Characterization of the Major Capsid Genes (g23) of T4-Type Bacteriophages in the Wetlands of Northeast China

To obtain genetic information and to evaluate the composition of T4-type bacteriophage (phage) communities in wetlands, environmental soil and water DNAs were obtained from two natural wetlands dominated by Carex lasiocarpa and Deyeuxia angustifolia plant species, and a neighboring paddy field in Sanjiang plain of northeast China. The biomarker gene of g23, which encodes the major capsid protein of T4-type phages, was amplified with primers MZIA1bis and MZIA6, and the PCR products were cloned and sequenced. In total, 96 and 50 different g23 clones were obtained from natural wetlands and a paddy field, respectively. A larger number of clones with low levels of identity to known sequences were found in water than in soil both in the natural wetlands and the paddy field, suggesting that many of T4-type phages in wetland water and paddy floodwater in Sanjiang plain are uncharacterized. Phylogenetic analyses showed that the g23 clones in natural wetlands, irrespective of water and soil, were distinctly different from those in marine waters, lake waters, and upland black soils, but were similar to those in paddy fields. The UniFrac analysis of g23 assemblages indicated that T4-type phage community compositions were different between soils and waters, and also were different between the natural wetlands and the paddy field. In general, the global analysis of g23 clone assemblages demonstrated that T4-type phage community compositions were different among natural wetlands, marines, lakes, paddy fields, and upland black soils.     

Bacterial Community Structure in Two Permafrost Wetlands on the Tibetan Plateau and Sanjiang Plain,China

Permafrost wetlands are important methane emission sources and fragile ecosystems sensitive to climate change. Presently, there remains a lack of knowledge regarding bacterial communities, especially methanotrophs in vast areas of permafrost on the Tibetan Plateau in Northwest China and the Sanjiang Plain (SJ) in Northeast China. In this study, 16S rRNA-based quantitative PCR (qPCR) and 454 pyrosequencing were used to identify bacterial communities in soils sampled from a littoral wetland of Lake Namco on the Tibetan Plateau (NMC) and an alluvial wetland on the SJ. Additionally, methanotroph-specific primers targeting particulate methane monooxygenase subunit A gene (pmoA) were used for qPCR and pyrosequencing analysis of methanotrophic community structure in NMC soils. qPCR analysis revealed the presence of 10¹⁰ 16S rRNA gene copies per gram of wet soil in both wetlands, with 10⁸ pmoA copies per gram of wet soil in NMC. The two permafrost wetlands showed similar bacterial community compositions, which differed from those reported in other cold environments. Proteobacteria, Actinobacteria , and Chloroflexi were the most abundant phyla in both wetlands, whereas Acidobacteria was prevalent in the acidic wetland SJ only. These four phyla constituted more than 80 % of total bacterial community diversity in permafrost wetland soils, and Methylobacter of type I methanotrophs was overwhelmingly dominant in NMC soils. This study is the first major bacterial sequencing effort of permafrost in the NMC and SJ wetlands, which provides fundamental data for further studies of microbial function in extreme ecosystems under climate change scenarios.     

三江平原自然湿地与人工湿地双向演替动态过程研究

基于遥感和GIS技术,分析1986～2005年三江平原自然湿地(湖泊、河流、沼泽湿地)与人工湿地(水田)的双向演替过程,统计分析自然地理环境背景(土壤类型、海拔高度、坡度和地貌类型)对此过程的影响。研究结果表明,1986～2005年间三江平原湿地双向演替过程以沼泽湿地与水田之间的相互转化为主。1986～1995年、1995～2000年和2000～2005年三时段内沼泽湿地转化为水田的面积占同期沼泽湿地转出总面积的比例分别为7.61%、37.99%和28.81%,相反,水田转化为沼泽湿地的面积占同期水田转出总面积的4.83%、13.69%和4.84%。三江平原发生沼泽湿地与水田双向演替过程的主要自然地理环境背景为土壤类型为草甸土和沼泽土,海拔高度为0～100 m,坡度为0～1°,地貌类型为低河漫滩、高河漫滩、洼地和一级阶地。     

Effects of reclamation of natural wetlands to a rice paddy on dissolved carbon dynamics in the Sanjiang Plain,Northeastern China

Natural wetlands play an important role in the global carbon cycle, and loss of dissolved carbon through water has been indicated as one of the most important carbon sources for riverine ecosystems. During the last century, a large natural wetland area was reported to be converted to other land use types such as rice paddy land around the world. In this study, we explored the dynamics of dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) in two natural freshwater wetlands and a rice paddy field, which was reclaimed from the natural wetlands in the Sanjiang Plain, Northeastern China, during the growing season (May–October) of 2009. The DOC and DIC concentrations in the two ecosystems were significantly different (P < 0.05). The mean DOC concentrations during the growing season in the surface water of the Deyeuxia angustifolia and Carex lasiocarpa wetlands were 49.88 ± 5.44 and 27.97 ± 1.69 mg/L, respectively, while it was only 8.63 ± 2.54 mg/L in the rice paddy field. Specific ultra-violet light absorption at 254 nm (SUVA₂₅₄) of DOC increased by an average of 19.54% in the surface water from the natural wetlands to rice paddy, suggesting that DOC mobilized in the natural wetlands was more aromatic than that in the rice paddy field. The mean DIC concentration in surface water of the rice paddy was 5.25 and 5.04 times higher than that in the natural D. angustifolia and C. lasiocarpa wetlands, respectively. The average ratio of DIC to dissolved total carbon (DTC) for the water sampled from the artificial drainage ditch in the rice paddy field was 61.82%, while it was 14.75% from the nearby channel of natural wetlands. The significant differences in dissolved carbon concentration in surface water and channels originating from different land use types suggested that reclamation of natural wetlands to rice paddy field would reduce DOC runoff and increase the DIC concentration to adjacent watersheds. Our study results for the changed pattern in dissolved carbon after the natural wetland was transformed to paddy field could have important implications for studying the impacts of the large-scale land use change to carbon cycle and management.     

Carbon sequestration in freshwater wetlands in Costa Rica and Botswana

Tropical wetlands are typically productive ecosystems that can introduce large amounts of carbon into the soil. However, high temperatures and seasonal water availability can hinder the ability of wetland soils to sequester carbon efficiently. We determined the carbon sequestration rate of 12 wetland communities in four different tropical wetlands—an isolated depressional wetland in a rainforest, and a slow flowing rainforest swamp, a riverine flow-through wetland with a marked wet and dry season, a seasonal floodplain of an inland delta—with the intention of finding conditions that favor soil carbon accumulation in tropical wetlands. Triplicate soil cores were extracted in these communities and analyzed for total carbon content to determine the wetland soil carbon pool. We found that the humid tropic wetlands had greater carbon content (P ≤ 0.05) than the tropical dry ones (96.5 and 34.8 g C kg^?1, respectively). While the dry tropic wetlands had similar sequestration rates (63 ± 10 g Cm^?2 y^?1 on average), the humid tropic ones differed significantly (P < 0.001), with high rates in a slow-flowing slough (306 ± 77 g Cm^?2 y^?1) and low rates in a tropical rain forest depressional wetland (84 ± 23 g Cm^?2 y^?1). The carbon accumulating in all of these wetlands was mostly organic (92–100%). These results suggest the importance of differentiating between types of wetland communities and their hydrology when estimating overall rates at which tropical wetlands sequester carbon, and the need to include tropical wetland carbon sequestration in global carbon budgets.     

农田开垦对三江平原湿地土壤种子库影响及湿地恢复潜力

种子库是湿地植被恢复的重要途径之一,不同时期的耕作土壤中残留的种子对开垦湿地恢复具有重要的作用.本文采用温室萌发法在两种水分条件下对三江平原天然湿地、不同开垦年限湿地种子库结构和规模进行了研究,以了解不同开垦年限湿地种子库特征及其在湿地植被恢复中的潜力.本次实验共萌发物种50种,随着开垦年限增加,萌发物种逐渐减少,天然湿地、开垦1年、3年、10年、20年的湿地分别为34种、31种、21种、21种和8种,萌发物种数与种子库规模均表现出极显著差异(F1=8.32,F2=5.946,P＜0.001).种子库密度以天然湿地和开垦1年湿地最大,分别为7624粒/m2,9836粒/m2.随着开垦年限增加,种子库规模逐渐减小,开垦3年、10年种子库密度为4336粒/m2,4872粒/m2.开垦20 a后,显著减少为432粒/m2.湿润条件下萌发物种数及种子密度显著高于淹水处理,种子库具有明显的分层现象,0-5 cm土层种子库规模显著高于5-10 cm.小叶章(Calamagrostis angustifolia)作为该地区优势物种,由最初的1192粒/m2,经过20 a开垦后在种子库中消失.研究表明,在一定的开垦年限范围内,开垦湿地土壤中仍然保留大量的湿地物种种子,在湿地恢复中具有重要的作用.     

人工和天然湿地芦苇根际土壤细菌群落结构多样性的比较

为认识人工湿地运行初期根际土壤细菌群落的结构多样性,本研究采用聚合酶链式反应-变性梯度凝胶电泳（PCR-DGGE）的方法,比较了嘉兴石臼漾人工构筑生态湿地和白洋淀天然湿地府河河口区域芦苇根际土壤的细菌群落结构多样性。研究结果显示,嘉兴石臼漾湿地在运行初期（1~1.5年）,根际土壤细菌的物种丰富度已与白洋淀湿地相近,但香农指数和均匀度指数均显著低于白洋淀湿地;随着污染物浓度的降低,土壤细菌群落基因型多样性指数增大。     

1954-2015年不同地貌分区下湿地农田化过程的时空特征——以完达山以北三江平原为例

以完达山以北三江平原（以下简称为小三江平原）为研究区,依据样带选择原则选取具有湿地农田化典型性的区域（即典型样带）。在地质地貌分区的基础上,基于特定历史时期的土地利用/覆被数据集构建长时间序列的耕地和沼泽湿地动态变化数据集,利用RS和GIS技术分析小三江平原典型样带内湿地农田化的时空变化规律,探究近60年小三江平原内湿地农田化的区位特征,结果表明：（1）1954-2015年,小三江平原的耕地面积显著增加,垦殖率达到了79.47%,耕地结构发生了显著的变化;（2）小三江平原湿地农田化具有明显的历史阶段性：在改革开放之前（1954-1976年）湿地农田化程度不是很大,改革开放初期（1976-1985年）开始发生明显的湿地农田化,到全面改革开放期（1985-1995年）湿地农田化程度加重,在改革开放转型期（1995-2005年）湿地农田化最严重,在深化改革开放期（2005-2015年）湿地农田化程度有所减小;（3）区域大的自然背景决定了小三江平原湿地农田化整体趋势：1954-2015年间,小三江平原湿地农田化最初发生在中幅度沉降第四纪缓慢上升区,逐步扩展到大幅度沉降第四纪缓慢沉降区和小幅度沉降第四纪缓慢上升区;（4）小三江平原湿地农田化具有明显的地貌区位特征：湿地农田化最初发生在冲积平原上,然后扩展到河流低阶地和高河漫滩上,随着时间的推移逐步扩展到低河漫滩和微高地上,最后蔓延到洼地上。     

Changes in Diversity and Functional Gene Abundances of Microbial Communities Involved in Nitrogen Fixation, Nitrification, and Denitrification in a Tidal Wetland versus Paddy Soils Cultivated for Different Time Periods

In many areas of China, tidal wetlands have been converted into agricultural land for rice cultivation. However, the consequences of land use changes for soil microbial communities are poorly understood. Therefore, we investigated bacterial and archaeal communities involved in inorganic nitrogen turnover (nitrogen fixation, nitrification, and denitrification) based on abundances and relative species richness of the corresponding functional genes along a soil chronosequence ranging between 50 and 2,000 years of paddy soil management compared to findings for a tidal wetland. Changes in abundance and diversity of the functional groups could be observed, reflecting the different chemical and physical properties of the soils, which changed in terms of soil development. The tidal wetland was characterized by a low microbial biomass and relatively high abundances of ammonia-oxidizing microbes. Conversion of the tidal wetlands into paddy soils was followed by a significant increase in microbial biomass. Fifty years of paddy management resulted in a higher abundance of nitrogen-fixing microbes than was found in the tidal wetland, whereas dominant genes of nitrification and denitrification in the paddy soils showed no differences. With ongoing rice cultivation, copy numbers of archaeal ammonia oxidizers did not change, while that of their bacterial counterparts declined. The nirK gene, coding for nitrite reductase, increased with rice cultivation time and dominated its functionally redundant counterpart, nirS, at all sites under investigation. Relative species richness showed significant differences between all soils with the exception of the archaeal ammonia oxidizers in the paddy soils cultivated for 100 and 300 years. In general, changes in diversity patterns were more pronounced than those in functional gene abundances.     

鄱阳湖苔草湿地甲烷释放特征

2009年5月-2010年4月在鄱阳湖南矶湿地国家级自然保护区选择以灰化苔草为建群种的洲滩,设置土壤-植物系统(TC)、剪除植物地上部分 (TJ)2个试验处理,利用密闭箱-气相色谱法测定了鄱阳湖典型苔草湿地的甲烷(CH₄)释放通量。结果表明:1)TC、TJ 2个试验处理CH₄释放速率变化范围分别为-0.094-17.75 mg · m^-2 · h^-1、-0.122-19.16 mg · m^-2 · h^-1,均表现出明显的季节变化规律;2)地表未淹水期间,剪草处理CH₄释放显著高于非剪草处理(t=2.69, P<0.05);地表淹水达到15 cm后,剪草处理CH₄释放明显低于非剪草处理。3)土壤5 cm温度、土壤水分与2处理非淹水期间CH₄释放速率均呈显著正相关,是非淹水期间CH₄通量变化的主要控制因子,2因子能够共同解释非淹水期苔草湿地65%-74%的CH₄通量变异;4)试验期间,苔草湿地CH₄释放量约为12.77 gC/m²,相当于同期土壤有机质分解碳排放量的4%,甲烷释放的碳消耗不足苔草湿地年NPP的1%。     

三江平原建三江地区30年湿地景观退化评价

因高强度农业开发,1975～2004年的30a间,三江平原自然湿地景观发生了剧变.评估该湿地景观面临的各种压力、分析其所处状态、揭示其演变规律,对于三江平原的湿地保护和恢复至关重要.选取1975年、1989年和2004年的三期Landsat TM遥感影像,基于压力-状态-响应的生态评价框架,对黑龙江省建三江地区景观演变进行分析.结果表明,(1)从1975年到2004年,建三江地区自然湿地大幅减少,农田大幅增加,景观多样性和破碎度显著提高;农业开发是自然湿地面临的主要压力,其中草甸和沼泽湿地是主要的开发对象.(2) 1975～1989年的农业开发强度高于1989～2004年.1975～1989年,农田、沟渠面积大幅增加,湿地面积大量减少;通过沟渠排水将湿地开发为旱田,导致该区生态环境质量下降,洪涝灾害频繁;1989～2004年,人们意识到湿地保护的重要性,自然湿地开垦减少,沟渠面积略有增加,并把部分旱田转为水田来达到"以稻治涝"的目的;同时,建立了多个湿地自然保护区并制定了相应的湿地保护条例,使得该区的湿地景观得到了一定的保护.(3) 当前三江平原湿地景观面临的问题依然严峻,尤其是排水沟渠的大量存在和旱田转化为水田后导致的水资源短缺和地下水位下降等问题,还将继续威胁现有湿地的存续,基于沟渠系统的综合性水资源管理势在必行.     

基于遥感的湿地景观格局季相分析

以中国东北地区三江平原北部为研究区域,利用2012年多季相遥感影像作为数据源,结合野外调查数据,应用面向对象的分类方法,根据影像的物候、时相等特征,提取不同月份的湿地信息,进行景观格局季相分析。结果表明:(1)研究区湿地面积、类型格局在同一年不同季节不同月份会有不同幅度的变化,总体呈现缓增骤减的态势。湿地主要分布在低洼地区,主要湿地类型为草本沼泽,其次为河流,其他湿地占总面积比例较小。(2)研究区各阶段湿地都有转化,主要发生在湿地和非湿地之间,多数表现在草本沼泽和草地之间的转化。(3)湿地分布和湿地转化面积主要集中在低海拔区域和低坡度区域,其中海拔100 m和坡度5°以下范围内的湿地分布面积和湿地转化面积占湿地总面积及湿地转化面积的绝大部分。(4)年内季节性湿地转化与降水、温度和湿地植被物候关系密切。     

三江平原孤立湿地景观空间结构

受人类活动的影响,近几十年来三江平原大片连续湿地逐渐破碎化,形成了大量孤立湿地。湿地景观格局分析已成为湿地生态和全球变化研究领域的热点,因此以三江平原遥感影像为数据源,利用GIS技术和景观指数模型,在60m分析粒度下,对三江平原孤立湿地景观空间结构进行分析。结果表明:1研究区的中南部孤立湿地的斑块数量较多,而中东部孤立湿地的斑块面积较大,且孤立湿地斑块之间的邻近程度和连接度较高,三江、洪河自然保护区及研究区西部孤立湿地斑块的形状较复杂;2随着湿地斑块数量的递减,非孤立湿地在景观连接中起到的作用逐渐增加,孤立湿地在景观连接中起到的作用逐渐减小,但面积相对较大的孤立湿地斑块重要值一直处于较高水平,在景观连接中起着重要作用;3三江平原孤立湿地景观空间结构是地形地貌、农业开发活动、国家政策等因子综合作用的结果,应加强对孤立湿地的保护。     

Characterization of Microbial Communities and Composition in Constructed Dairy Wetland Wastewater Effluent

Constructed wetlands have been recognized as a removal treatment option for high concentrations of contaminants in agricultural waste before land application. The goal of this study was to characterize microbial composition in two constructed wetlands designed to remove contaminants from dairy washwater. Water samples were collected weekly for 11 months from two wetlands to determine the efficiency of the treatment system in removal of chemical contaminants and total and fecal coliforms. The reduction by the treatment was greatest for biological oxygen demand, suspended solids, chemical oxygen demand, nitrate, and coliforms. There was only moderate removal of total nitrogen and phosphorus. Changes in the total bacterial community and ammonia-oxidizing bacterial composition were examined by using denaturing gradient gel electrophoresis (DGGE) and sequencing of PCR-amplified fragments of the gene carrying the α subunit of the ammonia monooxygenase gene (amoA) recovered from soil samples and DGGE bands. DGGE analysis of wetlands and manure samples revealed that the total bacterial community composition was dominated by bacteria from phylogenetic clusters related to Bacillus, Clostridium, Mycoplasma, Eubacterium, and Proteobacteria originally retrieved from the gastrointestinal tracts of mammals. The population of ammonia-oxidizing bacteria showed a higher percentage of Nitrosospira-like sequences from the wetland samples, while a higher percentage of Nitrosomonas-like sequences from manure, feces, raw washwater, and facultative pond was found. These results show that the wetland system is a natural process dependent upon the development of healthy microbial communities for optimal wastewater treatment.     

Effects of invasive Typha × glauca on wetland nutrient pools,denitrification, and bacterial communities are influenced by time since invasion

Invasive plants dramatically shift the structure of native wetland communities. However, less is known about how they affect belowground soil properties, and how those effects can vary depending on time since invasion. We hypothesized that invasion of a wetland by a widespread invasive plant (Typha × glauca) would result in changes in soil nutrients, denitrification, and bacterial communities, and that these effects would increase with time since invasion. We tested these hypotheses by sampling Typha-invaded sites of different ages (~40, 20, and 13 years), a Typha-free, native vegetation site, and a restored site (previously invaded ~30–40 years ago) but that had Typha return within 2 years of the restoration. At each site, we measured Typha stem density, plant species richness, soil nutrients, denitrification rates, and the abundance and composition of bacterial denitrifier communities. All Typha-dominated sites had the least plant species richness regardless of time since invasion. Additionally, sites that were invaded the longest exhibited significantly higher concentrations of soil organic matter, nitrate, and ammonium than the native site. In contrast, denitrification was higher in sites invaded more recently. Denitrifier diversity for the nirS gene was also significantly different, with highest nirS diversity in sites invaded the longest. Interestingly, the denitrifier communities within the restored site were most similar to the ones in T. × glauca sites, suggesting a legacy effect. Our study suggests this invader can alter important ecosystem properties, such as native species richness, nutrient pools, and transformations, as well as bacterial community composition depending on time since invasion.     

Aquatic invertebrate assemblages as potential indicators of restoration conditions in wetlands of Northeastern China

Wetland restoration has been implemented widely but evaluation of the effectiveness of wetland restoration has been limited. In this study, we aimed to investigate the utility of aquatic invertebrate assemblages as potential indicators of restoration condition in wetlands of the Sanjiang Plain, Northeastern China. Results from non‐metric multidimensional scaling analysis of invertebrate assemblages showed that study wetlands (n = 16) divided into two groups: natural wetlands and wetlands that have been restored for 4 years were classified as a group, and impaired wetlands and wetlands restored for only 1 year were classified into another group. After 4 years of recovery, 47.9% of invertebrate taxa found at the natural wetlands could also be found at the restored wetlands, primarily insects with aerial dispersal capabilities for rapid colonization. Indicator species analysis identified differences in community composition among wetland types, and Amphiagrion sp. and Bezzia sp. were indicators of the restored wetlands. In Northeastern China, aquatic invertebrate assemblages and certain indicator species may provide robust measures of wetland restoration. It is urgent for further exploration to monitor restored wetlands in the long‐time series and fully assess the efficiency of the restoration.     

Soil carbon stocks and quality across intact and degraded alpine wetlands in Zoige,east Qinghai-Tibet Plateau

The wetlands on the Qinghai-Tibet Plateau are experiencing serious degradation, with more than 90,000 hectares of marshland converted to wet meadow or meadow after 40 years of drainage. However, little is known about the effects of wetland conversion on soil C stocks and the quality of soil organic carbon (SOC) (defined by the proportion of labile versus more resistant organic carbon compounds). SOC, microbial biomass carbon, light fraction organic carbon (LFOC), dissolved organic carbon, and the chemical composition of SOC in the soil surface layer (0–10 cm), were investigated along a wetland degradation gradient (marsh, wet meadow, and meadow). Wetland degradation caused a 16 % reduction in the carbon stocks from marsh (178.7 ± 15.2 kg C m^?2) to wet meadow (150.6 ± 21.5 kg C m^?2), and a 32 % reduction in C stocks of the 0–10 cm soil layer from marsh to meadow (122.2 ± 2.6 kg C m^?2). Wetland degradation also led to a significant reduction in SOC quality, represented by the lability of the carbon pool as determined by a density fractionation method (L _LFOC), and a significant increase in the stability of the carbon pool as reflected by the alkyl-C:O-alkyl-C ratio. ¹³C NMR spectroscopy showed that the labile form of C (O-alkyl-C) declined significantly after wetland degradation. These results assist in explaining the transformation of organic C in these plateau wetland soils and suggest that wetland degradation not only caused SOC loss, but also decreased the quality of the SOC of the surface soil.     

三江自然保护区自然和干扰湿地节肢动物群落组成和生态指示

节肢动物是湿地生物多样性的重要组分，在维持湿地生态功能，指示湿地环境变化中发挥重要作用。在2020年7月对黑龙江三江国家级自然保护区沼泽湿地的23个采样点进行节肢动物样品采集，运用统计方法分析人类活动干扰对湿地节肢动物数量、群落组成、多样性的影响以及节肢动物对人类活动干扰的指示作用。共采集到节肢动物10目47科1825只，主要以双翅目和半翅目昆虫为主。自然湿地节肢动物的多度是干扰湿地的4.27倍；生物多样性指数在不同湿地类型之间存在一定差异，节肢动物的物种丰富度在自然湿地显著高于干扰湿地(P<0.05),而Pielou均匀度指数在干扰湿地显著高于自然湿地(P<0.05)。人类活动干扰对湿地节肢动物群落组成影响显著，聚类和非度量多纬尺度排序(NMDS)显示，两种湿地类型节肢动物群落结构相似性较低。指示值法分析显示，自然湿地的指示类群为叶甲科、蚁形甲科、叶蝉科、蚜科、盲蝽科、摇蚊科以及姬蜂总科，干扰湿地未发现指示类群。综上所述，湿地节肢动物对人类活动干扰响应十分敏感，可以作为指示湿地健康状况的关键生物类群。     

三江平原不同湿地类型土壤活性有机碳组分及含量差异

土壤活性有机碳对土壤干扰的反应较快,是土壤有机碳早期变化的敏感性指标。近50年来,三江平原湿地土壤有机碳库受农事活动影响较大。为了探讨不同湿地类型土壤活性有机碳主要组分土壤可溶性有机碳(Dissolved organic carbon,DOC)、微生物量碳(Microbial biomass carbon,MBC)和易氧化有机碳(Easily oxidized organic carbon,EOC)的分布差异及主要影响因子,选择了三江平原洪河自然保护区4种典型的湿地类型(小叶章+沼柳湿地、小叶章湿地、毛苔草湿地和芦苇湿地)为研究对象。分析了不同湿地类型土壤可溶性有机碳,微生物量碳和易氧化有机碳在0—30 cm土层内的分布特征和分配比例及其与有机碳、土壤养分和酶活性指标(蔗糖酶、纤维素酶和过氧化氢酶)之间的相关关系。结果表明:(1)4种湿地类型土壤DOC、MBC和EOC含量均随土层深度的增加而减少。不同湿地类型之间土壤活性有机碳含量在0—30 cm土层内存在显著性差异(P0.05),相对于长期淹水的毛苔草湿地和芦苇湿地而言,未淹水的小叶章+沼柳湿地和小叶章湿地具有较高的DOC,MBC和EOC含量。(2)土壤DOC、MBC和EOC占有机碳比例分别为0.27%—0.63%,1.27%—5.94%和19.63%—41.25%。土壤DOC所占比例呈先增后减的变化趋势,最大的比例均出现在10—20 cm。MBC所占比例在土壤剖面上则未表现出一致的变化规律,而EOC所占比例则随土层深度的增加而逐渐减少。(3)土壤DOC占SOC比例以小叶章湿地最高,MBC和EOC占SOC的比例则以小叶章+沼柳湿地最高。而长期淹水的毛苔草湿地和芦苇湿地则具有更低的DOC,MBC和EOC比例。(4)综合分析表明,4种湿地类型土壤DOC,MBC和EOC两两之间存在极显著相关性关系,它们除了与碳氮比相关性不显著外,与土壤有机碳,全氮,全磷养分和酶活性指标间相关性均达到极显著水平,尤其是与有机碳和全氮的相关性系数更高,此外DOC与纤维素酶,MBC与过氧化氢酶相关性更大。由此可见,土壤碳氮磷养分和酶活性是影响土壤活性有机碳组分分布的重要因素。     

Dominance of Candidatus Scalindua species in anammox community revealed in soils with different duration of rice paddy cultivation in Northeast China

The anaerobic ammonium-oxidizing (anammox) bacteria play an important role in the oxygen-limited zone for nitrogen cycling, but their roles in agricultural ecosystems are still poorly understood. In this study, soil samples were taken from the rhizosphere and non-rhizosphere and from surface (0–5 cm) and subsurface (20–25 cm) layers with 1, 4, and 9 years of rice cultivation history on the typical albic soil of Northeast China to examine the diversity and distribution of anammox bacteria based on 16S rRNA gene and hydrazine oxidoreductase encoding gene (hzo). By comparing these soil samples, no obvious difference was observed in community composition between the rhizosphere and non-rhizosphere or the surface and subsurface layers. Surprisingly, anammox bacterial communities of these rice paddy soils were consisted of mainly Candidatus Scalindua species, which are best known to be dominant in marine and pristine environments. The highest diversity was revealed in the 4-year paddy soil based on clone library analysis. Phylogenetic analysis of 16S rRNA gene and deduced HZO from the corresponding encoding gene showed that most of the obtained clones are grouped together with Candidatus Scalindua sorokinii, Candidatus Scalindua brodae, and Candidatus Scalindua spp. of seawater. The obtained clone sequences from all samples are distributed in two subclusters that contain sequences from environmental samples only. Tentative new species were also discovered in this paddy soil. This study provides the first evidence on the existence of anammox bacteria with limited diversity in agricultural ecosystems in Northern China.