The Effect Of Over Grazing On The Leaf And Stem Structures Of 11 Species In The Stepe Of Inner Mengolia

Representative communities of Artemisia frigida + Cleistogenes squarrosa which was the succession aberration of Leymus chinensis + Stipa grandis community were fenced in the Inner Mongolia typical steppe in 1983 and 1996 in order to observe the community succession processes.11 predominant plants were collected from unfenced community (degenerated community), community fenced for 7 years and community fenced for 20 years. Plant anatomical structures and Plasticity were compared to reveal the Influence of over grazing to plant structures.It was showed: the cuticle thickness of plant , mesophyll cell density of leaves were lower than those before fencing , for some species, leaf thickness,upper epidermis cells,maximum vessel wall thickness of leafs,vascular bundle density of leaf,xylem thickness/ phloem thickness of leaf and cell wall thinkness of stem mechanical tissues in community fenced for 20 years were smaller than those in degenerated community and in community fenced for 7 years. Xerophytic characters of the leaves and stems weakened in the fenced communities. Simultaneously plant conductive structure strengthened in fenced communities , concrete representations were as follow: vessel caliber,vessel amount,xylem thickness and vascular bundle width of stem became highter than that in degenerated communities.Compared with normal plants , small scaled plants did not have essential changes. Showing their structure were stable .But plant leaf and stem had environmental plasticity to some extant. plasticity of Artemisia frigida and Cleistogenes squarrosa were high; Leymus chinensis showed growth plasticity.