Average Well-color Development Values Research Articles

Effect of nitrogen addition on the carbon metabolism of soil microorganisms in a Calamagrostis angustifolia wetland of the Sanjiang Plain, northeastern China

PurposeSoil microorganisms are important mediators of land ecosystem functions and stability. However, carbon sources in different amounts of nitrogen addition are known to affect the function of soil microbial communities. Thus, this study sought to evaluate the effects of nitrogen addition on the carbon utilization capacity of soil microorganisms in the Sanjiang Plain wetland, northeastern China.MethodsThree nitrogen treatments (CK, 0 kg N ha−1 a−1; N40, 40 kg N ha−1 a−1; and N80 kg N ha−1 a−1) were evaluated in the Honghe National Nature Reserve of the Sanjiang Plain. The carbon metabolism capacity of soil microorganisms in the C. angustifolia wetland was investigated after five consecutive year’s nitrogen addition treatment using the Bio-Eco technique.ResultsDifferent amounts of nitrogen addition conditions resulted in significant differences in pH, ammonium nitrogen (NH4+), dissolved organic carbon (DOC), and soil microbial alpha diversity. The average well-color development (AWCD) in the Bio-Eco Plate assay increased gradually with incubation time, and different nitrogen levels significantly affected these AWCD values (P < 0.05), with the N40 treatment exhibiting the highest value. Furthermore, the N80 treatment had significantly lower Shannon and Pielou diversity indices (P < 0.05). N40 significantly promoted carbohydrate, amino acid, and ester utilization rates by soil microorganisms, whereas N80 significantly inhibited carbohydrate, amino acid, alcohol, amine, and organic acids utilization. Redundancy analysis (RDA) showed that the three treatments had remarkable differences in soil microbial community metabolism, and the cumulative variance contribution was 72.86%. In addition, RDA revealed that the N80 treatment was positively correlated with the TN, SMC, DON, and TOC but negatively correlated with DOC, NH4+, pH, and NO3−.ConclusionLong-term nitrogen addition leads to changes in soil microbial community structure and significantly alters the ability of soil microorganisms to utilize carbon sources in the Calamagrostis angustifolia wetland.

Effects of intercropping and nitrogen application on soil microbial metabolic functional diversity in maize cropping soil.

Soil microorganism is an important indicator of soil health and plays a critical role in biogeochemical processes. We collected soil samples from a multi-year in-situ field experiment with two cropping modes (maize monocropping and maize-potato intercropping) subjected to four nitrogen (N) levels (N0, 0 kg·hm-2; N125, 125 kg·hm-2; N250, 250 kg·hm-2; N375, 375 kg·hm-2). By using the Biolog-ECO microplate method, soil microbial metabolic activity, diversity and utilization of six carbon groups were analyzed. The results showed that N application significantly increased the average well color development (AWCD) values, Simpson and Shannon indices, with the highest value at N250 in mono- and inter-cropped soils. Moreover, N application promoted the utilization of amino acids, amines and phenolic compounds, but decreased the utilization of polymers. Compared with monocropping at the same N level, intercropping improved the AWCD values, Simpson and Shannon indices, with a maximal improvement at N250. Intercropping and nitrogen application significantly affected the metabolic activities of the six carbon-source groups. In addition, intercropping improved the utilization of labile carbon sources, such as amino acids and carbohydrates. Results of the redundancy analysis and linear regression showed that intercropping and N application elevated AWCD values by increasing soil temperature, water content, and soil organic carbon content. Therefore, the changes in soil physicochemical properties after intercropping were the main reason for the enhancement of microbial metabolic activity under N application.

Decomposition of different crop straws and variation in straw-associated microbial communities in a peach orchard, China

Crop residue is a major source of soil organic matter; therefore, application of crop straw to soil contributes to the sustainable development of organic agriculture. To better understand the transformation of crop straw in orchard soils, we investigated the relationship between the characteristics of straw decomposition and functional diversity of associated microbial communities in a long-term peach orchard, China. Mesh bags, each containing 30 g of corn or bean straw, were buried at a soil depth of 20 cm in a 12-year-old peach orchard for 360 d (October 2011–October 2012). Three treatments were applied, i.e., fresh corn straw, fresh corn straw with nitrogen fertilizer (urea, 10.34 g/kg), and fresh bean straw. Changes in straw residual rate, straw water content and soil conditions were monitored after treatment. The functional diversity of straw-associated microbial communities was analyzed by the Biolog-Eco microplate assay. During the decomposition process, straw residual rates did not vary considerably from 10 d (30.4%–45.4%) to 360 d (19.0%–30.3%). Irrespective of nitrogen addition, corn straw decomposed faster than bean straw. Corn straw with nitrogen fertilizer yielded the highest average well color development (AWCD) values (1.11–1.67), followed by corn straw (1.14–1.68) and bean straw (1.18–1.62). Although the AWCD values did not differ significantly among the three treatments, substantial differences occurred across various time periods of the decomposition process (P<0.01). In terms of carbon source utilization, the dominant microbial groups fed mainly on saccharides. Hard-to-decompose substances gradually accumulated in the middle and late stages of straw decomposition. Of the six categories of carbon sources tested, the utilization rate of aromatics was the lowest with corn straw, whereas that of polymers was the lowest with bean straw. Among different treatments, straw residual rate was negatively correlated to soil available phosphorous, soil available potassium and soil temperature (P<0.05), but not to soil water content. In some cases (corn straw with or without nitrogen fertilizer), straw residual rate was negatively correlated to straw water content, amino acid utilization and carboxylic acid utilization, and positively correlated with microbial species richness and evenness (P<0.05). Microbial community associated with corn and bean straw decomposition in soil was respectively dominated by aromatic- and polymer-metabolizing groups during the middle and late stages of this process, which could reduce the stability of microbial community structure and decrease the rate of straw decomposition in fruit tree orchard.

氮磷添加和栽植密度对大叶相思林土壤微生物群落功能多样性的影响

土壤微生物群落是土壤质量潜在的生态指标，在维持生态系统功能和服务中起着关键的作用。采用Biolog-ECO微平板法，探讨氮磷添加与不同栽植密度交互对大叶相思林（Acacia auriculiformis）土壤微生物功能多样性的影响，以便为建立合理的林分密度和氮磷施肥模式，提高土壤质量提供理论参考。以大叶相思林为研究对象，选择氯化铵（NH₄Cl）作为氮肥模拟大气氮沉降，用二水合磷酸二氢钠（NaH₂PO₄·2H₂O）进行磷添加。氮磷处理设置4个水平，即CK、施N、施P和施N+P。种植密度设置4个水平，即1667、2500、4444、10000株/hm²（分别以低密度、中密度、较高密度、高密度表示）。研究结果表明，施P显著提高了4个密度大叶相思林土壤微生物的AWCD值、碳源利用丰富度指数、McIntosh指数、Shannon指数和Simpson指数，而施N和N+P则相反。随着林分密度的减小，各处理的土壤微生物AWCD值趋于减少。通常低密度林分的土壤微生物的丰富度指数、Shannon-Wiener指数、McIntosh指数和Simpson指数较小。;Climate change affects the physiological activities of soil microbes, which causes changes of soil microbial community structure and functional diversity and cascades the effects on biogeochemical cycling and climate-ecosystem feedbacks. Among them, nitrogen (N) and phosphorus (P) are considered as the limiting factors that influences the plant biodiversity and primary productivity in forest ecosystems. The external N addition or atmospheric N deposition has been found to affect the aboveground biology processes and the underground biochemistry of soil, both directly and indirectly. Chronic elevated N input has been shown to lead to many adverse impacts, including soil acidification, nutrients imbalance, and the increased greenhouse gas emissions. Forest soils of southern China are P-limited, because they are highly weathered and leached, and little P is released even from the weathering of primary P-bearing minerals. As a result, P fertilization is widely used in the subtropical forests of southern China. As an important component in regulating belowground ecological processes, the soil microbes are primary mediators of organic matter decomposition and nutrient cycling, and thus play a key role in maintaining function and sustainability of terrestrial ecosystems. Additionally, changes in soil microbial function and community composition may trigger a series of responses, such as impacting litter and organic matter decomposition rates, humus formation nutrient transformation and cycling, and then alter the interaction between soil microbes and plant communities. In this study, Biolog-ECO microplate method was used to investigate the interactive effects of nitrogen and phosphorus additions and different stand densities on soil microbial functional diversity of Acacia auriculiformis stands, which can provide a basis for establishing reasonable stand density, fertilization method, and improve soil quality. NH₄Cl and NaH₂PO₄·2H₂O were selected to simulate atmospheric nitrogen and phosphorus additions with 4 treatments (CK, N, P and N+P) and stand density was set at 4 levels (1667, 2500, 4444, and 10000 seedlings/hm²). The results showed that P treatment promoted the average well color development (AWCD) values, richness index, McIntosh index, Shannon index, and Simpson index of soil microbes in the four density stands, while the N and N+P treatments were opposite. With the decrease of forest density, the AWCD values of soil microbes in all treatments decreased. Generally, soil microbial richness index, Shannon-Wiener index, McIntosh index and Simpson index were small in the low density stands.

Application of Erythromycin and/or Raoultella sp. Strain MC3 Alters the Metabolic Activity of Soil Microbial Communities as Revealed by the Community Level Physiological Profiling Approach.

Erythromycin (EM), a macrolide antibiotic, by influencing the biodiversity of microorganisms, might change the catabolic activity of the entire soil microbial community. Hence, the goal of this study was to determine the metabolic biodiversity in soil treated with EM (1 and 10 mg/kg soil) using the community-level physiological profiling (CLPP) method during a 90-day experiment. In addition, the effect of soil inoculation with antibiotic-resistant Raoultella sp. strain MC3 on CLPP was evaluated. The resistance and resilience concept as well as multifactorial analysis of data was exploited to interpret the outcomes obtained. EM negatively affected the metabolic microbial activity, as indicated by the values of the CLPP indices, i.e., microbial activity expressed as the average well-color development (AWCD), substrate richness (R), the Shannon–Wiener (H) and evenness (E) indices and the AWCD values for the six groups of carbon substrate present in EcoPlates until 15 days. The introduction of strain MC3 into soil increased the degradative activity of soil microorganisms in comparison with non-inoculated control. In contrast, at the consecutive sampling days, an increase in the values of the CLPP parameters was observed, especially for EM-10 + MC3-treated soil. Considering the average values of the resistance index for all of the measurement days, the resistance of the CLPP indices and the AWCD values for carbon substrate groups were categorized as follows: E > H > R > AWCD and polymers > amino acids > carbohydrates > miscellaneous > amines > carboxylic acids. The obtained results suggest a low level of resistance of soil microorganisms to EM and/or strain MC3 at the beginning of the exposure time, but the microbial community exhibited the ability to recover its initial decrease in catabolic activity over the experimental period. Despite the short-term effects, the balance of the soil ecosystem may be disturbed.

Microcosm-scale biogeochemical stabilization of Pb, As, Ba and Zn in mine tailings amended with manure and ochre

Mine tailings are major sources of metals and metalloids in the environment, making the physical and geochemical stabilization of tailings a serious environmental challenge. With a view to facilitate the development of covering vegetation and of decreasing the mobility of Pb in the acid tailings of a former Ag–Pb mine, laboratory microcosm experiments were performed to enable comparison of the effectiveness of several treatments. Tailings were mixed with 5% by weight of ochre, an iron-rich material produced during the treatment of a coal mine water, and with cow manure (0, 0.15, 1 and 2% by weight), either solely or in combination. They were then submitted to weekly watering over 84 days. All treatments raised the pH values from 4 to values between 7 and 8 and induced a strong decrease in the total dissolved Pb concentration in the percolating water (from 13 to 15 mg.L−1 to less than 0.5 mg.L−1). Several processes seemed to be involved in the immobilization of Pb by the amendments: precipitation as hydroxide, sulfate, carbonate and phosphate, and adsorption on iron hydroxides. A transient increase was observed in both Pb mobility and functional microbial diversity with 1% and 2% manure, with a peak after 28 days of incubation. This peak corresponded to an Average Well Color Development (AWCD) in Biolog™ Ecoplates increase from 0.5 to 0.8 with 1% manure and from 0.6 to 1.5 with 2% manure. However, at the end of experiment, Pb immobilization was strengthened by 2% manure and microbial functional biodiversity fell back, with AWCD values of 0.5 and 0.8 for 1% and 2% manure, respectively. Other toxic elements present in the tailings, namely As, Zn and Ba, were not strongly mobilized by the treatments, although cow manure slightly increased the leaching of Ba and As, which maximum concentrations in the leaching water reached 65 μg.L−1 Ba and 9 μg.L−1 As. All amendments improved the growth of ryegrass, which maximum dry biomass ranged from 38 mg/microcosm without amendment to 155 mg/microcosm with 0.15% manure. The results provide key information about the biogeochemical processes driving the mobility of Pb, As, Zn and Ba in acid mine tailings during the first 84 days following their amendment with iron-rich ochre and manure.

Tillage frequency affects microbial metabolic activity and short-term changes in CO2 fluxes within 1 week in karst ecosystems

Tillage disturbance can significantly affect soil microbial metabolic activity and CO2 fluxes. Nevertheless, the influence of different tillage frequencies on microbial metabolic activity and short-term temporal changes of CO2 fluxes remains unclear. We established an in situ experiment with the following treatments: no tillage (T0), semiannual tillage (T1), tillage every 4 months (T2), bimonthly tillage (T3), and monthly tillage (T4). The microbial metabolic activity (Biolog EcoPlate), short-term (hours to days) temporal changes in CO2 fluxes within 1 week, and soil properties were measured after 1 year of treatment. The highest CO2 emissions occurred in the first 72 h after tillage treatment and were significantly higher in T3 and T4 than in T0, T1, and T2 within 1 week. Average well color development (AWCD) values reflect microbial metabolic activity and were significantly higher in the tillage treatments (T1, T2, T3, and T4) than under no tillage. There was no significant difference in the Shannon diversity index under all treatments. A higher Simpson diversity index was observed under high tillage frequency in T2, T3, and T4 compared with T0 and T1, while the highest was observed in T2. The highest utilization of carboxylic acids, amino acids, and polymers occurred in T3 and T4 soils, whereas T2 had the highest utilization of carbohydrates, amines, and miscellaneous carbon sources. AWCD values and short-term CO2 fluxes were significantly correlated with annual changes in soil organic carbon (△SOC), annual changes in dissolved organic carbon (△DOC), microbial biomass carbon (MBC), and large macroaggregates (> 1 mm). These results suggest that frequent tillage disturbance increases microbial metabolic activity, which can stimulate short-term CO2 emissions through changes in soil aggregates, SOC, DOC, and MBC.

Functional Diversity of Soil Microbial Communities in Response to the Application of Cefuroxime and/or Antibiotic-Resistant Pseudomonas putida Strain MC1

Cefuroxime (XM), the most commonly prescribed antibiotic from the cephalosporin group, may cause changes in the structure of the soil microbial community, and these changes may also be reflected in the alteration of its functionality. Therefore, due to the lack of studies on this topic, the scope of this study was to assess the functional diversity and catabolic activity of the microbial community in soil treated with XM (1 mg/kg and 10 mg/kg soil) using the community-level physiological profile (CLPP) approach during a 90-day experiment. In addition, the effect of antibiotic-resistant Pseudomonas putida strain MC1 (Ps) was also evaluated. The resistance/resilience concept and multifactorial analysis were used to interpret the data. The results showed that the introduction of XM and/or Ps into the soil caused changes in the catabolic activity and functional diversity of the microbial community. A decrease in the values of the CLPP indices (i.e., microbial activity expressed as the average well-color development (AWCD), substrate richness (R), the Shannon-Wiener (H) and evenness (E) indices and the AWCD values for the six carbon substrate groups) for the XM-treated soil was generally detected up to 30 days. In turn, at the same time, the activity measured in the Ps-inoculated soil was higher compared to the control soil. A stimulatory effect of XM at 10 mg/kg (XM10) and XM10+Ps on the utilization pattern of each substrate group was found at the following sampling times (days 60 and 90). The AWCD values for the utilization of amines, amino acids, carbohydrates, carboxylic acids, miscellaneous compounds and polymers for these treatments were found to be up to 2.3-, 3.1-, 2.3-, 13-, 3.4- and 3.3-fold higher compared to the values for the nontreated control, respectively. The resistance of the CLPP indices and the AWCD values for the carbon substrate groups were categorized as follows: E &gt; H &gt; R &gt; AWCD and amino acids = carbohydrates &gt; polymers &gt; amines &gt; miscellaneous &gt; carboxylic acids, respectively. The results suggest a low initial resistance of the soil microbial community to XM and/or Ps, and despite the short-term negative effect, the balance of the soil ecosystem may be disturbed.

Soil microbial community structure and catabolic activity are significantly degenerated in successive rotations of Chinese fir plantations

This study examined the hypotheses that soil microbial community composition and catabolic activity would significantly degenerated by consecutive monoculture in Chinese fir plantations. The phospholipid fatty acids (PLFA) and community level physiological profiles (CLPP) methods were used to assess the variations of soil microbial community among the first rotation Chinese fir plantation (FCP), the second rotation plantation (SCP) and the third rotation plantation (TCP). The total content of PLFA biomarkers was highest in FCP, followed by SCP, and TCP was the least detected. Conversely, the fungi/bacteria ratio significantly increased in the SCP and TCP soils. The average well-color development (AWCD) values significantly decreased (FCP > SCP > TCP). However, the sum of AWCD values of amino acids, carboxylic acids and phenolic compounds were higher significantly in the SCP and TCP soils than FCP soils, suggesting that the microflora feeding on acids gradually became predominant in the continuous monoculture plantation soils. Soil C/N ratio was one of the most important factors to soil microbial diversity. Both the PLFA and CLPP results illustrated the long-term pure plantation pattern exacerbated the microecological imbalance in the rhizospheric soils of Chinese fir, and markedly decreased the soil microbial community diversity and metabolic activity.

Phytoremediation of diphenylarsinic-acid-contaminated soil by Pteris vittata associated with Phyllobacterium myrsinacearum RC6b

ABSTRACTA pot experiment was conducted to explore the phytoremediation of a diphenylarsinic acid (DPAA)-spiked soil using Pteris vittata associated with exogenous Phyllobacterium myrsinacearum RC6b. Removal of DPAA from the soil, soil enzyme activities, and the functional diversity of the soil microbial community were evaluated. DPAA concentrations in soil treated with the fern or the bacterium were 35–47% lower than that in the control and were lowest in soil treated with P. vittata and P. myrsinacearum together. The presence of the bacterium added in the soil significantly increased the plant growth and DPAA accumulation. In addition, the activities of dehydrogenase and fluorescein diacetate hydrolysis and the average well-color development values increased by 41–91%, 37–78%, and 35–73%, respectively, in the treatments with P. vittata and/or P. myrsinacearum compared with the control, with the highest increase in the presence of P. vittata and P. myrsinacearum together. Both fern and bacterium alone greatly enhanced the removal of DPAA and the recovery of soil ecological function and these effects were further enhanced by P. vittata and P. myrsinacearum together. Our findings provide a new strategy for remediation of DPAA-contaminated soil by using a hyperaccumulator/microbial inoculant alternative to traditional physicochemical method or biological degradation.

English

The effects of three years continuous application of different rates of bio-organic fertilizer (BOF) were evaluated on three kinds of the counts of soil microbes, microbial metabolic activity and disease index of Verticillium wilt through greenhouse pot experiments. The results showed that, the BOF not only reduced the occurrence of verticillium wilt in cotton and decreased the counts of V. dahliae, but also improved the number of fungi, bacteria, actinomycetes, and microbial activity. The number of V. dahliae reduced gradually and fungi, bacteria, actinomycetes and average well color development (AWCD) firstly increased and then decreased with increasing the amount of fertilization in different organic matter content of soil. The number of V. dahliae was significantly increased by three years of fertilization. It showed that application of bio-organic fertilizer only delays the growth in the number of pathogen in soil within a certain time. The numbers of bacteria, actinomycetes were increased and the number of fungi was slightly reduced with increase of fertilization period. Application of bio-organic fertilizer made AWCD significantly higher than no fertilization (CK). By cluster analysis and principal component analysis, the results showed that the classification similar to disease index of various treatments, and it coincided with the number of microorganisms and AWCD values. BOF not only can control and improve the metabolic characteristics of soil microbial communities, but also maintain a high soil biological activity.© 2016 Friends Science Publishers Keyword: BOF; BIOLOG; Cotton verticillium wilt; V. dahliae; Principal component analysis

Microbial community and functional diversity associated with different aggregate fractions of a paddy soil fertilized with organic manure and/or NPK fertilizer for 20 years

Microbial communities are sensitive to fertilizations, and the response of microbial communities to different fertilization regimes in bulk soils has been studied. However, it is unclear how microbial communities performance in soil aggregates. We determined the composition and functional diversity of the microbial community within different aggregate size fractions of a paddy soil fertilized with organic manure (OM) or/and mineral NPK fertilizer (NPK/NPKO) for 20 years, along with a control (no fertilizer, NoF). Soils were sampled in late December 2010 from a long-term experimental site established from an uncultivated wasteland in 1990. Five aggregate fractions, i.e., large macroaggregates (>2 mm), macroaggregates (1–2 mm), small macroaggregates (0.25–1 mm), microaggregates (0.053–0.25 mm), and non-aggregated silt and clay particles (<0.053 mm), respectively, were obtained by wet sieving. Microbial community composition was estimated based on phospholipid fatty acids (PLFAs) analysis. Microbial functional diversity was evaluated using the community level physiological profile method by Biolog Eco-microplate. The PLFA signature analysis revealed that microbial biomass tended to decrease with decreasing aggregate size. The application of fertilizer significantly increased the microbial biomass of large macroaggregates relative to the NoF treatment, but there was no significant difference among aggregates of the three fertilization treatments. Average well color development (AWCD) as well as all the functional diversity indices was almost highest in large macroaggregates and microaggregates of NoF, OM, and NPK treatments and in microaggregates of NPKO treatment, while all of them were lowest in silt and clay particles. NPKO treatment led to the greatest microbial functional diversity. AWCD values and McIntosh index (U) of most aggregates under the NPK treatment were significantly increased. The OM treatment did not significantly affect microbial functional diversity associated with different aggregate fractions. Aggregate fractions and fertilization significantly affected microbial community composition and functional diversity. Soil organic C and carbon to nitrogen (C/N) ratio dominated microbial community composition and metabolic profile associated with different aggregates, respectively.

土霉素对堆肥过程中酶活性和微生物群落代谢的影响

以猪粪和秸秆为试验材料，研究了土霉素对堆肥温度、种子发芽指数、C/N、纤维素酶、脲酶、过氧化氢酶以及微生物群落代谢的影响。结果表明，0 mg/kg（对照处理）的堆肥在第2天上升到 50 ℃以上，维持了 5 d，达到了无害化处理的要求。35 mg/kg土霉素处理（A1 处理）第4天升到 51.0 ℃，其高温期维持了 1 d。70 mg/kg 土霉素处理（A2 处理）第3天升到 50 ℃以上，高温期维持了 2 d。105 mg/kg 土霉素处理（A3 处理）和 140 mg/kg 土霉素处理（A4 处理）的温度在整个堆肥期间均未达到 50 ℃。在堆肥结束时各个处理的种子发芽指数均达到 80% 以上。CK（对照处理）、A1、A2、A3 和 A4 处理的 C/N 由 34.50 分别降为 16.64、16.07、19.48、18.45 和 19.83。堆肥的第1天，A1、A2、A3 和 A4 处理对纤维素酶活性的抑制率分别为 60.30%、21.30%、48.81% 和 76.05%，第3天，土霉素对纤维素酶活性起促进作用，在 4-30 d，A3、A4 处理对纤维素酶活性有抑制作用。在堆肥的前期（1-3 d），土霉素刺激脲酶活性，随着堆肥时间的延长，土霉素对脲酶活性由刺激变为抑制作用，在第18-30天 A3、A4 处理与 CK 相比有着显著的抑制作用。在堆肥第1天到第18天，土霉素基本上促进过氧化氢酶的活性，堆肥 18 d 之后土霉素对过氧化氢酶起着是抑制作用。用 Biolog（ECO Microplate）方法研究了土霉素对堆肥过程中微生物群落代谢的影响，结果表明，在升温期 CK 处理的平均颜色变化率AWCD（Average Well Color Development）在培养 60 h 之后大于其他处理，高温期 A2 处理的 AWCD 值最高，在降温期 CK 的 AWCD 值一直是最高的。对 Shannon 指数进行分析显示，堆肥的初始阶段土霉素降低微生物群落的功能多样性，随着时间的延长，土霉素增加微生物群落的功能多样性。对微生物利用六大类碳源分析表明，140 mg/kg 的土霉素浓度能够改变微生物利用碳源的种类。;An outdoor experiment was conducted to study the effect of oxytetraeyeline addition on composting temperature, seed germination index, ratio of carbon to nitrogen, cellulose, urease, catalase and microbial community metabolism during composting of pig manure mixed with wheat straw. The results showed that composting temperature was reached to 50 ℃ in the second day of composting and lasted for 5 days on treatment without addition of oxytetraeyeline (Control check,CK), which could meet the need of the requirement of harmlessness. The composting temperature was above 51.0 ℃ in the fourth day of composting with addition of 35 mg/kg oxytetracycline (A1 treatment), and the high temperature period maintained for 1 day. The temperature was above 50 ℃ in the third day of composting where 70 mg/kg oxytetracycline was added (A2 treatment), and the high temperature period only hold on for 2 days. The temperature could not reach to 50 ℃ over the whole time of composting on both A3 and A4 treatments where 105 mg/kg and 140 mg/kg of oxytetracycline were spiked respectively. The germination indices (<em>GI</em>) of seeds, which contained in the compost materials, were higher than 80% for all treatments at the end of the composting. The C/N ratios for all treatments were decreased from an initial value of 34.50 to 16.64, 16.07, 19.48, 18.45 and 19.83, respectively, when composting completed. Activities of cellulose on treatments those receiving oxytetracycline were inhibited by 60.30%, 21.30%, 48.81% and 76.05%, respectively, over CK treatment in the first day of the composting, and they were increased in the third day. Nevertheless, activities of cellulase were inhibited under A3 and A4 treatments compared with CK from day 4 to day 30. The activity of urease was increased by addition of oxytetracycline in the first 3 days, since then on, it was decreased. The higher concentrations of oxytetracycline (A3 and A4) had a significant inhibitory effect on activity of urease from day 18 to day 30. The catalase activity was enhanced generally by the addition of oxytetraeyeline from day 1 to day 18 compared to CK, from then on it was decreased over CK. The effect of oxytetracycline addition on microbial community metabolic profiles during composting was assayed with Biolog (ECO Microplate) method. The results showed that AWCD (Average Well Color Development) values of CK treatment were the highest after 60 h incubation during temperature raising period of the compost. The highest AWCD values were observed on A2 treatment during the high temperature period. AWCD values under CK were greater than other treatments over cooling period. Shannon index results suggested that the oxytetracycline addition could reduce the functional diversity of microbial communities in the initial stage of the composting, in contrast, it could increase the functional diversity of microbial communities at other stages of composting. The carbon source utilization data showed that the addition of 140 mg/kg of oxytetracycline could significantly change the types of carbon sources used by microorganisms.

Impact of allelopathic rice seedlings on rhizospheric microbial populations and their functional diversity

Field performance of rice allelopathic potential is indirectly regulated by the microflora in the rhizosphere. The present study aimed to investigate the dynamics of microbial populations and their functional diversities in the seedling rhizospheres of rice cultivars with varied allelopathic activities by employing agar plate bioassay, fumigation and BIOLOG analysis. Rice cultivars significantly affected the microbial carbon content in their associated rhizospheric soil. The microbial carbon contents were ranked in a decreasing order as Iguape Cateto (441.0 mg·kg –1) > IAC47 (389.7 mg·kg –1) > PI312777 (333.2 mg·kg –1) > Lemont (283.8 mg·kg –1) with the nil-rice control soil of 129.3 mg·kg –1. Similarly, the respiration rate of the soils was 1.404, 1.019, 0.671 and 0.488 μgC·g –1· h –1 for PI312777, Iguape Cateto, IAC47 and Lemont, respectively. The respiration rate was only 0.304 μ gC·g –1·h –1 for the control soil. The microbial flora in the rhizospheric soil of different rice cultivars was dominated by bacteria (58.4%–65.6%), followed by actinomycete (32.2%–39.4%) and fungi (2.2%–2.8%). BIOLOG analysis showed that the value of Average Well Color Development (AWCD) differed significantly among rice cultivars. It was always the highest in the rhizospheric soil of the strongly allelopathic rice cv. PI312777, and the lowest in the rhizospheric soil of the poorly allelopathic rice cv. Lemont. The AWCD value reached the maximum in all the sampled soils after 144 hours of incubation. The AWCD values from the rhizospheric soils of PI312777, IAC47, Iguape Cateto and Lemont were 1.89, 1.79, 1.60 and 1.43 times higher than that of the control soil. Principal Component Analysis (PCA) identified 3 principal component factors (PCF) in relation to carbon sources, accounting for 70.1%, 11.3% and 7.0% of the variation, respectively. 19 categories of carbon sources were significantly positively correlated to the 3 principal components. Phenolic acids, carbohydrates, amino acids and amides were significantly correlated to the principal component 1, phenolic acids, carbohydrates and fatty acids to the principal component 2, and carbohydrates and hydroxylic acids to the principal component 3. Amino acids and amides were the two main carbon sources separating the 3 principal component factors. In addition, the total microbial population in the rhizospheric soil was significantly positively correlated with AWCD, microbial biomass carbon, microbial respiration and Shannon index. There was a significantly positive correlation between the total microbial population and the inhibition rate (IR) on the root length of lettuce owing to the different allelopathic activities of the rice cultivars. These results suggest that changes in microbial population, activity and functional diversity in the rhizospheres are highly cultivar-dependent. These changes might play an important role in governing the rice allelopathic activity in the field.

Functional Diversity of Culturable Bacterial Communities in the Rhizosphere in Relation to Fine-root and Soil Parameters in Alder Stands on Forest, Abandoned Agricultural, and Oil-shale Mining Areas

Grey alder (Alnus incana) and black alder (Alnus glutinosa) stands on forest land, abandoned agricultural, and reclaimed oil-shale mining areas were investigated with the aim of analysing the functional diversity and activity of microbial communities in the soil–root interface and in the bulk soil in relation to fine-root parameters, alder species, and soil type. Biolog Ecoplates were used to determine community-level physiological profiles (CLPP) of culturable bacteria in soil–root interface and bulk soil samples. CLPP were summarized as AWCD (average well color development, OD 48 h−1) and by Shannon diversity index, which varied between 4.3 and 4.6 for soil–root interface. The soil–root interface/bulk soil ratio of AWCD was estimated. Substrate-induced respiration (SIR) and basal respiration (BAS) of bulk soil samples were measured and metabolic quotient (Q = BAS/SIR) was calculated. SIR and Q varied from 0.24 to 2.89 mg C g−1 and from 0.12 to 0.51, respectively. Short-root morphological studies were carried out by WinRHIZOTM Pro 2003b; mean specific root area (SRA) varied for grey alder and black alder from 69 to 103 and from 54 to 155 m2 kg−1, respectively. The greatest differences between AWCD values of culturable bacterial communities in soil–root interface and bulk soil were found for the young alder stands on oil-shale mining spoil and on abandoned agricultural land. Soil–root interface/bulk soil AWCD ratio, ratio for Shannon diversity indices, and SRA were positively correlated. Foliar assimilation efficiency (FOE) was negatively correlated with soil–root interface/bulk soil AWCD ratio. The impact of soil and alder species on short-root morphology was significant; short-root tip volume and mass were greater for black alder than grey alder. For the investigated microbiological characteristics, no alder-species-related differences were revealed.

Potential C-source utilization patterns of bacterial communities as influenced by clearing and land use in a vertic soil of Argentina

A sole-carbon-source catabolism assay (Biolog GN microplate) was used to study whether bacterial communities from the same vertic soil, but under different management history, showed distinctive patterns of C-substrate utilization. Two sampling depths (0–7.5 and 7.5–15 cm) were also investigated. The response of microbial communities to increasing periods of time — 16, 26 and 40 years (S2, S3, S4, respectively) — since native vegetation clearing and to land use was evaluated as related to the soil in its native condition (S1). Tenfold dilutions of soil suspensions were performed and aliquots of 10 −4 dilution were inoculated into each well of the Biolog GN microplates and then incubated. Activity on C-substrates was recorded as optical density at regular time intervals. Absorbance data from the 54-h incubation time were used to calculate the average well-color development (AWCD) in each plate, richness (number of catabolized C-sources) and diversity Shannon’s index. Principal component analysis (PCA) was performed to study patterns of C-source utilization. Number of bacteria was determined by plate counts on to tryptic soy agar (TSA) and expressed as colony-forming units (CFU) g −1 soil. The lowest AWCD values were found in the 40 years since clearing site (S4) in both depths, despite the fact that the largest number of bacteria was found in the top 0–7.5 cm. Samples from the native condition showed the largest richness and diversity on metabolized C substrates ( p<0.001) while S4 had the lowest values at a depth of 0–7.5 cm. The locations that were investigated could be differentiated by PCA. The Biolog GN assay showed to be sensitive to distinguish soil bacterial communities from sites with different times elapsed since clearing and management history. Larger differences among samples were detected at 0–7.5 cm depth. Distinctive patterns of ‘in vitro’ C-source utilization could be related to differences in chemical composition of soil organic matter.