Soil Microbial Characteristics Under Long-Term Heavy Metal Stress:A Case Study in Zhangshi Wastewater Irrigation Area,Shenyang

Soil samples were collected from Zhangshi Wastewater Irrigation Area in the suburb of Shenyang City,China,an area with a 30-year irrigation history with heavy metal-containing wastewater.The chemical properties and microbial characteristics of the soils were examined to evaluate the present situation of heavy metal pollution and to assess the soil microbial characteristics under long-term heavy metal stress.In light of the National Environmental Quality Standards of China,the soil in the test area was heavily polluted by Cd and to a lesser degree by Zn and Cu,even though wastewater irrigation ceased in 1993.Soil metabolic quotient (qCO_2) had a significant positive correlation,while soil microbial quotient (qM) had a negative correlation with content of soil heavy metals.Soil microbial biomass carbon (MBC) had significantly negative correlation with Cd,but soil substrate-induced respiration (SIR),dehydrogenase activity (DHA),cellulase activity, and culturable microbial populations had no persistent correlations with soil heavy metal content.Soil nutrients,except for phosphorous,showed positive effects on soil microbial characteristics,which to a certain degree obscured the adverse effects of soil heavy metals.Soil Cd contributed more to the soil microbial characteristics,but qM and qCO_2 were more sensitive and showed persistent responses to heavy metals stress.It could be concluded that qM and qCO_2 can be used as bioindicators of heavy metal pollution in soils.

Variation of Soil Microbial Biomass and Enzyme Activities at Different Growth Stages of Rice (Oryza sativa)

A pot experiment was conducted under submerged conditions with hybrid rice Zhenong 7 to study the variation in the soil microbial biomass carbon （Cmic）, soil microbial biomass nitrogen （Nmic）, soil respiration rate, soil microbial metabolic quotient, soil enzyme activities, chlorophyll content, proline content and peroxidase activity （POD） in rice leaf at different growth stages. The soil Cmic, Nmic and soil respiration rate significantly increased at the early stage and then declined during rice growth, but ascended slightly at maturity. However, soil metabolic quotient declined at all the stages. Soil urease activity increased at first and then decreased, while acid phosphatase and dehydrogenase activities descended before ascended and then descended again. Soil urease activity and acid phosphatase activity showed a peak value at the tillering stage about 30 days after rice transplanting, but the peak value of dehydrogenase activity emerged at about 50 days after rice transplanting and the three soil enzymatic activities were significantly different at the different developmental stages. As rice growing, chlorophyll content in rice leaf descended at the early stage then ascended and a peak value appeared at about the 70th after rice transplanting, after that declined drastically, while POD activity increased gradually, but proline content declined gradually. There was a slight relation between rice physiological indices and soil biochemical indices, which indicated that soil biochemical characteristics were affected significantly by rice growth in the interaction system of the rice. soil and microorganisms.

Changes in soil biochemical indicators at different wheat growth stages under conservation-based sustainable intensification of rice-wheat system

Soil microbes play critical roles in soil biogeochemistry, soil biological health and crop productivity. The current study evaluated the effects of tillage and residue management on changes in soil biochemical indicators at different growth stages of wheat after 5 years of rice-wheat system. Nine treatment combinations of tillage, crop establishment and crop residue management included three main plot treatments applied to rice:(1) conventional till direct dry seeded rice(CTDSR),(2) zero till direct dry seeded rice(ZTDSR), and(3) conventional puddled manual transplanted rice(CTPTR) and three subplot treatments in subsequent wheat:(1) conventional tillage with rice residue removed(CTW-R),(2) zero tillage with rice residue removed(ZTW-R) and(3) zero tillage with rice residue retained as surface mulch(ZTW+R). Irrespective of rice treatments, ZTW+R treatment had higher soil biochemical indicators compared with ZTW-R and CTW-R at all the growth stages of wheat. Generally, all the biochemical indicators were the highest at the flowering stage of wheat. Residual effect of rice treatments was also significant on biochemical quotients in wheat, which were the highest under ZTDSR followed by CTDSR and CTPTR. The present study provided three sensitive and reliable biochemical indicators(microbial biomass, basal soil respiration and microbial quotient) which respond rapidly to change in tillage and residue management practices in RWS of South Asia.

The static and cidal effects of veterinary antibiotics on soil microorganisms in the presence of organic and mineral amendments

●Gentamicin initially decreased microbial activity comparative to penicillin higher.●Recovery was comparatively high in oxytetracycline treated soils.●Organic amendments improved the resilience indices.●Unexpectedly the qCO_(2) decreased in the antibiotic treated soils.●The static effects of the applied antibiotics were higher than their cidal effects.This study aimed to describe the static and cidal adverse effects of antibiotics on soil microbial activity resulting from manure application.So,in the present study,the treatments included:without antibiotics;application of gentamicin,oxytetracycline,and penicillin each in different concentrations(50,100,and 200 mg kg−1 dry soil).They were applied in soils treated with and without organic and mineral conditioners(cow manure,biochar,and nano-zeolite).Soil microbial respiration and metabolic quotient were studied at three time periods(1−7,7−30,and 30−90 days)during a 90-day incubation of the treated soils.Antibiotics applied to the soil samples significantly decreased soil basal respiration(BR)values compared to those of the control,and the most significant decrease was observed for gentamicin.Gentamicin had a short intensive impact,alleviated by manure and biochar,on soil copiotrophs.After a significant initial reduction in substrate-induced respiration(SIR),gentamicin application then caused a substantial increase in SIR values.Unexpectedly metabolic quotient decreased in the antibiotic-treated soils.This study revealed that the static effects of the applied antibiotics in soil were greater than the cidal effects.

Relationship Between Vegetation Restoration and Soil Microbial Characteristics in Degraded Karst Regions: A Case Study

The mechanism of vegetation restoration on degraded karst regions has been a research focus of soil science and ecology for the last decade.In an attempt to preferably interpret the soil microbiological characteristic variation associated with vegetation restoration and further to explore the role of soil microbiology in vegetation restoration mechanism of degraded karst regions,we measured microbial biomass C and basal respiration in soils during vegetation restoration in Zhenfeng County of southwestern Guizhou Province,China.The community level physiological profiles(CLPP) of the soil microbial community to were estimated determine if vegetation changes were accompanied by changes in functioning of soil microbial communities.The results showed that soil microbial biomass C and microbial quotient(microbial biomass C/organic C) tended to increase with vegetation restoration,being in the order arboreal community stage > shrubby community stage > herbaceous community stage > bare land stage.Similar trend was found in the change of basal respiration(BR).The metabolic quotient(the ratio of basal respiration to microbial biomass,qCO 2) decreased with vegetation restoration,and remained at a constantly low level in the arboreal community stage.Analyses of the CLPP data indicated that vegetation restoration tended to result in higher average well color development,substrate richness,and functional diversity.Average utilization of specific substrate guilds was highest in the arboreal community stage.Principle component analysis of the CLPP data further indicated that the arboreal community stage was distinctly different from the other three stages.In conclusion,vegetation restoration improved soil microbial biomass C,respiration,and utilization of carbon sources,and decreased qCO 2,thus creating better soil conditions,which in turn could promote the restoration of vegetation on degraded karst regions.

Sensitivity of Labile Soil Organic Carbon Pools to Long-Term Fertilizer, Straw and Manure Management in Rice-Wheat System

Labile soil organic carbon （SOC） pools, estimated through chemical fractionation techniques, are considered sensitive indicators of management-induced changes in quality and composition of soil organic matter. Although the impacts of organic manure and crop residue applications on C sequestration in rice-wheat system are fairly well documented, their influence on labile SOC pools is relatively less known. Impacts of organic manure, rice straw, and inorganic fertilizer nitrogen （N） applications on soil total organic carbon （TOC） and SOC pools including water-extractable organic C （WEOC）, hot water-soluble organic C （HWOC）, potassium permanganate- oxidizable organic C （KMnO4-C）, microbial biomass C （MBC）, mineralizable organic C （Cmin）, and the oxidizable fractions of decreasing oxidizability （easily-oxidizable, oxidizable, and weakly-oxidizable） were investigated in an ll-year field experiment under rice-wheat system. The field experiment included treatments of different combinations of farmyard manure, rice straw, and fertilizer N application rates, with C inputs estimated to be in the range from 23 to 127 Mg ha-1. After 11 years of experiment, WEOC, HWOC, and KMnO4-C were 0.32%-0.50%, 2.2%-3.3%, and 15.0%-20.6% of TOC, respectively. The easily-oxidizable, oxidizable, and weakly-oxidizable fractions were 43%-57%0, 22%-27%, and 10%-19% of TOC, respectively. The applications of farmyard manure and rice straw improved WEOC, HWOC, KMnO4-C, easily-oxidizable fraction, Cmin, and MBC, though the rates of change varied considerably from -14% to 145% and -1170 to 83% of TOC, respectively. At the C input levels between 29 and 78 Mg C ha-1 during the ll-year period, the greatest increase was observed in WEOC and the minimum in KMnO4-C. Water-extractable organic C exhibited a relatively greater sensitivity to management than TOC, suggesting that it may be used as a sensitive indicator of management-induced changes in soil organic matter under rice-wheat system. All the other labile SOC pools exhibited almost the same sensitivity to management as TOC. Most of the SOC pools investigated were positively correlated to each other though their amounts differed considerably. Long-term applications of farmyard manure and rice straw resulted in build-up of not only the labile but also the recalcitrant pool of SOC, emphasizing the need for continued application of organic amendments for permanence of the accrued C under the experimental conditions.

Soil Microbial and Enzymatic Activities Across a Chronosequence of Chinese Pine Plantation Development on the Loess Plateau of China

Successional and seasonal effects on soil microbial and enzymatic properties were studied in Chinese pine （Pinus tabulaeformis） plantations in an age sequence of 3-, 7-, 13-, 21- and 28-year-old in northern Ziwuling region in the middle of Loess Plateau, China. The results indicated that plantation age and season affected soil microbial and enzymatic parameters significantly. Soil organic C, total N, microbial biomass C, microbial quotient, basal respiration, dehydrogenase, N-α-benzoyl-L-argininamide （BAA）-protease, urease and β-glucosidase increased quickly and tended to be highest at PF21 （21-year plantation）, thereafter they remained nearly at a constant level, whereas the metabolic quotient （qCO2） showed an initial increase and then decreased gradually. Measures of these soil properties showed significant seasonal fluctuations except for organic C and total N, which were found to be relatively stable throughout the study period, and the seasonal distributions were autumn 〉 spring 〉 summer 〉 winter for microbial biomass C, microbial quotient, dehydrogenase, and β-glucosidase; autumn 〉 summer 〉 spring 〉 winter for BAA-protease and urease; and summer 〉 autumn 〉 spring 〉 winter for basal respiration and qCO2. Significant season x age interaction was observed for biomass C, basal respiration, dehydrogenase and BAA-protease.

Dynamics of CO_2 Emission and Biochemical Properties of a Sandy Calcareous Soil Amended with Conocarpus Waste and Biochar

Biochar is a carbon-rich product obtained by biomass pyrolysis and considered a mean of carbon sequestration. In this research, a sandy calcareous soil from the Farm of the College of Food & Agriculture Sciences, King Saud University, Saudi Arabia, was amended with either woody waste of Conocarpus erectus L.(CW) or the biochar(BC) produced from CW at rates of 0(control), 10, 30 and 50 g kg-1. The effects of the amendments on soil p H, dissolved organic carbon(DOC), microbial biomass carbon(MBC), CO2 emission and metabolic quotient(q CO2) of the sandy calcareous soil were studied in a 60-d incubation experiment. The results showed that the addition of CW led to a significant decrease in soil p H compared to the control and the addition of BC. The CO2-C emission rate was higher in the first few days of incubation than when the incubation time progressed. The cumulative CO2-C emission from the soil amended with CW, especially at higher rates, was higher(approximately 3- to 6-fold) than that from the control and the soil amended with BC. The BC-amended soil showed significant increases in CO2-C emission rate during the first days of incubation as compared to the non-amended soil, but the increase in cumulative CO2-C emission was not significant after 60 d of incubation. On the other hand, CW applications resulted in considerably higher cumulative CO2-C emission, MBC and DOC than the control and BC applications. With the exception of 0 day(after 1 h of incubation), both CW and BC applications led to lower values of q CO2 as compared to the control. The power function kinetic model satisfactorily described the cumulative CO2-C emission. Generally, the lowest values of CO2 emission were observed in the soil with BC, suggesting that the contribution of BC to CO2 emission was very small as compared to that of CW.

Soil Microbial Activities in Beech Forests Under Natural Incubation Conditions as Affected by Global Warming

Microbial activity in soil is known to be controlled by various factors. However, the operating mechanisms have not yet been clearly identified, particularly under climate change conditions, although they are crucial for understanding carbon dynamics in terrestrial ecosystems. In this study, a natural incubation experiment was carried out using intact soil cores transferred from high altitude(1 500 m) to low(900 m) altitude to mimic climate change scenarios in a typical cold-temperate mountainous area in Japan. Soil microbial activities, indicated by substrate-induced respiration(SIR) and metabolic quotient(q CO2), together with soil physicalchemical properties(abiotic factors) and soil functional enzyme and microbial properties(biotic factors), were investigated throughout the growing season in 2013. Results of principal component analysis(PCA) indicated that soil microbial biomass carbon(MBC) andβ-glucosidase activity were the most important factors characterizing the responses of soil microbes to global warming. Although there was a statistical difference of 2.82 ℃ between the two altitudes, such variations in soil physical-chemical properties did not show any remarkable effect on soil microbial activities, suggesting that they might indirectly impact carbon dynamics through biotic factors such as soil functional enzymes. It was also found that the biotic factors mainly controlled soil microbial activities at elevated temperature,which might trigger the inner soil dynamics to respond to the changing environment. Future studies should hence take more biotic variables into account for accurately projecting the responses of soil metabolic activities to climate change.

Effects of biochar amendment and nitrogen fertilization on soil microbial biomass pools in an Alfisol under rain-fed rice cultivation

Field studies were conducted over 2 years to determine the response of soil microbial biomass pool to biochar and N fertilizer combinations in a rain-fed rice cropping system.Biochar was applied at four doses:0 t ha^(−1),3 t ha^(−1),6 t ha^(−1) and 12 t ha^(−1) in combination with N fertilizer at four rates:0 kg ha^(−1),30 kg ha^(−1),60 kg ha^(−1) and 90 kg ha^(−1) to a Typic Paleustalf Alfisol.Soil samples from two depths(0-10 and 10-20 cm)were collected to determine microbial biomass C(MBC),N(MBN),P(MBP),MBC/N ratio,MBC/P ratio,soil CO_(2) flux,microbial qCO_(2),cultivable bacterial and fungal abundance.Biochar and N fertilizer combination effects on MBC,MBN and MBP pools were dependent on biochar doses,N fertilizer rates and soil depth.MBC/N and MBC/P ratios were decreased after 2 years.Soil CO_(2) flux was maximum at post-seeding stage of rice plant,while decreasing trends occurred at active tillering and harvest stage.Increasing doses of biochar irrespective of its combination with N fertilizer rates decreased CO_(2) flux and microbial qCO_(2).Combinations of biochar and N fertilizer increased fungal/bacterial ratio and induced a shift to a more fungal-dominated population after 2 years.Our results sug-gest that combination of biochar doses(3-12 t ha^(−1))with N fertilizer rates had stimulatory effects on microbial biomass pools and activity with positive implications for organic carbon accumulation,nitrogen(N)and phosphorus(P)retention in tropical soils.

Changes in plant community and soil ecological indicators in response to Prosopis juliflora and Acacia mearnsii invasion and removal in two biodiversity hotspots in Southern India

Invasion of alien plant species can alter local plant diversity and ecosystem processes closely linked to soil organic carbon(SOC)and nutrient dynamics.Soil ecosystem processes such as microbial respiration and enzyme activity have been poorly explored under alien plant invasion and especially following invasive plant species removal.We studied the impact of Prosopis juliflora and Acacia mearnsii invasion and subsequent removal on local plant community composition and diversity and on soil microbial respiration and enzyme activity in two biodiversity hotspots in Southern India.Removal of Prosopis promoted recolonisation of local vegetation as indicated by a 38% and 28% increase in species richness and ground vegetation cover,respectively,compared to an unremoved site.Prosopis and Acacia removal led to a significant reduction in soil microbial biomass C(MBC),respiration,dehydrogenase and urease activity due to increased microbial respiration and N mineralisation rate.Higher metabolic quotients qCO_(2) in soil at Prosopis and Acacia removed sites indicate that MBC pools declined at a faster rate than SOC,resulting decreased MBC/SOC ratios compared to their respective removed sites.Natural and undisturbed ecosystems maintain more SOC through increased belowground and aboveground C input in the soil,resulting in a higher MBC content per unit SOC.Our results indicate that the interaction between above-and below-ground communities is a critical factor determining the structure and dynamics of local plant communities,especially in ecosystems affected by plant invasions.

Soil microbial attributes along a chronosequence of Scots pine(Pinus sylvestris var. mongolica) plantations in northern China

Soil microorganisms play a key role in soil organic matter dynamics, nutrient cycling, and soil fertility maintenance in forest ecosystems, and they are influenced by stand age and soil depth. However, few studies have simultaneously considered these two factors. In this study, we measured soil microbial biomass carbon (SMBC), soil microbial biomass nitrogen (SMBN), soil basal respiration (SBR) rate, and potential extracellular enzyme activity (EEA) in soil to a depth of 60 cm under 10-, 30-, and 40-year-old Scots pine (Pinus sylvestris var. mongolica) stands (Y10, Y30, and Y40, respectively) in plantations in northern China in 2011. Soil water content (SWC), soil pH, soil organic carbon (SOC), and soil total nitrogen (STN) were also measured to explore their effects on soil microbial indices across different stand ages and soil depths. Our results showed that SMBC, SMBN, and the SBR rate were generally higher for the Y30 stand than for the Y10 and Y40 stands. Potential EEA, except forα-glucosidase, decreased significantly with increasing stand age. Soil organic carbon,STN, SWC, and soil pH explained 67%of the variation in soil microbial attributes among the three stand ages. For the same stand age, soil microbial biomass and the SBR rate decreased with soil depth. Lower microbial biomass, lower SBR rate, and lower EEA for the mature Y40 stand indicate lower substrate availability for soil microorganisms, lower soil quality, and lower microbial adaptability to the environment. Our results suggest that changes in soil quality with stand age should be considered when determining the optimum rotation length of plantations and the best management practices for afforestation programs.