玉米连作及其施肥对土壤微生物群落功能多样性的影响

采用Biolog技术,借助吉林农业大学1984年建立的长期定位试验,以撂荒和非玉米连作(当季作物为芸豆)为对照,研究玉米连作及其不同施肥措施对土壤微生物功能多样性的影响。结果表明,反映土壤微生物活性的平均颜色变化率(AWCD)呈现出以下变化规律:撂荒(UC)非玉米连作(NCC)玉米连作不施肥(CK);玉米连作配施秸秆(S、SN、SNPK)玉米连作配施NPK(NPK)玉米连作不施肥(CK)玉米连作单施N(N)。微生物培养72h活性旺盛,各处理AWCD在0.395—0.732之间,其中撂荒AWCD显著高于非玉米连作和玉米连作不施肥(P0.05);玉米连作配施秸秆明显提高微生物活性,玉米连作配施秸秆(S、SN、SNPK)AWCD是玉米连作不施肥和单施化肥(N、NPK)的1.26—1.62倍。玉米连作不施肥土壤微生物群落多样性指数(H、E、S)低于撂荒处理,但高于非玉米连作处理,非玉米连作提高了土壤微生物优势度指数。玉米连作配施秸秆土壤微生物物种丰富度指数和均匀度指数高于玉米连作不施肥和玉米连作施化肥,玉米连作单施氮肥优势度指数较高,其它多样性指数降低。主成分分析结果表明,不同处理土壤微生物碳源利用特征出现分异:撂荒和玉米连作配施秸秆处理集中在第1主成分正方向,得分系数在2.39—4.17之间,土壤微生物碳源利用特征相似;玉米连作不施肥、玉米连作单施化肥和非玉米连作处理分布在第1主成分负方向,得分系数在-5.43—-1.59之间。土壤微生物利用的碳源主要是糖类、羧酸类、氨基酸和聚合物。玉米连作配施秸秆和撂荒有利于提高土壤微生物代谢活性和土壤微生物群落功能多样性,玉米连作单施化肥尤其单施氮肥土壤微生物活性和功能多样性下降。     

不同施肥处理下采煤矿区复垦土壤微生物功能多样性与共现性特征

土壤微生物功能多样性是土壤质量改善的重要指标,研究采煤矿区复垦土壤微生物功能多样性与共现性特征,对于矿区复垦及生态重建具有重要的理论和实践指导意义。本研究以玉米为复垦作物,采集了采煤矿区复垦1年后的撂荒(UL)、不施肥(CK)、施磷钾肥(PK)、单施化肥(NPK)、化肥解磷菌肥配施(NPKB)、单施有机肥(M)、有机肥化肥配施(MNPK)、有机肥化肥解磷菌肥配施(MNPKB)8个处理下的0～20 cm耕层土壤,利用Biolog-ECO微平板法结合多元分析对不同处理下土壤微生物群落的碳源利用情况、功能多样性和共现性特征进行探究。结果表明,复垦施肥能够显著提高土壤微生物对31种碳源的利用能力,并且可以显著提高土壤微生物群落的多样性和丰富度,其中MNPK处理与NPK处理的效果最佳。主成分分析(PCA)和双向聚类分析均表明,欠施肥处理组(UL、CK和PK)和完全施肥处理组(NPK、NPKB、M、MNPK和MNPKB)的组间碳源利用特征存在明显分异,而组内各处理的碳源利用图谱相似。完全施肥处理组的土壤微生物群落功能活性显著高于欠施肥处理组。共发生网络分析结果显示,与欠施肥处理组相比,完全施肥处理...     

长期施肥处理对红壤水稻土微生物群落结构和功能多样性的影响

利用磷脂脂肪酸分析法和微平板测定法研究红壤荒地开垦为水田耕种20年后,不同施肥处理条件下土壤微生物群落结构和功能多样性变化,并分析土壤微生物学指标与土壤养分含量变化的关系。结果表明,与不施磷处理相比,施磷处理的水稻年产量、土壤有机碳、全氮、碱解氮、全磷和速效磷含量平均提高了196.6%、11.4%、19.4%、14.0%、100.6%和300.1%;而与未施有机肥处理相比,施有机肥处理上述各指标平均提高了85.4%、23.8%、25.0%、15.0%、38.6%和86.8%。与对照相比,施用磷肥和施用有机肥处理的微生物总磷脂脂肪酸(PLFA)含量提高了13.6%~68.9%。磷肥和有机肥的施用也提高了各菌群微生物的PLFA含量。不同施肥处理土壤微生物群落平均吸光度(AWCD)值、Shannon指数、Simpson指数和Mc Intosh指数分别为0.17~0.30、2.79~3.03、0.93~0.94和1.46~2.27。磷肥和有机肥的施用提高了微生物群落的AWCD值和功能多样性指数。主成分分析表明,施用磷肥和施用有机肥的处理微生物群落结构和碳源利用方式明显区别于对照、单施氮肥和施用氮钾肥的处理。逐步回归分析显示,有机碳、全磷、全氮和速效磷是影响土壤微生物群落结构和功能多样性的关键因素。磷肥和有机肥的施用有利于促进土壤微生物活性和多样性,提高土壤生物功能和生产力。     

长期施肥对黄土旱塬农田土壤有机磷组分及小麦产量的影响

研究长期施肥对黄土旱塬农田土壤有机磷组分及小麦产量的影响,可为提高磷素转化利用率及合理利用肥料提供理论支持。本研究依托长武旱塬农田生态系统长期(1984—2016年)定位试验站,选取不施肥(CK)、单施氮肥(N)、单施磷肥(P)、施氮磷肥(NP)、单施有机肥(M)、氮肥配施有机肥(MN)、磷肥配施有机肥(MP)、氮磷肥配施有机肥(MNP)8个处理,研究其对土壤有机磷组分、小麦产量和土壤性质的影响。结果表明: 长期施肥后土壤有机磷含量为244.7～429.1 mg·kg^-1,除N处理外,其余各处理有机磷含量比CK均显著增加了15.4%～47.9%。长期施用磷肥改变了黄土旱塬农田表层土壤(0～20 cm)各有机磷组分含量,MP、MNP处理显著提高了活性有机磷及中活性有机磷含量;N、P和NP处理显著降低了中稳性有机磷含量;N、P、NP、MN、MP、MNP处理均显著提高了高稳性有机磷含量。各处理土壤有机磷组分与总有机磷含量比值为:中活性有机磷>高稳性有机磷>活性有机磷>中稳性有机磷。长期施肥后,与CK相比,氮、磷肥配施,尤其是与有机肥配施,显著增加了小麦生物产量和籽粒产量。土壤指标中,有机质、速效磷和无机磷与小麦产量呈显著正相关。MP、M处理可以显著提高黄土旱塬黑垆土中的速效磷、总磷、总无机磷、活性有机磷和中活性有机磷含量,表明有机肥与磷肥配施可以提高该地区更容易被作物吸收的磷组分。总之,氮磷肥配施并配施有机肥可以提高该地区磷供给,对小麦增产有促进作用,对提高黄土旱塬地区土壤质量有重要意义。     

长期施肥条件下菜田土壤微生物特征变化

对蔬菜地长期施肥土壤的8个主要处理进行了分析,探求不同培肥方式对土壤微生物生态特征的影响。结果表明：有机无机肥配施较单施无机肥可显著增加土壤细菌和放线菌的数量,提高土壤真菌的多样性;有机肥和低浓度氮肥配施处理的土壤细菌数量、真菌群落的多样性和均匀性显著高于其他处理;单施高浓度的氮肥显著降低土壤细菌的数量,真菌群落的多样性和均匀性也明显低于对照。     

长期施肥对黄土旱塬农田土壤微生物丰度的影响

以长武黄土高原农业生态试验站的长期定位试验为平台,通过荧光实时定量PCR (real-time PCR) 技术,研究不同施肥制度下的黄土旱塬农田土壤微生物群落丰度,揭示长期不同施肥制度对土壤微生物群落的影响规律.结果表明: 单施化肥处理细菌数量较CK裸地增加21％,古菌增加32％;化肥配施有机肥处理细菌数量增加37％,古菌数量增加36％.化肥配施有机肥处理显著增加了土壤细菌和古菌的丰度.30年长期施氮肥处理导致氨氧化细菌(AOB)的增幅达7.13倍,而氨氧化古菌(AOA)的增幅仅为0.2倍.AOB对施肥的响应程度较高,尤其是对氮肥具有较高的敏感性.与单施氮肥和氮肥混施有机肥处理相比,施磷肥处理显著增加了固氮酶铁蛋白和甲烷氧化菌含量,撂荒地的固氮酶铁蛋白、亚硝酸还原酶和甲烷氧化菌含量显著高于耕作土壤.结合土壤基本理化性质的相关性分析结果,pH、全氮和有机碳含量是影响土壤微生物群落丰度的重要因子.总之,长期施肥显著改变了黄土旱塬农田土壤各微生物丰度,不同施肥模式、耕作方式对微生物群落丰度具有显著影响.     

黄土丘陵区不同施肥处理对土壤微生物特性的影响

研究旨在探讨在土壤贫瘠的黄土丘陵区,施肥对土壤微生物产生的影响及其机理。试验以安塞站内长期定位施肥小区为研究对象,试验处理包括CK(对照)、N(氮肥)、P(磷肥)、M(有机肥)、NP(氮肥+磷肥)、MN(有机肥+氮肥)、MP(有机肥+磷肥)和MNP(有机肥+氮肥+磷肥),研究长期施肥对土壤微生物群落结构和呼吸的影响。0—20cm耕作层的土壤微生物活性和PLFA含量均高于20—40cm土层的微生物活性和PLFA含量,耕作层较20—40cm基础呼吸提高63.61%—116.78%,诱导呼吸提高53.45%—137.64%,总PLFA含量提高16.16%—43.67%。单施N和P增强了土壤呼吸强度,0—20cm基础呼吸强度分别升高34.11%和48.89%,诱导呼吸强度分别升高40.83%和63.59%,20—40cm基础呼吸分别升高40.83%和63.59%,诱导呼吸分别升高14.70%和20.49%。单施N显著改变G-微生物群落,0—20cm和20—40cm土层的PLFA含量分别显著升高63.19%和53.07%,单施P对土壤微生物群落结构同样产生显著影响,但是NP对微生物群落结构的影响不显著。有机无机肥配施显著提高土壤呼吸及微生物PLFA含量。通过三因素方差分析,单一氮肥因素对土壤微生物特性的影响不显著;单一磷肥因素对微生物的呼吸强度及部分磷脂脂肪酸含量产生显著影响,在耕作层中,磷肥因素对这些微生物特性的影响比率为11.4%—54.0%。通过RDA分析,表明土壤速效磷是影响黄土丘陵区微生物特性的主要因素。长期氮磷有机肥混施有助于提高土壤微生物的特性,进而改善农田生态系统的稳定和健康水平。     

低氮胁迫下有机无机肥配施对小麦根际土壤氮矿化和微生物群落结构的影响

受天气和劳动力限制,小麦拔节肥不能及时施入时有发生。有机无机肥配合施用有较长的养分供应期,但能否缓解小麦拔节期低氮胁迫仍不清楚。本研究利用real-time PCR、16S rRNA和ITS测序技术,分析推迟拔节肥下有机无机肥配比对土壤微生物群落结构的影响,探究微生物群落结构和根际氮矿化的关系,为小麦高效栽培提供科学依据。本研究依托于有机无机配比定位试验,共设置4个处理：单施化肥(T1)、15%、30%和45%羊粪配施化肥(T2、T3和T4)。施拔节肥前一天进行土壤样品采集(拔节肥推迟20天施入),测定根际土壤氮矿化势,细菌和真菌丰度、多样性和群落结构等指标。结果表明：与单施化肥相比,有机无机配施处理能显著提高根际土壤氮矿化势,T2、T3和T4处理分别是单施化肥处理的2.0、1.7和2.2倍;各处理根际土壤细菌丰度无显著差异,配施有机肥降低了真菌丰度;与单施化肥相比,T2、T3和T4处理细菌的Chao1指数分别显著增加了5.1%、7.0%和8.6%;真菌Shannon指数随有机肥配施比例增加呈降低趋势,与T2处理相比,T4处理真菌的Shannon指数显著降低18.9%。相关分析表明,氮...     

长期施肥对稻田土壤有机氮、微生物生物量及功能多样性的影响

以位于湖南省新化和宁乡县两个稻田肥力长期定位试验点的土样为材料,研究了不同施肥处理对稻田土壤有机氮组分、微生物生物量及功能多样性的影响.结果表明：与不施肥处理（CK）相比,化肥配施有机肥处理提高了稻田土壤酸解总氮（TAHN）及其组分中氨基糖氮（ASN）、氨基酸氮（AAN）和酸解氨态氮（AN）的含量,不同施肥处理对组分中酸解未知氮（HUN）的影响不尽相同.与CK相比,单施化肥处理对土壤微生物生物量碳、氮（MBC、MBN）含量的影响较小,化肥配施有机肥处理则显著提高了土壤MBC和MBN的含量.采用BIOLOG法对土壤微生物群落功能多样性进行测定,结果表明：中、高量有机肥处理提高了稻田土壤微生物的碳源利用率和微生物群落功能多样性;土壤微生物碳源利用的类型因长期不同施肥处理而产生差异.     

长期施肥黄土旱塬农田土壤-微生物-植物系统碳氮磷生态化学计量特征

探讨长期不同施肥制度对农田土壤、植物生态系统的碳(C)、氮(N)、磷(P)含量及其生态化学计量比的影响,可为揭示该系统能量平衡和养分循环,实现农业生态系统元素平衡及可持续发展提供参考意义。以位于黄土高原半干旱地区的长武国家黄土高原农业生态实验站长期施肥试验为研究对象,选取不施肥(CK)、单施氮肥(N)、单施磷肥(P)、施氮磷肥(NP)、单施有机肥(M)、氮肥配施有机肥(NM)、磷肥配施有机肥(PM)、氮磷肥配施有机肥(NPM)8个处理,分析了黄土旱塬典型农田土壤-微生物-植物生态系统中C、N、P含量及其生态化学计量变化规律。研究结果表明:1)长期单施有机肥和化肥配施有机肥处理可显著提高土壤和有机质C、N、P含量。2)氮、磷肥的输入显著降低了土壤和小麦C∶N、N∶P,施P显著降低了有机态C∶P和小麦C∶P;有机肥配施对微生物生物量和小麦C∶N∶P的影响更为明显。3)长期有机肥配施条件下土壤养分和小麦化学计量比存在较强的相关关系。微生物生物量碳与有机C、N、P呈显著正相关,土壤微生物生物量氮与土壤N、P总量呈显著正相关,微生物生物量磷与土壤C、N、P总量含量呈显著负相关;植株碳含量与微生物...     

植物、土壤及土壤管理对土壤微生物群落结构的影响

土壤微生物是土壤生态系统的重要组成部分,对土壤微生物群落结构多样性的研究是近年来土壤生态学研究的热点。本文综述了有关植物、土壤类型以及土壤管理措施对土壤微生物群落结构影响的最新研究结果,指出植物的作用因植物群落结构多样性、植物种类、同种植物不同的基因型,甚至同一植物不同根的区域而异;而土壤的作用与土壤质地和有机质含量等因素有关;植物和土壤类型在对土壤微生物群落结构影响上的作用存在互作关系。不同的土壤管理措施对土壤微生物群落结构影响较大,长期连作、大量的外援化学物质的应用降低了土壤微生物的多样性;而施用有机肥、免耕可以增加土壤微生物群落结构多样性,有利于维持土壤生态系统的功能。     

Estimating respiration of roots in soil: Interactions with soil CO2, soil temperature and soil water content

Little information is available on the variability of the dynamics of the actual and observed root respiration rate in relation to abiotic factors. In this study, we describe I) interactions between soil CO₂ concentration, temperature, soil water content and root respiration, and II) the effect of short-term fluctuations of these three environmental factors on the relation between actual and observed root respiration rates. We designed an automated, open, gas-exchange system that allows continuous measurements on 12 chambers with intact roots in soil. By using three distinct chamber designs with each a different path for the air flow, we were able to measure root respiration over a 50-fold range of soil CO₂ concentrations (400 to 25000 ppm) and to separate the effect of irrigation on observed vs. actual root respiration rate. All respiration measurements were made on one-year-old citrus seedlings in sterilized sandy soil with minimal organic material.Root respiration was strongly affected by diurnal fluctuations in temperature (Q₁₀ = 2), which agrees well with the literature. In contrast to earlier findings for Douglas-fir (Qi et al., 1994), root respiration rates of citrus were not affected by soil CO₂ concentrations (400 to 25000 ppm CO₂; pH around 6). Soil CO₂ was strongly affected by soil water content but not by respiration measurements, unless the air flow for root respiration measurements was directed through the soil. The latter method of measuring root respiration reduced soil CO₂ concentration to that of incoming air. Irrigation caused a temporary reduction in CO₂ diffusion, decreasing the observed respiration rates obtained by techniques that depended on diffusion. This apparent drop in respiration rate did not occur if the air flow was directed through the soil. Our dynamic data are used to indicate the optimal method of measuring root respiration in soil, in relation to the objectives and limitations of the experimental conditions.     

生物质炭对水稻土团聚体微生物多样性的影响

生物质炭施用对土壤微生物群落结构的影响已有报道,但土壤团聚体粒组中微生物群落对生物质炭施用的响应的研究还相对不足。以施用玉米秸秆生物质炭两年后的水稻土为对象,采用团聚体湿筛法,通过高通量测序对土壤团聚体的微生物群落结构与多样性进行分析,结果表明:(1)与对照相比,生物质炭施用显著促进了大团聚体(2000—250μm)的形成,并提高了团聚体的稳定性。(2)不同粒径团聚体间微生物相对丰度存在显著差异。在未施生物质炭的处理(C0)中,随着团聚体粒径增大,变形菌门、子囊菌门、β-变形杆菌目、格孢腔菌目的相对丰度逐渐降低,而酸杆菌门、担子菌门、粘球菌目、类球囊霉目的相对丰度逐渐升高。(3)生物质炭施用显著改变了团聚体间的微生物群落结构。与C0处理相比,生物质炭施用处理的大团聚体中变形菌门、鞭毛菌门和β-变形杆菌目的相对丰度分别显著提高了14.37%、33.28%和33.82%;微团聚体(250—53μm)中酸杆菌门、子囊菌门和粘球菌目的相对丰度分别显著降低了20.15%、19.93%和17.66%;粉、黏粒组分(53μm)中担子菌门的相对丰度升高90.25%,而子囊菌门和鞭毛菌门的相对丰度分别降低12.15%和12.58%。由此可见,生物质炭不仅改变土壤团聚体组成和分布,同时伴随着土壤微生物群落结构的改变。     

Available soil nitrogen in relation to fractions of soil nitrogen and other soil properties

The available N of 27 soils from England and Wales was assessed from the amounts of N taken up over a 6-month period by perennial ryegrass grown in pots under uniform environmental conditions. Relationships between availability and the distribution of soil N amongst various fractions were then examined using multiple regression. The relationship: available soil N (mg kg^–1 dry soil)=(N_min×0.672)+(N_inc×0.840)+(N_mom×0.227)–5.12 was found to account for 91% of the variance in available soil N, where N_min=mineral N, N_inc=N mineralized on incubation and N_mom=N in macro-organic matter. The N mineralized on incubation appeared to be derived largely from sources other than the macro-organic matter because these two fractions were poorly correlated. When availability was expressed in terms of available organic N as % of soil organic N (N_ao) the closest relationship with other soil characteristics was: N_ao=[N_inc×(1.395–0.0347×CN_mom]+[N_mom×0.1416], where CN_mom=CN ratio of the macro-organic matter. This relationship accounted for 81% of the variance in the availability of the soil organic N.The conclusion that the macro-organic matter may contribute substantially to the available N was confirmed by a subsidiary experiment in which the macro-organic fraction was separated from about 20 kg of a grassland soil. The uptake of N by ryegrass was then assessed on two subsamples of this soil, one without the macro-organic matter and the other with this fraction returned: uptake was appreciably increased by the macro-organic matter.     

The porosity of soil aggregates from bulk soil and from soil adhering to roots

Summary Total porosity and pore-size distribution (p.s.d.) were determined in soil aggregates taken in plots planted with maize and treated with farmyard manure and three rates of compost. Soil aggregates were collected from the soil adherent to the maize roots (root soil aggregates) and from bulk soil (bulk soil aggregates). Mercury intrusion porosimetry was used to evaluate the total porosity and the p.s.d. Treatments did not affect the total porosity of the bulk soil aggregates. The same was observed for the root soil aggregates. However the total porosity of the root soil aggregates was always lower than that of the bulk soil aggregates. The loss of total porosity was found to be due to a decrease in the percentage of larger pores with respect to the total.     

Linking soil bacterial biodiversity and soil carbon stability

Native soil carbon (C) can be lost in response to fresh C inputs, a phenomenon observed for decades yet still not understood. Using dual-stable isotope probing, we show that changes in the diversity and composition of two functional bacterial groups occur with this ‘priming'' effect. A single-substrate pulse suppressed native soil C loss and reduced bacterial diversity, whereas repeated substrate pulses stimulated native soil C loss and increased diversity. Increased diversity after repeated C amendments contrasts with resource competition theory, and may be explained by increased predation as evidenced by a decrease in bacterial 16S rRNA gene copies. Our results suggest that biodiversity and composition of the soil microbial community change in concert with its functioning, with consequences for native soil C stability.Substrate inputs can stimulate decomposition of native soil organic carbon (SOC; Kuzyakov et al., 2000), a phenomenon known as the ‘priming effect'' (Kuzyakov, 2010), and is considered large enough to influence ecosystem C balance (Wieder et al., 2013). Two functionally distinct groups of microorganisms are postulated to mediate priming: one that grows rapidly utilizing labile C, and one that grows slowly, breaking down recalcitrant SOC (Fontaine et al., 2003; Blagodatskaya et al., 2007). However, distinguishing these groups is technically challenging. Here, we used dual-stable isotope probing with ¹³C-glucose and ¹⁸O-water to identify bacteria in these two groups growing in response to single and repeated pulses of glucose. Organisms that utilize labile C for growth assimilate both ¹³C-glucose and ¹⁸O-water into their DNA, whereas organisms that grow using SOC incorporate only ¹⁸O-water. Differential isotope incorporation leads to a range of DNA densities separable through isopycnic centrifugation, which can then be characterized by sequencing (Radajewski et al., 2000).We sequenced fragments of bacterial 16S rRNA genes following single and repeated glucose pulses. We hypothesized that the single pulse of labile C would stimulate growth of opportunistic organisms, thus immobilizing nutrients and suppressing growth and diversity of the SOC-utilizing community, decreasing SOC decomposition (negative priming), a response analogous to that observed in plant communities in response to chronic N additions (Tilman, 1987; Clark and Tilman, 2008). We hypothesized that multiple glucose additions would stimulate growth of a more diverse bacterial community, including more native SOC-utilizing organisms that possess enzymes to decompose recalcitrant compounds, causing positive priming (Fontaine et al., 2003; Kuzyakov, 2010).Soil from a ponderosa pine ecosystem was amended weekly for 7 weeks with 500 μg C-glucose per gram soil (2.65 atom % ¹³C) in 100 μl deionized water or with 100 μl deionized water (n=5). Measurements of δ¹³C–CO₂ and [CO₂] enabled the partitioning of CO₂ into that derived from added glucose or from native SOC (C_SOC):where C_total is CO₂–C from glucose-amended samples, δ_total is the δ¹³C–CO₂ from glucose-amended samples, δ_glucose is the δ¹³C of the added glucose and δ_SOC is the δ¹³C–CO₂ evolved from the non-amended samples. Priming was calculated as the difference between SOC oxidation of the amended and non-amended samples. With this approach, any evolved CO₂ carrying the ¹³C signature of the added glucose is considered respiration of glucose, including ¹³C-labeled biomass and metabolites derived from prior glucose additions. Thus, this approach quantifies priming as the oxidation of SOC present at the beginning of the experiment, consistent with many other studies of priming (Cheng et al., 2003; De Graaff et al., 2010).In a parallel incubation for dual-stable isotope probing, the repeated-pulse samples received unlabeled glucose (500 μg C-glucose per gram soil) for 6 weeks while the non-amended and single-pulse samples received sterile deionized water. In week 7, samples received one of four isotope treatments (n=3): 97 atom % H₂ ¹⁸O (non-amended soil), 99 atom % ¹³C-glucose and 97 atom % H₂ ¹⁸O (single- and repeated-pulse soil), ¹²C-glucose and 97 atom % H₂ ¹⁸O (repeated-pulse soil) or ¹²C-glucose and H₂ ¹⁶O (repeated-pulse soil). After incubating for 7 days, soil was frozen at −40 °C. DNA was extracted, separated through isopycnic centrifugation, and two density ranges were sequenced for the bacterial 16S rRNA gene (Supplementary Figure 1): 1.731–1.746 g ml⁻¹ (hereafter called the SOC-utilizing community) and 1.759–1.774 g ml⁻¹ (hereafter called the glucose-utilizing community).Amplicons of the V3–V6 16S rRNA region were bar coded with broad-coverage fusion PCR primers and pooled before sequencing on a Genome Sequencer FLX instrument. These sequence data have been submitted to the GenBank database under accession number SRP043371. Data were checked for chimeras (Edgar et al., 2011), demultiplexed and quality checked (Caporaso et al., 2010). Taxonomy was assigned to genus at the ⩾80% bootstrap confidence level (Cole et al., 2009).We used the Shannon''s diversity index (H′), commonly used in microbial systems (Fierer and Jackson, 2006), to assess changes in microbial diversity. Analysis of variance was used to compare the amount of DNA within densities between isotope treatments (Supplementary Figure 2) and to test the effects of the treatments on the Shannon''s diversity (Figure 2) and Pielou''s evenness (Supplementary Figure 3) of the active bacterial communities, with post hoc Student''s t-tests, α=0.05. PRIMER 6 and PERMANOVA were used to create the nonmetric multidimensional scaling ordination and to compare bacterial communities between glucose treatments and the two sequenced density ranges.The single pulse of glucose suppressed SOC oxidation, whereas repeated pulses increased SOC oxidation (Figure 1). Few experiments to date have examined priming in response to repeated substrate amendments (Hamer and Marschner, 2005; Qiao et al., 2014), even though in nature soil receives repeated substrate pulses from litterfall and rhizodeposition. Our results demonstrate the dynamic response of SOC decomposition to repeated labile C inputs.Open in a separate windowFigure 1Weekly priming rates calculated as the difference in SOC respired between glucose-amended and non-amended soil (n=5).Dual-stable isotope probing was able to separate the growing bacteria into two groups with distinct DNA densities (P<0.001, PERMANOVA; Figure 3a), indicating differential uptake of ¹³C-glucose and ¹⁸O-water. In response to the initial glucose addition, the diversity of the growing glucose- and SOC-utilizing bacterial communities declined compared with the non-amended community (P<0.001, t-tests; Figure 2), driven by a strong decrease in evenness (Supplementary Figure 3). In the SOC-utilizing community, where DNA was labeled with ¹⁸O only, the relative abundance of Bacillus increased 4.9-fold compared with the non-amended control to constitute 31.6% of the community (Figure 3b). Bacillus survives well under low-nutrient conditions (Panikov, 1995), and is able to synthesize a suite of extracellular enzymes capable of degrading complex substrates (Priest, 1977), traits that are conducive for using SOC for growth. In the glucose-utilizing community, where DNA was labeled with both ¹³C and ¹⁸O, Arthrobacter increased 67.7-fold relative to the non-amended control to constitute 75.5% of the growing bacteria (Figure 3b). In culture experiments, Arthrobacter can rapidly take up and store glucose for later use (Panikov, 1995) and here we find it dominating the high-density DNA fractions, signifying that it is using the labeled glucose to grow. The increased biomass of Arthrobacter may have resulted in greater resource competition, thus reducing the diversity of the growing community, as is frequently found in plant communities (Bakelaar and Odum, 1978; Clark and Tilman, 2008).Open in a separate windowFigure 2Shannon''s diversity index (H′) of the non-amended, single-pulse, and repeated-pulse treatments (n=3) in the SOC- (mid-density) and glucose-utilizing (high-density) communities. Treatments with the same letter are not significantly different from each other (Student''s t, α=0.05).Open in a separate windowFigure 3(a) Nonmetric multidimensional scaling ordination showing differences in growing bacterial communities at the genus taxonomic level in the SOC-utilizing (mid-density; open symbols) and glucose-utilizing (high-density; closed symbols) groups of non-amended (Δ), single-pulse (○) and repeated-pulse (□) treatments (n=3). (b) Pie charts of genera in the SOC- and glucose-utilizing communities of the single- and repeated-pulse treatments (n=3). Genera with relative abundances >5% are listed in the figure legend.After repeated glucose amendments, the diversity of the growing community recovered to non-amendment levels (Figure 2) without strongly dominant organisms (Figure 3b and Supplementary Figure 3). The higher diversity found after repeated glucose pulses may be explained by trophic interactions where predators graze on prey populations that have been enlarged by resource addition, suppressing competition between prey species and causing secondary mobilization of nutrients (Clarholm, 1985). The decrease in total bacterial 16S rRNA gene copies in the repeated-pulse—compared with the single-pulse—treatment (Supplementary Figure 4) supports predation as a potential mechanism explaining the observed diversity increase after repeated glucose pulses.The recovery of diversity after repeated glucose pulses contrasts with resource competition theory (Tilman, 1987). When chronic additions of a limiting resource are applied, species diversity and evenness typically decrease (Bakelaar and Odum, 1978; Clark and Tilman, 2008) because competitive organisms become dominant. We observed this after the single glucose pulse, but not after repeated pulses. This diversity response may be the result of community shifts facilitated by short bacterial life cycles and the tens to hundreds of generations expected during the 7-week incubation (Behera and Wagner, 1974). In contrast, systems on which most ecological theory is based (for example, plants) might achieve perhaps 20 generations in a multi-decadal field experiment (Bakelaar and Odum, 1978; Clark and Tilman, 2008). With more generations, more community dynamics can occur, including increased resource cascades in which extracellular enzymes, metabolites or lysed cells of one functional group increase substrates for another (Blagodatskaya and Kuzyakov, 2008). Our results highlight the opportunity to test ecological theories in microbial ecosystems (Prosser et al., 2007), particularly as the short life cycles of microbes makes them well suited for pursuing ecological questions in an evolutionary framework (Jessup et al., 2004).The priming effect is ubiquitous, yet its drivers remain elusive. Our results suggest that changes in the diversity and composition of the growing bacterial community contribute to priming, and thus that ecosystem properties such as soil C storage may be sensitive to soil microbial biodiversity.     

耕作方式对潮土土壤团聚体微生物群落结构的影响

为探究不同耕作方式对潮土土壤团聚体微生物群落结构和多样性的影响,采用磷脂脂肪酸(PLFA)法测定了土壤团聚体中微生物群落。试验设置4个耕作处理,分别为旋耕+秸秆还田(RT)、深耕+秸秆还田(DP)、深松+秸秆还田(SS)和免耕+秸秆还田(NT)。结果表明:与RT相比,DP处理显著提高了原状土壤和>5 mm粒级土壤团聚体中真菌PLFAs量和真菌/细菌,为真菌的繁殖提供了有利条件,有助于土壤有机质的贮存,提高了土壤生态系统的缓冲能力;提高了5～2 mm粒级土壤团聚体中细菌PLFAs量,降低了土壤革兰氏阳性菌/革兰氏阴性菌,改善了土壤营养状况;提高了<0.25 mm粒级土壤团聚体中微生物丰富度指数。总的来说,深耕+秸秆还田(DP)对土壤团聚体细菌和真菌生物量有一定的提高作用,并且在一定程度上改善了土壤团聚体微生物群落结构,有利于增加土壤固碳能力和保持土壤微生物多样性。冗余分析结果表明,土壤团聚体总PLFAs量、细菌、革兰氏阴性菌和放线菌PLFAs量与土壤有机碳相关性较强,革兰氏阳性菌PLFAs量与总氮相关性较强。各处理较大粒级土壤团聚体微生物群落主要受碳氮比、含水量、pH值和团聚体质量分数的影响,较小粒级土壤团聚体微生物群落则主要受土壤有机碳和总氮的影响。     

酸性硫酸盐土水改旱后土壤化学性状的变异初报

探讨了酸性硫酸盐水稻土改为旱作后土壤化学性状的变异以及比较不同利用方式之间的经济效益．结果表明,酸性硫酸盐水稻土改种甜玉米和蔬菜后,土壤化学性状发生显著变化．耕层土壤酸度、水溶性硫酸根含量、土壤活性铝和活性铁含量均显著降低．经济效益得到显著提高．建议对水改旱后的环境效应进行深入研究以及进行定位观测,以便合理利用这一特殊的土壤资源     

Effect of soil moisture on bioremediation of chlorophenol-contaminated soil

A chlorophenol-contaminated soil was tested for the biodegradability in a semi-pilot scale microcosm using indigenous microorganisms. More than 90% of 4-chlorophenol and 2,4,6-trichlorophenol, initially at 30 mg kg^–1, were removed within 60 days and 30 mg pentachlorophenol kg^–1 was completely degraded within 140 days. The chlorophenols were degraded more effectively under aerobic condition than under anaerobic condition. Soil moisture had a significant effect with the slowest degradation rate of chlorophenols at 25% in the range of 10–40% moisture content. At 25–40%, the rate of chlorophenol degradation was directly related to the soil moisture content, whereas at 10–25%, it was inversely related. Limited oxygen availability through soil agglomeration at 25% moisture content might decrease the degradation rate of chlorophenols.     

Carbon input to soil may decrease soil carbon content

It is commonly predicted that the intensity of primary production and soil carbon (C) content are positively linked. Paradoxically, many long‐term field observations show that although plant litter is incorporated to soil in large quantities, soil C content does not necessarily increase. These results suggest that a negative relationship between C input and soil C conservation exists. Here, we demonstrate in controlled conditions that the supply of fresh C may accelerate the decomposition of soil C and induce a negative C balance. We show that soil C losses increase when soil microbes are nutrient limited. Results highlight the need for a better understanding of microbial mechanisms involved in the complex relationship between C input and soil C sequestration. We conclude that energy available to soil microbes and microbial competition are important determinants of soil C decomposition.