Distribution Characteristics Of Soil Organic Carbon Associated With Fe And Al Minerals Under Different Vegetation Restoration In Karst Area

Iron and aluminum minerals are important factors affecting the stability and accumulation of soil organic carbon.In order to explore the contribution of different soil organic carbon and iron-aluminum mineral complexes to the stability and accumulation of organic carbon during vegetation restoration,the cultivated land in karst area was used as the control（CK）,and the grassland restoration years were 5 a:C5,10 a:C10,15 a:C15,20 a:C20;shrub recovery period 5 a:G5,10 a:G10,15 a:G15,20 a:G20;the soil of garden restoration years 5 a:Y5,10a:Y10,15 a:Y15 was studied.The effects of different vegetation restoration on soil crystalline iron(Fe _DH),crystalline aluminum(Al _DH),crystalline iron-aluminum bound organic carbon(SOC_DH),short-range ordered iron(Fe _HH),short-range ordered aluminum(Al _HH),short-range ordered iron-aluminum bound organic carbon(SOC_HH),complexed iron(Fe _PP),complexed aluminum(Al _PP),iron-aluminum complexed organic carbon(SOC_PP)and the molar ratio of carbon to iron and aluminum（C/M）were analyzed,and the ways to promote organic carbon accumulation were revealed.The results of the study are as follow:（1）SOC_DH,SOC_HH and SOC_PP increased with the increase of vegetation restoration years.The size of the three components of carbon under the three vegetation restorations was:SOC_PP>SOC_DH>SOC_HH.SOC_DH content reached the peak at 0～5 cm of C10,G20 and Y5,which were8.25±0.24,7.42±0.23 and 8.57±0.34 g/kg,respectively.The SOC_HH content reached the peak at 0～5 cm of C15,G5 and Y15,which were 5.49±0.24,5.24±0.07 and 5.61±0.07 g/kg,respectively.SOC_PP content reached the peak at 0～5 cm of C10,G15 and Y5,which were 8.68±0.35,13.38±0.27 and 7.70±0.15 g/kg,respectively.The SOC_DH content under the three restorations was grassland>shrub>garden,SOC_HH:grassland>garden>shrub,SOC_PP:shrub>grassland>garden.（2）The contents of Fe _DH,Fe _HH and Fe _PP increased with the increase of vegetation restoration years,and Fe _DH reached the peak at C10,G5 and Y10,which were 9.08±0.61,11.97±1.21 and 9.41±0.66 g/kg,respectively.Fe _HH peaked at C10,G15 and Y15,which were 3.00±0.11,4.16±0.06 and 3.86±0.32 g/kg,respectively.Fe _PP peaked at C5,G5 and Y5 with 8.14±0.52,5.47±0.16 and 3.85±0.08 g/kg,respectively.The content of Fe _DH under 3 vegetation restoration was:shrub>garden>grassland,Fe _HH:shrub>grassland>garden,Fe _PP:grassland>shrub>garden.（3）Except for Al _HH,the aluminum content increased with the increase of vegetation restoration years.Al _DH peaked at C5,G5 and Y10 with 8.89±0.20,7.87±0.85 and 5.49±0.76g/kg,respectively.Al _HH reached the maximum at C5,and decreased with the increase of restoration years under shrub and garden restoration.Al _PP peaked at C10,G15 and Y5,which were 3.79±0.22,3.50±0.13 and 1.84±0.01 g/kg,respectively.The content of Al _DH under 3vegetation restoration was:garden>shrub>grassland,and Al _HH was:garden>grassland>shrub;Al _PP:shrub>grassland>garden.（4）In addition to Al _HH,the organic carbon and iron-aluminum mineral complex showed surface aggregation under the restoration of 3 vegetation.The main influencing factor of organic carbon and iron-aluminum mineral complex under grassland and shrub restoration is SOC,while the garden is TN.（5）SOC_DH,SOC_HH and SOC_PP all promoted the accumulation of soil organic carbon under3 vegetation restoration,and the accumulation of organic carbon in soil was driven by the interaction between crystalline iron-aluminum minerals and organic carbon,the interaction between short-range ordered iron-aluminum minerals and organic carbon,and the organic-iron-aluminum complex.The SOC content and annual growth under the three vegetation restorations were the largest in shrub vegetation.The distribution ratio of SOC_PP and the annual growth of SOC_PP were the largest in shrubs,indicating that shrubs were most conducive to promoting the stability and accumulation of soil organic carbon.In summary,different vegetation restorations can promote the content of soil organic carbon and iron-aluminum mineral complex to a certain extent,and shrubs are more conducive to promoting the stability and accumulation of soil organic carbon.Shrub restoration is a more suitable ecological restoration model in karst areas.