| As an important part of terrestrial ecosystem,the sandy land（desert）has potential carbon sink space and function.Due to severe wind erosion and desertification,poor soil,low productivity and single ecosystem structure,carbon sequestration ability is weak in the natural state.Artificial vegetation construction and sustainable restoration are effective measures to promote the formation and development of soil organic carbon pool and enhance the carbon sink capacity of ecosystem.In view of the unclear mechanism of the impact of artificial vegetation restoration on the formation and development of soil organic carbon pool and soil respiration in Mu Us sandy land during the process of desertification reversion,this paper uses the method of space instead of time,the artificial shrub forests（hereinafter referred to as YC1,YC2,YC3）of windbreak and sand fixation of Hedysarum laeve restored for 11a,20a and 32a after afforestation in Wushen Banner of Ordos City as the experimental objects,to study the characteristics of vegetation restoration,soil organic carbon accumulation,and respiratory evolution of artificial shrublands,and explore the impact of biological and abiotic environmental factors on soil carbon pool and respiration,Thus,the response mechanism of organic carbon accumulation and respiration in sandy soil to artificial vegetation restoration is explained.The results of this study will provide the basis for the evaluation and prediction of soil carbon pool,the study of soil and ecosystem carbon balance,and the practice of carbon sink enhancement management in the process of forest and grassland ecological construction in sandy land.The main results are as follows:1.With the increase of afforestation years in Hedysarum laeve shrub forest,the main growth indicators such as shrub cover and biomass,as well as the indexes such as herb cover,species composition,density and biomass,litter biomass and underground root biomass increased significantly in Mu Us Sandy land.The shrub cover of the restored 11a,20a and32a Hedysarum laeve shrub forest was 77.5%,93.2%and 97.0%,and the biomass was2258.13kg·hm-2,2675.83kg·hm-2 and 3443.4kg·hm-2,respectively.The available stock of branches and leaves per unit area were 1096.9kg·hm-2,2951.7kg·hm-2 and 3968kg·hm-2,respectively.The root biomass per unit area was 2602.2,6651.6 and 9072.9 kg·hm-2.In addition,the contents of soil organic matter,total nitrogen,total phosphorus,total potassium and other major nutrients were also significantly increased,and vegetation restoration had an obvious effect on the quality of aeolian sand.2.With the increase of Hedysarum laeve shrub forest vegetation restoration years,soil total organic carbon,organic carbon density,organic carbon physical component,organic carbon scientific component and biological component carbon content continued to increase.Among them,the 0-60cm soil layer of 11a,20a and 32a was restored:The average content of soil total organic carbon was 1.934g·kg-1,2.591g·kg-1,4.135 g·kg-1,and the total organic carbon density was 1.14 kg·m-2,1.63kg·m-2,2.62kg·m-2.The content of light and recombinant organic carbon of physical components were 1.409 g·kg-1 and 0.525 g·kg-1,1.951 g·kg-1 and 0.676 g·kg-1,2.853 g·kg-1 and 0.863 g·kg-1,respectively.The contents of active and inert organic carbon in chemical components were 0.06 g·kg-1 and 1.886 g·kg-1,0.087 g·kg-1 and 2.523 g·kg-1,0.140 g·kg-1 and 4.028 g·kg-1,respectively.The contents of biological components were 3.75 mg·kg-1,7.01 mg·kg-1 and 10.983 mg·kg-1,respectively.In soil organic carbon,the proportion of recombination and inert components is higher,and the proportion increases gradually with the increase of vegetation restoration years,and the stability of organic carbon pool is enhanced.3.At the annual scale,the Hedysarum laeve shrub forest diurnal variation of soil respiration rate in both growing and non-growing seasons followed the"single peak"curve,which was consistent with the diurnal variation of soil temperature.The highest value occurred between 14:00 and 16:00,and the lowest value occurred between 03:00 and06:00.The seasonal variation of soil respiration rate also showed a"single peak"curve,with the highest value appearing in July-August in the peak growth season and the lowest value appearing in January in winter.The average annual soil respiration rate of YC1,YC2 and YC3 plots were 0.491μmol·m-2·s-1,0.833μmol·m-2·s-1 and 1.313μmol·m-2·s-1,respectively.Compared with the average of 0.1445μmol·m-2·s-1 in unforested sandy land（CK）,Vegetation restoration significantly enhanced respiration（P<0.01）.At the annual scale,soil heterotrophic respiration accounted for 63.1%to 94.6%of total respiration,and the proportion in non-growing season was higher than that in growing season,and the proportion continued to increase with the increase of forest age.The soil respiration of the Hedysarum laeve shrub forest had obvious spatial heterogeneity.In the growing season,the negative slope was higher than the sunny slope,and the lower slope was higher than the upper slope.The opposite is true in the non-growing season.The total annual respiration fluxes of poplar and firewood forest in 11a,20a and 32a were 183.36 g C·m-2,310.83 g C·m-2 and 489.92g C·m-2,respectively,with heterotrophic respiration accounting for 76.2%-82.3%and autotrophic respiration for 17.7%-23.8%.4.The results of correlation analysis and multiple regression analysis showed that the continuous accumulation of aboveground vegetation biomass,dead root biomass and litter stock contributed a lot to the increase of soil total organic carbon and its components in Mu Us Sandy land Hedysarum laeve shrub forest,and the contribution of dead root biomass was the largest.The sustainable restoration of vegetation is the prerequisite for the formation and development of soil organic carbon pool.5.At the daily scale,soil total respiration and heterotrophic respiration were very significantly correlated with soil temperature 0-5cm and 5-10cm（P<0.001）,and significantly correlated with soil temperature 10-20cm（P<0.05）,while autotrophic respiration rate was not significantly correlated with soil temperature at each layer（P>0.05）.At the seasonal scale,soil total respiration rate,heterotrophic respiration rate and autotrophic respiration rate were very significantly positively correlated with soil temperature in the 0-20cm soil layer（P<0.001）,and the correlation between soil temperature and respiration rate in the 5-10cm soil layer was the strongest.Soil temperature could explain 83%-92.5%of total respiration,81.2%-85.1%of heterotrophic respiration and 60%-70%of autotrophic respiration.At the seasonal scale,soil respiration rate was positively correlated with water content in 0-5cm,5-10cm and 10-20cm soil layers（P<0.001）.The effect of soil temperature could explain 55.8%-75.2%of respiration,and the effect of soil moisture could explain 24.8%-45.2%.Compared with the single-factor fitting model,the nonlinear two-factor complex model(Rs=aeb TWc)can better reflect the effect of soil temperature and water interaction on respiration.6.At the interannual scale,Hedysarum laeve shrub forest vegetation coverage,community aboveground biomass,subsurface root biomass,litter biomass,soil microbial quantity and nutrient content were the main biological and abiotic factors affecting respiration.With the growth of forest age,the above factors had a positive driving effect on soil respiration,so that soil respiration continued to strengthen.Multiple linear regression model showed that soil organic matter content and aboveground biomass were the dominant factors affecting soil respiration during the growing season.Dead root biomass was the dominant factor affecting soil respiration in non-growing season.In conclusion,vegetation restoration of Hedysarum laeve shrub forest in Mu Us Sandy Land promoted the formation and development of soil organic carbon pool,and soil carbon storage function was continuously enhanced.At the same time,vegetation restoration drives soil respiration,which increases the rate and emission of CO2 from soil to the atmosphere.The results provided a warning for strengthening the management and accumulation of plantation vegetation in sandy land under the background of"double carbon... |
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