Study On Poisonous Plants On Songnen Grassland Influenced By Changes In Environmental Gradient

Songnen grassland , one of the most important base of the farming industry in China, has been damaged seriously in recent years due to improper ultilization, undergoing serious deterioration, grassland regression and a heavy loss of high quality forage. On the other hand, the variety of poisonous plants becomes increasingly inundant, which can make livestocks susceptible to poison and cause seriously economic loss. Obviously,it is very meaningful to study poisonous plants on Songnen grassland .The results of wild investigation showed: On Songnan grassland, there are plenty of poisonous plants, belonging to 32 Families, 72 genuses, and 100 species, which possess respectively 37.2% in Family, 21.49% in Genus and 12.9 in Species of the total plants quantities.The geographic distribution of poisonous plants in this area belong to 39 species in Mongolia flora, 54 species in Changbai flora, 43 species in Huabei flora and 23 species in Daxinganling flora. Among them, ChangBai Montain flora and Huabei flora are dominant. From the angle of ecological environment, the species of Mesophyte and Shygrophyte are the majority .It also proves that Songnen glassland belongs to Meadow stepp.Grazing intensity has significiant effect on poisonou plants of the Songnen grassland. With grazing indensity increased, obvious changes of poinsonous plants are observed as below: 1) High quality forage has decreased gradually, while the species and biomass of poisonous plant get increased greatly by means of biomass growth both the aboveground parts and underground parts;2)The content of poisonous components tends to increase significantly, and the contents of necessary elements, such as K, Na,Ca, Mg ,C1 are also measured to be increased;3) Grazing intensity also has some effect on ultrastructure of leaves of Stellera chamaejasme L.With grazing intensity inhenced, cuticle striations get poorer ,the size of stomatal apparatus shrinks and stomatal index trends to increase, while to the shape of leaf epidermal, the pattern of anticinal wall and the types of stomatal, the study hasn't observed any changes as grazing gradient increases. These changes on ultrastructure are adapted to physiological characteristics of poisonou plants.Water gradient plays very important role on the growing and distribution of poisonous plant on Songnan grassland. With the soil water getting reduced,the density of plants, l)the length of root and the plant biomass all tend to be increased,on the contrary the altitude of plants on the ground grow shorter slightly. 2) Poisonous components in vegetative organs of Stellera chamaejasme L.are reduced. In leaf cells, mineral elements K,Cl,Ca and Mg are increased as the content of soil water drops in order to control the osmosis of cells. 3) As soil waterdecreased,cuticle striations get richer ,the size of stomatal apparatus gets bigger and stomatal index trends to reduce. While to the shape of leaf epidermal, pattern of anticinal wall and types of stomatal,there are no distinct changes observed.With the increase of salinization gradient, poisonous plants are affected both on the plant growth and distribution :l)The species of poisonous plants, growing density, plant altitude aboveground, length of roots and biomass all trend to decrease while the alkaline-saline gradient increases, it indicates that alkaline-saline intimidates the growth of plant and their distribution;2)The contents of mineral elements have shown no changes in nutritional organs but in leaf cells,there is an increase;3) Cuticle striations get richer, the size of stomatal apparatus and stomatal index trend to reduce. While to the shape of leaf epidermal, the pattern of anticinal wall and the types of stomatal, there are no distinct changes observed.There are two main poisonous components including flavonoids and coumarins in vegetative organs of Stellera chamaejasme L. The content of the poisons varies in the different parts of Stellera chamaejasme L. The content of poisonous composions in root is the highest, while in theleaves and stems, the content is the lowest.In summary, three important control factors(grazing,water and salinization)all contribute to the growth and distribution of poisonous plant on Songnen grasslang. Grazing and drought facilitate the growth and distribution of poisonou plants efficiently, especially grazing gradient. Alkaline-saline mainly acts on distribution of poisonous plants. In order to control poisonous plants on grassland, we must enhance the management of grassland, constitute carrying capacity properly, prohibit overgrazing to effectively resolve the ecological problem in Songnen grassland.