Dwarfing and the underlying morphological changes of Poa alpigena plants in response to overgrazing conditions

Poa alpigena as the research object on alpine meadow in this paper,analyzed the change characteristics of the stem and leaf anatomical structures of Poa alpigena plants under the overgrazing and enclosed conditions aims to revealed the dwarfing of morphological mechanism in overgrazing.the results show that that leaf thickness, leaf epidermal thickness, epidermal cell area, and phloem thickness increased with increasing grazing intensity (p < 0.05). In contrast, xylem thickness, mesophyll cell area, and guide wall thickness decreased with increasing grazing intensity (p < 0.05). Mesophyll cell density was relatively unaffected by grazing intensity. Additionally, the plasticity indices were high (i.e., greater than 0.5) for leaf area, upper epidermal cutin layer thickness, and leaf xylem thickness. The plasticity indices were greater than 0.4 for stem tube diameter, epidermal cell size, and epidermal cuticle thickness. These results reflected the Poa alpigena stem and leaf structural changes induced by the water and mechanical stresses caused by grazing livestock. Thus, plateau plants adapt to grazing stress by increasing the thickness of their leaves, cuticles, and phloem. The Poa alpigena mesophyll cell area as well as the stem epidermal cell area and density decrease in response to minor changes in grazing intensity, which ultimately result in the shortened leaves and stems of dwarf plants.