Alpine Meadow Degradation Studies Based On Soil And Plant Biomarkers

Biomarkers are stable compounds with features of stereochemical structure,abundant information,specificity,long-time preservation and wide distribution.They are good indicators of climate and environmental changes,and are usually used for tracing the origin of organic matter in paleo-environment.Although biomarkers have important instrumental value in palaeo-environmental reconstruction,they are seldom applied in the study of grassland ecosystem,especially in alpine meadow plants and soils.Analyzing the distribution characteristics of alkanes,fatty acids,alcohols,ketones and other biomarkers in alpine meadow plants and soils is helpful to explore the relationships between soil organic matter and plants,and reveal the internal relationships between the alpine meadow plants and the soil biomarkers and the indicative role of the biomarkers on the degeneration and succession of the plant community.The kinds,concentration,the number of carbon atoms,the carbon number of main peaks of plant and soil biomarkers(fatty acids,hydrocarbons,alcohols,aldehydes and ketones)were analysed with gas chromatography-mass spectrometry(GC-MS),the main results and conclusions are as follows:1.Plants in the research area contain 68 kinds of fatty acids,including 10 kinds of polyunsaturated fatty acids,13 kinds of monounsaturated fatty acids and 45 kinds of saturated fatty acids.The carbon number distribution of fatty acids varies from 3 to 28,and the dominant carbon number is C16,C18,C20,C22 and C24.Fatty acids with even carbon number take predominance significantly.The distribution of n-fatty acid(C6-C28)content in plants is from 0.05 to 7964.32 mg/kg,and the total n-fatty acids content is from 380.19 to 11335.95 mg/kg.There are 41 kinds of fatty acids in the soil,including 3 kinds of polyunsaturated fatty acids,5 kinds of monounsaturated fatty acids and 33 kinds of saturated fatty acids,and the distribution of carbon number is the same as those of plants.The kind of fatty acids in plants of degraded meadow is more than that in 0~10 cm soil,and the kinds of fatty acid in 10~20 cm and 20~30 cm soil are more than that in 0~10 cm soil.The kind number of fatty acids in lightly and non-degraded meadow is in the order of 20~30 cm soil? 10~20 cm soil? 0~10 cm soil? plant,and the fatty acid kinds decrease with soil depth.There is no significant difference in the content of congener fatty acids in soil with different depths.2.The content distribution of n-alkanes in plants is from 0.81 to 22.88 mg/kg,and the content of C27,C29,C31 and C33 n-alkanes are higher than others.The content of n-alkanes with odd carbon number has an obvious distribution advantage over even carbon number n-alkanes.The proportion of C27,C29 and C31 n-alkanes in most plants is within 0~0.50 for C27 and 0.25~0.75 for C29 and C31,respectively.The CPItotal range of n-alkanes in plants is from 1.07 to 4.32,and the range of CPI25-36 is from 1.12 to 8.20.The content distribution of odd carbon n-alkanes in plants has a significant advantage.The ACLtotal range is from 23.52 to 27.22,and the ACL27-33 range is from 28.03 to 31.07.The range of Pwax value is from 0.60 to 0.92.The content of C22 in severely degraded meadow plants is significantly higher than that in plants of lightly degenerated meadow and non-degraded meadow.The content of C29 and C31 in the surface soil in degraded alpine meadow is lower than those in the subsoil,while the content of C29 and C31 in the surface soil in the non-degraded alpine meadow is higher than those in the subsoil.The correlation of long chain n-alkanes in plants and soils is significant(P<0.01).3.The range of alcohol kinds in the plants is from 2 to 21 and the carbon number of the alcohols is from 4 to 37.The kinds of unsaturated alcohols are higher than those of the saturated alcohols.The relationships of alcohol kinds between plants and soil in alpine meadow is that degraded plant > degraded soil > non degenerate plant > degenerated soil.The same alcohols in plants and soil are 9-Methyl-Z-10-pentadecen-1-ol,2-methyl-1-Hexadecanol,12-Methyl-E,E-2,13-octadecadien-1-ol,3,5-2-methylene-Cholestan-3-ol,and 2,2,4-Trimethyl-3-(3,8,12,16-tetramethyl-heptadeca-3,7,11,15-tetraenyl)-cyclohexanol,1-Heptatriacotanol,respectively.For the same alcohols,there is a significant correlation between plants and soils(R2=0.871).4.The carbon number range of aldehydes in plants is from 9 to 30,and the mean content is from 9.01 to 671.15 mg/kg.The carbon number range of aldehydes in the soil is from 7 to 22,and the content range is from 0.0007 to 0.3208 mg/kg.The plants have 20 kinds of unique aldehydes,and there are 3 kinds of unique aldehydes in the soil.There are 5 kinds of aldehydes in plants and soil,they are 1,1,3,3-tetramethoxy-Propane,Undecanal dimethyl acetal,7,11-Hexadecadienal,(Z)9-Octadecenal and 1,1-dimethoxy-Octadecane.There are 38 kinds of ketones in plants,while 6 kinds of ketones in soil.Plants and soil have 2 common ketones.They are 6,10,14-trimethyl-2-Pentadecanone and 5?-Norcholestan-2-one.By comparing the differences of biomarkers in soil and plants,it can be speculated that the long chain biomarkers in alpine meadow soil are derived from alpine meadow plants.The fact that the concentrations of C29 and C31 n-alkanes in soil increase with soil depth could reflect the past succession of alpine meadow plant community.9-Methyl-Z-10-pentadecen-1-ol,3,5-2-methylene-Cholestan-3-ol,and 1-Heptatriacotanol could indicate the past degradation of alpine meadow.The differences of kind and concentration of fatty acids between plants and soil can reveal moderate and severe degradation of alpine meadow,but cannot differentiate lightly degradation from normal health alpine meadow.