Investigation And Anaiysis On Soil Environment Of The Gymnadenia R.Br.Habitats In Tibet

Gymnadenia R.Br.as one of the precious medicinal herbs in Tibet,the source of medicinal materials has been dependent on natural wild resources because of its difficulty in artificial propagation.At present,with the increasing demand of the market,the blind exploitation has led to a sharp decline in its wild resources,and even to the end.Therefore,based on the investigation of the distribution characteristics and habitat environment of wild resources of Gymnadenia R.Br.in Tibet area,this study collected the soil of the Gymnadenia R.Br.Habitats.The relationship between population distribution and environmental factors of Gymnadenia R.Br.was systematically analyzed.The current study provided a scientific approach for the artificial cultivation in a larger scale in Tibet.The following are main conclusions:(1)The geographic distribution of Gymnadenia R.Br.is relatively narrow,which mostly shows a scattered or fragmental distribution.The distribution of Gymnadenia R.Br.is basically the same as that reported in the original literature.The newly increased population is located in the Suolang gully and Cui Jiu gully in Gyaca County,Shannan Prefecture.The altitudinal distribution of Gymnadenia R.Br.ranges from 2 800 to 4 600 m.Its habitat was forest gap and forest edge,forest grassland,alpine meadows,alpine shrubs which usually have a certain gradient.The mountain brown and alpine meadow soils are the main types of soil in the whole range of the species distribution.Its distribution area were characterized by typical plateau monsoon climate.(2)Gymnadenia R.Br.grew in the soils from acidic to neutral with the soil pH ranged between 4.6~7.4.The soil organic matter was ranged between 38.9~196.1 g/kg,with the average value of 101.3 g/kg.The total nitrogen was ranged between 1.8~7.0 g/kg,with the average value of 4.1 g/kg.The alkaline nitrogen was between159.8~592.6 mg/kg,with the average value of 345.2 mg/kg.The total phosphorus was between 0.4~1.5 g/kg,and the average value was 0.7 g/kg.The available phosphorus was ranged between 6.4~68.5 mg/kg,with the average value of 27.5 mg/kg.The total potassium was ranged between 12.8~23.8 g/kg,with the average value of 18.3 g/kg.The available potassium was ranged between 70.5~320.1 mg/kg,with the average value of 143.2 mg/kg.Overall,the soils were rich in organic matter,total nitrogen,alkaline N,but were low in soil phosphorus and potassium content.The evaluated results indicated that the level of soil fertility of Gymnadenia R.Br.habitat in Linzhi was high.(3)Climatic factors and elevation were the most important environmental factors affecting the population distribution of Gymnadenia R.Br.,followed by soil fertility factors.For the plant height,the favorable factors were higher soil nutrient status and air humidity in the original habitat.Excessive illumination and human disturbance were unfavorable factors.As altitude and slope position decreases,the density of distribution increases.Soil fertility and temperature during growing season were more favorable to increase population density,whereas,the excessive slope is an unfavorable factor.