, on soil nutrient cycling and ecosystem functioning. [Display omitted] •PH at different burn severities affected soil N parameters differently.•PH had no effect on soil nitrification rates in the mid-term.•Intensely burned patches exhibited lower denitrification rates in the mid-term.•Denitrification changes were not directly related to its main substrate, nitrate.•Denitrification was directly influenced by microbial biomass N, DOC, SWC and nirS.