Changes In Soil Microbial Composition Research Articles

Identifying and Remediating Soil Microbial Legacy Effects of Invasive Grasses for Restoring California Coastal Sage Scrub Ecosystems

As invasive grasses encroach upon native ecosystems, they have the potential to transform intact California coastal sage scrub (CSS) into non-native grasslands. This occurs—in part—due to legacy effects: changes in soil microbial composition elicited by grass invasions with long-term impacts on soil and native vegetation. Along with direct effects on CSS vegetation, legacy effects may alter microbial communities which may in turn impact native plant growth. To tease apart these factors, we monitored growth in three CSS species inoculated with either uninvaded soil or sterilized uninvaded soil that were subsequently planted into a site characterized by observed microbial legacy effects. Our findings indicate native plant growth can be explained by changes in soil microorganisms. Specifically, native Artemisia californica and Baccharis pilularis grew larger in plots with unsterilized uninvaded soil inoculum, which contained a larger abundance of Gemmatimonadetes and Glomus, compared to the sterilized soil inoculum plots. Therefore, microbial augmentation may not only improve restoration in post-invasive sites but long-term changes in soil microbial communities may be linked to native plant growth. Furthermore, adding uninvaded soil replete with native microbes has the potential to support restoration of invaded sites by promoting native plant survival and establishment in these restored ecosystems.

A less complex but more specialized microbial network resulted in faster fine-root decomposition in young stands of Robinia pseudoacacia

Microorganisms play an important role in litter decomposition. Bacteria and fungi colonize litter during the decomposition process; therefore, understanding the interactions of bacterial and fungal communities can yield insight into litter decomposition dynamics. Most studies have focused on leaf litter decomposition, but thus far, there has been little information on the dynamic changes in soil microbial composition at the different stages of fine-root decomposition. Therefore, we conducted a 210-day incubation experiment on the fine roots of Robinia pseudoacacia to explore how the temporal dynamics of soil enzyme activities and microbial communities are related to the decomposition of R. pseudoacacia at four different stand ages (15, 25, 35 and 45 years) during vegetation restoration. The results showed that the fine-root decomposition rate was higher for young stands of R. pseudoacacia. We found that the oxidase activity was significantly higher in the young stands (15 and 25 years) than in the old stands (35 and 45 years), while the hydrolase activity showed the opposite trend. The main reason for the higher decomposition rate in young stands of R. pseudoacacia was the high oxidase enzyme activities and less complex but more specialized microbial network of younger stands. The occurrence network was used to identify the keystone taxa by statistical analysis, and the key taxa changed from Acidobacteria to Proteobacteria during vegetation restoration. These findings demonstrate that vegetation restoration alters the soil microorganism community and network structure during fine-root decomposition of R. pseudoacacia. This finding is of great significance for understanding the role of microorganisms in regulating fine-root decomposition dynamics.

Influence of land‐use changes on microbial community structure and diversity in a semiarid region

AbstractLand‐use change and the conversion of land into croplands is one of the main drivers of soil degradation and the loss of soil organic carbon. Few studies have evaluated the impact of the expansion of the agricultural frontier on soil microbial communities in the Gran Chaco region in South America; therefore, the objective of this study was to explore how soil microbial communities respond to land‐use changes in a semiarid region of Argentina. The land uses selected were total and selective clearing with livestock (TC‐livestock and SC‐livestock), total clearing with agriculture (TC‐agriculture), and an undisturbed site (R‐Chancaní). Our results suggest that microbial abundances were strongly influenced by seasonal changes. In both seasons, the lowest values of total microbial biomass were observed in TC‐agriculture and TC‐livestock. In the wet season, TC‐agriculture had the lowest fungal abundance, and both total clearing sites (TC‐livestock and TC‐agriculture) had higher bacterial abundance than the other sites. Our data also showed that the Shannon and richness indices were highest at the farming sites, indicating a similar tendency in the diversity indexes in both dry and wet seasons. According to Pearson correlation analysis, humic substance (HS) content was a key driver influencing soil microbial communities, demonstrating that high HS content may significantly increase bacteria, fungi, and total phospholipid fatty acids. Microbial composition highly depended on seasonal changes. Overall, our results suggest that land‐use change altered microbial community structure and bacterial diversity, and that HS content played a crucial role in driving changes in soil microbial composition.

Investigation of soil microbiome under the influence of different mulching treatments in northern highbush blueberry

Microbial communities on soil are fundamental for the long-term sustainability of agriculture ecosystems. Microbiota in soil would impact the yield and quality of blueberries since microbial communities in soil can interact with the rhizosphere of plant. This study was conducted to determine how different mulching treatments induce changes in soil microbial composition, diversity, and functional properties. A total of 150 soil samples were collected from 5 different mulch treatments (sawdust, green weed mat, sawdust topped with green weed mat, black weed mat, and sawdust topped with black weed mat) at 3 different depths (bottom, middle, and top region of 20 cm soil depth) from 2 different months (June and July 2018). A total of 8,583,839 sequencing reads and 480 operational taxonomic units (OTUs) of bacteria were identified at genus level. Eight different plant growth promoting rhizobacteria (PGPR) were detected, and the relative abundances of Bradyrhizobium, Bacillus, and Paenibacillus were more than 0.1% among all soil samples. Sampling depth and month of soil samples impacted the amount of PGPR, while there were no significant differences based on mulch type. Functional properties of bacteria were identified through PICRUSt2, which found that there is no significant difference between mulch treatment, depth, and month. The results indicated that sampling month and depth of soil impacted the relative abundance of PGPR in soil samples, but there were no significant differences of functional properties and beneficial microbial communities based on mulch type.

Positive Effects of Crop Diversity on Productivity Driven by Changes in Soil Microbial Composition.

Intensive agriculture has major negative impacts on ecosystem diversity and functioning, including that of soils. The associated reduction of soil biodiversity and essential soil functions, such as nutrient cycling, can restrict plant growth and crop yield. By increasing plant diversity in agricultural systems, intercropping could be a promising way to foster soil microbial diversity and functioning. However, plant–microbe interactions and the extent to which they influence crop yield under field conditions are still poorly understood. In this study, we performed an extensive intercropping experiment using eight crop species and 40 different crop mixtures to investigate how crop diversity affects soil microbial diversity and activity, and whether these changes subsequently affect crop yield. Experiments were carried out in mesocosms under natural conditions in Switzerland and in Spain, two countries with drastically different soils and climate, and our crop communities included either one, two or four species. We sampled and sequenced soil microbial DNA to assess soil microbial diversity, and measured soil basal respiration as a proxy for soil activity. Results indicate that in Switzerland, increasing crop diversity led to shifts in soil microbial community composition, and in particular to an increase of several plant-growth promoting microbes, such as members of the bacterial phylum Actinobacteria. These shifts in community composition subsequently led to a 15 and 35% increase in crop yield in 2 and 4-species mixtures, respectively. This suggests that the positive effects of crop diversity on crop productivity can partially be explained by changes in soil microbial composition. However, the effects of crop diversity on soil microbes were relatively small compared to the effects of abiotic factors such as fertilization (three times larger) or soil moisture (three times larger). Furthermore, these processes were context-dependent: in Spain, where resources were limited, soil microbial communities did not respond to crop diversity, and their effect on crop yield was less strong. This research highlights the potential beneficial role of soil microbial communities in intercropping systems, while also reflecting on the relative importance of crop diversity compared to abiotic drivers of microbiomes and emphasizing the context-dependence of crop–microbe relationships.

A Review on the Impact of Silver Nanoparticles on Soil Microorganisms and Bioremediation as Heavy Metal Removal Technology

The increasing and varied use of silver nanoparticles (AgNPs) as antimicrobial on consumer products increases the risk of the nanomaterial release into the environment and potentially harm beneficial microorganisms in soil. Any change in soil microbial composition will lead to soil quality degradation that eventually reduce crop productivity. The negative effect of AgNPs on soil microorganism has been reported by researchers. There are technologies employed to remove heavy metals from soil such as chemical, physical, and biological technique. However, chemical and physical techniques have some disadvantages e.g high cost and partial removal. Therefore, biological technique including the use of microorganisms (bioremediation) become more favourable. The technique is considered as cost effectiveness and environmentally sustainable method. The present paper summarizes the impact of AgNPs on soil microorganisms and the use of microorganisms (bacteria, fungi, algae, and yeast) to eliminate heavy metals pollution in soil.

Diversity and composition of the Panax ginseng rhizosphere microbiome in various cultivation modesand ages

BackgroundContinuous cropping of ginseng (Panax ginseng Meyer) cultivated in farmland for an extended period gives rise to soil-borne disease. The change in soil microbial composition is a major cause of soil-borne diseases and an obstacle to continuous cropping. The impact of cultivation modes and ages on the diversity and composition of the P. ginseng rhizosphere microbial community and technology suitable for cropping P. ginseng in farmland are still being explored.MethodsAmplicon sequencing of bacterial 16S rRNA genes and fungal ITS regions were analyzed for microbial community composition and diversity.ResultsThe obtained sequencing data were reasonable for estimating soil microbial diversity. We observed significant variations in richness, diversity, and relative abundances of microbial taxa between farmland, deforestation field, and different cultivation years. The bacterial communities of LCK (forest soil where P. ginseng was not grown) had a much higher richness and diversity than those in NCK (farmland soil where P. ginseng was not grown). The increase in cultivation years of P. ginseng in farmland and deforestation field significantly changed the diversity of soil microbial communities. In addition, the accumulation of P. ginseng soil-borne pathogens (Monographella cucumerina, Ilyonectria mors-panacis, I. robusta, Fusarium solani, and Nectria ramulariae) varied with the cropping age of P. ginseng.ConclusionSoil microbial diversity and function were significantly poorer in farmland than in the deforestation field and were affected by P. ginseng planting years. The abundance of common soil-borne pathogens of P. ginseng increased with the cultivation age and led to an imbalance in the microbial community.

Changes in soil microbial community structure and function following degradation in a temperate grassland

Abstract Aims Grassland degradation represents a major challenge in the maintenance of grassland productivity. This process has dramatic impacts on energy flows and soil nutrient dynamics, thus directly or indirectly influencing soil microbes. Here, we aim to (i) examine changes in soil microbial composition, diversity and functionality in response to different levels of grassland degradation (i.e. non-degraded, moderately and severely degraded) in a temperate grassland in Inner Mongolia, and (ii) elucidate biotic and abiotic factors that are responsible for these changes. Methods The composition structure of soil microbial community was determined by high-throughput sequencing. The functionality of bacterial communities was examined using the tool of FAPROTAX, and functional guilds of fungal communities were quantified using the FUNGuild pipeline. Important Findings Grassland degradation significantly decreased soil bacterial diversity but it did not affect fungal diversity. Belowground biomass, soil organic carbon and total nitrogen were positively related to changes in diversity of bacterial community. Grassland degradation significantly increased the relative abundance of Chloroflexi (from 2.48% to 8.40%) and decreased Firmicutes (from 3.62% to 1.08%) of bacterial community. Degradation also significantly increased the relative abundance of Glomeromycota (from 0.17% to 1.53%) and decreased Basidiomycota (from 19.30% to 4.83%) of fungal community. The relative abundance of pathogenic fungi (Didymella and Fusarium) was decreased significantly by degradation. In addition, degradation had a significant impact on putative functionality of soil bacteria related to soil carbon and nitrogen cycling. Our results suggest that soil bacterial community is more sensitive than fungal community in response to degradation in the temperate grassland.

Bark decomposition in white oak soil outperforms eastern hemlock soil, while bark type leads to consistent changes in soil microbial composition

Bark decomposition is an underexamined component of soil carbon cycling and soil community assembly. Numerous studies have shown faster decomposition of leaf litter in “home” environments (i.e. within soil adjacent to the plant that produced the leaves), suggesting potential legacy effects from previous deposition of similar litter. This is expected to occur through, in part, accumulation of microorganisms that metabolize substrates the litter provides. Whether a similar “home-field advantage” (HFA) exists for bark decomposition is unknown, but this dynamic may differ because annual bark deposits to soil are minimal relative to leaf deposits. We hypothesized that (1) as with leaf litter, bark will be better decomposed near to the tree from which it was collected, and (2) that decomposing bark can initiate change in soil microbial composition. To test these hypotheses, we used a full factorial design that included two bark types (collected from eastern hemlock, Tsuga canadensis, and white oak, Quercus alba) and two soil types (‘home’ and ‘away’) within a temperate mixed hardwood forest at the Shale Hills Catchment in central Pennsylvania, USA. Bark was excised from 25 replicates of each tree type, buried in either home or away soil, and incubated belowground from July 2017 to June 2018. Decomposition was assessed through proportionate mass loss over time, while microbial composition in the bark and adjacent soil was assessed through high-throughput sequencing of 16S rRNA gene and fungal ITS fragments. Overall, bark degraded faster in white oak soils, and there was also an effect of bark type on decomposition. Although white oak bark decomposed more quickly in its home environment, this could be due to either soil conditioning or inherent differences in the soils in which each species grows. Soil microbial assemblages also sorted according to bark type rather than soil type, suggesting that bark strongly influences the composition of nearby microorganisms during decomposition. Our results suggest that both bark type and soil type are important factors during bark decomposition, but our findings suggest no clear evidence for HFA.

Soil nutrient and microbial activity responses to two years after maize straw biochar application in a calcareous soil

Biochar (BC) addition to soil is a strategy to enhance soil fertility, which may also affect microbial activity. However, little information is available on the responses of soil nutrients and microbial activities to BC in a calcareous soil. This study investigated the changes of soil nutrient contents and microbial activities in a calcareous soil two years after application of biochar at rate of 0, 2.5, 7.5 and 22.5 t/ha. The results showed that the contents of soil organic carbon (SOC), total nitrogen (TN), dissolved organic carbon (DOC), total dissolved nitrogen (TDN), and available phosphorus and potassium increased significantly with increasing BC addition rate, but no significant effect on soil pH. Soil microbial biomass carbon and nitrogen (MBC and MBN) had an increased and then decreased trend. BC amendment increased microbial biomass and promoted soil carbon- and nitrogen-cycling enzyme activities, the ratios of β-glucosaminidase/phosphomonoesterase, N-acetyl-β-glucosaminidase plus leucine aminopeptidase/phosphomonoesterase increased significantly with increasing BC addition rate. Redundancy analysis confirmed that DOC and MBN were dominant factors affecting soil microbial biomass, and soil pH, TDN, DOC, MBN and SOC were main factors regulating soil enzyme activities. Besides, principal component analysis revealed that difference in microbial community composition in one year after BC addition was mainly associated with the relative abundance of bacteria and fungi, the relative abundance of bacteria increased, while the ratios of Gram-negative/Gram-positive bacteria and fungi/bacteria, and relative abundance of fungi and arbuscular mycorrhizal fungi decreased in BC-amended soils with control. However, BC had no significant effect on microbial community composition after two years. These results suggest that application of maize BC to calcareous soils may have a great potential for improvements in the soil nutrients and enzyme activity, the changes in soil microbial composition deserve further studies.

Vertical changes of soil microbial properties in claypan soils

Microbial activity within the soil is critical for plant growth and development, and a major determinant of crop performance and yield. Claypan soils are characterized by a dense, impermeable subsoil that impedes root system development. Little is known about soil microbial properties in claypan soils or how microbial activity changes with depth in the soil profile. We explored how management practices mediate changes in soil microbial composition and potential enzyme activities with depth in a claypan soil. The soil microbial biomass and composition were examined through phospholipid fatty acid (PLFA) assay. We found that the soil organic carbon (SOC), microbial biomass, and oxidative enzyme activities declined with depth, while hydrolase activity increased in the upper layer of the claypan. Changes in soil management practices affected the degree of increase in hydrolase activity in subsoils, especially for N-acetyl-β-d-glucosaminidase. No accumulation of SOC in the claypan layer was observed. Contrary to our expectation, soil microbes deeper within the soil profile were phosphorus- and nitrogen-limited rather than carbon-limited. Vertical stratification of measured soil properties was found with an upper layer from 0 to 15 cm, an intermediate layer between 15 cm and approximately 30 cm, and the lowest layer of soils in the claypan below 30 cm. The interaction between clay content and changes in soil factors with depth resulted in an increased potential activity but unaltered microbial composition in the claypan layer.

Recycling organic residues in agriculture impacts soil-borne microbial community structure, function and N2O emissions

Recycling residues is a sustainable alternative to improve soil structure and increase the stock of nutrients. However, information about the magnitude and duration of disturbances caused by crop and industrial wastes on soil microbial community structure and function is still scarce. The objective of this study was to investigate how added residues from industry and crops together with nitrogen (N) fertiliser affect the microbial community structure and function, and nitrous oxide (N2O) emissions. The experimental sugarcane field had the following treatments: (I) control with nitrogen, phosphorus, and potassium (NPK), (II) sugarcane straw with NPK, (III) vinasse (by-product of ethanol industry) with NP, and (IV) vinasse plus sugarcane straw with NP. Soil samples were collected on days 1, 3, 6, 11, 24 and 46 of the experiment for DNA extraction and metagenome sequencing. N2O emissions were also measured. Treatments with straw and vinasse residues induced changes in soil microbial composition and potential functions. The change in the microbial community was highest in the treatments with straw addition with functions related to decomposition of different ranges of C-compounds overrepresented while in vinasse treatment, the functions related to spore-producing microorganisms were overrepresented. Furthermore, all additional residues increased microorganisms related to the nitrogen metabolism and vinasse with straw had a synergetic effect on the highest N2O emissions. The results highlight the importance of residues and fertiliser management in sustainable agriculture.

Comparative effects of prolonged freshwater and saline flooding on nitrogen cycling in an agricultural soil

Due to climate change, the frequency and duration of flood events are predicted to increase in many regions of the world. This is expected to cause large changes in soil functioning and to a progressive decline in soil quality such as reduced rates of nutrient cycling, enhanced greenhouse gas emissions and loss of soil biodiversity. There is a knowledge gap, however, on how temperate agricultural soils under different management practices (e.g. manure application) respond to prolonged river or coastal flooding. The main objective of this work was to determine the effects of a simulated prolonged flooding with saline and freshwater on soil N cycling, following application of a low C:N organic amendment (broiler litter) at two temperatures, representative of a winter and a spring flood event. Using laboratory mesocosms we simulated prolonged winter (6 °C) and spring (14 °C) flooding of soil amended with broiler litter. We also compared the effects of inundation with either river (freshwater) or coastal (saline) water. An agricultural grassland soil (Eutric Cambisol) was subjected to different combinations of treatments (flood with fresh or saline water, winter vs spring temperatures, with/without poultry manure). The impact of these treatments on soil solution N dynamics, greenhouse gas emissions (CO2, CH4, N2O) and microbial community structure (by PLFA analysis) were evaluated over an 11 week simulated flood event followed by an 8 week soil recovery period (without flood). Overall, potential losses of NH4+ and cumulative GHG emissions were increased by flooding and the presence of manure. CH4 emissions were found to dominate under freshwater flooding conditions and N2O under saline flooding. Significant releases of GHG occurred during both flooding and after floodwater removal. Temperature was less influential on regulating GHG under the different treatments. These releases in GHG were associated with disruption in N cycling and changes in soil microbial composition and these changes persisted after floodwater removal. Extreme flooding negatively impacts soil functioning, however, the magnitude of any changes remain critically dependent on flood duration and source of flood water, and management conditions. Further work is required at the field scale to understand the molecular basis of the responses observed in this study.

PH and substrate regulation of nitrogen and carbon dynamics in forest soils in a karst region of the upper Yangtze River basin, China

Nitrogen (N) is the most limiting nutrient for forest development. In this study, using a natural pH gradient, N and carbon (C) mineralization was investigated and the effects of soil pH as well as the total C and N contents and the soil C/N ratio were evaluated in forest soils after mountain closure in a karst region. The N availability was poor based on the low N mineralization potential (N0) and the low active fraction of soil total N (N0/total N), while high microbial decomposition activity was indicated by a high mineralization rate constant (kN). N0 was positively correlated with soil pH as well as the total C and N contents. Additionally, multiple regression analysis revealed that total CN (the product of the soil total C and total N contents) and the C/N ratio had more significant effects on N0 than soil pH. In contrast, the mineralization rate constants kN and kC were positively affected by soil pH. The results indicated that N availability was regulated by soil organic matter (SOM), while microbial activity was restricted by soil pH. Also, the lack of nitrification and the high C0/N0 ratio observed at soil pH <5.5 may be a strong indicator of alterations to the microbial composition prompted by severe soil acidification. Further research is required to determine the changes in soil microbial composition with the drop in soil pH and their effects on SOM decomposition and nutrient availabilities.

Effects of Straw Mulching and Little- or Zero-tillage on Microbial Diversity and Biomass C and N of Alluvial Soil in Chengdu Plain, China*

Soil microbes are considered one of the most important indexes of soil quality.Aiming to illustrate the mechanism and effect of straw mulching and little-or zero-tillage on soil quality,the changes in soil microbial composition,microbial biomass C and N,and soil fertility in paddy soils in the Chengdu Plain(Wenjiang County,Sichuan,China) were investigated through a fixed field experiment on rice and wheat/rape rotation(2003～2008).The results indicated that because of the increase of soil bacteria after straw mulching,the total microorganisms of ST(straw mulching and tillage) soil and SNT(straw mulching and no-tillage) soil increased by 51.7% and 12.8%,respectively,than CK(no straw mulching and tillage),which can improve rates of straw decomposition and nutrient release.Meanwhile,the total soil microorganisms changed at different growth stages of wheat,and the soil microorganisms at tillering stage were significantly more than those at seeding stage and maturity stage.The soil microbial biomass C of ST and SNT increased by 74.1% and 25.8%,respectively,and the soil microbial biomass N of ST and SNT increased by 60.2% and 12.1% as well,compared with the CK.Therefore,straw mulching can increase soil microbial composition and biomass remarkably,promote soil nutrient circulation and translation,increase soil organic matter content,and improve soil quality.

Microbial biomass and activity along a natural pH gradient in forest soils in a karst region of the upper Yangtze River, China

Mountain closure, considered an effective and economic measure for natural restoration of degraded forest ecosystems, has been widely carried out in the karst region of southwest China. The aim of this study was to evaluate microbial aspects of soil quality after mountain closure by analyzing soil microbial biomass, basal respiration, metabolic quotient, and relationships with basic chemical properties in Guizhou Province, a karst region of the upper Yangtze River. Soil quality was considered poor from the low levels of microbial biomass carbon (MBC), nitrogen (MBN), and microbial quotient (MBC/total C and MBN/total N), but high metabolic quotient (qCO2). Soil pH, showing marked variation from 4.1 to 7.9 in this karst region, was proved to significantly affect soil microbial biomass and activity. Soil microbial biomass, microbial quotient, and soil basal respiration declined significantly with decreasing soil pH, while qCO2 showed an apparently increasing, but not statistically significant, trend. The changes in microbial biomass and activity following the change in soil pH could possibly be because of a change in soil microbial composition, and more detailed research is necessary. Compared with soil pH, soil organic matter content was another, more important, factor that directly restricted microbial growth because of the serious loss as a result of disturbance. As a practical application based on microbial aspects, introduction of some N-fixing tree species may be an active and effective measure to improve soil fertility and thus to accelerate restoration of the forest ecosystem in the karst region.

Characterization of developing microbial communities in Mount St. Helens pyroclastic substrate

The 1980 eruption of Mount St. Helens created a unique opportunity to study microbial communities in a developing soil ecosystem containing little total carbon (C) or total nitrogen (N). We collected surface samples (0–5 cm) from areas near Mount St. Helens National Volcanic Monument 17 years after the eruption. The samples were from bare soil with no plant development, soil under living prairie lupine ( Lupinus lepidus) and dead prairie lupine in the pyroclastic plain near Spirit Lake, Washington. We also collected soil from a nearby forested area. Phospholipid fatty acids (PLFAs) from pyroclastic materials were analyzed to determine changes in soil microbial composition. Total bacterial DNA was also extracted from the soils and denaturing gradient gel electrophoresis (DGGE) of 16S rRNA genes and DNA sequence analysis of cloned 16S rRNA gene libraries were used to determine the influence of plants on microbial development. Both principal components analysis (PCA) of PLFA fingerprints and non-metric multidimensional scaling (NMS) of DGGE fingerprints distinguished the four soils. Lupine plants influenced the PLFA and DGGE fingerprints depending on the distance of the samples from the plant. DGGE and PLFA profiles from the forest soil were significantly different ( P=0.001, based on Monte Carlo permutation test) from those of the bare soil and soil with live lupine. Bacterial clone libraries were constructed, and 800 clones were analyzed by amplified ribosomal DNA restriction analysis (ARDRA) and grouped into operational taxonomic units (OTUs). A total of 51, 77, 58, and 42 different OTUs were obtained from forest soil, soil with live and dead lupine, and bare soil, respectively. Phylogenetic analysis revealed that 62% of the 228 OTUs were classified as Proteobacteria, Actinobacteria, Acidobacterium, Verrucomicrobia, Bacteroides, Cyanobacteria, Planctomycetes, and candidate divisions TM7 and OP10. Members of Proteobacteria represented 29% of the OTUs. Thirty-eight percent of the OTUs could not be classified into known bacterial divisions. This study emphasized the role of prairie lupine in the establishment of pioneering microbial communities and the subsequent roles the biotic components played in improving the quality of pyroclastic soil.

Altered soil microbial community at elevated CO(2) leads to loss of soil carbon.

Increased carbon storage in ecosystems due to elevated CO(2) may help stabilize atmospheric CO(2) concentrations and slow global warming. Many field studies have found that elevated CO(2) leads to higher carbon assimilation by plants, and others suggest that this can lead to higher carbon storage in soils, the largest and most stable terrestrial carbon pool. Here we show that 6 years of experimental CO(2) doubling reduced soil carbon in a scrub-oak ecosystem despite higher plant growth, offsetting approximately 52% of the additional carbon that had accumulated at elevated CO(2) in aboveground and coarse root biomass. The decline in soil carbon was driven by changes in soil microbial composition and activity. Soils exposed to elevated CO(2) had higher relative abundances of fungi and higher activities of a soil carbon-degrading enzyme, which led to more rapid rates of soil organic matter degradation than soils exposed to ambient CO(2). The isotopic composition of microbial fatty acids confirmed that elevated CO(2) increased microbial utilization of soil organic matter. These results show how elevated CO(2), by altering soil microbial communities, can cause a potential carbon sink to become a carbon source.