赤水河流域典型植被类型的土壤微生物群落结构与多样性

土壤微生物是反映土壤环境质量的重要指标,为明确赤水河流域典型植被类型土壤微生物群落特征及优势菌属,为生态系统的恢复与管理提供理论依据,采用高通量测序技术研究了赤水河流域的5种典型植被类型(灌丛、针阔混交林、常绿阔叶林、杉木林和竹林)土壤的微生物群落结构及多样性,并探讨了其主要影响因子。结果表明:(1)不同植被类型的细菌和真菌丰富度Chao1指数差异均不显著,说明二者所观测到的物种总数没有差异。Shannon指数显示各植被类型微生物多样性存在一定差异,细菌多样性以竹林最低,显著性低于灌丛和针阔混交林(p<0.05); 真菌多样性以灌丛和杉木林显著性高于其他3种植被类型(p<0.05)。(2)5种植被类型土壤细菌优势门(相对丰度>10%)主要有变形菌门(Proteobacteria)、放线菌门(Actinobacteriota)和酸杆菌门(Acidobacteriota)。其中变形菌门(Proteobacteria)在灌丛、针阔混交林和常绿阔叶林中占绝对优势(相对丰度为29.70%～33.62%),而放线菌门(Actinobacteriota)则在杉木林和竹林中最为丰富,相对丰度占比分别为32.88%,29.88%。各植被类型土壤真菌门以子囊菌门(Ascomycota)为绝对优势菌群(相对丰度>49%)。(3)5种植被类型土壤细菌和真菌中优势菌属差异较大。在细菌属水平上,针阔混交林和竹林分别以未定名的Vicinamibacterales和芽孢杆菌属(Bacillus)为优势,而其他3种植被类型则以节杆菌属(Arthrobacter)最丰富。在真菌属水平上,灌丛和常绿阔叶林中优势关键属为子囊菌门(Ascomycota)未分类真菌属(unclassified_p_Ascomycota),杉木林以被孢霉属(Mortierella)最丰富,而针阔混交林和竹林中均以沙蜥属(Saitozyma)相对丰度最高。(4)NMDS分析表明,土壤细菌与真菌群落空间分布差异显著。(5)冗余分析表明,土壤含水量、pH值和TN(总氮)对土壤细菌群落结构具有显著性的影响,而pH值、容重、TOC(总有机碳)、TN和TP(总磷)对真菌群落结构影响显著。综合分析可知,针阔混交林土壤细菌群落较丰富,杉木林土壤真菌生长较旺盛,而灌丛土壤细菌和真菌多样性均较高,应采取有效措施提高主要林分土壤养分,从而激发微生物的生长,改善土壤环境。     

Differential growth response of Curculigo orchioides to native arbuscular mycorrhizal fungal (AMF) communities varying in number and fungal components

The study reports diversity of arbuscular mycorrhizal fungal (AMF) species in the rhizosphere of an endangered anticancerous herb – Curculigo orchioides Gaertn. in its natural habitat. A total of 18 species of AMF, belonging to three genera (Acaulospora, Glomus and Gigaspora) were recorded, with Glomus microcarpum being the most abundant species type. The AMF species composition across the study sites appeared to be influenced by soil pH rather than soil P and vegetation. Acaulospora laevis spores were restricted to sites where the soil pH was acidic. The effectiveness of these native AMF species on growth performance of C. orchioides plants was compared under experimental conditions. In general, the mycorrhizal plants were superior in most of the evaluated parameters, but the extent to which the growth of mycorrhizal plants was influenced varied with the inocula used. The plants inoculated with mixed consortia containing maximum AMF species richness exhibited improved growth in comparison to consortia containing lower AMF diversity and monospecies cultures. The variable plant responses observed with any two consortia having same species richness in the present study could be due to variable component AMF species and their relative abundance. These results emphasize the need to protect the below-ground diversity of AMF and recommend their usage for restoration practices.     

鄱阳湖湿地不同环境条件土壤AM真菌群落特征及其影响因素

丛枝菌根(AM)真菌可以与湿地植物共生，并在湿地生态系统的修复与维护过程中具有重要作用。然而，不同环境条件下湿地土壤AM真菌群落分布特征及其影响因素仍然有待明晰。选择鄱阳湖湿地不同水位条件(高水位和低水位)2种典型植物群落(南荻和水蓼)为研究对象，运用高通量测序技术探究水位和植被类型对鄱阳湖湿地土壤AM真菌群落结构和多样性的影响，比较不同环境条件下AM真菌群落结构和多样性差异，分析其与土壤理化性质的关系。结果表明，AM真菌OTU数为21～38,水位和植被类型影响鄱阳湖湿地土壤AM真菌OTU数，高水位下AM真菌OTU数高于低水位，水蓼群落高于南荻群落。被鉴别出的菌属为Glomus、Claroideoglomus和Paraglomus,其中，Glomus是优势属，占比85%以上，其相对丰度在高水位下显著高于低水位(p<0.05),南荻群落高于水蓼群落。AM真菌多样性指数(Simpson和Shannon指数)受水位和植被类型以及二者交互影响(p<0.01),低水位下不同群落之间的AM真菌多样性指数无显著差异，而高水位下水蓼群落AM真菌多样性指数显著高于南荻群落(p<0.05...     

不同土壤类型下AM 真菌分布多样性及与土壤因子的关系

以禾本科植物群落为研究对象, 研究了宁夏六盘山林地、银川农耕地、暖泉农耕地、固原农耕地、盐池沙地、灵武沙地6 个采样地点5 种土壤类型(黑垆土、灌淤土、黄绵土、灰钙土、风沙土)下AM 真菌物种多样性及其与土壤因子的关系。结果表明: 5 种土壤类型采样点的植被根际土壤中共鉴定出5 属48 种AM真菌, 其中, 无梗囊霉属(Acaulospora)1 种, 巨孢囊霉属(Gigaspora)3 种, 球囊霉属(Glomus)37 种, 类球囊霉属(Paraglomus)1 种, 盾巨孢囊霉属(Scutellospora)6 种, 各采样点土壤均以球囊霉属为优势属。地球囊霉(G.geosporum)和木薯球囊霉(G. manihotis)是6 个采样地点中的优势种。不同土壤类型各采样点AM 真菌各属的频度存在明显差异, 球囊霉属在各点均有出现, 频度值最高。具有较高植被多样性的暖泉样点, AM 真菌的种属数量较多。土壤环境因子对AM 真菌孢子密度的影响因所处土壤、植被类型不同而异。pH、全盐、速效钾、速效磷等土壤肥力因子, 在PCA 轴上能最大程度地解释AM 真菌孢子密度与土壤环境因子之间相互关系的大部分信息。宁夏不同土壤类型区域中AM 真菌种类及分布一定程度上与该采样点的植被类型、植物多样性和土壤肥力特征相对应。     

冬麦免耕覆盖栽培对土壤丛枝菌根真菌多样性的影响

为揭示冬麦免耕覆盖栽培管理措施对土壤丛枝菌根真菌多样性的影响,以农田土壤生态系统为研究对象,利用Illumina MiSeq平台通过高通量测序的方法,对连续免耕覆盖栽培及有机肥管理下冬麦土壤丛枝菌根真菌群落组成及其与土壤环境因子间的相互关系进行研究。结果表明,丛枝菌根(AM)真菌在97%相似度下共获得4 515个AM真菌的操作分类单元(OTUs),分属于1门3纲4目8科10属155种。不同处理中,类球囊霉属(Paraglomus),球囊霉属(Glomus)和近明球囊霉(Claroideoglomus)为优势属,受农业综合管理措施中有机肥施用、免耕覆盖因子的影响,近明球囊霉、有隔球囊霉属相对丰度在不同处理间存在显著差异(P<0.05)。与耕作、不覆盖相比,免耕、覆盖措施提高了AM真菌多样性指数,但降低了AM真菌属的丰富度;与无肥条件相比,有机肥施用提高了AM真菌丰富度指数,但降低了AM真菌多样性指数。多元分析结果表明,土壤全磷及速效磷含量是影响AM真菌群落组成中优势属丰度变化的主要因素。免耕覆盖、有机栽培改变了土壤AM真菌的多样性及丰富度,土壤中丰度较低的AM真菌菌属更容易受到有机肥施用的影响;有机肥与免耕、覆盖管理的交互作用对AM真菌近明球囊霉属相对丰度有显著影响(P<0.05)。AM真菌群落对耕作覆盖、有机肥施用管理活动的响应受到农业综合管理活动及其相关因素交互作用的影响。本研究结果为合理农作物免耕覆盖、有机栽培管理提供了理论依据。     

Nematode communities of grazed and ungrazed semi-natural steppe grasslands in Eastern Austria

Soil nematode communities were investigated at eight semi-natural steppe grasslands in the National Park Seewinkel, eastern Austria. Four sites were moderately grazed by horses, cattle and donkeys, four were ungrazed. Nematodes were sampled on four occasions from mineral soil, and their total abundance, diversity of genera, trophic structure and functional guilds were determined. Altogether 58 nematode genera inhabited the grasslands, with Acrobeloides, Anaplectus, Heterocephalobus, Prismatolaimus, Aphelenchoides, Aphelenchus, Tylenchus and Pratylenchus dominating. Mean total abundance at sites was 185–590 individuals per 100 g soil. Diversity indices did not separate communities well, but cluster analysis showed distinct site effects on nematode generic structure. Within feeding groups the relative proportion of bacterial-feeding nematodes was the highest, followed by the fungal- and plant-feeding group. Omnivores and predators occurred in low abundance. The maturity indices and plant parasite indices were characteristic for temperate grasslands, but the abundance of early colonizers (c-p 1 nematodes) was low. A high density of fungal-feeding c-p 2 families (Aphelenchoidae, Aphelenchoididae) resulted in remarkably high channel index values, suggesting that decomposition pathways are driven by fungi. Nematode community indices of all sites pointed towards a structured, non-enriched soil food web. At most sites, grazing showed little or no effect on nematode community parameters, but total abundance was higher at ungrazed areas. Significant differences in the percentage of omnivorous nematodes, the sum of the maturity index, the number of genera and Simpson's index of diversity were found at one long-term grazed pasture, and this site was also separated by multi-dimensional scaling (MDS).     

Bacterial diversity and community structure along different peat soils in boreal forest

Bacteria in peat forest soil play important role in global carbon cycling. The distribution of bacteria population in different peat soils as a whole and how forest management practices alter the bacterial populations are still poorly known. Using pyrosequencing analysis of 16S rRNA gene, we quantified the diversity and community structure of bacteria in eight peat forest soils (pristine and drained) and two mineral forest soils from Lakkasuo, Finland with either spruce-dominant or pine-dominant tree species. In total, 191,229 sequences which ranged from 15,710 to 22,730 per sample were obtained and affiliated to 13 phyla, 30 classes and 155 genera. The peat forest soils showed high bacterial diversity and species richness. The tree species seems to have more strong impact on the bacterial diversity than the type of peat soil, which drives the changes in bacterial community structure. The dominant taxonomic groups across all soils (>1% of all sequences) were Proteobacteria, Acidobacteria, Actinobacteria, Bacteroidetes, Planctomycetes and Verrucomicrobia. The relative abundance of bacteria phylum and genus differed between soil types and between vegetation. Significant differences in relative abundance of bacteria phyla were only found for Gemmatimonadetes and Cyanobacteria between the pristine and the drained peat forest soils. At genus level, the relative abundance of several genera differed significantly between the peat soils with same or different tree species, including Burkholderia, Caulobacter, Opitutus, Mucilanginibacter, Acidocella, Mycobacterium, Bradyrhizobium, Dyella and Rhodanobacter.     

硒砂瓜连作对土壤真菌群落结构的影响

硒砂瓜是宁夏地区重要的经济作物,其连作严重影响硒砂瓜产量和品质。目前硒砂瓜连作对土壤真菌群落结构的影响尚不清楚。本研究采用Illumina MiSeq高通量测序技术,探讨硒砂瓜连作对土壤真菌群落结构的影响。研究发现,硒砂瓜连作土壤中真菌群落多样性指数和丰富度指数随连作年限的增加先上升后下降。供试土壤样本中共检测到真菌8门、25纲、244属,其中子囊菌门（Ascomycota）、接合菌门（Zygomycota）是优势菌门,占90%以上。与对照相比,连作30年土壤中子囊菌门丰度下降32.51%,接合菌门丰度上升29.89%。供试土壤中真菌主要的优势属为被孢霉属（Mortierella）、绿僵菌属（Metarhiziun）、假霉样真菌属（Pseudallescheria）、镰刀菌属（Fusarium）和青霉属（Penicillium）。与对照相比,连作5年土壤中假霉样真菌属丰度增加45.81%,连作10年土壤中镰刀菌属丰度增加26.74%,连作15年土壤中绿僵菌属下降26.83%,连作20年土壤中青霉属增加29.68%,连作25年土壤中绿僵菌属减少18.30%,连作30年土壤中被孢霉属丰度上升29.89%。土壤理化性质与硒砂瓜连作年限间无显著相关性,而与土壤真菌群落结构存在显著的相关性。土壤全磷、碱解氮、有效磷含量是影响土壤真菌群落最主要的因素。研究结果表明,导致硒砂瓜连作障碍的主要原因不是土壤理化性质变化,而是土壤真菌群落结构的改变。研究结果可为硒砂瓜土传病害的生物防治提供参考依据。     

西北地区赤霞珠葡萄根际土壤中AM真菌的多样性

对西北地区5个酿酒葡萄赤霞珠（Vitis vinifera L. cv. Cabernet Sauvignon）葡萄园根际土壤060 cm土层的AM真菌空间分布进行了研究。结果表明,葡萄根系可形成丛枝菌根,且侵染率较高,最高达79%; 在西北地区的5个样地中共分离出AM真菌4属22种,其中球囊霉属（Glomus）15种,无梗囊霉属（Acaulospora）4种,盾巨孢囊霉属（Scutellospora）2种,巨孢囊霉属（Gigaspora）1种。5个样地孢子密度大小顺序为: 陕西泾阳（JY）＞山西永济（YJ）＞陕西杨凌（YL）＞宁夏银川（YC）＞甘肃莫高（MG）。各样地葡萄根际土壤中AM真菌种的丰富度不同,陕西泾阳地区最高; 分布于葡萄根际的AM真菌按种类多少排序的属依次是: 球囊霉属无梗囊霉属盾巨孢囊霉属巨孢囊霉属,球囊霉属占据的比例保持着绝对优势; 根内球囊霉、摩西球囊霉、地表球囊霉在不同样地中均为优势菌株,副冠球囊霉,集球囊霉,细凹无梗囊霉是多数样地中的稀有种类。研究表明,葡萄与AM真菌具有良好的共生关系,二者协同进化产生了具有生态环境特异性的菌根真菌多样性; 葡萄根际存在较为丰富的丛枝菌根真菌资源,可供进一步开发利用。     

Fungal communities associated with the decomposition of a common leaf litter (Quercus leucotrichophora A. Camus) along an elevational transect in the Central Himalaya

Summary We studied the fungal communities associated with decomposing common leaf litter (Quercus leucotrichophora A. Camus) placed in five forests of Central Himalaya between the elevations of 330 and 2150 m. During the initial period of decay, conciding with the rainy season, a progressive increase in fungal counts and species diversity was observed in all forest sites. The sal forest site had a greater weight loss and supported the largest fungal densities, whereas the pine forest had a lower weight loss and the smallest fungal densities. Deuteromycetes were the dominant group in all the forest sites. Most of the species isolated during the annual cycle of the forest sites were of the accidental type. Species diversity and fungal counts on the common leaf litter were markedly affected by the environmental changes brought about by the native leaf litter. This effect was most obvious in the chir pine forest site where the leaf litter of the native dominant species was distinctly more resistant to decay than those of the other sites, making the soil environment of the site markedly different from that of other sites. The pattern of fungal-species changes with progressive decay of the substrate was similar to that suggested by the tolerance model of Connel and Slatyer.     

长期有机无机肥配施对东北黑土真菌群落结构的影响

【目的】分析长期有机无机肥配施对土壤真菌丰度、多样性及其群落特征的影响,探讨东北黑土真菌群落变化与施肥的相关性,为进一步调节土壤微生物结构,改善其生态功能提供参考依据。【方法】依托黑龙江省农业科学院36年长期定位试验站,选取4个不同施肥处理:不施肥处理（CK）、有机肥处理（M）、氮磷钾无机肥处理（NPK）和有机肥配施无机肥处理（MNPK）的耕作层土壤为研究对象,以真菌ITS基因为分子标靶借助qPCR技术和Illumina Miseq高通量测序平台,研究不同施肥处理对黑土中真菌群落丰度、多样性和组成的影响,并与土壤化学性质进行偶联分析,揭示群落与施肥的相关性。【结果】长期施用无机肥显著降低土壤pH,而有机无机配施可以有效缓解土壤酸化。NPK处理的ITS基因丰度显著高于MNPK;MNPK处理的细菌/真菌比值（26.91104）显著大于NPK,各处理比值由高到低为MNPK M CK NPK。细菌/真菌比值与土壤pH正相关;MNPK处理的真菌多样性指数值略大于NPK。Ascomycota和Zygomycota为土壤中主要真菌门,不同施肥处理之间真菌组成的相对丰度存在显著差异,对照处理Ascomycota的相对丰度为45.35%,MNPK和NPK处理分别为50.93%和56.16%。有机肥有利于降低病原真菌相对丰度,具有高度侵染性的Cochliobolus在MNPK（0.41%）和M（0.39%）中的相对丰度显著小于CK（3.25%）和NPK（2.08%）。CCA分析表明,土壤理化性质共解释土壤真菌群落结构变化的73.3%,有效磷（贡献量为32.4%,P=0.002）、铵态氮（贡献量为14.8%,P=0.01）和硝态氮（贡献量为16.2%,P=0.048）是3个重要的影响因子。【结论】不同施肥条件下土壤真菌丰度、多样性,以及菌群组成特征不同。与无机肥相比,有机肥无机肥配施能够有效改善真菌群落结构,降低真菌的丰度,增加真菌多样性,并提高土壤pH,减缓土壤酸化。土壤有效磷、铵态氮和硝态氮含量是影响黑土土壤真菌群落结构变化重要因素。     

黄土高原油松根际土壤酶活性及真菌群落多样性研究——以黄龙山林场为例

为了解黄土高原油松林根际土壤酶活性和真菌群落多样性,本研究分析了陕西黄龙县不同样区油松根际土壤脲酶、碱性磷酸酶、多酚氧化酶和过氧化氢酶活性,并采用巢式PCR-变性梯度凝胶电泳(PCR-DGGE)技术研究了油松根际土壤中真菌群落多样性。结果表明,该地区油松根际真菌群落相似性较高,但受坡向、海拔、土壤水分及人类扰动等诸多因素的影响,不同样区的真菌群落多样性和土壤酶活性存在差异。油松根际各土壤酶活性均表现出坡顶样地高于坡底样地,阴面样地高于阳面样地,林区路旁样地由于采样环境不同于林中样地,酶活性介于其他样地之间;丰富度(S)、Shannon-Wiener指数(H)、Simpson指数(D)、均匀度指数(EH)分析表明,该区域油松根际土壤真菌群落多样性分布特征与酶活性分布特征相一致。相关性分析表明,除过氧化氢酶外,其余酶活性之间、以及与真菌多样性均呈显著正相关(p0.05);土壤含水量与真菌多样性和土壤酶活性除多酚氧化酶外均呈显著正相关(p0.05);而土壤p H与各种酶活性之间均未达显著相关水平(p0.05)。土壤含水量是影响该地区真菌群落多样性与土壤酶活性主要因素之一。     

秸秆还田条件下腐熟剂对不同质地土壤真菌多样性的影响

为因地制宜鉴选适宜的秸秆腐熟剂,在西辽河平原灌区选择秸秆还田的砂壤土和中壤土连作玉米地,分别配施中农绿康腐熟剂、人元腐熟剂和农富康腐熟剂(简称中农、人元、农富康),以秸秆还田不施腐熟剂为对照,在玉米吐丝期取0～15 cm、15～30 cm、30～45 cm土层样品,采用高通量测序技术,研究不同质地土壤秸秆还田配施腐熟剂情况下土壤真菌群落结构的多样性。结果表明,砂壤土秸秆还田配施腐熟剂处理特有OTU(operational taxonomic units)数均比对照多,中壤土则相反。所有处理土壤中被孢霉门(Mortierellomycota)、子囊菌门(Ascomycota)、担子菌门(Basidiomycota)相对丰度较高;优势属均为被孢霉属(Mortierella)和低温酵母(Guehomyces)。不同腐熟剂对土壤质地产生不同影响,中壤土秸秆还田配施中农和农富康对土壤真菌组成及丰度无显著影响,而配施人元显著改变中壤土真菌组成及丰度;砂壤土秸秆还田配施中农和人元显著增加土壤真菌组成及丰度。LEfSe分析可知,砂壤土秸秆还田配施中农、中壤土秸秆还田配施人元和农富康3个处理土壤真菌多样性存在差异,对真菌多样性差异发挥显著性作用的门为担子菌门、子囊菌门,纲为伞菌纲(Agaricomycetes),目为腔菌目(Pleosporales)和伞菌目(Agaricales),种为Mortierella fimbricystis。这种响应差异也体现在同一腐熟剂对中壤土和砂壤土不同土层真菌的影响;随土层的下移,砂壤土和中壤土对照中被孢霉属相对丰度先增加后下降,低温酵母相对丰度下降;施用腐熟剂后(中壤土农富康除外),深层土壤低温酵母相对丰度比表层土壤高。砂壤土秸秆还田配施中农后0～15 cm土层中上述2个优势菌属相对丰度显著提高;而中壤土秸秆还田配施人元增加0～15 cm土层低温酵母相对丰度和15～30 cm、30～45 cm土层被孢霉属相对丰度。由此可见,秸秆还田条件下腐熟剂与土壤质地间响应不同,所以秸秆腐熟剂配施应因地制宜。     

Fungal community composition in sodic soils subjected to long-term rice cultivation

ABSTRACT

Rice cultivation is widely used to improve saline-sodic soils in Northeast China. However, the chronological effect of rice cultivation on soil fungal communities has not been studied. Therefore, this study investigated the variation of soil fungal communities in different rice cultivation years. Compared with the blank area, the rice cultivation for 20 years significantly decreased the pH and electrical conductivity by 16.6% and 70.1%, while significantly increased the soil organic carbon and available phosphorus by 90.6% and 17.4 times, respectively. Meanwhile, the relative abundance of Ascomycota and Basidiomycota significantly decreased and increased after rice cultivation, respectively. Moreover, some genera of arbuscular mycorrhizal fungi (AMF), e.g. Corymbiglomus, Glomus, and Rhizophagus, and pathogenic fungi (Thanatephorus cucumeris) disappeared, while Dentiscutata (one genus of AMF) appeared after rice cultivation. In addition, the fungal richness significantly increased when the rice cultivation less than 15 years and the fungal communities were similar between 15 and 20 years. Our findings showed that rice cultivation improved the nutrient availability and reduced salinity-alkalinity stress of sodic soils. After the rice cultivation for 15 years, the soil fungal community tended to be stable.     

Soil respiration rate and its sensitivity to temperature in pasture systems of dry-tropics

Abstract

Tree clearing is a topical issue the world over. In Queensland, the high rates of clearing in the past were mainly to increase pasture production. The present research evaluates the impact of clearing on some soil biological properties, i.e. total soil respiration, root respiration, microbial respiration, and microbial biomass (C and N), and the response of soil respiration to change in temperature.

In-field and laboratory (polyhouse) experiments were undertaken. For in-field studies, paired cleared and uncleared pasture plots were selected to represent three major tree communities of the region, i.e. Eucalyptus populnea, E. melanophloia, and Acacia harpophylla. The cleared sites were chosen to represent three different time-since-clearing durations (5, 11–13, and 33 years; n=18 for cleared and uncleared plots) to determine the temporal impact of clearing on soil biological properties. Experiments were conducted in the polyhouse to study in detail the response of soil respiration to changes in soil temperature and soil moisture, and to complement in-field studies for estimating root respiration.

The average rate of CO₂ emission was 964 g CO₂/m²/yr, with no significant difference (P<0.05) among cleared and uncleared sites. Microbial respiration and microbial biomass were greater at uncleared compared with those at cleared sites. The Q ₁₀-value of 1.42 (measured for different seasons in a year) for in-field measurements suggested a small response of soil respiration to soil temperature, possibly due to the limited availability of soil moisture and/or organic matter. However, results from the polyhouse experiment suggested greater sensitivity of root respiration to temperature change than for total soil respiration. Since root biomass (herbaceous roots) was greater at the cleared than at uncleared sites, and root respiration increased with an increase in temperature, we speculate that with rising ambient temperature and consequently soil temperature, total soil respiration in cleared pastures will increase at a faster rate than that in uncleared pastures.     

Assessing Impacts of Crested Wheatgrass AND Native Species Establishment on Soil Characteristics in Reclaimed LAND Using Bayesian Posterior Predictive Distributions

We examined the interacting effects of drastic disturbance and re‐vegetation communities on the development of soil properties over time. We compared soil characteristics from an undisturbed reference site with reclaimed mine sites that differed by vegetation type and time since reclamation: Three sites were seeded solely with crested wheatgrass (Agropyron cristatum) (11, 16, and 29 years old), and two were seeded with native cool‐season grass mixes (14 and 26 years old). We sampled soil at two depths (0–5 and 5–15 cm) for soil macroaggregate and microaggregate weights, aggregate carbon to nitrogen (C : N) ratios, and microbial abundance. We employed a Bayesian bivariate model to account for potential correlations in soil properties across depths and compared soil properties across sites using posterior predictive distributions. We found that all reclaimed soils, regardless of vegetation type, had total aggregate weights that were similar to the undisturbed reference soil but had a larger proportion of macroaggregates than the reference soil. Aggregate C : N ratios were similar between the undisturbed reference and crested wheatgrass soils, while the reclaimed native cool‐season grass soils had lower C : N ratios in the top 5 cm. Total microbial abundance in soils seeded with crested wheatgrass was an order of magnitude lower than that in soils occupied by native species (both reclaimed and undisturbed). The presence of crested wheatgrass on the reclaimed sites alone did not differentiate all soil properties across our reclamation sites, but seeding this single, aggressive species may have contributed to maintaining different belowground characteristics on reclaimed soils. Copyright © 2015 John Wiley & Sons, Ltd.     

Parasitism by Cuscuta australis affects the rhizhospheric soil bacterial communities of Trifolium repens L.

ABSTRACT

The effect of parasitism on belowground microbial communities is not well understood. 16S rRNA gene amplicon sequencing was used to test the effect of Cuscuta australis parasitism on the composition and diversity of bacterial community in the rhizospheric soil of the host plant Trifolium repens. 94569 sequences were obtained from the amplicons of non-parasitised, and 97172 sequences were obtained from the parasitised rhizospheric soil bacterial community. Parasitism of C. australis significantly decreased the relative abundance of the bacterial phylum Nitrospirae, while it significantly increased that of Verrucomicrobia. Parasitism of C. australis significantly decreased the relative abundance of 10 bacterial genera, while it significantly increased those of nine genera. The Chao 1 indexes of the rhizospheric soil bacterial community of parasitised T. repens were significantly lower than those of non-parasitised T. repens. Principal coordinate analysis (based on the genus) and principal component analysis (based on the predicted gene function of bacterial communities) showed that rhizospheric bacterial communities from parasitised and non-parasitised T. repens differed and can be divided into two groups. These results suggest that infection of the holoparasitic plant could indirectly change the composition, diversity, and function of rhizospheric soil bacteria of the host plant.     

Earthworm composition,diversity and biomass under three land use systems in south-eastern Australia

In south-eastern Australia, strips of planted native trees and shrubs (shelterbelts) are frequently established to restore ecosystem services altered by agriculture. Despite their wide use, little is known about the effects of establishing shelterbelts on soil macro invertebrates, especially earthworms, which are of major importance in soil processes. We assessed earthworm composition, diversity and biomass in three land use systems: native shelterbelts dominated by Acacia and Eucalyptus species, agricultural pastures and native remnant woodland fragments dominated by Eucalyptus blakelyi and/or Eucalyptus melliodora. Earthworm communities differed significantly among systems, with abundance, biomass and diversity greatest under pasture. Within shelterbelts we saw a shift from high earthworm biomass and density to low with increasing time after establishment. Soil edaphic variables did not correlate strongly with earthworm biomass or density, but were correlated with earthworm community composition. Overall the introduction of native woody vegetation was associated with a decline in density and biomass of earthworms, including a decrease in the relative abundance of exotic species. As such shelterbelts can be used to promote native earthworm relative abundance, which may be important for local diversity, soil function and landscape connectivity.     

Do bacterial and fungal communities in soils of the Bolivian Altiplano change under shorter fallow periods?

Traditional fallow periods in the Bolivian highlands are being shortened in an effort to increase short-term crop yields, with potential long-term impacts on soil microbial communities and their functions. In addition, native vegetation, such as Parasthrephia sp. or Baccharis sp. (both locally known as ‘thola’) are often removed as a fuel for cooking. We evaluated the effects of fallow period and thola on soils in 29 farmers' fields in two municipalities in the Bolivian Altiplano (Umala and Ancoraimes). Soil fungal and bacterial community responses were characterized using 454-pyrosequencing. Soils in Ancoraimes had significantly higher levels of organic matter, nitrogen and other macronutrients compared to Umala. Ancoraimes soils also supported more diverse fungal communities, whereas Umala had more diverse bacterial communities. Unexpectedly, the longer fallow periods were associated with significantly lower fungal diversity in Umala and lower bacterial diversity in Ancoraimes. Fungi assigned to genera Bionectria, Didymella, and Alternaria, and bacteria assigned to genera Paenibacillus, Segetibacter, and Modestobacter decreased in frequency with longer fallow period. The presence of thola was not associated with significantly different overall soil fungal or bacterial diversity, but was associated with higher frequency of some genera, such as Fusarium and Bradyrhizobium. Our results indicate that fallow period has a range of effects on soil communities, and that the removal of thola may impact the dynamics of these communities.     

Impacts of habitat disturbance on termites and soil water storage in a tropical Australian savanna

This study examines changes in the abundance and diversity of soil macroinvertebrate taxa and soil water storage across different disturbance treatments in a tropical savanna woodland in northern Australia. Nine plots representing three habitat disturbance treatments (uncleared savanna woodland; 25-year-old regrowth following past clearing; cleared areas) were sampled for macrofauna using soil pits in April 2003. Sub-surface soil moisture (0-0.4 m) was measured at 0.1 m intervals over the 2002/2003 wet season. Termites represented 55% of total individuals sampled. Abundance of soil macrofauna was greatest in uncleared plots and lowest in cleared plots, with the latter treatment also having the lowest taxon diversity. Mean abundances of termites, earthworms and ants were greatest in uncleared treatment plots. Five termite species from four genera were present, with Microcerotermes nervosus constituting 47% of termite species identified. Of the wood-, grass- and polyphagous-feeding termites present, wood-feeding species were restricted to uncleared treatment plots and grass-feeders to regrowth treatment plots. A shift in termite nesting habits from epigeal to hypogeal was observed from uncleared to cleared treatments. Soil water storage was lowest in the dry season and highest during the monsoon, and varied significantly across habitat disturbance treatments at the start and end of the wet season. Cleared plots were least effective in the capture of the first wet season rains, and uncleared treatment plots showed the greatest capacity to retain soil water during the transition from wet to dry season. The negative effects of habitat disturbance on soil water storage may have been partially mediated by the observed changes in soil macrofauna, especially termites.