Study On Soil Aggregate And Its Organic Carbon Stability In The Sandy Plantation Of Northwest Liaoning

There are large number of artificial forest resources in semi-arid area of Northwestern Liaoning Province.Those plantations It play an important role in defending wind and sand,carbon sequestration and its sink enhancement.The distribution and pattern of soil aggregates are important factors affecting the decomposition,and stabilization of soil organic carbon.Evaluating soil structure of artificial forest and studying its soil organic carbon characteristic scientifically is of great significance for forestry development of Northwest Liaoning.However,the study on soil structure and its organic carbon distribution and stability of semi-arid areas are not enough.Therefore,this study selected three typical artificial forests which include Pinus sylvestris plantation(PF),Poplar plantation(PP),Pinus sylvestris and Poplar mixed plantation(PMF)in this area to study its soil aggregates and its organic carbon,and its relationships.Meanwhile,the best grew and oldest Pinus sylvestris plantation(PBF)was also selected as the contrast.The main results are as follows:(1)The soil aggregates of sandy plantations in the Northwestern Liaoning were mainly based on micro-aggregates(<0.25mm),accounting for 54.69%-72.79%of total aggregates,while the macro-aggregates(>0.25mm)were only 27.21-45.31%.Moreover,soil aggregates of the four forest types were dominated by 0.25-0.053mm,and with 56.04%,43.68%,61.56%and 63.18%in PBF,PF,PMF and PP,respectively,and the latter two types were significant higher than the former two types.Soil aggregates of>2mm ranged from 11.97%-30.28%,of which PF was significantly higher than the other three forest types.In addition,soil aggregates of<0.053mm was significant higher than 2-1mm,1-0.5mm and 0.5-0.25mm,and while soil aggregate of 2-lmm only account for 1.69%-3.04%.The soil textures of this four sandy plantations in Northwest Liaoning were similar and with sandy particles of 2-0.02mm ranging from 86.76%-90.46%,while soil particles of<0.002mm and 0.2-0.02nmm were of 6.42%-8.02%and 3.07%-5.22%,respectively.Besides,the differences of soil particles among this four forest types were insignificant.(2)The range of soil organic carbon content in different types of plantations were 6.77-10.26g/kg,and with the sequences of PMF>PF>PBF>PP.The change trends of soil total nitrogen was similar to organic carbon,and with 0.99g/kg,0.89g/kg,0.91g/kg and 0.89g/kg in PMF,PF,PBF and PP,respectively.The organic carbon and total nitrogen in surface soil were significantly correlated,and its correlated coefficient was 0.765(P<0.01).Moreover,,both soil organic carbon and total nitrogen were affected by soil aggregate,especially soil aggregate of<0.053mm,which showed an positively correlation ship with soil organic carbon(R=0.458,P<0.05).The contents of organic carbon in different soil aggregates were different,and with the highest organic carbon content of 10.14-18.34 g/kg and the lowest organic carbon content of 4.36-6.09 g/kg in soil aggregates of 1-0.5mm and 0.25-0.053mm,respectively.The differences in organic carbon of the same soil aggregates between forest types were insignificant.Moreover,the content of total nitrogen in the soil aggregates have the similar variation.The total nitrogen content of soil aggregate of 1-0.5mm was highest,0.86-1.29g/kg,while soil aggregates of 0.25-0.053mm had the lowest of 0.45-0.56g/kg.In addition,the relationship between organic carbon and total nitrogen of the soil aggregates were positive,with the significant correlation coefficients(P<0.01).(3)The content of the surface soil organic carbon and total nitrogen were greatly influenced by the composition of aggregate,especially the content of<0.053mm aggregate,the content of the soil organic carbon increased significantly with the increase of the graded aggregate content(R=0.458,P<0.05).The content of the organic carbon of each graded aggregate was significantly affected by the percentage of the reunite content of the<0.053 mm particle.The content of the organic carbon and total nitrogen in the surface soil and the graded aggregate has a certain relevance,and the content of the organic carbon and total nitrogen in the surface soil and the<0.053mm graded aggregate reached significant correlation(P<0.05).(4)The environmental factors had a significaant impact on the stability of soil organic carbon.The decomposition rate of soil organic carbon(respiration rate meter)of the PBF seed forest showed a significant positive correlation with the soil water content and soil temperature.The range of variation of the soil respiration rate was 423.22-448.41mmol/mol,and it decreased with the decrease of temperature and the soil moisture in the late period of growing season.In conclusion,characteristics and distribution of soil aggregates and its organic carbon in sandy plantation were clarified in Northwest Liaoning Province,and it were of significance and importrance for better understand forest ecosystem carbon cycle and forest sustainable management in this area.