Differences in Soil Microbial Biomass and Activity for Six Agroecosystems with a Management Disturbance Gradient

Different management practices in six agroecosystems located near Goldsboro, NC, USA were conducted including a successional field (SU), a plantation woodlot (WO), an integrated cropping system with animals (IN), an organic farming system (OR), and two cash-grain cropping systems employing either tillage (CT) or no-tillage (NT) to examine if and how microbial biomass and activity differ in response to alterations in disturbance intensity from six land management strategies. Results showed that soil microbial biomass and activity differed, with microbial activity in intermediately disturbed ecosystems (NT, OR, IN) being significantly higher (P ＜ 0.01) than systems with either high or low disturbance intensities. There was also a significant and a highly significant ecosystem effect from the treatments on microbial biomass C (MBC) (P ＜ 0.05) and on microbial activity (respiration) (P ＜ 0.01), respectively. Multiple comparisons of mean respiration rates distinctly separated the six ecosystem types into three groups: CT ＜ NT, SU and WO ＜ OR and IN.Thus, for detecting microbial response to disturbance changes these results indicated that the active component of the soil microbial community was a better indicator than total biomass.

Changes of soil microbial communities during decomposition of straw residues under different land uses

Monitoring soil microbial communities can lead to better understanding of the transformation processes of organic carbon in soil. The present study investigated the changes of soil microbial communities during straw decomposition in three fields, i.e., cropland, peach orchard and vineyard. Straw decomposition was monitored for 360 d using a mesh-bag method. Soil microbial metabolic activity and functional diversity were measured using the Biolog-Eco system. In all three fields, dried straws with a smaller size decomposed faster than their fresh counterparts that had a larger size. Dried corn straw decomposed slower than dried soybean straw in the early and middle stages, while the reverse trend was found in the late stage. The cropland showed the highest increase in microbial metabolic activity during the straw decomposition, whereas the peach orchard showed the lowest. There was no significant change in the species dominance or evenness of soil microbial communities during the straw decomposition. However, the species richness fluctuated significantly, with the peach orchard showing the highest richness and the cropland the lowest. With different carbon sources, the peach orchard utilised carbon the most, followed by the cropland and the vineyard. In all three fields, carbon was utilized in following decreasing order： saccharides〉amino acids〉polymers〉polyamines〉carboxylic acids〉aromatic compounds. In terms of carbon-source utilization, soil microbial communities in the peach orchard were less stable than those in the cropland. The metabolic activity and species dominance of soil microbial communities were negatively correlated with the straw residual percentage. Refractory components were primarily accumulated in the late stages, thus slowing down the straw decomposition. The results showed that dried and crushed corn straw was better for application in long-term fields. The diversity of soil microbial communities was more stable in cropland than in orchards during the straw decomposition.

Microbial community structure and functional metabolic diversity are associated with organic carbon availability in an agricultural soil

Exploration of soil environmental characteristics governing soil microbial community structure and activity may improve our understanding of biogeochemical processes and soil quality. The impact of soil environmental characteristics especially organic carbon availability after 15-yr different organic and inorganic fertilizer inputs on soil bacterial community structure and functional metabolic diversity of soil microbial communities were evaluated in a 15-yr fertilizer experiment in Changping County, Beijing, China. The experiment was a wheat-maize rotation system which was established in 1991 including four different fertilizer treatments. These treatments included： a non-amended control（CK）, a commonly used application rate of inorganic fertilizer treatment（NPK）; a commonly used application rate of inorganic fertilizer with swine manure incorporated treatment（NPKM）, and a commonly used application rate of inorganic fertilizer with maize straw incorporated treatment（NPKS）. Denaturing gradient gel electrophoresis（DGGE） of the 16 S r RNA gene was used to determine the bacterial community structure and single carbon source utilization profiles were determined to characterize the microbial community functional metabolic diversity of different fertilizer treatments using Biolog Eco plates. The results indicated that long-term fertilized treatments significantly increased soil bacterial community structure compared to CK. The use of inorganic fertilizer with organic amendments incorporated for long term（NPKM, NPKS） significantly promoted soil bacterial structure than the application of inorganic fertilizer only（NPK）, and NPKM treatment was the most important driver for increases in the soil microbial community richness（S） and structural diversity（H）. Overall utilization of carbon sources by soil microbial communities（average well color development, AWCD） and microbial substrate utilization diversity and evenness indices（H＇ and E） indicated that long-term inorganic fertilizer with organic amendments incorporated（NPKM, NPKS） could significantly stimulate soil microbial metabolic activity and functional diversity relative to CK, while no differences of them were found between NPKS and NPK treatments. Principal component analysis（PCA） based on carbon source utilization profiles also showed significant separation of soil microbial community under long-term fertilization regimes and NPKM treatment was significantly separated from the other three treatments primarily according to the higher microbial utilization of carbohydrates, carboxylic acids, polymers, phenolic compounds, and amino acid, while higher utilization of amines/amides differed soil microbial community in NPKS treatment from those in the other three treatments. Redundancy analysis（RDA） indicated that soil organic carbon（SOC） availability, especially soil microbial biomass carbon（Cmic） and Cmic/SOC ratio are the key factors of soil environmental characteristics contributing to the increase of both soil microbial community structure and functional metabolic diversity in the long-term fertilization trial. Our results showed that long-term inorganic fertilizer and swine manure application could significantly improve soil bacterial community structure and soil microbial metabolic activity through the increases in SOC availability, which could provide insights into the sustainable management of China＇s soil resource.

Combined Effects of Nutrient and Pesticide Management on Soil Microbial Activity in Hybrid Rice Double Annual Cropping System

Combined effects on soil microbial activity of nutrient and pesticide management in hybrid rice double annual cropping system were studied. Results of field experiment demonstrated significant changes in soil microbial biomass phospholipid contents, abundance of heterotrophic bacteria and proteolytic bacteria, electron transport system (ETS)/dehydrogenase activity, soil protein contents under different management practices and at various growth stages. Marked depletions in the soil microbial biomass phospholipid contents were found with the advancement of crop growth stages, while the incorporation of fertilizers and/or pesticides also induced slight changes, and the lowest microbial biomass phospholipid content was found with pesticides application alone. A decline in the bacterial abundance of heterotrophic bacteria and proteolytic bacteria was observed during the continuance of crop growth, while the lowest abundance of heterotrophic bacteria and proteolytic bacteria was found with pesticides application alone, which coincided with the decline of soil microbial biomass. A consistent increase in the electron transport system activity was measured during the different crop growth stages of rice. The use of fertilizers (NPK) alone or combined with pesticides increased it, while a decline was noticed with pesticides application alone as compared with the control. The soil protein content was found to be relatively stable with fertilizers and/or pesticides application at various growth stages in both crops undertaken, but notable changes were detected at different growth stages.

Lindane Degradation and Effects on Soil Microbial Activity

The degradation of U-14C-lindane in two Egyptian soils was determined in a three-month laboratory incubation. Lindane mineralization was slow and limited in both soils. Evolution of 14CO2 increased with time but only reached 3. 5 to 5. 5 % of the initial 14C-concentration within 90 days. At that time both soils contained about 88 % of the applied radiocarbon; 33 % to 37% of the initial dose was unextractable and assumed bound to the soils. The methanol-ex-tractable 14C primarily contained lindane with traces of minor metabolites. Radiorespirometry was used to eva1uate the effect of lindane on soil microbial activity. Low concentrations of the insecticide initially supressed 14CO2 evolution from U-14C-glucose and microbial activity was significantly inhibited by 10 mg lindane/kg soil.

Linkages between soil microbial stability and carbon storage in the active layer under permafrost degradation

The Qinghai-Tibet Plateau(QTP)distributes the largest extent of high-altitude mountain permafrost in the world(Zou et al.,2017),which has different characteristics from high-latitude permafrost(Yang et al.,2010)and stores massive soil carbon.

热带次生林利用方式与土壤微生物活性

热带次生林利用方式与土壤微生物活性许炼烽，朱伍坤（国家环保局华南环境科学研究所，广州５１０６５５）ＷａｙｓｏｆＵｔｉｌｉｚｉｎｇＴｒｏｐｉｃａｌＳｅｃｏｎｄａｒｙＦｏｒｅｓｔａｎｄＳｏｉｌＭｉｃｒｏｂｉａｌＡｃｔｉｖｉｔｙ．￥ＸｕＬｉａｎｆｅｎｇ；Ｚ...

Dissipation of polycyclic aromatic hydrocarbons and microbial activity in a field soil planted with perennial ryegrass

Dissipation and plant uptake of polycyclic aromatic hydrocarbons （PAHs） in contaminated agricul- tural soil planted with perennial ryegrass were investigated in a field experiment. After two seasons of grass cultivation the mean concentration of 12 PAHs in soil decreased by 23.4% compared with the initial soil. The 3-, 4-, 5-, and 6- ring PAHs were dissipated by 30.9%, 25.5%, 21.2%, and 16.3% from the soil, respectively. Ryegrass shoots accumulated about 280 ug.kg1, shoot dry matter biomass reached 2.48 x 104kg-ha1, and plant uptake accounted for about 0.99% of the decrease in PAHs in the soil. Significantly higher soil enzyme activities and microbial community functional diversity were observed in planted soil than that in the unplanted control. The results suggest that planting ryegrass may promote the dissipation of PAHs in long-term contaminated agricultural soil, and plant-promoted microbial degradation may be a main mechanism of phytoremediation.

Effect of Lead Contamination on Soil Microbial Activity Measured by Microcalorimetry

Microcalorimetry was used to investigate the microbial activity in three types of soil （orchard soil, crop soil, forest soil） in Wuhan, China, and to evaluate the influence of different concentrations of lead （Pb^2＋） on soil microbial activity. The experimental results revealed that due to different physical and chemical characteristics of the soils, soil microbial activity in three soil samples were in a descending sequence： orchards soil, crops soil, forest soil. Six levels ofPb viz. 0, 10, 20, 40, 80, 160 μg·g^-1 were applied in these soils, and the results showed that an in- crease of the amount of Pb^2＋ is associated with a decrease in microbial activity in the soils due to the toxic effect of Pb^2＋. In order to gain further insight of the sequential change of microorganisms, determination of colony forming units （CFU） was performed to provide a negative linear correlation between the heat effect and the respective number of microorganisms in the system.

Soil legacy effects and plant-soil feedback contribution to secondary succession processes

Secondary succession is the process by which a community develops into a climax community over time.However,knowledge on the mechanisms,relating to soil legacy effects(soil chemistry and enzyme activity)and plant-soil feedback(PSF),driving community succession remains limited.In this work,we examined the PSF associated with three succession stage species through a 2-year greenhouse experiment.Setaria viridis,Stipa bungeana,and Bothriochloa ischemum were selected to represent dominant and representative early-,mid-,and late-successional stage species,respectively,of semiarid grasslands on the Loess Plateau.In response to the different soil origin,the shoot biomass of early-,mid-,and late-species were all higher when grown in their own soil than in other species’soils,which indicated that the PSF of three species were positive.Over two growth periods,the early-species experienced a negative PSF,but the mid-and late-species experienced negative,neutral and positive PSF in the soil of early-,mid-and late-species,respectively.Our study demonstrates that soil legacy effects and PSF have a significant impact on community succession processes.

Effects of Bacterial-Feeding Nematode Grazing and Tea Saponin Addition on the Enhanced Bioremediation of Pyrene-Contaminated Soil Using Polycyclic Aromatic Hydrocarbon-Degrading Bacterial Strain

As one of the most widely distributed bacterial predators in the soil, the role of bacterivorous nematodes on the enhanced bioremediation of polycyclic aromatic hydrocarbon-contaminated soils is crucial, but remains to be investigated.A microcosm-level study was conducted to examine the effects of bacterial-feeding nematode grazing and tea saponin(TS) addition on bioremediation of a pyrene-contaminated soil enhanced by the polycyclic aromatic hydrocarbon(PAH)-degrading bacterial strain Sphingobium sp.PHE9.After 180 d of incubation, the highest pyrene dissipation(71.3%) was achieved through a combination of Sphingobium sp.PHE9 inoculation with nematode and TS addition.Meanwhile, high counts of culturable PAH-degrading bacteria, soil enzyme activity, and biodiversity indices were observed under the combined treatment, implying that the microbiological function of the contaminated soil was significantly restored.Additionally, the results of Tenax~ extraction with the first-order three-compartment model indicated that rate-limiting factors varied among treatments.The lack of degrading microorganisms was the main rate-limiting factor for the treatments involving TS/nematode addition, and inadequate bioaccessible pyrene was the vital rate-limiting factor in the treatments involving Sphingobium sp.PHE9 inoculation.The proposed combined clean-up strategy proved to be a promising bioremediation technology for aged pyrene-contaminated soils.

Downed logs improve soil properties in old-growth temperate forests of northern Iran

Dead trees, particularly downed logs, play an important role in the dynamics of forest ecosystem. Contribution of decaying wood to C and nutrient pools of forest soils depends on the tree species and degree of wood decay. However, the extent to which the downed logs affect the soil properties of temperate forests has rarely been evaluated. In this study, a mixed beech forest was selected in Liresar region of Mazandaran Province, northern Iran, to investigate if and how the presence of downed logs affected soil quality and function by comparing soils underneath degraded logs and nearby soils of the two dominant tree species(beech and hornbeam). We then explored how these effects occurred as downed logs decomposed by comparing the woods of both tree species at four degrees of decomposition. Degree of decay of downed logs was classified into four classes(DC1–DC4). Eight dead trees of each tree species were selected at the center of each sample plot. Three composite soil samples underneath each decaying log and 100 cm away from a decaying log were collected at two soil depths(0–15 and 15–30 cm) to analyze soil main physicochemical properties and microbial activity. The results revealed that downed logs affected soil physical(5% wetter than control soils), chemical(2% lower pH, 100% increase in organic C and total N in the case of hornbeam, and 2% increase in P), and biological characteristics(soil microbial respiration enhanced by 10%, and microbial biomass C 620 and 351.5 mg kg-1 and microbial biomass N 66.47 and 32.18 mg kg-1, respectively, in the cases of beech and hornbeam), thus resulting in significantly different soil microsites from those without downed logs. Presence of downed logs increased soil microbial activity and soil fertility as wood decayed. Thus, the presence of downed logs is an important factor influencing forest soils and should be taken into consideration in forest management practices.

Impact of Salinity on Respiration and Organic Matter Dynamics in Soils is More Closely Related to Osmotic Potential than to Electrical Conductivity

Osmotic potential （OP） of soil solution may be a more appropriate parameter than electrical conductivity （EC） to evaluate the effect of salts on plant growth and soil biomass. However, this has not been examined in detail with respect to microbial activity and dissolved organic matter in soils with different texture. This study evaluated the effect of salinity and sodicity on respiration and dissolved organic matter dynamics in salt-affected soils with different texture. Four non-saline and non-sodic soils differing in texture （S-4, S-13, S-24 and S-40 with 4%, 13%, 24~ and 40~~ clay, respectively） were leached using combinations of 1 mol L-1 NaC1 and 1 mol L-1 CaC12 stock solutions, resulting in EC （1：5 soil：water ratio） between 0.4 and 5.0 dS m-1 with two levels of sodicity （sodium absorption ratio （SAR） 〈 3 （non-sodic） and 20 （sodic）, 1：5 soil：water ratio）. Adjusting the water content to levels optimal for microbial activity~ which differed among the soils, resulted in four ranges of OP in all the soils： from -0.06 to -0.24 （controls, without salt added）, -0.55 to -0.92, -1.25 to -1.62 and -2.77 to -3.00 Mpa. Finely ground mature wheat straw （20 g kg-1） was added to stimulate microbial activity. At a given EC, cumulative soil respiration was lower in the lighter-textured soils （S-4 and S-13） than in the heavier-textured soils （S-24 and S-40）. Cumulative soil respiration decreased with decreasing OP to a similar extent in all the soils, with a greater decrease on Day 40 than on Day 10. Cumulative soil respiration was greater at SAR ---- 20 than at SAR 〈 3 only at the OP levels between -0.62 and -1.62 MPa on Day 40. In all the soils and at both sampling times, concentrations of dissolved organic C and N were higher at the lowest OP levels （from -2.74 to -3.0 MPa） than in the controls （from -0.06 to -0.24 MPa）. Thus, OP is a better parameter than EC to evaluate the effect of salinity on dissolved organic matter and microbial activity in different textured soils.

Soil depth- and root diameter- related variations affect root decomposition in temperate pine and oak forests

Aims Assessment of factors regulating root decomposition is needed to understand carbon and nutrient cycling in forest ecosystems.the ob-jective of this study is to examine the effects of soil depth and root diameter on root decomposition and to analyze the relationship of root decomposition with factors such as soil environmental conditions and initial litter quality.Methods two decomposition experiments were conducted in natural pine(Pinus densiflora)and oak(Quercus serrata)forests over a 2-year period using the litterbag technique.For the soil depth experiment,216 litterbags containing fine roots(∅=0-2 mm)were buried at 0-10-,10-20-and 20-30-cm soil depths.Soil properties and soil enzyme activities and microbial biomass at each soil depth were analyzed.For the root diameter experiment,216 litterbags containing roots 0-1-,1-2-and 2-3-mm in diameter were buried at 10-cm soil depth.the initial litter qualities(carbon(c),nitrogen(N),calcium(ca)and phosphorus(P)concentrations)for each of the root diameter classes were analyzed.Litterbags were retrieved after 3,6,12 and 24 months in each forest type.Important Findingsthe root decomposition rate was significantly altered by soil depth and root diameter.After 2 years,the root decay constant at 0-10-cm depth(pine:0.35 and oak:0.41)was significantly higher than that at 10-20-cm(0.31 and 0.37)and 20-30-cm(0.32 and 0.33)depths in the P.densiflora and Q.serrata forests.Enzyme activities and microbial biomass declined with soil depth,which may be associated with decreasing soil moisture and organic matter.the decay constant for the 0-1-mm roots(pine:0.32 and oak:0.37)was higher than that of 1-2-mm(0.29 and 0.33)and 2-3-mm roots(0.26 and 0.33)for the P.densiflora and Q.serrata forests.Difference in initial P concentration and c/N ratio among the different diameter roots were linearly related with root decomposition.In particular,the increasing c/N ratio with root diameter resulted in decreases in the decomposition rate.these results indicate the surface soil microbial activities and initial c/N ratio of root litter as important drivers of c dynamics in temperate pine and oak forests.