Table of Contents

Soils, Volume 1, Issue 1 (December 2017)

  • Issues are regarded as officially published after their release is announced to the table of contents alert mailing list.
  • You may sign up for e-mail alerts to receive table of contents of newly released issues.
  • PDF is the official format for papers published in both, html and pdf forms. To view the papers in pdf format, click on the "PDF Full-text" link, and use the free Adobe Readerexternal link to open them.
View options order results:
result details:
Displaying articles 1-5
Export citation of selected articles as:

Research

Open AccessArticle Relevance of Reactive Fe:S Ratios for Sulfur Impacts on Arsenic Uptake by Rice
Soils 2017, 1(1), 1; doi:10.3390/soils1010001
Received: 12 June 2017 / Revised: 12 July 2017 / Accepted: 28 July 2017 / Published: 9 August 2017
PDF Full-text (2091 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Human arsenic exposure from rice consumption is a global concern. Due to the vast areas of naturally contaminated soils in rice-producing regions, the only possibility for reducing hazardous exposure is to prevent As uptake and translocation to rice grain. Sulfur inhibits As mobility
[...] Read more.
Human arsenic exposure from rice consumption is a global concern. Due to the vast areas of naturally contaminated soils in rice-producing regions, the only possibility for reducing hazardous exposure is to prevent As uptake and translocation to rice grain. Sulfur inhibits As mobility both in soil and plant, indicating that soil S content may be a primary factor controlling As uptake; indeed, gypsum (CaSO4·H2O) has been proposed as a potential amendment. Here, we investigated S controls on rice As uptake within two naturally contaminated soils (15.4 and 11.0 mg As per kg soil, respectively) from Cambodia, by adding gypsum at two levels (20 and 60 mg per kg soil). We found that although gypsum initially decreased As release to soil solution, the concentrations then increased compared to the control treatment. Further, As concentrations in rice biomass were generally insignificantly affected by the gypsum treatments and trended in opposite directions between the two soils. Single and multivariate statistical tests indicated that Fe exerted stronger control on As uptake in rice than S and that the initial ratio of reactive Fe to sulfate-S had an overriding impact on As uptake in rice. However, in the soil with higher inherent sulfate content (91 mg SO42−-S per kg soil) the additional S provided by gypsum appeared to increase the ability of the rice plant to prevent As translocation to grain. We conclude that S may contribute to regulating grain As concentrations, but that the effect is highly dependent on S:Fe(As) ratios. Thus, at modest amendment rates, gypsum has limited potential for minimizing As concentration in rice when applied to naturally contaminated soil, particularly if the reactive Fe(III) content is high. Full article
(This article belongs to the Special Issue Rhizosphere Processes)
Figures

Figure 1

Open AccessArticle Legacy of Rice Roots as Encoded in Distinctive Microsites of Oxides, Silicates, and Organic Matter
Soils 2017, 1(1), 2; doi:10.3390/soils1010002
Received: 1 June 2017 / Revised: 2 August 2017 / Accepted: 3 August 2017 / Published: 9 August 2017
PDF Full-text (4536 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Rice (Oryza sativa) is usually grown under flooded conditions, leading to anoxic periods in the soil. Rice plants transport oxygen via aerenchyma from the atmosphere to the roots. Driven by O2 release into the rhizosphere, radial gradients of ferric Fe
[...] Read more.
Rice (Oryza sativa) is usually grown under flooded conditions, leading to anoxic periods in the soil. Rice plants transport oxygen via aerenchyma from the atmosphere to the roots. Driven by O2 release into the rhizosphere, radial gradients of ferric Fe and co-precipitated organic substances are formed. Our study aimed at elucidating the composition and spatial extension of those gradients. Air-dried soil aggregates from a paddy field were embedded in epoxy resin, cut, and polished to produce cross sections. Reflected-light microscopy was used to identify root channels. With nano-scale secondary ion mass spectrometry (NanoSIMS), we investigated transects from root channels into the soil matrix and detected 12C, 16O, 12C14N, 28Si, 27Al16O, and 56Fe16O to distinguish between embedding resin, organic matter, oxides, and silicates. Image analyses reveal high occurrences of 56Fe16O within and in close proximity of oxide-encrusted root cells, followed by a thin layer with high occurrences of 27Al16O and 12C14N. In two of the three transects, 28Si only occurs at distances larger than approximately 10 µm from the root surface. Thus, we can distinguish distinct zones: the inner zone is composed of oxide encrusted root cells and their fragments. A thin intermediate zone may occur around some roots and comprises (hydr)oxides and organic matter. This can be distinguished from a silicate-dominated outer zone, which reflects the transition from the rhizosphere to the bulk soil. Full article
(This article belongs to the Special Issue Rhizosphere Processes)
Figures

Open AccessArticle Evidence for the Root-Uptake of Arsenite at Lateral Root Junctions and Root Apices in Rice (Oryza sativa L.)
Soils 2017, 1(1), 3; doi:10.3390/soils1010003
Received: 12 July 2017 / Revised: 8 August 2017 / Accepted: 11 August 2017 / Published: 14 August 2017
PDF Full-text (2898 KB) | HTML Full-text | XML Full-text
Abstract
The uptake of arsenite (As(III)i) at the Casparian band via Lsi1 and Lsi2 Si transporters is responsible for ~75% of shoot As(III)i uptake in rice and, therefore, ~25% of shoot As(III)i is taken up by other transport pathways. We
[...] Read more.
The uptake of arsenite (As(III)i) at the Casparian band via Lsi1 and Lsi2 Si transporters is responsible for ~75% of shoot As(III)i uptake in rice and, therefore, ~25% of shoot As(III)i is taken up by other transport pathways. We hypothesized that areas devoid of Casparian bands—lateral root junctions and root apices—can transport As(III)i into roots. We analyzed the elemental distribution and As concentration, speciation, and localization in rice roots from soil-grown and solution-grown plants. With solution-grown plants dosed with As(III)i, we sectioned roots as a function of distance from the root apex and analyzed the cross-sections using confocal microscopy coupled to synchrotron X-ray fluorescence imaging and spectroscopy. We observed elevated As(III)i associated with lateral root junctions and root apices in rice. As(III)i entered the stele at lateral root junctions and radially permeated the root interior in cross-sections 130–140 µm from the root apex that are devoid of Casparian bands. Our findings suggest that lateral root junctions and rice root apices are hot-spots for As(III)i transport into rice roots, but the contribution to shoot As requires further research. Full article
(This article belongs to the Special Issue Rhizosphere Processes)
Figures

Figure 1

Open AccessArticle Molecular and Microscopic Insights into the Formation of Soil Organic Matter in a Red Pine Rhizosphere
Soils 2017, 1(1), 4; doi:10.3390/soils1010004
Received: 15 June 2017 / Revised: 23 August 2017 / Accepted: 24 August 2017 / Published: 26 August 2017
Cited by 1 | PDF Full-text (5369 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Microbially-derived carbon inputs to soils play an important role in forming soil organic matter (SOM), but detailed knowledge of basic mechanisms of carbon (C) cycling, such as stabilization of organic C compounds originating from rhizodeposition, is scarce. This study aimed to investigate the
[...] Read more.
Microbially-derived carbon inputs to soils play an important role in forming soil organic matter (SOM), but detailed knowledge of basic mechanisms of carbon (C) cycling, such as stabilization of organic C compounds originating from rhizodeposition, is scarce. This study aimed to investigate the stability of rhizosphere-produced carbon components in a model laboratory mesocosm of Pinus resinosa grown in a designed mineral soil mix with limited nutrients. We utilized a suite of advanced imaging and molecular techniques to obtain a molecular-level identification of newly-formed SOM compounds, and considered implications regarding their degree of long-term persistence. The microbes in this controlled, nutrient-limited system, without pre-existing organic matter, produced extracellular polymeric substances that formed associations with nutrient-bearing minerals and contributed to the microbial mineral weathering process. Electron microscopy revealed unique ultrastructural residual signatures of biogenic C compounds, and the increased presence of an amorphous organic phase associated with the mineral phase was evidenced by X-ray diffraction. These findings provide insight into the formation of SOM products in ecosystems, and show that the plant- and microbially-derived material associated with mineral matrices may be important components in current soil carbon models. Full article
(This article belongs to the Special Issue Rhizosphere Processes)
Figures

Figure 1

Open AccessArticle Ectomycorrhizal Fungi and Mineral Interactions in the Rhizosphere of Scots and Red Pine Seedlings
Soils 2017, 1(1), 5; doi:10.3390/soils1010005
Received: 7 June 2017 / Revised: 8 September 2017 / Accepted: 15 September 2017 / Published: 19 September 2017
PDF Full-text (3343 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Ectomycorrhizal fungi and associated bacteria play a key role in plant-driven mineral weathering and uptake of mineral-derived nutrients in the rhizosphere. The goal of this study was to investigate the physical and chemical characteristics of bacteria-fungi-mineral interactions in biofilms of Scots and red
[...] Read more.
Ectomycorrhizal fungi and associated bacteria play a key role in plant-driven mineral weathering and uptake of mineral-derived nutrients in the rhizosphere. The goal of this study was to investigate the physical and chemical characteristics of bacteria-fungi-mineral interactions in biofilms of Scots and red pine rhizospheres. In three experiments, seedlings were grown in columns containing silica sand amended with biotite and calcium-feldspar, and inoculated with pure cultures of ectomycorrhizal fungi or a soil slurry. Uninoculated seedlings and unplanted abiotic columns served as controls. After nine months, the columns were destructively sampled and the minerals were analyzed using scanning electron and atomic force microscopy. Element release rates were determined from cation concentrations of input and output waters, soil exchange sites, and plant biomass, then normalized to geometric surface area of minerals in each column. The results revealed that various ectomycorrhizal fungal species stimulate silicate dissolution, and biofilm formation occurred at low levels, but direct surface attachment and etching by fungal hyphae was a minor contributor to the overall cation release from the minerals in comparison to other environmental conditions such as water applications (rain events), which varied among the experiments. This research highlights the importance of experimental design details for future exploration of these relationships. Full article
(This article belongs to the Special Issue Rhizosphere Processes)
Figures

Figure 1

Back to Top