Abstract：
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.
摘要：
Pyric食草动物,控制焚烧和有针对性的放牧相结合，是恢复被遗弃的有效策略，灌木侵占的牧场以开放生态系统。这种做法可能会通过改变土壤硝化和反硝化速率来影响土壤氮库，并可能通过硝酸盐浸出和氮气排放导致氮损失增加。这项研究,位于比利牛斯山脉西南部，在实施燃烧六个月后，研究了火药草食性对金雀花侵占的温带牧场中土壤硝化和反硝化潜力以及矿质氮含量的影响。该研究包括三种治疗方法：严重程度高的烧伤加放牧，低严重程度的燃烧加放牧，以及未燃烧和未放牧的区域（对照）。我们测量了土壤硝化和反硝化潜力(净和总)，氮或有机碳对反硝化细菌的限制，以及大量的亚硝酸盐和一氧化二氮还原细菌。其他土壤和植被数据补充了这些测量结果。结果表明，烤烟对硝化潜力没有显著影响，这是低且高度可变的。然而,与对照组相比，它降低了高严重烧伤地区的总反硝化潜力和一氧化二氮减少量。反硝化速率与微生物生物量氮直接相关，土壤有机碳，土壤含水量和携带nirS细菌的丰度。与预期相反，尽管在燃烧地区最高，但土壤硝酸盐的有效性并未直接影响反硝化。总的来说,该研究表明，在温带开放生态系统中，热食草动物不会显着影响中期硝化速率，但可能会降低严重燃烧地区的反硝化率。这些发现强调了评估土地管理做法的潜在影响的重要性，比如烤烟草食动物，对土壤养分循环和生态系统功能的影响。
