| Summary: | The effect of grazing on leaf photosynthesis has been extensively studied. However, the influence of grazing on photosynthesis in other green tissues, especially spike, has remained poorly understood. This study investigated the impact of different grazing intensities (light grazing (LG), medium grazing (MG), and heavy grazing (HG)) on leaf and spike photosynthesis parameters and photosynthetic pigments of three grass species (<i>Stipa purpurea</i>, <i>Achnatherum inebrians</i>, and <i>Leymus secalinus</i>) on an alpine steppe in the Qilian Mountains. Grazing promoted leaf photosynthesis rate in <i>S. purpurea</i> and <i>L. secalinus</i> but reduced it in <i>A. inebrians</i>. Conversely, spike photosynthesis rate decreased in <i>S. purpurea</i> and <i>L. secalinus</i> under intense grazing, while there was no significant difference in spike photosynthesis rate in <i>A. inebrians</i>. The leaf and spike net photosynthetic rate (Pn) and transpiration rate (Tr) in <i>S. purpurea</i> were the greatest among the three species, while their organ temperatures were the lowest. On the other hand, grazing stimulated leaf chlorophyll biosynthesis in <i>S. purpurea</i> and <i>L. secalinus</i> but accelerated leaf chlorophyll degradation in <i>A. inebrians</i>. Furthermore, spike chlorophyll biosynthesis was inhibited in the three species under grazing, and only <i>L. secalinus</i> had the ability to recover from the impairment. Grazing had a positive effect on leaf photosynthesis parameters of <i>S. purpurea</i> and <i>L. secalinus</i> but a negative effect on those of <i>A. inebrians</i>. However, spike photosynthesis parameters were negatively influenced by grazing. Among the three species investigated, <i>S. purpurea</i> displayed the greatest ability for leaf and spike photosynthesis to withstand and acclimate to grazing stress. This study suggests that moderate grazing enhanced leaf photosynthetic capacity of <i>S. purpurea</i> and <i>L. secalinus</i> but reduced it in <i>A. inebrians</i>. However, spike photosynthetic capacity of three grass species decreased in response to grazing intensities.
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