Effect Of Grazing Disturbance On Soil Active Organic Carbon In Mountain Forest-the Arid Valley Ecotone In The Upper Reaches Of Minjiang River

Soils were selected from four plantations, including article Robinia, article Poplar, Grassland and Berberis aggregate shrub in mountain forest-the arid valley of ecoton-e in Li County in the upper Minjiang River. Three different grazing strength were set by different distance between grazing-path and the sample points:light disturbance(LD)(0-5m), moderate disturbance(MD)(5-10m) and heavy disturbance(HD)(>10m). The measurement of Soil total organic carbon, Microbial biomass carbon, Mineralize carbon, Labile organic carbon, Light fraction organic carbon, Particulate organic carbon and Dissolved organic carbon were made, because the TOC and its active compositions can reflect the effect of grazing on soil characteristics. The percentages in TOC of these active compositions, qCO2, CMI and the relationship between them also were analysed. This thesis intend to give a relatively detailed analysis of grazing in mountain ecosystem and in artificial forests, to provide reference in the mechanisms of transform of SOC and regulating the measures of rebuilding ecosystem environment in mountain forest-the arid valley of ecotone in the upper Minjiang River. The results indicated:(1)The amount of TOC、MBC、MC、DOC、LOC、LFOC and POC became low along with the increased grazing strength in article Robinia and article Poplar, but they were reduced before and then increased in Grassland and Berberis aggregate shrub. It depends on the accessibility of livestock and the availability of vegetation under each plantation.(2)The descending ranges of MBC、MC、DOC、LOC、LFOC、POC and CMI were1.09-8.92times larger than that of TOC. The change regularity of the amount of active compositions and the percentage of active compositions from TOC were similar along with the grazing strength, and the percentage is not a constant. This shows that the change of active compositions are faster than TOC, and the active compositions are early sensitive detection index. But the percentage of POC form TOC increased by9.12%and13.63in Grassland and Berberis aggregate shrub by MD, while the amount of POC reduced. The percentage of POC form TOC was increased4.87times faster than the amount of POC. This shows change of POC/TOC is faster the amount of POC, and the percentage of sand grain increased with the strength of grazing disturbance.(3) The qCo2increased by15.14%-100.54%with the strength of grazing (except of MD in Berberis aggregate shrub) in four plantations in surface soil. This shows the microorganisms turnover became faster, and the utilization rate of TOC became lower, and the release of CO2became more along grazing disturbance.(4)CMI decreased and then increased in surface soil along the strength of grazing, while decreased in10-20cm. It decreased by6.2%-70.41%.The reason is that the plant root near to grazing-path holds back water of runoff, which make higher microbial activity, faster decomposition rate of soil organic matter, and then the soil active organic matter was accumulated in a short time.(5)The results indicated that it correlated significantly positive among TOC、MBC、 MC、LOC、FOC and POC;no significant correlations were found between DOC and TOC, but significant positive correlations were found between DOC and LFOC, water content; significant negative correlation were found between bulk density and DOC, LOC, LFOC, and between pH and MBC、DOC,POC; no significant correlations were found between vegetation coverage and soil organic carbon.