DeLuca, Thomas H.Zackrisson, OlleNilsson, Marie-CharlotteSun, Shouqin...
9页
查看更多>>摘要：Feather mosses and associated cyanobacteria serve as an important source of nitrogen (N) in boreal forests; however, few studies have effectively traced the N2 fixation in-situ for more than one year. The purpose of this study was to assess the long-term fate of N2 fixed in feather moss carpets in boreal forests of northern Sweden. We conducted a seven-year 15N2(g) labelling and tracing experiment in a boreal forest with a moss bottom layer dominated by Pleurozium schreberi Brid (Mitt). Mesocosms of forest floor with and without mosses present were exposed to a 10% 15N2(g) atmosphere for five days after which samples of moss, shrub, pine seedling and O horizon were taken at varied intervals and analysed for delta 15N. Plots were split and burned in year seven to assess the effect of fire on liberating moss N for uptake by Scots pine (Pinus sylvestris L.) seedlings. Feather mosses treated with 15N2(g) were highly enriched in 15N one month after labelling which subsequently declined after seven years to 13% of the original 15N enrichment in green tissue. No measurable 15N enrichment was observed in shrubs or the O horizon in the presence of labelled mosses until greater than five years after the labelling experiment. Fire can liberate moss N, but we did not observe a direct effect of fire on N uptake by pine seedlings. This long-term study indicates that N2 fixed by cyanobacteria in feather moss carpets is conserved in moss tissue for extended periods and slowly transferred to the forest soil O horizon as moss tissue decomposes suggesting that moss N2 fixation is most important as an ecosystem N source at long time scales.
Demarmels, R.Watts-Williams, S. J.McLaughlin, M. J.Kafle, A....
11页
查看更多>>摘要：Arbuscular mycorrhizal fungi (AMF) are plant symbionts that promote plant growth and provide important plant and ecosystem functions. These abilities have great economical potential which has resulted in an increasing number of commercially available AMF inoculants. Here, we present the results of a global study in which we evaluate the effectiveness of 28 commercial AMF inoculants to colonize host plants under greenhouse and field conditions. This evaluation includes three independent studies across three continents (Australia, Europe, and North America). The Australian and European studies tested 25 different commercial AMF inoculants in nonsterilized and sterilized soils under greenhouse conditions and compared them against laboratory cultures of the AMF Rhizophagus irregularis. This is supplemented by the North American study which evaluated the effects of three commercial inoculants under field conditions. In the greenhouse trials using non-sterilized soil, we observed that the addition of commercial inoculants did not lead to enhanced mycorrhizal colonization and inoculation increased plant biomass in only one out of 25 treatments. In sterilized soil, 84% of the mycorrhizal inoculants did not lead to mycorrhizal root colonization, demonstrating that these products did not contain viable propagules. In contrast, the laboratory cultures of the AM fungus Rhizophagus irregularis resulted in substantial root colonization (48% and 79%) in the Australian and European bioassay. Moreover, only five out of 25 treatments enhanced plant biomass when added to sterilized soil. Metagenomic analysis of field roots in the North American field trial revealed changes in the mycorrhizal community after inoculation. For one inoculant, this was accompanied by increased biomass production. This global evaluation of commercial inoculants raises concerns over unreliable products which do not contain viable propagules and do not result in mycorrhizal root colonization. Under field conditions, effects on plant growth are dependent on changes within the mycorrhizal community. The results of this study highlight the need for standardized quality control of AMF inoculants and further research on their establishment and effects under field conditions.
查看更多>>摘要：Current mechanistic knowledge of soil nitrogen (N) cycling mediated by microorganisms lacks in understanding of the functional links between activities of proteolytic extracellular enzymes that provide substrate for nitrifying populations. This relates specifically to soils of different acidity and organic residue treatments. Our hypothesis was that organic residues of high decomposability applied to less acidic soils promote proteolytic enzyme activities modulating the abundance of nitrifiers. This was justified by the presumed benefit of available substrates to microorganisms under less acidic soil conditions. Organic inputs of high (HQR) and medium (MQR) quality differing in decomposability ((Lignin+Polyphenol)/N ratio of 5.1 (HQR) versus 8.1 (MQR)) were incubated in less acidic (S5.1) and more acidic (S4.3) soils for 60 days. Soil samples were obtained at defined time intervals and analyzed for potential activities of alanine aminopeptidases (AAP), leucine aminopeptidases (LAP), and thermolysin-like proteases (TLP), along with the abundance of nitrifying bacteria (AOB) and archaea (AOA). Analysis of covariance (ANCOVA) revealed a significant positive relationship of proteolytic enzyme activities with abundance of AOB and AOA, even though the extent of this relationship was more dependent on soil pH and time than organic residue quality. Notably, the positive relationships were pronounced at the later stages of the incubation period. Within the course of the incubation, AOB benefitted from the release of N substrates (NH4+, NO3 , DON) spurred by proteolysis in S5.1. For MQR and HQR, AOA showed comparable dynamics in S4.3, indicating a niche specialization between AOB and AOA depending on soil acidity and resource availability.
查看更多>>摘要：The rhizosphere harbors complex bacterial communities, which are critical for plant growth and health. Significant differences exist between bacterial communities in the rhizosphere and bulk soils, however, limited research has explored co-occurrence patterns, environmental adaptations, and assembly mechanisms of rhizosphere bacterial communities. Using 16S rRNA high-throughput sequencing, we investigated the taxonomic and phylogenetic diversity of bacterial communities in both rhizosphere and bulk soils from a rice cropping experimental system in China. In addition to investigating differences in bacterial composition, we examined cooccurrence patterns, estimated environmental breadth and phylogenetic signals, and analyzed community assembly processes in these environments. Significant differences were observed between rhizosphere composition and bulk soil (p < 0.05) even some bacteria in the rice rhizosphere may come from the bulk soil around roots. The distribution patterns and ecological functions between communities in the rice rhizosphere and bulk soil were also significantly different. Lower beta-diversity values among bacterial communities in the rice rhizosphere indicated that they had a higher stability than those in the bulk soils. In addition, rice rhizosphere communities had a wider phylogenetic diversity and lower functional redundancy when compared with bulk soils. Moreover, the results of environmental breadth analysis revealed that communities in bulk soils were more environmentally constrained than rhizosphere communities. Our null model revealed that deterministic processes drove community assembly in bulk soils (59.57%), whereas stochastic processes determined those in the rice rhizosphere (53.85%). Available potassium was decisive in determining the balance between stochasticity and determinism in both communities. Our study provides insights on the mechanisms underlying the assembly and maintenance of bacterial diversity in rice cropping soils, in response to environmental changes.
查看更多>>摘要：Global salinization is impacting both terrestrial and freshwater systems. Riparia link these systems and are likely impacted by increased sodium, but impacts are understudied. The sodium ecosystem respiration hypothesis posits that increased sodium under sodium-limitation should stimulate decomposition. We tested this hypothesis in an inland subtropical riparian system by adding 0.067% NaCl every 2 weeks to 1 m2 plots (n = 10) or just H2O (n = 10) and measuring decomposition rates of red maple litter across 9 months. Additionally, we measured leaf sodium content of 4 riparian plant species. Contrary to our predictions, decomposition was 21% slower in sodium addition plots than in controls, but invertebrate decomposer communities did not differ between treatments. Plants had 1.4- to 4-fold higher leaf sodium content after 9 months, but soil sodium content did not differ. This is the first evidence of sodium stress for mesic inland terrestrial ecosystems. Slower decomposition supports the Sodium Subsidy-Stress hypothesis and extends the sodium ecosystem respiration to include sodium-stress impacts on ecosystem functions when sodium occurs in excess of optimal sodium levels. Changes to decomposition and leaf sodium content in riparia demonstrate sodium can impact both green and brown food webs and ultimately affect exchange across terrestrial-aquatic boundaries.
Bouguerra, SirineGavina, AnaNatal-da-Luz, TiagoSousa, Jose Paulo...
9页
查看更多>>摘要：Despite the high array of potential applications of cobalt oxide nanomaterial (nano-Co3O4), data regarding its toxicity to soil biota is limited, compromising the capability of predicting the risks of this metal oxide nanomaterial (MO-NM). In a previous study the predicted no effect concentration of nano-Co3O4 to soil (PNECsoil) was estimated to be 5.3 mg kg(-1) soil(dw). Given limitations in available data, this threshold was obtained through the application of assessment factors, which are known to overestimate the risks, by being a deterministic and highly protective approach. Thus, this PNECsoil value could be refined if there were more ecotoxicological data. Aiming to contribute to fill this lack of data, this work intended to assess the impact of nano-Co3O4 on soil microorganisms, by measuring soil enzymes activity (dehydrogenase, acid phosphatases, arylsulphatase, CM-cellulase, urease), the nitrogen mineralization, the soil microbial biomass carbon and the soil basal respiration at a range of concentrations up to 1000 mg of nano-Co3O4 kg(-1) soil(dw). The results showed that the arylsulphatase (87.8-296.3 mg kg(-1)soil(dw)), the acid phosphatase (87.8-1000 mg kg(-1)soil(dw)) and the soil basal respiration at the lowest concentration tested (87.8 mg kg(-1)) were significantly affected by the nano-Co3O4 exposure. Conversely, significant stimulatory effects were observed in enzymes activity related to carbon (296.3-666.7 mg kg(-1)soil(dw)) and nitrogen cycling (87.8-296.3 and 1000 mg kg(-1)soil(dw)) and basal respiration (131.7-197.5 and 666.7-1000 kg(-1)soil(dw)). Microbial biomass carbon was not significantly affected in any test treatment but showed a tendency to increase with increasing nano-Co3O4 concentration. Multiple mechanisms may be involved in the interaction of this NM with soil enzymes and soil microbial cells. The data obtained did not allow any adjustment to the previous PNECsoil value by taking into account the soil microbial community, because the results obtained point for effects at concentrations lower than the range tested in this study (87.8 mg nano-Co3O4 kg(-1)soil(dw)) in terrestrial environment.
Goyer, ClaudiaNeupane, SaraswotiZebarth, Bernie J.Burton, David L....
11页
查看更多>>摘要：Compost application may be an effective means to rapidly increase soil organic matter, soil quality, and soil microbial community diversity in intensive potato crop production systems. This study compared three contrasting compost products with a no compost control on soil chemical properties and soil bacterial and fungal community composition and diversity. The three composts consisted of municipal source separate waste compost (SSOC), forestry and poultry manure compost (FPMC), and forestry residues waste compost (FRC) with low, medium and high forestry waste percentages in their feedstock, respectively. Soil samples were collected on four dates over 11 months after compost application in October 2014. Soil pH, dissolved organic carbon and readily mineralizable C (respiration) were significantly greater in FPMC-and SSOC-treated soils compared to FRCtreated and control soils. Compost application influenced the relative abundances of several bacterial phyla in soils compared to control soils but not the relative abundances of fungal phyla. Several compost-borne bacterial (average of 383 operational taxonomic units (OTUs)) and fungal (average of 66 OTUs) species could be detected in soil throughout the following growing season after compost product application suggesting that these species succeeded in establishing in soils. The beta-diversity of bacterial and fungal communities in soils differed significantly among treatments and sampling dates, indicating that the applied composts resulted in a change in the bacterial and fungal community diversity. Convergence of bacterial community diversity was observed among treatments over time but not for fungal community. The application of diverse compost products clearly changed the soil chemical properties which in turn influenced the bacterial and fungal communities. The effects of compost application on microbial communities were persistent, and could still be observed nearly a year after compost was applied.
查看更多>>摘要：The mineralization of soil organic nitrogen (N) catalyzed by N-hydrolyzing enzymes plays a major role in ecosystems N cycling. However, the responses of this biochemical process to N deposition, particularly different N types, remain unclear. Here, a field experiment was conducted in a temperate forest to investigate how different types of N deposition influences the interaction between soil organic N fractions and N-hydrolyzing enzymes, i.e., protease, N-acetyl-beta-glucosaminidase, urease and amidase in the 0-10 cm and 10-20 cm layers. Four treatments including nil N (CK), inorganic N (NH4NO3, IN), organic N (urea and glycine 1:1, ON) and mixed N (inorganic and organic N 7:3, Mix-N) deposition were included. We found no effects of IN deposition on N-hydrolyzing enzymes activities and soil organic N fractions. In contrast, ON and Mix-N deposition significantly increased urease activity in surface soil and protease, urease, and amidase activities in subsoil. Mix-N deposition resulted in the greatest increase in hydrolysable ammonia-N (85%), labile organic N (76%) and stable organic N (101%), followed by ON deposition. Moreover, structural equation modeling revealed that amidohydrolases (urease and amidase) was actively involved in the conversion of labile organic N to ammonia-N, which was promoted by ON and Mix-N deposition but showed no response to IN deposition. In summary, mixed inorganic and organic N deposition favors the accumulation and subsequent enzymatic turnover of organic N in forest soils. Our findings suggest that different components in N deposition should be considered when examining N deposition effects on ecosystem N cycling.
查看更多>>摘要：Fusarium wilt of bananas is a serious soil-borne fungal disease that currently threatens banana production worldwide. There is currently no direct and effective agricultural method for controlling the disease effectively. In this study, a pot experiment was conducted to evaluate the effects of different pineapple cultivars that were planted in a banana orchard soil with high incidences of this disease. The goal of studying this banana-pineapple plantation system was to improve the soil microbial community structure to enhance the control of a number of Fusarium in the banana soil. The soil culturable microorganisms showed that the order of the number of Fusarium from high to low was banana continuous cropping (B) > fallow (CK) > "Golden pineapple" planting (B_GP) > "Bali pineapple" planting (B_BP) > "Tai nong 17 pineapple" planting (B_PP). The MiSeq sequencing results showed that the relative abundance of Fusarium was consistent with the culturable microbial results. Banana-pineapple rotations significantly reduced the abundance of total fungi and F. oxysporum as well as the fungal diversity. The number of Fusarium were significantly reduced, and the banana-pineapple plantings changed the bacterial and fungal communities of soil microbes by increasing the relative abundance of beneficial bacterial and fungal genera such as Desulfurispora, Brockia, Gp1, and Purpureocillium, Talaromyces, respectively. In addition, planting different pineapple cultivars could reduce the soil pH, available nitrogen (AN), available phosphorus (AP) and available potassium (AK), while the organic matter (OM) was increased. Besides, different pineapple cultivars with different soil microbial community structures, and soil fertility indices significantly reduced the relative abundance of Fusarium in the banana orchard soil, and the degree of reduction was from high to low as follows: "B_PP" > "B_GP" > "B_BP". Our result supports the good application prospects of this rotation for reducing the incidence of soil-borne Fusarium of bananas.
查看更多>>摘要：Soil metabolites strongly affect microbial community structure and function. Yet the response of soil microbial communities to plant rhizosphere metabolism and their interaction mechanism is poorly understood. In this study, we aimed to explore the influence of Pinus sylvestris var. mongolica (P. sylvestris) rhizosphere metabolites on microbial diversity, and clarify the dominant factors driving the variation in the rhizosphere microbial community along chronosequence. Gas chromatography-mass spectrometry (GC-MS) and high-throughput sequencing were used to determine the rhizosphere metabolites and microbial community composition, respectively. The results showed that P. sylvestris can release a variety of rhizosphere metabolites (such as fatty acids, monoacylglycerides, and diterpenes) with certain ecological functions, and these metabolites significantly affected the rhizosphere microbial alpha diversity and community composition. Simultaneously, the edaphic factors, such as pH, soil moisture, organic carbon, total phosphorus, NO3--N, NH4+-N, and available phosphorus concentrations, also significantly affected the rhizosphere microbial community. However, partial Mantel test and variation partitioning analysis confirmed the rhizosphere metabolites had a stronger relationship with the variation of rhizosphere bacterial and fungal communities than edaphic factors. Overall, our study highlights the regulatory role of the rhizosphere metabolites of P. sylvestris in shaping microbial community, and provides an insight into the rhizosphere microecological during vegetation restoration process in the Mu Us Desert.
NSTL
Elsevier