Microbial Carbon Utilization Research Articles

Long-term litter type treatments alter soil carbon composition but not microbial carbon utilization in a mixed pine-oak forest

Changes in litter and nutrient inputs into soil could have significant consequences on forest carbon (C) dynamics via controls on the structure and microbial utilization of soil organic C (SOC). In this study, we assessed changes in physical fractions (250–2000 μm, 53–250 μm, and < 53 μm soil aggregates) and chemical fractions (labile, intermediate and recalcitrant pools) of SOC in the top 20 cm mineral soil layer and their influences on microbial substrate utilization after eight years of experiment in a mixed pine-oak forest. The litter treatments included: control (Lcon), litter removal (Lnil), fine woody litter addition (Lwoody), leaf litter addition (Lleaf) and a mix of leaf and fine woody litter (Lmix). Nitrogen (N) addition (application rates of 0, 5 and 10 g N m−2 year−1, respectively) was also applied. We found that complete removal of forest-floor litter (Lnil) significantly reduced the pool sizes of all SOC fractions in both the physical and chemical fractions compared with treatments that retained either leaf litter (Lleaf) or mixture of leaves and fine woody materials (Lmix). The type of litter was more important in affecting SOC fractions than the quantity of inputs; neither the level of N addition rate nor its interaction with litter treatment had significant effects on both physical and chemical SOC fractions. Microbial respiration differed significantly among the treatments of varying litter types. However, the effectiveness of microbial C utilization inferred by microbial C use efficiency and biomass-specific respiration was not affected by either the litter treatments or N addition. These results suggest that despite significant changes in SOC composition due to long-term treatments of forest-floor litter and N addition in this mixed pine-oak forest of temperate climate, microbial C utilization strategies remain unaffected.

Combination of plant-growth-promoting and fluoranthene-degrading microbes enhances phytoremediation efficiency in the ryegrass rhizosphere

Plant- and/or microbe-based systems can provide a cost-effective, sustainable means to remove contaminants from soil. Microbe-assisted phytoremediation has potential utility for polycyclic aromatic hydrocarbons such as fluoranthene (Flu) removal from soils; however, the efficiency varies with the plant and microbes used. This study evaluated the Flu removal efficiency in a system with ryegrass (Lolium multiflorum), an IAA-producing Arthrobacter pascens strain (ZZ21), and/or a Flu-degrading Bacillus cereus strain (Z21). Strain ZZ21 significantly enhanced the growth of ryegrass. Ryegrass in combination with both strains (FIP) was the most effective method for Flu removal. By day 60, 74.9% of the Flu was depleted in the FIP treatment, compared with 21.1% in the control (CK), 63.7% with ryegrass alone (P), 69.0% for ryegrass with ZZ21 (IP), and 72.6% for ryegrass with Z21 (FP). FIP treatment promoted ryegrass growth, accelerated Flu accumulation in plants, and increased soil microbial counts. Microbial carbon utilization was significantly higher in soil in the FIP than with the CK treatment. Principal component analysis of the distribution of carbon substrate utilization showed that microbial functional profiles diverged among treatments, and this divergence became more profound at day 60 than day 30. Microbial inoculation significantly enhanced microbial utilization of phenols. Microbes in the FIP soil dominantly utilized amines/amides and phenols at day 30 but shifted to carbohydrates by day 60. Together, the combination of IAA-producing microbes and Flu-degrading microbes could promote plant growth, facilitate Flu degradation, and change soil microbial functional structure.

Elucidating microbial carbon utilization and nitrous oxide dynamics with 13C-substrates and N2O isotopomers in contrasting horticultural soils

Quantifying how cropping systems influence soil C and nutrient turnover is important not only for better understanding the processes that regulate soil functioning, but also for long-term food production goals. We conducted an incubation study on soils collected from adjacent sites with a long-term legacy of annual vegetable, and perennial asparagus, haskap, and apple production. Soils were amended with 13C-labelled vanillin or glucose and incubated for 42 d. Gas and soil samples were collected to measure CO2, N2O, their isotopic signatures, and soil inorganic N and microbial biomass carbon (MBC) dynamics. Throughout the incubation, soil NO3−-N remained highest from vegetable soils, followed by soils from asparagus, haskap, and apple production. In contrast, soils from apple production supported the highest levels of MBC, whereas soil MBC from vegetable production was lowest. In general, glucose-C was utilized more readily than vanillin-C, but differences in glucose-derived CO2-C were more distinct among soils than vanillin-derived CO2-C. Soils from a history of vegetable production had the highest metabolic quotients – indicating poor substrate use efficiency, whereas substrate-C was used most efficiently from soils under apple production. Substrate-C use efficiency inversely corresponded to patterns in denitrifier-N2O production based on 15N2O isotopomers. In general, soils from the intensive vegetable cropping legacy were most susceptible to gaseous losses of both C and N-CO2 by way of soil organic matter priming, and N2O via increased denitrification with additions of labile substrates. Hence, the legacy of past cropping system management had consequences for how C and N was processed in soil.

Straw and biochar strongly affect functional diversity of microbial metabolism in paddy soils

The application of straw and biochar is widely practiced for the improvement of soil fertility. However, its impact on microbial functional profiles, particularly with regard to paddy soils, is not well understood. The aim of this study was to investigate the diversity of microbial carbon use patterns in paddy soils amended with straw or straw-derived biochar in a 3-year field experiment in fallow soil and at various development stages of a rice crop (i.e., tillering and blooming). We applied the community level physiological profiling approach, with 15 substrates (sugars, carboxylic and amino acids, and phenolic acid). In general, straw application resulted in the greatest microbial functional diversity owing to the greater number of available C sources than in control or biochar plots. Biochar amendment promoted the use of α-ketoglutaric acid, the mineralization of which was higher than that of any other substrate. Principal component analyses indicated that microbial functional diversity in the biochar-amended soil was separated from those of the straw-amended and control soils. Redundancy analyses revealed that soil organic carbon content was the most important factor regulating the pattern of microbial carbon utilization. Rhizodeposition and nutrient uptake by rice plants modulated microbial functions in paddy soils and stimulated the microbial use of N-rich substances, such as amino acids. Thus, our results demonstrated that the functional diversity of microorganisms in organic amended paddy soils is affected by both physicochemical properties of amendment and plant growth stage.

Microbial Carbon Source Metabolic Profile in Rice Rhizosphere and Non-rhizosphere Soils with Different Long-term Fertilization Management

Rhizosphere and non-rhizosphere soil samples under different long-term fertilization treatments including control without fertilizer (CK), chemical fertilization alone (NPK), rice residues combined with NPK (NPKS), 30% manure plus 70% chemical fertilizers (LOM), and 60% manure plus 40% chemical fertilizers (HOM) were collected from a paddy field in a red soil hilly area in Ningxiang City, Hunan Province, China. The characteristics of microbial carbon utilization in the soils were studied. Results of 18O-H2O tracer analysis showed that both soil microbial biomass carbon content (MBC) and microbial growth rate (CGrowth) were highest in the HOM treatment, whereas they were lowest in CK. In the rhizosphere soil, the highest basal respiration was observed in HOM, and the lowest values were in CK and NPK. Microbial carbon utilization efficiency (CUE) was highest in NPK but lowest in the LOM and HOM treatments. In non-rhizosphere soil, no significant differences between basal respiration and CUE were observed among the fertilization treatments. Results from MicroRespTM showed that the ability of microorganisms to metabolize exogenous carbon sources was higher in non-rhizosphere soil than in rhizosphere soil. The application of organic materials (rice residues or manure) increased the microbial metabolic rate of carboxylic acids, amino acids, and carbohydrates in the order carboxylic acids > amino acids and carbohydrates > complex compounds. Redundancy analysis of the microbial metabolism patterns of various carbon substrates showed that:① CK was well separated from the fertilization treatments; ② NPK was grouped with NPKS, whereas LOM and HOM were grouped together and were separate from NPK and NPKS. This indicates that the fertilization treatments changed the microbial carbon metabolism patterns. The above-mentioned results indicated that the fertilization treatments did not affect microbial CUE and basal respiration. However, exogenous carbon source input (such as root exudates) and the application of organic materials can increase microbial basal respiration, and thus, reduce microbial CUE.

Ridge-furrow with film mulching practice ameliorates soil microbial metabolic activity and carbon utilization in rhizosphere soil of rapeseed (Brassica napus L.)

The farming practices of ridge-furrow with film mulching (RFFM) have been extensively reported as a valuable technique for improving crop productivity and enhancing water-use efficiency. However, research on the high-yield mechanism of RFFM measures under drought stress from the perspective of microbial diversity has been scared. Field experiments were conducted to analyze the effects of conventional flat planting (FP), no film mulching (NR), white polyethylene film mulching (WR), black polyethylene film mulching (BR), and biodegradable film mulching (BDR) with 40 and 80 cm furrow width levels on soil temperature, soil water storage (SWS), microbial carbon utilization, and yield of winter oilseed rape. The RFFM significantly increased the SWS as well as rapeseed yield and yield components. However, these treatments did not cause obvious differences in soil temperature. A relative high value of average color change rate (AWCD) was observed during the incubation time of 24–216 h, and it reached the peak value at 240 h. The AWCD in the furrow with 80 cm width was greater than that of 40 cm. The RFFM also could improve the utilization intensities of soil microorganism on the carbon sources of carbohydrates, amino acids, and miscellaneous in rapeseed rhizosphere. This result was consistent with that of the principal component analysis. The Shannon–Wiener diversity index, Simpson’s diversity index, and Shannon–Wiener evenness in BDR40, BR40, and BR80 were significantly higher than other treatments, respectively. In addition, correlation analysis results suggested that the indicator of affecting the diversity of carbon source was mainly due to the water storage capacity. The methods of film mulching have a remarkable effect on microbial diversity. The yield of BR and BDR were significantly higher than other treatments. Compared with FP, RFFM increased rapeseed yield by 9.61–86.10%. In the year of less rainfall, production has decreased in comparison with the first season, while BDR80 guarantees continuous high yield and substantially promoted carbon utilization and soil microbial diversity. Soil microbial diversity is positively correlated with soil water content, which is beneficial to increase production. Wider furrow (80 cm) is recommended a sustainable high-yield method due to convenient labor in the region in Southwest China.

Stabilizing effects on a Cd polluted coastal wetland soil using calcium polysulphide

In this study, different dosages of calcium polysulphide (CaSx) were used as an amendment to investigate effects on the immobilizing of Cd in a wetland soil by pot experiment. In addition to chemical analysis (pH and bioavailable Cd concentration), changes in soil enzyme activities, microbial carbon utilization capacity, metabolic and community diversity were examined to assess dynamic impacts on soil environmental quality and toxicity of Cd resulting from ameliorant dosing. Soil pH increased immediately upon CaSx amendment compared to the unamended control (CK), and then declined slowly to a level lower than CK. Diethylenetriamine pentaacetic acid (DTPA) extractable Cd concentration was determined to characterize the bioavailability of Cd in the soil. The CaSx dose-dependent effect observed that with increasing CaSx dosage, the immobilizing efficiency decreased. Soil urease and catalase activity assays and Biolog EcoPlate assay indicated that early stage addition of CaSx significantly inhibited soil microbial activities. However, mid and late stage time periods showed the inhibition effects were alleviated, and the microbial activities could be recovered in 1% and 2% CaSx treatments. Moreover, with increasing incubation time, microbial community diversity and richness were significantly recovered in 1% and 2% CaSx treatments compared to the CK. No considerable changes were observed in the 5% CaSx treatment. Conclusively, the 1% CaSx amendment was an efficient and safe dosage for the stabilization of Cd contaminated wetland soil. This study contributes to the development of in situ remediation ameliorants and technologies for heavy metal polluted wetland soils.

Tillage and crop succession effects on soil microbial metabolic activity and carbon utilization in a clay loam soil

Soil microorganisms play important roles in nutrient cycling and ecosystem functioning. Knowledge on the responses of soil microbial metabolic characteristics to agricultural practices is critical to better understand soil microbial processes in agroecosystems. The study aimed to explore the responses of soil microbial metabolic activities and their carbon utilization under different tillage and crop succession systems in a 12-year field experiment in a clay loam soil of Jilin Province, China. This experiment was set up in a split-plot design with four replicates including no-tillage (NT) and conventional tillage (CT) as main plots and continuous corn (CC) and corn-soybean succession (CS) treatments as subplots. Soil samples were collected from 0 to 5 cm and 5–15 cm depths. The results showed that compared with CT, NT increased soil organic carbon, soil microbial biomass carbon, basal respiration and microbial coefficient at 0–5 cm depth. Greater basal respiration was observed under CC than under CS at both depths. Compared with NTCC, NTCS decreased microbial functional diversity at 0–5 cm depth and increased microbial metabolic quotient at 5–15 cm depth. Redundancy analysis indicated that crop succession management induced the changes in soil microbial carbon utilization. Compared with other soil environmental factors, NO3−-N and soil moisture significantly affected soil microbial metabolic activities. No significant correlation was found between microbial carbohydrate utilization and soil organic carbon in this study. Structural equation modeling analysis suggested that corn-soybean succession practice could stimulate the consumption of aromatic acids, which indirectly affected the accumulation of soil organic carbon.

Characteristics of soil organic carbon mineralization in low altitude and high altitude forests in Wuyi Mountains, southeastern China

Examining the variations of soil organic carbon mineralization at different altitudes is crucial for better understanding of soil organic carbon (SOC) dynamics. We selected the low altitude and high altitude broad-leaved forest soils in Wuyi Mountains as the research object, and incubated them under particular annual average temperature (17 and 9 ℃, respectively) in laboratory to investigate the difference of SOC mineralization characteristics. The results showed that the cumulative SOC mineralization had no significant difference between forest soils at low and high altitude in a 126-day incubation period under ambient temperature. Soil organic carbon content of high altitude soil was significantly higher than that from low altitude. The dynamics of SOC mineralization could fitted by the first-order kinetics. Both mineralization potential (CP) and mineralization rate constant (K) values of two soils had no significant difference, but CP/SOC value and mineralization ratio were significantly higher at low altitude, indicating that the carbon sequestration capacity of low altitude soil was relatively lower than that of high altitude under ambient temperature. Soil microbial biomass carbon and microbial quotients were significantly higher than that of low altitude with the increase of incubation time, indicating that the ability of microbial carbon assimilation was greater at high altitude. On the other hand, the activities of β-1,4-glucosidase and cellobiohydrolase in high altitude soil were higher, suggesting that more labile carbon would be decomposed by soil microbes. The carbon sequestration capacity and microbial carbon utilization efficiency in high altitude soil would be reduced and thus result in a decline of soil organic carbon storage under the scenarios of climate warming.

Effects of Burning on Carbon Utilization of Soil Microorganisms and Plant Growth of Carex brevicuspis Communities at Lake Poyang Wetlands, China

Fire causes disturbance of wetland ecosystems and has a major influence on soil microbial communities, plant growth and ecosystem function. However, the impact of fire disturbance on soil microbial metabolism and its relationship with plant growth remains poorly understood. Burned zones, unburned zones and transition zones with low intensity fire were surveyed in an area dominated by Carex brevicuspis communities. Results show a significant difference in soil properties, microbial biomasses, microbial carbon utilization pattern and plant growth in different zones. The lowest average value of soil carbon content, nitrogen content and moisture occurred in burned zones, while the highest occurred in unburned zones. Furthermore, soil microbes under burned zones had the highest biomasses, average well color development value and richness index. Plant growth decreased in the following order: burned > transition > unburned zones. Redundancy analysis indicated that this variation can be explained mostly by the difference of carbon utilization patterns of soil microbes. Correlation and regression analyses show that soil microbial metabolism had a significant correlation with the plant growth variables tested in this study. Overall, our results suggest that fire changes the soil microenvironment and further changes the soil microbial metabolic patterns and plant growth in the Lake Poyang wetland.

Temporal and Spatial Variations of Microbial Carbon Utilization in Water Bodies from the Dajiuhu Peatland, Central China

To investigate the microbial utilization of organic carbon in peatland ecosystem, water samples were collected from the Dajiuhu Peatland and nearby lakes, central China across the year of 2014. The acridine orange (AO) staining and Biolog Eco microplates were used to numerate microbial counts and determine the carbon utilization of microbial communities. Meanwhile, physicochemical characteristics were measured for subsequent analysis of the correlation between microbial carbon utilization and environmental factors. Results indicated that total microbial counts were between 106–107 cells/L. Microbial diversities and carbon utilization rates showed a similar pattern, highest in September and lowest in November. Microbial communities in the peat pore waters preferred to utilize N-bearing carbon sources such as amines and amino acids compared with microbial communities in lakes. The network analysis of microbial utilization of 31 carbon substrates clearly distinguished microbial communities from peat pore waters and those from lakes. Redundancy analysis (RDA) showed the total organic nitrogen content (P=0.03, F=2.5) and daily average temperature (P=0.034, F=2.4) significantly controlled microbial carbon utilization throughout the sampling period. Our report is the first one to address the temporal and spatial variations of carbon utilization of microbial communities which are closely related to the decomposition of organic matter in the Dajiuhu Peatland in context of climate warming.

Feed in summer, rest in winter: microbial carbon utilization in forest topsoil

BackgroundEvergreen coniferous forests contain high stocks of organic matter. Significant carbon transformations occur in litter and soil of these ecosystems, making them important for the global carbon cycle. Due to seasonal allocation of photosynthates to roots, carbon availability changes seasonally in the topsoil. The aim of this paper was to describe the seasonal differences in C source utilization and the involvement of various members of soil microbiome in this process.ResultsHere, we show that microorganisms in topsoil encode a diverse set of carbohydrate-active enzymes, including glycoside hydrolases and auxiliary enzymes. While the transcription of genes encoding enzymes degrading reserve compounds, such as starch or trehalose, was high in soil in winter, summer was characterized by high transcription of ligninolytic and cellulolytic enzymes produced mainly by fungi. Fungi strongly dominated the transcription in litter and an equal contribution of bacteria and fungi was found in soil. The turnover of fungal biomass appeared to be faster in summer than in winter, due to high activity of enzymes targeting its degradation, indicating fast growth in both litter and soil. In each enzyme family, hundreds to thousands of genes were typically transcribed simultaneously.ConclusionsSeasonal differences in the transcription of glycoside hydrolases and auxiliary enzyme genes are more pronounced in soil than in litter. Our results suggest that mainly fungi are involved in decomposition of recalcitrant biopolymers in summer, while bacteria replace them in this role in winter. Transcripts of genes encoding enzymes targeting plant biomass biopolymers, reserve compounds and fungal cell walls were especially abundant in the coniferous forest topsoil.

Soil microbial carbon utilization, enzyme activities and nutrient availability responses to Bidens pilosa and a non-invasive congener under different irradiances

Two Bidens species (Bidens pilosa and B. bipinnata) that originate from America have been introduced widely in pan-tropics, with the former regarded as a noxious invasive weed whereas the latter naturalized as a plant resource. Whether the two species exhibit different effects on the belowground system remains rarely studied. This study was conducted to investigate soil microbial carbon (C) utilization, enzyme activities and available nitrogen, phosphorus and potassium contents under the two species in a subtropical garden soil of southern China under different levels of light intensity. Results showed that the microbial C utilization and enzyme activities were not significantly different under the two species, implying that the strong invasiveness of B. pilosa could not be due to the plant-soil microbe interactions, at least plant-induced alterations of microbial community function to utilize C substrates. Alternatively, available soil nitrogen and potassium contents were significantly higher under B. pilosa than under B. bipinnata in full sun, indicating that the strong invasiveness of B. pilosa could result from rapid nutrient mobilizations by B. pilosa. However, the differences turned non-significant as light intensity decreased, suggesting that light availability could substantially alter the plant effects on soil nutrient mobilizations.

No synergistic effects of water and nitrogen addition on soil microbial communities and soil respiration in a temperate desert

Soil microbial communities play an important role in regulating land–atmosphere CO2 exchange in terrestrial ecosystems. However, their responses to climate change are unclear. We explored the effects of water and nitrogen addition and their interaction on soil microbes and the resulting impacts on soil carbon emissions in the Gurbantunggut Desert, northwestern China. A manipulative 30% increase in precipitation and 5gNm−2year−1 deposition alone and in combination was applied across three years from 2011 to 2013. Water addition significantly increased microbial biomass and respiration, metabolic quotient, and the utilization of carbohydrates, carboxylic acids and amino acids. Water addition did not change the microbial community composition. Nitrogen addition only significantly increased soil bacterial PLFAs, while exerting no significant impacts on soil fungal PLFAs, microbial respiration and soil respiration. Moreover, nitrogen addition had no significant impacts on microbial community composition. Water and nitrogen addition in combination did not generate synergistic effects on microbial communities and soil respiration. Across treatments in three years, soil respiration and microbial respiration were positively correlated with microbial total PLFAs, microbial carbon utilization profiles, while being independent of microbial community structure. This study suggests water addition can increase soil carbon emission through increasing microbial utilization of labile carbon, and water plus nitrogen addition had no synergistic effects on soil microbial communities and soil respiration, demonstrating nitrogen is not a limiting factor for soil microbial communities in the scenario of increasing precipitation in this desert ecosystem.

Phospholipid 13C stable isotopic probing during decomposition of wheat residues

Disentangling the kinetics of the soil microbial community succession, which is simultaneously driven by newly added plant materials and extant soil organic matter (SOM), can enrich our knowledge on microbial carbon (C) utilization patterns under residue amendment. This understanding might be useful to predict the rapid responses of specific microbial functional groups and develop strategies for balancing the terrestrial C budget. Therefore, our objective was to characterize and estimate the parameters of the microbial community dynamics profiled by phospholipid fatty acids (PLFA) from 13C-labeled wheat residues and SOM. We conducted a 21-day microcosm study using two different arable systems (conventional tillage, CT; no-till, NT) amended with three types of 13C-labeled wheat residues (grains, leaves and roots). The abundances and isotopic fractions of 13CO2 flux and 13C-labeled PLFA were measured via gas trace isotope ratio mass spectrometry (IRMS) and gas chromatography-combustion-isotope ratio mass spectrometry (GC-c-IRMS), respectively. A double exponential model was used to describe the synthesis-degradation kinetics of PLFA from different microbial origins. We found that the PLFA formation generally reaches its maximal abundance within 7 days (except for PLFA from actinomycetes). The SOM- and wheat residue-derived C fluxes, as well as their PLFA profiles, were inconsistently impacted by the residue quality or the tillage regime over the incubation period. Specifically, the abundances of residue-derived CO2 and PLFAs significantly decreased in the following order: grains>leaves>roots. However, those abundances derived from SOM were the lowest with the leaf residue treatments. Residue-derived PLFA patterns were highly influenced by fungi and G− bacteria, while G+ bacterial and actinomycete PLFAs were preferentially linked to extant SOM mineralization. Compared to the residue-derived counterparts, the SOM-derived microbes were characterized by higher G+/G− bacteria and cy17:0/C16:1ω7c ratios, as well as lower fungi/bacteria PLFA ratios. Such distinction between residue and SOM was also evidenced by the contrasting tillage effects on C mineralization and the ratios of cy17:0/C16:1ω7c and fungal/G− bacterial PLFA. Our study provides evidence with important implications for adapting the microbial-mediated processes of soil C management through residue quality control.

长期施肥对新疆灰漠土土壤微生物群落结构与功能多样性的影响

A long-term( 20 years) stationary experiment was carried out in a grey desert soil field of Xinjiang to study the effects of fertilization on soil microbial community characteristics and functional diversity. Traditional microbial cultivation method and Biolog technique were used to analyze soil microbial community,the number of bacterial physiological groups and microbial carbon utilization. Ten fertilization treatments were studied,i. e.,abandonment( CK0),cultivated without fertilization( CK),different chemical fertilizer treatments( N,NK,NP,PK,and NPK),NPK and organic materials( NPKM1),NPK and double organic materials( NPKM2),as well as NPK and straw( NPKS). Results showed that,( 1)compared with CK treatment,data on the cultivable microorganisms illustrated that the numbers of bacteria,actinomycetes and fungi in CK0 treatment all increased significantly( P 0. 05). Effects of different chemical fertilizer treatments were different. The numbers of bacteria( except PK treatment),and actinomycetes( except PK and N treatments) increased by8. 14—135. 70% and 15. 30—44. 78%,respectively. The numbers of fungi( except NK treatment) decreased by 10. 00—38. 33%. The numbers of microorganisms were the highest in NPKM1 and NPKM2 treatments. The bacteria numbers of NPKM1 and NPKM2 treatments increased by 162. 20% and 173. 75%,when comparing with CK treatment. The numbers of actinomycetes increased by 34. 39% and 39. 37%,while the numbers of actinomycetes increased by 63. 33% and 488.33%. However,the numbers of microorganisms decreased obviously( P 0. 05),the numbers of bacteria,actinomycetes and fungi decreased by 14. 17%,21. 27% and 63. 33%.( 2) Studies of soil bacterial physiological groups showed that,the amounts of Azotobacter and Nitrifier in CK treatment were higher than those of CK0 treatment( P 0. 05),but the amounts of Ammoniation and Cytophaga in CK treatment were lower( P 0. 05). Effects of different chemical fertilizer treatments and NPKS treatment were very different. Effect of NPK treatment was obviously the best( P 0. 05). However,NPKM1 and NPKM2 treatments could obviously improve the amount of soil bacterial physiological groups related with N transformation.( 3) Carbon utilizations of soil microbial community showed that,the order of soil microbial activities was,NK,NPKM1,NPKM2 N,NPK,CK PK,NPKS CK0,NP. Soil microbial diversity indices of CK0 treatment were the highest. Compared with CK treatment,all fertilization treatments were not significantly different in Simpson index and Mc Intosh index. Shannon index in NPKM1,NPKM2 and NK treatments were the highest,other fertilizer treatments were not significantly different from,or significantly lower than CK. Carbohydrates,Amino acids,Carboxylic acids and Amines /amides were the main carbon resources for microbial utilization.( 4) Cluster analysis indicated that carbon utilizations by soil microbial community for different N treatments were similar( except NP treatment). Correlation between bacteria,fungi and soil nutrient contents were significant, but no significant correlation relationships existed among the cultivable microorganisms,soil bacterial physiological groups and carbon utilizations of soil microbial community. To sum up,the effects of long-term fertilization on diversities of soil microbial community structure and function in grey desert soil of Xinjiang were remarkable. Long-term cultivation without fertilization decreased the diversities of soil microbial community structure and function. Different chemical fertilizer treatments had varied effects. NPK and NPKM treatments could improve the diversities of soil microbial community structure and function.

Impact of iron limitation on primary production (dissolved and particulate) and secondary production in cultured Trichodesmium sp.

Diazotrophic cyanobacteria play an important role in biogeochemical cycles of carbon and nitrogen and, hence, in oceanic productivity in the tropical and subtropical regions of the ocean. Although many studies have examined the impact of iron (Fe) limitation on particulate primary production and dinitrogen (N2) fixation in the colonial cyanobacterium Trichodesmium, none have looked at the impact of Fe limitation on the percentage extracellular release (PER) and secondary production (SP) in Fe-limited cultures of this cyanobacterium. Here, we present the results of a series of culture experiments during which we examined the impact of 3 concentrations of dissolved iron (DFe) on total primary production (TPP = dissolved + particulate primary production, i.e. DPP + PPP), PER and on SP. Under severe Fe limitation (5 nM DFe), biomass, growth rates, TPP and N2 fixation were strongly reduced, while PER increased relative to the rates ob served at the highest Fe concentration. Moreover, reducing Fe concentration induced an increase in the percentage of photosynthetically fixed C used for algal growth, while the percentage of C used to support algal respiration decreased. Reduced Fe concentrations also induced a decrease in SP and in the SP:DPP ratio, indicating that the efficiency of transfer of fixed carbon from autotrophic to heterotrophic processes is reduced. This suggests that Fe, either directly through influencing cellular processes or indirectly through influencing organic matter structure or nitrogen availability, is controlling SP and, thus, microbial carbon utilization. These results suggest that the amount of carbon entering into the microbial loop may be reduced under Fe limitation, thus leading to an accumulation of dissolved organic carbon with potentially important impacts on microbial carbon cycling and, ultimately, on the biological carbon pump

Transformation of dissolved organic matters in swine, cow and chicken manures during composting

The changes of dissolved organic matters (DOMs) extracted from swine, cow and chicken manures were assessed by Fourier transform infrared, ultraviolet, gel permeation chromatography (GPC), excitation–emission-matrix fluorescence (EEM-FL), Biolog Eco and 1H NMR during 60-day composting. Pumice was adopted to eliminate the disturbing of common organic bulking agents. The results showed chicken manure had the highest DOC, DTN (dissolved total nitrogen) and lowest DOC/DTN among the three manures; cow manure had the highest volatile solids, lowest DTN, slowest DOMs hydrolysis rate and the fastest bio-stabilization rate. 1H NMR showed the decrease rates of OC band and saturated carbon chain were distinctly faster than that of olefinic and aromatic structures. The molecular size distribution of DOMs in the three manures was in the range of 1–10kDa detected by GPC. Microbial carbon utilization capacity decreased in cow manure with composting time, but the contrast was observed in the chicken and swine manures.

Functional diversity of soil microorganisms in Casuarina equisetifolia woodlands of different stand ages in Hainan Island

Aims Soil microbes play a key role in matter recycling and accumulation of allelochemicals. We studied the functional diversity of microbial communities in order to illustrate variations in soil microbial community diversity among different Casuarina equisetifolia woodlands. Methods Young, middle-aged, and mature forest of C. equisetifolia woodlands in the Haikou Guilinyang littoral zone were chosen as subjects of the study. Soil microbial functional diversity in those stands was determined by using Biolog micro-plate technique. Important findings The soil microbial carbon utilization was higher in bare land and the mature forest than the middle-aged and young forest. With increasing stand age, the values of Shannon-Wiener index(H') and McIntosh and Simpson diversity indices all increased. The H' significantly differed among different woodlands. However, there were no significant differences in the McIntosh and Simpson diversity indices between the young and middle-aged forest. Principal component analysis demonstrated that there was a significant difference in the soil microbial metabolic activities among different woodlands, in particular concerning monosaccharides and amino acids. The soil microbial community diversity increased with increasing stand age, which might be due to a joint action among many factors such as litter, the secondary metabolites of plant root secretion, soil nutrients, and specific soil microorganisms.

Root and arbuscular mycorrhizal mycelial interactions with soil microorganisms in lowland tropical forest

Tropical forests have high rates of soil carbon cycling, but little information is available on how roots, arbuscular mycorrhizal fungi (AMF), and free-living microorganisms interact and influence organic matter mineralization in these ecosystems. We used mesh ingrowth cores and isotopic tracers in phospholipid fatty acid biomarkers to investigate the effects of roots and AMF mycelia on (1) microbial community composition, microbial carbon utilization, and hydrolytic enzyme activities for large, potted tropical trees and (2) enzyme activities and litter mass loss in a lowland tropical forest. Under the tropical tree, plant-derived carbon was incorporated predominantly into bacterial groups in both rhizosphere and AMF-only soils. Gram-positive bacteria incorporated additional soil-derived carbon in rhizosphere soils, which also contained the highest microbial biomass. For hydrolytic enzymes, β-glucosidase and N-acetyl β-glucosaminidase activities were highest in rhizosphere soils, while phosphomonoesterase activity was highest in AMF-only soil. In the forest, leaf litter mass loss was increased by the presence of roots, but not by the presence of AMF mycelia only. Root-microbial interactions influenced organic matter cycling, with evidence for rhizosphere priming and accelerated leaf litter decomposition in the presence of roots. Although AMF mycelia alone did not stimulate organic matter mineralization, they were a conduit of carbon to other soil microorganisms.