Characteristics and its influencing factors of forest soil dominant bacterial community in different elevations on the southern slope of Daiyun Mountain, Fujian Province of eastern China
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摘要:目的 探讨土壤细菌群落在戴云山保护区不同海拔梯度(900 ~ 1 500 m)分布特征,为理解海拔影响森林土壤结构和功能提供理论依据。方法 基于高通量测序探讨不同海拔土壤细菌群落组成及多样性,并分析环境因子对土壤优势细菌群落结构的影响过程。结果 (1)随海拔升高,土壤全磷含量总体呈逐渐递减;土壤有效磷含量整体呈单峰模式;土壤全碳和全氮含量呈双峰变化趋势。(2)不同海拔中土壤细菌优势菌门为变形菌门、酸杆菌门和放线菌门(相对丰度 > 10%)。(3)不同海拔梯度土壤细菌多样性指数如物种数、Chao1指数、Shannon-Wiener多样性指数和ACE指数沿海拔梯度呈先上升后下降的趋势,均在1 100 m处达到峰值,且达到显著水平(P < 0.05)。(4)微生物共现网络分析表明戴云山不同海拔土壤优势细菌群落具有明显模块化结构,关键类群包括变形菌门、酸杆菌门、放线菌门、拟杆菌门和疣微菌门的部分属,其中变形菌门的细菌关键类群最多。结论 海拔、坡度、pH值、土壤全氮、水解氮和土壤有效磷是驱动不同海拔森林土壤优势细菌群落结构及多样性的主要因子。Abstract:Objective We aimed to explore the distribution characteristics of forest soil bacterial communities in different elevations (900−1500 m) in Daiyun Mountain, Fujian Province of eastern China.Method We used high-throughput sequencing to study the composition and diversity of soil bacterial communities at different elevations, and analyzed the effect of environmental factors on soil dominant bacterial communities.Result (1) With the increasing of elevation, the content of soil total phosphorus showed a monotonic decreasing trend, the content of soil available phosphorus showed an unimodal trend, and the contents of soil total carbon and nitrogen presented a bimodal distribution trend. (2) In Daiyun Mountain, the dominant phyla bacteria in soil were Proteobacteria, Acidobacteria and Actinobacteria (relative abundance > 10%). (3) The soil diversity indices, such as species number, Chao1 index, Shannon-Wiener index and ACE index, increased first and then decreased along the elevation gradients, reaching a maximum at 1100 m. (4) The co-occurrence network analysis further indicated that soil dominant bacterial community had an obviously modular structure at different elevations of Daiyun Mountain. The keystone taxa included the genera from the phylum of Proteobacteria, Acidobacteria, Actinobacteria, Bacteroidetes and Verrucomicrobia, and the phylum of Proteobacteria had the maximum keystone genera.Conclusion The elevation, slope, pH value, soil total nitrogen, hydrolysable nitrogen, and available phosphorus are the main factors affecting the forest soil dominant bacterial community structure and diversity at the different elevations of Daiyun Mountain.
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活性碳纤维作为一种新型吸附材料,以比表面积高、吸附容量大、吸附脱附速率快、耐热耐酸碱等优点,被广泛应用于环境净化、催化剂载体、储能材料等领域[1-2]。活性碳纤维的孔隙结构是影响各项性能的关键因素。在活化过程中,碳基体与活化剂之间的反应导致大量孔隙的生成,而不仅仅是纤维表面的烧失,这表明活化反应具有选择性。作为活化前驱体,炭化过程的产物碳纤维由乱层石墨多晶结构组成[3],其微观晶体结构对活化孔结构形成具有重要的影响。在活化过程中,活化剂优先侵蚀碳纤维的无定形区、晶胞缺陷处、晶界处和初始孔隙处,而后进入有序化较高的微晶区域。上述位置的碳基体以不同的速率与活化剂反应,从而形成孔洞,随着活化继续进行,孔结构进一步变深、扩宽[4-5]。
近年,为缓解石化资源危机,利用林业生物质资源制备活性碳纤维受到了广泛关注。其中,基于木材液化物制备的活性碳纤维具有丰富的孔隙结构[6-7],且在污染物净化[8-10]、抗菌性能[11-14]、电化学特性[15-17]等方面表现出优良的性能。目前,针对木材液化物纤维在炭化、活化过程中微晶结构的变化已进行了一系列研究。马晓军等[18]研究表明:800 ~ 1 000 ℃炭化温度下,木材液化物原丝形成大量多苯稠环结构,碳网重组并进行有序化生长,石墨化程度显著提高。赵广杰[19]指出:木材苯酚液化物原丝分子网状交联结构在300 ~ 600 ℃炭化过程中被破坏并发生重排,进而形成初步的碳网结构;700 ℃以上,碳网继续生长,聚合度逐渐提高。Liu等[20]指出:较高的活化温度或较长的活化时间会导致木材液化物活性碳纤维乱层石墨结构的破坏,使其结晶化程度降低。Li等[21]研究了CO2活化过程中木材液化物活性碳纤维的微晶结构随着活化温度升高的变化规律,由微晶尺寸数据推断600 ℃之前微晶结构正在经历芳环结构向多层石墨堆叠结构的转变,而600 ℃以后,石墨网有序化程度逐步提高,乱层石墨晶体结构逐渐稳定,晶胞尺寸逐渐增大。Liu等[22]比较了利用木材液化物原丝和碳纤维分别制备的活性碳纤维微晶结构的区别,得出:前者具有更大的晶体尺寸和更致密的乱层石墨结构,而后者微孔数量较多,微孔孔径较大。Ma等[23]通过添加木炭制备中孔木材液化物活性碳纤维,微晶结构研究表明:木炭的添加打断了活性碳纤维的碳平面,限制了乱层石墨片层的生长和排列,进而影响了乱层石墨片层的发育和有序堆积,导致了中孔结构的增加。Liu等[24]研究指出:木材液化物活性碳纤维中孔结构源于纤维缺陷的扩大,中孔结构的形成加剧了乱层石墨微晶结构的瓦解。以上研究充分证实了不同炭化与活化过程中纤维微晶结构变化与孔结构形成的相关性,然而尚未详细阐明微晶结构演变对孔结构形成的作用及影响规律。
为进一步揭示木材液化物活性碳纤维孔结构形成机制,本研究通过控制炭化温度获得具有不同微晶结构的杉木液化物碳纤维,并以水蒸气作为活化剂在800 ℃下进行活化,采用元素分析仪、X射线衍射仪和氮气吸附仪分别考察了随着活化时间延长,杉木液化物活性碳纤维元素组成、微晶结构和孔结构的变化,探讨了微晶结构演变和孔结构形成两者之间的作用机制及影响规律。
1. 材料与方法
1.1 材 料
将杉木(Cunninghamia lanceolata)木粉粉碎至20 ~ 80目,并在(105 ± 5) ℃下干燥24 h。苯酚(分析纯)为北京笃信精细制剂厂生产。磷酸(分析纯),质量分数37%,北京化工厂生产。六次甲基四胺(分析纯)为西陇化工股份有限公司生产。甲醛(分析纯),质量分数37%,广东光华科技股份有限公司生产。盐酸(分析纯),质量分数37%,北京化工厂生产。
1.2 研究方法
1.2.1 杉木苯酚液化物的制备
将20 g杉木木粉与苯酚按质量比1∶6混合加入三口烧瓶中,并加入苯酚质量8%的磷酸作为催化剂进行杉木木粉液化工艺。开启冷凝器,在1 053 r/min的搅拌速率下,液化混合物以5 ℃/min的升温速率在油浴中加热至160 ℃并保温2.5 h。而后撤去油浴,待三口烧瓶冷却至室温,撤去冷凝器,将液化产物通过50 mL砂芯漏斗(直径为8 cm,G3型,孔径为15 ~ 40 μm),抽真空过滤制得杉木苯酚液化物。
1.2.2 纺丝与固化
将10 g杉木苯酚液化物和0.5 g六次甲基四胺混合加入纺丝管,开启搅拌器,以5 ℃/min的升温速率在空气中加热至(175 ± 2) ℃,并保温20 min合成纺丝液,而后在120 ~ 130 ℃进行纺丝制备初始纤维。将得到的初始纤维浸入含有7.4 mL甲醛、6 mL盐酸和1.4 mL蒸馏水的酸溶液中,以0.25 ℃/min的升温速率加热至90 ℃,保温2 h进行固化工艺。待固化结束后取出纤维,经蒸馏水洗涤后放入(85 ± 2) ℃烘箱干燥2 h,得到原丝。
1.2.3 炭化过程
将约5 g的原丝以2 ℃/min的升温速率在N2保护下分别加热至设定的炭化温度(500、700、900 ℃)并保温1 h。之后以4 ℃/min的速率将温度调整至800 ℃,结束炭化过程。待炭化产物冷却至室温,取出炭化产物得到杉木苯酚液化物碳纤维(liquefied wood carbon fibers,LWCFs)。LWCFs-500、LWCFs-700和LWCFs-900分别代表炭化温度为500、700、900 ℃的LWCFs。
1.2.4 活化过程
将约5 g的前驱体纤维以2 ℃/min的升温速率在N2保护下分别加热至设定的炭化温度(500、700、900 ℃)并保温1 h。之后以4 ℃/min的速率将温度调整至800 ℃,此时开启水蒸气(流量为6.69 g/min),活化20、40 min制备活性碳纤维。待活化产物冷却至室温,取出活化产物得到杉木苯酚液化物活性碳纤维(activated liquefied wood carbon fibers,ALWCFs)。ALWCFs-500-20代表炭化温度为500 ℃,活化时间为20 min的ALWCFs,其他样品名称含义与之相同。
1.2.5 元素分析检测
采用美国公司(Thermo)生产的A FLASH EA1112型元素分析仪对所有样品的碳、氢、氮元素质量分数进行测试。测试条件为:以He为载气,碳、氢、氮元素分解温度为950 ℃。氧元素质量分数计算公式如下:
WO=(1−WC−WH−WN)×100% 式中:WC、WH、WN分别表示碳、氢、氮元素的质量分数。
1.2.6 X射线衍射仪检测
采用日本公司(SHIMAZU)生产的XRD-6000型X射线衍射仪采集样品的X射线衍射图谱。具体操作如下:将约0.5 g的干燥样品在研钵中研磨15 min,放入样品台中压实后开始检测。铜靶辐射(辐射管额定电压为40 kV,额定电流为30 mA,波长为0.154 nm),扫描频率为2 (°)/min,2θ角扫描区间值为15° ~ 60°,测量步长为0.2°。
样品的石墨层间距(d002)、石墨层堆叠厚度(Lc002)由(002)衍射面求得,石墨网横向尺寸(La110)由(110)衍射面求得,依据Scherrer公式[25]计算。
d002=λ/(2sinθ002) Lc002=0.94λ/(βcosθ002) La110=1.84λ/(βcosθ110) 式中:λ表示入射X射线的波长,取0.154 nm;β表示该晶面衍射峰的半峰宽;θ为该衍射峰所对应的衍射角。
1.2.7 孔结构检测
采用美国公司(Quantachrome)生产的Autosorb iQ型氮气吸附分析仪进行测定。将0.0500 g的ALWCFs待测样品装入干燥的测试管,经300 ℃脱气3 h,在−196 ℃下测定不同相对压强下的N2吸附/脱附等温线。采用Brunauer-Emmett-Teller法[26]计算BET比表面积SBET;由相对压力约为0.99时的液氮吸附量换算成液氮体积,得到总孔容Vt;采用t-plot法[27]计算微孔比表面积Smi和微孔孔容Vmi;采用Barrett, Joyner & Halenda(BJH)法[28]计算中孔孔容VBJH;采用Horvath-Kawazoe(HK)法[29]计算峰值孔径DHK;由BET法计算平均孔径Da;由Density Functional Theory(DFT)法[30]计算孔径大小与分布。
2. 结果与分析
2.1 元素组成变化
不同炭化–活化过程中LWCFs与ALWCFs的元素质量分数及变化趋势分别见表1和图1。在炭化样品中,随着炭化温度升高,碳元素质量分数逐渐增加,氢、氧元素质量分数减少。其中,炭化温度由700 ℃升高至900 ℃过程中,氢、氧元素质量分数的减少十分明显,这表明脂肪族官能团和含氧官能团的热解在高于700 ℃以后变得剧烈。在同一活化时间下,随着炭化温度升高,碳元素质量分数逐渐增加,氢、氧元素质量分数逐渐减少。综上可知,炭化温度的提高促进了非碳元素的挥发,且有利于活化过程中碳元素的富集。
表 1 不同炭化–活化过程中LWCFs和ALWCFs的元素质量分数变化Table 1. Changes of element percentage compositions for LWCFs and ALWCFs by different carbonization-activation processes样品名称 Sample name 质量分数 Mass fraction/% C H N O LWCFs-500 88.76 1.15 0.61 9.49 LWCFs-700 89.21 1.17 0.64 9.00 LWCFs-900 91.71 0.84 0.64 6.82 ALWCFs-500-20 91.25 1.04 0.58 7.14 ALWCFs-700-20 93.23 1.03 0.62 5.12 ALWCFs-900-20 94.31 0.79 0.6 4.30 ALWCFs-500-40 93.45 1.14 0.57 4.86 ALWCFs-700-40 94.25 0.99 0.64 4.13 ALWCFs-900-40 95.10 0.69 0.57 3.64 图 1 不同炭化–活化过程中LWCFs和ALWCFs的元素质量分数变化图LWCFs对应的活化时间为0 min,ALWCFs对应的是活化时间为20 ~ 40 min。LWCFs correspond to the activation time of 0 min, and ALWCFs correspond to the activation time of 20–40 min.Figure 1. Changes of element percentage compositions for LWCFs and ALWCFs by different carbonization-activation processes2.2 微晶结构变化
图2为不同炭化–活化过程中LWCFs与ALWCFs的XRD衍射图谱。从图中可以看出:LWCFs与ALWCFs在2θ为19° ~ 21°和44°附近均出现衍射峰,分别对应于石墨碳层的(002)衍射面和(110)衍射面[31-32]。这两处衍射峰和形态特点说明LWCFs与ALWCFs的微晶结构均由乱层石墨微晶堆叠而成,属于多晶乱层石墨结构。
不同炭化–活化过程中LWCFs与ALWCFs的微晶结构参数见表2。相关微晶结构参数在不同炭化–活化过程中的变化趋势分别见图3和图4。LWCFs的d002值均大于石墨微晶的层间距(0.335 4 nm),表明石墨化程度较低[33-34]。
表 2 不同炭化–活化过程LWCFs和ALWCFs的微晶结构参数Table 2. Microcrystalline structure parameters for LWCFs and ALWCFs prepared by different carbonization-activation processes样品名称
Sample name2θ/(°) d002/nm Lc002/nm Lc002/d002 La110/nm La110/Lc002 LWCFs-500 20.3 0.437 0.505 1.16 1.683 3.33 LWCFs-700 20.8 0.427 0.509 1.19 1.606 3.16 LWCFs-900 20.8 0.427 0.515 1.21 1.651 3.21 ALWCFs-500-20 20.6 0.430 0.512 1.19 2.365 4.62 ALWCFs-700-20 20.6 0.430 0.512 1.19 2.274 4.44 ALWCFs-900-20 19.9 0.446 0.501 1.12 2.870 5.72 ALWCFs-500-40 19.4 0.457 0.538 1.18 2.245 4.17 ALWCFs-700-40 20.2 0.439 0.464 1.06 2.217 4.78 ALWCFs-900-40 21.4 0.415 0.447 1.08 2.779 6.23 注:θ为衍射峰所对应的衍射角,d002为墨层间距,Lc002为石墨层堆叠厚度,La110为石墨网横向尺寸。Notes:θ is the diffraction angle corresponding to the diffraction peak, d002 is the spacing between graphite layers, Lc002 is the stacking thickness of graphite layers, and La110 is the transverse size of graphite network. 随着炭化温度升高,LWCFs(002)衍射峰的2θ角从20.3°偏移至20.8°,d002值减少0.01 nm,Lc002值增加0.01 nm,轴向石墨层数Lc002/d002增加0.05。可见,炭化温度的升高使LWCFs的乱层石墨微晶结构更加致密,微晶间排列更趋于规整,且轴向尺寸逐渐增大。LWCFs的La110值与La110/Lc002随着炭化温度由500 ℃升至700 ℃逐渐减小,在此过程中LWCFs的化学结构因热解产生破坏并逐步向多层堆叠的乱层石墨结构转变。当炭化温度升高至900 ℃,LWCFs的La110值与La110/Lc002增大,此时乱层石墨微晶结构更趋有序、规整,横向微晶发生了生长。
活化过程中,当炭化温度为700和900 ℃时,Lc002值随着活化时间延长呈减小趋势,在活化时间高于20 min时,Lc002值的减少尤为明显,其中,ALWCFs-700-40的Lc002值较LWCFs-700减小了8.8%,ALWCFs-900-40的Lc002值较LWCFs-900减小了13.2%,这是由活化过程中水蒸气对乱层石墨轴向微晶的侵蚀所致,且随着活化时间的延长,侵蚀程度明显加重。与上述情况相反,当炭化温度为500 ℃时,Lc002随着活化时间的延长呈增加趋势,ALWCFs-500-40的Lc002值较LWCFs-500增加了6.5%。这是由于LWCFs-500纤维结构中有较多的晶体缺陷和较大的初始孔隙,活化反应优先在这些缺陷和孔隙处发生,以至于水蒸气没有充分进入微晶内部[4]。
随着活化时间延长至20 min,La110值增加显著,其中,900 ℃炭化时的增加率最高,ALWCFs-900-20较LWCFs-900增加了73.8%。La110值的升高表明乱层石墨网络横向尺寸的增大,这是源于微晶间碰撞所产生的横向重排,在900 ℃下最为剧烈,这与上文中LWCFs横向微晶结构的变化趋势一致,进一步证实900 ℃下乱层石墨碳网结构的充分生长[35]。随着活化时间延长至40 min,3种炭化温度下的La110值仅略微降低,表明该阶段微晶的横向结构基本稳定,这可能是由于此时乱层石墨结构的生长已趋于饱和,主要以碳原子的活化热解为主。
对于500和700 ℃炭化样品,d002值随活化时间的延长呈增大趋势,其中,ALWCFs-500-40的d002值较LWCFs-500增加了4.6%,ALWCFs-700-40的d002值较LWCFs-700增加了2.8%,可见活化作用没有使乱层石墨结构变得更为致密,这是由于活化过程中挥发物的蒸发以及孔结构的形成使微晶结构变得松散。而ALWCFs-900-40的d002值大幅减少,较LWCFs-900减少了2.8%,表明高温活化下,轴向微晶结构已经高度分散,并产生了塌陷或紧缩。轴向石墨层数Lc002/d002的减小与Lc002值的变化趋势相符,这进一步验证了活化过程是对轴向乱层石墨片层结构的侵蚀,且在900 ℃活化过程中侵蚀最为剧烈。
2.3 孔结构变化
图5为不同炭化–活化过程中ALWCFs的N2吸附/脱附等温曲线。从中可以看出:ALWCFs的等温线类型均属于Ⅰ型,表明微孔结构占据主导地位。表3列出了不同炭化–活化过程中ALWCFs的孔结构参数。从中可以看出:炭化温度的提高有利于ALWCFs孔结构的形成。较样品ALWCFs-500-20,ALWCFs-700-20和ALWCFs-900-20的SBET分别增加了12.5%和4.3%,Vt分别增加了15.9%和2.6%;较样品ALWCFs-500-40,ALWCFs-700-40和ALWCFs-900-40的SBET分别增加了7.9%和18.6%,ALWCFs-900-40 的Vt增加了12.5%。其中,炭化温度的提高对ALWCFs微孔结构形成有明显的促进作用,且活化时间越长,微孔结构增加越显著。较样品ALWCFs-500-20,ALWCFs-700-20和ALWCFs-900-20的Smi分别提高了8.1%和5.0%,Vmi分别提高了8.9%和4.6%;较样品ALWCFs-500-40,ALWCFs-700-40和ALWCFs-900-40的Smi分别提高了19.9%和25.1%,Vmi分别提高了17.3%和25.5%。结合微晶分析结果可以得出:水蒸气对乱层石墨轴向微晶内部的侵蚀是形成微孔结构主要途径。低炭化温度样品微晶结构有序化程度较低,水蒸气会优先侵蚀其微晶缺陷和初始孔隙处,这一定程度上减缓了水蒸气对轴向微晶内部的侵蚀。而高的炭化温度形成的微晶有序化程度较高,有助于加快水蒸气进入轴向微晶内部的速率。
表 3 不同活化时间制备的ALWCFs的孔结构参数Table 3. Pore structure parameters for ALWCFs prepared by different activation time样品名称
Sample nameSBET/
(m2·g−1)Vt/
(cm3·g−1)Smi/
(m2·g−1)Vmi/
(cm3·g−1)VBJH/
(cm3·g−1)DHK/nm Da/nm ALWCFs-500-20 861 0.464 650 0.259 0.230 0.443 2.15 ALWCFs-700-20 969 0.538 703 0.282 0.284 0.428 2.22 ALWCFs-900-20 898 0.476 683 0.271 0.226 0.448 2.12 ALWCFs-500-40 1 068 0.590 793 0.318 0.314 0.458 2.21 ALWCFs-700-40 1 152 0.562 951 0.373 0.241 0.463 1.95 ALWCFs-900-40 1 267 0.664 992 0.399 0.373 0.468 2.09 注:SBET为比表面积;Vt为总孔容;Smi为微孔比表面积;Vmi为微孔孔容;VBJH为中孔孔容;DHK为峰值孔径;Da为平均孔径。Notes:SBET is the specific surface area, Vt is the total pore volume, Smi is the micropore specific surface area, Vmi is the micropore volume, VBJH is the mesopore volume, DHK is the peak pore width, and Da is the average pore width. ALWCFs中孔结构随着炭化温度升高呈现不同的变化趋势。对于500和700 ℃炭化样品,活化初期的中孔结构主要来源于水蒸气对晶体缺陷或初始孔隙处的活化作用,活化20 min时,两者VBJH均高于ALWCFs-900-20。随着活化时间延长至40 min,ALWCFs-700-40的VBJH急剧下降,ALWCFs-900-40的VBJH明显提高,这是由于水蒸气对轴向微晶内部的侵蚀加重,前者的中孔结构受到破坏,而后者微孔结构进一步扩大。
ALWCF孔径大小和分布变化趋势进一步证实了以上结果。图6为不同活化时间ALWCF的DHK和Da的变化趋势图。3种炭化温度下,DHK均随着活化时间的延长而增大,且900 ℃炭化–活化样品的DHK最高,表明了900 ℃炭化样品在活化过程微孔结构扩大最显著。Da的变化表明,仅500 ℃炭化–活化样品的Da随活化时间的延长而增加,700 ℃炭化–活化样品的Da随活化时间的延长下降最为显著。图7为不同活化时间下的ALWCFs的DFT孔径大小分布图。从中可以观察到:当活化20 min时,ALWCFs中多数为孔径小于1 nm的微孔。这些微孔的孔径大小分布随着炭化温度的升高而逐渐扩宽。当活化40 min时,炭化温度的升高使孔径大小分布在0.6 ~ 1.5 nm的微孔范围内和2 ~ 2.5 nm的中孔范围内的逐渐扩大,样品ALWCFs-900-40的孔径大小分布扩大最为明显,这是由于随着活化时间的延长,轴向微晶的侵蚀加重促进了孔结构的形成与扩大,同时,碳基体中的孔隙通道变多变宽,水蒸气更容易到达活化位点,这进一步加剧了孔径的扩大。
3. 结 论
本研究通过500 ~ 900 ℃炭化过程得到不同微晶结构的LWCFs,并将这些LWCFs经800 ℃水蒸气活化20 ~ 40 min,考察了不同炭化–活化过程中ALWCFs的元素组成、微晶结构和孔结构的变化,探讨了微晶结构对ALWCFs孔结构形成的作用机制及影响,揭示了微晶结构演变规律以及ALWCFs孔结构形成路径。得到如下结论:
(1)随着炭化温度的升高,LWCFs碳元素质量分数逐渐升高,氢、氧元素质量分数减少,高于700 ℃以后氢、氧元素质量分数减少显著;ALWCFs碳元素质量分数逐渐增加,氢、氧元素质量分数逐渐减少。以上表明,炭化温度的提高促进了非碳元素的挥发,且有利于活化过程中碳元素的富集。
(2)炭化温度的升高使LWCFs的乱层石墨微晶轴向尺寸逐渐增大,结构更加致密,900 ℃时横向微晶发生了生长。在活化过程中,高的炭化温度能够显著促进水蒸气对轴向微晶的侵蚀,且随着活化时间的延长,侵蚀程度加重。此外,活化初期微晶间进行碰撞产生横向重排,乱层石墨网络横向尺寸显著增大,炭化温度的升高利于活化过程中横向微晶的生长,而进一步延长活化时间横向微晶结构无显著变化。
(3)炭化温度的升高提高了ALWCFs的比表面积和总孔容,对微孔结构形成有明显的促进作用,且活化时间越长,微孔结构增加越显著。水蒸气对乱层石墨轴向微晶内部的侵蚀是形成微孔结构的主要途径。低的炭化温度(500和700 ℃)有利于ALWCFs在活化初期中孔结构的形成,主要来源于水蒸气对晶体缺陷或初始孔隙处的活化作用;随着活化时间的延长,轴向微晶的侵蚀加重,初期中孔发生了瓦解。高温(900 ℃)炭化样品在活化初期中孔结构较少,但随着活化时间的延长,微孔结构的逐步扩大导致了中孔结构明显增多。ALWCFs孔径大小和分布变化趋势进一步证实了上述结论。
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图 4 不同因子对土壤优势细菌群落β多样性的解释度
ELE. 海拔;SWC. 土壤含水量;ST. 土壤表层温度;pH. pH值;AP.土壤有效磷;TC. 土壤全碳;HN. 水解氮;TN. 土壤全氮;TK. 土壤全K;SLO. 坡度;TP. 土壤全磷。**和***分别表示在P < 0.01和P < 0.001显著相关。下同。ELE, elevation; SWC, soil water content; ST, soil surface temperature; pH, pH value; AP, soil available phosphorous; TC, soil total carbon; HN, hydrolyzed nitrogen; TN, soil total nitrogen; TK, soil total potassium; SLO, slope; TP, soil total phosphorus. ** and *** indicate significant correlations at P < 0.01 and P < 0.001 level, respectively. The same below.
Figure 4. Interpretation rate of different factors to the beta diversity of soil dominant bacterial community
表 1 戴云山样地基本概况
Table 1 Basic information of sample plots in Daiyun Mountain
样地编号
Sample plot No.经度
Longitude纬度
Latitude森林类型
Forest type主要树种
Main tree species海拔
Elevation/m平均温度
Average temperature/℃坡度
Slope/(°)坡向
AspectDYS-900 118°10′36″E 25°38′46″N CEBF CG + CL 915 23.2 28 SW DYS-1000 118°10′38″E 25°38′51″N CEBF CL + CG 1 001 22.6 35 SW DYS-1100 118°10′43″E 25°38′57″N CEBF CL + CG 1 091 21.5 40 S DYS-1200 118°10′53″E 25°39′06″N CEBF CL + MT 1 201 21.4 35 S DYS-1300 118°10′55″E 25°39′22″N CEBF ER + PT 1 321 21.2 35 S DYS-1400 118°10′58″E 25°39′32″N CF PT + ER 1 411 20.4 30 S DYS-1500 118°10′57″E 25°39′47″N CF PT + RS 1 501 19.8 23 W 注:CEBF.针阔混交林;CF.针叶林;CG.青冈;CL.杉木;MT.红楠;PT.黄山松;ER. 窄基红褐柃;RS.映山红;SW.西南;S.南;W.西。Notes: CEBF, coniferous and evergreen broadleaved forest; CF, coniferous forest; CG, Cyclobalanopsis glauca; CL, Cunninghamia lanceolata; MT, Machilus thunbergii; PT, Pinus taiwanensis; ER, Eurya rubiginosa var. attenuata; RS, Rhododendron simsii; SW, southwest; S, south; W, west. 表 2 不同海拔土壤理化性质
Table 2 Soil physical and chemical properties of soil at different elevations
海拔
Elevation/mpH 土壤含水量
Soil water content (SWC)/%全碳
Total carbon (TC)/(g·kg−1)全氮
Total nitrogen (TN)/(g·kg−1)全磷
Total phosphorus (TP)/(g·kg−1)全钾
Total potassium (TK)/(g·kg−1)水解氮
Hydrolyzed nitrogen (HN)/(mg·kg−1)有效磷
Available phosphorus (AP)/(mg·kg−1)900 3.87 ± 0.01a 35.51 ± 0.41c 39.68 ± 0.6e 3.66 ± 0.03d 0.36 ± 0.002a 20.91 ± 0.24a 242.18 ± 12.00c 1.18 ± 0.03c 1 000 3.66 ± 0.02c 46.86 ± 2.65b 90.59 ± 1.9a 4.72 ± 0.04b 0.28 ± 0.003ab 13.41 ± 0.36d 333.05 ± 89.54abc 1.87 ± 0.01a 1 100 3.81 ± 0.05b 44.01 ± 3.39b 52.84 ± 0.6c 3.02 ± 0.05e 0.21 ± 0.002b 13.54 ± 0.10d 281.48 ± 26.89bc 1.30 ± 0.01b 1 200 3.86 ± 0.01a 43.50 ± 3.58b 68.21 ± 0.0b 4.85 ± 0.07b 0.24 ± 0.064ab 16.59 ± 0.13c 385.62 ± 81.16ab 0.74 ± 0.00d 1 300 3.51 ± 0.01d 43.91 ± 3.68b 89.64 ± 0.1a 5.28 ± 0.24a 0.20 ± 0.068b 16.41 ± 0.34c 377.75 ± 63.56ab 0.46 ± 0.04e 1 400 3.52 ± 0.01d 34.71 ± 0.96c 50.07 ± 0.0d 4.11 ± 0.03c 0.20 ± 0.045b 18.41 ± 0.25b 325.68 ± 94.28abc 0.43 ± 0.06e 1 500 3.67 ± 0.01c 54.19 ± 3.66a 34.66 ± 0.2f 3.11 ± 0.08e 0.19 ± 0.036b 16.36 ± 0.13c 418.52 ± 30.77a 0.24 ± 0.04f 注:同列不同字母表示差异显著(P < 0.05)。下同。Notes: different letters indicate significant difference in the same column (P < 0.05). The same below. 表 3 不同海拔土壤细菌的多样性指数
Table 3 Soil bacterial diversity indices at different elevations
海拔
Elevation/m物种数
Species numberChao 1指数
Chao 1 index香农指数
Shannon indexACE指数
ACE index900 2 775.33 ± 8.97c 3 001.18 ± 21.24d 9.48 ± 0.02d 3 028.24 ± 11.69c 1 000 3 017.33 ± 4.84b 3 299.03 ± 12.63bc 9.56 ± 0.01c 3 310.89 ± 5.03b 1 100 3 222.00 ± 16.04a 3 508.03 ± 22.30a 9.77 ± 0.01a 3 529.94 ± 21.80a 1 200 2 998.33 ± 18.48b 3 341.49 ± 31.92b 9.65 ± 0.01b 3 315.42 ± 24.55b 1 300 3 031.33 ± 16.37b 3 310.06 ± 24.92bc 9.61 ± 0.02b 3 329.75 ± 23.93b 1 400 3 026.33 ± 19.37b 3 263.20 ± 30.45bc 9.64 ± 0.02b 3 296.76 ± 28.56b 1 500 2 992.33 ± 19.01b 3 256.32 ± 26.72c 9.62 ± 0.01b 3 303.86 ± 25.17b 表 4 环境因子与土壤细菌优势门群落间的显著性检验
Table 4 Significant test between environmental factors and dominant phyla of soil bacterial communities
环境因子
Environmental factor模型检验F值
Model test F value显著性检验P值
Significance test P value海拔 Elevation 20.251 2 0.001*** 坡度 Slope 6.459 2 0.001*** pH值 pH value 3.434 8 0.009** 土壤全氮
Soil total nitrogen3.309 6 0.015* 水解氮
Hydrolyzed nitrogen2.645 5 0.039* 土壤有效磷
Soil available phosphorus4.562 7 0.003** 注:*表示在P < 0.05水平上显著相关;**表示在P < 0.01水平上显著相关;***表示在P < 0.001水平上显著相关。整个拟合方程显著度F = 6.772,P = 0.001***。Notes: * indicates significant correlation at P < 0.05 level, ** indicates significant correlation at P < 0.01 level, *** indicates significant correlation at P < 0.001 level. The significance of whole stimulated equation is F = 6.772, with P = 0.001***. -
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