The ability of large herbivores to increase primary production in many grassland ecosystems has been linked to their stimulation of plant available soil nitrogen (N) and enrichment in shoot N content. However, herbivores have additional effects on the structure of grassland vegetation that may also impact the efficiency that plants use shoot N to produce biomass per unit time (i. e., nitrogen production, NP). Knowledge of any effect that herbivores have on NP will provide a better understanding of how herbivores can mechanistically feedback on grassland processes. The influence of herbivores on NP was examined by comparing plant production and shoot N content inside and outside exclosures at ten grasslands in Yellowstone National Park (YNP), an N–limited ecosystem, where animals previously have been shown to increase soil N availability, shoot N content, and plant production. NP was measured aboveground (NP_A, g shoot growth g shoot N⁻¹ day⁻¹), belowground (NP_B, g belowground growth g shoot N⁻¹ day⁻¹), and at the whole grassland level (NP_W, g whole plant growth g shoot N⁻¹ day⁻¹). The study was conducted over a three-year period (1999–2001) during which precipitation varied markedly. Grazers increased annual NP_A, NP_B and NP_W by 32%, 55%, and 48%, respectively, in 1999, an average to wetter than average year across the widely distributed sites. Herbivores had no effect on NP measures during 2000 and 2001, two drought years. These findings revealed that grazer facilitation of grassland production in YNP was at least partially due to a previously unrecognized enhancement of NP by herbivores, which was likely dependent on moisture conditions.

大型草食动物增加许多草原生态系统初级生产力的能力与它们对植物有效土壤氮（N）的刺激和芽N含量的增加有关。然而，食草动物对草地植被的结构有额外的影响，这也可能影响效率植物在每单位时间使用芽N来生产生物量（即氮产量，NP）。知道草食动物对NP的任何影响将使人们更好地了解草食动物如何对草地过程进行机械反馈。通过比较黄石国家公园（YNP）的10个草场中氮的含量，研究草食动物对NP的影响，研究了黄石国家公园（YNP）的氮含量有限的生态系统，以前已证明动物会增加土壤N的利用率，氮含量与植物产量有关。在地上（NP _A，g芽生长g芽N ^-1天^-1），地下（NP _B，g地下生长g芽N ^-1天^-1）测量NP）和整个草地水平（NP _W，g整个植物的生长g梢N ^-1天^-1）。该研究历时三年（1999年至2001年），在此期间降水变化显着。在1999年，Grazers的年度NP _A，NP _B和NP _W分别增加了32％，55％和48％，在分布广泛的站点中，平均水平比平均水平要高。草食动物在两个干旱年份的2000年和2001年期间对NP措施没有影响。这些发现表明，放牧者对YNP草地生产的促进至少部分是由于之前未认识到草食动物对NP的增强作用，这很可能取决于水分条件。