| Nitraria tangutorum nebkhas is a type of biological aeolian landform widely distributed in arid,semi-arid and semi-humid desert areas.It plays an important role in fixing flow sand,improving soil quality and maintaining regional ecological environment stability.In this paper,taking the Nitraria tangutorum nebkhas in the eastern margin of Qaidam Basin as the research objects,the distribution characteristics of Nitraria tangutorum roots,soil physical and chemical properties in the nebkhas profile and the spatial distribution characteristics of the surface soil physical and chemical properties were analyzed by collecting soil samples of samples of the profile of Nitraria tangutorum nebkhas and its underground and the land between nabkhas,and the soil samples at high density from different parts of the surface layer and within 1.2 m outside the shrub of nebkhas.The ultimate purpose of this study is to identify the influence of Nitraria tangutorum nabkhas on the distribution of soil physical and chemical properties,the “Fertile Island” effect were proved.The main conclusions are as follows:(1)The soils in each soil layer in profile are weakly or not obviously developed.The soil color of each soil layer is not very different with mostly brownish yellow,the texture is mostly sandy loam,and there is no obvious stratification in the profile.At the same time,each soil layer of the profile distributes a certain amount of roots,and there are obvious gravel interlayers in the soil layer below the ground level of the profile.(2)In the Nitraria tangutorum nebkhas profile,root specific root length and specific surface area all showed decreasing trends with increasing soil depth,while the average diameter showed a small increasing trend,and all the roots were thicker in the soil layer below 50 cm of the profile than in the upper layer.Meanwhile,the root biomass was more distributed in the soil layer below 60 cm.The lateral roots were more branched in the shallow 0-40 cm soil layer,which was the main area for water and nutrient uptake by the root system(3)The particles in Nitraria tangutorum nebkhas profile are mainly composed of fine sand,with an average content of 48.56 %;followed by ultra-fine sand,medium sand and fine silt,with an average content of 17.90 %,13.89 % and 11.17 %;coarse silt,clay and coarse sand were less in content,with an average content of 6.44%,1.73% and 0.44 %,respectively.Moreover,with the increase of soil layer,the content of soil clay powder showed an increasing trend,and the content of sand decreased showed a decreasing trend.The average soil bulk density and water content were 1.36 g/cm3 and 2.09 %,respectively.Soil bulk density and water content tend to increase with the soil depth.(4)The average particle size of the sediment in profile varies from 3.15 to 4.28Φ,which is composed of very fine sand and fine sand,and its standard deviation,skewness coefficient and kurtosis were-1.37,-0.19 and 1.21,respectively,with good particle sorting,showing a negative skewness and narrow distribution.The sediment is deposited through saltating over a short-range transport mainly under the action of wind.With the increase of soil depth,The average particle size of the sediments tends to become finer,and the standard deviation showed a decreasing trend.The skewness changed from near symmetry to negative skewness,and the kurtosis changed from medium to sharp narrow,which reflected that the variation law of sedimentary power in the deep layer was weaker than that in the shallow layer,and the influence of gradual wetting of the climate.(5)The total soil potassium content of Nitraria tangutorum nebkhas in the study area was moderate,while the rest of the soil chemical indexes were deficient,and the soil showed strong alkalinitye.Soil organic matter,total nitrogen,alkali-hydrolyzable nitrogen,available phosphorus and available potassium showed an overall decreasing trend with increasing soil depth and showed obvious surface aggregation.However,total potassium and cation exchange capacity did not change significantly in the profile.Soil p H increased first and then decreased and then increased,and the soil alkalinity was the weakest at the surface 0-5 cm depth.Soil bulk density was positively correlated with total nitrogen and p H(P<0.05),while the rest of the chemical indexes were significantly negatively correlated with soil bulk density(P<0.01).All soil chemical indexes(except p H)showed significant positively correlations with soil water content(P<0.01).Organic matter,total nitrogen,alkali-hydrolyzable nitrogen,total potassium,available potassium and cation exchange capacity were significantly positively correlated with extremely fine sand(P<0.05).Soil total potassium,available nitrogen,organic matter and cation exchange capacity were significantly negatively correlated with coarse sand(P<0.05).(6)The “Fertile Island” effect appears below the Nitraria tangutorum nebkhas profile and its ground plane.Compared with the land between nabkhas,there are more fine sand,fine sand,medium sand and other particles in each soil layer of its profile,with maximum enrichment rates of 1.50,1.79 and 1.31,respectively.On belowground level of Nitraria tangutorum nebkhas,the contents of extremely fine sand and fine sand in each soil layer were also higher than those in the land between nabkhas,with maximum enrichment rates of1.48 and 1.53,respectively.The soil bulk density in the sand pile section and below was smaller than that in the land between nabkhas,and the enrichment of water content is mainly reflected in the soil layer belowground level of nebkhas and is the most obvious at 10-20 cm,reaching 1.49.Soil organic matter,total nitrogen,total potassium,available phosphorus,available potassium and alkali-hydrolyzable nitrogen all showed enrichment in each soil layer of nebkhas profile,with alkali-hydrolyzable nitrogen showing the highest enrichment with an enrichment rate of 2.57.Soil nutrient “Fertile Island” effect showed an overall decreasing trend with increasing profile depth.In contrast,only available nutrients belowground level of nebkhas showed enrichment.The soil p H value was lower in the sand pile section and below than that in the land between nabkhas.(7)The soil properties showed obvious high-value and low-value areas in different parts of Nitraria tangutorum nebkhas surface and between nabkhas.The distribution of fine particles such as silt,very fine sand and fine sand in different parts of the surface layer of the sand pile was higher than that in the land between nabkhas,while the distribution of fine particles such as medium sand in the land between nabkhas was higher than that in different parts of the surface layer of the nabkhas.Soil organic matter,total nitrogen,alkali-hydrolyzable nitrogen,total phosphorus,available phosphorus,total potassium and available potassium all showed obvious “Fertile Island” effect in stable nabkhas,while the“Fertile Island” effect was not formed in the activation stage of sand nebkhas.The distribution of soil nutrient content and fine particle content such as soil silt and extremely fine sand in the windward slopes were higher than those in the leeward slopes.In short,the improvement of soil particle composition was slow,and the enrichment of soil nutrients in the profile was obvious,especially the enrichment of soil nutrients in the surface layer of the nebkhas was the strongest.The activities of grazing and artificial reclamation should be appropriately reduced to reduce the damage to the surface soil of the Nitraria tangutorum nebkhas.The results could provide reference for the scientific utilization of Nitraria tangutorum nebkhas and ecological environment protection in Qaidam Basin area... |
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