Frequent fire and grazing by megafauna are important determinants of tallgrass prairie plant community structure. However, fire suppression and removal of native grazers have altered these natural disturbance regimes and changed grassland plant communities with potential long‐term consequences for soil carbon (C) and nitrogen (N) storage. We investigated multidecade changes in soil C and N pools in response to contrasting long‐term burning and grazing treatments. Fire suppression with or without grazers and exclusion of grazers in annually burned prairie increased soil C content and shifted the δ¹³C signature of soil C over time, concomitant with changes in plant community composition. Soil δ¹³C values indicated that increased soil C content was associated with an increased contribution from plants using a C₃ photosynthetic pathway (i.e., woody shrubs) under fire suppression. Soil N content also increased when fire was suppressed, relative to frequently burned grassland, but the rate of increase was slower when grazers were present. Additionally, changes in δ¹⁵N values suggested that grazing increased the openness of the N cycle, presumably due to greater N losses. By coupling long‐term fire and grazing treatments with plant community data and soil samples archived over three decades, we demonstrate that human‐caused changes to natural disturbance regimes in a tallgrass prairie significantly alter soil C and N cycles through belowground changes associated with shifts in the plant community. Since natural disturbance regimes have been altered in grasslands across the world, our results are relevant for understanding the long‐term biogeochemical consequences of these ongoing land use changes.

中文翻译：

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三个十年来不同的土地利用和植物群落变化改变了高草草原的土壤碳和氮含量

大型动物的频繁着火和放牧是决定草丛大草原植物群落结构的重要决定因素。但是，灭火和清除天然食草动物已经改变了这些自然干扰机制，并改变了草地植物群落，对土壤碳（C）和氮（N）的储存具有长期的潜在影响。我们针对长期燃烧和放牧的对比研究了土壤碳和氮库的数十年变化。灭火用或不用在每年烧掉的草原食草动物和食草动物的排除增加土壤碳含量和移位δ ¹³与植物群落的组成变化的土壤碳Ç签名随着时间的推移，伴随。土壤δ ¹³C值表明，土壤C含量的增加与使用C ₃光合作用途径（即木质灌木）的植物在灭火时的贡献增加有关。相对于经常燃烧的草地，抑制火势时土壤氮含量也增加，但是当存在放牧者时，土壤氮含量的增长速度较慢。此外，改变δ ¹⁵N值表明放牧增加了N循环的开放性，大概是由于N损失增加所致。通过将长期的火和放牧处理与植物群落数据和过去三十年内归档的土壤样品相结合，我们证明了人为引起的高草草原自然扰动状况的变化通过与土壤变化相关的地下变化显着改变了土壤的碳和氮循环。植物群落。由于世界范围内草原的自然干扰机制已经改变，我们的结果与了解这些持续的土地利用变化的长期生物地球化学后果有关。