【作者】 刘加彬；

【导师】 吴斌； 张宇清；

【作者基本信息】 北京林业大学 ， 复合农林学， 2014， 博士

【摘要】 土壤是陆地生态系统最大的碳库,其较小幅度的变化就会引起大气C02浓度的变化,进而影响到全球气候变化。因此,如何增加土壤碳库储量就显得极为重要。植物能将部分通过光合作用固定的C02储存在土壤中,这是影响土壤碳库的重要生物途径。我国半干旱区广泛开展的植被恢复,对土壤有机碳库的储量和稳定性的影响尚不明确。另外,最近的研究表明,半干旱区沙地土壤与大气间存在CO2无机交换过程,在此过程中,土壤可以不通过光合作用等生物途径直接以无机的方式吸收大气CO2,这可能是影响土壤碳库的一种非生物途径。然而,由于相关研究处于初级阶段,这一观点并没有被学术界广泛认可。研究分别比较了毛乌素沙地南缘,沙地营造油蒿(Artemisia ordosica)、杨柴(Astragalus mongolicum)和沙柳(Salix psammophila)前后以及退化草地上营造柠条(Caragana microphylla)前后,在0-100cm深度范围内,土壤有机碳、土壤轻组有机碳和土壤重组有机碳的数量变化。另外,研究采用灭活方法排除了土壤呼吸干扰后,对土壤与大气间C02的无机交换过程进行了长期连续地定位观测,分别对土壤无机CO2通量与土壤温度和土壤温度变率间的关系进行了详细分析。在向未经人为干扰的自然土壤喂食13C02后,研究分别量化了储存在土壤固相、气相和逃逸的同位素13C的数量,从而追踪了从大气中进入土壤的C02的去向。研究结果显示：(1)在毛乌素沙地南缘,虽然沙地营造油蒿、杨柴和沙柳样地的土壤总有机碳累积速率分别可达59.7g m-2y-1、56.5g m-2y-1和27.6gm-2y-1,但是在增加的土壤有机碳中,周转速率较快、稳定性较差的轻组有机碳分别占42.7%、80.6%和59.8%。过高的轻组有机碳比例,致使沙地营造灌木累积土壤有机碳的作用受到极大的制约。退化草场营造柠条后,在0-60cm深度范围内,土壤有机碳及其密度组分并无显著变化,而由于深层(60-100cm)土壤中周转速率较慢的重组有机碳减少,退化草场营造柠条后0-100cm深度范围内土壤有机碳流失了9.3%。(2)在毛乌素沙地南缘,以无机形式直接吸收大气C02是沙地土壤固碳的重要途径。通量观测结果表明,沙地土壤与大气间存在C02无机交换过程。在此过程中,沙地土壤能够持续稳定地从大气中吸收C02,净速率高达0.10μmol m-2s-1。同位素示踪结果也表明,未经人为干扰的自然土壤能够吸收大气C02,大部分吸收的13C能以固态形式稳定地保存在土壤固相中；储存在土壤固相、气相和逃逸的13C数量分别占总吸收数量的72.9%、<0.1%和7.1%。土壤与大气间CO2的无机交换对温度的变化反应十分灵敏,其过程与土壤温度变率却存在非常强的正相关关系(γ>0.90,P<0.01),温度的下降和上升分别伴随着土壤吸收和排放大气CO2的过程。在毛乌素沙地南缘,流沙地和退化草地营造灌木,并不是增加土壤碳唯一途径,而沙地土壤以无机形式吸收大气CO2应是其重要的固碳途径之一。这可能会改变该区域土壤仅依靠保存有机碳而实现固碳作用的传统认知,但对这种非生物固碳途径的详细机理,还有待于进一步深入研究。更多还原

【Abstract】 Soil is the largest organic carbon pool in the biosphere, and its subtle fluctuations of such a huge carbon pool may potentially alter the atmospheric CO2concentration and the global climate. So it is very important to increase the current soil carbon pool. Part of CO2captured by photosynthesis can be stored in the soil by plant, which is a significant pattern for compensating the soil carbon pool. Vegetation rehabilitation was being widely established in semi-arid area in China, its effect on storage and stability of soil carbon is still unknown. In addition, soil in desert can absorb CO2from atmosphere, excluding photosynthesis, may be the other pattern for increasing the soil carbon pool. However, it has not been accepted universally, because the related studies locate in the initial stage.We compared the soil organic carbon and its density fractions at the depth of0-100cm after planting Artemisia ordosica, Astragalus mongolicum, Salix psammophila on shifting sand land and planting Caragana microphylla on degraded pasture in Mu Us Desert. After eliminating soil respiration by sterilization, we continuously measured the abiotic soil CO2flux in a long term, and analysised the effect of soil temperature and the rate of change in soil temperature on abiotic soil CO2flux. We quantified the CO2in soil solid phase, vapor phase and escapation, and traced the whereablout of the ’CO2, following adding CO2on natural soil. The conclusions are as follows:In Mu Us Desert, after planting shrubs on sand land, the accumulation rates under A. ordosica, A. mongolicum and S. psammophila were59.7g m·2y-1,56.5g m-2y-1and27.6g m-2y-1, respectively. The proportions of light fraction of soil organic carbon with the fast turnover rate in the increased carbon were42.7%、80.6%and59.8%. The high proportions of light fraction of soil organic carbon in increased soil organic carbon resulted in restricting soil organic carbon sequestration. After planting C. microphylla on degraded pasture, there was no significant difference in soil organic carbon at the depth of0-60cm between shrubland and degraded pasture. The induce of heavy fraction of soil organic carbon with slow turnover rate in the deep layer (60-100cm) results in the9.3%of erosion for the total soil organic carbon within0-100cm depth.In Mu Us Desert, soil in semi-arid area can absorb CO2from atmosphere is an important pattern for increasing the soil carbon pool. There is an abiotic CO2exchange process between soil and atmosphere. During this process, soil from our study site sequesteres atmospheric CO2at a rate of0.10μmol m-2s-1continuously and most of the absorbed CO2is stored in the solid phase. The added13CO2stored in the soil solid phase, in vapor phase and emitted form soil accountted for72.9%,<0.1%and7.1%of the absorbed13CO2, respectively. The abiotic CO2exchange between soil and atmosphere respond to temperature sensitively. The abiotic soil carbon flux was strongly positively correlated with the rate of change in soil temperature (γ>0.90, p<0.01). CO2absorption and emission by soil is driven by the rate of falling and rising of soil temperature, respectively.In Mu Us Desert, vegetation rehabilitation is not the sole way to sequestrate the soil carbon, and abiotic pattern plays an important role in the soil carbon sink. This study may change the traditional standpoint which soil only conserve organic carbon to realize carbon sequestration, while the detailed mechanism of abiotic pattern should be studied in the future study. Our results areis also benefit to assess the capacity of soil carbon sink and identify the carbon cycle in desert ecosystem.更多还原