【作者】 郑蔚；

【导师】 杨玉盛；

【作者基本信息】 福建师范大学 ， 自然地理学， 2017， 硕士

【摘要】 土壤呼吸作为陆地生态系统和大气间第二大碳通量,其中大约有50%以上来自土壤微生物的矿化作用,在调节全球生态系统碳循环的过程中占有重要地位。但传统对土壤呼吸的研究仅关注表观土壤呼吸,缺乏对深层土壤CO2排放及其微生物响应机制的研究。而深层土壤(深度>20cm)有机碳含量占1m厚度土壤的50%以上,因此,开展深层土壤CO2排放速率的研究及其对未来气候变化(气候变暖和氮沉降)的响应将为准确评估气候变化对全球生态系统碳循环的影响提供科学依据。本文通过在亚热带杉木幼林中模拟土壤增温(W)和氮添加(N)处理,利用Fick’s扩散法则研究不同深度(0—10 cm、10—20 cm、20—40 cm和 40—60 cm)土壤 CO2 排放速率,采用氯仿熏蒸法、酶动力学和磷脂脂肪酸分析法分别测定土壤微生物生物量、碳获取酶(分解纤维素的纤维素水解酶:β—1,4—葡萄糖苷酶(BG),β—D—葡萄糖苷酶(CBH);用于分解木质素的氧化酶:苯酚氧化酶(PHO)和过氧化物氧化酶(PEO))与氮获取酶(乙酰—β—氨基葡萄糖苷酶(NAG))和微生物群落结构,研究气候变化对土壤CO2排放、微生物生物量、群落结构和胞外酶活性的影响。结果显示:(1)对照(CT)处理中,年均表观土壤CO2排放速率为2.36μmolm-2 s-1,深层土壤(20—60 cm)的贡献率为10%。W显著增加表观土壤CO2排放速率(17%),提高深层土壤贡献率(19%)。但是,N处理中表观土壤CO2排放速率显著减少(7%),其中,降低表层土壤(0—20 cm)CO2排放速率(11%),增加深层土壤CO2排放速率(44%)与深层贡献率(16%)。增温和氮添加同时处理(WN)对土壤表观CO2排放速率没有显著影响,但增加深层土壤贡献率(27%)。(2)与CT相比,W显著提高深层土壤微生物生物量碳(MBC)含量,其中20—40 cm和 40—60 cm 的 MBC 分别增加 29%和 51%,但减少 0—10 cm(6%)和10—20 cm(30%)的 MBC。N 显著减少 0—10 cm土壤 MBC(15%),但对深层土壤MBC含量没有显著影响。WN抑制表层土壤MBC(27%)含量。(3)W和N处理均对表层0-10cm土壤微生物群落结构没有显著影响,但改变表层10cm以下土壤微生物群落结构。与CT各土壤层次相比,W和WN提高10cm以下土壤革兰氏阳性菌(G+)的相对丰度,N提高10cm以下土壤革兰氏阴性菌(G-)的相对丰度。(4)W和N均提高表层土壤酶活性,但W降低深层土壤酶活性,而N增强20—40 cm的土壤酶活性,对40—60 cm的土壤酶活性无显著的影响。在0—10 cm和 10—20 cm,W 和 N 均显著提高 BG(26%—44%)、CBH(18%—66%)、NAG(13%—74%)、PHO(32%—69%)和 PEO(18%—20%)。在 20—40cm,W 降低BG(28%)、CBH(32%)、NAG(32%)和 PEO(13%),N 提高 BG(5%)和 CBH(16%),降低 PHO(50%)和 PEO(12%)。在 40—60 cm,W 降低 BG(31%)和PHO(14%),N 降低 BG(58%)、CBH(53%)、PHO(59%)和 PEO(32%)。研究表明,增温和氮添加均增加深层土壤CO2排放,但氮添加降低表层土壤CO2排放,增温则提高表层土壤CO2排放。此外,增温提高表层土壤酶活性和深层微生物生物量,降低表层土壤微生物生物量和深层土壤酶活性。因此,0-20 cm的土壤CO2排放主要受微生物胞外酶活性驱动,20—60cm则主要受微生物生物量驱动。综上所述,在未来气候变暖和N沉降背景下,深层土壤的固碳能力降低可能成为重要碳源,而且表层土壤与深层土壤的C02排放受不同的机制调控,增强有关深层土壤碳动态对气候变化响应的相关研究就显得尤为迫切。更多还原

【Abstract】 As the second largest carbon(C)flux between the atmosphere and terrestrial ecosystems,soil respiration(Rs)plays vital roles in regulating ecosystem C cycling.More than 50%of soil respiration from the microbial mineralization of soil organic matter(SOM).At present,the research of soil carbon emissions mostly focus on surface soil,while soil carbon emissions and the response of microorganisms at different depths are not well knowa Although carbon concentrations decline with soil depth in profiles,the total contribution from subsurface soil layers(below 30 cm soil depth)can be 50%of the total organic C in a 1 m profile.In order to estimate and predict the impact of climate changes on ecosystem C cycle accurately,it’s necessary to gain more knowledge regarding the C emissions and microorganisms in subsurface soil.To elucidate the effect of.global climate change on soil carbon oxidate(CO2)emissions,microbial biomrass,cormmunity structure and extracellular enzyme activities,we simulated soil warming(W)and nitrogen addition(N)at a young Chinese fir mesocosm The Fick’s laws of diffusion was used to estimate soil CO2 flux at different depths(0-10 cm,10-20 cm,20-40 cm and 40-60 cm).Microbial biomass C and nitrogen was monitored by chloroform fumigation extraction.Microbial community composition and extracellular enzyme activities were assessed by phospholpid fatty acids(PLFAs)analysis and kinetics of enzymatic activities,respectively.Enzyme activities involve the C-acquire(β-glucosidase(BG),β-D-cellobiosidase(CBH),phenoloxidase(PHO)and peroxidase(PEO))and nitrogen-acquire(N-acetyl-β-D-glucosaminidase(NAG)).(1)Results showed that the annual average of CO2 efflux was 2.36 μmol m-2 S-1 in control treatment,and subsurface soil contributed 10%of soil CO2 production W significantly increased surface soil CO2 fluxes(17%),improved the contribution of subsoil(20-60 cm)to soil CO2 emission(19%).But N decreased surface soil CO2 fluxes(7%),including a reduction of CO2 production in the topsoil(11%in the 0-20 cm layer),and an increase in subsoil(44%).However,the combination of nitrogen addition and soil warming(WN)did not affect surface soil CO2 fluxes,increased the contribution of CO2 production in subsoil(27%)instead.(2)W significantly increased microbial biomass carbon(MBC)at depths of 20-40 cm(29%)and(51%)in comparison to CT,whiling decreased MBC at depths of 0-10 cm and 10-20 cm by 60%and 30%,respectively.N reduced MBC by 15%at 0-10 cm layer,but did not affect MBC at others layers.WN inhibited MBC(27%)at 0-10 cm layer.(3)W and N did not affect microbial communities at 0-10 cm soil layer,but significantly modified microbial communities below 10 cm soil depth.W and WN significantly enhanced the abundances of Gram-positive bacteria below 10 cm depth in comparison to CT.However,N improved the abundances of Gram-negative bacteria below 10 cm depth.(4)W and N enhanced enzyme activities in topsoil Nevertheless,W inhibited enzyme activities in subsoil,N stimulating enzyme activities at 20-40 cm layer.In 0-10 cm and 10-20 cm layers,W and N dramatically improved BG(26%-44%),CBH(18%-66%),NAG(13%-74%),PHO(32%-69%)and PEO(18%-20%).In 20-40 cm layer,W induced a reduction in BG(28%),CBH(32%),NAG(32%)and PEO(13%).While N stimulated BG(5%)and CBH(16%),inhibited PHO(50%)and PEO(12%).In 40-60 cm layer,W significantly decreased BG(31%)and PHO(14%)as well as N decreased BG(58%),CBH(53%),PHO(59%)and PEO(32%).This finding illuminated that warming and nitrogen addition all stimulated the CO2 emission in subsoil;nitrogen addition decreased it in topsoil,while warming increased it in topsoil.In the other hand,warming stimulated extracellular enzyme activities in subsoil and microbial biomass in topsoil,but suppressed microbial biomass in topsoil and extracellular enzyme activities in subsoil.In consequence,soil enzymes may drive CO 2 production in 0-20 cm soil depth,so does microbial biomass in 20-60 cm soil depth.In summary,the capacities of carbon storage in subsoil weakens in the context of global climate changes,which is important as a source for CO2 in the global carbon cycle.The mechanisms controlling C dynamics are the different in topsoil and subsoil.Our results suggest that the validity of predictive future soil C dynamics would be improved by the inclusion of both soil organic carbon mineralization and microorganisms response to global climate changes in subsoil.更多还原