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Effects Of Enclosure On Soil And Organic Carbon Decomposition Characteristics Of Pinus Sylvestris Var. Mongolica Plantation On Sandy Land

Posted on:2020-08-21Degree:MasterType:Thesis
Country:ChinaCandidate:L T MaFull Text:PDF
GTID:2370330590488817Subject:Agriculture
Abstract/Summary:PDF Full Text Request
Pinus sylvestris var.mongolica plantation is an important part of the Three Northern Protection forest in the semi-arid region of Northwest Liaoning Province,it plays a vital role in wind and sand control and carbon sequestration and carbon sink enhancement.According to the investigation,there are many kinds of human disturbance activities in Pinus sylvestris var.mongolica plantation in the this area,such as grazing,tillage and harvesting,which have a certain impact on the local forest ecosystem and become an important factor limiting the development of Pinus sylvestris var.mongolica plantation.Soil organic carbon?SOC?is an very important part of global carbon pool.The decomposition of SOC takes the form of soil respiration,while CO2released by soil respiration plays an important role in regulating global carbon balance.In this study,the soil of Pinus sylvestris var.mongolica plantation in sandy land of Northwest Liaoning Province was studied as the research object,two different treatments were carried out,that is,exclosed and unexclosed.The effects of exclosure and unexclosed on soil respiration rate,soil organic carbon content,soil total nitrogen content,soil aggregate composition and organic carbon content of Pinus sylvestris var.mongolica plantation in sandy land were studied by analyzing the soil respiration rate,soil organic carbon content,total nitrogen content,soil aggregate composition and organic carbon content of Pinus sylvestris var.mongolica plantation in sandy land.The main conclusions are as follows:?1?After the treatment exclosure,the total percentage of 0.053-0.25mm and0.25-0.5mm aggregates accounted for 53.17%of soil,while it was 85.65%in unexclosed treatment soil.Besides,the organic carbon content of 2-5mm and>5mm aggregates in unexclosed treatment was significantly higher than that in exclosed treatment.It shows that exclosure treatment can reduce both the percentage content of small size aggregates and the organic carbon content of large size aggregates.?2?Both contents of soil organic carbon and total nitrogen were the highest in 0-10cm and the lowest in 40-50 cm,and the contents of 0-10cm layer in exclosed plot was higher than unexclosed treatment,while the other soil layer contents were higher in unexclosed treatment.It indicated that exclosed treatment would strengthen the surface accumulation of soil organic carbon and total nitrogen.The highest content of organic carbon and total nitrogen was 12.13g/kg and 0.77g/kg in exclosed treatment.The highest content of organic carbon and total nitrogen was 9.97g/kg and 0.59g/kg in unexclosed treatment.Soil C/N in different treatment was the lowest in 10-20cm layer?14.84 in exclosed treatment,34.03 in unexclosed treatment?and the highest in40-50cm layer?15.01 in exclosed treatment and 40.50 in unexclosed treatment?.After exclosured,soil microbial diversity index increased except Shannon index,but did not reach significant level compared with unexclosed treatment?p>0.05?.?3?The diurnal?normal conditions and after rainfall?,monthly and inter-annual changes of soil respiration rate in exclosed treatment were lower than those in unexclosed treatment,indicating that exclosed treatment could reduce soil respiration rate.The peak time of diurnal variation of soil respiration rate was different under normal conditions in different treatment treatment.When the largest soil respiration rate was 5.33?mol·m-2·s-1appeared at 08:00 in exclosed treatment,it was7.35?mol·m-2·s-1at 10:00 in unexclosed treatment.The change range of soil respiration rate after rainfall in exclosed treatment was 4.73?6.91?mol·m-2·s-1,and that in unexclosed treatment was 6.17?10.40?mol·m-2·s-1.The monthly variation of soil respiration rate in different treatment was the highest in the growing season?July and August?in the whole year.From May 2017 to December 2018,continuous measurements were carried out on two treatments.The overall soil respiration rate in2018 was higher than that in 2017,and in 2017,the soil respiration rate in exclosed treatment was higher,and in 2018,the soil respiration rate in unexclosed treatment was higher,indicating that the soil respiration rate would change with the change of exclosed years.?4?It was found that the correlation between soil respiration rate and soil temperature and moisture would change after enclosure treatment.The larger the time scale,the higher the degree of change.However,the correlation between soil respiration rate and air temperature and moisture was lower.In different treatments,the diurnal variation of soil respiration rate under normal conditions was significantly correlated with soil moisture.In different treatment,the change of soil respiration rate after rainfall was significantly correlated with soil temperature and air temperature.In exclosed treatment,the monthly variation of soil respiration rate was significantly correlated with soil temperature,while in unexclosed treatment,the monthly variation was significantly correlated with soil temperature,moisture and air humidity.The inter-annual variation of soil respiration rate in exclosed treatment was significantly correlated with soil temperature,air temperature and humidity,while that in unexclosed treatment was significantly correlated with soil temperature,water and air humidity.In conclusion,exclosure changed soil structure and physical and chemical properties,reduces small-scale aggregates,increases large-scale aggregates,increased the contents of organic carbon and total nitrogen in surface soil and microbial diversity index,on the other hand,it decreased the soil respiration rate,and the correlation-ship between soil respiration rate and its environmental factors changed at different time scales after exclosure treatment.It provide scientific evidence for better utilization of forest soil resources in this area.
Keywords/Search Tags:exclosure, sandy land, Pinus sylvestris var.mongolica, soil respiration, soil aggregate
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