Fungal and bacterial growth following the application of slurry and anaerobic digestate of livestock manure to temperate pasture soils

How land-application of digestate sourced from anaerobic digestion (AD) of animal waste influences the functioning of a mixed pasture agroecosystem is not well characterised, particularly with regard to the response of the actively growing microbial community. We studied the impact of the liquid AD digestate on the decomposer community in two different soils, seeded with two different common grassland crops; a mixture of either grass or grass/clover in a greenhouse experiment. We studied bacterial (leucine incorporation into bacteria) and fungal (acetate incorporation into ergosterol) growth responses to AD cattle slurry digestate, undigested cattle slurry, mineral fertiliser (NPK and N) added at a rate equivalent to 150?kg?N?ha^?1, and a no-fertiliser control treatment. Differences in fungal and bacterial growth were evident between the soil and sward types. However, the fertilisers consistently stimulated a higher bacterial growth than the no-fertiliser control, and liquid digestate resulted in a level of bacterial growth higher or equal to that of mineral fertiliser, whilst undigested slurry resulted in lower bacterial growth. These fertiliser effects on bacterial growth mirrored the effects on plant growth. In contrast, the fungal community responded only marginally to fertiliser treatments. We conclude that the application of digestate stimulates the bacterial decomposer community in a similar way to that of mineral fertilisers. Our results suggest that mineral fertiliser can be exchanged for liquid digestate with limited impact on the actively growing soil microbial community that, in turn, regulate important soil processes including nutrient cycling in agricultural soils.     

Phosphorus availability in soils amended with wheat residue char

Plant availability and risk for leaching and/or runoff losses of phosphorus (P) from soils depend among others on P concentration in the soil solution. Water-soluble P in soil measures soil solution P concentration. The aim of this study was to understand the effect of wheat residue char (biochar) addition on water-soluble P concentration in a wide range of biochar-amended soils. Eleven agricultural fields representing dominant soil texture classes of Swedish agricultural lands were chosen. Concentrations of water-soluble P in the soils and in biochar were measured prior to biochar incorporation to soils in the laboratory. Experiments with three dominant soil textures—silt loam, clay loam, and an intermediate loam soil with different rates of biochar addition (i.e., 0.5, 1, 2, and 4 %; w/w) showed that the highest concentration of water-soluble P was achieved at an application rate of 1 %. At higher application rates, P concentrations decreased which coincided with a pH increase of 0.3–0.7 units. When the 11 soils were amended with 1 % (w/w) biochar, water-soluble P concentrations increased in most of the soils ranging from 11 to 253 %. However, much of the water-soluble P added through the biochar was retained (33–100 %). We concluded that wheat residue char can act as a source of soluble P, and low and high additions of biochar can have different effects on soil solution P concentration due to possible reactions with Ca and Mg added with biochar.     

Responses of soil microbial communities to manure and biochar in wheat cultivation of a rice-wheat rotation agroecosystem in East China

Soil contamination in agroecosystems remains a global environmental problem. Biochar has been suggested as an organic amendment to alleviate soil pollution, sequester carbon(C), and improve soil fertility. However, information on how bacterial and fungal communities in acidic bulk and rhizosphere soils respond to swine manure and its biochar is still lacking. In this study, biochar and swine manure were applied at two rates of 1.5 and 3 t ha^-1 in a rice-wheat rotation field to assess ...     

Soil Organic Carbon,Biochar, and Applicable Research Results for Increasing Farm Productivity under Australian Agricultural Conditions

The conversion of vegetative biomass waste to biochar (biologically derived charcoal) is a source of carbon (C) that can be used to increase the level of soil organic C (SOC) in agricultural soils. This review collates available research into the effects of biologically derived C species with respect to the direct and indirect effects on agricultural productivity and their potential for use in Western Australian agricultural systems. There is a growing requirement to quantify the effect of specific biochar applications for agroecological purposes and to verify biosequestered C for climate-change-mitigation activities. This work provides a review and assessment of safe biochar application rates and examines the present levels of scientific uncertainty surrounding the efficacy and reliability of applying biochar to soils in relation to crop productivity.     

等碳投入的有机肥和生物炭对红壤微生物多样性和土壤呼吸的影响

施用有机肥是快速培育瘠薄土壤的一个重要措施。针对中亚热带第四纪红黏土发育的红壤旱地,建立了玉米和花生单作系统等碳量投入有机肥和生物炭的田间试验,利用聚合酶链式反应—变性梯度凝胶电泳(polymerase chain reaction-denaturing gradient gel electrophoresis,PCR-DGGE)方法研究了土壤细菌和真菌群落组成和多样性的变化,分析了土壤呼吸速率(CO2通量)的变化及其与微生物多样性的关系。两年的试验表明,不同施肥方式导致微生物群落结构显著分异,施用有机肥和生物炭显著增加了细菌多样性,但施肥第二年真菌多样性有下降趋势。秸秆和猪粪配施显著增加了土壤呼吸速率,土壤呼吸速率与细菌和真菌多样性呈显著正相关,细菌多样性对土壤呼吸的影响(相对贡献率为71%)显著高于真菌(29%)。土壤磷素(全磷和速效磷)含量的变化是驱动红壤微生物多样性变化的主导因素,其对细菌和真菌多样性的相对贡献率分别为44.8%和47.4%。因此,合理配施秸秆和猪粪可以快速提高瘠薄红壤的生物功能。     

Effects of biochars produced from different feedstocks on soil properties and sunflower growth

The use of biochar as a soil amendment is gaining interest to mitigate climate change and improve soil fertility and crop productivity. However, studies to date show a great variability in the results depending on raw materials and pyrolysis conditions, soil characteristics, and plant species. In this study, we evaluated the effects of biochars produced from five agricultural and forestry wastes on the properties of an organic‐C‐poor, slightly acidic, and loamy sand soil and on sunflower (Helianthus annuus L.) growth. The addition of biochar, especially at high application rates, decreased soil bulk density and increased soil field capacity, which should impact positively on plant growth and water economy. Furthermore, biochar addition to soil increased dissolved organic C (wheat‐straw and olive‐tree‐pruning biochars), available P (wheat‐straw biochar), and seed germination, and decreased soil nitrate concentration in all cases. The effects of biochar addition on plant dry biomass were greatly dependent upon the biochar‐application rate and biochar type, mainly associated to its nutrient content due to the low fertility of the soil used. As a result, the addition of ash‐rich biochars (produced from wheat straw and olive‐tree pruning) increased total plant dry biomass. On the other hand, the addition of biochar increased the leaf biomass allocation and decreased the stem biomass allocation. Therefore, biochar can improve soil properties and increase crop production with a consequent benefit to agriculture. However, the use of biochar as an amendment to agricultural soils should take into account its high heterogeneity, particularly in terms of nutrient availability.     

Effects of biochar application on soil potassium dynamics and crop uptake

Biochar has been suggested as a possible means for enhancing soil fertility, including soil potassium (K). However, understanding of the effects of biochar on soil K dynamics remains limited. In this study, a pot trial was conducted to investigate the influence of biochar application (0, 5, 10, and 25 g kg^?1 soil) on soil K dynamics and crop K uptake under a winter wheat–maize rotation in two types of soil (an Alfisol, which contained a high initial available K and an Entisol, which contained a high abundance of 2 : 1 K‐bearing minerals). Changes in soil K in various forms following biochar application and cropping were determined, and their contributions to plant K uptake were evaluated. Soil microbial activity, especially the development of K‐dissolving bacteria (KDB), was evaluated to obtain insights into its effects on the weathering of K‐bearing minerals in the soils. During the wheat growth period, crop K uptake was more enhanced (13.6–40.5% higher) in the Alfisol than in the Entisol due to the higher availability of water‐soluble and exchangeable K, while K fixation occurred in the Entisol because of the higher content of 2 : 1 K‐bearing minerals. During the maize period, crop K uptake was generally higher in the Entisol soil due to the release of non‐exchangeable K. In addition, biochar application enhanced the growth of KDB in both soils, which was associated with changes in soil pH and water‐soluble K. However, improved mineral K release was observed only in the Entisol. It is concluded that biochar application could be a feasible soil amendment to improve soil K availability, but crop K uptake responses may vary depending on soil types. Soils abundant in 2 : 1 K‐bearing minerals tend to prolong biochar effects on crop K uptake. Biochar application enhanced the growth of KDB, which may facilitate mineral K weathering in soils with abundant K‐bearing minerals.     

生物黑炭对玉米苗期根际土壤氮素形态及相关微生物的影响

生物黑炭被作为土壤改良剂应用逐渐被认可,但其应用机制特别是生物黑炭对氮素形态和根际微生物的影响机理尚不明确,影响其推广。本文采用盆栽试验,研究了玉米和水稻秸秆烧制的生物黑炭按不同量施入土壤后,对玉米苗期株高、生物量和根际土壤氮素形态及相关微生物的影响。结果表明,施入60 g·kg-1玉米黑炭和40~60 g·kg-1水稻黑炭均对玉米苗期株高有显著(P0.05)降低作用,其中水稻黑炭的降低效果更为明显;分别施入60 g·kg-1玉米黑炭和20~60 g·kg-1水稻黑炭后,玉米植株地上部生物量均显著降低。施入60 g·kg-1玉米黑炭后根际土壤含水量和微生物量氮显著提高。随两种生物黑炭施入量的不断增加,玉米苗期根际土壤全氮、硝态氮含量以及固氮作用强度也显著增加,且均在60 g·kg-1施用量下达最大值。施用40 g·kg-1玉米黑炭可显著提高玉米苗期根际土壤氨态氮含量。同时,施用两种生物黑炭后,均不同程度地抑制了玉米根际土壤中细菌总体数量,促进了固氮菌和纤维素降解菌的生长,其中施入60 g·kg-1玉米黑炭的效果最为明显。综上,玉米和水稻秸秆生物黑炭的适量施用,可以促进玉米根际土壤氮素的循环转化,影响相关微生物的群落结构,且与水稻秸秆相比,玉米秸秆生物黑炭的施用效果更加明显。本文针对作物生长、土壤氮素形态及相关微生物数量3个方面研究生物黑炭施入土壤对氮有效性的影响,能够更全面、更准确地将生物黑炭如何影响土壤氮素转化展现出来,促进生物黑炭的深入开发利用,对黑土肥力保护具有一定意义。     

Short-term biochar effect on soil physicochemical and microbiological properties of a degraded alpine grassland

Soil remediation is an important part of the restoration process of degraded terrestrial ecosystems. Due to its unique properties, biochar is being used widely as an effective soil modifier in agricultural systems, but research is still rare on biochar application in grassland ecosystems, especially in degraded alpine grasslands. In this study, we conducted a plot experiment to investigate the effect of biochar application on soil physicochemical properties and microorganisms at the 0–20 cm soil depth of a degraded alpine grassland in Qinghai-Tibet Plateau, China. The experiment consisted of four corn straw biochar application levels (0%, 0.5%, 1% and 2%, with the percentage representing the ratio of biochar weight to the dry weight of soil in the surface 20 cm soil layer). When the biochar addition increased from 0% to 2%, total nitrogen, total organic carbon and available phosphorus in the 0–10 cm soil layer increased by 41%, 55% and 45%, respectively, in the second year after biochar addition. Meanwhile, soil electrical conductivity decreased, and soil water content increased. Total microbial, fungal and bacterial biomasses in the 0–10 cm soil layer increased from 9.15 to 12.68, 0.91 to 1.34, and 3.85 to 4.55 μg g^-1, respectively. The relative biomasses of saprophytic fungi and methanotrophic bacteria decreased, while the relative biomasses of ectomycorrhizal fungi and arbuscular mycorrhizal fungi increased. These results indicate that biochar has a great potential in improving microbial activity and soil fertility in soil remediation of the degraded alpine grassland.     

Influence of long-term fertilisation and crop rotation on changes in fungal and bacterial residues in a tropical rice-field soil

Amino sugars, as a microbial residue biomarker, are highly involved in microbial-mediated soil organic matter formation. However, accumulation of microbial biomass and responses of bacterial and fungal residues to the management practices are different and poorly characterized in rice soils. The objectives of this study were to evaluate the effects of mineral fertiliser (MIN), farmyard manure (FYM) and groundnut oil cake (GOC) on crop yield and co-accumulation of microbial residues and microbial biomass under rice-monoculture (RRR) and rice–legume–rice (RLR) systems. In the organic fertiliser treatments and RLR, rice grain yield and stocks of soil and microbial nutrients were significantly higher than those of the MIN treatment and RRR, respectively. The increased presence of saprotrophic fungi in the organic fertiliser treatments and RRR was indicated by significantly increased ergosterol/C_mic ratio and extractable sulphur. In both crop rotation systems, the long-term application of FYM and GOC led to increased bacterial residues as indicated by greater accumulation of muramic acid. In contrast, the higher fungal C/bacterial C ratio and lower ergosterol/C_mic ratio in the MIN treatment, is likely caused by a shift within the fungal community structure towards ergosterol-free arbuscular mycorrhizal fungi (AMF). The organic fertiliser treatments contributed 22 % more microbial residual C to soil organic C compared to the MIN treatment. Our results suggest that the negative relationship between the ratios ergosterol/C_mic and fungal C/bacterial C encourages studying responses of both saprotrophic fungi and AMF when assessing management effects on the soil microbial community.     

四种农业土壤上生物炭-土壤的交互效应

Soils in south-western Australia are highly weathered and deficient in nutrients for agricultural production. Addition of biochar has been suggested as a mean of improving soil C storage, texture and nutrient retention of these soils.~Clay amendment in sandy soils in this region is a management practice used to improve soil conditions, including water repellence.~In this study a woody biochar (Simcoa biochar) was characterised using scanning electron microscopy before, and four weeks after, it was incorporated into each of four soils differing in clay content and organic matter. Scanning electron microscopy of Simcoa biochar after incubation in soil showed different degrees of attachment of soil particles to the biochar surfaces after 28 d. In addition, the effects of three biochars, Simcoa biochar, activated biochar and Wundowie biochar, on soil microbial biomass C and soil respiration were investigated in a short-term incubation experiment. It was hypothesised that all three biochars would have greater potential to increase soil microbial activity in the soil that had higher organic matter and clay. After 28-d incubation in soil, all three biochars had led to a higher microbial biomass C in the clayey soil, but prior to this time, less marked differences were observed in microbial biomass C among the four soils following biochar application.     

Structure of the microbial biomass and trophic groups of nematodes in soddy-podzolic soils of a postagrogenic succession in the southern taiga (Tver oblast)

The structure of the microbial biomass and trophic nematode groups were studied in soddy-podzolic soils under phytocenoses of a secondary succession initiated by the growth of forests on agricultural lands in the southern taiga. The microbial biomass became greater with the increasing amount of fungal mycelium, and the bacterial pool little changed in these soils. Bacteriovorous nematodes predominated (64% of the total number of nematodes) in the soils of a potato field, where the bacterial biomass was maximal; it was greater or close to the fungal biomass. In the soil under a mown meadow, where the fungal biomass was greater, the populations of fungivorous and bacteriovorous nematodes were close in number and share in the nematode complex (by 40%). In the soil under a spruce forest (climax stage), the main biomass pool was composed of fungi (97%), whose biomass is maximal, while fungivorous nematodes and nematodes with a mixed type of feeding occupy the dominant positions (69% in the nematode complex). In the course of the succession, the number of fungivorous and bacteriovorous nematodes decreased, but their ratio increased from 0.4 in the soil of the potato field to 0.8–1.0 under the meadows and mixed forest and to 2.0 in the soil under the sorrel spruce forest. These changes corresponded to the increasing microbial pool and the share of the fungal biomass in it.     

Effect of biochar on aerobic processes,enzyme activity,and crop yields in two sandy loam soils

Biochar added to agricultural soils may sequester carbon and improve physico-chemical conditions for crop growth, due to effects such as increased water and nutrient retention in the root zone. The effects of biochar on soil microbiological properties are less certain. We addressed the effects of wood-based biochar on soil respiration, water contents, potential ammonia oxidation (PAO), arylsulfatase activity (ASA), and crop yields at two temperate sandy loam soils under realistic field conditions. In situ soil respiration, PAO, and ASA were not significantly different in quadruplicate field plots with or without biochar (20 Mg ha^?1); however, in the same plots, volumetric water contents increased by 7.5 % due to biochar (P?=?0.007). Crop yields (oat) were not significantly different in the first year after biochar application, but in the second year, total yields of spring barley increased by 11 % (P??1, applied during two consecutive years, substantiated that biochar was not inhibitory to PAO and ASA as reference plots consistently showed lowest activities. For PAO, it was found that soil pH, rather than biochar rates, was a driving environmental variable. For ASA, the methodological approach was challenged by product sorption, but results did not suggest that biochar significantly stimulated the enzyme activity. Crop yields of maize in field experiments with 10–100 Mg biochar ha^?1 were unaffected by biochar except for a negative effect of the highest annual rates of 50 Mg ha^?1 in the first year after application. In conclusion, the present wood-based biochar poorly affected the measured microbial processes and generally resulted in similar crop yields in reference and biochar-amended soil plots.     

Microbial growth rate measurements reveal that land-use abandonment promotes a fungal dominance of SOM decomposition in grazed Mediterranean ecosystems

The present study investigated the effects of land-use abandonment on the soil decomposer community of two grazed Mediterranean ecosystems (an annual grassland with scattered holm oaks and a low-density shrubland). To test the influence of grazing abandonment, a set of plots within each site were fenced and kept undisturbed during 4–5 years, during which above-ground plant community structure was monitored. After that, soil samples were collected from grazed and abandoned plots corresponding to the three different soil conditions: away from (“grass”) and below tree canopies (“oak”) within the annual grassland, and from the shrubland (“shrub”). Soil samples were split into two different layers (0–5 and 5–15 cm) and then analyzed for saprotrophic fungal (acetate into ergosterol incorporation) and bacterial (leucine incorporation) growth rates. Ergosterol content (as a fungal biomass estimator) and a standard set of soil chemistry variables were also measured. After 5 years of grazing exclusion, saprotrophic fungal growth rate clearly increased in both grass and oak surface layers whereas bacterial growth rate was not altered. This translated into significantly higher fungal-to-bacterial (F/B) growth rate ratios within the ungrazed plots. Similar trends were observed for the shrub soils after 4 years of exclusion. On the contrary, abandonment of grazing had negligible effects on the ergosterol content, as well as on the soil chemical variables (soil organic carbon, total N, C/N ratio, and pH), in all the three soil conditions assessed. These results indicated a shift toward a more fungal-dominated decomposer activity in soils following cessation of grazing and highlighted the sensitivity of the microbial growth rate parameters to changes associated with land use. Moreover, there were evidences of a faster fungal biomass turnover in the ungrazed plots, which would reflect an accelerated, though not bigger, fungal channel in soil organic matter mineralization.     

柳枝稷生物炭对来自不同地区的两种土壤上植物生物量和微生物动态的影响

Biochar amendments to soils may alter soil function and fertility in various ways, including through induced changes in the microbial community. We assessed microbial activity and community composition of two distinct clayey soil types, an Aridisol from Colorado (CO) in the U.S. Central Great Plains, and an Alfisol from Virginia (VA) in the southeastern US following the application of switchgrass (Panicum virgatum) biochar. The switchgrass biochar was applied at four levels, 0%, 2.5%, 5%, and 10%, approximately equivalent to biochar additions of 0, 25, 50, and 100 t ha^-1, respectively, to the soils grown with wheat (Triticum aestivum) in an eight-week growth chamber experiment. We measured wheat shoot biomass and nitrogen (N) content and soil nutrient availability and N mineralization rates, and characterized the microbial fatty acid methyl ester (FAME) profiles of the soils. Net N mineralization rates decreased in both soils in proportion to an increase in biochar levels, but the effect was more marked in the VA soil, where net N mineralization decreased from -2.1 to -38.4 mg kg^-1. The 10% biochar addition increased soil pH, electrical conductivity, Mehlich- and bicarbonate-extractable phosphorus (P), and extractable potassium (K) in both soil types. The wheat shoot biomass decreased from 17.7 to 9.1 g with incremental additions of biochar in the CO soil, but no difference was noted in plants grown in the VA soil. The FAME recovery assay indicated that the switchgrass biochar addition could introduce artifacts in analysis, so the results needed to be interpreted with caution. Non-corrected total FAME concentrations indicated a decline by 45% and 34% with 10% biochar addition in the CO and VA soils, respectively, though these differences became nonsignificant when the extraction efficiency correction factor was applied. A significant decline in the fungi:bacteria ratio was still evident upon correction in the CO soil with biochar. Switchgrass biochar had the potential to cause short-term negative impacts on plant biomass and alter soil microbial community structure unless measures were taken to add supplemental N and labile carbon (C).     

生物炭用量对塿土微生物量及碳源代谢活性的影响

目的研究果树树干、枝条制成的生物炭添加4～5年后,其添加量对土微生物量及碳源代谢活性的影响,为生物炭改良土的合理应用提供数据支撑和理论依据。方法基于陕西关中土的长期田间试验,采用氯仿熏蒸—浸提法及Biolog-ECO检测法,研究了生物炭不同添加量 (0、20、40、60、80 t/hm2) 下冬小麦不同生育期土壤微生物量C、N、P、C/N的动态变化及土壤微生物的碳源代谢活性。结果当生物炭添加量为40～60 t/hm2时,显著提高了土壤微生物量碳;当生物炭添加量 ≥ 40 t/hm2时,显著提高了土壤微生物量C/N;添加生物炭对土壤微生物量N、P没有显著影响。当生物炭添加量为20 t/hm2时,显著增加了土壤微生物量碳的季节波动;当生物炭添加量为40～60 t/hm2时,显著增加了土壤微生物量C/N的季节波动;当生物炭添加量为20～60 t/hm2时,显著降低了土壤微生物量P的季节波动;添加生物炭对土壤微生物量N的季节波动没有显著影响。添加生物炭对土壤微生物碳源代谢活性没有显著影响,但高量生物炭的添加有降低土壤微生物整体代谢活性的趋势。当生物炭添加量为60 t/hm2时,显著降低了土壤丰富度指数,显著提高了均匀度指数;当生物炭添加量 ≥ 60 t/hm2时,显著降低了Shannon-Wiener指数、Simpson指数。添加生物炭对土壤微生物利用糖类、氨基酸类、多聚物类、多酚化合物类、多胺类碳源的利用率没有显著影响,但生物炭添加量为60 t/hm2时,土壤微生物显著降低了对羧酸类碳源的利用率;糖类、羧酸类、氨基酸类是土中微生物比较偏好、利用率较高的碳源。结论生物炭添加4～5年后,在第7季作物冬小麦生育期内,其不同添加量对土壤微生物量及微生物功能多样性的影响依然有显著的差异。生物炭添加量为40 t/hm2时,可以显著提高土壤微生物量碳和C/N,显著降低土壤微生物量磷的季节波动;生物炭添加量大于40 t/hm2时,土壤微生物的整体代谢活性,表征土壤微生物功能多样性的丰富度指数、Shannon-Wiener指数、Simpson指数,土壤微生物对糖类、氨基酸类、多胺类碳源的利用率均呈现降低趋势。因此,生物炭添加量必须控制在合理的范围内,避免对土壤产生不良影响。     

15N-氨基糖探针技术新用法:区分和量化土壤真菌和细菌固持无机氮速率

土壤微生物对无机氮的固持作用是构成土壤保氮机制的重要组成。作为土壤微生物的两大主要类群,真菌和细菌是微生物固持无机氮作用的主要参与者。然而,由于土壤微生物的高度复杂多变性,如何有效区分和量化土壤中真菌和细菌各自对无机氮的固持作用是个难题。针对该问题,本文采用“氨基糖稳定同位素探针（AS-SIP）”技术来区分和表征土壤中真菌、细菌各自对无机氮的固持速率。基于此进一步揭示了农业利用和外源碳输入分别对土壤真菌、细菌各自固持硝态氮作用的影响及原因,构建了土壤中真菌、细菌各自固持无机氮实际速率的估算模型,为区分和量化土壤中真菌、细菌各自对无机氮的实际固持速率提供了更为可信的新方法。本文介绍了AS-SIP 技术原理、主要技术优势、应用案例、不足之处以及改进对策,以期推进该方法的应用和发展。     

Soil organic carbon and microbial communities respond to vineyard management

The farming practices in vineyards vary widely, but how does this affect vineyard soils? The main objective of this study was to evaluate the effects of vineyard management practices on soil organic matter and the soil microbial community. To this end, we investigated three adjacent vineyards in the Traisen valley, Austria, of which the soils had developed on the same parent material and under identical environmental/site conditions but were managed differently (esp. tillage, fertilizer application, cover crops) for more than 10 yrs. We found that topsoil bulk density (BD) decreased with increasing tillage intensity, while subsoil BD showed the opposite trend. Soil organic carbon (SOC) stocks in 0–50 cm depth increased from 10 kg m^?2 in an unfertilized and frequently tilled vineyard to 17 kg m^?2 in a regularly fertilized but less intensively tilled vineyard. Topsoil microbial biomass per unit SOC, estimated by the sum of microbial phospholipid fatty acids (PLFAs), followed this trend, albeit not statistically significantly. Principal component analysis of PLFA patterns revealed that the microbial communities were compositionally distinct between different management practices. The fungal PLFA marker 18:2ω6,9 was highest in the vineyard with the lowest amount of extractable Cu (by 0.01 m CaCl₂), and the bacterial‐to‐fungal biomass ratio was positively correlated with extractable Cu. Our results indicate that tillage and fertilizer application of vineyards can strongly affect vineyard soil properties such as BD and SOC stocks and that the application of Cu‐based fungicides may impair soil fungal communities.     

Effects of straw and its biochar applications on the abundance and community structure of CO2-fixing bacteria in a sandy agricultural soil

Purpose

Crop straw and biochar application can potentially increase carbon sequestration and lead to changes in the microbial community in agricultural soils. Sequestration of CO₂ by autotrophic microorganisms is key to biogeochemical carbon cycling in soil ecosystems. The effects of straw and its biochar, derived from slow pyrolysis, on CO₂ fixation bacteria in sandy soils, remain unclear. Therefore, this study compared the response of abundance and community of CO₂ fixation bacteria to the two straw application methods in a sandy agricultural soil. The overall aim of the study was to achieve an efficient use of straw residues for the soil sustainablility.

Materials and methods

We investigated the soil organic carbon content and autotrophic bacteria over four consecutive years (2014–2018) in a field experiment, including the following four treatments: whole maize straw amendment (S), whole maize straw translated biochar amendment (B), half biochar and half straw amendment (BS), and control (CK) without straw or biochar amendment. The autotrophic bacterial abundance and community structure were measured using molecular methods of real-time PCR, terminal restriction fragment length polymorphisms (T-RFLP), and a clone library targeting the large subunit gene (cbbL) of ribulose-1,5-bisphosphate carboxylase/oxygenase.

Results and discussion

The results showed that the content of soil total organic carbon (TOC), dissolved organic carbon (DOC), and microbial biomass carbon (MBC) in B, S, and BS treatments was significantly increased compared with the CK treatment. Soil TOC and available potassium (AK) in the B treatment significantly increased by 15.4% and 23.3%, respectively, but soil bulk density, DOC, and MBC significantly decreased by 8.5%, 10.6%, and 14.5%, respectively, compared with the S treatment. The abundance of the cbbL gene as well as of the bacterial 16S rRNA gene increased significantly in straw or biochar application treatments as compared to the CK treatment. The B treatment, but not the BS treatment, significantly increased the cbbL gene abundance when compared to the S treatment. No significant differences were observed in the bacterial 16S rRNA gene abundance among the three straw or biochar applications. The application of straw biochar could increase the diversity of the autotrophic bacteria, which also altered the overall microbial composition. Physicochemical properties of the soil, such as soil pH, SOC, and bulk density, can help explain the shift in soil microbial composition observed in the study.

Conclusions

Taken together, our results suggest that straw biochar, rather than straw application, leads to an increase in the abundance and diversity of CO₂-fixing bacteria, which would be advantageous for soil autotrophic CO₂ fixation.

     

Risk control effectiveness of phosphorus-containing passivators on Cd-contaminated agricultural soils to be strictly controlled

Purpose

Phosphorus (P)-containing passivators have a stabilizing effect on cadmium (Cd)-contaminated agricultural soils to be safely used, offering good potential for risk control of Cd-contaminated agricultural soils to be strictly controlled. In this study, an incubation experiment was conducted to evaluate the risk control effects of using hydroxyapatite (HAP) and monocalcium phosphate (MCP) on Cd-contaminated agricultural soils to be strictly controlled.

Materials and methods

Samples of topsoil were collected (0–20 cm) from agricultural land near a lead–zinc mine in Southwestern China containing 32.07 mg kg^?1 Cd with a pH of 7.28. The amounts of passivators added were equal to approximately 3% of the soil by weight. The soil Cd content, physicochemical properties, enzyme activity, and microbial community were analyzed.

Results

The results showed that the application of HAP and MCP decreased the activity and mobility of Cd in soils to be strictly controlled. HAP was more effective in decreasing the exchangeable Cd (Cd_Ex) than MCP (rate of decrease was 48.1% for HAP and 24.4% for MCP). According to the results of the geometric mean (GMean) and the integrated total enzyme activity (TEI) index, the total soil enzyme activity of the HAP treatment was higher than that of CK and MCP treatment. HAP and MCP significantly decreased the Chao and Shannon bacterial community indices and the Shannon index of the soil fungal community. HAP increased Actinobacteria abundance, which is beneficial to soil fertility enhancement and plant growth, and MCP increased Rhizobiales abundance, which promotes soil P cycling and plant growth. Primary driving factors for the changes in bacterial and fungal community composition in the stabilized soils were CEC and Cd_Ex for bacteria and Cd bound to carbonates (Cd_Car) and residual Cd (Cd_Res) for fungi.

Conclusions

HAP is more suitable for risk control of Cd-contaminated agricultural soils to be strictly controlled than MCP from the perspective of soil Cd activity and mobility, soil enzyme activity, and diversity and composition of the soil microbial community.