Responses Of Microbial Community Composition Research Articles

Comparative Study on the Effects of Different Soil Improvement Methods in Blueberry Soil

Soil improvement methods can result in changes in the microbial community in blueberry soil. Bacterial communities play an important role in soil fertilizer and plant nutrient acquisition. In this study, the response of microbial community composition, microbial function, and the nitrogen (N) cycle to different improvement methods was analyzed using high-throughput sequencing to investigate the best soil improvement method from a microbial perspective. The results showed that the highest microbial diversity was observed in the treatment involving peat combined with mushroom bran (T2), followed by the peat combined with acidified rice husk (T2) both in the rhizosphere and roots. The dominant phyla were Proteobacteria and Actinobacteria both in the blueberry rhizosphere soil and roots. Interestingly, Acidobacterium and Paludibaculum, belonging to the Acidobacteria phylum, exhibited the most significant influence and were most predominant in the T2 treatment rhizosphere soil. The T2 treatment promoted the growth of N fixation functional bacteria both in the rhizosphere soil and roots. At the module level, the T2 treatment enhanced N fixation and suppressed the assimilatory and dissimilatory nitrate reduction reactions, denitrification, and nitrification in the blueberry rhizosphere. Additionally, the T2 treatment increased the abundance of root endophytic microbes involved in N fixation. Overall, our findings suggest that the addition of peat combined with acidified rice husk is the optimal soil improvement method for blueberry cultivation.

Response of microbial community composition and function to land use in mining soils of Xikuang Mountain in Hunan.

Nine land types in the northern mining area (BKQ) (mining land, smelting land, living area), the old mining area (LKQ) (whole-ore heap, wasteland, grassland), and southern mining area (NKQ) (grassland, shrubs, farmland) of Xikuang Mountain were chosen to explore the composition and functions of soil bacterial communities under different habitats around mining areas. The composition and functions of soil bacterial communities were compared among the sampling sites using 16S rRNA high-throughput sequencing and metagenomic sequencing. α diversity analysis showed the soil bacterial diversity and abundance in the old mining area were significantly higher than those in the northern mining area. β diversity analysis demonstrated that the soil bacterial community composition was highly similar among different vegetation coverages in the southern mining area. Microbial community function analysis showed the annotated KEGG function pathways and eggNOG function composition were consistent between the grassland of the old mining area and the grassland of the southern mining area. This study uncovers the soil bacterial community composition and functions among different habitats in the mining areas of Xikuang Mountain and will underlie soil ecosystem restoration in different habitats under heavy metal pollution around the mining areas there.

Soil Nutrient Availability Regulates Microbial Community Composition and Enzymatic Activities at Different Soil Depths along an Elevation Gradient in the Nanling Nature Reserve, China

Improving our understanding of how soil microbial community composition and enzyme activities vary with elevation will elucidate the impact of climate change on ecosystem function. We collected soil samples at three elevations (1000 m, 1200 m, 1400 m) from two soil depths in a subtropical forest in the Nanling Nature Reserve to analyze soil nutrient availability and the Gram-positive (GP) to Gram-negative (GN) bacteria ratio. We conducted a vector analysis of soil enzymatic stoichiometry to examine the spatial distribution of soil microbial C, N, and P limitations. The soil C:N ratio decreased with increasing elevation. The GP:GN ratio and vector length (read-outs of relative C versus nutrient limitation) were the highest at 1400 m due to lower C availability. At an elevation of 1200 m, lower P availability was reflected in higher soil C:P and N:P ratios and lower GP:GN ratios, as lower P availability suppressed microbial C decomposition. Furthermore, the GP:GN ratio and vector length showed contrasting responses to variations in soil depth. The validation of enzyme vector analysis to capture the responses of microbial community composition to soil properties is dependent on environmental conditions and should be considered in the development of future soil organic C (SOC) dynamics models.

Responses of microbial community composition and respiration to soil moisture in eroded soil

Soil moisture (SM) is one of the most limited factors on the Loess Plateau, but its effects on the microbial community and respiration are still unclear. To investigate the effects of stepwise wetting and constant SM on the soil microbial community and respiration rates, eroded soil under afforestation on the Loess Plateau was examined. The soils were sampled and incubated with constant gravimetric SM of 5 %, 30 % and 45 % and wetting treatments with SM increasing from 5 % to 30 % (5–30 %), from 5 % to 30 % to 45 % (5–30–45 %) and from 30 % to 45 % (30–45 %). As shown in the results, bacterial richness and Shannon diversity were lower in the wetting treatments of 5–30 % and 5–30–45 % than those in 5 %, 30 % and 45 % SM constant treatments. Contrary, the values were similar in the 30 % SM constant and the 30–45 % SM wetting treatment, which were the highest among all the treatments. The dominant bacterial species converted from Actinobacteria to Alphaproteobacteria and Acidobacteria with SM increasing. No significant differences were observed in fungal Shannon diversity, richness and communities under varying conditions. Consequently, the wetting treatments influenced the bacteria more significantly than fungi. A greater Birch effect occurred with a two-step increase in SM (i.e., 5–30–45 %) than the one-step wetting treatment (i.e., 30–45 %), while a dampened Birch effect was observed with higher previous soil respiration. However, excessive moisture did not enhance or even inhibit microbial respiration. Our work indicated that even short-term changes in the antecedent SM can significantly affect bacterial communities and dynamic of carbon flux. The responses of microbe and respiration were not only dependent on the current SM but also related to the antecedent SM condition. This study benefits plant-soil-water relationship management during afforestation on the Loess Plateau of China.

Biochar and biochar-polylactic acid composite enhance biodegradation of hexachlorobenzene in soil by altering microbial community

It is of great scientific and practical importance to explore the mechanisms of accelerated degradation of hexachlorobenzene (HCB) in soil. However, the response of microbial community composition and structure, and their links to anaerobic reductive dechlorination in paddy soils remains unclear yet. We examined impacts of biochar and biochar-polylactic acid composite addition on the diversity, composition, and structure of soil prokaryotic community and their different contribution to HCB anaerobic dechlorination. The results showed that both biochar and biochar-polylactic acid composite addition could promote HCB dechlorination in paddy soils. Soil prokaryotic community richness and diversity were not significantly impacted by biochar but were remarkably affected by biochar-polylactic acid composite amendment. Random forest analysis and structural equation models indicated that the relative abundance of indicator taxa, soil Eh, and Fe2+ content best explained (p < 0.01) the HCB dechlorination with biochar addition, while soil Eh, Fe2+ content, and microbial diversity were the most important predictors of HCB dechlorination with biochar-polylactic acid composite addition. Together, our findings suggest that biochar amendment promoted anaerobic dechlorination of HCB in paddy soils by increasing the relative abundance of specific bacterial genera, while biochar-polylactic acid composite promoted HCB dechlorination by enhancing microbial community diversity. Therefore, biochar and biochar-polylactic acid composite showed distinct effect on the composition and diversity of soil prokaryotic community and different contribution to HCB dechlorination. Overall, our results suggested that biochar-polylactic acid composite could be used as soil remediation material to efficiently accelerate dechlorination of HCB.

Responses of microbial community composition and function to biochar and irrigation management and the linkage to Cr transformation in paddy soil

Combining biochar with irrigation management to alter the microbial community is a sustainable method for remediating soils contaminated by heavy metals. However, studies on how these treatments promote Cr(VI) reduction are limited, and the corresponding microbial mechanisms are unclear. Therefore, we conducted a pot experiment to explore the responses of soil microbial communities to combined biochar amendment and irrigation management strategies and their involvement in Cr transformation in paddy soils. Six treatments were established using varying concentrations of biochar (0, 1, and 2% [w/w]) combined with two irrigation management strategies (continuous flooding [CF] and dry–wet alternation [DWA]). The results showed that the combined biochar addition and irrigation management strategy significantly altered soil pH, redox potential, organic matter content, and Fe(II) and sulfide concentrations. In addition, the Cr(VI) concentration under CF irrigation management was conspicuously lower (48.2–54.4%) than that under DWA irrigation management. Biochar amendment also resulted in a substantial reduction (8.8–27.4%) in Cr(VI) concentration. Moreover, the changes in soil physicochemical properties remarkably affected the soil microbial community. The microbial diversity and abundance significantly increased with biochar amendment. Furthermore, the combined biochar amendment and CF strategy stimulated the growth of Geobacter- and Anaeromyxobacter-related Fe(III)-reducing bacteria, Gallionella-related Fe(II)-oxidizing bacteria, and Desulfovibro- and Clostridium-related sulfate-reducing bacteria, which simultaneously facilitated the generation of Fe(II) and sulfide, thereby enhancing Cr(VI) reduction. Consequently, our results suggest that the effectively increased abundance of Fe-reducing/oxidizing bacteria and sulfate-reducing bacteria via combined CF irrigation management and biochar addition may be a key factor in reducing Cr(VI) in paddy soil. The keystone genera responsible for Cr(VI) reduction were Geobacter, Anaeromyxobacter, Gallionella, Desulfovibro, and Clostridium. This study provides novel insights into the coupling mechanism of the Fe/S/Cr transformation mediated by Fe-reducing/oxidizing bacteria and sulfate-reducing bacteria.

Passive Treatment for Acid Mine Drainage Partially Restores Microbial Community Structure in Different Stream Habitats

The assessment of the degree to which biological communities in streams impaired by acid mine drainage (AMD) are restored by passive treatment has focused primarily on eukaryotic-cell organisms and microbial processes. The responses of microbial community structure to passive treatment have received much less attention, even though functional processes such as nutrient cycling and organic matter decomposition depend on taxonomic composition. Our objective was to determine the degree to which passive treatment restored microbial communities in three types of habitats: aqueous, leaf, and sediment. To assess their recovery, we compared the community composition in these habitats based on 16S rRNA gene sequencing at three different stream sites: an untreated AMD site (U), a remediated site below AMD passive treatment (T), and an unimpaired reference site (R). The acidity, conductivity, and soluble metal concentrations at T were found to be elevated compared to R, but generally 1–2 orders of magnitude less than at U. Microbial community composition was found to be synergistically affected by habitat type and AMD impact, with the similarity among communities in the three habitats increasing with the severity of the AMD. Sediment- and leaf-associated microbial communities at U were characterized by taxa that are tolerant to severe AMD. The absence of the nitrogen oxidizing bacterium Nitrospira in sediment communities at T and U was found to correspond to higher NH4+ concentrations compared to R, possibly because of the presence of iron oxyhydroxide precipitate. In contrast, the microbial composition was found to be similar between the T and R sites for both aqueous and leaf communities, indicating that passive treatment was more able to restore these communities to the reference condition than sediment communities. The remediation of AMD streams should consider the habitat-specific responses of microbial community composition and be guided by future studies that empirically couple changes in taxonomic composition to measured functional processes.

Response of microbial community composition and function to emergent plant rhizosphere of a constructed wetland in northern China

To understand the mechanisms by which emergent plants influence the microbial communities in wetland sediments, we analyzed the response of microbial composition, abundance, metabolic activity, and metabolic genes to three emergent plant species [Cyperus alternifolius L. (Cyp), Typha angustifolia L. (Typ), and Phragmites australis (Cav.) Trin. ex Steud. (Phr)], and determined the important physicochemical properties of the soils and root exudates in Zhaoniu River Constructed Wetland in northern China. We found the composition of both the microbial communities and the metabolic genes differed between rhizosphere and non-rhizosphere sediments. The rhizosphere microbial abundance in Phr in summer was significantly higher than in the other two plants and in the non-rhizosphere. The rates of microbial respiration and ammonia oxidation in rhizosphere sediments were significantly higher than those in non-rhizosphere sediments. Our statistical analyses showed that the total organic carbon (TOC) concentration in root exudates and the oxidation–reduction potential (ORP) significantly influenced the differences in the composition, abundance, and metabolic activities of the microbial community and metabolic genes between rhizosphere and non-rhizosphere sediments, suggesting that the secretion of root exudates and oxygen by emergent plants was the main mechanism affecting the composition and function of the microbial community. As the result of the high levels of TOC and the ORP, the rhizosphere sediments showed relatively high abundances of the genes related to biodegradation of xenobiotic compounds. By contrast, non-rhizosphere sediments showed relatively high abundances of genes related to carbon fixation and sulfate reduction, possibly due to the low levels of TOC and ORP. Plants with an enhanced ability to secrete root exudates and oxygen, such as Phr, should be preferred in constructed wetlands to increase the metabolic activity of sediment microbial communities. This study extends our understanding of the mechanisms by which the plant rhizosphere affects the ecological functions of wetlands.

Response of microbial community composition in soils affected by coal mine exploitation

Surface mining activities, despite their benefits, lead to the deterioration of local and regional environmental quality and play a role in global ecosystem pollution. This research aimed to estimate the culturable microbial population structure at five locations near the opencast coal mine "Kakanj" (Bosnia and Herzegovina) via agar plate and phospholipid fatty acids (PLFA) method and to establish its relationship to the physical and chemical properties of soil. Using the ICP-OES method, the heavy metal pollution of all examined locations (overburden, former grass yard, forest, arable soil, and greenhouse) was observed. Substantial variations among the sites regarding the most expressed indicators of heavy metal pollution were noted; Cr, Pb, Ni, and Cu content ranged from 63.17 to 524.47, 20.57 to 349.47, 139.13 to 2785.67, and 25.97 to 458.73mg/kg, respectively. In the overburden sample, considerable low microbial activity was detected; the bacterial count was approximately 6- to 18-fold lower in comparison with the other samples. PLFA analysis showed the reduction of microbial diversity, reflected through the prevalence of normal and branched saturated fatty acids, their ratio (ranged from 0.92 to 7.13), and the absence of fungal marker 18:2ω6 fatty acid. The principal component analysis showed a strong negative impact of heavy metals Na and B on main microbial and PLFA profiles. In contrast, stock of main chemical parameters, including Ca, K, Fe, and pH, was positively correlated with the microbial community structure.

Effect of Different Fertilization Practices on Soil Microbial Community in a Wheat–Maize Rotation System

Little information is known about the effects of different fertilization practices on soil microbiome in intensively managed crop rotations. The objective of this research was to investigate the response of microbial community composition (phospholipid fatty acid, PLFA) and extracellular enzyme activity to fertilization treatments through a three-year experiment. Treatments were: Control (without fertilizer, CK), chemical fertilizer (NPK), NPK + pig manure (NPKM), NPK + straw (NPKS), and NPK + both manure and straw (NPKMS). We found that fertilization had no effect on the microbial abundance except arbuscular mycorrhizal fungi (AMF) PLFA. Soil microbial community composition was significantly affected by crop species and to a lesser extent by fertilization, with a greater influence on the wheat harvest. In addition, soil enzyme activities were enhanced by fertilization, especially in wheat season. Over three years, compared with NPK treatment, addition of organic manure or straw (NPKS and NPKMS) significantly increased the activities of the enzymes except invertase and urease, and the effect was greater at wheat harvest than the maize harvest. Our results indicate that the response of soil microbial community structure and enzyme activities to fertilization takes precedence than microbial biomass in the short term. The temporal variation in soil microbial community structure and enzyme activities in the crop rotation indicate that crop species may be carefully considered for sustainable agricultural intensification management.

Microbial responses to temperature sensitivity of soil respiration in a dry fallow cover cropping and submerged rice mono-cropping system

Soil heterotrophic respiration (SHR) increases exponentially with temperature and this general information has been incorporated into soil carbon models. However, the positive feedback of warming to SHR remains uncertain, mostly due to the differential response of soil microbial community to warming under dry and flooded conditions in a rice mono-cropping system. In this study, we aimed to evaluate the relationship between SHR and microbial functional groups during the fallow and flooded rice cultivation seasons under changing temperature in a rice mono-cropping system. Field experiments were conducted to investigate SHR, soil microbial functional groups and biomass, and temperature sensitivity of SHR (Q10) under dry fallow conditions during the cover cropping season and under flooded conditions during the rice cropping season. We found that SHR increased with increasing air and soil temperature, carbon availability, and soil microbial community composition and biomass in the fallow season, whereas a decrease in SHR in spite of an increase in temperature and carbon availability was observed under flooded conditions during the rice cropping season. Furthermore, a nonlinear response of microbial community composition and biomass with SHR was noticed during the flooded rice cropping season. This suggests that flooding could be the limiting factor for temperature sensitivity of SHR as well as microbial community composition in a rice mono-cropping system. Flooding the soil significantly (p < 0.01) decreased Q10. We therefore conclude that temperature, moisture region and carbon availability, rather than only soil microbial community composition are responsible for the spatiotemporal variation in SHR in a rice mono-cropping system in this region.

Soil pH rather than nutrients drive changes in microbial community following long-term fertilization in acidic Ultisols of southern China

Long-term intensive cultivation and heavy fertilization improve the nutritional conditions in acidic Ultisols, but also sharply accelerate soil acidification. However, the impact of such dramatic environmental changes on soil microorganisms is unclear. The aims of this work were to investigate the responses of microbial community composition and metabolic function to long-term fertilization, and to determine the key factors that primarily drive microbial changes in acidic Ultisols. A long-term fertilization experiment under a winter wheat–summer maize rotation was established in 1990 in acidic Ultisols of southern China. Soils were collected from four treatments in June 2014: (1) non-fertilization control (CK); (2) only N fertilization (N); (3) N, P, and K fertilization (NPK); and (4) NPK plus manure (NPKM; 70% of total N obtained from manure). The amount of N used in all N treatments was 300 kg N ha−1 year−1. The soil pH, cation exchange capacity (CEC), soil organic carbon (SOC), total nitrogen (TN), phosphorus (TP) and potassium (TK), available nitrogen (AN), phosphorus (AP), and potassium (AK) were measured. Soil microbial community composition and metabolic function were determined by phospholipid fatty acids analysis (PLFA) and community-level physiological profile (CLPP) method, respectively. Compared with CK, NPKM significantly increased total PLFA biomass and average well color development (AWCD); NPK increased total PLFA biomass by 2.2 times, but its AWCD was not significantly different from CK, indicating that microbial metabolic efficiency in NPK decreased. N decreased total PLFA biomass by 27.9%, while almost completely inhibiting metabolic activity. NPKM maintained microbial functional diversity indexes at similar levels as CK, while NPK and N significantly decreased microbial functional diversity indexes. Redundancy analysis (RDA) revealed that soil microbial community composition and metabolic pattern were more stably maintained by application of manure compared to chemical fertilizers. Soil pH showed the primary effect on microbial community composition, metabolic activity, and functional diversity indexes. This research demonstrated that the negative effects of Ultisol acidification induced by long-term application of chemical N fertilizer on microorganisms overwhelmed the positive effects of soil nutrition improvement. The inhibiting effect of serious acidification on microbial metabolic function was stronger than that on community composition. Microorganisms live in a low active metabolic state to resist serious Ultisols acidification. Therefore, fertilization in acidic Ultisols should be based on the premise of preventing soil further acidification.

Responses of Microbial Community Composition to Temperature Gradient and Carbon Steel Corrosion in Production Water of Petroleum Reservoir.

Oil reservoir production systems are usually associated with a temperature gradient and oil production facilities frequently suffer from pipeline corrosion failures. Both bacteria and archaea potentially contribute to biocorrosion of the oil production equipment. Here the response of microbial populations from the petroleum reservoir to temperature gradient and corrosion of carbon steel coupons were investigated under laboratory condition. Carbon steel coupons were exposed to production water from a depth of 1809 m of Jiangsu petroleum reservoir (China) and incubated for periods of 160 and 300 days. The incubation temperatures were set at 37, 55, and 65°C to monitoring mesophilic, thermophilic and hyperthermophilic microorganisms associated with anaerobic carbon steel corrosion. The results showed that corrosion rate at 55°C (0.162 ± 0.013 mm year-1) and 37°C (0.138 ± 0.008 mm year-1) were higher than that at 65°C (0.105 ± 0.007 mm year-1), and a dense biofilm was observed on the surface of coupons under all biotic incubations. The microbial community analysis suggests a high frequency of bacterial taxa associated with families Porphyromonadaceae, Enterobacteriaceae, and Spirochaetaceae at all three temperatures. While the majority of known sulfate-reducing bacteria, in particular Desulfotignum, Desulfobulbus and Desulfovibrio spp., were predominantly observed at 37°C; Desulfotomaculum spp., Thermotoga spp. and Thermanaeromonas spp. as well as archaeal members closely related to Thermococcus and Archaeoglobus spp. were substantially enriched at 65°C. Hydrogenotrophic methanogens of the family Methanobacteriaceae were dominant at both 37 and 55°C; acetoclastic Methanosaeta spp. and methyltrophic Methanolobus spp. were enriched at 37°C. These observations show that temperature changes significantly alter the microbial community structure in production fluids and also affected the biocorrosion of carbon steel under anaerobic conditions.

Variations in soil microbial community composition and enzymatic activities in response to increased N deposition and precipitation in Inner Mongolian grassland

It has been predicted that the precipitation and atmospheric nitrogen (N) deposition will increase in northern China. Though a variety of publications have documented the effects of increased precipitation and N deposition on aboveground plant community, the responses of soil microbial community composition and function to these possible global changes still remain largely unknown. In this study, we take advantage of a long-term (9-year) field experiment that was established in a typical steppe in Inner Mongolia, China. The responses of microbial community composition and soil enzymatic activities to simulated N deposition and increased precipitation were examined. It was found that the low level of N addition showed no influence on the relative abundance of bacteria, but the relatively high N deposition increased the relative abundance of bacteria. The increased precipitation in combination with N addition, estimated at all N levels, significantly decreased the relative abundance of fungi and fungi/bacteria ratio. Increased precipitation played important roles in enhancing microbial activity in this semi-arid region. It was observed that water supply increased the activities of the five of the enzymes determined, including peroxidase (PER), polyphenol oxidase (PPO), β-Glucosidase (BG), protease (PRO) and alkaline phosphomonoesterase (alkaline PME). The activity of cellulase was reduced by long-term increased precipitation treatment, but was stimulated by simulated N deposition, which may due to the changes in litter components under projected climate change. The influences of N deposition on the microbial enzymatic activities might be alleviated (such as PER), strengthened (acid PME), or not affected by the projected precipitation increment. We also found that the overall changes in soil enzymatic activity patterns are more sensitive to environmental changes than the variations in soil microbial community composition, which may be explained by the microbial function redundancy and the limitations of research method. By all accounts, in future scenarios of increased precipitation in combination with N deposition, the proportion of soil fungi would be reduced, and the microbial community composition might be shifted to be bacteria-dominant. We also predicted that with the increasing of N deposition level, the activities of cellulolase would be enhanced, whereas the activities of ligninolytic enzymes (PER and PPO) would be reduced sharply.

Shifts in microbial biomass and community composition in subtropical paddy soils under a gradient of manure amendment

To study the responses of microbial community composition to excessive manure amendment and their relationships with soil nutrients, a pot experiment was conducted using soils of different fertilities under a gradient (0–44.8 Mg ha–1) of manure amendment. After four rice-growing seasons, the soil nutrients were enriched by intense manure amendment, especially the phosphorus (P) content, and the P-related nutrient stoichiometry was altered. The total P content increased by 1.51 and 1.09 g kg–1 with the highest manure input in fertile and infertile soils, respectively. For the two soils, both the carbon (C)-to-P and nitrogen (N)-to-P ratios decreased up to around 55 and 4, respectively, by increasing amendment rates from 0 to 44.8 Mg ha–1. The microbial biomass C (MBC) in the infertile soil increased steadily from 330.73 to 445.93 mg kg–1 under amendment rates increasing from 2.8 to 44.8 Mg ha–1. In fertile soil, MBC increased significantly from 590.46 to 784.54 mg kg–1 and slowly to 875.56 mg kg–1 before remaining constant. The metabolic quotient (qCO2) increased about 2.5-fold when the amendment rate increased from 11.2 to 44.8 Mg ha–1. The fungal-to-bacterial ratio doubled with the highest manure amendment rate at the expense of actinomycetes, and the community composition shifted at amendment rates ≥22.4 Mg ha–1. Changes in the composition of microbial communities were associated with the increase in the soil P content and reduced C-to-P and N-to-P ratios. In conclusion, an imbalance in P accumulation with excessive manure amendment may affect the functions of the soil ecosystem by reshaping the soil microbial communities.

Controls on soil microbial community stability under climate change.

Soil microbial communities are intricately linked to ecosystem functioning because they play important roles in carbon and nitrogen cycling. Still, we know little about how soil microbial communities will be affected by disturbances expected with climate change. This is a significant gap in understanding, as the stability of microbial communities, defined as a community's ability to resist and recover from disturbances, likely has consequences for ecosystem function. Here, we propose a framework for predicting a community's response to climate change, based on specific functional traits present in the community, the relative dominance of r- and K-strategists, and the soil environment. We hypothesize that the relative abundance of r- and K-strategists will inform about a community's resistance and resilience to climate change associated disturbances. We also propose that other factors specific to soils, such as moisture content and the presence of plants, may enhance a community's resilience. For example, recent evidence suggests microbial grazers, resource availability, and plant roots each impact on microbial community stability. We explore these hypotheses by offering three vignettes of published data that we re-analyzed. Our results show that community measures of the relative abundance of r- and K-strategists, as well as environmental properties like resource availability and the abundance and diversity of higher trophic levels, can contribute to explaining the response of microbial community composition to climate change-related disturbances. However, further investigation and experimental validation is necessary to directly test these hypotheses across a wide range of soil ecosystems.

Implication of Temporal Dynamics of Microbial Abundance and Nutrients to Soil Fertility under Biochar Application – Field Experiments Conducted in a Brown Soil Cultivated with Soybean, North China

A short-term experiment was conducted to investigate responses of microbial community composition and nutrients dynamics to biochar-amended brown soil. We examined the effect of biochar on microbial abundance by plate counting method and microbial community composition changes by DGGE, as well as effect on total and available nutrients N, P and K content. Soil pH measurement was also incorporated into our study. The overall results showed that bacterial abundance increased more than actinomycetes, but fungal abundance decreased slightly in biochar amended soil in later sampling times. In terms of microbial community composition, DGGE analysis for bacteria exhibited some specific lanes in biochar treatments. Bacterial community was more sensitive to sampling time, but fungal community was influenced greatly by biochar addition. In our study, total C content increased significantly, as biochar rate and sampling time preceded. Total N increased slightly in later sampling time, and thus C and N ratio increase was obtained. Total P and K changes were not obvious. Extractable N and pH increased. Microbial utilization was assumed to contribute to extractable P and K decrease in later sampling times. Results suggested that biochar incorporation to brown soil might bring potential benefit to soil fertility from N retention in soil. Microbial turnover may feedback P and K to soil as well in the long term. There may also be an implication of beneficial effect on disease alleviation lead by microbial community imbalance.

Response of Microbial Community Composition and Function to Soil Climate Change

Soil microbial communities mediate critical ecosystem carbon and nutrient cycles. How microbial communities will respond to changes in vegetation and climate, however, are not well understood. We reciprocally transplanted soil cores from under oak canopies and adjacent open grasslands in a California oak-grassland ecosystem to determine how microbial communities respond to changes in the soil environment and the potential consequences for the cycling of carbon. Every 3 months for up to 2 years, we monitored microbial community composition using phospholipid fatty acid analysis (PLFA), microbial biomass, respiration rates, microbial enzyme activities, and the activity of microbial groups by quantifying (13)C uptake from a universal substrate (pyruvate) into PLFA biomarkers. Soil in the open grassland experienced higher maximum temperatures and lower soil water content than soil under the oak canopies. Soil microbial communities in soil under oak canopies were more sensitive to environmental change than those in adjacent soil from the open grassland. Oak canopy soil communities changed rapidly when cores were transplanted into the open grassland soil environment, but grassland soil communities did not change when transplanted into the oak canopy environment. Similarly, microbial biomass, enzyme activities, and microbial respiration decreased when microbial communities were transplanted from the oak canopy soils to the grassland environment, but not when the grassland communities were transplanted to the oak canopy environment. These data support the hypothesis that microbial community composition and function is altered when microbes are exposed to new extremes in environmental conditions; that is, environmental conditions outside of their "life history" envelopes.

Response of microbial community composition and activity in agricultural and grassland soils after a simulated rainfall

Rainfall in Mediterranean climates may affect soil microbial processes and communities differently in agricultural vs. grassland soils. We explored the hypothesis that land use intensification decreases the resistance of microbial community composition and activity to perturbation. Soil carbon (C) and nitrogen (N) dynamics and microbial responses to a simulated Spring rainfall were measured in grassland and agricultural ecosystems. The California ecosystems consisted of two paired sets: annual vegetable crops and annual grassland in Salinas Valley, and perennial grass agriculture and native perennial grassland in Carmel Valley. Soil types of the respective ecosystem pairs were derived from granitic parent material and had sandy loam textures. Intact cores (30 cm deep) were collected in March 1999. After equilibration, dry soil cores (approx. −1 to −2 MPa) were exposed to a simulated Spring rainfall of 2.4 cm, and then were measured at 0, 6, 24, and 120 h after rewetting. Microbial biomass C (MBC) and inorganic N did not respond to rewetting. N 2O and CO 2 efflux and respiration increased after rewetting in all soils, with larger responses in the grassland than in the agricultural soils. Phospholipid fatty acid (PLFA) profiles indicated that changes in microbial community composition after rewetting were most pronounced in intensive vegetable production, followed by the relict perennial grassland. Changes in specific PLFA markers were not consistent across all sites. There were more similarities among microbial groups associated with PLFA markers in agricultural ecosystems than grassland ecosystems. Differences in responses of microbial communities may be related to the different plant species composition of the grasslands. Agricultural intensification appeared to decrease microbial diversity, as estimated from numbers of individual PLFA identified for each ecosystem, and reduce resistance to change in microbial community composition after rewetting. In the agricultural systems, reductions in both the measures of microbial diversity and the resistance of the microbial community composition to change after a perturbation were associated with lower ecosystem function, i.e. lower microbial responses to increased moisture availability.