Effect of heat-disturbance on microbial biomass carbon and microbial respiration in Chinese fir(Cunninghamia lanceolata) forest soils

Prescribed fire has now become the usual management practice in the Chinese fir （Cunninghamia lanceolata （Lamb.） Hook.） plantation in southern China. Heat generated during fire may affect carbon （C） dynam- ics in soils. We investigated the microbial biomass C （MBC） and microbial respiration in two Chinese fir forest soils （one is not exposed to fire for the past 88 years, and the other is recently exposed to prescribed fire） after soil heating （100 and 200 ℃） under three moisture regimes [25, 50 and 75 % of water holding capacity （WHC）]. For both soils, significant reduction in MBC with increasing heating temperature was found. Soils without exposing to fire previously had significantly greater MBC concentra- tion than the fire-exposed soils when heated at 100 or 200 ℃. Lower soil water content resulted in higher MBC concentrations in both soils. In contrast, both soils had the highest soil microbial respiration rate at 50 % WHC. Soils without exposing to fire previously had the greatest microbial respiration rates at 200 ℃, while the fire-ex- posed soils when heated at 100 ℃ had greatest microbialrespiration rates. During 14-days post-heat incubation, soil MBC in both soils was greatest after heating at 200 ℃ and 25 % WHC. However, soil previously exposed to fire had the lowest CO2 evolution when incubated at 25 % WHC.

Responses of soil microbial respiration to plantations depend on soil properties in subtropical China

Assessing the impact of plantation on microbial respiration （MR） is vitally important to understand the interactions between belowground metabolism and land use change. In this study, cumulative MR was determined by alkali absorption method in 1, 3, 7, 14, 21,28, 35, 42, 49, and 56 days from the soil in a representative plantations in the subtropical region of China. The treatment of plantations contained no plant （CK）, orange trees （Citrus reticulata）＋Bahia grass （Paspalum notatum） （GB）, orange trees （C. reticulata）＋Bahia grass （P. notatum）＋soybean （Giycine max （L.） Merrill） （GBH）. Results showed that plantation had significant effects on microbial respiration and the responses of microbial respiration to plantation from different soil layers and topographies were different： in 0-20 cm in uphill： GB〉GBH〉CK; in 20-40 cm in uphill： GBH〉CK〉GB; in 0-20 cm in downhill： GBH〉CK〉GB; in 20-40 cm in downhill： GB〉CK〉GBH. Furthermore, plantation also altered the relationships between MR and soil properties. In CK, microbial respiration was positively correlated with NH4＋ and soil total N, and negatively correlated with soil moisture, pH, NO3-, and microbial biomass carbon （MBC）. In GB, microbial respira- tion under GB significantly negatively correlated with dissolved organic carbon （DOC）. In GBH, microbial respiration under GBH was positively correlated with NH4＋, MBC, total soil carbon （TC）, and total soil nitrogen （TN）, and negatively correlated with soil moisture （SM）, pH, NO-, and DOC. The underlying mechanisms could be attributed to soil heterogeneity and the effects of plantation on soil properties. Our results also showed that plantation significantly increased soil C storage, which suggested plantation is a key measure to enhance soil C sequestration and mitigate global CO2 emission, especially for the soil with low initial soil carbon content or bared soil.

Growing-season soil microbial respiration response to long-term no tillage and spring ridge tillage

No tillage(NT)and spring ridge tillage(SRT)are two common applications of conservation tillage.Although conservation tillage is known to exert major control over soil microbial respiration(SMR),the growing-season SMR response to these two applications remains elusive.In order to better understand the influence of conservation tillage practices,this experiment was conducted in an experimental field using NT and SRT for 17 years.In situ measurements of SMR,soil temperature and soil water content(SWC)were performed.Soil samples were collected to analyze soil porosity,soil microbial biomass(SMB)and soil enzymatic activities.Results show that the two conservation tillage systems had a significant difference(p<0.05)in terms of SMR;the SMR of NT was 14.7 mg∙C/m^(2)∙h higher than that of SRT.In terms of soil temperature and soil enzymatic activities,the two treatments were not significantly different(p>0.05).Despite SRT increasing the proportion of micro-porosities and meso-porosities,the soil macro-porosities for NT were 7.37%higher than that of SRT,which resulted in higher bacteria and fungi in NT.Owing to SRT damaged the hypha,which had disadvantage in soil microbe protection.Inversely,less soil disturbance was a unique advantage in NT,which was in favor of improving soil macro-pores and SWC.Redundancy analyses(RDA)showed SMR was positively correlated with soil macro-pores,SMB and SWC.Furthermore,the Pearson correlation test indicated that SMB and soil enzymatic activities did not have a significant correlation(p>0.05).This study results suggest that SRT is more conducive to carbon sequestration compared with NT in cropland.

Alteration of microbial properties and community structure in soils exposed to napropamide

The effect of pesticide napropamide （N,N-diethyl-2-（1-naphthalenyloxy） propanamide） on soil microorganisms for long-term （56 d） was assessed by monitoring changes in soil microbial biological responses. Soils were treated with napropamide at 0, 2, 10, 20, 40, and 80 mg/kg soil and sampled at intervals of 1, 3, 7, 14, 28, 42, and 56 d. The average microbial biomass C declined in napropamide-treated soils as compared to control. The same trend was observed on microbial biomass N after napropamide application. We also determined the basal soil respiration （BSR） and observed a high level in soils treated with napropamide during the first 7 d of experiment. But with the passage of incubation time, BSR with napropamide decreased relatively to control. Application of napropamide at 2-80 mg/kg soil had inhibitory effects on the activity of urease and invertase. Activity of catalase was enhanced during the initial 7 d of napropamide application, but soon recovered to the basal level. The depressed enzyme activities might be due to the toxicity of napropamide to the soil microbial populations. To further understand the effect of napropamide on microbial communities, a PCR- DGGE-based experiment and cluster analysis of 16S rDNA community profiles were performed. Our analysis revealed an apparent difference in bacterial-community composition between the napropamide treatments and control. Addition of napropamide apparently increased the number of bands during the 7-14 d of incubation. These results imply that napropamide-induced toxicity was responsible for the disturbance of the microbial populations in soil.

Shifts of sediment bacterial community and respiration along a successional gradient in a typical karst plateau lake wetland(China)

Bacteria are important regulators of carbon cycling in lakes and are central to sediment ecosystem processes.However,the sediment microbial communities and their respiratory responses to the lake wetland succession are poorly understood.In this study,we collected sediment samples from four different succession points(the Potamogeton lucens zone,the Scirpus tabernaemontani zone,the Scirpus triqueter zone,and the Juncus effusus zone)in the Caohai Wetland of the Guizhou Plateau(China).The bacterial communities at these succession points were studied using a high-throughput sequencing approach.The sediment microbial respiration(SR)was measured using static chambers in the field and basal respiration(BR)was determined in the laboratory.The results show that the dominant bacterial taxa in the sediment was Proteobacteria(34.7%),Chloroflexi(17.8%),Bacteroidetes(7.3%),Acidobacteria(6.6%),and Cyanobacteria(6.1%).Principal coordinate analysis showed that the microbial community structure differs significantly at different sampling points along the successional gradient,indicating that the bacterial community structure is sensitive to the lake wetland succession.Different hydrological regimes and soil characteristics such as NH_(4)^(+)-N,Fe^(2+),Mn^(2+),and sediment organic carbon(SOC)content may be important factors responsible for the differences in the sediment microbial characteristics of the different successional stages in the Caohai wetland.Additionally,it was found that the SR increased significantly from the P.lucens zone to the J.effusus zone,but BR had the opposite response.The shifts in the bacterial community structure along the successional gradient may be the main reason for the observed differences in sediment respiration.

Microbial Properties of a Ferric Lixisol as Affected by Long Term Crop Management and Fertilization Regimes in Burkina Faso, West Africa

We used an ongoing long-term field trial established since 1960 in Burkina Faso, to study the microbial properties of a Ferric Lixisol under various crop management and fertilization regimes. Microbial respiration rate, microbial biomass carbon (MBC) and soil bacteria’s number were assessed in soil samples taken at 0 - 20 cm depth. The crop management were continuous cropping of sorghum (Sorghum bicolor L.) (S/S) and rotation between sorghum and cowpea (Vigna unguiculata L.) (S/C), while the fertilization regimes were: 1) Control (te);2) Low rate of mineral fertilizer (fm);3) Low rate of mineral fertilizer + sorghum straw restitution (fmr);4) Low rate of mineral fertilizer + low rate of manure (fmo);5) High rate of mineral fertilizer (FM);and vii) High rate of mineral fertilizer + high rate of manure (FMO). The manure is applied every second year. The results indicate that sorghum/cowpea rotation significantly increase MBC and bacteria number as compared to continuous sorghum cropping. MBC ranged from 335.5 to 54.85 μg C g−1 soil with S/S and from 457.5 to 86.6 μg C g−1 soil with S/C. Application of high level of manure and mineral fertilizer increase microbial respiration rate and MBC. The highest MBC was observed with FMO and the lowest with the control. In general, the metabolic quotient (qCO2) was negatively impacted by the fertilization and cowpea rotation. For S/S rotation, qCO2 of the control was 1.5 to 2 times that of the treatments with low mineral fertilizer (fmr, fmo and fm) and 3 times that of the high rate of fertilization (FM and FMO). With S/C rotation, qCO2 of the control was 2 times of that fmr, FM and FMO and 0.8 times that of fmo and fm. Soil bacteria in the fmr were 63.6 and 12.4 times the control in the S/S and S/C rotations, respectively. In sum, combined application of manure and mineral fertilizer with crop rotation is the best management practices to improve in sustainable way microbial activities in tropical soil.

Effects of soil salinity on rhizosphere soil microbes in transgenic Bt cotton fields

With increased cultivation of transgenic Bacillus thuringiensis （Bt） cotton in the saline alkaline soil of China, assessments of transgenic crop biosafety have focused on the effects of soil salinity on rhizosphere microbes and Bt protein residues. In 2013 and 2014, investigations were conducted on the rhizosphere microbial biomass, soil enzyme activities and Bt protein contents of the soil under transgenic Bt cotton （variety GK19） and its parental non-transgenic cotton （Simian 3） cultivated at various salinity levels （1.15, 6.00 and 11.46 dS m-1）. Under soil salinity stress, trace amounts of Bt proteins were ob- served in the Bt cotton GK19 rhizosphere soil, although the protein content increased with cotton growth and increased soil salinity levels. The populations of slight halophilic bacteria, phosphate solubilizing bacteria, ammonifying bacteria, nitrifying bacteria and denitrifying bacteria decreased with increased soil salinity in the Bt and non-Bt cotton rhizosphere soil, and the microbial biomass carbon, microbial respiration and soil catalase, urease and alkaline phosphatase activity also decreased. Correlation analyses showed that the increased Bt protein content in the Bt cotton rhizosphere soil may have been caused by the slower decomposition of soil microorganisms, which suggests that salinity was the main factor influencing the relevant activities of the soil microorganisms and indicates that Bt proteins had no clear adverse effects on the soil microorganisms. The results of this study may provide a theoretical basis for risk assessments of genetically modified cotton in saline alkaline soil.

Trade-off between microbial carbon use efficiency and specific nutrient-acquiring extracellular enzyme activities under reduced oxygen

Mangroves are one of the most ecologically sensitive ecosystems to global climate change,which have cascading impacts on soil carbon(C),nitrogen(N)and phosphorus(P)cycling.Moreover,mangroves are experiencing increasing N and P loadings and reduced oxygen availability due to intensified climate change and human activities.However,both direct and interactive effects of these perturbations on microbially mediated soil C,N and P cycling are poorly understood.Here,we simultaneously investigated the effects of N and P loadings and reduced oxygen on microbial biomass,microbial respiration,and extracellular enzyme activities(EEAs)in mangrove soils.We calculated the microbial metabolic quotient(qCO_(2)),which is regarded as a useful inverse metric of microbial C use efficiency(CUE).Our results show that reduced oxygen significantly increases both qCO_(2) and microbial specific EEAs(enzyme activity per unit of microbial biomass)for C-,N-and P-acquisition regardless of N or P loadings.Furthermore,we found that qCO_(2) positively correlated with microbial specific EEAs under reduced oxygen,whereas no clear relationship was detected under ambient oxygen.These results suggest that reduced oxygen increases microbial specific EEAs at the expense of increasing microbial respiration per unit biomass,indicating higher energy cost per unit enzyme production.

Root exclusion methods for partitioning of soil respiration:Review and methodological considerations

Soil respiration is a vital process in all terrestrial ecosystems,through which the soil releases carbon dioxide(CO_(2))into the atmosphere at an estimated annual rate of 68–101 Pg carbon,making it the second highest terrestrial contributor to carbon fluxes.Since soil respiration consists of autotrophic and heterotrophic constituents,methods for accurately determining the contribution of each constituent to the total soil respiration are critical for understanding their differential responses to environmental factors and aiding the reduction of CO_(2)emissions.Owing to its low cost and simplicity,the root exclusion(RE)technique,combined with manual chamber measurements,is frequently used in field studies of soil respiration partitioning.Nevertheless,RE treatments alter the soil environment,leading to potential bias in respiration measurements.This review aims to elucidate the current understanding of RE,i.e.,trenching(Tr)and deep collar(DC)insertion techniques,by examining soil respiration partitioning studies performed in several ecosystems.Additionally,we discuss methodological considerations when using RE and the combinations of RE with stable isotopic and modeling approaches.Finally,future research directions for improving the Tr and DC insertion methods in RE are suggested.

Influencing factors and partitioning of respiration in a Leymus chinensis steppe in Xilin River Basin, Inner Mongolia, China

Based on the static opaque chamber method,the respiration rates of soil microbial respiration,soil respiration,and ecosystem respiration were measured through continuous in-situ experiments during rapid growth season in semiarid Leymus chinensis steppe in the Xilin River Basin of Inner Mongolia,China. Soil temperature and moisture were the main factor affecting respiration rates. Soil temperature can explain most CO2 efflux variations （R2=0.376-0.655） excluding data of low soil water conditions. Soil moisture can also effectively explain most of the variations of soil and ecosystem respiration （R2=0.314-0.583）,but it can not explain much of the variation of microbial respiration （R2=0.063）. Low soil water content （≤5%） inhibited CO2 efflux though the soil temperature was high. Rewetting the soil after a long drought resulted in substantial increases in CO2 flux at high temperature. Bi-variable models based on soil temperature at 5 cm depth and soil moisture at 0-10 cm depth can explain about 70% of the variations of CO2 effluxes. The contribution of soil respiration to ecosystem respiration averaged 59.4%,ranging from 47.3% to 72.4%; the contribution of root respiration to soil respiration averaged 20.5%,ranging from 11.7% to 51.7%. The contribution of soil to ecosystem respiration was a little overestimated and root to soil respiration little underestimated because of the increased soil water content that occurred as a result of plant removal.

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.