Microbial Biomass C Contents Research Articles

Effect of soil redistribution on various organic carbons in a water- and tillage-eroded soil

The information gap concerning the effect of soil redistribution on various carbon (C) pools will limit our understanding regarding the fate of eroded C. In this study, we selected a water- and tillage-eroded hillslope with a horizontal length of 45m from the Sichuan Basin, China, to determine the impact of soil redistribution on particulate organic C from 0.0053 to 2mm soil particles (POC), light fraction organic C (LFOC), dissolved organic C (DOC) and microbial biomass C (MBC). Soil erosion was evaluated at 5-m intervals from the summit to lower parts and soil deposition at the bottom of the hillslope. Within the erosional sites, tillage erosion- and water erosion-dominated subsites were identified. The POC content firstly decrease and then increased downslope, while the DOC exhibited an opposite pattern to the POC. The MBC content decreased downslope, while the LFOC increased. Overall, the erosional sites had lower POC and LFOC contents than depositional sites, demonstrating the depletion of POC and LFOC induced by soil erosion and the enrichment of POC and LFOC by soil deposition. Conversely, the contents of DOC and MBC were greater in the erosional sites than depositional sites. It was also observed that the LFOC distribution was strongly linked to fine (<0.05mm) soil particles, indicating a preferentially transport of the light fraction C downslope in the process of water erosion. In addition, tillage erosion-dominated subsites had higher values of POC/SOC and DOC/SOC than water erosion-dominated subsites, suggesting lower depletion of POC and DOC by tillage erosion than water erosion. Likewise, the higher MBC/SOC values were found in tillage erosion-dominated subsites, thus implying that more SOC may be assimilated into microbial C under tillage erosion than water erosion. Our study confirms the need to consider microbial response to the dynamic replacement of erosion depleted SOC.

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) dynamics 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 °C) 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 concentration than the fire-exposed soils when heated at 100 or 200 °C. 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 °C, while the fire-exposed soils when heated at 100 °C had greatest microbial respiration rates. During 14-days post-heat incubation, soil MBC in both soils was greatest after heating at 200 °C and 25 % WHC. However, soil previously exposed to fire had the lowest CO2 evolution when incubated at 25 % WHC.

Response of soil carbon dioxide fluxes, soil organic carbon and microbial biomass carbon to biochar amendment: a meta‐analysis

AbstractBiochar as a carbon‐rich coproduct of pyrolyzing biomass, its amendment has been advocated as a potential strategy to soil carbon (C) sequestration. Updated data derived from 50 papers with 395 paired observations were reviewed using meta‐analysis procedures to examine responses of soil carbon dioxide (CO2) fluxes, soil organic C (SOC), and soil microbial biomass C (MBC) contents to biochar amendment. When averaged across all studies, biochar amendment had no significant effect on soil CO2 fluxes, but it significantly enhanced SOC content by 40% and MBC content by 18%. A positive response of soil CO2 fluxes to biochar amendment was found in rice paddies, laboratory incubation studies, soils without vegetation, and unfertilized soils. Biochar amendment significantly increased soil MBC content in field studies, N‐fertilized soils, and soils with vegetation. Enhancement of SOC content following biochar amendment was the greatest in rice paddies among different land‐use types. Responses of soil CO2 fluxes and MBC to biochar amendment varied with soil texture and pH. The use of biochar in combination with synthetic N fertilizer and waste compost fertilizer led to the greatest increases in soil CO2 fluxes and MBC content, respectively. Both soil CO2 fluxes and MBC responses to biochar amendment decreased with biochar application rate, pyrolysis temperature, or C/N ratio of biochar, while each increased SOC content enhancement. Among different biochar feedstock sources, positive responses of soil CO2 fluxes and MBC were the highest for manure and crop residue feedstock sources, respectively. Soil CO2 flux responses to biochar amendment decreased with pH of biochar, while biochars with pH of 8.1–9.0 had the greatest enhancement of SOC and MBC contents. Therefore, soil properties, land‐use type, agricultural practice, and biochar characteristics should be taken into account to assess the practical potential of biochar for mitigating climate change.

Soil microbial biomass carbon and fatty acid composition of earthworm Lumbricus rubellus after exposure to engineered nanoparticles

The aim of this work was to investigate the effect of engineered nanoparticles (NPs) on soil microbial biomass C (MBC) and on earthworm Lumbricus rubellus. An artificial soil was incubated for 4 weeks with earthworms fed with vegetable residues contaminated by NPs, consisting of Ag, Co, Ni and TiO2. After the treatments, soils were analysed for MBC and total and water soluble metal-NPs, whereas earthworms were purged for 28 days and then analysed for fatty acids (FAs) and total metal-NPs. Longitudinal sections of earthworms were investigated by environmental scanning electron microscopy (ESEM), equipped with energy-dispersive X-ray spectroscopy (EDS), to provide insights about the retention and localization of NPs within earthworms. The nanoparticles reduced the MBC content in the following order Ag > Co > Ni, whereas TiO2 did not affect it. The ESEM-EDS analysis confirmed NP retention in earthworm guts and tissues. The solid/water coefficient of partition suggested that NPs interfered with living organisms due to their presence in suspension. Among the 27 FAs identified in earthworm tissues, the eicosapentaenoic acid (20:5ω3) was the most abundant. The degree of unsaturation of FAs was reduced by supplying NP-contaminated food.

Humic Haplustox under different land uses in a high altitude environment in the Agreste region of Pernambuco, Brazil

The Garanhuns Plateau in the Agreste region of the State of Pernambuco, Brazil is characterized by humid climatic conditions due to orographic rains, unlike the surrounding semiarid region. These soils are subjected to intense agricultural use and are extremely important for the regional economy. This study was carried out in the municipality of Brejão in the Agreste region with the aim of assessing changes in humic Haplustox soils subjected to different land uses. Four plots with different vegetation covers (native forest, secondary shrubby vegetation (capoeira), traditional cropping system, and planted pasture) were selected, and samples were taken from a soil profile and four small pits surrounding it at each site. Physical and chemical properties were assessed, including aggregate stability, humic organic fractions, and a microbiological evaluation through determination of basal respiration, microbial biomass carbon, and metabolic quotient. The soils under study showed physical and chemical properties typical of a Haplustox, such as low nutrient content, low cation exchange capacity, and high levels of acidity and Al saturation. The total organic carbon (TOC) contents were high regardless of the type of land use. Aggregates &lt; 2 mm were dominant in all the conditions under study. The TOC content was higher in the soil under capoeira, 43.91 g kg-1 on the surface, while 34.36 and 33.43 g kg-1 of TOC were observed in the first layer of forest and pasture soils, respectively. While the microbial biomass C (MBC) was greater than 700 mg kg-1 in the forest and pasture areas (in the 0-5 cm layer), and 588 mg kg-1 in the soil under capoeira, these numbers were not statistically different. In the cultivated soil area, there was a reduction of around 28 % in TOC and MBC contents. Agricultural activity contributed to degradation of the humic horizon, as can be seen from a significant decrease in the TOC and changes in the relative distribution of the humic fractions. In contrast, aggregate stability was not altered as a function of the different land uses; the soil under planted pasture and capoeira were similar to the soil under native forest. Humin was the most important humified fraction for C reserves, contributing over 40 % of the TOC in these soils.

Contrasting effects of bamboo leaf and its biochar on soil CO2 efflux and labile organic carbon in an intensively managed Chinese chestnut plantation

The effects and associated mechanisms of the application of organic residues or their derived biochar on the dynamics of soil organic C and soil CO2 efflux in planted soils are poorly understood. This paper investigated the impact of bamboo leaf and the derived biochar applications on soil CO2 efflux and labile organic C in an intensively managed Chinese chestnut plantation in a 12-month field study. The treatments studied included Control, application of bamboo leaf (Leaf), and application of biochar (Biochar). The Leaf treatment increased (P < 0.05) soil CO2 efflux and concentrations of water-soluble organic C (WSOC) and microbial biomass C (MBC). The Biochar treatment increased soil CO2 efflux and WSOC and MBC only in the first month after application, but such effects diminished thereafter. The annual cumulative soil CO2 emission was increased by 16 % by the Leaf treatment as compared to the Control, but there was no difference between the Biochar and Control treatments. The soil organic C (SOC) storage was increased by biochar addition but not by bamboo leaf addition. An exponential relationship between soil temperature and soil CO2 efflux was observed regardless of the treatment. Soil CO2 efflux was correlated to soil WSOC (P < 0.05) but not to soil MBC or moisture content. The apparent temperature sensitivity (Q 10) of soil CO2 efflux was ranked as Leaf > Biochar > Control. In comparison with the application of fresh bamboo leaf, pyrolyzed bamboo leaf (biochar) application decreased CO2 effluxes and increased C sequestration in the soil.

Soil C turnover, microbial biomass and respiration, and enzymatic activities following rangeland conversion to wheat–alfalfa cropping in a semi-arid climate

Conversion from rangeland to cropland potentially influences soil organic matter (SOM) dynamics and biochemical properties. The purpose of the current study was to assess changes in soil properties and investigate the interaction between SOM and enzyme activities following cultivation of native rangelands for more than 40 years. The quantities of soil organic carbon (C) and microbial biomass C (MBC), aggregate stability, microbial respiration rate (MRR), potential C mineralization (PCM) and the activities of soil enzymes involved in C, N, P and S cycling at the 0–20 and 20–40 cm depths were evaluated in never-cultivated natural rangelands and their corresponding farmlands with similar soil type and climatic conditions at Dehnow located in Central west, Iran. Cultivation in native rangelands resulted in a significant decline of most soil properties in farmlands, depending on soil sampling depths. Conversion of rangelands to their farmland counterparts decreased soil C (50–66 %), MBC (48–61 %), MRR (20–44 %), PCM (45–59 %), the activities of urease (5–17 %), invertase (7–28 %) and arylsulfatase (17–20 %) per soil mass, while increased C turnover rate (61–63 %), microbial metabolic quotient (qCO2) values (41–54 %) and enzyme activities per unit C and MBC (61–190 %) without affecting microbial quotient (MBC/C ratio) values and the activities of soil phosphatases per soil mass. The decreases in soil microbial and biochemical properties were largely the result of a substantial decline in soil C contents and aggregate stability by tillage activities in farmlands. Although the absolute activities of soil enzymes (i.e., activity per dry soil mass) showed inconsistent responses to land use changes and were even less responsive than soil organic C and MBC contents to changing land uses, the specific enzyme activities expressed either per unit of C or MBC tended to increase considerably and consistently with this conversion and were more sensitive than soil C and MBC contents. Soil C turnover rates and metabolic quotients were found to correlate positively with the specific enzyme activities, indicating an interaction between SOM and enzyme activities. The specific enzymatic activity could be an appropriate and integrative simple index to (1) assess soil quality changes, (2) detect changes in soil microbial community; and even (3) associate the losses of SOM with the presence of metabolically more active decomposer biota in rangelands cultivated for the long term.

Soil respiration and microbial biomass after residue addition are influenced by the extent by which water-extractable organic C was removed from the residues

Little is known about the effect of addition of plant residues from which water-extractable organic C (WEOC) was partially removed on soil microbial activity and growth. Two incubation experiments were conducted in a sandy clay loam amended with barley (Hordeum vulgare L.) residues (ground to 0.5–1 mm) from which WEOC was removed by extraction (Experiment 1) or leaching (Experiment 2). For the first experiment, the residues were extracted 5 times to maximise WEOC removal. There were three treatments: unamended control soil, soil amended with original residue or with extracted residue. Cumulative respiration increased rapidly within the first 5 days with the original residues, whereas it started more slowly with extracted residues. By the end of the experiment (day 18) compared to the original residues, cumulative respiration was 18% lower with extracted residues, but the microbial biomass C (MBC) concentration was 27% greater. For the second experiment, the residue was leached 1 to 8 times to reduce WEOC concentrations by 29 and 80%, respectively. There were four treatments: unamended control, soil amended with original residue, residue leached once and eight times. Cumulative respiration was reduced by up to 21% by partial removal of WEOC compared to the original residues in the first 10 days, but by day 28 (end of experiment) it was greatest with residues leached 8 times where it was 5% greater than with the original residues. This treatment also had a 16% higher MBC concentration on day 28 than soil with the original residue. It is concluded that nearly complete removal of WEOC reduced soil respiration compared to the original residues in the first week after residue addition. However, when removal is incomplete and a small proportion of WEOC (20%) remains in the residues, respiration may increase later above that of the original residues.

Addition of a clay subsoil to a sandy topsoil changes the response of microbial activity to drying and rewetting after residue addition – a model experiment

AbstractThe effect of drying and rewetting (DRW) on C mineralization has been studied extensively but mostly in absence of freshly added residues. But in agricultural soils large amounts of residues can be present after harvest; therefore, the impact of DRW in soil after residue addition is of interest. Further, sandy soils may be ameliorated by adding clay‐rich subsoil which could change the response of microbes to DRW. The aim of this study was to investigate the effect of DRW on microbial activity and growth in soils that were modified by mixing clay subsoil into sandy top soil and wheat residues were added. We conducted an incubation experiment by mixing finely ground wheat residue (20 g kg–1) into top loamy sand soil with clay‐rich subsoil at 0, 5, 10, 20, 30, and 40% (w/w). At each clay addition rate, two moisture treatments were imposed: constantly moist control (CM) at 75% WHC or dry and rewet. Soil respiration was measured continuously, and microbial biomass C (MBC) was determined on day 5 (before drying), when the soil was dried, after 5 d dry, and 5 d after rewetting. In the constantly moist treatment, increasing addition rate of clay subsoil decreased cumulative respiration per g soil, but had no effect on cumulative respiration per g total organic C (TOC), indicating that the lower respiration with clay subsoil was due to the low TOC content of the sand‐clay mixes. Clay subsoil addition did not affect the MBC concentration per g TOC but reduced the concentration of K2SO4 extractable C per g TOC. In the DRW treatment, cumulative respiration per g TOC during the dry phase increased with increasing clay subsoil addition rate. Rewetting of dry soil caused a flush of respiration in all soils but cumulative respiration at the end of the experiment remained lower than in the constantly moist soils. Respiration rates after rewetting were higher than at the corresponding days in constantly moist soils only at clay subsoil addition rates of 20 to 40%. We conclude that in presence of residues, addition of clay subsoil to a sandy top soil improves microbial activity during the dry phase and upon rewetting but has little effect on microbial biomass.

Drying and rewetting – Effect of frequency of cycles and length of moist period on soil respiration and microbial biomass

Rewetting of dry soil induces a flush of respiration, but less is known about the effect of the number of drying and rewetting (DRW) cycles on the distribution of respiration and how the length of the moist period influences respiration and microbial biomass in residue-amended soil. Two experiments were conducted. In the first experiment, the effect of number of DRW cycles on soil respiration and microbial biomass was assessed. We exposed a sandy loam amended with finely ground pea residues (C/N 26) to up to three DRW cycles, each cycle consisting of one week drying and one week moist incubation. Soils which were maintained moist throughout served as controls. The flush in respiration was greatest in the first DRW where it was 3 times higher than in the following cycles, but did not differ between the second and third DRW. Cumulative respiration at the end of the experiment was highest in the constantly moist soil and lowest with three DRW cycles (20% lower than in the constantly moist soil). Microbial biomass C did not differ between the constantly moist treatment and the DRW treatments on days 14 and 28, but at the end of the experiment (d 42) the MBC concentration was 40% higher in the treatments with 2 and 3 DRW cycles than in the constantly moist treatment. The second experiment was conducted to test the hypothesis that the amount of C respired at the end of the preceding cycle may influence respiration in the second cycle. In this experiment, the soil was maintained moist or subjected to two DRW cycles where the length of the moist period in the first cycle lasted between one and five days followed by 7 days dry. The second moist period was three days in all DRW treatments. Cumulative respiration at the end of the experiment was lowest in the soil with one moist day in the first cycle (1 mg CO2–C g−1) and highest in the constantly moist control (1.6 mg CO2–C g−1). Among the DRW treatments, cumulative respiration over the entire incubation period (two DRW cycles) was about 30% higher in treatments with four to five moist days in the first DRW than in the treatments with one, two or three moist days which did not differ in cumulative respiration. Cumulative respiration in the second cycle was about 30% higher in treatments with 1–2 moist days in the first cycle compared to treatments with 3–5 moist days. Both cumulative respiration in the second DRW cycle and in the second moist period were negatively correlated with cumulative respiration at the end of the first period. Microbial biomass C (MBC) differed little between the moisture treatments except for a 50% higher MBC concentration at the end of the first moist period in the treatment with 1 moist day. It can be concluded that cumulative respiration is reduced by DRW and that the negative effect of DRW on cumulative respiration is exacerbated if the moist period after rewetting is short. The finding that cumulative respiration in the second DRW cycle is negatively correlated with cumulative respiration in the first cycle indicates that substrate availability at the start of the second cycle plays an important role in respiration in the second cycle.

Short-term responses of soil enzyme activities and carbon mineralization to added nitrogen and litter in a freshwater marsh of Northeast China

Soil organic matter decomposition is regulated by nutrient availability. Adding nitrogen (N) and litter could affect the stability of soil organic carbon (SOC). An incubation experiment was conducted to examine the effects of ammonium nitrate (AN), urea (U), and litter amendment on activities of soil microbial extracellular enzyme, soil microbial biomass C (MBC), dissolved organic C (DOC), and C mineralization in freshwater marsh. The results showed that adding N including AN and U decreased soil urease activity, MBC, DOC, and soil pH. However, litter amendment and combined litter and N amendment increased the enzymes activities of urease and invertase, MBC and DOC concentrations. The response of soil C mineralization to N and litter additions was different, being inhibited with AN addition while stimulated with littler addition and the combined litter and N addition, initially stimulated but inhibited thereafter with urea addition. Our results suggest that adding N is helpful for improving marshland soil C stocks via decreasing soil cumulative CO2–C emissions, labile organic carbon concentration of MBC and DOC. However, adding litter could reduce C storage stability by stimulating soil C mineralization and increasing soil labile C fractions and enzyme activities.

Drying and rewetting frequency influences cumulative respiration and its distribution over time in two soils with contrasting management

Understanding the factors determining cumulative respiration upon rewetting of dry soil is critical for predicting C efflux from soils. The response of respiration to drying and rewetting may be influenced by land management due to its effect on the soil organic C pool and differ between soil size fractions. An incubation experiment was conducted with soils collected from two plots with a long history of different management (wheat-fallow and permanent pasture). The soils were sieved to 4–10 mm and <2 mm to obtain two size factions. There were five moisture treatments with the same length (48 days). The constantly moist control (CM) was maintained at 50% of WHC throughout. In the drying and rewetting (DRW) treatments, the number of dry and moist days was equal but the number of DRW events ranged from one to four (1–4DRW). Respiration was measured daily, microbial biomass C (MBC) was determined six days after rewetting in each DRW cycle and on day 48 (end of the experiment). The proportion of soil in the 4–10 mm size fraction decreased over time with a greater decrease in pasture than in wheat soil and in the DRW treatments compared to the constantly moist treatment (CM). Cumulative respiration at the end of the experiment was greater in the <2 mm than in the 4–10 mm fraction in both soils and was highest in CM and 1DRW. In wheat soil, cumulative respiration decreased from 1DRW to 3DRW, whereas it decreased only between 2 and 3DRW in pasture soil. In treatments with two to four DRW, the proportion of total cumulative respiration was lowest in the last cycle. In 2DRW, cumulative respiration was smaller in the second than in the first moist period whereas the reverse was true for 3DRW and 4DRW. Cumulative respiration in the second moist period was greater in 3DRW than in 2DRW (8 and 12 prior moist days) whereas cumulative respiration in the third moist period was greater in 4DRW than in 3DRW (12 and 16 prior moist days). At the end of the experiment, the MBC concentration in the 4–10 mm fraction was unaffected by moisture treatment, whereas in the <2 mm fraction, it was greatest in CM and lowest in 4DRW. We conclude that the response of respiration to drying and rewetting is more strongly influenced by management than size fraction. In a given soil, the cumulative respiration upon rewetting is influenced not only by the number of DRW cycles but also the number of moist days prior to rewetting.

Addition of glucose increases the activity of microbes in saline soils

Adaptation of soil microbes to salinity requires substantial amounts of energy. We hypothesised that addition of glucose would increase microbial activity and growth and alleviate the negative effect of salinity on microbes. An incubation experiment was conducted with four salinity levels by using one non-saline and three saline soils of similar texture (sandy clay loam), with electrical conductivities (EC1:5) of 0.1, 1.1, 3.1 and 5.2 dS m–1. Glucose was added to achieve five organic carbon concentrations (0, 0.5, 1, 2.5, 5 g C kg–1). Soluble nitrogen (N) and phosphorus (P) were added to achieve a carbon (C) : N ratio of 20 and a C : P ratio of 200 to ensure that these nutrients did not limit microbial growth. A water content of 50% of the water-holding capacity (optimal for microbial activity in soils of this texture) was maintained throughout the incubation. Soil respiration was measured continuously over 21 days; microbial biomass C and available N and P were determined on days 2, 5, 14 and 21. Cumulative respiration was increased by addition of glucose and was reduced by salinity. The percentage decrease in cumulative respiration in saline soils compared with non-saline soil was greatest in the unamended soil and lowest with addition of 5 g C kg–1. At this rate of C addition, the percentage decrease in cumulative respiration increased with increasing salinity level. Microbial biomass C (MBC) concentration on days 2 and 5 was strongly increased by ≥1 g C kg–1 but decreased over time with the strongest decrease at the highest C addition rate. The MBC concentration was negatively correlated with EC at all C rates at each sampling date. Addition of C resulted in N and P immobilisation in the first 5 days. Biomass turnover as a result of depletion of readily available C released previously immobilised N and P after day 5, particularly in the soils with low salinity. This study showed that over a period of 3 weeks, addition of glucose increased microbial activity and growth in saline soils and alleviated the negative impact of salinity on microbes.

The combined effects of earthworms and arbuscular mycorrhizal fungi on microbial biomass and enzyme activities in a calcareous soil spiked with cadmium

Earthworms and arbuscular mycorrhizal fungi (AMF) are known to independently affect soil microbial and biochemical properties, in particular soil microbial biomass (SMB) and enzymes. However, less information is available about their interactive effects, particularly in soils contaminated with heavy metals such as cadmium (Cd). The amount of soil microbial biomass C (MBC), the rate of soil respiration (SRR) and the activities of urease and alkaline phosphatase (ALP) were measured in a calcareous soil artificially spiked with Cd (10 and 20mgCdkg−1), inoculated with earthworm (Lumbricus rubellus L.), and AMF (Glomus intraradices and Glomus mosseae species) under maize (Zea mays L.) crop for 60 days. Results showed that the quantity of MBC, SRR and enzyme activities decreased with increasing Cd levels as a result of the elevated exchangeable Cd concentration. Earthworm addition increased soil exchangeable Cd levels, while AMF and their interaction with earthworms had no influence on this fraction of Cd. Earthworm activity resulted in no change in soil MBC, while inoculation with both AMF species significantly enhanced soil MBC contents. However, the presence of earthworms lowered soil MBC when inoculated with G. mosseae fungi, showing an interaction between the two organisms. Soil enzyme activities and SRR values tended to increase considerably with the inoculation of both earthworms and AMF. Nevertheless, earthworm activity did not affect ALP activity when inoculated with G. mosseae fungi, while the presence of earthworm enhanced urease activity only with G. intraradices species. The increases in enzyme activities and SRR were better ascribed to changes in soil organic carbon (OC), MBC and dissolved organic carbon (DOC) contents. In summary, results demonstrated that the influence of earthworms alone on Cd availability is more important than that of AMF in Cd-polluted soils; and that the interaction effects between these organisms on soil microorganism are much more important than on Cd availability. Thus, the presence of both earthworms and AMF could alleviate Cd effects on soil microbial life.

Microbial biomass, activity, and community structure in horticultural soils under conventional and organic management strategies

Maintaining a diverse functional and taxonomic microbial community in central to preserving soil quality and for ensuring food security. Growing evidence suggests that organic farming systems possess higher quality soils with robust microbial activity in comparison to conventionally managed systems. Although plastic tunnel greenhouses are widely used, their effects on microbial communities are largely unknown. We examined how four treatments impacted soils and their microbial communities: (1) organic management in greenhouses (Or-Gr) and (2) open fields (Or-Op), and (3) conventional management in greenhouses (Co-Gr) and (4) open fields (Co-Op). We measured physicochemical and microbiological parameters, community-level physiological profiles, and phospholipid fatty acid (PLFAs) contents of soils (0–20 cm depth). Both organic and greenhouse management significantly increased total organic C (SOC), total N, microbial biomass C (MBC) and N (MBN), and basal- and substrate-induced respiration (P < 0.05). Or-Gr had significantly higher total, bacterial (both Gram-positive and -negative), and fungal PLFA concentrations (P < 0.05) than the other treatments. Generally, soil quality followed the series Or-Gr > Or-Op > Co-Gr > Co-Op. MBC, MBN, and PLFA concentrations were positively correlated (r > 0.90, P < 0.01) with SOC, total N, and cation exchange capacity and negatively with soil pH. Organic and greenhouse management had a significant interaction effect. Our findings suggest that greenhouse management should be promoted for food security.

Effect of Biochar on Microorganisms Quantity and Soil Physicochemical Property in Rhizosphere of Spinach (&lt;i&gt;Spinacia oleracea&lt;/i&gt; L.)

To investigate the effects of biochar on greenhouse soil, three biochar treatments, i.e. 0 t ha-1 (C0), 12.5 t ha-1 (C1) and 25 t ha-1 (C2), were applied to the rhizosphere of spinach (Spinacia oleracea L.). And the microbial biomass C (MBC), the quantities of the bacteria, fungi, actinomyces, ammonifying bacteria, azotobacter and denitrifying bacteria, pH, oxidation-reduction potential (Eh), and mineral nutrient content were studied. The results indicated that MBC contents with C2 and C1 treatments were significantly (P＜0.01) higher than those with C0 treatment, and the quantities of bacteria, fungi, actinomyces, ammonifying bacteria, azotobacter, and denitrifying bacteria under C1 treatment were 1.06 fold, 2.18 fold, 1.17 fold, 1.47 fold, 2.94 fold and 0.38 fold of those with C0 treatment in rhizosphere of spinach, while those with C2 treatment were 1.25 fold, 2.08 fold, 1.24 fold, 1.41 fold, 4.92 fold and 1.76 fold of those with C0 treatment. The total phosphorus, total carbon, total sulphur, total potassium content, carbon/nitrogen, and Eh with C2 and C1 treatments were higher than in those with C0 treatment. Our results suggest that biochar can be used as ameliorant to improve quantity of microorganisms and physical and chemical properties of greenhouse soil.

Short-term effects of nitrogen addition and vegetation removal on soil chemical and biological properties in a freshwater marsh in Sanjiang Plain, Northeast China

Nitrogen (N) is commonly a limited nutrient in wetland ecosystems. Nitrogen addition affects the ecosystem carbon (C) balance and alters soil C storage through soil chemical and biological changes. In the present study, the effects of N addition and vegetation removal after one growing season on soil properties were examined in a Calamagrostis angustifolia freshwater marsh in Northeast China. Specifically, available N (NH 4 + –N and NO 3 − –N), microbial biomass C (MBC), and dissolved organic C (DOC) concentrations in the soil were analyzed. In addition, activities of soil enzyme (β-glucosidase, invertase , and urease) were investigated. The results showed that N addition resulted in significant increase of NH 4 + –N and NO 3 − –N in both topsoil and subsoil , and vegetation removal enhanced these effects. Soil MBC concentrations increased after N addition and vegetation removal but DOC concentrations did not change significantly. As to soil enzyme activities , N addition stimulated the β-glucosidase activity in the topsoil and invertase and urease activities in both soil layers. Vegetation removal enhanced the effect of N addition on β-glucosidase and invertase activities but inhibited the effect on urease activity. These results suggested that N addition affects soil biochemical process indirectly through marshland vegetation. ► Nitrogen addition has significant effects on marshland soil biochemical properties. ► Short-term nitrogen addition does not significantly affect soil DOC pool in marshland. ► Nitrogen addition can affect the soil biochemical process indirectly through vegetation. ► Nitrogen addition and vegetation removal significantly increased soil MBC pool.

Soil organic matter characteristics, biochemical activity and antioxidant capacity in Mediterranean land use systems

The characteristics of soil quality were measured in adjacent agricultural (horticultural cropping sequence, HC), native grassland (naturally grazed, NG) and forest (indigenous wood of holm-oak, F) soils. The objective of the research was to assess the influence of different land uses on soil organic matter characteristics, biochemical activity and antioxidant capacity in selected fields of the Mediterranean environment in central Italy under a specific climatic regime.Land use induced significant changes in the content and quality of soil organic matter, biochemical activity and antioxidant capacity, with more pronounced differences between soils under HC and F than soils under HC and NG. The HC soil showed the lowest amounts of total organic carbon (TOC), microbial biomass C (MB-C), water-soluble organic C (WSOC), water- and alkali-soluble phenols. The organic matter of HC was characterized by the lowest percentage of MB-C and of light fraction carbon (LF-C). The dehydrogenase activity (DH-ase), metabolic potential (MP), hydrolyzing coefficient (HyC), potentially mineralizable C (C0) and C mineralized (Cm) were clearly lower in HC. The specific respiration activity of biomass (qCO2) was the highest in HC soil (1.3μg CO2–CμgbiomassC−1) and lowest in F soil (0.5μgCO2–CμgbiomassC−1) and was inversely related with pH, TOC and MB-C contents. The antioxidant capacity of soils (TEAC) was the highest in NG and related to the amount of alkali-soluble phenols. The rate constant of organic matter mineralization (k) appeared to depend on TEAC rather than the relative amounts of the labile C pools. These results seem to explain the role of phenols as controller of the mineralization rate of organic matter.

Impacts of 22-year organic and inorganic N managements on soil organic C fractions in a maize field, northeast China

Impacts of 22-year organic and inorganic N managements on total organic carbon (TOC), water-soluble organic C (WSOC), microbial biomass C (MBC), particulate organic C (POC) and KMnO4 oxidized organic C (KMnO4-C) concentrations, C management index (CMI), and C storage in surface soil (0–20 cm) were investigated in a maize (Zea may L.) field experiment, Northeast China. The treatments included, CK: unfertilized control, M: organic manure (135 kg N ha− 1 year− 1), N: inorganic N fertilizer (135 kg N ha− 1 year− 1) and MN: combination of organic manure (67.5 kg N ha− 1 year− 1) and inorganic N fertilizer (67.5 kg N ha− 1 year− 1). TOC concentration and C storage were significantly increased under the M and MN treatments, but not under the inorganic N treatment. The organic treatments of M and MN were more effective in increasing WSOC, MBC, POC and KMnO4-C concentrations and CMI than the N treatment. The M treatment was most effective for sequestrating SOC (10.6 Mg ha− 1) and showed similar increase in degree of grain yield to the N and MN treatments, therefore it could be the best option for improving soil productivity and C storage in the maize cropping system.

The application of bentonite and zeolite for soil amelioration in acidic sandy soil

In a pot experiment, we have studied the effect of bentonite and zeolite in different dosages [control; 5; 10; 15; 20 g kg-1] on acidic (pHH2O=5.65) humus sandy soil. The experiment was set up in 2007 and 2008 in the greenhouse of the UD CASE Department of Agrochemistry and Soil Science. As a test plant, perennial ryegrass (Lolium perenne L.) was used. In laboratory examinations, pH(H2O), pH(KCl), hidrolytic acidity, nitrate-N content, readily available phosphorus and potassium content were determined. Among soil microbial parameters, the total number of bacteria, the cellulose-decomposing bacteria, the carbon-dioxide production, the microbial biomass-C content of soil, and the saccharase enzyme activity were measured. In the experiment the biomass of the test plant was determined.The effect of bentonite and zeolite in different dosages can be summarized as follows:− The pH increased under the effect of low dosages. With the increasing of the pH the hydrolytic acidity - at the bentonite treatments significantly – decreased. − Regarding the readily available nutrient content of the soil, low and medium dosages proved to be effective. High dosages of bentonite treatments reduced the nitrate-N content, the readily available phosphorus, and potassium content of soil, by zeolite treatments the high dosages reduced the nitrate-N content of soil. − Regarding the measured soil microbial parameters in both treatments low and medium dosages proved to be also effective, but the high dosages didn’t cause decreasing at the total number of bacteria, and by zeolite treatments the biomass-C content of soil.− Also the bentonite and zeolite treatments enlarged the biomass of the test plant. We experienced significant increasing by bentonite treatments by the effect of medium and high dosages, while in zeolite treatments only the high dosage caused significantly increasing in plant biomass. The largest dosages decrease the plant biomass. − Under the statistical analysis we found many medium and tight correlation between the studied parameters.