退化红壤不同植被恢复类型的土壤弹尾虫群落结构

以退化红壤的侵蚀裸地、旱生性草坡、稀疏针叶林、针叶林、针阔混交林5种植被恢复类型及常绿阔叶林（对照）为研究对象,对各类型植被的土壤弹尾虫群落进行了调查,共捕获弹尾虫2亚目7科23属,其中符跳属、类符跳属、小圆跳属等为优势类群.应用个体密度、类群数及多样性指数等指标,研究了植被类型对弹尾虫群落特征的影响.结果表明：各项指标以常绿阔叶林为最高,裸地最低,基本没有弹尾虫存在;旱生性草坡、稀疏针叶林、针叶林和针阔混交林4种植被恢复类型的土壤弹尾虫群落得到了一定恢复,但各类型之间土壤弹尾虫群落没有明显差异,均处于恢复的早期阶段;Bray-Curtis指数显示,侵蚀裸地与顶级常绿阔叶林的差异最大（0.99）,其它植被恢复类型与顶级常绿阔叶林的差异也较明显,但各植被恢复类型间弹尾虫群落的差异较小.     

退化红壤不同植被恢复类型的土壤弹尾虫群落结构

以退化红壤的侵蚀裸地、旱生性草坡、稀疏针叶林、针叶林、针阔混交林5种植被恢复类型及常绿阔叶林（对照）为研究对象,对各类型植被的土壤弹尾虫群落进行了调查,共捕获弹尾虫2亚目7科23属,其中符跳属、类符跳属、小圆跳属等为优势类群.应用个体密度、类群数及多样性指数等指标,研究了植被类型对弹尾虫群落特征的影响.结果表明：各项指标以常绿阔叶林为最高,裸地最低,基本没有弹尾虫存在;旱生性草坡、稀疏针叶林、针叶林和针阔混交林4种植被恢复类型的土壤弹尾虫群落得到了一定恢复,但各类型之间土壤弹尾虫群落没有明显差异,均处于恢复的早期阶段; Bray-Curtis指数显示,侵蚀裸地与顶级常绿阔叶林的差异最大（0.99）,其它植被恢复类型与顶级常绿阔叶林的差异也较明显,但各植被恢复类型间弹尾虫群落的差异较小.     

长春市不同土地利用生境土壤螨类群落结构特征

2003年7月和9月对长春市郊区天然次生林、农田、防护林和市区公园绿地等典型土地利用生境进行土壤螨类调查,Tullgren法提取土壤螨类,应用个体密度、类群数量、群落多样性、丰富度和均匀度、甲螨群落MGP分析和捕食性螨类MI等指数,研究土壤螨类的群落生态结构特征,了解土地利用差异对土壤螨类群落结构的影响。研究区共捕获土壤螨类3亚目92属8703只,其中隐气门亚目（Cryptostigmata）54属5091只,前气门亚目（Prostigmata）17属1582只,中气门亚目21属2030只。研究结果表明：长春市土地利用差异对土壤螨类群落结构特征影响明显,其中地表凋落物的移除和耕作活动是影响螨类群落结构的主要因素,地表凋落物的移除显著减少螨类群落的类群数、个体密度、群落多样性和丰富度,耕作活动促进螨类个体向土壤剖面下层移动,而地表植物群落类型对土壤螨类群落生态结构特征影响差异不显著。     

九龙大雾山北坡的植物群落

九龙大雾山北坡的植物群落可划分为南亚热带常绿阔叶林、南亚热带山地常绿阔叶林、南亚热带常绿针叶林、南亚热带灌丛,以及南亚热带山坡草地等几个群落类型,它们均属于次生性植被,是华南南亚热带植被的主要代表类群。     

东北松嫩草原重度退化草地两种典型植被恢复处理方式间土壤螨类群落特征比较

于2005年5—10月在东北松嫩草原中南部十三泡草场,采用室内Tullgren法分离获取螨类,对土壤螨类进行采样,应用类群数、个体密度、多样性指数和MI指数等多个群落参数,研究植被恢复方式对重度碱化退化草地土壤螨类群落特征的影响。共捕获土壤螨类1104只,分别隶属于3亚目41属。结果表明,重度碱化退化草地土壤螨类稀少;围栏封育和种植碱茅两种植被恢复方式均能改善该类草地土壤螨类群落环境,提高了螨类的类群数、个体密度、群落多样性以及中气门螨类MI指数。但围栏封育和种植碱茅两种植被恢复方式之间也存在明显差异,种植碱茅较围栏封育更能显著提高土壤螨类个体密度;种植碱茅样地土壤螨类MI指数显著高于围栏封育样地,捕食性螨类K-选择类群比例更高,土壤螨类群落环境更好。对于松嫩草原重度碱化退化草地,选择种植碱茅方式可能更利于草地土壤螨类群落的恢复与重建。     

贡嘎山东坡典型植被类型土壤动物群落特征

为了掌握贡嘎山垂直植被带间土壤动物群落结构及多样性,2012年5月至10月间对贡嘎山东坡的常绿阔叶林、落叶阔叶林、针阔混交林和暗针叶林4种典型植被土壤动物群落进行了调查。共捕获土壤动物347只,隶属于10纲29目68类,其中山蛩属(Spirobolus)为优势类群。土壤动物的群落密度、生物量以及多样性呈常绿阔叶林落叶阔叶林针阔混交林暗针叶林趋势,其中密度、类群丰富度和Shannon-Wiener指数的变化具有显著差异(P0.05);落叶阔叶林和针阔混交林间的土壤动物群落结构差异明显,其他植被类型间的差异性受季节影响。从各功能群结构来看,腐食性和杂食性土壤动物占主要地位;各功能群的生物量均以常绿阔叶林和落叶阔叶林较高,针阔混交林和暗针叶林较低,而相对生物量的变化趋势各不相同,仅有腐食性功能群的生物量及植食性功能群的相对生物量在各垂直植被带间有显著差异(P0.05)。群落密度、生物量、类群丰富度、Shannon-Wiener指数以及腐食性和捕食性功能群的生物量与土壤温度呈显著相关(P0.05)。研究结果表明:贡嘎山东坡土壤动物的群落组成、多样性及功能群结构在各典型植被类型间有明显差异,土壤温度是影响土壤动物垂直分布格局的主要环境因子。     

松嫩草原中度退化草地不同植被恢复方式下土壤螨类群落特征的差异

应用类群数、个体密度、多样性指数和MI指数等多个群落参数,研究不同植被恢复方式下松嫩草原中度退化草地土壤螨类群落特征的差异。研究结果表明,与过度放牧样地相比,种植苜蓿和围栏封育样地的土壤环境相对优越,它们拥有较高的土壤螨类类群数、个体密度和群落多样性以及中气门螨类MI指数。在土壤螨类群落结构所有参数中,多样性指数(H′)和中气门螨类MI指数,种植苜蓿和围栏封育样地均明显高于过度放牧样地,这些差异反映了种植苜蓿和围栏封育对中度退化草地土壤螨类的群落结构具有明显改善作用。然而研究结果也显示,围栏封育样地土壤螨类群落多样性指数(H′)和中气门螨类MI指数尽管明显高于过度放牧样地,但是依然显著低于种植苜蓿样地,表明选择种植苜蓿较围栏封育可能更利于松嫩草原中度退化草地土壤螨类群落的恢复与重建。     

峨眉山世界遗产地表土孢粉组合及其生态和古环境启示

通过峨眉山40个样点表土孢粉组合及其与植物群落之间关系的分析,结果表明:(1)花粉组合中木本植物含量(83.3%)占绝对优势,松属、杉科、桤木属、蔷薇科、桦属、枫杨属、蒿属、毛茛科和水龙骨科为主要孢粉类型;(2)中山常绿阔叶林花粉组合未能反映植被的群落特征;低山常绿阔叶林间人工次生林和常绿落叶阔叶混交林花粉组合只能反映母体植被的部分组成;针叶林花粉组合基本可以指示母体植被的群落特征;灌丛草甸花粉组合能够较好地反映母体植被的群落组成;针阔混交林花粉组合不仅可以很好地指示群落特征,花粉高含量类型还可以与植物群落优势种很好地对应;(3)主要花粉类型冷杉属、杜鹃花科、蔷薇科、珙桐属、槭属和盐肤木属具低代表性;枫杨属、栲属/柯属、桤木属和杉科花粉具超代表性;(4) DCA表明,通过花粉百分含量,能较好地区分人类扰动植被、阔叶林和针叶林,但常绿阔叶林、常绿落叶阔叶混交林和针阔混交林之间,针叶林和灌丛草甸之间难以区分;(5)利用孢粉学恢复热带亚热带常绿阔叶代表类群樟科群落和第三纪孑遗落叶阔叶属种珙桐群落时,受其主体植物花粉外壁薄,易破碎影响,原生植被优势种缺失;因此,孢粉实验改良和保存环境研究,与其他生物学指标(植物大化石和气孔器)综合分析在重建古植物群落中具有重要意义;(6)植物(如冷杉)花粉含量一定程度上能够指示其林分结构。本研究可为热带亚热带山地及相似地区利用孢粉学进行地质时期气候与环境重建提供理论支持和基础资料,并对植被生态恢复提供实践和参考。     

广东黑石顶自然保护区森林次生演替过程中的群落动态

对黑石顶自然保护区森林次生演替过程中的群落结构、物种组成及物种多样性变化的研究结果表明：在皆伐裸地恢复阶段最初的２～４ 年,先锋种、阳生性种及中生性种的幼苗同时大量出现于次生裸地上;演替至１０ 年时,群落中先锋种的数量占绝对优势,阳生性种保持稳定,中生性种趋于减少;针阔叶混交林阶段,先锋种趋于减少,阳生性种趋于增加;阳生性常绿阔叶林阶段,先锋种基本衰退,而阳生性种占绝对优势,同时中生性种趋于增加;演替至中生性常绿阔叶林阶段,阳生性种逐渐消退,中生性种的数量占优势。皆伐裸地恢复阶段为群落垂直结构的形成期,仅有Ⅲ级以下立木,乔木层无明显分层,群落的个体密度无明显变化;由恢复阶段进入针阔叶混交林初期为群落垂直结构分化期,群落中出现大量Ⅲ、Ⅳ级立木,乔木层可分为３ 个亚层,但群落的个体密度因自疏作用而显著下降;针阔叶混交林阶段为群落垂直结构的相对稳定期,Ⅴ级立木多度和胸高断面积呈演替系列的第一个高峰,同时群落的个体密度显著增大;阳生性常绿阔叶林阶段为群落垂直结构的变动期,群落中Ⅴ级立木多度和胸高断面积大幅度下降,个体密度无明显变化;中生性常绿阔叶林阶段为群落垂直结构的稳定期,群落中各立木级趋于更加完善,胸高断面积达到演     

三峡库区不同植被类型土壤养分特征

通过三峡库区8个植被类型370个样地的群落调查和土壤分析,研究了不同植被类型、土壤类型、海拔对表层土壤有机质及全氮、速效磷、速效钾含量的影响.结果表明:(1)三峡库区不同植被类型土壤有机质、全氮平均含量规律为阔叶林＞竹林＞针叶林＞灌丛＞草丛,森林土壤有机质及全氮平均含量丰富;速效磷平均含量表现为草丛＞落叶阔叶林＞灌丛＞暖性针叶林＞常绿落叶阔叶混交林＞温性针叶林＞竹林＞常绿阔叶林,草丛与其他植被类型差异显著;速效钾平均含量表现为常绿落叶阔叶混交林＞落叶阔叶林＞灌丛＞针叶林＞竹林＞草丛＞常绿阔叶林,竹林、草丛、常绿阔叶林与常绿落叶阔叶混交林、落叶阔叶林、灌丛、针叶林差异显著.(2)不同土壤类型养分含量差异显著,黄棕壤中有机质、全氮含量高,分别为6.83%、0.44%,紫色土中速效磷含量高,达到54.24mg/kg.(3)随海拔升高,有机质、全氮含量呈明显增加趋势,速效磷、速效钾含量变化趋势不明显.     

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     

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.