湘中紫色丘陵区不同植被类型根际与非根际土壤理化特征

[目的]探索湘中紫色丘陵区不同植被类型根际与非根际土壤的理化特征,为湘中地区生态修复提供理论依据。[方法]以典型抽样方法调查湘中丘陵区草丛(G)、草灌(GS)、灌木(S)和乔灌(AS)4种典型植被,研究其根际与非根际土壤理化性质的差异,通过典型相关分析揭示根际与非根际土壤理化指标间的耦合关系。[结果]研究区草丛和灌木根际土壤中细砂粒(0.25~0.05mm)含量分别显著(p0.05)低于乔灌63.84%和76.97%;粉粒(0.02~0.002mm)含量表现为草和灌木分别显著高于乔灌的38.48%和37.66%。根际土壤0.25~0.05mm微团聚体含量均表现为乔灌高于其他植被,0.02~0.002mm微团聚体含量均表现为灌木高于其他植被。草灌与灌木非根际土壤有机质含量显著(p0.05)低于根际土壤148.05%和121.92%,灌木和草灌根际土壤有机质含量显著(p0.05)高于乔灌土壤84.28%和92.08%;草灌根际土壤全氮含量显著(p0.05)高于非根际土壤83.33%,草灌根际土壤碱解氮含量显著(p0.05)高于乔灌土壤200.83%;不同植被类型根际/非根际土壤磷含量差异不明显,总体来看,同一植被根际土壤全磷含量低于非根际土壤,而有效磷表现为乔灌最低;乔灌根际土壤速效钾含量分别显著(p0.05)低于草丛和草灌土壤125.15%和137.71%,除草灌外,其余植被类型根际土壤全钾含量均低于非根际土壤。典范相关分析表明土壤有机质和全量养分含量,2~1,1~0.5,0.25~0.05mm土粒含量,2~1,1~0.5mm团聚体3组理化性状间相互关系密切。[结论]改善土壤理化性质,促进湘中丘陵地区生态恢复,应注重协调土壤养分、颗粒组成及团聚体之间的耦合关系。     

土壤优化采样策略研究进展

[目的]对现有的采样方式进行系统地总结归纳,并探寻一种优化的采样策略,对采样强度、分析成本及其研究精度三方面进行均衡,即以最小的经济投入换取最大化的试验精度。[方法]广泛查阅近几年国内外的相关文献,对土壤优化采样策略的设定进行了系统的总结。将优化采样策略的理论分为合理采样数和样点布设两方面,就此分别介绍确定采样数的3种方法和确定样点布设的4种方式,详细介绍其发展现状,并对该领域今后的研究进行展望。[结果]目前的优化采样法大多基于模型来优化采样设计的研究,其初步采样的方式忽略了空间相关性所导致的信息损失,必然在一定程度上造成试验结果的偏差和人力物力的浪费。而且,研究尺度多集中在县级以下,没有对采样方案的设计确立统一的评价体系和标准。[结论]未来优化采样设计在样点优先级方面还应进行更加深入的研究。     

A case study on the estimation accuracy of soil properties and fertilizer rates for different soil‐sampling grids

Soil testing is used to help make fertilizer recommendations for greater yields and profits. But the increase of soil‐sampling density raises costs of sample collection and analyses. The aim of this study was to compare grid‐cell sampling densities (1, 2, and 4 ha) in terms of the estimation accuracy of macronutrients (P, K, Mg) availability and pH and to investigate how sampling density affects the amount of fertilizers and lime recommended and correctly applied to winter wheat (Triticum aestivum L.). The distribution of liming requirements and available nutrients were quite similar for the 1‐ and 2‐ha grids but notably different for the 4‐ha grid. However, the whole‐field average values of pH and P, K, and Mg concentrations in soil obtained for different sampling densities were very similar, thus placing, respectively, the soil of the studied area in the same class of liming needs and nutrient availability. The range and estimation errors of these parameters decreased with sampling‐grid size increase. The amount of lime and fertilizers to be applied on the field and the portion of a field correctly limed or fertilized depended on the soil chemical property considered. If one treats the 1‐ha grid as the reference and the most correct soil‐sampling approach, 2‐ha grid offered the greatest part of the field to be adequately fertilized with lime, P, and K. However, fertilization with Mg was much more appropriate if the recommendation was based on 4‐ha, than on a 2‐ha soil‐sampling grid. To gain an insight into soil variation and soil process occurring at small scale, laboratory and geostatistical analyses on individual soil samples may be necessary in some cases. Possibly, such costly research can deliver relevant information which could be then applied into farmer's practice.     

Spatially tracking carbon through the root–rhizosphere–soil system using laser ablation‐IRMS

The intimate relationships between plant roots, rhizosphere, and soil are fostered by the release of organic compounds from the plant into soil through various forms of rhizodeposition and the simultaneous harvesting of nutrients from the soil to the plant. Here we present a method to spatially track and map the migration of plant‐derived carbon (C) through roots into the rhizosphere and surrounding soil using laser ablation‐isotope ratio mass spectrometry (LA‐IRMS). We used switchgrass microcosms containing soil from field plots at the Kellogg Biological Station (Hickory Corners, Michigan, USA) which have been cropped with switchgrass since 2008. We used a ¹³CO₂ tracer to isotopically label switchgrass plants for two diel cycles and tracked subsequent movement of labeled C using the spatially specific (< 100 µm resolution) δ¹³C analysis enabled by LA‐IRMS. This approach permitted assessment of variable C flow through different roots and enabled mapping of spatial variability of C allocation to the rhizosphere. Highly ¹³C‐enriched C (consistent with production during the ¹³CO₂ application period) extended ≈ 0.5–1 mm from the root into the soil, suggesting that the majority of recent plant‐derived C was within this distance of the root after 48 h. Tracking the physical extent of root exudation into the rhizosphere can help evaluate the localization of plant‐microbe interactions in highly variable subsurface environments, and the use of the isotopic label can differentiate freshly fixed C (presumably from root exudates) from other types of subsurface C (e.g., plant necromass and microbial turnover). The LA‐IRMS technique may also serve as a valuable screening technique to identify areas of high activity for additional microbial or geochemical assays.     

Rhizospheric organic compounds in the soil–microorganism–plant system: their role in iron availability

Poor iron (Fe) availability in soil represents one of the most important limiting factors of agricultural production and is closely linked to physical, chemical and biological processes within the rhizosphere as a result of soil–microorganism–plant interactions. Iron shortage induces several mechanisms in soil organisms, resulting in an enhanced release of inorganic (such as protons) and organic (organic acids, carbohydrates, amino acids, phytosiderophores, siderophores, phenolics and enzymes) compounds to increase the solubility of poorly available Fe pools. However, rhizospheric organic compounds (ROCs) have short half‐lives because of the large microbial activity at the soil–root interface, which might limit their effects on Fe mobility and acquisition. In addition, ROCs also have a selective effect on the microbial community present in the rhizosphere. This review aims therefore to unravel these complex dynamics with the objective of providing an overview of the rhizosphere processes involved in Fe acquisition by soil organisms (plants and microorganisms). In particular, the review provides information on (i) Fe availability in soils, including mineral weathering and Fe mobilization from soil minerals, ligand and element competition and plant‐microbe competition; (ii) microbe–plant interactions, focusing on beneficial microbial communities and their association with plants, which in turn influences plant mineral nutrition; (iii) plant–soil interactions involving the metabolic changes triggered by Fe deficiency and the processes involved in exudate release from roots; and (iv) the influence of agrochemicals commonly used in agricultural production systems on rhizosphere processes related to Fe availability and acquisition by crops.     

Improving minimum detectable differences in the assessment of soil organic matter change in short‐term field experiments

The demand for information on cropping system impact on soil organic matter (SOM) calls for efforts to improve the utilization of short‐term field experiments (e.g., to evaluate the parameterization of cropping systems in models). Those approaches have coped with the problem of determining small SOM changes within a large background mass. Thus, objectives of this survey are (1) the improvement of the minimum detectable difference (MDD) in SOM in the hudycrop short‐term field experiment by methods of sampling design and data treatment, (2) the verification to what extend the hudycrop short‐term field experiment allows for the determination of management induced effects on SOM, and (3) the investigation to what extent the obtained results may be suitable to evaluate the parameterization of a SOM balance model. The design of the hudycrop is suitable for excluding outliers plotwise. The estimation of plot means can be improved by the sampling design. Instead of determining a single plot mean in a mixed sampling procedure, the design provides multiple values for each plot, allowing for the identification of extreme values before calculating plot means. In consequence, minimum detectable differences decrease by a factor of 0.53 for soil organic C (SOC) and 0.63 for soil total N (STN) masses, allowing for detection of changes in the magnitude of 3.7 and 2.6% of background SOC and STN levels, respectively. Differences between treatments, however, are significant with corrected values (after outlier exclusion) for the crop production systems with the highest impact (potatoes and mulched red clover). Determining outliers based on Student's t‐test gives the lowest MDD and is therefore considered to be the most suitable method in this case. Correlations between apparent changes and SOM balances according to the HU‐MOD–2 model, used in this survey, indicate that the experimental design, in principal, is suitable for the evaluation of the parameterization of crop production systems in models. Still, an improved precision in SOM change detection is necessary. Reasonable options for that purpose are discussed in the paper.     

玉米根际和非根际土壤细菌微多样性与土壤有机碳矿化的关系

[目的]运用高级别分类学分辨率揭示玉米根际和非根际土壤中细菌群落微多样性,并探讨微多样性与土壤有机碳矿化的关系,从更精细的分类学分辨率水平上为玉米根际土壤中微生物驱动的碳循环提供理论依据。[方法]以西北农林科技大学曹新庄试验农场为依托,采取田间生长条件下玉米根际和非根际两种土壤类型。利用高通量测序技术,比较OTUs和ASVs两种分类学分辨率水平上玉米根际和非根际土壤中的细菌群落结构,揭示细菌群落的微多样性。同时通过培养试验检测根际和非根际土壤的有机碳矿化特性。[结果]通过比较OTUs和ASVs两种分类学分辨率水平上的细菌群落,OTUs和ASVs两种方式显示出相似的细菌群落结构。在玉米根际和非根际土壤类型中,ASVs在更高分类学分辨率水平上描绘细菌群落组成,同时揭示了普遍存在于OTUs内的不同菌株或生态型。此外,两种不同生长策略(r-策略和K-策略)细菌物种的相对丰度差异是导致根际和非根际土壤细菌群落结构不同的主要因素。培养试验表明,根际土壤有机碳矿化量显著高于非根际土壤。3 a的连续采样分析结果表明,根系是田间成熟玉米根际和非根际土壤理化性质差异的主要因素而受时间(2019—2021年...     

不同取样方式下土壤质地空间插值的精度分析

为研究土壤质地的合理取样方式,进而研究其空间变异情况,为田间施肥及灌溉提供依据,本试验利用地统计学方法和GIS技术,在重庆市彭水县重庆烟草试验站,利用289个表层土样,研究了16 m间距的栅格取样法(对照,253个土样,扣除36个验证样点)、34 m间距的栅格取样法(115个土样)和随机取样法(115个土样)3种取样方式下土壤质地的空间插值精度。3种土壤颗粒指标中粉粒占68.43%,砂粒含量最少,占12.68%,黏粒含量略高于砂粒。砂粒和黏粒具有中等强度的变异性,粉粒具弱变异性,且数据符合正态分布。地统计分析显示,在分析该区域土壤质地时,采用栅格取样方法应适当增大取样间距,而采用随机取样方法可适当缩小取样间距。交叉检验显示,土壤质地成分在3种取样方式下的插值精度均以对照最大,栅格取样次之,随机取样最小。综合考虑插值误差、样品采集和分析成本及时效性等因素,本研究建议在该区域进行土壤质地空间变异规律分析为生产服务时应采用随机取样。     

Volatile organic compounds in the roots and rhizosphere of Pinus spp.

Plant roots normally release a complex mixture of chemicals which have important effects in the rhizosphere. Among these different root-emitted compounds, volatile isoprenoids have received very little attention, yet they may play important and diverse roles in the rhizosphere, contributing to the regulation of microbial activity and nutrient availability. It is therefore important to estimate their abundance in the rhizosphere, but so far, there is no reliable sampling method that can be used to measure realistic rates of root emissions from plants growing in field conditions, or even in pots. Here, we measured root content of volatile isoprenoids (specifically monoterpenes) for Pinus pinea, and explored the feasibility of using a dynamic bag enclosure method to measure emissions from roots of intact pot-grown plants with different degrees of root cleaning. We also investigated a passive diffusion method for exploring monoterpenes in soil at incremental distances from mature Pinus sylvestris trees growing in field conditions. Total monoterpene content of P. pinea roots was 415±50 μg g⁻¹ fresh wt in an initial screening study, and between 688±103 and 1144±208 μg g⁻¹ dry wt in subsequent investigations. Emissions from shaken-clean roots of intact plants and roots of intact plants washed to remove remaining soil after shaken-clean experiments were 119±14 and 26±5 μg g⁻¹ dry wt h⁻¹, respectively. Emissions from intact roots in soil-balls were an order of magnitude lower than from shaken-clean roots, and probably reflected the amount of emitted compounds taken up by physical, chemical or biological processes in the soil matrix surrounding the roots. Although monoterpene content was not significantly different in droughted roots, emission rates from droughted roots were generally significantly lower than from well-watered roots. Finally, passive sampling of monoterpenes in the soil at different distances from mature P. sylvestris trees in field conditions showed significantly decreasing sampling rates with increasing distance from the trunk. We conclude that it is feasible to measure volatile isoprenoid emissions from roots but the method of root preparation affects magnitude of measured emissions and therefore must be decided according to the application. We also conclude that the rhizosphere of Pinus species is a strong and previously un-characterized source of volatile isoprenoid emissions and these are likely to impact significantly on rhizosphere function.     

Analysis of bacterial communities on alkaline phosphatase genes in soil supplied with organic matter

Abstract

We studied the effects of the application of organic matter (OM) and chemical fertilizer (CF) on soil alkaline phosphatase (ALP) activity and ALP-harboring bacterial communities in the rhizosphere and bulk soil in an experimental lettuce field in Hokkaido, Japan. The ALP activity was higher in soils with OM than in soils with CF, and activity was higher in the rhizosphere for OM than in the bulk soil. Biomass P and available P in the soil were positively related to the ALP activity of the soil. As a result, the P concentration of lettuce was higher in OM soil than in CF soil. We analyzed the ALP-harboring bacterial communities using polymerase chain reaction based denaturing gradient gel electrophoresis (DGGE) on the ALP genes. Numerous ALP genes were detected in the DGGE profile, regardless of sampling time, fertilizer treatment or sampled soil area, which indicated a large diversity in ALP-harboring bacteria in the soil. Several ALP gene fragments were closely related to the ALP genes of Mesorhizobium loti and Pseudomonas fluorescens. The community structures of the ALP-harboring bacteria were assessed using principal component analysis of the DGGE profiles. Fertilizer treatment and sampled soil area significantly affected the community structures of ALP-harboring bacteria. As the DGGE bands contributing to the principal component were different from sampling time, it is suggested that the major bacteria harboring the ALP gene shifted. Furthermore, there was, in part, a significant correlation between ALP activity and the community structure of the ALP-harboring bacteria. These results raise the possibility that different ALP-harboring bacteria release different amounts and/or activity of ALP, and that the structure of ALP-harboring bacterial communities may play a major role in determining overall soil ALP activity.     

Rhizosphere effects on Cu availability and fractionation in sewage sludge‐amended calcareous soils

Rhizosphere processes have a major impact on copper (Cu) availability and its fractions in soils. A greenhouse experiment with wheat was performed to investigate availability (using seven chemical procedures) and fractionation of Cu in the rhizosphere of ten agricultural soils (Typic Calcixerepts) amended with sewage sludge (1% w/w) using rhizoboxes. The results show that available Cu concentrations in rhizosphere soils were significantly (P < 1%) lower than in bulk soils. In comparison with the bulk soils, in the rhizosphere soils the concentration of Cu associated with organic matter and residual Cu increased by 24 and 4%, respectively, whereas exchangeable Cu, Cu associated with iron‐manganese oxides, and Cu associated with carbonate decreased by 20, 14, and 12%, respectively. Dissolved organic carbon (DOC) and Cu associated with iron‐manganese oxides and Cu associated with organic matter in the rhizosphere and bulk soils were significantly correlated (P < 5%). The results show that the differences between rhizosphere and bulk soils in chemical conditions such as DOC concentrations can change the proportion of soil Cu fractions and, therefore, Cu availability for wheat in calcareous soils amended with sewage sludge. The results show that the wheat root‐induced modifications of chemical and biological soil conditions do not only lead to Cu depletion in mobile soil Cu fractions, but also to modification in soil Cu fractions which are commonly considered as more stable.     

Collecting in situ precipitated iron oxides in their natural soil environment

Avoiding chemical and physical artifacts during sampling is crucial for realistic analyses of mineral and other colloids in soil. We developed a sampler, which allows for the in situ collection of Fe oxides that precipitate in their natural environment in a Bg horizon of a Calcaric Gleysol. Simultaneous measurements of redox‐sensitive parameters confirmed temporal changes from Fe‐reducing to Fe‐oxidizing conditions on site.     

不同样点数量对土壤有机质空间变异表达的影响

以南京市六合区为研究区,通过完全随机和限制最小采样间距抽样分别设置5个样点系列,基于每个样点系列100次重复抽样的变异结构推断及空间预测误差结果,探讨了不同样点数量对土壤有机质(SOM)空间变异表达的影响。结果表明,两种抽样方式降低样点数量后推断的SOM含量的块金效应(C0/C0+C)均随样点数量减少而降低且限制最小采样间距抽样推断的C0/C0+C要低于完全随机抽样方法,说明适当的减少样点数量以便降低与SOM变异尺度不匹配的样点对变异结构推断的影响有助于提高SOM空间变异结构表达的可靠性。普通Kriging预测的SOM误差对比则表明,尽管两种抽样方式下空间预测的均方根误差(RMSE)随样点数量变化而波动,但均低于全部样点的预测误差;通过限制最小采样间距减少样点至250个时,SOM空间预测的RMSE最低,较全部样点预测误差降低了6%,因此,为了实现样点密度与SOM变异尺度相匹配,合理设置土壤采样点的间距及样点数量较单纯的增加采样点数量更为重要。     

美国新墨西哥州卡皮林火山土壤性质的空间变异性

Non-agricultural lands are surveyed sparsely in general. Meanwhile, soils in these areas usually exhibit strong spatial variability which requires more samples for producing acceptable estimates. Capulin Volcano National Monument, as a typical sparsely-surveyed area, was chosen to assess spatial variability of a variety of soil properties, and furthermore, to investigate its implications for sampling design. One hundred and forty one composited soil samples were collected across the Monument and the surrounding areas. Soil properties including pH, organic matter content, extractable elements such as calcium (Ca), magnesium (Mg), potassium (K), sodium (Na), phosphorus (P), sulfur (S), zinc (Zn), and copper (Cu), as well as sand, silt, and clay percentages were analyzed for each sample. Semivariograms of all properties were constructed, standardized, and compared to estimate the spatial variability of the soil properties in the area. Based on the similarity among standardized semivariograms, we found that the semivariograms could be generalized for physical and chemical properties, respectively. The generalized semivariogram for physical properties had a much greater sill value (2.635) and effective range (7 500 m) than that for chemical properties. Optimal sampling density (OSD), which is derived from the generalized semivariogram and defines the relationship between sampling density and expected error percentage, was proposed to represent, interpret, and compare soil spatial variability and to provide guidance for sample scheme design. OSDs showed that chemical properties exhibit a stronger local spatial variability than soil texture parameters, implying more samples or analysis are required to achieve a similar level of precision.     

Equivalence or complementarity of soil‐solution extraction methods

Several methods are used for the extraction of soil solution. The objective of this study was to find out to what extent the different extraction methods yield complementary or equivalent information. Soil solutions were sampled once at 10 different forest sites in Germany, with 4 sampling points per site, using 5 different extraction methods. Concentrations of the major ions in the 1:2 extracts and the equilibrium soil‐pore solutions (obtained from percolation of field‐fresh soil cores) were generally lower than in desorption solutions, suction‐cup solutions, and saturation extracts. Surprisingly, the latter three methods generally yielded equivalent results. However, possible systematic differences between these methods could have been masked by the high small‐scale spatial variability within the sites.     

Determination of the extent of rhizosphere soil

Abstract

The extent of the rhizosphere was investigated by using root volume and root length in ten replications. The experiment was conducted using split cylindrical pots, 23 cm long and 7.5 cm in diameter. Sorghum (Sorghum bicolor) plants were grown in a calcareous soil of low phosphorus (P) status. Fertilized soil (750 g soil and 250 g sand) was placed in a closed‐bottom PVC tube. At harvest, plant roots were gently removed from the pots and the roots were shaken five times in order to reduce variation between samples. The soil that was easily shaken from the root surface was assumed to be non‐rhizosphere soil, and the soil adhering to the root segment after a gentle shake was considered to be rhizosphere soil. The rhizosphere thickness was found to have a range of 0.39 to 0.64 mm from the root surface (0.51 mm average thickness). Rhizosphere soil mass was also calculated and found to be on average 22% of the total soil mass.     

秸秆、猪粪混施对麦田根际土壤过氧化氢酶与蔗糖酶活性的影响

本研究于2012—2014年在成都平原稻麦轮作区开展田间试验,分析秸秆、猪粪施用对小麦各生育期内根际及非根际酶活性的动态变化影响,为种养废弃物的合理施用提供科学依据。试验共设置不施肥对照、纯化肥、秸秆全量还田+纯化肥、秸秆全量还田+低量猪粪替代化肥、秸秆全量还田+高量猪粪替代化肥等5个处理。结果表明,同一处理下的根际土壤过氧化氢酶和蔗糖酶活性均显著强于非根际土壤(P0.05);猪粪还田处理能提高土壤的过氧化氢酶活性,秸秆和猪粪还田处理能提高土壤蔗糖酶的活性;从小麦的整个生育期来看,其根际及非根际土壤过氧化氢酶活性均呈减弱趋势;而根际土壤蔗糖酶活性在小麦生育期内存在较大波动,非根际蔗糖酶活性呈"单峰"变化。     

Effects of Rhizosphere and Long-Term Fertilization Practices on the Activity and Community Structure of Denitrifiers Under Double-Cropping Rice Field

The soil physicochemical properties, soil denitrification rates (PDR), denitrifiers via nitrite reductases (nirK and nirS) and nitrous oxide reductase (nosZ), abundance and community composition of denitrifiers in both the rhizosphere and bulk soil from a long-term (32 year) fertilizer field experiment conducted during late rice season were investigated by using the MiSeq sequencing, quantitative PCR, terminal restriction fragment polymorphism (T-RFLP). The experiment including four treatments: without fertilizer input (CK), chemical fertilizer alone (MF), rice straw residue and chemical fertilizer (RF), and organic manure and chemical fertilizer (OM). The results showed that the application of rice straw residue and organic manure increased soil organic carbon (C), total nitrogen (N), and NH₄⁺-N contents. The nirK, nirS, and nosZ copy numbers with OM and RF treatments were significant higher than that of the MF and CK treatments in the rhizosphere and bulk soil (p < 0.05). The principal coordinate analysis (PCoA) analysis showed that the different parts of root zone are the most important factors for the variation of denitrifying bacteria community, and the different fertilization treatments is the second important factors for the variation of denitrifying bacteria community. The MiSeq sequencing result showed that nirK, nirS and nosZ-type denitrifiers communities within bulk soil had lower species diversity compared with rhizosphere soil, and were dominated by Rhizobiales, Rhodobacterales, Burkholderiales, and Pseudomonadales. As a result, the application of fertilization practices had significant effects on soil N and PDR levels, and affected the abundance and community composition of N-functional microbes.     

Silicon pools and fluxes in soils and landscapes—a review

Silicon (Si) is the second‐most abundant element in the earth's crust. In the pedosphere, however, huge spans of Si contents occur mainly caused by Si redistribution in soil profiles and landscapes. Here, we summarize the current knowledge on the different pools and fluxes of Si in soils and terrestrial biogeosystems. Weathering and subsequent release of soluble Si may lead to (1) secondarily bound Si in newly formed Al silicates, (2) amorphous silica precipitation on surfaces of other minerals, (3) plant uptake, formation of phytogenic Si, and subsequent retranslocation to soils, (4) translocation within soil profiles and formation of new horizons, or (5) translocation out of soils (desilication). The research carried out hitherto focused on the participation of Si in weathering processes, especially in clay neoformation, buffering mechanisms for acids in soils or chemical denudation of landscapes. There are, however, only few investigations on the characteristics and controls of the low‐crystalline, almost pure silica compounds formed during pedogenesis. Further, there is strong demand to improve the knowledge of (micro)biological and rhizosphere processes contributing to Si mobilization, plant uptake, and formation of phytogenic Si in plants, and release due to microbial decomposition. The contribution of the biogenic Si sources to Si redistribution within soil profiles and desilication remains unknown concerning the pools, rates, processes, and driving forces. Comprehensive studies considering soil hydrological, chemical, and biological processes as well as their interactions at the scale of pedons and landscapes are necessary to make up and model the Si balance and to couple terrestrial processes with Si cycle of limnic, fluvial, or marine biogeosystems.     

Silicon pools and fluxes in soils and landscapes—a review

Silicon (Si) is the second‐most abundant element in the earth's crust. In the pedosphere, however, huge spans of Si contents occur mainly caused by Si redistribution in soil profiles and landscapes. Here, we summarize the current knowledge on the different pools and fluxes of Si in soils and terrestrial biogeosystems. Weathering and subsequent release of soluble Si may lead to (1) secondarily bound Si in newly formed Al silicates, (2) amorphous silica precipitation on surfaces of other minerals, (3) plant uptake, formation of phytogenic Si, and subsequent retranslocation to soils, (4) translocation within soil profiles and formation of new horizons, or (5) translocation out of soils (desilication). The research carried out hitherto focused on the participation of Si in weathering processes, especially in clay neoformation, buffering mechanisms for acids in soils or chemical denudation of landscapes. There are, however, only few investigations on the characteristics and controls of the low‐crystalline, almost pure silica compounds formed during pedogenesis. Further, there is strong demand to improve the knowledge of (micro)biological and rhizosphere processes contributing to Si mobilization, plant uptake, and formation of phytogenic Si in plants, and release due to microbial decomposition. The contribution of the biogenic Si sources to Si redistribution within soil profiles and desilication remains unknown concerning the pools, rates, processes, and driving forces. Comprehensive studies considering soil hydrological, chemical, and biological processes as well as their interactions at the scale of pedons and landscapes are necessary to make up and model the Si balance and to couple terrestrial processes with Si cycle of limnic, fluvial, or marine biogeosystems.