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ŠUMARSKI LIST 9-10/2018 str. 82     <-- 82 -->        PDF

reductions were 70.1%, 32.5%, and 56.4%, respectively (Figure 1, Table 1). As compared with the mild tourism disturbance, the moderately disturbed soil also had different degrees of declining organic carbon content. Additionally, the soil impacted by severe and moderate tourism disturbances had significantly lower TN contents than the soil impacted by mild disturbance (p<0.05) (Figure 2, Table 1).
These results are in accordance with the numerous studies that have indicated that tourism disturbance reduces the organic matter content of the soil (Qin et al., 2006; Gong et al., 2009; Lu et al., 2011; Svajda et al., 2016). Repeated trampling in an area causes soil bareness and destroys the litter layer and humus layer. Furthermore, trampling on compacted soil negatively impacts the growth and development of plant roots, thus leading to reduced plant return. These effects cause the organic matter content to decrease (Lu et al., 2011). The soil nitrogen is closely related to the organic matter content. Thus, when tourism disturbances reduce the organic matter content, the nitrogen content of the soil is likewise reduced (Gong et al., 2009).
The severely disturbed soil had significantly lowerDOC than both the moderately and mildly disturbed soils, but the difference in the DOC content between the latter two soils was not significant (Figure 2). DOC is the main component of soil organic matter, which is derived mainly from plant litter and the decomposition of humus, microbial biomass, and root exudates (Wang et al., 2016). In this research, it was visually observed that severe disturbance decreased vegetation coverage and reduced litter, accordingly the DOC content decreased in the soil.
In the three sample plots of the plant community, as compared with mild disturbance, severe disturbance obviously reduced the NO3-–N, NH4+–N, and DON contents in the soil, and moderate disturbance also reduced these contents to varying degrees. Soil NO3-–N and NH4+–N are biologically available nitrogen that can be directly absorbed and utilized by plants. Through mineralization, NH4+–N and NH4+–N are created from organic nitrogen and then transformed into NO3-–N by nitrification (Li et al., 2015; Wen et al., 2016). As tourism disturbance reduces the TN content in the soil, the mineralization source of NO3-–N and NH4+–N also decreases. Furthermore, tourism trampling increases the soil density and reduces the soil moisture, which weakens the microbial activities in the soil and then reduces soil mineralization and nitrification (Li et al., 2015).
Additionally, the severe disturbance also significantly lowered the soil DON content. The source of soil DON is same as that of soil DOC. The decreased DON content was probably primarily caused by decreases in vegetation coverage and litter as a result of severe disturbance, as is suggested in the work of other researchers (Ueda et al., 2013; Mobley et al., 2014).