黄土丘陵区不同植被类型根际微生物群落功能多样性研究

为了解生态恢复过程中土壤微生物功能特征,采用Biolog-Eco微平板法分析了黄土丘陵区人工灌木(柠条 Caragana korshinskii、沙棘 Hippophaer rhamnoides)、人工草地(沙打旺 Astragalus adsurgens、柳枝稷 Panicum virgatum)和天然草地(阿尔泰狗哇花 Heteropappus altaicus、茵陈蒿 Artemisia capillaries)的根际微生物碳源代谢多样性特征。结果表明:柠条、阿尔泰狗哇花和茵陈蒿的根际微生物对糖类的代谢能力显著高于沙棘、沙打旺和柳枝稷;阿尔泰狗哇花和茵陈蒿对氨基酸类、酚酸类和聚合物类的代谢能力较高。茵陈蒿和阿尔泰狗哇花的微生物代谢功能多样性高于其他4种植物。柠条、阿尔泰狗哇花和茵陈蒿具有相似的根际微生物代谢功能。黄土丘陵区植被类型显著影响微生物群落碳源利用能力,天然草地根际微生物群落代谢功能多样性优于人工灌木和人工草地。     

Density, structure, and diversity of the cultivable arylsulfatase-producing bacterial community in the rhizosphere of field-grown rape and barley

In this study we investigated the arylsulfatase-producing bacterial community (ARS-BC) in the rhizosphere soils of field-grown rape in comparison with that of barley. For this, the rhizosphere soils from both plant species were sampled four times during plant growth. Soil arylsulfatase (ARS) activity and the density and the structure of the cultivable ARS-BC on M9-Xsulf medium were then determined. ARS activity in rape rhizosphere was greater than in barley rhizosphere and evolved along the phenology in the two rhizosphere soils. In parallel, the average density of ARS-BC in the rape rhizosphere was higher than that in the barley rhizosphere. Moreover, ARS activity is correlated with ARS-BC density both in rape and barley rhizosphere soils. The structure of the ARS-BC in the rape rhizosphere was different from that in the barley rhizosphere. In the rape rhizosphere, the ARS-BC was substantially more structured than in the barley rhizosphere. Among the ARS-BC, Actinobacteria and Pseudomonads were significantly present in the both rhizosphere soils. Actinobacteria predominated in the barley rhizosphere while Pseudomonads were mostly represented under rape. It is possible that the differences in ARS activity observed between rape and barley can be attributed to a different ARS-BC size and/or a different ARS-BC structure under these two plant covers. This impact of rape may be connected to a selective effect of rhizodeposits released by rape roots to the functional bacterial community. Our findings suggest that plant species, via their rhizodeposits, may affect the functional bacterial community and thus influence the dynamic of S in soil.     

Microbial response to exudates in the rhizosphere of young beech trees (Fagus sylvatica L.) after dormancy

Plants act as an important link between atmosphere and soil: CO2 is transformed into carbohydrates by photosynthesis. These assimilates are distributed within the plant and translocated via roots into the rhizosphere and soil microorganisms. In this study, 3 year old European beech trees (Fagus sylvatica L.) were exposed after the chilling period to an enriched ¹³C–CO₂ atmosphere (δ¹³C = 60‰ – 80‰) at the time point when leaves development started. Temporal dynamics of assimilated carbon distribution in different plant parts, as well as into dissolved organic carbon and microbial communities in the rhizosphere and bulk soil have been investigated for a 20 days period. Photosynthetically fixed carbon could be traced into plant tissue, dissolved organic carbon and total microbial biomass, where it was utilized by different microbial communities. Due to carbon allocation into the rhizosphere, nutrient stress decreased; exudates were preferentially used by Gram-negative bacteria and (mycorrhizal) fungi, resulting in an enhanced growth. Other microorganisms, like Gram-positive bacteria and mainly micro eucaryotes benefited from the exudates via food web development. Overall our results indicate a fast turnover of exudates and the development of initial food web structures. Additionally a transport of assimilated carbon into bulk soil by (mycrorhizal) fungi was observed.     

From the micro-scale to the habitat: Assessment of soil bacterial community structure as shown by soil structure directed sampling

Natural structural units of a luvisol under maize crop were studied to assess if soil structure directed sampling could improve the understanding of arrangements of bacteria in spatially constraint location. Three habitats were defined: (i) soil around fine lateral roots (rhizo-aggregates), (ii) soil close to basal roots (core clods) and (iii) unplanted soil between rows (bare soil clods). These habitats were also investigated with maize plants resulting from Azospirillum lipoferum CRT1 inoculated seeds as a model of enhanced fine root system. Rhizo-aggregates were clearly separated from each other (disconnected habitat) in contrast to micro-samples (fragments) from clods, which belong to cohesive macro-structures. Genetic fingerprints on metagenomic extracts were used to characterize the structure of bacterial communities on 95 micro-samples from the three habitats. For eubacteria, automated RISA (Ribosomal Intergenic Spacer Analysis) of ITS (Internal Transcribed Spacer) profiles were performed. PCR-RFLP on nifH gene were used to describe the N-fixer guilds. Exploratory multivariate analyses (PCA and MDS) revealed bacterial community patterns in the sampled habitats. On the basis of ITS profiles, rhizo-aggregates harboured closely related communities, distant from those of the unplanted soil, and each sampled rhizo-aggregate could therefore be considered as a sub-unit of the whole macro-habitat, comprising all the fine roots. The observed low dissimilarity of disconnected rhizo-aggregates is likely to result from the direct influence of maize root tips on the recruitment of rhizosphere bacteria. Molecular fingerprints of nifH from basal root clods (core) were more similar to bare soil than to rhizo-aggregates, indicating similar ecological conditions without, or with, at least, poor maize exudating root influence. Although our study was performed on a limited number of situations, the distribution of bacteria was revealed to be patterned by soil structure units, which is a first step to improve the modelling of microbial ecology in soils.     

硫在稻根微域中化学行为及其对水稻吸收重金属的影响机理

我国水稻种植面积和产量分别占世界23%和40%.人类活动,如农药和除草剂施用、采矿、污水灌溉,已经导致了一些地区水稻土污染.开发能够控制、减少水稻对重金属吸收和经食物链传递的技术与方法,对确保食物安全具有重要意义.硫(S)有6个化合态,土壤硫化合物种类多,其在土壤中转化相当复杂,在土壤环境化学研究中具有重要地位.本文收集了国内外有关文献,评述了S在水稻土中的含量、形态及转化,重点阐述了S在根际微域化学行为及其与水稻吸收重金属之间的关联,并提出了未来应开展的主要研究方向.     

根际微生物对药材道地性的影响

在植物、土壤与微生物所构成的根际微生态系统中,微生物对于土壤肥力的形成、养分的转化吸收、植物生长发育以及植物病虫害的生物防治具有重要的作用.通过对影响根际微生物种群结构因素分析以及根际微生物影响土壤养分释放和植物生长等功能的初步探讨,以期为药材道地性的研究提供新的思路和方法,指导道地药材的生产和实践.     

根际通气对盆栽玉米生长与根系活力的影响

针对盆栽作物生长空间有限且通气不良的生长环境问题,为改善根际气体环境,试验设每隔2d通气1次(T1)、每隔4d通气1次(T2)两个通气处理,以不通气(CK)为对照,研究根际通气对盆栽玉米生长及根系活力的影响。结果表明,T1和T2处理均能提高玉米株高、叶面积、叶绿素含量,促进地上部分和地下部分干物质的积累。T1、T2处理有利于提高玉米根冠比和根系活力,拔节期T1和T2处理的根冠比分别是CK的1.27倍、1.18倍,根系活力分别为CK的1.26倍和1.54倍;抽穗期根冠比分别为CK的1.18倍、1.09倍,根系活力分别为CK的1.22倍和1.40倍。同时,通气处理能够促进作物吸收土壤内的养分。研究结果表明,根际通气能够增强盆栽玉米的根系活力,促进植株的生长发育。     

Stand level estimation of root respiration for two subtropical plantations based on in situ measurement of specific root respiration

In this study, the stand level root respiration was estimated for two monoculture plantations: Acacia crassicarpa and Eucalyptus urophylla, based on in situ measurement of specific root respiration using simplified root chamber method. The respiration rates of fine roots (<5 mm) were significantly higher than those of coarse roots (>5 mm) for both A. crassicarpa and E. urophylla species. The root respiration of A. crassicarpa showed a clear seasonal pattern with a higher value in the wet season. For E. urophylla, the seasonal pattern was observed for fine roots but not for coarse roots. After determining the biomass of fine roots and coarse roots and their specific rates of respiration at different time points, root respiration at the stand level (R_a) was estimated using a direct up-scaling model. We found that the R_a accounted for 14% and 19% of total soil respiration (R_s) for A. crassicarpa and E. urophylla, respectively. The fine (R_Tf) and coarse (R_Tc) root respiration at the stand level accounted for about 47% and 53% of the R_a for A. crassicarpa, and accounted for 58% and 42% for E. urophylla. This suggests that coarse root respiration cannot be ignored when estimating the root respiration at the stand level. Our results showed that the Q₁₀ values were more accurate in representing the temperature dependence when the confounding effect of soil moisture was considered. This study introduces an alternative approach to estimate stand level root respiration, but its reliability is largely dependent on the accuracy of root biomass quantification.     

铁处理有机物料接种蚯蚓对苹果根际和蚯蚓粪中有机酸的影响

以8年生红富士苹果树为试材,用不同形态、不同浓度的铁处理玉米秸秆接种蚯蚓,玉米秸秆被蚯蚓转化为蚯蚓粪后,研究对根际和蚯蚓粪有机酸的影响.苹果根际和蚯蚓粪中检测到的有机酸主要有草酸、苹果酸、酒石酸、琥珀酸和丙二酸,以草酸含量为高.没有用铁处理有机物料的根际有机酸高于用铁处理的,Fe3+处理有机物料的根际有机酸含量大于Fe2+处理,蚯蚓粪中的有机酸含量均以5 000 mg/kg浓度的铁处理最高.     

复合生防菌群对连作土壤大豆根际可培养微生物区系的影响

土壤微生物区系的变化是引起大豆连作障碍的主要因素之一。本实验采用盆栽试验,研究了复合生防菌群对大豆根际土壤可培养微生物区系的调节作用。结果表明,复合生防菌群可以明显改变大豆根际微生物区系组成。在大豆不同时期,复合生防菌群处理的大豆根际细菌、真菌和放线在数量发生较大改变。在大豆真叶期和复叶期,复合生防菌群接种处理大豆根际细菌较对照增幅分别达到71.8%和114.3%,而根际真菌较对照减少12.9%和22.3%.。在大豆真叶期,复合生防菌群接种处理大豆根际放线菌数量较对照减少9.9%,而在复叶期,根际放线数量较对照增加27.4%。此外,研究结显示,施用复合生防菌可有效降低土传病原菌镰孢菌属（Fusarium）和丝核菌属（Rhizoctonia）的比例,并且提高根瘤菌（Rhizobium）、固氮菌（Azotobacter）、木霉属（Trichoderma）、假单胞菌属（Pseudomonas）和芽孢杆菌属(Bacillus)等有益菌的比例。总之,该复合生防菌群对改善连作土壤大豆根际微生物区系方面有良好的效果。