干湿交替条件下土壤氨基糖含量的动态变化

通过室内模拟培养试验,研究了恒湿和干湿交替条件下土壤中3种微生物来源氨基糖含量的动态变化,并且利用氨基葡萄糖和胞壁酸的比值分析了干湿交替条件下土壤真菌和细菌对土壤有机质转化的相对贡献.结果表明:恒湿条件下,细菌来源的胞壁酸在土壤中的分解速率大于真菌来源的氨基葡萄糖,氨基半乳糖在土壤中的分解速率较慢;干湿交替改变了土壤中3种氨基糖的分解特征,与恒湿处理相比,干湿交替培养前期以胞壁酸为代表的细菌残余物的分解速率高于以氨基葡萄糖为代表的真菌残余物,随着干湿交替频率的增大,以氨基葡萄糖为代表的真菌残余物分解速率高于以胞壁酸为代表的细菌残余物.可见,干湿交替条件改变了以氨基糖为代表的土壤氮素的微生物转化过程.     

东北黑土氨基糖的矿化动态及其对外源物质添加的响应

采用间歇淋洗好气培养法研究了东北黑土中3种不同微生物来源氨基糖(氨基葡萄糖、胞壁酸和氨基半乳糖)的矿化动态以及对葡萄糖添加和葡萄糖与氮肥配施的响应.结果表明:土壤中不同种类的氨基糖具有不同的矿化特征.培养期间胞壁酸含量减少25.4%而氨基葡萄糖含量降低7.1%,表明细菌来源的胞壁酸在土壤中的矿化速率快于真菌来源的氨基葡萄糖,但氨基葡萄糖的矿化数量(68.4 mg·kg^-1)显著高于胞壁酸(15.4 mg·kg^-1).葡萄糖添加以及葡萄糖与氮肥配施均显著提高了土壤中氨基葡萄糖和胞壁酸的含量,但两种处理的影响有所不同.相比之下,氨基半乳糖在土壤中矿化较慢,并且受外源物质的影响较小,表现出较高的稳定性.     

外源氮素添加对森林土壤氨基糖转化的影响

采用室内模拟培养法研究了不同数量氮素添加条件下森林土壤中3种微生物来源的氨基糖含量的动态变化,并且利用氨基葡萄糖和胞壁酸的比值分析了氮素添加条件下土壤真菌和细菌对土壤氮素转化和积累的相对贡献。结果表明:土壤中氨基糖含量的动态变化与土壤中的养分状况密切相关;当向土壤中添加氮源时,微生物会利用外加氮源合成自身的细胞壁物质,并且高氮处理胞壁酸含量高于低氮处理,而高氮处理氨基葡萄糖含量则低于低氮处理,说明随施氮量的增加更有利于以胞壁酸为代表的细菌残留物在土壤中的积累,不利于以氨基葡萄糖为代表的真菌残留物的积累,氨基半乳糖对氮素添加的响应较小;当土壤中养分缺乏时,氨基糖能够发生不同程度的分解;添加氮源条件下,真菌和细菌来源氨基糖的比值发生变化,细菌对土壤氮素转化的贡献大于真菌,并且高氮处理细菌的贡献更大。本研究表明,氮素添加改变了以氨基糖为代表的土壤氮素的微生物转化过程。     

不同供氮水平对施用玉米秸秆后黑土氨基糖转化的影响

采用室内恒温(25 ℃)培养方法,设置4个氮素添加水平(0、60.3、167.2、701.9 mg N·kg^-1,依次标记为N₀、N_low、N_mid、N_hig),培养38周,研究不同无机氮素添加水平对施入玉米秸秆黑土的氨基糖转化的影响.结果表明：与对照样品相比,添加秸秆可显著促进氨基糖的微生物合成与积累,且在培养前期氨基糖的总量随着无机氮素添加水平的增加而增加,N_mid和N_hig处理氨基糖积累量显著高于N_low和N₀处理;随着培养时间的延长氨基糖总量有所下降,N_low和N₀处理的下降幅度高于N_mid和N_hig处理.不同无机氮素供应水平对各氨基单糖的影响也有所不同,以胞壁酸为代表的细菌细胞壁物质比真菌细胞壁残留物如氨基葡萄糖更易受到土壤碳氮供给的影响,但真菌细胞壁物质对土壤有机质的截获和稳定作用大于细菌.说明对于C/N较大的玉米秸秆,土壤中无机氮素的供给对氨基糖在土壤中的积累转化有明显影响,氮素缺乏会抑制微生物生长,使氨基糖的合成作用减弱,在微生物体中截获的氮源减少,不利于土壤氮素的积累.     

氮磷添加对长白山温带森林土壤微生物群落组成和氨基糖的影响

在长白山阔叶红松林中设置氮添加(N,50 kg N·hm^-2·a^-1)、磷添加(P,25 kg P·hm^-2·a^-1)和氮磷添加(NP,50 kg N·hm^-2·a^-1+25 kg P·hm^-2·a^-1)试验,分析氮磷添加对有机层和矿质层土壤微生物群落组成和氨基糖的影响。结果表明: 在有机层土壤中,N、P添加使总微生物生物量显著降低19.5%和24.6%,P添加还使细菌和真菌生物量分别显著降低23.8%和19.3%;在矿质层土壤中,N、P和NP添加使总微生物生物量显著增加94.8%、230.9%和115.0%,细菌和真菌生物量在施肥处理下显著增加。N添加下有机层土壤真菌与细菌生物量比值(F/B)显著增大,而NP添加使矿质层土壤F/B显著减小。革兰氏阳性菌与革兰氏阴性菌比对N、P和NP添加有显著正响应。土壤氨基糖对不同处理的响应不同。在有机层土壤中,N、P和NP添加使氨基葡萄糖含量分别减少41.3%、48.8%和36.4%,而N和NP添加分别使胞壁酸含量显著增加43.0%和71.1%;在矿质层土壤中,氨基葡萄糖和胞壁酸含量在N添加下无显著变化,而在P和NP添加下显著增加。在施肥处理下,有机层土壤中氨基葡萄糖与胞壁酸比值显著减小,表明N、P添加增加了细菌对土壤有机碳积累的相对贡献。N、P添加后土壤氨基糖含量的变化与微生物群落组成的变化密切相关,且二者均受到土壤化学性质变化的影响。     

外源无机氮素形态对土壤氨基糖动态的影响

微生物生长对底物的可利用性存在不同的响应,外源氮素的形态可以显著影响微生物代谢过程,而土壤氨基糖作为微生物细胞壁残留物,其形成、分解和周转特征与外源碳氮供给密切相关,对土壤氨基糖的研究与同位素标记技术相结合,可以进一步反映微生物对底物的利用特征.本文以葡萄糖及15N标记的NH4+和NO3-为底物,利用气相色谱-质谱联机技术,通过测定氨基糖中同位素富集比例,跟踪新形成(标记)和原有(非标记)的土壤氨基糖的动态变化.结果表明:在培养过程中,15N标记的氨基糖含量显著增加,NH4+向氨基糖的转化显著高于NO3-,反映出微生物对NH4+的选择性利用.土壤中原有的氨基糖也发生了不同变化.其中,非标记氨基葡萄糖在N H4+为底物时,其含量有所增加,但在NO3-为底物时含量逐渐下降;非标记胞壁酸含量在2个处理中均不断下降,尤其以NO3-为底物时更为显著;非标记氨基半乳糖含量的增减幅度均小于20％.这种特异性变化表明,不同来源的微生物细胞壁残留物对土壤氮素周转和稳定的作用不同,真菌细胞壁残留物易于在土壤中积累,有利于土壤有机质的稳定,而细菌细胞壁残留物容易分解,在土壤有机质周转过程中起重要作用.     

引入固氮树种对辽东落叶松人工林土壤团聚体氨基糖的影响

土壤微生物残留物是稳定性碳库的重要组分,然而固氮树种引入对落叶松人工林土壤团聚体微生物残留物分布的影响还不清楚.为了阐明固氮树种对不同团聚体粒级内微生物残留物分布的影响,本研究以氨基糖作为微生物残留物的生物标识物,比较了辽东日本落叶松人工纯林和落叶松与固氮树种赤杨混交林土壤团聚体氨基糖的分布特征.结果表明: 赤杨引入不影响团聚体氨基糖的分布,但显著提高了团聚体氨基糖含量.与纯林相比,混交林土壤不同团聚体各粒级总氨基糖含量增加1.3～1.7倍.其中,混交林土壤团聚体内总氨基糖增加量的66.5%～66.9%来自氨基葡萄糖,30.0%～30.6%来自氨基半乳糖,2.5%～3.2%来自胞壁酸.赤杨引入显著提高了>2000 μm和<250 μm团聚体中的氨基葡萄糖/胞壁酸值,但不影响250～2000 μm粒级团聚体中真菌和细菌残留物的相对贡献.此外,赤杨引入增加了土壤不同团聚体内的氨基糖对土壤有机碳的贡献,但不影响团聚体粒级之间的微生物贡献,说明赤杨对微生物贡献的影响存在空间均一性.     

赤杨对辽东落叶松人工林土壤氨基糖积累的影响

微生物残留物是土壤稳定性碳库的重要组成部分,然而其对固氮树种的响应还不清楚。以辽东山区日本落叶松(Larix kaempferi)人工纯林和落叶松-赤杨混交林为研究对象,以氨基糖作为微生物残留物的生物标识物,研究了赤杨对落叶松人工林根际和非根际土壤氨基糖积累的影响。结果表明,混交林中落叶松根际和非根际各氨基糖单体含量均显著高于纯林,说明赤杨引入有利于土壤微生物残留物的积累。其中,混交林落叶松根际及非根际土壤氨基糖葡萄糖含量分别比纯林高出99.5%(P0.01)和154%(P0.01);胞壁酸含量分别比纯林高出66.1%(P0.01)和132.3%(P0.01)。赤杨引入对氨基葡萄糖/胞壁酸比值的影响不显著,但显著增加氨基糖对土壤有机碳的贡献。冗余度分析表明全氮是驱动土壤中氨基糖发生变化的主要因子。表明赤杨引入显著提高微生物固持的土壤碳库和有机碳稳定性,这对落叶松人工林合理经营具有重要意义。     

不同施肥处理下水稻根际和非根际土壤中氨基糖积累特征

以水稻长期定位施肥试验土壤为研究对象,选取不施肥(CK)、化肥(NPK)、秸秆还田+化肥(NPKS)、30%有机肥+70%化肥(LOM)和60%有机肥+40%化肥(HOM)5种处理,分析水稻分蘖旺期根际土和非根际土中氨基糖积累特征.结果表明: 与CK和NPK处理相比,长期施用有机物料(NPKS、LOM、HOM)显著增加了水稻根际土和非根际土中有机碳、总氨基糖及其氨基单糖(胞壁酸、氨基葡萄糖和氨基半乳糖)含量.不同施肥处理下3种氨基单糖的积累规律不同,说明不同微生物对施肥处理的响应趋势和强度有所不同.受稻田翻耕等均匀化土壤的农事操作影响,各处理总氨基糖含量在根际土与非根际土间无显著差异.氨基糖碳对土壤有机碳积累的贡献范围为24.0～28.3 mg·g^-1,且以NPKS处理最高,HOM和CK处理最低.真菌氨基葡萄糖/胞壁酸比值范围为24.4～36.6,说明该试验点所有处理的根际土与非根际土中有机质的降解与转化过程以真菌为主导,且与NPK和CK相比,NPKS处理的真菌参与度提高,而施用HOM处理的细菌参与度提高.     

氨基糖单体碳氮同位素的分析及其应用

氨基糖(AS)作为有机质中在分子水平识别的重要组分,研究其来源与转化能更好地认知微生物对有机质的调控作用。作为一种新兴技术,氨基糖单体同位素分析(CSIA-AS)为研究氨基糖各组分在自然环境中的变化特征提供了更详细的信息。本文系统总结了CSIA-AS技术的测定方法及其在氨基糖循环转化研究中的应用,气相色谱-同位素比值质谱法(GC-IRMS)和离子色谱-同位素比值质谱法(IC-IRMS)作为2种主要的氨基糖同位素测定方法,各有利弊,但进行相应的校正后均可实现可靠的测定结果。氨基糖各组分在土壤有机质中具有相对较低的周转时间,细菌来源的胞壁酸相对葡萄糖胺、半乳糖胺和甘露糖胺具有更高的矿化速率。氨基糖在环境中的来源和代谢转化受底物的影响,这与微生物群落对不同碳、氮源的特异性响应有关。CSIA-AS技术的推广需要进一步的方法优化并将其与微生物甄别等其他手段相结合,以此来更好地阐释有机质的来源、转化和归宿及其调控机制。     

Sequestration and turnover of bacterial- and fungal-derived carbon in a temperate grassland soil under long-term elevated atmospheric pCO2

Temperate grasslands contribute about 20% to the global C budget. Elevation of atmospheric CO₂ concentration (pCO₂) could lead to additional C sequestration into these ecosystems. Microbial‐derived C in the soil comprising about 1–5% of total soil organic carbon may be an important ‘pool’ for long‐term storage of C under future increased atmospheric CO₂ concentrations. In our study, the impact of elevated pCO₂ on bacterial‐ and fungal‐derived C in the soil of Lolium perenne pastures was investigated under free air carbon dioxide enrichment (FACE) conditions. For 7 years, L. perenne swards were exposed to ambient and elevated pCO₂ (36 and 60 Pa pCO₂, respectively). The additional CO₂ in the FACE plots was depleted in ¹³C compared with ambient plots, so that ‘new’ (<7 years) C inputs in the form of microbial‐derived residues could be determined by means of stable C isotope analysis. Amino sugars in soil are reliable organic biomarkers for indicating the presence of microbial‐derived residues, with particular amino sugars indicative of either bacterial or fungal origin. It is assumed that amino sugars are stabilized to a significant extent in soil, and so may play an important role in long‐term C storage. In our study, we were also able to discriminate between ‘old’ (> 7 years) and ‘new’ microbial‐derived C using compound‐specific δ¹³C analysis of individual amino sugars. This new tool was very useful in investigating the potential for C storage in microbial‐derived residues and the turnover of this C in soil under increased atmospheric pCO₂. The ¹³C signature of individual amino sugars varied between ?17.4‰ and ?39.6‰, and was up to 11.5% depleted in ¹³C in the FACE plots when compared with the bulk δ¹³C value of the native C3 L. perenne soil. New amino sugars in the bulk soil contributed up to 16% to the overall amino sugar pool after the first year and between 62% and 125% after 7 years of exposure to elevated pCO₂. Amounts of new glucosamine increased by the greatest amount (16–125%) during the experiment, followed by mannosamine (?9% to 107%), muramic acid (?11% to 97%), and galactosamine (15–62%). Proportions of new amino sugars in particle size fractions varied between 38% for muramic acid in the clay fraction and 100% for glucosamine and galactosamine in the coarse sand fraction. Summarizing, during the 7‐year period, amino sugars constituted only between 0.9% and 1.6% of the total SOC content. Therefore, their absolute significance for long‐term C sequestration is limited. Additionally new amino sugars were only sequestered in the silt fraction upon elevated pCO₂ exposure while amino sugar concentrations in the clay fraction decreased. Overall, amino sugar concentrations in bulk soil did not change significantly upon exposure to elevated pCO₂. The calculated mean residence time of amino sugars was surprisingly low varying between 6 and 90 years in the bulk soil, and between 3 and 30 years in the particle size fractions, representing soil organic matter pools with different but relatively low turnover times. Therefore, compound‐specific δ¹³C analysis of individual amino sugars clearly revealed a high amino sugar turnover despite more or less constant amino sugar concentrations over a 7 years period of exposure to elevated pCO₂.     

Variations in Soil Microbial Communities and Residues Along an Altitude Gradient on the Northern Slope of Changbai Mountain,China

Altitudinally-defined climate conditions provide specific vegetation types and soil environments that could influence soil microbial communities, which in turn may affect microbial residues. However, the knowledge is limited in terms of the degree to which microbial communities and residues present and differ along altitude. In this study, we examined the soil microbial communities and residues along the northern slope of Changbai Mountain, China using phospholipid fatty acid (PLFA) and amino sugar analysis, respectively. Soil samples were taken from five different vegetation belts defined by climates. Principal component analysis (PCA) revealed substantial differences in soil microbial community composition among study sites, appeared to be driven primarily by soil pH and C/N ratio on the first principal component (PC1) which accounted for 50.7% of the total sample variance. The alpine tundra was separated from forest sites on the second principal component (PC2) by a signifiscantly higher amount of fungal PLFA (18:2ω6,9). Soil pH and C/N ratio were also correlated with the ratios of Gram-positive to Gram-negative bacteria (Gm⁺/Gm⁻), glucosamine to galactosamine (GluN/GalN), and glucosamine to muramic acid (GluN/MurA). Both total PLFAs and amino sugars were positively correlated with soil organic carbon, inorganic nitrogen, available phosphorus and potassium. We concluded that soil pH and C/N ratio were the most important drivers for microbial community structure and amino sugar pattern, while substrate availability was of great importance in determining the concentrations of microbial communities and residues. These findings could be used to facilitate interpretation of soil microbial community and amino sugar data derived from measurements in latitude or managed forests.