不同气候条件下土壤有机碳水热响应驱动机制研究

Driving Mechanism of Soil Organic Carbon Response to Increase Hydrothermal Conditions in Different Climatic Regimes

土壤有机碳(SOC)是陆地生态系统中最大的碳库,其对气候变化的响应直接影响全球碳循环。然而,关于土壤有机碳对长期水热变化的响应及其微生物调控机制尚不清楚。借助跨气候带土壤移置试验平台,开展了一项8年的土壤移置试验,其中将寒温带地区(中国海伦)的黑土剖面移置到温带和中亚热带地区(即封丘和鹰潭)来模拟土壤水热条件增加。水热增加提高了植被生物量,地上部植株C/N与微生物酶活性;降低了土壤有机碳、全氮、微生物残体碳(MNC)和活性矿物的相对含量。并且,微生物残体碳对有机碳的贡献也随着水热条件的增加而降低。通过计算ΔMNC/ΔSOC以表征水热增加后微生物残体碳损失速率。结果发现,ΔMNC/ΔSOC随着水热条件的增加而显著增加,封丘地区为72.50%±9.35%,而在鹰潭达到了82.67%±2.37%。重要的是,土壤活性矿物的变化与ΔMNC/ΔSOC呈强烈的负相关关系,突出了矿物保护在调控ΔMNC/ΔSOC发挥的关键作用。这些结果表明,水热增加降低了土壤矿物对微生物残体碳的保护和/或刺激了土壤中微生物对微生物残体碳的利用,通过减少微生物残体碳促进了有机碳的显著损失。

The Mollisol in north-eastern China is rich in organic matter,which supports high crop yields and agricultural production.Soil organic carbon(SOC)is the largest carbon pool in terrestrial ecosystems,which responds to climate change directly affects the global carbon cycle.Understanding the response of SOC to increased hydrothermal conditions is important for soil conservation in the context of global climate change.【Objective】This study aimed to analyze the response of SOC to long-term increasing hydrothermal conditions and their driving factors.【Method】Based on a soil transplantation experiment,large transects of Mollisol in a cold temperate region(Hailun,HL)were translocated to warm temperate(Fengqiu,FQ)and mid-subtropical(Yingtan,YT)regions to simulate the increasing conditions of MAT and MAP.The experiment was started in 2005,soil samples were collected in August 2013.The SOC and microbial necromass C(MNC)were measured to investigate the changes and drivers of SOC after 8 years of increasing hydrothermal conditions.【Results】The results showed that the increased hydrothermal conditions increased plant biomass,litter C/N,and potential activities of hydrolytic enzymes while decreasing the content of SOC,MNC and soil activity minerals.Moreover,the contribution of MNC to SOC also decreased as hydrothermal conditions increased.The ratio of ΔMNC and ΔSOC was calculated to characterize the change in microbial necromass C per unit decrease in SOC,which could be considered a quantitative representation of necromass loss efficiency.ΔMNC/ΔSOC increased with increasing hydrothermal activity,with values of 72.50%±9.35%in FQ and 82.67%±2.37%in YT.The correlation and Random forest analysis showed that ΔMNC/ΔSOC positively correlated with the changes in MAT,MAP,α-D-Glucosidase,β-N-Acetyl Glucosaminidase,plant biomass and Straw C/N,while negatively correlated with the changes in pH,poorly crystalline Fe and Al oxyhydroxides,organically complexed Fe and Al,and exchangeable Ca.Structural equation modeling(SEM)indicated that ΔMNC/ΔSOC increased with increasing hydrothermal conditions,while decreased with soil mineral protection,with standardized coefficients of 0.64 and-0.24,respectively.It was confirmed in the variance partitioning analysis(VPA),which showed that hydrothermal conditions together with changes in soil mineral protection explained 83.69%of the variance in ΔMNC/ΔSOC.The above results indicate that hydrothermal conditions and soil mineral protection play decisive role in regulating ΔMNC/ΔSOC.【Conclusion】In conclusion,long-term increases in hydrothermal conditions reduce the protection of MNC by soil minerals and/or stimulate the utilization of MNC by soil microorganisms.As evidenced by increased soil N limitation that allowed microbes to decompose more MNC and weakened the conservation capacity of minerals for MNC,contributing to the significant loss of SOC by reducing MNC.