The aim of this study is to investigate the abundance, diversity, and distribution of archaea and bacteria as affected by environment parameters in paddy soils, with focus on putative functional microbial groups related to redox processes. Because there is generally a high iron content in the soil, we also want to test a hypothesis that soil iron concentration significantly affects microbial diversity and distribution.
Materials and methodsQuantitative PCR and barcoded pyrosequencing of 16S ribosomal RNA genes were employed to investigate the abundance and community composition of archaeal and bacterial communities in 27 surface paddy soil samples. Pearson’s correlation, analysis of variance, partial least squares regression, principal coordinates analysis, and structural equation models were performed for the analyses of gene copy numbers, α-diversity, β-diversity, and relative abundances of archaea and bacteria and their relationships with environmental factors.
Results and discussionArchaeal abundance was correlated greatest with temperature, but bacterial abundance was affected mainly by soil organic matter and total nitrogen content. Soil pH and concentrations of different ions were associated with archaeal and bacterial β-diversity. The relative abundances of Euryarchaeota and Thaumarchaeota were 61.3 and 13.1% of archaea and correlated with soil pH, which may affect the availability of substrates to methanogens and ammonia oxidizers. Dominant bacterial phyla were Proteobacteria (32.4%), Acidobacteria (17.8%), Bacteroidetes (9.3%), and Verrucomicrobia (6.0%). The relative abundances of putative bacterial reducers of nitrate, Fe(III), sulfate, and sulfur, and oxidizers of ammonia, nitrite, reduced sulfur, and C1 compounds had positive, negative, or non-significant correlations with the concentrations of their substrates. Soil iron concentration was correlated only with the distributions of some putative iron-reducing bacteria.
ConclusionsIn paddy soils characterized by dynamic redox processes, archaea and bacteria differ in relationships of abundance, diversity, and distribution with environmental factors. Especially, the concentrations of electron donors or acceptors can explain the distributions of some but not all the putative functional microbial groups related to redox processes. Depending on pH range, soil pH has a strong impact on microbial ecology in paddy soils.
相似文献A field experiment was conducted to assess the role of nitrogen (N) and water addition in shaping soil fungal communities and co-occurrence networks in temperate grassland, northern China.
Materials and methodsWe measured soil fungal and plant community compositions, and also soil properties including available N, phosphorus, potassium concentrations, soil pH, and soil moisture. Soil fungal co-occurrence networks were constructed using a random matrix theory–based network inference approach.
Results and discussionPlant species richness was decreased by N addition but increased by water addition, whereas fungal richness was decreased by N addition. The fungal community composition was significantly changed by both N addition and water addition. Soil fungal α diversity and β diversity were explained by a combination of variations in plant species richness and plant functional composition, and also by changes in soil pH via the soil acidification pathway induced by N and water addition. The fungal co-occurrence networks were more complex and clustered under water addition than that in ambient precipitation.
ConclusionsOur results suggested that plant functional composition, plant species richness, and soil acidification should be incorporated into ecosystem models for predicting soil fungal communities under future climate changes in terrestrial ecosystems.
相似文献Submerged plants make an important contribution to nitrogen cycling in lakes including in the rhizosphere microenvironment through microbial activities. The main objective of this study was to investigate the abundance of functional genes for nitrogen cycling and the ecological relationship between these genes in the rhizosphere sediment of a freshwater lake in summer.
Materials and methodsSediment from the rhizosphere of four submerged macrophytes (Ceratophyllum demersum, Hydrilla verticillata, Potamogeton maackianus, and Vallisneria spiralis) was sampled in Lake Liangzi, China, in summer. The anammox bacteria community structure and abundance of five functional genes for nitrogen cycling, ammonia monooxygenase (amoA) of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA), anammox 16S rRNA, and nitrite reductase genes (nirK and nirS) in the sampled sediment, were determined.
Results and discussionA total of 100 anammox gene sequences were grouped into eight operational taxonomic units (OTUs) and genus Ca. Kuenenia was the dominant species in Lake Liangzi in summer. Quantitative polymerase chain reaction (qPCR) revealed that gene copies of AOA amoA (2.42?×?106 copies g?1) were more than one order of magnitude higher than those of AOB amoA (1.98?×?105 copies g?1). The nirS gene (4.13?×?108 copies g?1) was more abundant than the nirK gene (7.28?×?107 copies g?1). There was no significant difference in the abundance of the AOB amoA gene among the rhizosphere of the four macrophytes. Redundancy analysis (RDA) showed a positive correlation between the abundance of the anammox 16S rRNA gene, AOA amoA and AOB amoA, which suggested two of these microbes may have provided a substrate for anammox bacteria in summer.
ConclusionsThe diversity of anammox in the rhizosphere of submerged macrophytes of the freshwater lake in summer was very low, but the plant species could affect the abundance of most nitrogen circulating bacteria, especially for anammox bacteria. Anammox 16S rRNA gene was positively correlated with four other functional genes, indicating that all four genes had significant effects on anammox bacteria.
相似文献Phosphorus (P) and potassium (K) are two important essential nutrient elements for plant growth and development but their availability is often limited in calcareous soils. The objective of this study was to determine the effects of applying microbial inoculants (MI, containing effective strains of Bacillus megaterium and Bacillus mucilaginous) on the availability of P and K, plant growth, and the bacterial community in calcareous soil.
Materials and methodsA greenhouse experiment was conducted to explore the effects of the addition of MI (control: without MI addition; treatment: with MI addition at the rate of 60 L ha?1) on the concentrations of P and K in soil and plant, soil bacterial community diversity and composition, and chili pepper (Capsicum annuum L.) growth.
Results and discussionThe results showed that MI inoculation significantly increased the fruit yields by 28.5% (p?<?0.01), available P and K in the rhizosphere soil by 32.1% and 28.1% (p?<?0.05), and P and K accumulation in the whole plants by 40.9% and 40.2%, respectively (p?<?0.05). Moreover, high-throughput sequencing revealed that Proteobacteria, Acidobacteria, Bacteroidetes, Chloroflexi, and Gemmatimonadetes were the dominant phyla of soil bacteria. MI application did not significantly impact the diversity and composition of soil bacterial communities, but increased relative abundances of bacterial genera Flavobacterium responsible for promoting root development across growing stages (p?<?0.05), and changed the soil bacterial community structure associated closely with soil properties of available P, K, and pH in soil.
ConclusionsThe application of MI improved the bioavailability of P and K and plant growth due to its impact on the soil bacterial community structure.
相似文献Hulunbuir steppe has flat terrain and wide riparian zone of rivers and lakes on it. Owing to climate change, these riparian zones are often submerged or dried. This not only results in the instability of biodiversity in these regions but also affects the soil biogeochemical cycles. Soil C:N:P ecological stoichiometry plays a vital role in predicting and understanding the balance of multiple chemicals in ecological interactions. However, few studies have examined the soil C:N:P ecological stoichiometry in riparian zones of Hulunbuir steppe under different submergence states. Our objectives were to explore whether submergence frequencies impact soil C:N:P stoichiometry and identify the key factors.
Materials and methodsFour study sites were selected along the Hui river in Hulunbuir steppe, and three plots of different submergence frequencies, high (HF-sub, 5 to 7 times per year), moderate (MF-sub, 2 to 3 times per year), and low (LF-sub, unflooded or flooded once per year), were selected for each study site. Soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), their ecological stoichiometric ratios (soil C:N, N:P, and C:P), soil ammonia nitrogen (NH4+-N), nitrate nitrogen (NO3?-N), available phosphorus (AP), soil pH, electrical conductivity (EC), soil moisture content (SMC), soil bulk density (SBD), porosity, and hardness were measured and analyzed.
Results and discussionThe results indicated that soil C:N:P ecological stoichiometry was notably affected by submergence frequency across the four study sites (P?<?0.05). SOC, TN, TP, and their stoichiometric ratios changed regularly with the submergence frequency change, whereas their trends were inconsistent at different drainage basins. Soil C:N decreased with the decrease in submergence frequency but kept in a narrow scope, whereas the N:P and C:P were changed greatly under different submergence frequencies. Further analysis found that these significant variations in N:P and C:P were mainly due to the changes in soil TP which suggested there might be a P limitation in the riparian zones. The results of redundancy analysis (RDA) and path analysis indicated that soil AP and NO3?-N were the key indirect factors affecting soil C:N:P ecological stoichiometry under different submergence frequencies, and SMC was an indirect factor.
ConclusionsWe demonstrated that the soil C:N:P ecological stoichiometry was significantly affected by the submergence frequency in the riparian zones of Hulunbuir steppe. Soil N:P and C:P were more susceptible to change than C:N under different submergence frequencies. If the contents of soil AP and NO3?-N were appropriate, soil C:N:P ecological stoichiometry will be more beneficial to regulating the cycle and balance of soil nutrient elements in the riparian zones, which can promote the riparian zones to provide better ecological functions.
相似文献Yellow clay paddy soil (Oxisols) is a low-yield soil with low nitrogen use efficiency (NUE) in southern China. The nitrification inhibitor nitrapyrin (2-chloro-6- (tricholoromethyl)-pyridine, CP) has been applied to improve NUE and reduce environmental pollution in paddy soil. However, the effects of nitrapyrin combined with nitrogen fertilizers on ammonia oxidizers in yellow clay paddy soil have not been examined.
Materials and methodsA randomized complete block design was set with three treatments: (1) without nitrogen fertilizer (CK), (2) common prilled urea (PU), and (3) prilled urea with nitrapyrin (NPU). Soil samples were collected from three treatments where CK, PU, and NPU had been repeatedly applied over 5 years. Soil samples were analyzed by quantitative PCR and 454 high-throughput pyrosequencing of the amoA gene to investigate the influence of nitrapyrin combined with nitrogen on the abundance and community structure of ammonia oxidizers in yellow clay paddy soil.
Results and discussionThe potential nitrification rate (PNR) of the soil was significantly correlated with the abundances of both ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB). Application of urea significantly stimulated AOA and AOB growth, whereas nitrapyrin exhibited inhibitory effects on AOA. Phylogenetic analysis showed that the most dominant operational taxonomic units (OTUs) of AOA and AOB were affiliated with the Nitrosotalea cluster and Nitrosospira cluster 12, respectively. AOA and AOB community structures were not altered by urea and nitrapyrin application.
ConclusionsNitrogen fertilization stimulated nitrification and increased the population sizes of AOA and AOB. Nitrapyrin affected the abundance, but not community structure of ammonia oxidizers in yellow clay soil. Our results suggested that nitrapyrin improving NUE and inhibiting PNR was attributable to the inhibition of AOA growth.
相似文献The carbon (C), nitrogen (N), and phosphorus (P) concentrations of leaves can reflect soil nutrient supply conditions and changes in soil. An understanding of species adaptability and nutrient use efficiency in extreme ecosystems can help land managers choose effective methods to improve management and community structure of introduced plants which may induce biological invasion and limit the regeneration of native species.
Materials and methodsWe selected the Leucaena leucocephala forests in three ages (9, 15, and 26 years old) in the Jiangjiagou Gully to study the relationships between (i) soil factors and forest age and (ii) leaf nutrient concentrations. Soil factors and leaf nutrients were measured in nine sampling quadrats of 10?×?10 m of each plot. We used ANOVA to examine differences in leaf variables and soil factors at different ages of L. leucocephala forest. Pearson’s correlation analysis and linear regression analysis were conducted to identify the relationships between soil factors and leaf variables. Then, we used analysis of covariance to examine combined effects of forest ages and soil factors on leaf variables.
Results and discussionLeaf N was significantly correlated with available P, while leaf P was significantly correlated with both available P and available N. Leaf N and P had no significant relationship with soil total N and P. Leaf C:N:P stoichiometries had a higher significant correlation with total N, available N, and soil water content.
ConclusionsOur findings illustrate that available N and available P are the main limitations for L. leucocephala, though available P imposed a stronger limitation than available N. Moreover, soil water content played an indispensable role on nutrient accumulation and the soil ecological environment. Our results provide useful information to improve L. leucocephala community structure and reduce soil degradation in a dry-hot valley.
相似文献A large area of desert land in the desert-oasis ecotone in northwestern China is being reclaimed for continuous cotton production for several decades. However, little is known about the possible effect of reclamation and long-term monocultural cotton cultivation on soil properties and microbial communities in the desert-oasis ecotone area.
Materials and methodsSoil samples were collected from the 0–20-cm mineral soil from croplands that had been continuously planted cotton for 5, 25, and 50 years after reclamation, as well as a desert land (t?=?0, before reclamation, used as the control). Soil physical and chemical properties, enzyme activities, and bacterial and fungal community diversities were determined.
Results and discussionSoil organic carbon, total nitrogen, and enzyme activities increased up to 25 years after reclamation, and further monocultural cotton cropping was not beneficial to improve soil quality. Soil urease, alkaline phosphatase, and sucrase activities increased by 121~205%, 100~167%, and 206~719% in croplands as compared with the desert land, respectively, after reclamation with the highest value at 25 years of cotton cultivation. Bacterial richness and diversity increased from desert land to the 5-year-old cropland and then remained stable after 5 years of cotton cropping, and soil fungal richness and diversity were not affected by reclamation and cropping years.
ConclusionsCrop rotation or fallow should be considered to maintain or improve soil quality over the long-term monocultural cropping.
相似文献To control the severe soil and water losses on the Loess Plateau, China, a series of vegetation restoration projects were conducted. A better understanding of the effect of vegetation types on the soil infiltration capacity is important for the sustainable development of vegetation restoration. The aim of this study was to establish a soil infiltration capacity index (SIC) and to analyze the mechanism influencing variations in the soil infiltration capacity after vegetation restoration on the Loess Plateau.
Materials and methodsEight vegetation types (community dominated by Artemisia scoparia, Stipa bungeana, Artemisia gmelinii + S. bungeana, A. gmelinii + Stipa grandis, A. gmelinii + Artemisia giraldii, Sophora viciifolia, Caragana korshinskii, and Robinia pseudoacacia) and bare land as the control were selected for this study. The SIC was established by a steady infiltration rate (SR, 50–60 min) and stage I average infiltration rate (ARSI, 0–5 min) according to principal component analysis (PCA). Path analysis was used to investigate how the soil properties and plant fine root affected the soil infiltration capacity.
Results and discussionThe SIC values of the eight vegetation types were all higher than that of the bare land. The R. pseudoacacia community had the highest SIC value (0.43), followed by the A. scoparia community (0.30) while the bare land (??0.56) had the lowest value. Path analysis showed that the increase in the fractal dimension and non-capillary porosity of soil particles enhanced the SIC directly. Increases in the clay content increased the SIC by affecting the fractal dimension of soil particles, while increases in the fine root density reduced the SIC by affecting the non-capillary porosity. Plant functional groups (grasses and legumes) affected SIC indirectly via non-capillary porosity and plant root.
ConclusionsA comprehensive index, the SIC, was established to describe the soil infiltration capacity by the PCA method. Based on a comparison with bare land, vegetation restoration enhanced the soil infiltration capacity. The R. pseudoacacia community was the most effective at improving the soil infiltration capacity. The improvement in infiltration was closely related to direct increases in the soil non-capillary porosity and soil particle fractal dimension.
相似文献Fine sediment accumulates upstream of hydroelectric dams. To ensure that dams can operate properly, part of the sediment has to be dredged and land managed. In parallel, using topsoil from agricultural parcels for urban greening or land restoration is currently controversial because arable surface areas are decreasing. An alternative idea for protecting these natural resources consists in reusing fine dredged sediment to construct multifunctional soils. This agronomic use is only possible if sediment can provide acceptable physical and chemical properties for plant growth.
Materials and methodsFour dredged sediments with contrasted initial agronomic properties and one control soil were mixed or not with green waste compost (40% v/v) and used to construct triplicate 30-cm depth soils in lysimetric containers (1.11?×?0.71 m). The 30 constructed soils were exposed to the in situ conditions and sown with ryegrass (Lolium perenne). The evolution of soil chemical and physical properties and plant development were studied every 6 months for 18 months.
Results and discussionAbove- and below-ground biomass production of the constructed soils contrasted according to the sediment properties and to compost addition. A statistical approach identified eight soil parameters linked to biomass production. Among these parameters, soil structure, quantified from aggregate stability, played a fundamental role. A focus on physical properties confirmed that some sediments were only partially adapted to ryegrass support. Compost addition improved sediment physical properties over time, but caused temporary N deficiency during the first months after installation which limited shoot biomass production. Exogenous plant species developed on the constructed Technosols, especially on the soils where the lack of structure and N deficiency had the strongest effect.
ConclusionsAll sediments were suitable for plant growth over the 18 months of the study. A few soil properties emerged as markers of the fertility of sediment-made Technosols. Among them, the soil structure was one of the most determining parameters. It can be assessed by measuring aggregate stability, macroporosity, the crustability index, and bulk density, while available nutrients (N, P, K) and pH seem sufficient to assess chemical fertility. The balance between the properties of the sediment-made Technosols and the needs of the plants seems to be an essential lever for the establishment of functional soil-plant systems for urban greening or for ecological restoration.
相似文献