Preliminary Study On The Photosynthetic Regulation Mechanism Of Ovegrrazing-induced Dwarf In Leymus Chinensis

Due to the effects of long-term overgrazing,plants on the grassland showed a draw phenotype,such as shorter height,shorter and narrower blade,et.And these phenomena remained after the removal of overgrazing disturbance.Our team found that these phenomena remained when planted in the greenhouse and homogenous garden,and supposed that draw phenotype maybe caused by the grazing-induced stress memory based on large numbers of experiments.In this paper,to explore the regulational mechanism of grazing-reduced dwarf phenomenon in plants on grassland,we studied the differences of morphological characters,photosynthetic physiology,and stomatal characteristics between two treatments of Leymus chinensis and contrasted their ability to adapt to castration by an clipping experiment.The main findings are as follows:(1)Compared with the non-grazing Leymus chinensis,the progeny of Leymus chinensis after long-term overgrazing showed obvious characteristics of avoiding grazing,such as plant dwarf and smaller leaves.These features can be stable existence at least in the first generation of Leymus chinensis clonal reproduction.After re-clipping treatments,the growth rate of plant height and leaf length in long-term overgrazing Leymus chinensis was relatively stable and conservative,while the non-grazing Leymus chinensis showed a large change range.Finally,the plant height and leaf length in over-grazing Leymus chinensis had a smaller plasticity index under different clipping treatments,and was less affected by clipping treatments than non-grazing Leymus chinensis,so it had greater ability when faced with grazing stress again.(2)The decline of net photosynthetic rate was one of the main reasons of overgrazing-induced dwarf in Leymus chinensis.The narrower stomatal width and lower stomatal conductance may lead to the lower net photosynthetic rate in over-grazing Leymus chinensis.Q-PCR analysis showed that the seven genes involved in the regulation of stomatal development and regulation was down-regulated,up to a maximum of 36 times;while the CP3L-1 gene was up-regulated by about 3 times.The regulation mechanism of overgrazing-induced dwarf in Leymus chinensis maybe as the follows: “ down-regulation of ABCCL4? the narrower stomata?lower stomatal conductance?lower net photosynthetic rate?dwarf”.(3)The change in net photosynthetic rate in Leymus chinensis was consistent with the growth rate of plant height and leaf length under different clipping treatments.The net photosynthetic rate of over-grazing Leymus chinensis had no significant changes while the net photosynthetic rate of non-grazing Leymus chinensis significantly increased under clipping treatments.So it could be inferred that the conservation of the net photosynthetic rate of over-grazing Leymus chinensis led to the conservation of morphological traits,and finally over-grazing Leymus chinensis showed the grazing evasion,which was one of the mechanisms to adapt to grazing disturbance.