Study On Plant Stoichiometric Characteristics Of Typical Communiti In The Loess Plateau Hilly Region Of Northern Shaanxi

In this paper,two typical communities are chose as the main objects in the Loess Plateau Hilly region of northern Shaanxi China.Through field vegetation surveys,sample collection and determination and statistical analysis,organic C,total N and total P of the leaf,branch,and soil,as well as their ratios in 29 sample plots were analyzed.Simultaneously,the effects of different environmental factors on plant stoichiometric characteristics in different communities were explored.These can evaluate the adaptation status of returning farmland to community in order to provide scientific basis for the restoration and reconstruction of degraded vegetation in this area.The main conclusions are as follows: 1.Plant stoichiometrric characteristics and relationships with soil nutrients in Robinia pseudoacacia communities of different planting ages.With increasing planting age,the C,N,P contents in leaves and branches,as well as the N/P ratio in leaves increased initially and then decreased,with the highest value in 40a(40 years old).The C/N and C/P ratios in leaves and in branches decreased initially and then increased with the increase of planting age.The N,P contents,and C/N and C/P ratios in leaves had nonlinear relationships with R.pseudoacacia age.The average N,P contents,and C/N,C/P ratios in leaves were affected significantly by planting age(P > 0.05).With increasing planting age,soil C,N,P contents,and C/P,N/P ratios in R.pseudoacacia communities increased initially and then decreased.Soil total N content was the main factor influencing C and N contents in leaves and C,N,P contents and C/P ratio in branches.The C,P contents and C/N,C/P ratios in leaves and C/N ratio in branches were influenced by the soil N/P ratio.The C content and N/P ratio in leaves were affected by the soil organic C content.2.Plant stoichiometrric characteristics and relationships with soil nutrients in Robinia pseudoacacia communities of different watersheds.With increasing latitude,the C,N,P contents in leaves and branches increased,the C/N and C/P ratios in leaves and in branches decreased,the N/P in leaves and branches increased initially and then decreased.With increasing latitude,soil C,N contents,and C/P,N/P ratios in R.pseudoacacia communities decreased,soil total P content increased,soil C/N ratio increased first and then decreased.Soil organic C content was the main factor influencing organic C and N contents,C/N and C/P ratios in leaves and branches.The total N content and C/N,N/P ratios in leaves and organic C content,total P content and C/N ratio in branches were influenced by the soil total N content.The organic C content in leaves and total P content in branches affected by soil C/P ratio.The soil C/N ratio was the main factor of N/P ratio in branches.Therefore,soil organic C content and total N content are the major factor of plant stoichiometric characteristics in Robinia pseudoacacia communities of different watersheds.3.Plant stoichiometric characteristics in Robinia pseudoacacia communities of different slopes and their environmental interpretationFrom the shady slope to the sunny slope,the organic C content,total N content,C/N,C/P and N/P ratios increased,while the total P content in leaves and branches was the opposite trend.From the shady slope to the sunny slope,the soil organic C content,the total N content,the C/P and N/P ratios tend to decreased,soil total P content tend to increased,the soil C/N ratio increased first and then decreased.The organic C content,total N contents,C/N,C/P ratios in leaves and branches and total P content in leaves of Robinia pseudoacacia of different slopes were affected by soil organic C content.C/N and N/P ratios in leaves and branches,and total P content in branches were influenced by soil C/P ratio.Organic C content,total N content in leaves and total N and P contents in branches were affected by soil N/P ratio.Soil total N content is the significant factor influencing organic C,total N contents in leaves,and total N,P contents in branches.The contribution rates of eco-factors to plant stoichiometric characteristics were listed as follows: slope(40.0%)> slope(27.6%)> age(19.0%)> elevation(13.6%).Thence,soil organic C,total N content,and C/N,N/P ratios are the major factors of plant stoichiometric characteristics in Robinia pseudoacacia communities of different watersheds.4.The response of plant stoichiometric characteristics in Artemisia annua community to the micro terrain.From the eastern slope to the top of the hilltop,the organic C,total N,total P contents,C/N ratio in aerial parts and roots,and the C/P,N/P ratios in roots all increased first and then decreased,the C/P ratio in roots and N/P ratios in aerial parts showed the opposite trend,the N/P ratio in roots and C/P ratios in aerial parts decresed.From the uphill to the top of the hilltop,the organic C,total N,total P contents in aerial parts and organic C content in roots increased first and then decreased,while the C/N to N/P ratios showed the opposite trend.From the eastern upper-slope to the top of the hilltop,the soil organic C and total N contents,C/P and N/P ratios were increased first and then decreased,and the soil total P content and C/N ratio were no significantly change.The slope had significant effect on the total P content in aerial part.The slope-positon had considerable effect on the organic C content,C/N ratio in aerial parts and organic C content in roots.The slope-positon had a significant effect on soil organic carbon content and soil CN ratio.In summary,with the changes of age,watershed,slope direction and slope position,the adaptability of different plant communities is different.The soil factor,which affected the plant stoichiometric characteristics in Robinia pseudoacacia communities in different ages,is the soil total nitrogen content.When Robinia pseudoacacia grew to 40 years old,it is the most suitable time for the local soil and the surrounding environment.It is suggested that appropriate artificial intervention should be made to the Robinia pseudoacacia community in order to ensure the well growth of the plant.From Wuqi,Ansai,Yan'an,to Yichuan,The response of the plant and soil stoichiometric characteristics in Robinia pseudoacacia communities is sensitive to the latitude.Therefore,the latitude is the main factor affecting the stoichiometric characteristics of Robinia pseudoacacia.Soil organic C content is the main soil factor that affected the metering characteristics of plant in Robinia pseudoacacia communities in different watersheds.Plants in Robinia pseudoacacia communities grow well in Yichuan,which is the most suitable place for it.From the perspective of the slope,Robinia pseudoacacia is more suitable for growing in the shady slope.The soil organic C content is the major factor that affected the plant stoichiometric characteristics in Robinia pseudoacacia communities of the different slopes.The slope direction is the largest factor that influencing plant stoichiometric characteristics in Robinia pseudoacacia communities in the four factors of slope direction,slope position,age,and altitude.Under the condition of micro terrain,the growth status of Artemisia argyi communities was the best in the northern middle-slope,and the soil had the highest nutrient content in the northern lower-slope.The aspect and slope position affected the plant and soil stoichiometric characteristics in Artemisia argyi communities significantly.Therefore,it is suggested that appropriate artificial intervention should be carried out in the high-age locust community,and the arrangement of Robinia pseudoacacia should be increased in Yichuan and shady slope,and Artemisia sacrorum community in the shady slope should be constructed to promote the restoration of plant communities and the reduction of soil erosion in Loess plateau hilly region.