查看更多>>摘要：During the last decade it has been increasingly acknowledged that carbon (C) contained in root exudates can accelerate decomposition of soil organic matter (SOM), a phenomenon known as rhizosphere priming effect (RPE). However, the controlling factors and the role of different soil microorganisms in RPE are not yet well understood. There are some indications that the response of the soil microbial decomposers to labile C input in the rhizosphere depends on microbial demand of nutrients for growth and maintenance, especially that of C and nitrogen (N). To test this hypothesis, we assessed SOM decomposition induced by C-13-glucose additions during one week in forest soils with different C:N ratios (11.5-22.2). We estimated SOM respiration, the potential activity (concentration) of a range of extracellular enzymes, and incorporation of C-13 and deuterium (D) in microbial phospholipid fatty acids (PLFAs).Glucose additions induced positive priming (a 12-52% increase in SOM respiration) in all soil types, but there was no linear relationship between priming and the soil C:N ratio. Instead, priming of SOM respiration was positively linked to the C:N imbalance, where a higher C:N imbalance implies stronger microbial N limitation. The total oxidative enzyme activity and the ratio between the activities of C and N acquiring enzymes were lower in soil with higher C:N ratios, but these findings could not be quantitatively linked to the observed priming rates. It appears as if glucose addition resulted in priming by stimulating the activity rather than the concentration of oxidative enzymes. Microbial incorporation of D and C-13 into in PLFAs demonstrated that glucose additions stimulated both fungal and bacterial growth. The increased growth was mainly supported by glucose assimilation in fungi, while the increase in bacterial growth partly was a result of increased availability of C or N released from SOM. Taken together, the findings suggest that the soil C:N ratio is a poor predictor of priming and that priming is more dependent on the C:N imbalance, which reflects both microbial nutrient demand and nutrient provision.
查看更多>>摘要：Stover mulching over no-till soil is regarded as a promising practice to increase soil organic carbon (SOC) in croplands against climate change. Microbial necromass is a significant source of SOC stock and unequivocally controlled by the microbial community. Yet, a complete link that spans from agricultural practices to microbial community features, to soil necromass C, and eventually to SOC is poorly understood. Here, we conducted a 10-y corn field experiment with five treatments, which included conventional tillage (CT), no-tillage without stover (NT-0), and no-tillage with low, medium, and high amounts of stover mulching (NT-low, NT-medium, and NT-high) in a Molisol of northeastern China. We investigated the stocks and changes in total SOC and its microbial necromass C along a soil depth down to 40 cm, and we evaluated how SOC dynamics and stabilization processes were associated with microbial community features. We characterized microbial community diversity and structure using 16S rRNA and internal transcribed spacer (ITS) sequencing, and we characterized microbial biomass and necromass using phospholipid fatty acid and amino sugar biomarkers. Compared with conventional tillage, no-tillage with medium and high amounts of stover mulching increased SOC stocks in the upper 0-40 cm of soil by > 0.4% per year. No-tillage treatments (without and with stover) had almost no effect on the proportion of total microbial necromass C to SOC, but greatly modified the ratio of fungal necromass C to bacterial necromass C, which increased in top layers (0-5 cm) and decreased in deep layers (10-40 cm). SOC was governed mainly by fungal necromass C, which was correlated positively with fungal biomass. Fungal necromass C, not bacterial necromass C, was more closely associated with microbial community composition. Our results suggested that no-tillage with medium stover mulching was the optimal treatment to achieve the best trade-off between stover input and SOC storage. Differentiating microbial C pools from total SOC and, notably, separating fungal and bacterial necromass C pools can refine our mechanistic understanding of SOC storage as well as its association with microbial biota.
Hettiaratchi, Patrick A.Jayasinghe, PoornimaDunfield, Peter F.Smirnova, Angela, V...
11页
查看更多>>摘要：Current literature provides conflicting information on the role vegetation plays when considering methane (CH4) oxidation potential of engineered Biosystems, such as landfill biocovers (LBCs), bio-windows and methane biofilters. The primary objective of this study was to determine whether the impact of vegetation on biological CH4 oxidation was positive or negative and to explain the reasons for the observations using a variety of experiments. A total of eight flow-through columns (two alfalfa, two native grass, two canola and two bare-soil replicates) were set up outdoors to simulate field operation in cold climatic conditions. Each column was layered with 18 cm of topsoil and 32 cm of compost mixture (compost 30%: topsoil 70% v/v) as packing material and treated with CH4 fluxes ranging from 180 to 815 g CH4 m(-2) d(-1). The bare-soil columns exhibited the highest CH4 oxidation rate of 455 g CH4 m(-2) d(-1), while the maximum CH4 oxidation rates for the vegetated columns ranged between 147 and 171 g CH4 m(-2) d(-1) with the alfalfa column showing the lowest. Gas profiles of vegetated columns showed high concentrations of nitrogen (N-2) and oxygen (O-2) at all depths, possibly due to increased permeability created by the plant root systems. Quantitative Polymerase Chain Reaction (q-PCR) assessment showed that pmoA gene copy numbers, indicative of methanotrophic population levels, were higher in bare-soil columns than in vegetated columns. The Illumina based sequencing of 16S rRNA gene showed that Type I methanotrophs dominated both vegetated and bare-soil columns. Soil incubation experiments conducted to determine oxidation kinetic parameters also indicated greater methanotrophic activity in the bare-soil columns than in vegetated columns. The plant data collected at the end of the column experiments provided clear evidence of CH4 escape due to preferential pathways created by plant roots (reaching 38 cm, 31.5 cm and 26.5 cm by alfalfa, canola and native grass, respectively) that resulted in decreased CH4 oxidation in vegetated columns. The study results clearly demonstrate that vegetation decreases CH4 oxidation at high loading rates, notwithstanding the type of vegetation.
Barbato, R. A.Jones, R. M.Douglas, T. A.Doherty, S. J....
10页
查看更多>>摘要：Permafrost is thawing at unprecedented rates, significantly altering landscapes and ecosystem trajectories by changing subsurface conditions, vegetation characteristics, and soil properties. Dormant microbes become active as temperatures rise and permafrost soils warm and thaw. To determine the effects of sample location and warming on the permafrost microbiome, we collected permafrost from five distinct locations within the Cold Regions Research and Engineering Laboratory's Permafrost Tunnel (PT) near Fairbanks, Alaska and warmed them in a laboratory incubation study. Heterotrophic respiration was continuously monitored and metagenomes were analyzed at select incubation temperatures. Under frozen conditions, microbial respiration rates from different PT locations were similar, ranging from 2 to 12 mg C-CO2 kg(-1) d(-1). During thaw, respiration increased in samples from three PT locations, but remained stable for two locations. Analysis of the shotgun metagenomes showed how the microbial communities and their potential function changed as a function of location and incubation temperature. This indicates a differential response of permafrost microbes based on their origin. These findings have important implications for developing accurate forecasts of microbial community assemblages during thaw in that location should be considered as a strong influencing factor.
Clough, Tim J.Wrage-Moennig, NicoleLuo, JiafaHu, Chunsheng...
8页
查看更多>>摘要：Poorly crystalline iron (Fe) oxides are commonly deposited on the surface of rice roots, forming an Fe plaque. This Fe plaque is an important area for Fe redox reactions because the poorly crystalline Fe is available for microbial transformations. However, it remains unclear what the mechanisms are that cause the root Fe plaque to affect CO2 emissions from paddy soils. Thus, this study investigated the effects of Fe plaque on paddy soil CO2 emissions and the associated mechanisms. Paddy soil with rice plant roots containing an Fe plaque-coating had 1.5-fold larger CO2 emissions and higher expression levels of genes involved in soil carbon (C) degradation than Fe plaque-free roots, indicating that Fe plaque stimulated paddy soil derived CO2 emissions. Fe plaque-coated rice roots, immersed in a C-13-labeled glucose solution, emitted more CO2, with a higher abundance of (CO2)-C-13, than the Fe plaque-free roots. These differences were not observed when the surfaces of the rice roots were sterilized. These results indicate that the Fe plaque-stimulated CO2 emissions were due to soil microbial respiration, not autotrophic root respiration. Chelating the dissolved Fe on the root surface eliminated Fe plaque stimulation of CO2 emissions, while Fe(III) supplementation correlated with enhanced CO2 emissions. The stoichiometric mole ratio of the enhanced CO2 emissions to the Fe(II) generated was comparable to the theoretical ratio of Fe(III) when used as an electron acceptor for organic C decomposition. These results showed that the Fe plaque enhancement of CO2 emissions was coupled to Fe(III) reduction. Limiting the stimulating effects of Fe plaque on CO2 emissions may be a potentially useful approach for mitigating organic C loss from paddy soils.
查看更多>>摘要：It remains unclear how soil microbes respond to labile organic carbon (LOC) inputs and how temperature sensitivity (Q(10)) of soil organic matter (SOM) decomposition is affected by LOC inputs in a short-term. In this study, C-13-labeled glucose was added to a pristine grassland soil at four temperatures (10, 15, 20, and 25 ?), and the immediate utilization of LOC and native SOM by microbes was measured minutely in a short-term. We found that the LOC addition stimulated the native SOM decomposition, and elevated temperature enhanced the in-tensity of microbial response to LOC addition. The ratio between microbial respiration derived from LOC and native SOM increased with higher temperature, and more LOC for respiration. Additionally, LOC addition increased the Q(10) of SOM decomposition, and the Q(10) of LOC decomposition is higher than that of native SOM. Overall, these findings emphasize the important role of temperature and LOC inputs in soil C cycles.
查看更多>>摘要：The efficiency of soil organic carbon (SOC) sequestration as a suitable negative emission technology depends mainly on plant-derived organic carbon input and its allocation to stabilised SOC pools. These processes may be affected by fertiliser use and soil type. The purpose of this study was to investigate the effect of the organic fertiliser (poultry manure compost), the mineral fertiliser (rock phosphate) and their mixture on organic carbon (OC) transfer from plant to soil. We studied OC allocation to protected SOC pools of a Luvisol and a Neoluvisol. We carried out a growth chamber experiment with C-13-enriched atmosphere, where ryegrass plants were grown for 7 wk in the two soil types which were amended with the three different fertiliser sources. We quantified root-derived OC input in three SOC density fractions and soil microbial biomass after 7 wk . We found that the addition of poultry manure compost and its mixture with rock phosphate led to more root biomass and more root-derived OC transfer to active pools compared to rock phosphate alone. Soil amended with poultry manure compost had higher microbial biomass contents than soil with mineral fertilisation due to higher available organic phosphorus. We also noticed variations in the dynamics of the stabilised OC pools amongst soils, which could be attributed to the impact of phosphorus fertiliser sources on SOC stabilisation processes. We concluded that organic and mineral phosphorus fertilisers may have a contrasting impact on OC flow from plant to soil and in particular on the allocation of root-derived OC to labile or stable SOC fractions.
查看更多>>摘要：Deforestation of the Atlantic rainforest in Brazil and its conversion into sugarcane fields, pose a serious threat to the local biodiversity. The change in land use affects not only macro-organisms, but also microbial communities such as the obligate symbiotic arbuscular mycorrhizal fungi (AMF). We characterized AMF communities along 200-m transects from native forests and into sugarcane fields. Meta-barcoding, and subsequent community and network analyses were used to illustrate the distribution of communities along the transects. Conversion of forest into sugarcane fields did not change alpha diversity, but resulted in a biotic homogenization of the communities. The communities in the sugarcane field was not a subset of the forest community, but recruited taxa from other unsampled species pools. We found a peak in richness in the transition zones which suggests that the AMF community admix across the border. A difference in nestedness and high turnover among transects indicate that forest AMF are locally specialized and have a restricted geographical range.
Dunfield, KariJin, Virginia L.Lehman, R. MichaelOsborne, Shannon M....
12页
查看更多>>摘要：Crop rotations have well-known aboveground and belowground benefits. At regional to continental scales, the unifying mechanisms of how diversified rotations alter soil organic matter (SOM) dynamics have not been demonstrated. We assessed how increasing crop rotational diversity across a soil-climate gradient affected the integrated response of SOM chemistry, microbial community composition, and its enzymatic potential to degrade SOM. Agroecosystems with the same crop rotational diversity (all sampled during the corn phase) shared similarities in molecular SOM patterns with a strong microbial signature, pointing to common transformation processes. Differences in SOM chemistry between rotations were mainly characterized by shifts in microbial necromass markers and in lipids produced or transformed by microbes rather than by intact plant lipids. Microbial resource allocation to enzymes, which catalyze the decomposition of organic matter, differed between systems. Lower resource investment into recalcitrant C-degrading enzymes with increasing crop diversity indicates higher resource availability for the microbial community. Our multivariate analyses suggest that this could be regulated via relative changes in microbial functional groups - emergence of relatively more nonoxidase producing microorganisms like arbuscular mycorrhizal fungi rather than an absolute decrease in oxidase producing microbes. These uniform responses to increased crop rotational diversity over a wide geographical area point to enhanced stabilization of microbial-derived SOM and functional shifts in the microbial community as a common mechanism underlying the positive plant-soil feedback in diversified cropping systems.
查看更多>>摘要：Rewetting dry soil induces enormous changes in microbial growth and biogeochemistry. Upon drying-rewetting (D/RW), bacteria have been shown to exhibit two different responses: (1) a more resilient response where bacteria start growing immediately with a quick recovery after rewetting and (2) a less resilient response where there is a pronounced lag-period before bacterial growth starts to increase exponentially. A shift towards a more resilient bacterial growth response has previously been shown to be induced by exposing soils to repeated cycles of D/RW. Here, we test the hypothesis that this response is driven by selection for a bacterial community with traits for quick colonization of labile carbon (C) resources made available upon D/RW. To do so, we compared the responses of soils that had been exposed to either (i) three cycles of D/RW, (ii) three pulses of glucose addition to moist soil or (iii) three pulses of litter addition to moist soil, before all soils were subjected to a D/RW event where bacterial growth, fungal growth and respiration rates were monitored. As expected, exposing the soil to a series of D/RW events resulted in a more resilient bacterial growth response, as well as a faster recovery of fungal growth. Pre-treating the soils with pulses of glucose accelerated the recovery of bacteria after D/RW, but did not select for a bacterial resilience that could match the pre-treatment with exposure to D/RW. Pretreatment with pulses of litter showed a trend for an accelerated recovery of bacterial growth to D/RW, but to a lesser extent than that induced by pulses of glucose. In contrast, pre-treatment of soil with either pulses of glucose or pulses of litter both led to a faster recovery of fungal growth following D/RW, matching that induced by repeated D/RW cycles. These results suggest that selection for quick colonizers partly explains the shift to a more resilient microbial response to repeated cycles of D/RW, accounting for ca. 60% increase in bacterial resilience and 100% of the increase in fungal resilience compared that induced by repeated D/RW cycles.
NSTL
Elsevier