Priming and microbial nutrient limitation in lowland tropical forest soils of contrasting fertility

Priming is an increase in soil organic carbon decomposition following input of labile organic carbon. In temperate soils where biological activity is limited commonly by nitrogen availability, priming is expected to occur through microbial acquisition of nitrogen from organic matter or stimulated activity of recalcitrant-carbon degrading microorganisms. However, these priming mechanisms have not yet been assessed in strongly weathered tropical forest soils where biological activity is often limited by the availability of phosphorus. We examined whether microbial nutrient limitation or community dynamics drive priming in three lowland tropical forest soils of contrasting fertility (‘low’, ‘mid’ and ‘high’) by applying C₄-sucrose (alone or in combination with nutrients; nitrogen, phosphorus and potassium) and measuring (1) the δ¹³C-signatures in respired CO₂ and in phospholipid fatty acid (PLFA) biomarkers, and (2) the activities of enzymes involved in nitrogen (N-acetyl β-glucosaminidase), phosphorus (phosphomonoesterase) and carbon (β-glucosidase, cellobiohydrolase, xylanase, phenol oxidase) acquisition from organic compounds. Priming was constrained in part by nutrient availability, because priming was greater when sucrose was added alone compared to when added with nutrients. However, the greatest priming with sucrose addition alone was detected in the medium fertility soil. Priming occurred in parallel with stimulated activity of phosphomonoesterase and phenol oxidase (but not N-acetyl β-glucosaminidase); when sucrose was added with nutrients there were lower activities of phosphomonoesterase and phenol oxidase. There was no evidence according to PLFA δ¹³C-incorporation that priming was caused by specific groups of recalcitrant-carbon degrading microorganisms. We conclude that priming occurred in the intermediate fertility soil following microbial mineralization of organic nutrients (phosphorus in particular) and suggest that priming was constrained in the high fertility soil by high nutrient availability and in the low fertility soil by the low concentration of soil organic matter amenable to priming. This first study of priming mechanisms in tropical forest soils indicates that input of labile carbon can result in priming by microbial mineralization of organic nutrients, which has important implications for understanding the fate of organic carbon in tropical forest soils.     

An Integrated Study to Analyze Soil Microbial Community Structure and Metabolic Potential in Two Forest Types

Soil microbial metabolic potential and ecosystem function have received little attention owing to difficulties in methodology. In this study, we selected natural mature forest and natural secondary forest and analyzed the soil microbial community and metabolic potential combing the high-throughput sequencing and GeoChip technologies. Phylogenetic analysis based on 16S rRNA sequencing showed that one known archaeal phylum and 15 known bacterial phyla as well as unclassified phylotypes were presented in these forest soils, and Acidobacteria, Protecobacteria, and Actinobacteria were three of most abundant phyla. The detected microbial functional gene groups were related to different biogeochemical processes, including carbon degradation, carbon fixation, methane metabolism, nitrogen cycling, phosphorus utilization, sulfur cycling, etc. The Shannon index for detected functional gene probes was significantly higher (P<0.05) at natural secondary forest site. The regression analysis showed that a strong positive (P<0.05) correlation was existed between the soil microbial functional gene diversity and phylogenetic diversity. Mantel test showed that soil oxidizable organic carbon, soil total nitrogen and cellulose, glucanase, and amylase activities were significantly linked (P<0.05) to the relative abundance of corresponded functional gene groups. Variance partitioning analysis showed that a total of 81.58% of the variation in community structure was explained by soil chemical factors, soil temperature, and plant diversity. Therefore, the positive link of soil microbial structure and composition to functional activity related to ecosystem functioning was existed, and the natural secondary forest soil may occur the high microbial metabolic potential. Although the results can''t directly reflect the actual microbial populations and functional activities, this study provides insight into the potential activity of the microbial community and associated feedback responses of the terrestrial ecosystem to environmental changes.     

Contrasting diurnal variations in soil organic carbon decomposition and root respiration due to a hysteresis effect with soil temperature in a Gossypium s. (cotton) plantation

Cool-season grasses commonly harbor fungal endophytes in their aerial tissues. However the effects of these symbionts on soil microbial communities have rarely been investigated. Our objective was to explore microbial community responses in soils conditioned by plants of the annual grass Lolium multiflorum with contrasting levels of infection with the endophyte Neotyphodium occultans. At the end of the host growing season, we estimated the functional capacity of soil microbial communities (via catabolic response profiles), the contribution of fungi and bacteria to soil activity (via selective inhibition with antibiotics), and the structure of both microbial communities by molecular analyses. Soil conditioning by highly infected plants affected soil catabolic profiles and tended to increase soil fungal activity. We detected a shift in bacterial community structure while no changes were observed for fungi. Soil responses became evident even without changes in host plant biomass or soil organic carbon or total nitrogen content, suggesting that the endophyte modified host rhizodepositions during the conditioning phase. Our results have implications for the understanding of the reciprocal interactions between above and belowground communities, suggesting that plant-soil feedbacks can be mediated by this symbiosis.     

镜泊湖岩溶台地不同植被类型土壤微生物群落特征

为了探讨不同演替阶段植被类型土壤微生物群落特征,分别选取镜泊湖岩溶台地草本、矮灌木、高灌木、小乔木与灌木混生(简称混生)群落、落叶阔叶林及针阔混交林6种典型植被类型,进行植物群落调查和对土壤微生物生物量、群落结构和多样性指标、土壤物理化学性质的测定。结果表明：从土壤微生物量、土壤微生物群落组成、土壤微生物代谢动力学过程和代谢功能多样性的角度来看,各种植被类型土壤微生物群落具有明显的差异。演替前期的草本群落土壤微生物量碳氮、细菌生物量、真菌生物量,代谢活性及丰富度指数均最低,但Shannon-Wiener多样性指数和均匀度指数显著(P<0.05)高于其他植被类型。矮灌木土壤微生物群落组成显著受植被类型的影响。高灌木群落和混生(小乔木与灌木混生)群落具有极强的相似性, 但在碳源利用类型上两者表现出一定的差异。落叶阔叶林代谢活性最高,碳源利用能力最强,能利用BIOLOG微孔板中的所有31种碳源,这与其具有较高的微生物量碳氮和细菌生物量一致,其代谢功能丰富度最高。演替后期的针阔混交林下的土壤pH最低,真菌比例升高,在碳源丰富的条件下具有极强的竞争优势(仅次于落叶阔叶林),但在碳源贫瘠的条件下其利用碳源能力较弱(仅高于草本)。植被可能主要通过土壤全磷和有机质影响土壤微生物代谢功能多样性。     

Ex-situ enzyme activity and bacterial community diversity through soil depth profiles in penguin and seal colonies on Vestfold Hills, East Antarctica

The soils impacted by sea animal excreta are important sources of nutrients in Antarctic terrestrial ecosystems, and soil microorganisms are the principal drivers of carbon and nitrogen cycling. However, microbial diversity and enzyme activities in these soils have still received little attention. In this paper, we investigated the distribution characteristics of bacterial community in four penguin and seal colony soil profiles collected in East Antarctica, using 16S rDNA-DGGE and real-time quantitative PCR. Soil microbial biomass carbon (C_mic), soil respiration (SR), and enzyme activities involved in carbon, nitrogen, and phosphorus metabolisms were also measured. Overall soil C_mic, SR, enzyme activities, and bacterial abundance decreased with depth. The bacterial abundance had a significant correlation with soil organic carbon and total nitrogen and highly corresponded to the relative content of penguin guano or seal excreta in these soil profiles. The 16S rDNA-DGGE revealed the complicated bacterial community structure in penguin and seal colony soils, and the band richness and dominant bands decreased with soil depth. Cluster analysis of DGGE profiles indicated that bacterial community in those soil profiles were divided into four main categories with the bacterial genetic similarity of 22 %, and the majority of the sequenced bands were Proteobacteria (α, β, γ), Actinobacteria, Bacteroidetes, Deinococcus-Thermus, Chloroflexi, and Firmicutes. Our results indicated that the deposition of penguin guano or seal excreta, which caused the variability in soil soil organic carbon, total nitrogen, pH, and soil moisture, might have an important effect on the vertical distribution pattern of bacterial abundance and diversity in Antarctic soil profiles.     

Changes in Bacterial and Archaeal Community Structure and Functional Diversity along a Geochemically Variable Soil Profile

Spatial heterogeneity in physical, chemical, and biological properties of soils allows for the proliferation of diverse microbial communities. Factors influencing the structuring of microbial communities, including availability of nutrients and water, pH, and soil texture, can vary considerably with soil depth and within soil aggregates. Here we investigated changes in the microbial and functional communities within soil aggregates obtained along a soil profile spanning the surface, vadose zone, and saturated soil environments. The composition and diversity of microbial communities and specific functional groups involved in key pathways in the geochemical cycling of nitrogen, Fe, and sulfur were characterized using a coupled approach involving cultivation-independent analysis of both 16S rRNA (bacterial and archaeal) and functional genes (amoA and dsrAB) as well as cultivation-based analysis of Fe(III)-reducing organisms. Here we found that the microbial communities and putative ammonia-oxidizing and Fe(III)-reducing communities varied greatly along the soil profile, likely reflecting differences in carbon availability, water content, and pH. In particular, the Crenarchaeota 16S rRNA sequences are largely unique to each horizon, sharing a distribution and diversity similar to those of the putative (amoA-based) ammonia-oxidizing archaeal community. Anaerobic microenvironments within soil aggregates also appear to allow for both anaerobic- and aerobic-based metabolisms, further highlighting the complexity and spatial heterogeneity impacting microbial community structure and metabolic potential within soils.     

黄土丘陵沟壑区地形变化对土壤微生物群落功能多样性的影响

研究黄土高原丘陵沟壑区破碎地形对土壤微生物功能多样性的影响,对于理解复杂地形区生态过程与系统功能的空间变化具有重要意义。选择陕西省安塞县陈家洼为研究区,依据坡面地形变化选择不同坡位土壤,采用Biolog微平板培养法探究地形变化对土壤微生物群落功能多样性的影响。实验发现,土壤微生物群落培养的平均颜色变化率(AWCD)增长曲线总的呈现出坡下部坡中部坡上部的规律,且坡下部AWCD值与坡中部、坡上部间差异显著(P0.05);坡下部土壤微生物群落功能多样性显著高于坡中部和坡上部,但不同土层深度(0—10 cm、10—20 cm)间无显著性差异(P0.05);对土壤微生物群落功能多样性差异贡献较大的碳源是糖类、羧酸类和多酚化合物类碳源;土壤含水率高低是不同坡位土壤微生物群落功能多样性差异显著的主要原因;微生物群落丰富度(H)和均一度(D)与土壤全氮含量正相关,优势度(U)反之,土壤全碳、全磷和p H对土壤微生物群落结构和功能多样性差异作用不显著。     

车八岭山地常绿阔叶林冰灾后土壤微生物群落功能多样性

研究了我国南方冰灾后常绿阔叶林林冠开度及土壤养分的空间异质性对土壤微生物功能多样性的影响.在受冰灾影响的粤北车八岭山地常绿阔叶林2 hm2固定样地中按照冠层受损程度选取16个20 m×20 m的样方,用半球面影像技术获取林冠开度,并取0～20 cm的表层土壤混合样品分析土壤的理化性质,同时应用Biolog技术分析微生物功能多样性.按林冠开度梯度对各样方土壤微生物群落利用单一碳源的分析发现,林冠开度大的样方土壤微生物的活性、丰富度、多样性和均匀度都较低,反之则较高.聚类分析的结果与林冠开度的梯度有高度的一致性.主成分分析表明各样方土壤微生物功能多样性具有显著差异(第一轴p<0.005;第二轴p<0.001),其结果与聚类结果基本吻合.冗余分析揭示了土壤全磷、全钾、全氮、速效氮、有机碳、容重、总孔隙度和林冠开度的综合作用对土壤微生物功能多样性有显著影响(p<0.005),其中林冠开度与土壤微生物群落功能多样性的关系最密切.土壤微生物功能多样性受土壤养分的影响,具体表现为:与土壤有机碳呈明显的正相关;与全氮正相关;与速效氮、全磷负相关.研究说明冰灾所造成林冠开度和土壤养分的空间异质性会影响到土壤微生物功能多样性,而土壤微生物功能多样性可用于对生境恢复的指示和评价.     

湿地土壤微生物功能多样性及碳氮组分对长期氮输入的响应

氮输入对湿地生态系统碳氮循环具有重要影响,研究湿地土壤微生物功能多样性及碳氮组分对氮输入的响应,对于明确湿地土壤碳氮循环微生物驱动机制具有重要意义。依托长期野外氮输入模拟试验,利用Biolog-ECO微平板技术,分析不同浓度氮输入:N1(6 g N m^-2 a^-1)、N2(12 g N m^-2 a^-1)和N3(24 g N m^-2 a^-1)对湿地土壤表层(0-15 cm)和亚表层(15-30 cm)微生物碳源代谢活性、功能多样性和碳氮组分的影响。结果表明:N2处理显著提高了亚表层土壤微生物碳源代谢活性和McIntosh指数,N3处理显著降低了表层土壤微生物Shannon指数和Shannon-evenness指数。随氮输入浓度增加湿地表层土壤微生物对糖类的利用率显著降低,N3处理表层土壤微生物对胺类的利用率以及亚表层土壤微生物对醇类的利用率显著提高。N1处理显著提高了湿地表层土壤全氮和微生物量碳含量;N2、N3处理显著提高了土壤铵态氮、硝态氮含量;N3处理显著降低了土壤pH值。湿地土壤pH、总碳、溶解性有机碳含量是影响微生物碳源代谢活性和功能多样性的重要因素,土壤溶解性有机碳、铵态氮、全氮含量、含水率是影响微生物碳源利用变化的主要因子。     

高原鼢鼠扰动及恢复年限对高寒草甸土壤养分和微生物功能多样性的影响

为了研究高原鼢鼠扰动后退化高寒草甸恢复演替的动态过程,利用常规实验室分析方法和Biolog-ECO生态板法对青藏高原东缘高寒草甸土壤养分和微生物功能多样性进行分析.结果表明: 高原鼢鼠扰动显著降低了土壤有机质、全氮、速效氮和速效磷含量,对土壤全磷和全钾含量无显著影响;在一定植被恢复年限内,土壤微生物的碳源利用率、Shannon、Pielou和McIntosh指数随着植被恢复年限的增加而升高;主成分分析表明,碳水化合物和氨基酸是土壤微生物利用的主要碳源类型;冗余分析表明,土壤pH、有机质、全氮、速效氮和全钾是影响土壤微生物代谢活性和功能多样性的主要因子.不同植被恢复年限土壤微生物功能多样性的变化可能是对地上植被、土壤微生物群落组成和土壤养分变化的响应.     

荒坡地种植巨菌草对土壤微生物群落功能多样性及土壤肥力的影响

研究种植于荒坡地、不同生长年限(1、2、3、5a)的巨菌草对土壤微生物群落功能多样性及肥力的影响。结果表明,不同生长年限巨菌草土壤微生物对不同碳源的利用随培养时间延长而增大,培养72—96 h变化最明显,培养144 h后各土壤AWCD值均达到最大值。总体上AWCD值大小依次为:2年生3年生1年生5年生CK,不同生长年限的巨菌草土壤AWCD值均比对照高,且差异显著,2年生AWCD值最高,其次为3年生,1年生、5年生巨菌草土壤AWCD值差异不显著。对培养96 h土壤微生物利用碳源特性进行主成分分析,31个碳源中提取的与土壤微生物碳源利用相关的主成分8个,其中主成分1至主成分8分别能够解释变量方差的25.39%、18.89%、11.28%、9.31%、6.84%、5.60%、5.26%、4.71%,合计解释变量方差的87.27%;主成分1、主成分2能够区分不同生长年限巨菌草土壤的微生物群落特征,2年生、3年生巨菌草土壤微生物功能多样性与CK相比,差异显著;与主成分1显著相关的碳源主要是糖类,氨基酸,羧酸和多聚物,与主成分2显著相关的碳源主要是氨基酸。不同生长年限的巨菌草的Shannon(H)、均匀度、Brillouin指数均高于CK,且差异显著,2年生与3年生差异不显著,1年生与5年生差异不显著。总体上不同生长年限巨菌草的土壤的pH值、有机质、碱解氮、有效磷、速效钾的含量比对照高,其中3年生巨菌草的土壤有机质含量比对照高98.20%,5年生巨菌草土壤的碱解氮含量比对照高93.2%;除1年生巨菌草外,有机质、碱解氮含量均与对照差异显著。在荒坡地种植巨菌草,可增加土壤微生物群落功能多样性,在一定程度上提高土壤肥力,荒坡地种植巨菌草能产生一定的生态正效应。     

凋落物对土壤有机碳与微生物功能多样性的影响

森林凋落物是影响土壤微生物群落和有机碳含量的重要因素,但其作用的程度和机制尚不清楚,研究该问题对于分析森林生态系统碳循环和资源管理具有重要意义。研究凋落物去除与添加处理下土壤有机碳含量与土壤微生物对碳源利用的差异,明确凋落物去除与添加对土壤微生物群落代谢功能及其多样性的影响,探究不同处理下SOC含量变化的土壤微生物群落代谢机理。选取承德市雾灵山1405-1435 m海拔范围内核桃楸-蒙古栎混交林的表层土壤,采用室内培养结合Biolog-ECO方法,测定了培养第21天的土壤有机碳（soil organic carbon,SOC）含量及微生物群落的AWCD值、Shannon-Wiener多样性指数、Simpson优势度指数、McIntosh均匀度指数、Pielou丰富度指数,分析培养期内凋落物的不同处理下SOC含量与微生物功能多样性的变化特征。结果表明：1）不同凋落物处理对SOC含量与土壤微生物群落多样性具有显著影响（P<0.05）,DL > HL > NL > CK;2）不同凋落物处理下土壤微生物群落代谢活性和土壤微生物对碳源的利用程度具有显著差异（P<0.05）,碳水化合物类和氨基酸类是土壤微生物的主要碳源;3）不同处理的SOC含量与土壤微生物多样性具有正相关关系。双倍凋落物添加在短期内对土壤微生物多样性影响难以达到显著水平且在一定程度上对土壤微生物的代谢活性具有抑制作用,土壤微生物群落功能多样性对SOC含量具有重要影响。     

独山子区优势草本植物根际与非根际土壤微生物功能多样性

以独山子区3种优势草本植物的根际与非根际土壤为研究对象,采用Biolog-ECO微平板法对土壤微生物功能多样性进行了研究。结果表明:3种不同植物根际与非根际土壤微生物代谢活性(AWCD)、丰富度指数Shannon(H)和均匀度指数Mc Intosh(U)均存在不同差异,且博乐蒿根际土壤微生物功能多样性均优于非根际土壤及其他两种植物;根际土壤微生物对糖类、脂类、酸类和胺类碳源物质比较敏感,非根际土壤微生物敏感于酸类、氨基酸类以及糖类碳源,根际土壤微生物对碳源的利用能力更强,且不同植物根际环境微生物碳源利用特征不同;微生物活性、丰富度指数和微生物均匀度指数与土壤pH值、SOM、AP和NO-3-N存在显著正相关(P0.05);博乐蒿根际土壤养分含量与微生物活性均较高,对环境的适应性更强,在独山子区生态环境管理与建设中可对其进行关注。     

The earliest stages of ecosystem succession in high-elevation (5000 metres above sea level), recently deglaciated soils

Global climate change has accelerated the pace of glacial retreat in high-latitude and high-elevation environments, exposing lands that remain devoid of vegetation for many years. The exposure of 'new' soil is particularly apparent at high elevations (5000 metres above sea level) in the Peruvian Andes, where extreme environmental conditions hinder plant colonization. Nonetheless, these seemingly barren soils contain a diverse microbial community; yet the biogeochemical role of micro-organisms at these extreme elevations remains unknown. Using biogeochemical and molecular techniques, we investigated the biological community structure and ecosystem functioning of the pre-plant stages of primary succession in soils along a high-Andean chronosequence. We found that recently glaciated soils were colonized by a diverse community of cyanobacteria during the first 4-5 years following glacial retreat. This significant increase in cyanobacterial diversity corresponded with equally dramatic increases in soil stability, heterotrophic microbial biomass, soil enzyme activity and the presence and abundance of photosynthetic and photoprotective pigments. Furthermore, we found that soil nitrogen-fixation rates increased almost two orders of magnitude during the first 4-5 years of succession, many years before the establishment of mosses, lichens or vascular plants. Carbon analyses (pyrolysis-gas chromatography/mass spectroscopy) of soil organic matter suggested that soil carbon along the chronosequence was of microbial origin. This indicates that inputs of nutrients and organic matter during early ecosystem development at these sites are dominated by microbial carbon and nitrogen fixation. Overall, our results indicate that photosynthetic and nitrogen-fixing bacteria play important roles in acquiring nutrients and facilitating ecological succession in soils near some of the highest elevation receding glaciers on the Earth.     

Diversity of cultivable Azotobacter in the semi-arid alfisol receiving long-term organic and inorganic nutrient amendments

Monitoring the biological processes and microbial diversity is essential for sustaining the soil health for long-term productivity. In the present study, the impact of long-term nutrient management systems on changes in Azotobacter diversity of Indian semi-arid alfisol was assessed. Three soils, i.e., unfertilized control, soils amended with organic manures (OM), and with inorganic chemical fertilizers (IC) from century-old experimental fields were evaluated for Azotobacter diversity by Amplified Ribosomal DNA Restriction Analysis (ARDRA). Bray–Curtis’s similarity index of the ARDRA data of the isolates was analyzed by non-metric multi-dimensional scaling and hierarchical cluster analysis. The results revealed that the long-term organically managed soil recorded significantly higher soil organic carbon, microbial biomass carbon, and total culturable bacterial counts, whereas the chemical fertilized and control soils remained unaffected. Though the Azotobacter population was significantly higher in OM soil than IC and control soils, the genetic diversity was unaffected due to long-term addition of either organic manures or inorganic chemical fertilizers. This result implies the importance of continuous addition of organic manures and also the optimal use of inorganic chemical fertilizers without disturbing the biological properties of the soil.     

秦岭地区不同林分土壤微生物群落代谢特征

利用BIOLOG微孔板法研究了秦岭山脉的锐齿栎(Quercus aliena var.acutidentata)、油松(Pinus tabuliformis)、华山松(Pinus armandii)、松栎混交、云杉(Picea asperata)6个林地5种典型林分土壤微生物群落代谢特征。发现:(1)5种典型林分中,华山松的平均颜色变化率(AWCD)最高,然后是锐齿栎1云杉油松锐齿栎2松栎混交。位于不同林场的锐齿栎林地土壤AWCD值差异较大;(2)土壤微生物功能多样性指数与平均颜色变化率表现一致,6种林分之间差异显著,且不同的林分土壤微生物对6种碳源利用差异较大。(3)主成分分析显示各土壤微生物功能多样性具有显著差异,其综合因子得分为华山松锐齿栎1油松云杉锐齿栎2松栎混交。(4)冗余分析表明土壤p H、有机质、全氮、碱解氮、速效磷和速效钾的综合作用对土壤微生物群落功能多样性有显著影响,其中速效磷和p H与土壤微生物功能多样性最密切。     

外来物种刺槐对土壤微生物功能多样性的影响

以延河流域不同植被区内人工刺槐(Robinia pseudoacacia)群落和乡土植物群落的土壤微生物为研究对象,利用Biolog微平板技术对土壤微生物功能多样性进行测定,分析人工引种刺槐在不同环境梯度(3个植被区)下对土壤微生物功能多样性的影响。结果表明:刺槐对不同环境梯度下的土壤微生物的影响明显不同。从草原区到森林区,刺槐林之间土壤微生物群落的平均颜色变化率(AWCD)和土壤微生物功能多样性指数均没有显著变化;但与乡土植物群落比较,草原区、森林草原区和森林区土壤AWCD分别表现为刺槐乡土植物、刺槐乡土植物、刺槐乡土植物;在草原区和森林草原区刺槐林土壤微生物群落的群落丰富度指数(S)、Shannon-Wiener指数(H)、Simpson指数(D)、Mc Intosh指数(U)均大于乡土植物,森林区刺槐林群落丰富度指数(S)、Shannon指数(H)、Simpson指数(D)均小于乡土植物;刺槐林和乡土植物群落下土壤微生物碳源利用存在差异,主要体现在对糖类、氨基酸类的利用上。PCA分析显示主成分1贡献较大的碳源有24种,在主成分分离中起主要贡献作用的是糖类、氨基酸类和羧酸类。土壤碳氮含量能影响土壤微生物功能多样性指数,土壤含水量和温湿度能够影响碳源的利用类型。刺槐对土壤微生物功能多样性的影响存在区域差异,在评价刺槐对土壤生态过程与功能的影响时必须要考虑这种空间差异性。     

The active microbial diversity drives ecosystem multifunctionality and is physiologically related to carbon availability in Mediterranean semi‐arid soils

Biogeochemical processes and ecosystemic functions are mostly driven by soil microbial communities. However, most methods focus on evaluating the total microbial community and fail to discriminate its active fraction which is linked to soil functionality. Precisely, the activity of the microbial community is strongly limited by the availability of organic carbon (C) in soils under arid and semi‐arid climate. Here, we provide a complementary genomic and metaproteomic approach to investigate the relationships between the diversity of the total community, the active diversity and ecosystem functionality across a dissolved organic carbon (DOC) gradient in southeast Spain. DOC correlated with the ecosystem multifunctionality index composed by soil respiration, enzyme activities (urease, alkaline phosphatase and β‐glucosidase) and microbial biomass (phospholipid fatty acids, PLFA). This study highlights that the active diversity (determined by metaprotoemics) but not the diversity of the whole microbial community (evaluated by amplicon gene sequencing) is related to the availability of organic C and it is also connected to the ecosystem multifunctionality index. We reveal that DOC shapes the activities of bacterial and fungal populations in Mediterranean semi‐arid soils and determines the compartmentalization of functional niches. For instance, Rhizobales thrived at high‐DOC sites probably fuelled by metabolism of one‐C compounds. Moreover, the analysis of proteins involved in the transport and metabolism of carbohydrates revealed that Ascomycota and Basidiomycota occupied different nutritional niches. The functional mechanisms for niche specialization were not constant across the DOC gradient.     

水田改果园后土壤性质的变化及其特征

近年来,水田改作经济林地,在我国南方地区非常普遍。为深入了解这一转变对土壤质量的影响,以浙江省典型水稻土(青粉泥田)及其改果园不同年限的系列表层土壤(0—15 cm)为研究对象,应用磷脂脂肪酸生物标记等方法,研究了水田改果园后土壤理化性质和微生物群落结构等性质的变化以及它们之间的关系。结果表明,水田改果园后,土壤中大于0.25 mm水稳定性团聚体、盐基饱和度、p H值、有机质、全氮和碱解氮等随着改果园年限的延长而显著降低(P0.05)。土壤微生物生物量碳氮、微生物商和土壤呼吸强度随改果园年限增加而显著下降(P0.01)。土壤微生物群落结构也发生明显变化:磷脂脂肪酸总量显著降低(P0.01),微生物种类减少,原生动物在土壤微生物中所占比例增加,革兰氏阴性细菌与革兰氏阳性细菌比值降低(P0.01),好氧细菌/厌氧细菌和甲烷氧化菌/细菌增加(P0.01),表征养分胁迫的环丙基脂肪酸/前体物和异式脂肪酸/反异支链脂肪酸显著增加(P0.01)。冗余分析表明,土壤含水率、有机质和碱解氮是决定水田和果园土壤微生物群落结构差异的最重要因子(P0.01);改果园后,土壤微生物群落结构发生了阶段性变化,不同利用方式对微生物群落结构的影响程度要大于同一利用方式耕作不同年限对微生物群落结构的影响。研究表明,水田改果园后土壤理化性质以及生物学性质发生退化,土壤质量下降;而水田中微生物数量和种类都比较丰富,因而认为水田是土壤(地)可持续利用的一种有效方式。     

宁南山区典型植物根际与非根际土壤微生物功能多样性

选择宁南山区9种典型植物的根际与非根际土壤为研究对象,采用Biolog方法对土壤微生物功能多样性进行了研究。结果表明:9种不同植物根际土壤与非根际土壤的微生物活性(AWCD)、微生物多样性指数和微生物均匀度指数均存在明显差异;除冰草外,其他各种植物的根际土壤的微生物活性AWCD、微生物多样性指数和微生物均匀度指数均比非根际土壤的高;9种典型植物根际土壤微生物主要碳源利用类型是羧酸类和氨基酸类,非根际土壤微生物主要碳源利用类型是羧酸类、胺类、氨基酸类;微生物活性、微生物多样性指数和微生物均匀度指数两两之间均达到了极显著相关,与土壤化学性质各指标之间均未达到显著相关水平。