查看更多>>摘要：Enzymes produced by microorganisms and plants are very sensitive to variations in soil microclimate, yet most enzyme assays are conducted under oxic conditions irrespective of the origin of environmental samples. It remains unclear how short-term aeration (minutes to hours) affects the hydrolytic and oxidative enzymes in anoxic systems. This key gap in current methods was addressed by measuring the kinetics of hydrolytic phosphomonoesterase, beta-glucosidase, and leucine aminopeptidase and the activities of oxidative phenol oxidases and peroxidases by fluorogenic substrates under oxic (+O-2) and anoxic conditions (-O-2). Aeration effects were tested in a flooded paddy soil with growing rice (research task 1: moderate O-2 limitation) and without rice (research task 2: strong O-2 limitation). We tested two hypotheses explaining possible effects of short-term aeration on hydrolytic versus oxidative enzymes. (1) Aeration promotes Fe(II) oxidation, which leads to the accumulation of phenolics through the "iron-gate" mechanism, thus suppressing the activities of hydrolytic enzymes compared to the anoxic conditions. (2) Aeration stimulates phenol oxidases that degrade phenolics according to the "enzyme latch" concept, thus eliminating the suppression of hydrolytic enzymes. The activities of hydrolytic enzymes were lower by 5-43% in both experiments under + O-2 compared to -O-2. In contrast, the activities of peroxidases and phenol oxidases were 2-14 times higher under + O-2 than under -O-2. Thus, the activation of oxidative enzymes under + O-2 was uncoupled from the hydrolytic activities. This contradicts both the "iron gate" and the "enzyme latch" mechanisms. We explain the short-term suppressive effect of O-2 in assays by increased concentrations of reactive oxygen species, which decreased microbial activity. We conclude that our modification of enzyme assays under anoxic conditions is required for samples taken from low-oxygen environments to avoid underestimation due to rapid suppression of hydrolytic enzyme activities by O-2.
Osborn, Ernest D.McBride, Steven G.Kupper, Joseph V.Nelson, Jim A....
4页
查看更多>>摘要：ABS T R A C T Identifying general patterns in microbial community responses to global change factors remains a challenge in soil ecology, partially due to different methods used to characterize microbial communities among studies. In this study, we used DNA-based (qPCR, sequencing) and PLFA approaches to assess microbial responses to both land use change and drought-rewetting. Both methods detected microbial community responses to land use change but the drought-rewetting responses detected by the two methods were qualitatively different: PLFAs revealed clear effects of soil drying on microbial communities, which 16S sequencing did not. In contrast, sequencing revealed strong responses to rewetting, which PLFAs did not show. Further, PLFAs revealed a marked increase in fungal:bacterial (F:B) ratios following drought, which was not evident in our qPCR data. Overall, our results show that full elucidation of microbial community responses to global change will require the use of multiple methodological approaches.
Martin, Gregory D.Morrissey, Ember M.Carson, Walter P.Freedman, Zachary B....
12页
查看更多>>摘要：Healthy forests are vital components of terrestrial ecosystems for their raw materials, high biodiversity, cycling of nutrients, and potential to sequester carbon. However, these ecosystems are sensitive to disturbances, and anthropogenic activities pose a serious threat to forest ecosystems globally. For example, human activities have dramatically altered multiple historical disturbance regimes in forests, including suppressing fire, increasing the density of large herbivores, and reducing the size of canopy gaps, among other disturbances. Such disturbances can have dramatic impacts on microbially-mediated forest soil functions, but more research is needed to determine the collective impacts of these disturbances. In this study, we investigated the interactive effects of disturbances, namely the legacies of fire, large herbivore densities, and canopy gap creation, in a deciduous forest soil. We determined that forest floor and mineral soil carbon and nitrogen pools were shaped by multiple disturbances, but fire was more influential than the other disturbances. The abundance of several functionallyrelevant microbial taxa were significantly impacted by fire, and the effect was more pronounced in the mineral soil than in the forest floor. Together, these findings demonstrate that multiple disturbances, especially a legacy of fire, exerts long-term control over soil carbon, nitrogen and microbial dynamics in a deciduous forest system.
查看更多>>摘要：Fungal communities inhabiting plant roots and the soil diverge because they are shaped by differences in abiotic environment and plant filtering. Therefore, these two communities will also likely respond differently to climate change. However, such responses are poorly understood, especially for climate extremes with increasing fre-quency and intensity. Based on a long-term field experiment that simulated two types of extreme drought (chronic/intense) of once-in-20-year occurrence in the temperate grassland, we studied the response of soil and root fungal communities to extreme drought in association with plant communities. The species richness, community composition, and network stability of the root fungi were sensitive to extreme drought and showed legacy effects during recovery; notably, these responses were independent of extreme drought types. The sensitivity of the root community was mainly driven by rare symbiotic and saprotrophic fungal species, with abundant species remaining stable. In contrast, except for species relative abundances, soil fungal communities were resistant to drought. Structural equation modelling revealed that plant communities mediate drought ef-fects on root fungal communities but not soil communities. Our findings highlight the climate sensitivity of root fungal communities and their response asymmetry to soil communities, with potentially profound consequences for ecosystem stability and functionality.
Schimel, JoshuaWeintraub, Michael N.Moorhead, Daryl
3页
查看更多>>摘要：How carbon partitions between microbial biomass and CO2 (carbon use efficiency, CUE) is key in all soil carbon cycling models. Traditional methods to estimate CUE focus on the physiological partitioning of specific substrates, typically labeled with isotopes. However, an alternative approach (Sinsabaugh et al., 2016) is based on community-level resource capture using assays of extracellular enzymes; although this uses the same name (CUE), it measures something distinctly different from the isotopic methods. Rather, it assesses how microbes shift resource use in response to substrate stoichiometry.
Hopple, A. M.Pennington, S. C.Megonigal, J. P.Bailey, V....
10页
查看更多>>摘要：Coastal forests worldwide are vulnerable to a dramatic transition from upland to wetland as sea-level rise accelerates and regimes of precipitation and storms change. However, the biogeochemical impacts of shifting salinity and inundation disturbance that foreshadow forest to wetland state transitions are largely unknown. This experiment used a natural salinity gradient in a tidal creek in eastern Maryland, U.S.A., to examine how soil respiration and chemistry may change under novel salinity and inundation disturbance regimes. Soil monoliths were transplanted in a reciprocal design among plots varying in seawater exposure and elevation above the creek. We monitored the monoliths' carbon dioxide (CO2) flux for two years and performed soil chemical analyses at the end of the experiment. Soil CO2 flux was affected by changing disturbance regimes and responses were dependent upon the salinity and inundation legacies associated with each study location. Lowland soil CO2 flux was resistant to changing salinity and inundation disturbance, with transplanted soil monolith chemistry composition in between that of its origin and destination. Conversely, upland soil CO2 flux was sensitive to changing salinity and inundation disturbance and remained suppressed throughout the 2-year study when exposed to wetter, saline conditions. Additionally, transplanted upland soil chemistry composition was like that of its destination, rather than origin, with upland soils displaying higher pH, base saturation, and nutrient availability relative to lowland soils. We hypothesize that reductions in soil respiration rates were driven by loss of soil nutrients and osmotic and redox stress on microbial communities following exposure to seawater. Together, our results suggest that disturbance legacies shape coastal forest soil responses to changing salinity and inundation disturbance regimes. However, fully understanding the dependence of system responses on disturbance legacies requires future study across a variety of systems and spatial and temporal scales.
查看更多>>摘要：Although widely used in ecology, comparative analyses of diversity and niche properties are still lacking for microorganisms, especially focusing on niche variations. Quantifying the niches of microbial taxa is necessary to then forecast how taxa and the communities they compose might respond to environmental changes. In this study, we first identified important topoclimatic, edaphic, spatial and biotic drivers of the alpha and beta di-versity of bacterial, archaeal, fungal and protist communities. Then, we calculated the niche breadth and position of each taxon along the important environmental gradients to determine how these vary within and among the taxonomic groups. We found that edaphic properties were the most important drivers of both, community di-versity and composition, for all microbial groups. Protists and bacteria presented the largest niche breadths on average, followed by archaea, with fungi displaying the smallest. Niche breadth generally decreased towards environmental extremes, especially along edaphic gradients, suggesting increased specialization of microbial taxa in highly selective environments. Overall, we showed that microorganisms have well defined niches, as do macro-organisms, likely driving part of the observed spatial patterns of community variations. Assessing niche variation more widely in microbial ecology should open new perspectives, especially to tackle global change effects on microbes.
查看更多>>摘要：The addition of residues (maize straw) to soil stimulates microbial activity and significantly changes the decomposition rates of soil organic matter (SOM), which is referred to as priming effects (PEs). PE patterns are influenced by microorganisms utilising various substrates. However, the varied functional traits of keystone taxa and structure traits of the bacterial community associated with the PEs patterns remain elusive. Therefore, we established a microcosm by adding C4 maize residue (C4 plants have a different 13C signature than C3 plants) to C3 soil amended for 120 d to observe the dynamics of PEs. High-throughput sequencing techniques were used to detect the succession of bacteria; keystone taxa were identified using network analysis. Negative PE (early stage) and positive PE (late stage) were observed during residue decomposition. At the end of the incubation, residue with N resulted in a positive PE, while residue alone had a minimal effect on the decomposition of native SOC. Furthermore, the bacterial community structure displayed distinct successions during residue decomposition. Correspondingly, network analysis revealed differences in the keystone taxa between the early and late stages. Bacillus, Streptomyces, Arthrobacter, and Agromyces were the keystone taxa during the early stage, whereas BD2-11 terrestrial, Bacteroidales, Sphingomonadaceae, and Xanthomonadales were the keystone taxa at the late stage. These putative keystone taxa have different functional traits as drivers of community function, thus linking them to either negative or positive PE. In addition, network modules of bacterial communities differed in the early versus late stages and showed different module-trait relationships during PE. Therefore, the different modules are aggregated in response to distinct PE patterns. This study provides deeper insights into the network structure of bacterial community corresponding to PE patterns and highlights the importance of keystone taxa in PE.
查看更多>>摘要：Peatlands are C-rich but N-poor ecosystems that function as an important C sink but also as significant CH4 sources and thus contribute to global warming. To confirm that N fertilization strongly reduces peatland CH4 emissions by stimulating nitrite-dependent anaerobic methane oxidation (n-damo), we investigated CH4 efflux and concentration in the soil profiles of a peatland subjected to long-term N fertilization. Contrary to previously reported increase of CH4 emissions from paddy, forest and grassland soils, N fertilization of peatland reduced CH4 efflux by 87%, especially during the hottest summer months (from 3.8 mg m(-2) h(-1) in the unfertilized control to 0.5 mg m(- 2) h(-1) in the N-fertilized site). The CH4 efflux was strongly reduced because the high organic matter content of the peat indirectly stimulated n-damo by providing CH4 (methanogens use organic matter to produce methane) and nitrite (denitrifiers use organic matter as an energy source). N fertilization reduced the CH4 concentration by 50-95% (from 7800-9500 ppm in the unfertilized control to 370-4800 ppm in the N fertilized site) in the top 30-cm soil, whereas the abundance of Methylomirabilis bacteria increased for 170% and its activity raised for 220% compared to the unfertilized control soil. Consequently, the topsoil is a hotspot of Methylomirabilis activity that use NO2- to oxidize CH4 and play an important role in reducing CH4 emissions in N-fertilized peatlands.
查看更多>>摘要：Some soil microbes can methylate arsenic (As) and produce dimethylarsenate (DMA) as a main product. Excessive accumulation of DMA by rice plants can cause the straighthead disease, a physiological disorder leading to substantial yield losses. DMA can also be demethylated in soil, but the mechanism and the microbes involved are not well understood. We investigated the dynamics of methylated As species, including monomethylarsenate (MMA), DMA and dimethyl-monothioarsenate (DMMTA), in three paddy soils that produced the straighthead disease. The soils were incubated under flooded conditions with or without the addition of 2-bromoethanesulfonate (BES), a specific inhibitor of methanogenesis. DMA and DMMTA concentrations in porewater increased initially as soil redox potential decreased, and then decreased rapidly coinciding with the production of methane. BES addition largely suppressed methanogenesis and the disappearance of DMA and DMMTA, but not of MMA. BES addition suppressed the transcript levels of archaeal 16S rRNA and, particularly, mcrA gene encoding methyl-coenzyme reductase subunit A. Among the core genera of archaea, the absolute abundances of Methanomassiliicoccus and Methanosarcina were decreased significantly by BES in the three soils. In a pot experiment with two soils, BES addition significantly increased DMA accumulation in rice husks and the incidence of the straighthead disease in rice. The results suggest that DMA and DMMTA demethylation in paddy soil is coupled to methanogenesis with Methanomassiliicoccus and Methanosarcina likely playing an important role.
NSTL
Elsevier