| Human linear engineering, such as railway, highway, high-tension lines, produce plenty of Land Used for Engineering Construction with different areas in the alpine steppe regions of Qinghai-Tibet plateau, and the restoration of these Lands Used for Engineering Construction is not only related to improve the service function of the alpine steppe ecosystem, but is related to these engineering safety. In Land Used for Engineering Construction, Land Used for Roadbed Construction(LURC) with playground shape is the most widely distribution and the largest area, and its restoration strategy consists of artificial establishment and natural restoration. Although the natural restoration of LURC needs a long time, it shows merits with less investment and strong stability of restorable plant community and avoiding disasters transformation, The restoration of LURC in western countries has begun in1943, focusing on the impact of the plant growth promoter, herbicides and fertilizer on planting vegetation, and native plants restoration strategy in the21st century. The restoration of LURC in China has started from the Highway construction and which is regulated by LURC area and restoration time that the natural restoration experiences. The previous studies shows that natural restoration time of LURC within100m distance away from highway needs20years in the alpine steppe regions of Qinghai-Tibet plateau. The restoration of LURC requires the artificial establishment if the LURC has not developped a stable plant community after20years. Thus, quantifying suitable areas of LURC which could establish the stable plant community after20years is not only important to select the rational restoration strategy for existing LURC, but also is important to reduce the permanent bare patch by controlling construction area in the future. Taking the undisturbed alpine steppe as control, this study systematically analyzed plant composition, total cover, height, diversity, aboveground biomass, economic groups, plant niche, soil moisture and nutrient content features in different LURC areas which experienced19-21years natural restoration in the alpine steppe regions of Qinghai-Tibet plateau. The soil and vegetation restoration degree were used to estimate the area effectiveness of LURC and this study proposed the suitable restoration area of LURC with playground shape. The main conclusions are as following,1Quantifying the suitable area of LURC with playground shape for natural restoration from plant community composition and coverThe total cover, height, aboveground biomass of restoration plant community were80%,81%and82%of undisturbed alpine steppe, respectively, when the LURC area was or was less than156m2. They were56%,62%and51%of undisturbed alpine steppe when the LURC area was more than156m2. The Carex moorcroftii was dominant plant when the LURC area was or was less than254m2, and it scattered when the LURC area was more than254m2. The Stipa purpurea, an indicator plant for alpine steppe, often appeared when the LURC area was or was less than156m2, and it was not identified when the LURC area was more than156m2. Therefore, the suitable area of LURC for natural restoration was156m2from the total cover, height, aboveground biomass, and was254m2from plant composition.2Proposing the suitable area of LURC with playground shape for natural restoration from plant diversityThe a plant diversity of restoration plant community at254m2LURC was less than that at control, but it was significantly greater than that at LURC whose area was more than254m2(P<0.05). The β diversity and economic group of restoration plant community was similar to those of control when LURC area was or was less than254m2, implying that the structure of restoration plant community is stable, the replacement rate of plant species was very low, and the economic group was optimal. Therefore, the suitable area of LURC for natural restoration was254m2from the restoration of plant diversity.3Finding the suitable area of LURC with playground shape for natural restoration from soil moisture and nutrient contentThe moisture content of restoration soil ranging from19%to25%fell into the rational range of alpine steppe soil and the organic matter content of restoration soil was similar to that of control when the LURC area was or was less than156m2. The nitrogen content of restoration soil when the LURC area was or was less than156m2was less than that of control, but greater than that of restoration soil when the LURC area was more than156m2(P<0.05). The total potassium and available potassium content of restoration soil was greater than that of control when the LURC area was or was less than254m2, but was less than that of control when the LURC area was more than254m2(P<0.05). Therefore, the suitable area of LURC was156m2from the restoration of soil water and nutrients.4Presenting the appropriate area of LURC with playground shape for natural restoration from C, N, P stoichiometry viewThe C, N, P stoichiometry of C. moorcroftii and soil in restoration community was similar to those of undisturbed alpine steppe when the LURC area was or was less than156m2, and they were frequent fluctuations when the LURC area was more than156m2. Therefore, the suitable area of LURC was156m2from C, N, P stoichiometry.5Estimating the appropriate area of LURC with playground shape for natural restoration from vegetation and soil restoration degreeThe vegetation restoration degree when the LURC area was or was less than254m2was greater than that when the LURC area was more than254m2. The soil restoration degree when the LURC area was or was less than156m2was greater than that when the LURC area was more than156m2. The suitable area of LURC was254m2from vegetation restoration and was156m2from soil restoration.This study showed that the plant community of natural restoration was better than that of control when the LURC area was55m2, and was similar to that of control when the LURC area was156m2, and it was possible to develop the natural restoration plant community when the LURC area was254m2and was impossible to develop the natural restoration plant community when the LURC area was more than254m2even if the LURC experienced the20years. |
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