Efficiency And Mechanism Of Soil Inorganic Carbon Accumulation Following Vegetation Restoration Of Shelter Forest In Mu Us Sandy Land

The soil inorganic carbon pool following vegetation restoration in desert region may be a potential carbon sink and also a key component of understanding the carbon cycle process of terrestrial systems.Therefore,we selected the quick sand,semi-fixed sandy land,15?54a shrub and arbor windbreak and sand-fixing forest of Mu Us sandy land as the research objects.The evolution characteristics of soil inorganic carbon?SIC?and water-soluble inorganic carbon?WSIC?and the accumulation and distribution of SIC in soil sand,silt and clay were analyzed during the restoration of sand-fixing forest;The content and?¹³C of SIC and soil organic carbon?SOC?was determined to analyzed the relationship between SOC and SIC and its transfer law,the proportion of Pedogenic carbonates in SIC was obtained;the soil physical-chemical factors were determined to revealed the factors affecting the accumulation of soil inorganic carbon,This study deeply understand the ecological restoration process of semi-arid desertification and provides scientific basis for the carbon cycle mechanism.The main results are as follows:?1?Studies on SIC content,density evolution and its component distribution show that:The content of SIC and WSIC in shelter forest exhibit an increasing trend with the age of the forest.From 0?10 cm to 80?100 cm,the SIC content of the 54a shrub forest was 5.04 and 4.47times that of the quicksand,and the 54a arbor forest was 29.44 and 11.30 times the quicksand.The WSIC of shelter forest is significantly higher than quicksand and the difference between soil layers is not significant.Compared to the quicksand,the average WSIC increment of 15-54a shrub forest was 4.17?12.01 mg/kg,and the increment in 26-54a arbor forest was4.69?16.96 mg/kg.The density of SIC and WSIC and their content showed a similar pattern,the SIC density from quicksand to 54a shrub forests in 0?10 cm and 0?100 cm layers increased by 0.22 Mg/hm²and 1.59 Mg/hm²,respectively,54a arbor forest increased 1.4 Mg/hm²?7.16Mg/hm²,respectively.The SIC in sand,silt,and clay of arbor forest in 0?10 cm and 10?20 cm increased significantly with the forest age,the largest concentration of SIC in all sizes particles of shrub is at 46a.The maximum and minimum components of SIC contributed to total SIC in shelter forestare silt inorganic carbon and water-soluble inorganic carbon,with their average contribution ratios of 59.98%and 1.32%,respectively.?2?Studies on the correlation between SOC and SIC and its transfer laws in sand-fixing forests show that:There is a positive correlation between SIC and SOC of fixing-sand forest in bulk soil and its different size particle,and WSIC has the greatest correlation with SOC.The?¹³C-SIC was significant among different years-old shrubs,in order of 54a shrubs?-4.31‰?<quicksand?-3.87‰?<26a shrubs?-3.24‰?<46a shrubs?-2.51‰?,54a arbor forest have highest?¹³C-SIC?-3.47‰?,26a arbor forest?-3.91‰?are similar to quicksand.There was no difference in?¹³C-SOC between shrub and arbor forests,with an average of-26.83‰.During the process of transferring SOC to SIC in sand-fixing forest,CO₂ was fixed in the soil to form PC.The amount of fixed soil CO₂ and carbon transfer from SOC to SIC in the shrub forest increased with stand ages?46a?,decreased slightly in 54a forest,but continued to increase in the arbor forest.The fixed soil CO₂content of quicksand,26a,46a,and 54a shrub forests was 2.88,6.60,28.95,and 27.14 mg/kg,respectively,and the carbon transfer from SOC to SIC was 0.02,0.43,7.23,6.24 mg/kg,26a,46a,54a arbor forest fixed soil CO₂amount were1.17,16.16,173.48 mg/kg,the carbon transfer amount of SOC to SIC was 0.05,2.51,50.17mg/kg.The ratio of fixed CO₂ from the quicksand to the 54a shelter forestwas decreased from99%to 52%in the atmosphere,and increased from 1%to 48%in the soil respiration.From quicksand to 54a shrubs and arbor forests,the proportion of PC to SIC increased from 30%to64%and 73%,and the increment of PC content was 118.48 mg/kg and 788.55 mg/kg,respectively.?3?Studies on soil physical and chemical factors in sand-fixing forests and their effects on SIC indicate:The vegetation restoration of shelter foresthas a significant effect on the physical and chemical properties of 0-20 cm soil.There is no significant difference in p H value and total potassium content with the increase of forest age.The soil bulk density is significantly reduced.26?54a arbor forest soil cation exchange capacity,clay content,total nitrogen,available nitrogen,total phosphorus,available phosphorus and available potassium are 1.62?1.89 times,1.08?1.82 times,1.62?7.08 times,3.48?4.42 times,1.63?1.23 times,1.06?2.78 times,1.59?5.72 times of quicksand land respectively;26?54a arbor forest soil cation exchange capacity,clay content,total nitrogen,available nitrogen,total phosphorus and available potassium content are 1.63?2.02 times,1.02?1.87 times,2.17?7.42 times,2.79?3.58times,1.04?1.45 times,1.65?4.10 times of quicksand respectively.From quicksand to 54a shrub forest,Ca²⁺and Mg²⁺increased by 27.66 and 1.82 mg/kg,respectively,and from quicksand to 54a arbor forest increased by 41.61 and 1.41 mg/kg,respectively.Redundancy analysis shows that SIC and SOC are positively correlated with Ca²⁺,Mg²⁺,total nitrogen,clay content,cation exchange capacity,available potassium,available phosphorus,available nitrogen,and total phosphorus,among which SIC has the strongest correlation with Ca²⁺.The amount of cation exchange and available potassium have the strongest correlation with SOC.In summary,the cumulative effect of SIC on the vegetation restoration process of sand fixing forest in Mu us Sandy Land in northern Shaanxi is obvious.SIC is mainly stored in soil silt.Vegetation restoration is beneficial to the formation of soil PC,and also promotes the transfer of SOC to SIC.Ca²⁺is the key driving factor of soil inorganic carbon accumulation in windbreak and sand-fixing forests.