| The forest and shrub meadow vegetation distributed in the high and cold mountainous area of Western Sichuan plays an important role in water conservation and conservation of water and soil.And the middle and lower reaches of the Yangtze River can be effectively protected.With the continuous increase of human activities,the ecological environment of the high mountain area in the west of Sichuan is deteriorating,and the natural disasters are frequent.The ecological security of the middle and lower reaches of the Yangtze River is seriously infringed.Zheduo mountain is located in the high and cold mountainous area of West Sichuan,it is the transition zone from the first step to the second level and belongs to the typical fragile eco-environment area.In this paper,we take the soil of Zheduo mountain in Ganzi region as the research object,the soil nutrient status of 15 samples of five elevation gradients at altitude of 3400 m,3600 m,3800 m,4000 m and 4200 m are studied,the response of various stoichiometric ratios to the soil layer and altitude is analyzed,The soil fertility and soil fertility level in this area are discussed,in order to reveal the soil nutrient status in the ecologically fragile area of the high cold mountain area in Western Sichuan,it's a theoretical support for vegetation restoration and eco-environmental protection in the Western Sichuan.The main conclusions are as follows.(1)Soil nutrients are not the same in different altitudes and soil layers,with the elevation of altitude,the total phosphorus content of soil increased gradually,and the total nitrogen and alkali hydrolysable nitrogen in the soil showed an increasing trend,the content of soil organic carbon,available phosphorus,total potassium and available potassium fluctuated greatly,and the regularity was not obvious.With the increase of soil depth,soil organic carbon,total nitrogen,and alkali hydrolysable nitrogen are decreased gradually,and there was a more obvious phenomenon of surface aggregation.The total phosphorus in soil decreased,while the effective phosphorus and total potassium had no obvious regularity.There is a certain correlation between the nutrient indicators,soil organic carbon has significant positive correlation with total nitrogen,alkali hydrolysable nitrogen,total phosphorus and available potassium(P<0.01).Total nitrogen in soil is significantly correlated with alkali hydrolysable nitrogen,total phosphorus and available potassium.Soil alkali hydrolysable nitrogen has a significant positive correlation with total phosphorus and available potassium.At the same time,altitude also affects soil nutrient content.Soil total nitrogen,alkali hydrolysable nitrogen and total phosphorus have very significant positive correlation with altitude.There is a significant positive correlation between organic carbon and altitude(P<0.05).(2)The vegetation type has great influence on the soil C/N/P,which leads to the larger spatial variability of soil carbon,nitrogen and phosphorus.With the increase of altitude,N/K and P/K gradually increased,and the increasing trend of C/K was not significant(P>0.05),but there was no obvious change in the ratio of other kinds of Soil Eco stoichiometry.With the deepening of the soil layer,C/P,C/K,N/P and N/K decreased gradually in all the altitudes,while C/N and P/K showed a decreasing trend.The soil ecological stoichiometry are correlated with soil total nitrogen,and 83.33% stoichiometric ratios are positively related with organic carbon significantly,the stoichiometric ratio of 66.67% with nitrogen was significantly positively correlated,suggesting that the mineralization ability of soil nitrogen in the area of strong,high risk of nitrate leaching.(3)The p H value of soil in the study area is between 4.09-6.59 and it is acid soil.Organic carbon is the main factor affecting the amount of cation exchange in the soil,and there is a very significant positive correlation between them(r=0.858).The content of soil base ions in the study area is Ca2+> Mg2+>K+>Na+.The contribution of the exchangeable salt ions to the change of salt base saturation and p H value is mainly Ca2+,K+?Na+ is the second,Mg2+ is small,soil fertility at all altitudes is in the middle and low level.Through the analysis of the amount of cation exchange in the soil,in addition to the altitude of 3800 m has the strong ability to preserve fertilizer in this area,the ability to maintain fertilizer at other altitudes is at the middle level.(4)Different altitude soil nutrient indexes can be divided into four main components,the first principal component mainly reflects the soil total nutrients and cation exchange properties,the second principal components mainly responded to soil acid-base degree,the third principal components mainly responded to soil trace elements,while the fourth principal components mainly responded to soil potassium.The total score of three points at the altitude of 3800 m is quite different,it shows that the soil nutrient status in the forest zone is more unstable than that of other altitudes.High altitude area accounts for a large proportion in the first and second principal components,the level of soil fertility is in the middle,and the soil fertility in other areas is lower.This is different from the conclusion of the salt base saturation,The reasons for this difference need to be further studied.(5)The soil nutrients in the study area can be divided into 5 types by systematic cluster analysis,the characteristics of class I are Low content of organic carbon,total nitrogen,alkali hydrolysable nitrogen,total phosphorus,cation,total exchangeable salt base,salt base saturation.The characteristics of class II are high content of total phosphorus and salt base,low content of total potassium and available potassium.Class III is characterized by high phosphorus,available potassium and high p H value.The characteristic of class IV is that the content of effective phosphorus is low and the other nutrients are at the middle leve.The characteristic of class V is that the total amount of organic carbon,total nitrogen,alkali hydrolysable nitrogen,total potassium,cation,exchangeable salt base is high,and the content of p H is low.All in all,soil nutrients are greatly influenced by vegetation and elevation.The soil fertility at 3800 m above sea level is strong,but the nutrient status is unstable.According to the classification standard of soil fertility in Du Gang's paper,the soil fertility at all elevations is in the middle and low level,which is different from the conclusion that the soil fertility level in the high altitude area are middle and upper by the principal component analysis. |
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