Content Of Soil Fixed Ammonium And Its Influencing Factors In The Mu Us Desert

Fixed ammonium was an important component of soil nitrogen pool and plays a significant role in plant growth.However,previous studies on fixed ammonium were mainly based on farmland and grassland ecosystems,and most of the soil types studied were paddy soil,and loess,the content of fixed ammonium in aeolian sandy soil and its influencing factors are largely unexplored,which limits our understanding of the formation of soil fertility and nitrogen cycle in desert.In this study,we determined soil fixed ammonium in three sampling plots（bare sandy land,Salix psammophila land and Artemisia ordosica land）in the Mu Us Desert,using field in-situ sampling and laboratory analysis to determine the fixed ammonium and total nitrogen in aeolian sandy soil under different plant communities,and analyzed the influence of the physical and chemical properties of the soil on it.The main results and conclusions are as follows:（1）In terms of the content of fixed ammonium.The content of fixed ammonium in the soil of A.ordosica land was significantly higher than that of bare sandy land and S.psammophila land.The content of fixed ammonium was 23.03±1.88 mg/kg in the A.ordosica land,16.63±0.61 mg/kg in bare sandy land,and 16.82±1.25 mg/kg in S.psammophila land.In terms of total nitrogen content,the total nitrogen content（274.71±8.38 mg/kg）of A.ordosica land was significantly higher than that of bare sandy land（145.99±9.45 mg/kg）and S.psammophila land（197.15±6.74 mg/kg）,and the soil total nitrogen content of S.psammophila land was significantly higher than that of bare sandy land.The average content of soil fixed ammonium in the study area was 18.63 mg/kg,accounting for 8.77%of the soil nitrogen pool.There was a significant positive correlation between soil fixed ammonium and total nitrogen content.（2）There were remarkable differences in soil particle composition among the three sampling plots（P<0.05）.There was a significant positive correlation between the fine particle soil and the fixed ammonium content.In the three sampling plots,the different particle composition had significant effects on the fixed ammonium content（P<0.001）.In bare sandy land,the fixed ammonium content of fine-particle soil（21.46±0.84 mg/kg）was notably higher than that of medium-particle（17.43±0.73mg/kg）and coarse-particle soil（12.27±0.76 mg/kg）.The content of fixed ammonium in soil with medium-particle was remarkably higher than that in soil with coarse-particle.In the S.psammophila land,the fixed ammonium content of fine-grained soil（23.92±1.40 mg/kg）was significantly higher than that of medium-grained（17.02±1.46 mg/kg）and coarse-grained soils（12.83±0.84 mg/kg）,but there was no prominent difference in the content of fixed ammonium between medium and coarse soils.In A.ordosica land,the characteristics of fixed ammonium content in different particle sizes were parallel to those of bare sandy land.The fixed ammonium content of fine-particle,medium-particle and coarse-particle soil was 28.98±1.89 mg/kg,22.74±2.49 mg/kg and 11.90±0.76 mg/kg.There were also dramatic differences in soil water content between the three sampling plots,which showed that the A.ordosica land was the most,the S.psammophila land ranked the second,and the bare sandy land was the least.The soil water content was significantly correlated with the fixed ammonium content.The soil bulk densities were similar across the three sampling plots,and there was no a natable relationship with fixed ammonium.（3）The main soil mineral components of the three sample plots were quartz（Si O₂）,plagioclase（Na[Al Si₃O₈]-Ca[Al₂Si₂O₈]）,orthoclase（K[Al Si₃O₈]）,calcite（Ca CO₃）,anorthite（Ca O.Al₂O₃.2Si O₂）,calcium aluminum silicate（Ca₂Al₂（Si O₃）₅）and albite（Na₂O·Al₂O₃·6Si O₂）.The results of NMDS and Adonis analysis together showed that the mineral composition of the three sampling plots was significantly different.Except for quartz minerals,the content of plagioclase was the highest in the bare sandy land,the content of orthoclase was the highest in the S.psammophila land and A.ordosica land.There was no significant correlations between the fixed ammonium content and the mineral composition of the three sampling plots.Contents of soil ammonium nitrogen and nitrate nitrogen were significantly different among the three sampling plots,which showed that the A.ordosica land was the most,but there was no correlation between them and the fixed ammonium.There was no significant difference in soil p H in the three sampling plots,and there was no natable relationship with fixed ammonium.Our results show that the physical and chemical properties are different among in the bare sandy land,S.psammophila land and A.ordosica land.The shrub species A.ordosica promotes soil refinement,enhances in water content and enriches nutrients,resulting in that the content of fixed ammonium in A.ordosica land is the most.Vegetation mainly affects the content of fixed ammonium by affecting particle composition,soil water content and soil nutrient status.Fixed ammonium is an important component of aeolian soil fertility.Increasing soil fine-grained matter through the establishment of vegetation help to increase the content of fixed ammonium,which is of great significance to the control of land desertification and the improvement of biological productivity.