Penetration of pea radicles into saturated soil cores related to organic matter amendments

Soil Research ◽  
1981 ◽  
Vol 19 (3) ◽  
pp. 343
Author(s):  
P Willoughby ◽  
ST Willatt
Keyword(s):  
Organic Matter ◽  
Saturated Soil ◽  
Root Penetration ◽  
Soil Cores ◽  
Soil Matrix ◽  
Microbial Decomposition ◽  
Pea Seedlings ◽  
Decomposition Of Organic Matter ◽  
Different Depths ◽  
Incubation Temperatures

The radicles of pea seedlings penetrated to different depths in saturated cores prepared from Goulburn Valley orchard soil according to the amount and type of organic matter added to the soil. Additions of ground straw and glucose restricted the penetration of the roots when grown for 4 days at constant temperature. Longer incubation times and higher incubation temperatures imposed on the cores before growing the seedlings further restricted the roots in the presence of added peat, straw or glucose. The restrictions to root penetration can be attributed to poor oxygen supply into the saturated soil matrix and to phytotoxins produced by the microbial decomposition of organic matter contained in the soil cores. The results suggest that structural units in an irrigated soil should not be larger than about 6 mm in diameter if roots are to fully exploit the soil volume.

scholarly journals Microbial Decomposition of Organic Matter Derived from Phytoplankton Cellular Components in Seawater

2004 ◽  
Vol 19 (2) ◽  
pp. 128-136 ◽  
Author(s):  
Yuka Ohnishi ◽  
Minoru Fujii ◽  
Shinichiro Murashige ◽  
Atsushi Yuzawa ◽  
Hitoshi Miyasaka ◽  
...  
Keyword(s):  
Organic Matter ◽  
Microbial Decomposition ◽  
Decomposition Of Organic Matter ◽  
Cellular Components

scholarly journals Root exudate input stimulates peatland recalcitrant DOC decomposition by r-strategic taxa of Gammaproteobacteria and Bacteroidetes

2020 ◽  
Author(s):  
Jiří Mastný ◽  
Jiří Bárta ◽  
Eva Kaštovská ◽  
Tomáš Picek
Keyword(s):  
Organic Matter ◽  
Community Composition ◽  
Plant Community ◽  
Root Exudates ◽  
Early Stage ◽  
Gene Copy Number ◽  
Gene Copy ◽  
Plant Community Composition ◽  
Microbial Decomposition ◽  
Decomposition Of Organic Matter

Abstract Background In peatlands, decomposition of organic matter is limited by harsh environmental conditions and low decomposability of the plant material. Increased microbial decomposition of organic matter in peatland ecosystems may become an important phenomenon in the near future after the expected shift in plant community composition from Sphagnum to vascular plants due to climate change. Such a change in plant community composition will lead to increased root exudates flux to the soil and stimulation of microbial growth and activity. The aim of our study was to evaluate the effect of root exudates on the decomposition of recalcitrant dissolved organic carbon (DOC) and identify the microorganisms responsible for this process. Results Decomposition of recalcitrant DOC was stimulated by a high levels of 13 C labelled root exudates addition whereas it was suppressed by a low levels of root exudates addition. Recalcitrant DOC decomposition was positively related to the exudate C/N ratio as a result of enhanced “microbial nutrient mining” due to a deepening of microbial nutrient limitation. The early stage of incubation immediately following the exudate addition was characterized by the preferential use of the added compounds at the expense of recalcitrant DOC. At the same time, r-strategic bacteria (identification based on average 16SrRNA gene copy number) belonging to mainly to Gammaproteobacteria and Bacteriodete s phyla relatively increased within the microbial community. At the later stage, this more abundant bacterial community was replaced by a less abundant community composed of bacteria mostly belonging to Alphaproteobacteria and Acidobacteria . The most important taxa with the potential to decompose complex compounds were indentified: Mucilaginibacter ( Bacteriodete s), Burkholderia and Pseudomonas ( Gammaproteobacteria ) among r-strategists and Bryocella and Candidatus Solibacter ( Acidobacteria ) among K-strategists. Conclusions Increased inputs of root exudates, with a higher C/N ratio, may stimulate decomposition of peatland recalcitrant DOC. In this, bacteria were found to be more important than fungi. Our experiment indicates that r-strategic bacteria as well as K-strategists can be important in stimulated decomposing of recalcitrant peatland DOC.

Carbon mineralisation and pore size classes in undisturbed soil cores

Soil Research ◽  
2013 ◽  
Vol 51 (1) ◽  
pp. 14 ◽  
Author(s):  
Liesbeth Bouckaert ◽  
Steven Sleutel ◽  
Denis Van Loo ◽  
Loes Brabant ◽  
Veerle Cnudde ◽  
...  
Keyword(s):  
Organic Matter ◽  
Pore Network ◽  
Order Kinetic ◽  
Soil Cores ◽  
Undisturbed Soil ◽  
Soil Matrix ◽  
X Ray ◽  
C Mineralisation ◽  
The Impact ◽  
Undisturbed Soil Cores

Soil pore network effects on organic matter turnover have, until now, been studied indirectly because of lack of data on the 3D structure of the pore network. Application of X-ray computed tomography (X-ray CT) to quantify the distribution of pore neck size and related pore sizes from undisturbed soil cores, with simultaneous assessment of carbon (C) mineralisation, could establish a relationship between soil organic matter (SOM) decomposition and soil pore volumes. Eighteen miniature soil cores (diameter 1.2 cm, height 1.2 cm) covering a range of bulk densities were incubated at 20°C for 35 days. Respiration was modelled with a parallel first- and zero-order kinetic model. The cores were scanned at 9.44 µm resolution using an X-ray CT scanner developed in-house. Correlation analysis between the slow pool C mineralisation rate, ks, and pore volume per pore neck class yielded significant (P < 0.05) positive correlations: r = 0.572, 0.598, and 0.516 for the 150–250, 250–350, and >350 µm pore neck classes, respectively. Because larger pores are most probably mainly air-filled, a positive relation with ks was ascribed to enhanced aeration of smaller pores surrounding large pores. The weak and insignificant relationship between the smallest pore neck class (<9.44 µm) and ks could be explained by obstructed microbial activity and mobility or diffusion of exo-enzymes and hydrolysis products as a result of limited oxygen availability. This study supports the hypothesis that the impact of soil structure on microbial processes occurs primarily via its determination of soil water distribution, which is possibly the main driver for the location of C mineralisation in the soil matrix.

scholarly journals Nitrate addition stimulates microbial decomposition of organic matter in salt marsh sediments

2019 ◽  
Vol 25 (10) ◽  
pp. 3224-3241 ◽  
Author(s):  
Ashley N. Bulseco ◽  
Anne E. Giblin ◽  
Jane Tucker ◽  
Anna E. Murphy ◽  
Jonathan Sanderman ◽  
...  
Keyword(s):  
Organic Matter ◽  
Salt Marsh ◽  
Microbial Decomposition ◽  
Nitrate Addition ◽  
Decomposition Of Organic Matter ◽  
Marsh Sediments ◽  
Salt Marsh Sediments

Controlling Erosion

1999 ◽  
Author(s):  
Robert F. Keefer
Keyword(s):  
Organic Matter ◽  
Organic Material ◽  
Soil Structure ◽  
Soil Microorganisms ◽  
Soil Aggregation ◽  
Water Infiltration ◽  
Root Penetration ◽  
Animal Remains ◽  
Decomposition Of Organic Matter ◽  
Structure Improvement

Erosion can be controlled by four main means, that is, improving soil structure, covering soil with plants, covering soil with mulch, and using special structures. Soil structure is related to the soil tilth, or physical condition of a soil, with respect to ease of tillage or workability as shown by the fitness of a soil as a seedbed and the ease of root penetration. Other terms relating to soil structure improvement are soil aggregation and the formation of aggregates. Aggregates form when a cementing substance is present in a soil. The most important cementing substances in soil are soil polysaccharides and soil polyuronides produced as by-products from microorganisms during decomposition of organic matter. Other less important cementing substances in soil include clays, Ca, and Fe. Formation of aggregates results in improved water infiltration with reduction in erosion. Decomposition of organic matter in soils can be shown as an equation: . . . Plant and animal remains + O2 + soil microorganisms → CO2 + H2O + elements + humus + synthates + energy . . . The decomposition process has the following features: . . . 1. Oxygen is required; thus soil aeration is important. Anytime a soil is stirred or mixed by cultivation, spading, plowing, some organic matter decomposition occurs. 2. Readily available decomposable organic material is required for the microbes to work on. Green organic material, such as grass clippings, is an excellent substrate. 3. Many different types of soil microorganisms are involved in this process. Decomposition is more rapid in soils at pH 7 (neutral). 4. A product of organic decomposition is humus. Humus has many desirable features that improve a soil for plant growth. 5. Plant or animal remains are not effective in soil aggregation until they begin to decompose. 6. The more rapid the decomposition, the greater effect of soil aggregation. . . . Microbial synthates consist of polymers called “polysaccharides” and “polyuronides.” A polymer is a long-chain compound made up of single monomer units hooked together acting as a unit. The term “poly” means “many” and “saccharide” means “sugar.”

Contrast-enhanced repacked soil cores as a proxy for soil organic matter spatial arrangement

Soil Research ◽  
2019 ◽  
Vol 57 (6) ◽  
pp. 535
Author(s):  
Ilaria Piccoli ◽  
Nicola Dal Ferro ◽  
Patrice J. Delmas ◽  
Andrea Squartini ◽  
Francesco Morari
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Contrast Agents ◽  
Mineral Soil ◽  
Morphological Characteristics ◽  
Linear Attenuation Coefficient ◽  
Morphological Operations ◽  
Soil Cores ◽  
Soil Matrix ◽  
X Ray

Soil organic matter (SOM) plays a key role in soil structure formation, although the bidirectional relationship between SOM and the soil pore network is complex and needs further investigation. Despite great advances provided by X-ray computed microtomography (µCT), it has only been used in a few studies to investigate the organic matter 3D-arrangement within the soil matrix. Results are based on the X-ray linear attenuation coefficient (α), and mixtures of organic and mineral soil fractions could imply overlapping of information that makes any segmentation procedure difficult. The aim of this study was to visualise, segment, and quantify the particulate organic matter fraction (POM) within the soil matrix through X-ray µCT in combination with contrast agents (phosphomolybdic acid and silver nitrate). Two series of repacked soil cores, ‘dry’ and ‘wet’, were scanned through X-ray µCT at a 7-µm resolution. Different segmentation approaches were tested to separate POM from other soil phases: manual, global, and local thresholding methods. Reported algorithms were also compared with a supervised grey value-based (GV) approach followed by morphological operations. Results showed contrast agents increased α of POM, simplifying its identification and the following segmentation on dry cores. The POM was discriminated from the mineral fraction and its content correctly estimated. This was particularly accurate when applying manual thresholding or GV approach with respect to indicator kriging, suggesting that operator-based ability to set threshold level is still the best solution for accurate POM segmentation. Beyond single-phase accounting, different thresholding algorithms and morphological operations also affected POM morphological characteristics. In particular, the simpler was an object shape, the easier was its segmentation. Improvements are thus required to increase the efficiency of automated thresholding algorithms. Moreover, wet cores were exposed to washing-out phenomena that compromised any digital image processing and further POM quantification, implying that more effort should be made to find other suitable staining agents.

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