Soil Dissolved Organic Carbon And Its UV-Visible Spectral Characteristics Under Different Vegetation Conditions In Qingling Mountains

The structure and composition of soil dissolved organic matter is an important evaluation index in evaluating soil fertility,and it has important value and significance in the field of ecology.The study was conducted on the soil of Larix gmelinii plantation,Pinus tabulaeformis,Pinus tabulaeformis-Betula platyphylla mixed forest soil and a valley wetland meadow soil as the object,which lie in the Taibai county of shaanxi province,belong to Qinling Montains,It was studied that distribution characteristics and correlation of soil DOC,organic carbon(SOC),total nitrogen(TN),total phosphorus(TP),pH,DOC ultraviolet-visible spectrum characteristic parameter under different vegetation conditions.The main results are as follows:1.Larix gmelinii,pinus tabulaeformis forest,Pinus tabulaeformis-Betula platyphylla mixed soil under natural forest,meadow,from 0cm to 50 cm depth of soil,DOC content decreased with soil depth.Table clustering was found in the vertical section distribution of soil DOC content.Four vegetation types are follows as: soil DOC content of natural pinus tabulaeformis > Pinus tabulaeformis-Betula platyphylla mixed forest > meadow > larix gmelinii.2.The content of SOC,TN and TP in soil SOC,TN and TP decreased with soil depth in the soil 0-50 cm depth under the four planting types.Table together in SOC content soil vertical distribution,the average soil SOC content in the order: meadow > pinus tabulaeformis forest > larix gmelinii > Pinus tabulaeformis-Betula platyphylla mixed forests;Average TN content in the order: meadow > larix gmelinii > pinus tabulaeformis forest > Pinus tabulaeformis-Betula platyphylla mixed forests;Average TP content in the order: meadow > larix gmelinii > Pinus tabulaeformis-Betula platyphylla mixed forest > pinus tabulaeformis forest.Soil DOC showed significant positive correlation with soil SOC,TN,TP and N/P,with no significant correlation with C/N and significant negative correlation with soil pH value.The soil pH value increases with the increase of soil depth.3.Four vegetation types are the ultraviolet-visible spectral curve of soil DOC absorbance value decreases with the increase of the wavelength,the ultraviolet-visible absorption spectrum curve and the coordinate axis of area decreases with the increase of soil depth.In the range of uv-visible region,the absorption curve presents a single wave peak,and the maximum absorbance value appears at 200 nm,presenting the end absorption;A absorption platform and the shoulder absorption phenomenon present from 230 nm to 280 nm.With the increase of soil depth,characterization of the size of the aggregation degree and molecular weight index parameters A240/A420 ratio drops,representing the degree of substituent complex A253/A203 that deep relative surface ratio decreased,the characterization of organic matter humification degree A250/A365 ratio tends to decrease,the characterization of organic matter humification degree and molecular weight A300/A400 ratio tends to decrease,DOC aggregation with depth increases with the enhancement,the molecular structure of substituents by more complex carbonyl and carboxyl,hydroxyl and other changes to the structure is more simple an aromatic ring,average molecular weight increases;The composition of DOC is still dominated by rich acid with small molecular weight.Deep soil DOC is more stable.4.The correlation between SOC and DOC in the soil 0-50 cm depth was significant(R=0.742,P<0.01).The correlation between DOC and uv-visible spectrum A200(R=0.896,P<0.01)and A280(R=0.874,P<0.01)was significant.