Grazing Intensity Alters Leaf and Spike Photosynthesis, Transpiration, and Related Parameters of Three Grass Species on an Alpine Steppe in the Qilian Mountains

Abstract

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 (Stipa purpurea, Achnatherum inebrians, and Leymus secalinus) on an alpine steppe in the Qilian Mountains. Grazing promoted leaf photosynthesis rate in S. purpurea and L. secalinus but reduced it in A. inebrians. Conversely, spike photosynthesis rate decreased in S. purpurea and L. secalinus under intense grazing, while there was no significant difference in spike photosynthesis rate in A. inebrians. The leaf and spike net photosynthetic rate (Pn) and transpiration rate (Tr) in S. purpurea were the greatest among the three species, while their organ temperatures were the lowest. On the other hand, grazing stimulated leaf chlorophyll biosynthesis in S. purpurea and L. secalinus but accelerated leaf chlorophyll degradation in A. inebrians. Furthermore, spike chlorophyll biosynthesis was inhibited in the three species under grazing, and only L. secalinus had the ability to recover from the impairment. Grazing had a positive effect on leaf photosynthesis parameters of S. purpurea and L. secalinus but a negative effect on those of A. inebrians. However, spike photosynthesis parameters were negatively influenced by grazing. Among the three species investigated, S. purpurea 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 S. purpurea and L. secalinus but reduced it in A. inebrians. However, spike photosynthetic capacity of three grass species decreased in response to grazing intensities.

Photosynthetic Behavior of Argania spinosa (L.) Skeels Induced under Grazed and Ungrazed Conditions

“…Chla+b/Car represents a good indicator of plant stress detection and tolerance and is sensitive to photooxidative damage. Our study indicated that grazing significantly increased Chla+b/Car, suggesting that grazed trees show a lower oxidative stress intensity [43].…”

“…Grazed trees exhibited significantly higher chlorophyll content than ungrazed trees during spring. These results suggest that grazing stimulated total chlorophyll synthesis [43] and could induce a compensation mechanism against herbivores [40]. The trees increased the photosystem components used to promote photosynthesis efficiency by improving the transfer of electrons through the reaction centers.…”

Integrated transcriptome and proteome analyses reveal potential mechanisms in Stipa breviflora underlying adaptation to grazing

“…Photosynthesis is a determining factor of plant productivity (Flexas & Carriquí, 2020; Li et al, 2021; Ma et al, 2021). According to a previous study on the diurnal dynamics of photosynthesis in S. breviflora , the plants showed the peak electron transfer rate, Rubisco enzyme activity, photosynthetic rate, E , G s , and the C i between 09:00 a.m. and 10:00 a.m.…”

Transcriptome and anatomical analysis of Stipa breviflora in response to different grazing intensities in desert steppe

“…There was a study that investigated the impact of different grazing intensities [light grazing (LG), medium grazing (MG), and heavy grazing (HG)] on leaf photosynthesis parameters and photosynthetic pigments of three grass species on an alpine steppe in the Qilian Mountains. Grazing had a positive effect on the leaf photosynthesis parameters of S. purpurea and L. secalinus ( Li et al., 2021 ). However, it is not clear how grazing regulates photosynthesis and light compensation.…”