不同植被群落下喀斯特土壤养分及生物化学性质特征

为了探讨植被群落对喀斯特土壤养分和生物化学性质的影响,对贵州茂兰国家级自然保护区不同植被群落下土壤养分、基础呼吸、微生物量碳及酶活性进行比较研究。结果表明:不同植被群落之间土壤养分含量差异显著,土壤总有机碳、全氮、全磷、碱解氮和有效磷表现为裸露地<草丛<灌丛≤乔林;土壤基础呼吸表现为裸露地<灌丛<乔林<草丛,诱导微生物量碳为裸露地<灌丛<草丛=乔林,而熏蒸微生物量碳为裸露地<草丛<灌丛<乔林;不同植被群落下土壤蔗糖酶活性高于裸露地,但不同植被群落间差异不显著,土壤脲酶活性有着裸露地<草丛=灌丛<乔林的趋势,而土壤碱性磷酸酶活性表现为裸露地<灌丛<乔林<草丛;土壤呼吸商和诱导微生物量与熏蒸微生物量比值均表现为乔林=灌丛<草丛=裸露地。结果分析表明,不同植被群落下喀斯特土壤养分水平及其凋落物差异影响着土壤微生物群落结构及活性,而土壤微生物执行着土壤营养元素生物化学过程,其群落结构和活性又影响着土壤养分水平及养分有效性。     

The Impact of Allolobophora molleri on Soil Biology Under Different Organic Amendments

We investigated the effects of the endogenous Allolobophora molleri earthworm on the enzyme activities, the humus–enzyme complexes and the microbial community of a Plagic Antrosol soil which had been amended with different sources of organic matter. During a period of 300 days, the soil was amended with the organic fraction of a municipal solid waste at a rate of 10% or poultry manure at a rate of 7·6%, respectively, in order to apply the same amount of organic matter to the soil. At the end of the experiment, soil enzymatic activities were highest in organic amended soils with earthworms, followed by the organic‐amended soils without earthworms. The reason being, the earthworms stimulate microbial action by increasing the surface area for microbial colonization of the substrate and enzymatic through comminuting the organic wastes. The evolution of soil humus–enzyme complexes indicated the highest values of enzymes adsorbed to humus with the highest humic acid contents. The presence of A. molleri in organic‐amended soils significantly (p < 0·05) increased the soil microbial diversity. Possibly, the progressive breakdown of organic matter applied to the soil by earthworms does appear to produce new organic substrates which therefore promote the appearance of new microorganisms in the soil capable of degrading these substrates. Copyright © 2016 John Wiley & Sons, Ltd.     

Assessment of biogeochemical trends in soil organic matter sequestration in Mediterranean calcimorphic mountain soils (Almería, Southern Spain)

Total soil organic matter levels and humic acid formation processes in mountain calcimorphic soils from Sierra María-Los Vélez Natural Park (Almería, Southern Spain) were found to differ depending on soil use (pine and oak forests, and cleared areas either cultivated or affected by bush encroachment). Biogeochemical indicators such as the concentration of exchangeable cations, or the concentration of the different types of humic substances were neither influenced by the type of vegetation nor soil use. In fact, multidimensional scaling and multiple correlations suggest that soil carbon sequestration processes are controlled by small-scale topographical features and their impact on water holding capacity. From a qualitative viewpoint, there were two more or less defined sets of soils: one set consisted of soils with humic acids with marked aliphatic character, displayed intense 2920 cm⁻¹ infrared band, and had low optical density. The resolution-enhanced infrared spectra suggested typical lignin patterns and well-defined amide bands, which point to a selective preservation of comparatively young organic matter. This situation contrasts with that in other set of soils with low C levels (<20 g kg⁻¹) where humic acids with featureless infrared spectra showed high aromaticity and were associated with perylenequinonic chromophors of fungal origin: this is considered the consequence of overlapping biogeochemical mechanisms involving both microbial synthesis and condensation processes. The results from visible and infrared derivative spectroscopies suggest that the reliability of statistically assessing the biogeochemical performance of the different uses on the site studied in terms of the intensity of the prevailing humic acid formation mechanisms, i.e., accumulation of inherited macromolecular substances in the former set, vs. microbial synthesis including the condensation of precursors of low molecular weight substances in the latter.     

Modelling changes in soil organic matter after planting fast-growing Pinus radiata on Mediterranean agricultural soils

The Kyoto Protocol explicitly allows the storage of carbon (C) in ecosystems resulting from afforestation to be offset against a nation's carbon emissions and paves the way for carbon storage in soils to be eligible as carbon offsets in the future. More information is required about how afforestation affects carbon storage, especially in the soil. We report a study in which soil carbon storage in first‐rotation Mediterranean Pinus radiata plantations, established on former cereal fields and vineyards, was measured and modelled. Measurements were made on plantations of several ages, as well as repeat measurements at the same site after 5 years. We tested the ability of two widely used soil organic matter models (RothC and Century) to predict carbon sequestration in Mediterranean forest soils. Increases in the top 5 cm of soil of about 10 g C m^?2 year^?1 were observed after afforestation of former vineyards, but nitrogen (N) either remained the same or decreased slightly. During afforestation, most organic matter accumulated in the ectorganic layers at a rate of 19 g C m^?2 year^?1 in former vineyards and 41 g C m^?2 year^?1 in former cereal fields. The RothC and Century models were sensitive to previous land use and estimated a carbon sequestration potential over 20 years of 950 and 700 g C m^?2, respectively. The accurate simulation of the dynamics of soil organic matter by RothC, together with measured above‐ground inputs, allowed us to calculate below‐ground inputs during afforestation. The Century model simulated total C and N, including the ectorganic horizons, well. Simulations showed a depletion of N in the below‐ground fractions during afforestation, with N limitation in the former vineyard but not on former cereal land. The approach demonstrates the potential of models to enhance our understanding of the processes leading to carbon sequestration in soils.     

天台山不同林型土壤酶活性与土壤微生物、呼吸速率以及土壤理化特性关系研究

天台山8种不同林型土壤环境酶活性的模糊数学分析表明,不同土壤环境总体酶活性水平的相似优先比顺序为:云锦杜鹃土壤黄山松林土壤茶园土壤竹林土壤金钱松林土壤日本花柏林土壤柳杉林土壤七子花林土壤。不同酶之间以及酶与土壤环境因子之间存在着不同程度的相关关系。因子分析揭示了控制天台山不同土壤因素综合作用的主要因子为:土壤7种酶、土壤微生物数量、土壤呼吸速率和土壤总有机质。     

Dynamics and origin of the non-hydrolysable organic fraction in a forest and a cultivated temperate soil, as determined by isotopic and microscopic studies

We isolated the non‐hydrolysable macromolecular organic fraction (insoluble fraction resistant to drastic laboratory hydrolyses) from a temperate, loamy, forest soil (Lacadée, France) and from the soil of an adjacent plot cleared 35 years ago and continuously cropped with maize. The quantitative, morphological (light, scanning and transmission electron microscopy) and isotopic (bulk δ¹³C, individual compound δ¹³C and radiocarbon dating) features of these two non‐hydrolysable fractions were determined and compared. It appeared that: (i) extensive degradation of the non‐hydrolysable material inherited from the forest soil occurred upon cropping, revealing that its resistance to drastic laboratory hydrolyses is not paralleled by a great resistance to natural biodegradation triggered by change in land use; (ii) only small inputs of maize‐derived compounds occurred in the non‐hydrolysable fraction of the cultivated soil so that, in spite of extensive degradation, the forest‐inherited carbon still predominates; (iii) the non‐hydrolysable fractions of both soils comprise the same components (wood debris, spores, pollen, and, predominantly, granular organic aggregates), which correlate with the previously identified chemical components (charcoal, aliphatic lipid components and melanoidin‐like components); (iv) the non‐hydrolysable fraction of the cropped soil shows a greater contribution of aliphatic moieties, reflecting differential degradation of the components of the non‐hydrolysable material inherited from the forest soil; (v) this degradation resulted in enrichment in the oldest components; and (vi) no relationship is observed, in the two Lacadée soils, between resistance to drastic laboratory hydrolyses, on the one hand, and stability towards biodegradation in situ, on the other. These observations, added to recent ones on other types of soils, suggest that such a conspicuous uncoupling between non‐hydrolysable and stable carbon is probably a general feature of organic matter in soil as opposed to sedimentary organic matter.     

Seasonal influence of climate manipulation on microbial community structure and function in mountain soils

Microbial communities drive soil organic matter (SOM) decomposition through the production of a variety of extracellular enzymes. Climate change impact on soil microbial communities and soil enzymatic activities can therefore strongly affect SOM turnover, and thereby determine the fate of ecosystems and their role as carbon sinks or sources.To simulate projected impacts of climate change on Swiss Jura subalpine grassland soils, an altitudinal soil transplantation experiment was set up in October 2009. On the fourth year of this experiment, we measured microbial biomass (MB), microbial community structure (MCS), and soil extracellular enzymatic activities (EEA) of nine hydrolytic and oxidative extracellular enzymes in the transplanted soils on a seasonal basis.We found a strong sampling date effect and a smaller but significant effect of the climate manipulation (soil transplantation) on EEA. Overall EEA was higher in winter and spring but enzymes linked to N and P cycles showed higher potential activities in autumn, suggesting that other factors than soil microclimate controlled their pool size, such as substrate availability. The climate warming manipulation decreased EEA in most cases, with oxidative enzymes more concerned than hydrolytic enzymes. In contrast to EEA, soil MB was more affected by the climate manipulation than by the seasons. Transplanting soils to lower altitudes caused a significant decrease in soil MB, but did not affect soil MCS. Conversely, a clear shift in soil MCS was observed between winter and summer. Mass-specific soil EEA (EEA normalized by MB) showed a systematic seasonal trend, with a higher ratio in winter than in summer, suggesting that the seasonal shift in MCS is accompanied by a change in their activities. Surprisingly, we observed a significant decrease in soil organic carbon (SOC) concentration after four years of soil transplantation, as compared to the control site, which could not be linked to any microbial data.We conclude that medium term (four years) warming and decreased precipitation strongly affected MB and EEA but not MCS in subalpine grassland soils, and that those shifts cannot be readily linked to the dynamics of soil carbon concentration under climate change.     

Excessive Nitrogen Inputs in Intensive Greenhouse Cultivation May Influence Soil Microbial Biomass and Community Composition

Intensive greenhouse vegetable‐production systems commonly utilize excessive fertilizer inputs that are inconsistent with sustainable production and may affect soil quality. Soil samples were collected from 15 commercial greenhouses used for tomato production and from neighboring fields used for wheat cropping to determine the effects of intensive vegetable cultivation on soil microbial biomass and community structure. Soil total nitrogen (N) and organic‐matter contents were greater in the intensive greenhouse tomato soils than the open‐field wheat soils. Soil microbial carbon (C) contents were greater in the greenhouse soils, and soil microbial biomass N showed a similar trend but with high variation. The two cropping systems were not significantly different. Soil microbial biomass C was significantly correlated with both soil total N and soil organic matter, but the relationships among soil microbial biomass N, soil total N, and organic‐matter content were not significant. The Biolog substrate utilization potential of the soil microbial communities showed that greenhouse soils were significantly higher (by 14%) than wheat soils. Principal component (PC) analysis of soil microbial communities showed that the wheat sites were significantly correlated with PC1, whereas the greenhouse soils were variable. The results indicate that changes in soil microbiological properties may be useful indicators for the evaluation of soil degradation in intensive agricultural systems.     

Forest floor development and biochemical properties in reconstructed boreal forest soils

Following resource extraction by surface mining in the oil sands region of northeastern Alberta, sites are reclaimed by reconstructing soils using a variety of salvaged organic and mineral materials, and planted to native tree species. This study assessed the influence of three distinct stand types (Populus tremuloides Michx., Pinus banksiana Lamb., and Picea glauca (Moench) Voss) on forest floor development (thickness, morphology, total carbon and nitrogen contents), soil organic matter composition, and associated soil microbial communities. Forest floor and top mineral soil (0–5 cm) samples were collected from 32 sites reclaimed 16–33 years ago. Soil organic matter composition was measured using ramped-cross-polarization ¹³C nuclear magnetic resonance, and microbial communities were characterized using phospholipid fatty acid analysis. Morphological characteristics indicated little mesofaunal or fungal activities within the forest floors. Stands dominated by P. tremuloides fostered more rapid forest floor development than the coniferous (P. banksiana and P. glauca) stands, and showed a significant increase in forest floor thickness with time since reclamation. Within the P. tremuloides stands, forest floor development was accompanied by temporal changes in soil organic matter composition that reflected inputs from the canopy. Soil microbial community composition differed among reclamation treatments of the reconstructed soils, specifically as a function of their subsoil mineral textures, when canopy cover was below 30%. Above 30%, significant differences became apparent among stand types. Taken together, our results document how canopy cover and stand type were both important factors for the reestablishment of plant–soil relationships at these sites. Furthermore, achieving a canopy cover of 30% emerged as a critical threshold point during soil reclamation.     

Soil Fertility,Mineral Nitrogen,and Microbial Biomass in Upland Soils of the Central Amazon under Different Plant Covers

Amazon is the largest state in Brazil and majority of the state is covered by the largest tropical rainforest of the world. Most soils of the Amazon region soils are acidic and infertile. When the Amazon forest land is cleared for agricultural use by burning the vegetation, the efficient nutrient recycling mechanisms are disrupted. However, nutrient contents in the deforested burn land increased temporarily. The objective of this study was to evaluate the soil fertility, mineral nitrogen (N), and microbial activity of carbon (C), N, and phosphorus (P) resulting from the replacement of the primary forest with pasture (Brachiaria brizantha) and commercial plantations of rubber (Hevea spp.), cupuaçu (Theobroma grandiflorum), and citrus trees (Citrus sinensis) cultivated in Xanthic Ferralsol and secondary forest under Acrisols Dystric Nitosols. The results showed that ammonium-N predominates in the 0- to 10-cm soil depth in both primary forest and areas with secondary forest, citrus plantation, and pasture. There was no increase in soil fertility with management of the cultivated areas under the secondary forest, but in the pasture there was a significant increase in the stock of organic C and total N and high C/N ratios, the inverse of what occurred with the C of the microbial biomass. The primary forest had the greatest values of C and P of the microbial biomass and the lowest metabolic quotient. Of the successions studied, the rubber trees were the plant cover with the smallest changes in terms of quality of the organic matter in the soil.     

Mineralization of soil organic matter initiated by the application of an available substrate to the profiles of surface and buried podzolic soils

The priming effect (PE) initiated by the application of ¹⁴C-glucose was studied for copiotrophic microbial communities of organic horizons and for oligotrophic microbial communities of mineral soil horizons, as well as for mineral horizons of buried soils depleted in the input of fresh organic matter. The intensity of the PE depended on the reserves of C_org, the initial amount of the microbial biomass, and the enzymatic activity, which decreased from the organic to the mineral soil horizons. The ratio of the PE to the applied carbon was two times higher in the mineral horizons as compared with the organic horizons. This is explained by the predominance of K-strategists capable of decomposing difficultly available organic compounds in the mineral horizons, so that the turnover of the microbial biomass in the mineral horizons was more active than that in the organic horizons. The predominance of K-strategists was confirmed by the close correlation between the PE and the activity of the cellobiohydrolase enzyme decomposing cellulose (R = 0.96). In general, the absolute value of the PE was controlled by the soil organic matter content, whereas the specific PE was controlled by the functional features of the microorganisms. It was shown that the functional features of the soil microorganisms remained unchanged under the conditions of their preservation in the buried soil.     

Soil Organic Carbon and Nitrogen Fractions in Temperate Alley Cropping Systems

Abstract

Alley cropping may promote greater sequestration of soil organic carbon. The objective of this study was to examine spatial variability of soil organic carbon (C) and nitrogen (N) fractions relative to tree rows in established alley cropping systems in north central Missouri. Soils were collected to a depth of 30 cm from two alley cropped sites, a 19‐yr‐old pecan (Carya illinoinensis)/bluegrass (Poa trivialis) intercrop (pecan site) and an 11‐yr‐old silver maple (Acer saccharinum)/soybean (Glycine max)–maize (Zea mays) rotation (maple site). Particulate organic matter (POM) C constituted 15–65% and 14–41% of total organic C (TOC) at the pecan and maple sites respectively, whereas POM N comprised 3 to 24% of total N (TKN). TOC and TKN were on average 13% and 18% higher at the tree row than at the middle of the alley for surface soils (0–10 cm) at the pecan site, respectively. Similarly, POM C was two to three times higher at the tree row than the alley for subsurface soils at the maple site. No differences in microbial biomass C and N between positions were observed. Observed results suggest the existence of spatially dependent patterns for POM C, TOC, and TKN, relative to tree rows in alley cropping.     

红壤恢复林地微团聚体形成与稳定的影响机制研究进展

微团聚体是土壤团粒结构的基本组成单元,较大团聚体具有更强的稳定性,其形成与稳定对于土壤有机碳的长期吸存起着决定性作用。目前关于微团聚体形成与稳定性的研究多专注于农业土壤,红壤侵蚀地植被恢复后土壤团聚体稳定性、有机碳分布及微生物群落特征研究也主要集中在大团聚体上,而土壤微团聚体的动态变化及其主要影响因素尚不明确,对于其内在机制更缺乏了解。通过总结土壤微团聚体的形成过程及稳定性,综述了凋落物、根系和菌根对土壤微团聚体形成与稳定的影响,阐述了土壤微团聚体内微生物群落、化学结合态有机碳及有机碳结构是土壤有机碳稳定的重要机制,并提出了未来微团聚体研究方向,以期揭示红壤侵蚀退化地森林恢复过程中微团聚体形成和稳定的生物化学机制,从而为深入阐明有机质—土壤团聚结构—微生物—化学耦合作用和森林土壤碳吸存机制提供参考。     

Carbon isotopes of water‐extractable organic carbon in a depth profile of forest soil imply a dynamic relationship with soil carbon

Although considerable research has been conducted on the importance of recent litter compared with older soil organic matter as sources of dissolved organic carbon (DOC) in forest soils, a more thorough evaluation of this mechanism is necessary. We studied water‐extractable organic carbon (WEOC) in a soil profile under a cool‐temperate beech forest by analysing the isotopic composition (¹³C and ¹⁴C) of WEOC and its fractions after separation on a DAX‐8 resin. With depth, WEOC became more enriched in ¹³C, which reflects the increasing proportion of the hydrophilic, isotopically heavier fraction. The ¹⁴C content in WEOC and its fractions decreased with depth, paralleling the ¹⁴C trend in soil organic matter (SOM). These results indicate a dynamic equilibrium of WEOC and soil organic carbon. The dominant process maintaining the WEOC pool in the mineral soil appears to be the microbial release of water‐soluble compounds from the SOM, which alters in time‐scales of decades to centuries.     

Land‐Use Effects on Soil Nutrient Cycling and Microbial Community Dynamics in the Everglades Agricultural Area,Florida

Soil subsidence has become a critical problem since the onset of drainage of the organic soils in the Everglades Agricultural Area (EAA), which may impair current land uses in the future. The objectives of this study were to characterize soil microbial community‐level physiology profiles, extracellular enzymatic activities, microbial biomass, and nutrient pools for four land uses: sugarcane, turfgrass, pasture, and forest. Long‐term cultivation and management significantly altered the distribution and cycling of nutrients and microbial community composition and activity in the EAA, especially for sugarcane and turf fields. The least‐managed fields under pasture had the lowest microbial biomass and phosphorus (P) levels. Turf and forest had more microbial metabolic diversity than pasture or the most intensively managed sugarcane fields. Land‐use changes from sugarcane cropping to turf increased microbial activity and organic‐matter decomposition rates, indicating that changes from agricultural to urban land uses may further contribute to soil subsidence.     

Temperature sensitivity of soil organic matter decomposition in southern and northern areas of the boreal forest zone

Much effort has been made to improve understanding of factors controlling the temperature dependence of soil organic matter (SOM) decomposition. The question of how soils formed in different geographical locations and conditions respond to temperature changes is still open. In addition to climate, residence times of soil organic matter are controlled by its decomposability and microbial community. In this work we hypothesized that the decomposition of SOM is adapted to the prevailing SOM quality and climatic conditions. This should result in different temperature vs. decomposition curves for northern and southern soils. We studied short-term temperature dependence of SOM decomposition near the northern and southern borders of the boreal forest zone using a Gaussian model. As carbon mineralization rate is driven by microbial activity, we focused on organic carbon fractions available to microbes and the size, composition and functioning of microbial communities in the soil. Despite differences in microbial community structure and behavior, similar amounts and qualities of the microbially available carbon led to similar temperature dependences of carbon mineralization in the north and south. The overall soil respiration rate level was higher in spruce forest sites than in pine forest sites irrespective of climate conditions. Our results do not mean that there is no risk of carbon losses from northern soils due to warming climate conditions. As temperature sensitivity of the decomposition increases with decreasing temperature regime, the proportional increase in the decomposition rate in northern latitudes might lead to significant carbon losses from the soils.     

Influence of vegetation types and soil properties on microbial biomass carbon and metabolic quotients in temperate volcanic and tropical forest soils

Abstract

There is limited knowledge about the differences in carbon availability and metabolic quotients in temperate volcanic and tropical forest soils, and associated key influencing factors. Forest soils at various depths were sampled under a tropical rainforest and adjacent tea garden after clear-cutting, and under three temperate forests developed on a volcanic soil (e.g. Betula ermanii and Picea jezoensis, and Pinus koraiensis mainly mixed with Tilia amurensis, Fraxinus mandshurica and Quercus mongolica), to study soil microbial biomass carbon (MBC) concentration and metabolic quotients (qCO₂, CO₂-C/biomass-C). Soil MBC concentration and CO₂ evolution were measured over 7-day and 21-day incubation periods, respectively, along with the main properties of the soils. On the basis of soil total C, both CO₂ evolution and MBC concentrations appeared to decrease with increasing soil depth. There was a maximal qCO₂ in the 0–2.5 cm soil under each forest stand. Neither incubation period affected the CO₂ evolution rates, but incubation period did induce a significant difference in MBC concentration and qCO₂ in tea soil and Picea jezoensis forest soil. The conversion of a tropical rainforest to a tea garden reduced the CO₂ evolution and increased the qCO₂ in soil. Comparing temperate and tropical forests, the results show that both Pinus koraiensis mixed with hardwoods and rainforest soil at less than 20 cm depth had a larger MBC concentration relative to soil total C and a lower qCO₂ during both incubation periods, suggesting that microbial communities in both soils were more efficient in carbon use than communities in the other soils. Factor and regression analysis indicated that the 85% variation of the qCO₂ in forest soils could be explained by soil properties such as the C:N ratio and the concentration of water soluble organic C and exchangeable Al (P < 0.001). The qCO₂ values in forest soils, particularly in temperate volcanic forest soils, decreased with an increasing Al/C ratio in water-soluble organic matter. Soil properties, such as exchangeable Ca, Mg and Al and water-soluble organic C:N ratio, were associated with the variation of MBC. Thus, MBC concentrations and qCO₂ of the soils are useful soil parameters for studying soil C availability and microbial utilization efficiency under temperate and tropical forests.     

稻田土壤微生物残体积累对外源秸秆输入的响应研究进展

稻田土壤碳循环是我国陆地生态系统碳循环的重要组成部分。促进稻田生态系统碳的固定及稳定对减缓全球气候变化起着不容忽视的作用。微生物主导的有机碳转化过程是土壤碳循环研究的核心,微生物同化代谢介导的细胞残体迭代积累在土壤有机碳长期截获和稳定过程中发挥重要作用。与旱地土壤相比,关于稻田土壤中微生物残体积累动态对外源有机物质如作物秸秆输入的响应及主要影响因子的认识还相对有限,对微生物通过同化作用参与土壤固碳的过程和机制尚缺乏系统认识。基于此,本文介绍了微生物残体对土壤有机碳库形成和积累的重要性及评价指标,重点探讨了秸秆还田对稻田土壤微生物残体积累动态以及外源秸秆碳形成细胞残体转化过程的影响,分析了影响微生物残体积累转化的主要气候因素和土壤因素,最后提出了未来应借助先进的光谱和高分辨率成像技术并结合同位素示踪对微生物残体的稳定性与机理开展更为深入的研究。     

Effects of Ant Mounds on the Plant and Soil Microbial Community in an Alpine Meadow of Qinghai–Tibet Plateau

Ants are important soil engineers, affecting the structure and function of ecosystems. To address the impacts of ants (Camponotus herculeanus ) on the properties of an alpine meadow ecosystem of Qinghai–Tibet Plateau, we investigated the effects of ant mounds on plant biomass, soil physicochemical properties, microbial diversity, and functions. We found that the total biomass of plant community was significantly greater in ant mound periphery. Plant species richness in ant mounds was reduced compared with that of control plots without ant mounds. Significant changes in physicochemical properties of soil were also observed. Soil organic matter, total nitrogen, available phosphorous, total potassium, and available potassium increased in ant mound soil due to the excavation activities by ants as well as the accumulation of organic matter and other nutrients during mound construction. For example, roots/soil contents (g/g) and soil moisture in ant mound soils were lower than those in controls. Microbial community composition and microbial biomass were clearly changed in ant mound soils. BIOLOG analysis further indicated that the functional diversity of the microbial community of ant mound soil increased and differed from that of controls. This study indicates that ant‐induced modification of soil properties indirectly influences plant biomass and species composition, and ant mounds have different microbial communities from those of control soil. Copyright © 2016 John Wiley & Sons, Ltd.     

Degradation and humification of maize straw in soil microcosms inoculated with simple and complex microbial communities

Microbial communities are responsible for soil organic matter cycling and thus for maintaining soil fertility. A typical Orthic Luvisol was freed from organic carbon by thermal destruction at 600°C. Then the degradation and humification of ¹⁴C‐labelled maize straw by defined microbial communities was analysed. To study the role of microbial diversity on the humification of plant material, microcosms containing sterilized soil were inoculated with a natural microbial community or with microbial consortia consisting of bacterial and fungal soil isolates. Within 6 weeks, 41 ± 4% of applied ¹⁴C‐labelled maize straw was mineralized in the soil microcosms containing complex communities derived from a soil suspension, whilst the most efficient communities composed of soil isolates mineralized less than 35%. The humification products were analysed by solution state ¹³C‐NMR‐spectroscopy and gel permeation chromatography (GPC). The analyses of humic acids extracts by solution state ¹³C‐NMR‐spectroscopy revealed no difference in the development of typical chemical functional groups for humic substances during incubation. However, the increase in specific molecular size fractions of the extracted humic acids occurred only after inoculation with complex communities, but not with defined isolates. While it seems to be true that redundancy in soil microbial communities contributes to the resilience of soils, specific soil functions may no longer be performed if a microbial community is harshly affected in its diversity or growth conditions.