Effects of simulated warming on soil ammonia-oxidizing bacteria and archaea communities in an alpine forest of western Sichuan,China

Ongoing climate change, characterized by winter warming, snow cover decline and extreme weather events, is changing terrestrial ecosystem processes in high altitude and latitude regions. Winter soil processes could be particularly sensitive to climate change. In fact, winter warming and snow cover decline are interdependent in cold biomes, and have a synergistic effect on soil processes. Soil microorganisms not only play crucial roles in material cycling and energy flow, but also act as sensitive bio-indicators of climate change. However, little information is available on the effect of winter warming on forest soil ammonia-oxidizing bacteria (AOB) and archaea (AOA). The alpine and subalpine forest ecosystems on the eastern Tibet Plateau have important roles in conserving soil, holding water, and maintaining biodiversity. To understand the changes in AOB and AOA communities under climate change scenarios, an altitudinal gradient experiment in combination with soil column transplanting was conducted at the Long-term Research Station of Alpine Forest Ecosystems, which is situated in the Bipeng Valley of Lixian County, Sichuan, China. Thirty intact soil columns under an alpine forest at an altitude of 3582 m were transplanted and incubated at 3298 m and 3023 m forest sites, respectively. Compared with the 3582 m, we expected air temperature increases of 2 °C and 4 °C at the 3298 m and 3023 m, respectively. However, the temperatures in the soil organic layer (OL) and mineral soil layer (ML) increased by 0.27 °C and 0.13 °C, respectively, at 3023 m and ? 0.36 °C and ? 0.35 °C at 3298 m. Based on a previous study and with simultaneous monitoring of soil temperature, the abundances of AOB and AOA communities in both the OL and ML were measured by qPCR in December 2010 (i.e., the onset of the frozen soil period) and March 2011 (i.e., the late frozen soil period). The soil columns incubated at 3023 m had relatively higher AOB abundances and lower AOA/AOB ratios than those at 3298 m, while higher AOA abundances and AOA/AOB ratios were observed at 3298 m. The abundance of the microbial community at the late frozen period was higher than that at the onset of frozen soil, and the changes in microbial community abundance at the late frozen period were more substantial. Furthermore, the nitrate nitrogen (N) concentrations in both the OL and ML were significantly higher than ammonia N concentrations, implying that soil nitrate N is the primary component of the inorganic N pool in the alpine forest ecosystem. Additionally, the responses of AOA and AOB in the soil OL to soil column transplanting were more sensitive than the responses of those in ML. In conclusion, climate warming alters the abundance of the ammonia-oxidizing microbial community in the alpine forest ecosystem, which, in turn, might affect N cycling.     

Abundance and composition of ammonia-oxidizing bacteria and ammonia-oxidizing archaea communities of an alkaline sandy loam

The abundance and composition of soil ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) communities under different long-term (17 years) fertilization practices were investigated using real-time polymerase chain reaction and denaturing gradient gel electrophoresis (DGGE). A sandy loam with pH (H(2)O) ranging from 8.3 to 8.7 was sampled in years 2006 and 2007, including seven fertilization treatments of control without fertilizers (CK), those with combinations of fertilizer nitrogen (N), phosphorus (P) and potassium (K): NP, NK, PK and NPK, half chemical fertilizers NPK plus half organic manure (1/2OMN) and organic manure (OM). The highest bacterial amoA gene copy numbers were found in those treatments receiving N fertilizer. The archaeal amoA gene copy numbers ranging from 1.54 x 10(7) to 4.25 x 10(7) per gram of dry soil were significantly higher than those of bacterial amoA genes, ranging from 1.24 x 10(5) to 2.79 x 10(6) per gram of dry soil, which indicated a potential role of AOA in nitrification. Ammonia-oxidizing bacteria abundance had significant correlations with soil pH and potential nitrification rates. Denaturing gradient gel electrophoresis patterns revealed that the fertilization resulted in an obvious change of the AOB community, while no significant change of the AOA community was observed among different treatments. Phylogenetic analysis showed a dominance of Nitrosospira-like sequences, while three bands were affiliated with the Nitrosomonas genus. All AOA sequences fell within cluster S (soil origin) and cluster M (marine and sediment origin). These results suggest that long-term fertilization had a significant impact on AOB abundance and composition, while minimal on AOA in the alkaline soil.     

亚高山/高山森林土壤有机层氨氧化细菌和氨氧化古菌丰度特征

为了解季节性冻融作用对川西亚高山/高山地区土壤氨氧化微生物群落的影响,采用qPCR技术,以氨单加氧酶基因的α亚基(amoA)为标记,在生长阶段、冻结阶段、融化阶段中的9个关键时期调查了该地区不同森林群落：岷江冷杉(Abies faxoniana)原始林(PF)、岷江冷杉(A. faxoniana)和红桦(Betula albosinensis)混交林(MF)、岷江冷杉次生林(SF)土壤有机层的氨氧化细菌(ammonia-oxidizing bacteria, AOB)和氨氧化古菌(ammonia-oxidizing archaea, AOA)丰度的特征。结果表明,三个森林群落土壤有机层中都具有相当数量的氨氧化细菌和古菌,均表现出从生长阶段至冻结阶段显著降低,在冻结阶段最低,但冻结阶段后显著增加,在融化阶段为全年最高的趋势。土壤氨氧化微生物类群结构(AOA/AOB)受负积温影响明显。冻结后期三个森林群落土壤负积温最大时,AOA数量明显高于AOB,但其他关键时期土壤氨氧化微生物类群结构与群落类型密切相关。高海拔的PF群落土壤有机层表现为AOA>AOB(冻结初期除外),低海拔的SF群落中表现为AOB>AOA(冻结后期除外),而MF群落则仅在融冻期和生长季节末期表现为AOB>AOA。这些结果为认识亚高山/高山森林及其相似区域的生态过程提供了一定的科学依据。     

Seasonal variations in plant nitrogen acquisition in an ectomycorrhizal alpine forest on the eastern Tibetan Plateau,China

Plant and Soil - Plant nitrogen (N) acquisition plays an important role in regulating plant growth and ecosystem functions. However, the seasonal variations in the relative contributions of...     

Elevational diversity and distribution of ammonia-oxidizing archaea community in meadow soils on the Tibetan Plateau

Unraveling elevational diversity patterns of plants and animals has long been attracting scientific interests. However, whether soil microorganisms exhibit similar elevational patterns remains largely less explored, especially for functional microbial communities, such as ammonia oxidizers. Here, we investigated the diversity and distribution pattern of ammonia-oxidizing archaea (AOA) in meadow soils along an elevation gradient from 4400 m to the grassline at 5100 m on the Tibetan Plateau using terminal restriction fragment length polymorphism (T-RFLP) and sequencing methods by targeting amoA gene. Increasing elevations led to lower soil temperature and pH, but higher nutrients and water content. The results showed that AOA diversity and evenness monotonically increased with elevation, while richness was relatively stable. The increase of diversity and evenness was attributed to the growth inhibition of warm-adapted AOA phylotypes by lower temperature and the growth facilitation of cold-adapted AOA phylotypes by richer nutrients at higher elevations. Low temperature thus played an important role in the AOA growth and niche separation. The AOA community variation was explained by the combined effect of all soil properties (32.6%), and 8.1% of the total variation was individually explained by soil pH. The total AOA abundance decreased, whereas soil potential nitrification rate (PNR) increased with increasing elevations. Soil PNR positively correlated with the abundance of cold-adapted AOA phylotypes. Our findings suggest that low temperature plays an important role in AOA elevational diversity pattern and niche separation, rising the negative effects of warming on AOA diversity and soil nitrification process in the Tibetan region.     

Abundance and community composition of ammonia-oxidizing archaea and bacteria in two different zones of Lake Taihu

The abundance and community composition of ammonia-oxidizing archaea and ammonia-oxidizing bacteria in the surface sediments of 2 different zones (Meiliang Bay and Eastern Lake Taihu) of Lake Taihu were investigated using real-time quantitative polymerase chain reaction and clone libraries. The amoA gene copy numbers in the surface sediment of Meiliang Bay ranged from 4.91?× 10(5) to 8.65?× 10(6) copies/g dry sediment for the archaeal amoA gene and from 3.74?× 10(4) to 3.86?× 10(5) copies/g dry sediment for the bacterial amoA gene, which were significantly higher than those of Eastern Lake Taihu (P?< 0.05). Concentrations of ammonia (NH(4)(+)), total nitrogen, organic matter, and pH of the sediments exhibited significantly negative correlations with the abundance of ammonia-oxidizing archaea or ammonia-oxidizing bacteria (P?< 0.05 or P?< 0.01, respectively). The potential nitrification rates show remarkable correlations with the copy numbers of the archaeal amoA gene. Diversity of the archaeal amoA gene in Eastern Lake Taihu was significantly higher than that of Meiliang Bay, whereas the bacterial amoA gene diversity was comparable for the 2 lake zones. The data obtained in this study would be useful to elucidate the role of ammonia-oxidizing archaea and ammonia-oxidizing bacteria in the nitrogen cycle of freshwater ecosystems.     

青藏高原东缘封育和退化高寒草甸种子库差异

采用幼苗萌发法研究了青藏高原东部高寒草甸封育和退化地区土壤种子库的差异.结果表明:(1)两个样地总共有10161株幼苗萌发,分属55个物种,23个科.封育样地多年生植物比例高于退化样地,禾草和单子叶植物比例在两个样地间差异不大.(2)退化样地土壤种子库种子密度((6105±1530) m-2)显著高于封育样地((3883±798) m-2),而物种丰富度差异不显著.所研究区域拥有较为丰富的种子库资源,退化地区资源更丰富,说明恢复不存在种子限制问题,土壤种子库可以成为植被恢复的潜在资源.(3)种子密度和物种丰富度在垂直分层上差异显著,且随着深度的增加而显著减小.(4)用Srensen coefficient指数计算出土壤种子库和地上植被之间的相似性在整体上较低,封育样地(45.3%)略高于退化样地(40.4%),两个样地地上植被之间的相似性为50%,而种子库之间相似性高达84.6%,说明种子库起到一个"缓冲器"的作用.(5)Shannon-Wiener多样性指数分析显示,无论在地上植被或种子库中,物种多样性都是封育样地显著高于退化样地.过度放牧不仅导致地上植被的生物多样性丧失,而且使种子库中的物种多样性降低,而封育管理可以维持地上植被和种子库中的物种多样性.     

若尔盖高原湿地土壤氨氧化古菌的多样性

【目的】研究自然界中氨氧化古菌(ammonia-oxidizing archaea,AOA)对于理解全球氮循环起着至关重要的作用,但人们对高原湿地AOA种群生态还知之甚少。本研究旨在了解若尔盖高原湿地土壤AOA群落组成及多样性。【方法】从若尔盖高原阿西(A'xi)、麦西(Maixi)和分区(Fenqu)3个典型牧区采集土壤样品,提取土壤总DNA,利用AOA氨单加氧酶(ammonia monooxygenase,amoA)基因通用引物扩增amoA基因,构建amoA基因克隆文库。从每个克隆文库中随机挑选80个阳性克隆子用于后续限制性酶切片段长度多态性(restriction fragment length polymorphism,RFLP)分析,挑选不同酶切类型的克隆子进行测序、比对,利用MEGA 5.0软件构建amoA基因系统发育树。【结果】从3个克隆文库共240个AOA amoA基因阳性克隆中得到15条代表序列,通过Mothur软件进行OTUs(operational taxonomic units)分类得到7个不同的分类单元。其中OTU 6为优势类群,在3个克隆文库均有发现,约占所有特异性克隆子的27%。15条amoA基因序列分属于Zoige Wetland Clade 1(4 OTUs)、Zoige Wetland Clade 2(2 OTUs)和Zoige Wetland Clade 3(1OTU)3个系统发育分支。BLAST分析显示所有OTUs均归于泉古菌门(Crenarchaeota)。相关性分析表明,若尔盖高原湿地AOA多样性指数与土壤铵态氮和硝态氮含量存在显著的相关性(P0.05)。【结论】若尔盖高原湿地中AOA多样性较低,均属于泉古菌,且与土壤中氨态氮和硝态氮密切相关。     

青藏高原东缘高寒森林小型兽类地表洞穴选择与生境特征

高寒森林地表的小型兽类洞穴是生态系统重要的景观特征,对于认识小型兽类的分布格局及其生态功能具有重要意义.为此,以青藏高原东缘典型高寒森林生态系统小型兽类洞穴为对象,于2015年夏季(7—9月)研究了其地表分布与生境特征.结果表明: 小型兽类洞穴平均洞口密度为182.8个·hm^-2,不同森林植被类型显著影响洞穴密度,表现为针叶林(328.6个·hm^-2)>针阔混交林(160.0个·hm^-2)>灌木林(125.0个·hm^-2)>阔叶林(81.5个·hm^-2)>竹林(66.7个·hm^-2). Mann-Whitney U Test和主成分分析表明,小型兽类栖息样地的乔木郁闭度、乔木均高、乔木胸径、乔木密度、地表植被盖度、倒木密度、倒木覆盖度、灌木均高都显著大于非栖息样地;乔木因子是决定小型兽类生境选择的首要因子,贡献率最大(44.8%),其次是倒木因子(23.2%)和灌草丛因子(13.9%).说明高寒森林地表有明显的小型兽类洞穴分布,其分布格局主要受植被和倒木的影响.     

Effects of disturbance intensity on seasonal dynamics of alpine meadow soil seed banks on the Tibetan Plateau

Background and Aims

Information on soil seed bank processes is crucial for understanding vegetation dynamics. Despite the documented importance of soil seed banks in many ecosystems, their role is not fully understood in some sensitive habitats, such as the alpine meadows of the Tibetan Plateau.

Methods

We studied the seasonal dynamics of the germinable soil seed bank under four disturbance intensities in an alpine meadow on the Tibetan Plateau as well as seed size distribution relative to disturbance intensity. Composition of the seed bank was compared with that of the standing vegetation.

Results

Density of buried seeds increased with disturbance intensity, but species richness and species diversity decreased. Seed density and species richness of the seed bank varied seasonally in all layers (0–2, 2–7, 7–12 cm) and the whole (0–12 cm). The species composition of seed bank was not significantly influenced by season. There was no trend in seed size distribution as disturbance increased. Seasonal seed bank turnover rates increased with increase in disturbance. The result of the NMDS showed that species composition of seed bank and vegetation exhibited a fairly uniform pattern in each season.

Conclusions

Although as a whole the species composition of the vegetation and seed bank showed a relatively low degree of similarity in each season, similarity was highest in the most disturbed habitat. There was no alteration in species composition of seed bank regardless of disturbance intensity, but seed density decreased as disturbance increased. Disturbances in alpine plant communities might increase persistence of regeneration niches. Regeneration from the seed bank together with vegetative reproduction contributed to aboveground vegetation in highly disturbed habitats. Clonal species played an important role in regeneration of vegetation in slightly disturbed areas, where there was little contribution of ruderals from soil seed banks.     

Distribution patterns of ammonia-oxidizing archaea and bacteria in sediments of the eastern China marginal seas

Ammonia-oxidizing archaea (AOA) and bacteria (AOB) vary in their contribution to nitrification in different environments. The eastern China marginal seas (ECMS) are featured by complex river runoffs and ocean currents, forming different sediment patches. Here, via quantitative PCR and clone library analysis of the amoA genes, we showed that AOB were more abundant than AOA in ECMS sediments. The abundance, diversity and richness of AOA, but not AOB, were higher in the East China Sea (ECS) than in the Yellow Sea (YS) and Bohai Sea (BS). Nitrosopumilus (AOA) and Nitrosospira (AOB) were predominant lineages, but their abundances varied significantly between ECS, and BS and YS. This was mainly attributed to salinity and dissolved oxygen of the bottom water. The discovery of a high abundance of Nitrosophaera at estuarine sites suggested strong terrigenous influence exerted on the AOA community. In contrast, variations in ocean conditions played more important roles in structuring the AOB community, which was separated by bottom water dissolved oxygen into two groups: the south YS, and the north YS and BS. This study provides a comprehensive insight into the spatial distribution pattern of ammonia-oxidizing prokaryotes in ECMS sediments, laying a foundation for understanding their relative roles in nitrification.     

Soil seed bank dynamics in alpine wetland succession on the Tibetan Plateau

The primary goal was to address several questions with regard to how soil seed banks change in a successional series. How does the composition of the viable seed bank change, and how does the relationship of the soil seed bank and vegetation change with succession? Can the seed bank be regarded as a potential as a source of seeds for wetland restoration? We collected soil seed bank samples and sampled the vegetation in four different successional stages and used the NMDS (nonmetric multidimensional scaling) to evaluate the relationship of species composition between the seed banks and vegetation. The difference of seed density and species richness in different habitats and soil depths also was compared. Viable seeds of half (37) the species in the early-successional stage were found in all the successional stages. Similarity between seed bank and vegetation increased with succession. Both seed density and species richness in the seed bank increased with successional age and decreased with soil depth. The majority of species from the early-successional stage produced long-lived seeds. Seed density and species richness increased with succession, mainly as a result of increasing seed production, and hypotheses predicting decreasing density of buried seeds and species richness were not confirmed. Seed banks play a minor role in contributing to the regeneration of vegetation, and managers cannot rely on soil-stored seed banks for restoration of wetlands.     

Plant and soil responses of an alpine steppe on the Tibetan Plateau to multi-level nitrogen addition

Background

Although plant growth in alpine steppes on the Tibetan Plateau has been suggested to be sensitive to nitrogen (N) addition, the N limitation conditions of alpine steppes remain uncertain.

Methods

After 2 years of fertilization with NH₄NO₃ at six rates (0, 10, 20, 40, 80 and 160 kg N ha^?1 yr^?1), the responses of plant and soil parameters as well as N₂O fluxes were measured.

Results

At the vegetation level, N addition resulted in an increase in the aboveground N pool from 0.5?±?0.1 g m^?2 in the control plots to 1.9?±?0.2 g m^?2 in the plots at the highest N input rate. The aboveground C pool, biomass N concentration, foliar δ¹⁵N, soil NO₃ ^?-N and N₂O flux were also increased by N addition. However, as the N fertilization rate increased from 10 kg N ha^?1 yr^?1 to 160 kg N ha^?1 yr^?1, the N-use efficiency decreased from 12.3?±?4.6 kg C kg N^?1 to 1.6?±?0.2 kg C kg N^?1, and the N-uptake efficiency decreased from 43.2?±?9.7 % to 9.1?±?1.1 %. Biomass N:P ratios increased from 14.4?±?2.6 in the control plots to 20.5?±?0.8 in the plots with the highest N input rate. Biomass N:P ratios, N-uptake efficiency and N-use efficiency flattened out at 40 kg N ha^?1 yr^?1. Above this level, soil NO₃ ^?-N began to accumulate. The seasonal average N₂O flux of growing season nonlinearly increased with increased N fertilization rate and linearly increased with the weighted average foliar δ¹⁵N. At the species level, N uptake responses to relative N availability were species-specific. Biomass N concentration of seven out of the eight non-legume species increased significantly with N fertilization rates, while Kobresia macrantha and the one legume species (Oxytropics glacialis) remained stable. Both the non-legume and the legume species showed significant ¹⁵N enrichment with increasing N fertilization rate. All non-legume species showed significant increased N:P ratios with increased N fertilization rate, but not the legume species.

Conclusions

Our findings suggest that the Tibetan alpine steppes might be N-saturated above a critical N load of 40 kg N ha^?1 yr^?1. For the entire Tibetan Plateau (ca. 2.57 million km²), a low N deposition rate (10 kg N ha^?1 yr^?1) could enhance plant growth, and stimulate aboveground N and C storage by at least 1.1?±?0.3 Tg N yr^?1 and 31.5?±?11.8 Tg C yr^?1, respectively. The non-legume species was N-limited, but the legume species was not limited by N.     

Community composition of ammonia-oxidizing bacteria and archaea in soils under stands of red alder and Douglas fir in Oregon

This study determined nitrification activity and nitrifier community composition in soils under stands of red alder (Alnus rubra) and Douglas fir (Pseudotsuga menziesii) at two sites in Oregon. The H.J. Andrews Experimental Forest, located in the Cascade Mountains of Oregon, has low net N mineralization and gross nitrification rates. Cascade Head Experimental Forest, in the Coast Range, has higher net N mineralization and nitrification rates and soil pH is lower. Communities of putative bacterial [ammonia-oxidizing bacteria (AOB)] and archaeal [ammonia-oxidizing archaea (AOA)] ammonia oxidizers were examined by targeting the gene amoA, which codes for subunit A of ammonia monooxygenase. Nitrification potential was significantly higher in red alder compared with Douglas-fir soil and greater at Cascade Head than H.J. Andrews. Ammonia-oxidizing bacteria amoA genes were amplified from all soils, but AOA amoA genes could only be amplified at Cascade Head. Gene copy numbers of AOB and AOA amoA were similar at Cascade Head regardless of tree type (2.3-6.0 x 10(6)amoA gene copies g(-1) of soil). DNA sequences of amoA revealed that AOB were members of Nitrosospira clusters 1, 2 and 4. Ammonia-oxidizing bacteria community composition, determined by terminal restriction fragment length polymorphism (T-RFLP) profiles, varied among sites and between tree types. Many of the AOA amoA sequences clustered with environmental clones previously obtained from soil; however, several sequences were more similar to clones previously recovered from marine and estuarine sediments. As with AOB, the AOA community composition differed between red alder and Douglas-fir soils.     

Abundance and diversity of ammonia-oxidizing archaea in a biological aerated filter process

Ammonia-oxidizing archaea (AOA) represent an important group of ammonia-oxidizing microorganisms that are able to convert ammonia to nitrite, a function which is crucial for the removal of nitrogen from wastewater. In this study, we investigated the abundance and diversity of AOA in a full-scale wastewater treatment plant (WWTP) which used a biological aerated filter (BAF) as the main processing mode. According to the quantitative PCR results, AOA clearly outnumbered ammonia-oxidizing bacteria (AOB) during the whole process. The abundance of AOA amoA genes in the filter layer of BAF was highest with the value varied from 6.32 × 10³ to 3.8 × 10⁴ copies/ng DNA. The highest abundance of AOB amoA genes was 1.32 × 10² copies/ng DNA, recorded in the effluent of the ACTIFLO® settling tank. The ratios of AOA/AOB in the WWTP were maintained at two or three orders of magnitude. Most AOA obtained from the WWTP fell within the Nitrosopumilus cluster. The abundance of AOA and AOB was significantly correlated with ammonium nitrogen concentrations and pH value. The community structure of AOA was significantly influenced by dissolved oxygen concentrations, pH value and chemical oxygen demand.     

模拟增温对西藏高原高寒草甸土壤供氮潜力的影响

过去几十年青藏高原呈现显著的增温趋势,冬季增温幅度显著高于生长季的季节非对称特征。气候变暖会对生态系统氮素循环产生重要影响,但关于全年增温与冬季增温对高寒生态系统氮循环的不同影响仍缺乏研究。在青藏高原高寒草甸区开展模拟增温试验,研究季节非对称增温对高寒草甸生态系统氮循环的影响。该试验布设于2010年7月,设置3种处理(不增温、冬季增温与全年增温)。研究结果发现,开顶箱增温装置造成了小环境的暖干化:显著提高了地表空气温度和表层土壤温度,降低了表层土壤含水量。冬季增温会加剧土壤中氮素的流失,所以在经历了冬季增温后土壤氮含量显著降低;在生长季节,土壤氮素周转速率受土壤水分的调控,在降雨较少的季节,增温引起的土壤含水量降低会抑制土壤氮周转速率。对于土壤微生物量而言,高寒草甸土壤微生物量碳表现出明显的季节动态,在生长季旺盛期较低,在生长季末期和初冬季节反而较高,这说明为了降低对土壤养分的竞争,高寒草甸植物氮吸收与土壤微生物氮固持在时间上存在分离。研究结果表明,冬季增温导致的土壤养分含量变化会影响随后生长季植物群落的生产力、结构组成与碳氮循环等过程,对生态系统过程产生深远的影响。     

青藏高原东部近林线紫果云杉原始林的群落结构与物种组成

原始云杉林是青藏高原东部林区近林线森林的重要类型之一,但关于其林分结构与多样性的科学认识到目前为止仍然是贫乏的.为了揭示云杉原始林的层次结构及其相互关系、维管植物组成特点,选择四川省壤塘县北部日柯沟近林线的紫果云杉(Picea purpurea)原始林为对象,调查了6个40 m×50 m样地的乔木层结构,并在样地内采用机械布点的方法设置180个小样方,调查了林下灌木层、草本层和苔藓层结构以及灌草层物种组成.结果显示:(1)云杉原始林为复层异龄林,乔木层分化明显,可划分为4个亚层;幼树密度不高但集中分布于林窗及其边缘(144±93株/ha);(2)林下灌木盖度与物种丰富度低,层片结构简单,呈明显的斑块状分布;而草本层与苔藓层发达,盖度与物种丰富度均较高;(3)6个样地共发现维管植物124种,隶属于30科68属.其中草本109种,灌木15种,以温带区系成分占优势,特有性缺乏;生活型以地面芽植物为主体(61.29%).综合分析表明,该林分为藓类云杉林,群落结构完整、稳定,自然更新能力强,与本区域内亚高山或高山林线森林具有相似的物种组成和多样性特点,但群落结构则明显不同.     

白洋淀湖滨湿地岸边带氨氧化古菌与氨氧化细菌的分布特性

摘要：本研究通过分子生物学分析方法,以amoA基因为标记,考察了氨氧化古菌（Ammonia-Oxidizing Archaea, AOA）和氨氧化细菌（Ammonia-Oxidizing Bacteria,AOB）在华北平原的白洋淀这一典型湖泊的湖滨湿地岸边带系统中的生物多样性和丰度分布。在前人的研究中,氨氧化古菌在海洋、原生态土壤和人为干扰土壤等环境中主导氨氧化过程的完成。但本研究发现,在湿地岸边带系统中氨氧化过程并不是完全由氨氧化古菌主导完成,即氨氧化古菌和氨氧化细菌在不同区域分别占据主导地位。根据主导微生物的不同,可以将湿地岸边带区域划分为陆相区、中间区和湖相区。在湿地岸边带陆相区,氨氧化古菌主导氨氧化过程,氨氧化古菌的amoA基因丰度是氨氧化细菌的526倍（AOA：1.23?108每克干土;AOB：2.34?105每克干土）;在岸边带湖相区,氨氧化细菌主导氨氧化过程,氨氧化古菌的amoA基因丰度只有氨氧化细菌的1/50倍（AOA：3.17?106每克干土;AOB：1.39?108每克干土）;在岸边带中间区,两种微生物对氨氧化过程的贡献相当,二者的amoA基因丰度也相当 (AOA：9.83?106, AOB：4.08?106)。研究还发现,湿地中间区的微生物生物多样性高于陆相区和湖相区。在湿地中间区,氨氧化古菌和氨氧化细菌的生物多样性都最高,分别有5和7个操作分类单元（OTUs）;相比之下,岸边带陆相区和湖相区的多样性依次降低,陆相区的氨氧化古菌和氨氧化细菌分别有3和6个操作分类单元,湖相区的氨氧化古菌和氨氧化细菌分别有2和6个分类单元。本研究的两个结论进一步反映了湿地岸边带极强的空间异质性。