近期6则土壤科学研究进展|研究

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以下为近期6则土壤科学研究进展。

来源：相关机构网站

细菌胞外聚合物在土壤表面的吸附机制

来源：土壤与农业可持续发展国家重点实验室网站（2018年4月13日）

土壤中细菌的生长与代谢过程伴随着胞外聚合物的产生，胞外聚合物含丰富的羧基、羟基、磷酸根等官能团，可在土壤表面发生吸附并影响土壤的电化学性质及土壤对养分的保持能力。但胞外聚合物在土壤表面的吸附能力受pH、离子强度等溶液条件的影响，已有研究大多采用纯矿物或合成的铁铝氧化物，对细菌保温聚合物在实际土壤中的吸附行为知之甚少。

徐仁扣课题组借助原位红外光谱技术(ATR-FTIR)结合电化学分析方法，研究了两种细菌胞外聚合物（EPS)在红壤和黄棕壤胶体表面的吸附容量及其结合机制。研究发现黄棕壤吸附较多的EPS-C和EPS-N，而红壤对EPS-P具有更高的吸附容量。EPS-C、EPS-N和 EPS-P 在红壤和黄棕壤表面的吸附量均随着pH的增加而降低。随着离子强度的增加，EPS-C、EPS-N和 EPS-P 在红壤表面的吸附量持续降低，而在黄棕壤表面呈现先增加后维持稳定的趋势。ATR-FTIR分析表明EPS在红壤表面的饱和吸附量高于黄棕壤。红壤和黄棕壤粘土矿物组成特别是铁铝氧化物含量不同是两种土壤对EPS-C、EPS-N和 EPS-P吸附存在明显差异的主要原因。研究发现静电作用对EPS吸附起着重要作用，此外，EPS中的蛋白质和磷酸基与土壤矿物之间的键合作用也对吸附有贡献。本研究可为解释细菌及其EPS对土壤养分保持与循环的影响提供理论依据。

Ren LY, Hong ZN, Qian W, Li JY, Xu RK. Adsorption mechanism of extracellular polymeric substances from two bacteria on Ultisol and Alfisol. Environmental Pollution, 2018, 237: 39-49

Abstract

The primary objective of this study was to identify the capacity and mechanism of extracellular polymeric substance (EPS) adsorption on soil colloids of Alfisol and Ultisol at different pH and ionic strengths. Two kinds of EPS were extracted from Bacillus subtilis and Pseudomonas fluorescens by centrifugation, and their adsorption on Ultisol and Alfisol was investigated using a batch adsorption experiment and attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FTIR). The average diameter of EPS from B. subtilis and P. fluorescens was 1825 and 1288 nm, respectively, and both the EPS were negatively charged. The zeta potentials of the two EPS became more negative with increasing solution pH from 3 to 8 and less negative with increasing ionic strength from 0 to 80 mM. The maximum adsorption capacity of EPS-C and EPS-N on Alfisol was higher than that on Ultisol, whereas the maximum adsorption capacity of EPS-P on Alfisol was lower than that on Ultisol. The adsorption of EPS-C, EPS-N, and EPS-P of both the EPS on Ultisol and Alfisol decreased with increasing solution pH from 3 to 8. Adsorption of EPS-C, EPS-N, and EPS-P of both the EPS on Alfisol significantly increased with increasing ionic strength from 0 to 10 mM, whereas it remained constant, slightly increased, or reduced, when the ionic strength was increased from 10 to 80 mM. The adsorption of EPS-C, EPS-N, and EPS-P on Ultisol slightly increased with increasing ionic strength from 0 to 80 mM. Saturation coverage determined by ATR-FTIR showed that adsorption of whole EPS on Ultisol was higher than that on Alfisol at pH 6 after 60 min. Thus, electrostatic force between EPS and soil colloids played an important role in EPS adsorption. Besides, proteins and phosphate groups in EPS also contributed to EPS adsorption on soil colloids.

在竹林土壤微生物群落结构和功能演变研究方面取得进展

来源：土壤与农业可持续发展国家重点实验室网站（2018年4月12日）

我国竹林面积占全世界的1/3 左右，其中毛竹(Phyllostachy edulis)林约387万公顷，占我国竹林总面积的72%，主要分布在南方，其碳储量约为409Tg，占我国森林碳储量的2.4%。由于毛竹林生长快、更新周期短，在长期尺度上碳储量潜力很大。土壤微生物驱动了竹林系统的碳循环过程，其中细菌主要分解简单有机物（碳水化合物、有机酸和氨基酸），而真菌分解难降解有机物，细菌和真菌群落演变协同影响了竹林土壤碳转化和碳汇潜力。目前，我国毛竹林土壤微生物的地理分布格局和形成规律仍不清楚，尤其是土壤微生物群落结构演变影响竹林碳代谢的机制缺乏系统研究。

土壤与农业可持续发展国家重点实验室孙波课题组针对我国南方毛竹主产区（福建、浙江、湖南、江西），通过野外采样和高通量测序方法，发现在不同地点毛竹林土壤真菌与细菌群落有显著差异，细菌群落b多样性主要受扩散限制影响，而真菌群落受到较强环境选择影响；真菌网络交互作用显著高于细菌网络，对毛竹林土壤碳源代谢的影响更大。研究结果表明，细菌中酸杆菌门(Acidobacteria)占主导，真菌中子囊菌门(Ascomycota)占主导；只有细菌群落在区域尺度上表现出显著的距离-衰减关系，说明扩散限制是影响细菌b多样性的重要生态过程；细菌群落b多样性受到年均降雨量的直接影响和间接影响（土壤碳储量），而真菌群落b多样性主要受年均温和年均降雨量的直接影响；在区域尺度上真菌b多样性解释了土壤碳代谢图谱的17.7%，显著高于细菌（解释了约2.6%）；真菌生态网络的网络密度比细菌更高，且物种间的交互作用更密切，显著影响了土壤碳代谢过程。

总体上，与细菌群落相比，真菌受到较少的扩散限制作用和较强的环境选择作用，具有较高的生态网络密度，在含有木质素较高的竹林凋落物碳代谢过程中起到更重要的作用。上述研究为在区域尺度上升揭示竹林土壤微生物群落结构和功能的协同演变机制提供了新视角。

这一成果得到了中国科学院重点部署项目和国家重点基础研究发展计划项目的资助。

Xiao X, Liang YT, Zhou S, Zhuang SY, Sun B. Fungal community reveals less dispersal limitation and potentially more connected network than that of bacteria in bamboo forest soils. Molecular Ecology, 2018, 27: 550-563

Abstract

A central aim of this microbial ecology research was to investigate the mechanisms shaping the assembly of soil microbial communities. Despite the importance of bacterial and fungal mediation of carbon cycling in forest ecosystems, knowledge concerning their distribution patterns and underlying mechanisms remains insufficient. Here, soils were sampled from six bamboo forests across the main planting area of Moso bamboo in southern China. The bacterial and fungal diversities were assessed by sequencing 16S rRNA and ITS gene amplicons, respectively, with an Illumina MiSeq. Based on structural equation modelling, dispersal limitation had strongest impact on bacterial beta diversity, while the mean annual precipitation had a smaller impact by directly or indirectly mediating the soil organic carbon density. However, only the mean annual temperature and precipitation played direct roles in fungal beta diversity. Moreover, the co‐occurrence network analyses revealed a possibly much higher network connectivity in the fungal network than in the bacteria. With less dispersal limitation, stronger environmental selection and a potentially more connected network, the fungal community had more important roles in the soil carbon metabolisms in bamboo forests. Fungal beta diversity and the clustering coefficient explained approximately 14.4% and 6.1% of the variation in the carbon metabolic profiles among sites, respectively, but that of bacteria only explained approximately 1.7% and 1.8%, respectively. This study explored soil microbial spatial patterns along with the underlying mechanisms of dispersal limitation, selection and connectivity of ecological networks, thus providing novel insights into the study of the distinct functional traits of different microbial taxa.

我国南方毛竹林土壤微生物群落结构的演变及其对碳代谢功能的影响

草原灌丛化对土壤细菌群落的影响取得进展

来源：土壤与农业可持续发展国家重点实验室网站（2018年4月12日）

由于全球气候变化，草原灌丛化在世界范围内广泛发生，并且具有越演越烈的趋势。目前，全球近10%-20%的干旱半干旱地区正经历草原灌丛化，而我国的内蒙古地区有近 510 万公顷草原发生灌丛化。

中国科学院南京土壤研究所褚海燕课题组通过采集内蒙古草原灌丛化典型区域的土壤样品，利用Illumina Miseq高通量测序技术研究了草原灌丛化对土壤细菌群落的影响。

结果发现：1）草原灌丛化显著增加了土壤细菌群落的多样性，改变表层（0-10 cm）以及深层（20-50 cm）土壤的细菌群落组成；草原灌丛化对土壤细菌群落的影响主要是通过改变土壤pH来实现的；3）此外，草原灌丛化显著增加下层土壤（30-50 cm）硝化螺菌属的相对丰度，进而可能会影响土壤的硝化潜力。

本研究阐明了土壤细菌群落对草地灌丛化的响应规律，为揭示全球变化背景下灌丛化对草原生态系统的影响机制提供了科学依据。

Xiang XJ, Sean M. Gibbons, Li H, Shen HH, Feng JY, Chu HY. Shrub encroachment is associated with changes in soil bacterial community composition in a temperate grassland ecosystem. Plant and Soil, doi: 10.1007/s11104-018-3605-x

Abstract

Aims

The effects of shrub encroachment on plant and soil properties have been well studied. However, little is known about how shrub encroachment influences soil bacterial communities. We investigated the effects of shrub encroachment on grassland soil bacterial communities along a soil depth gradient in the Inner Mongolian region of China.

Methods

The belowground bacterial communities were examined using high-throughput sequencing of the 16S rRNA gene (V4-V5 region, Illumina MiSeq).

Results

Bacterial alpha-diversity was higher in shrub-encroached soils than in control grassland soils. Bacterial OTU richness was highest at 0–20 cm soil depths, while phylogenetic diversity was greatest at 10–20 cm soil depths. At each soil depth layer, shrub encroachment was associated with a significant shift in bacterial community composition. Change in soil pH was the factor most strongly related to change in bacterial community composition associated with shrub encroachment at all four depth horizons in the soils. Shrub encroachment appears to alter the distribution of bacterial life history strategies in the surface soil (i.e., showing an enrichment in copiotrophs and a depletion in oligotrophs) and shrubs are associated with an increase in nitrification potential in deeper soil horizons.

Conclusions

Our results indicate that the influence of shrub encroachment on bacterial community composition extends deep into the soil. The intensity of shrub encroachment at this study site suggests that this ecosystem is undergoing dramatic succession towards shrub-dominance, which will likely trigger shifts in ecosystem function.

在评估杀虫剂氯虫苯甲酰胺的土壤污染风险方面取得进展

来源：土壤与农业可持续发展国家重点实验室网站（2018年4月12日）

氯虫苯甲酰胺（Chlorantraniliprole）是第一个具有新型邻酰胺基苯甲酰胺类化学结构的广谱杀虫剂，由杜邦公司开发。氯虫苯甲酰胺在我国刚要开始广泛使用，主要用于防治二化螟、稻纵卷叶螟、白背飞虱、小菜蛾等。目前对氯虫苯甲酰胺的研究主要集中在田间药效试验和检测分析方法上，而对其在土壤中环境行为的研究相对较少，尤其缺少其对土壤微生物活性和微生物群落结构的影响的研究工作。而这些研究对于合理评价氯虫苯甲酰胺的环境污染风险和对氯虫苯甲酰胺进行安全合理使用非常关键。

土壤与农业可持续发展国家重点实验室李忠佩课题组对氯虫苯甲酰胺潜在的土壤污染风险进行评估，针对我国亚热带不同母质发育的典型水稻土，设置不同施药水平添加氯虫苯甲酰胺，研究氯虫苯甲酰胺的降解动态和在降解过程中对土壤微生物活性和微生物群落的影响。室内85天的培养试验结果表明低浓度的氯虫苯甲酰胺（1mg/kg，相当于田间施药量）对微生物碳源代谢活性和细菌群落结构产生短暂的影响，会很快恢复；而高施药量（10 mg/kg）下，氯虫苯甲酰胺对微生物碳源代谢和细菌群落结构则会产生较大的和较长时间的影响，很难恢复。

该研究结果提示我们在田间施药时，一定要遵守推荐施药量，不可以过量施用氯虫苯甲酰胺，以免对土壤微生物群落产生较大的危害。

Wu M, Li GL, Chen XF, Liu J, Liu M, Jiang CY, Li ZP. Rational dose of insecticide chlorantraniliprole displays a transient impact on the microbial metabolic functions and bacterial community in a silty-loam paddy soil. Science of The Total Environment, 2018, 616-617: 236-244

Abstract

Chlorantraniliprole (CAP) is a newly developed insecticide widely used in rice fields in China. There have been few studies regarding its effects on soil microbial functional diversity and bacterial community composition. An 85-day microcosm experiment was performed to reveal the dissipation dynamics of CAP under different application doses in a silty-loam paddy soil in subtropical China. The half-life of CAP was 51.3 and 62.5 d for low (1 mg kg− 1) and high (10 mg kg− 1) application dose, respectively. We used a combination of community level physiological profile (CLPP) and 16S rRNA gene sequencing analysis to get insights into the soil microbial features responded to CAP during the experiment. Non-metric multidimensional scaling (NMDS) performed on CLPP and the sequence results indicated that the soil microbial functional diversity and bacterial community composition were significantly changed by CAP application at day 14, and recovered to the similar level as no CAP treatment (CK) under low dose of CAP at day 36. However, high dose of CAP imposed longer effect on these soil microbial features, and was still significantly different from CK at day 36. Mcrobial taxa analysis at phylum level showed that high dose of CAP decreased the relative abundance of Nitrospirae at day 14, while increased Bacteroidetes and decreased Actinobacteria, Nitrospirae, and Firmicutes at day 36 in relative to CK. Low dose of CAP only increased Crenarchaeota and decreased Nitrospirae at day 14. The response ratio (RR) analysis was used to quantify significant responses of OTUs to different doses of CAP and found that CAP significantly affected the microbes involving the N transformation. This study provides a basic information to aid in the development of application regulations regarding the safe use of CAP in soil and inspire us to apply CAP at rational dose to minimize its ecotoxicity on soil microbes.

在自然生物膜的功能冗余性及持续性研究中取得进展

来源：土壤与农业可持续发展国家重点实验室网站（2018年4月12日）

在受到外界胁迫时，生态系统的组成及功能会产生多种变化。对于微生物群落而言，组成发生变化而功能维持不变（即功能冗余性）是较为常见的一种现象。自然生物膜是在稻田、沟、塘、浅水湖泊等湿地系统中广泛存在的典型微生物聚集体，具有独特的聚集结构和复杂的群落组成，在湿地生态系统污染物富集、营养盐循环等过程中发挥着不可忽视的作用。人工纳米颗粒越来越多地被使用并释放到环境中，并可对自然生物膜等微生物聚集体产生胁迫作用。研究自然生物膜在纳米颗粒胁迫下群落结构及功能的变化对于深入认识自然生物膜的生态功能及纳米颗粒的环境行为有重要价值。

土壤与农业可持续发展国家重点实验室吴永红课题组系统地研究了纳米二氧化钛（TiO2-NPs）胁迫下自然生物膜的响应机制及其污染物去除功能。研究发现，TiO2-NPs胁迫对自然生物膜的光合作用效率及生物量的积累有一定的抑制作用，但是与对照相比并无显著性差异。部分TiO2-NPs可穿透细胞膜，而且在与生物膜接触后，TiO2-NPs的粒径变大，说明发生了聚集作用。TiO2-NPs胁迫下自然生物膜胞外蛋白含量显著增加，而且EPS红外光谱中多个官能团的吸收峰发生偏离，表明EPS在自然生物膜抵抗纳米颗粒胁迫中起着重要作用。此外，TiO2-NPs暴露后自然生物膜维持着较强的COD及Cu去除能力，且与对照组之间无显著差异。说明自然生物膜可通过调整群落结构及代谢等过程来维持原本的污染物去除功能，具有较高的功能冗余性及持续性。

Liu JZ, Tang J, Wan JJ, Wu CX, Bruce Graham, Philip G. Kerr, Wu YH. Functional sustainability of periphytic biofilms in organic matter and Cu 2+ removal during prolonged exposure to TiO 2 nanoparticles. Journal of Hazardous Materials, doi: 10.1016/j.jhazmat.2017.08.068

Abstract

Responses of microbial communities to nanotoxicity in aquatic ecosystems are largely unknown, particularly with respect to relationship between community dynamics and functions. Here, periphytic biofilms were selected as a model of species-rich microbial communities to elucidate their responses when exposed to titanium dioxide nanoparticles (TiO2-NPs). Especially, the relationships between the functions (e.g. organic matter and Cu2+ removal) and community dynamics after long-term exposure to TiO2-NPs were assessed systematically. After 5 days exposure to TiO2-NPs (5 mg L−1), periphytic biofilms showed sustainable functions in pollutant removal and strong plasticity in defensing the toxic disturbance of TiO2-NPs, including photosynthesis and carbon metabolic diversity. The sustainable pollutant removal functions of periphytic biofilms were attributed to their functional redundancy. Specifically, periphytic biofilms altered their composition with cyanobacteria, Sphingobacteriia and Spirochaetes being the newly dominant taxa, and changed the carbon substrate utilization pattern to maintain high photosynthesis and metabolic rates. Moreover, extracellular polymeric substances (EPS) especially proteins were overproduced to bind the NPs and thereby reduce the nanotoxicity. The information obtained in this study may greatly help to understand the interactions between microbial community dynamics and function under NPs exposure conditions and functional redundancy is an important mechanism of periphytic biofilms to maintain sustainable functions.

森林土壤反硝化过程的氮同位素分馏效应研究获进展

来源：中国科学院网站（2018年4月8日）

反硝化过程被认为是生态系统气态氮损失的主要途径，也是导致生态系统氮限制的重要机制。但是，由于缺乏从生态系统尺度上直接测定反硝化作用速率的技术，在过去对氮循环的研究中，生态系统尺度上的反硝化速率一直难以量化。近年来，硝酸盐的15N/14N比值被用于量化生态系统尺度上的反硝化速率。但是，利用15N同位素自然丰度量化需要考虑反硝化过程中的同位素分馏效应。研究发现在不同环境和实验条件下，反硝化过程中氮同位素分馏效应（15ε）的差异非常大，并且15ε对生态系统尺度上反硝化速率测定的影响非常大。尽管目前对15ε的研究很多，但是多数研究都集中于反硝化细菌纯培养、淡水环境、沉积物和农业土壤，缺乏对森林土壤的研究。因此，为了加强对森林土壤反硝化过程中同位素分馏效应的理解，减少森林生态系统反硝化速率测定的不确定性，研究森林土壤反硝化过程中N和O同位素分馏效应是至关重要的。

基于此，中国科学院沈阳应用生态研究所稳定同位素生态学研究团队在研究员方运霆带领下，选择清原典型的温带落叶松林和混交林，以及海南典型的热带原始林和次生林为研究对象，测定四个森林土壤原生微生物群落反硝化过程中的同位素分馏效应以及氮氧同位素分馏效应的比值（△δ¹⁸O:△δ¹⁵N）。结果表明森林土壤反硝化过程中氮同位素分馏效应（¹⁵ε）为31‰到65‰（图1），远高于以往反硝化细菌纯培养和其他环境条件下（淡水环境，海洋沉积物和农业土壤）的研究结果（5‰到30‰）（图2）。氧同位素分馏效应（¹⁸ε）为11‰到39‰，与以往研究结果相当（5‰到24‰）。另外，森林土壤反硝化过程中△δ¹⁸O:△δ¹⁵N比值为0.28到0.60（平均值为0.38 ± 0.02）（图1），低于以往陆地生态系统研究所报道的反硝化过程中的△δ¹⁸O:△δ¹⁵N比值（0.5到1）。研究结果表明不同气候区或不同土壤类型反硝化分馏效应可能存在差异。研究人员进一步应用该研究结果中的反硝化分馏效应估算陆地生态系统反硝化速率，发现在过去的研究中陆地生态系统反硝化作用对总氮损失的贡献可能被高估。

以上研究成果以High nitrogen isotope fractionation of nitrate during denitrification in four forest soils and its implications for denitrification rate estimates 为题于3月28日在线发表在Science of the Total Environment 期刊。博士王盎为第一作者；方运霆和中国林业科学研究院热带林业研究所副研究员陈德祥为共同通讯作者。相关工作得到了中国国家重点研发项目、中科院先导专项（B）、国家基金委、中科院重点科技前沿项目、中科院百人计划项目和中科院热带森林生态学重点实验室开放课题的支持。

图1. 森林土壤厌氧培养下，反硝化过程中N同位素分馏效应和△δ¹⁸O:△δ¹⁵N比值 

图2. 不同环境和实验条件下的N同位素分馏效应（¹⁵ε） 

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