Disentangling the effects of OM quality and soil texture on microbially mediated structure formation in artificial model soils

Geoderma ◽  
2021 ◽  
Vol 403 ◽  
pp. 115213
Author(s):  
Franziska B. Bucka ◽  
Vincent J.M.N.L. Felde ◽  
Stephan Peth ◽  
Ingrid Kögel-Knabner
2020 ◽  
Author(s):  
Kristina Witzgall ◽  
Alix Vidal ◽  
David Schubert ◽  
Carmen Höschen ◽  
Steffen Schweizer ◽  
...  

<p>Soil texture and microorganisms are key drivers controlling the fate of organic matter (OM) originating from decaying plant litter, and thus the stabilization of soil organic matter (SOM). However, the understanding of the mutual interactions between microbial litter decay and soil structure formation controlled by different soil textures remains incomplete. We monitored the fate of litter-derived OM (using <sup>13</sup>C isotopic enrichment) from decaying litter (shredded maize leaves) to microorganisms and SOM in two differently textured soils (sand and loam). The two soils were incubated with litter mixed in the top layer in microcosms for 95 days during which regular CO<sub>2</sub> and <sup>13</sup>CO<sub>2</sub> measurements were conducted. After the incubation, each microcosm was divided in three to separate a top, center and bottom layer. Using a physical soil fractionation scheme, we assessed the fate of litter-derived OM to free and occluded particulate OM (POM), as well as mineral associated OM (MAOM). All SOM fractions were analysed with respect to their mass distribution, C, N, and <sup>13</sup>C contents, and for their chemical composition using compound-specific <sup>13</sup>C-CPMAS NMR spectroscopy. The effects of contrasting textures on the total microbial community structure were studied using phospholipid fatty acids (PLFA) and the incorporation of litter-derived C into individual PLFAs was assessed via <sup>13</sup>C-PLFA. Lastly, scanning electron microscopy and nano scale secondary ion mass spectroscopy (NanoSIMS) analysis of free POM of both textures enabled qualitative insights directly at the biogeochemical interface of the microbial hot spot of decaying plant litter.</p><p>We were able to clearly demonstrate higher contents of litter-derived OM still residing as free POM in the loamy textured soil after the 95 day-incubation, while higher contents were found in occluded and MAOM in the sandy textured soil. This indicated that the overall litter decomposition was refrained in the finer-textured soil, whereas microbial alteration and allocation of litter-derived compounds was promoted in the coarser textured soil. This was further corroborated by higher respiration and higher amounts of respired litter-derived CO<sub>2</sub>-C in the sandy soil. The PLFA analysis showed a coherent pattern between the textures, with similar community structures in all treatments and significant increases in microbial abundance in the top layers induced by litter addition. This increase was found most pronounced in fungal biomarkers, which was in line with the <sup>13</sup>C-PLFA measurements revealing over 90% of fungal biomarkers to be of litter-origin (compared to 30-40% in the other microbial groups). The labelled PLFA profiles also confirmed the importance of fungi as a vector for litter-derived OM into deeper layers of the soil columns, with significantly higher litter-derived fungal markers also in center and bottom layers. The NanoSIMS measurements verified the high <sup>13</sup>C enrichment in fungal hyphae and further revealed clay minerals embedded in enriched microbial-derived extracellular polymeric substances and intertwined with hyphae directly on top of the POM. Based on this comprehensive data, we highlight that regardless of the texture, plant litter in association with microbial-derived products represent a hot spot for soil structure formation by harbouring a core for aggregation and MAOM formation.</p>


2018 ◽  
pp. 76-89
Author(s):  
E. M. Avraamova ◽  
V. N. Titov

The analysis of present-time directions in the study of social development has allowed to identify the resource approach as the most productive one which enables to assess social dynamics through the range of resource characteristics of different population groups and abilities of the relevant groups to apply development resources in the current economic and institutional conditions. Basing on the sociological survey conducted by ISAP RANEPA, the quantitative estimation of material and social recourses of the population has been made; integral values of the resource potential have been calculated as well. The issues of social structure formation are analyzed through the aspect of resource availability; the barriers of Russian middle-class enlargement are defined.


2015 ◽  
Vol 2 (2) ◽  
pp. 148-158
Author(s):  
Surianto

Spodosol soil of Typic Placorthod sub-group of East Barito District is one of the problem soils with the presence of hardpan layer, low fertility, low water holding capacity, acid reaction and it is not suitable for oil palm cultivation without any properly specific management of land preparation and implemented best agronomic practices. A study was carried out to evaluate the soil characteristic of a big hole (A profile) and no big hole (B profile) system and comparative oil palm productivity among two planting systems. This study was conducted in Spodosol soil at oil palm plantation (coordinate X = 0281843 and Y = 9764116), East Barito District, Central Kalimantan Province on February 2014, by surveying of placic and ortstein depth and observing soil texture and chemical properties of 2 (two) oil palm's soil profiles that have been planted in five years. Big hole system of commercial oil palm field planting on the Spodosol soil area was designed for the specific purpose of minimizing the potential of a negative effect of shallow effective planting depth for oil palms growing due to the hardpan layer (placic and ortstein) presence as deep as 0.25 - 0.50 m. The big hole system is a planting hole type which was vertical-sided with 2.00 m x 1.50 m on top and bottom side and 3.00 m depth meanwhile the 2:1 drain was vertical-sided also with 1.50 m depth and 300 m length. Oil palm production was recorded from the year 2012 up to 2014. Results indicated that the fractions both big hole profile (A profile) and no big hole profile (B profile) were dominated by sands ranged from 60% to 92% and the highest sands content of non-big hole soil profile were found in A and E horizons (92%). Better distribution of sand and clay fractions content in between layers of big hole soil profiles of A profile sample is more uniform compared to the B profile sample. The mechanical holing and material mixing of soil materials of A soil profile among the upper and lower horizons i.e. A, E, B and C horizons before planting that resulted a better distribution of both soil texture (sands and clay) and chemical properties such as acidity value (pH), C-organic, N, C/N ratio, CEC, P-available and Exchangeable Bases. Investigation showed that exchangeable cations (Ca, Mg, K), were very low in soil layers (A profile) and horizons (B profile) investigated. The low exchangeable cations due to highly leached of bases to the lower layers and horizons. Besides, the palm which was planted on the big hole system showed good adaptation and response positively by growing well of tertiary and quaternary roots that the roots were penetrable into deeper rooting zone as much as >1.00 m depth. The roots can grow well and penetrate much deeper in A profile compared to the undisturbed hardpan layer (B profile). The FFB (fresh fruit bunches) production of the non-big hole block was higher than the big hole block for the first three years of production. This might be due to the high variation of monthly rainfall in-between years of observation from 2009 to 2014. Therefore, the hardness of placic and ortstein as unpenetrable agents by roots and water to prevent water loss and retain the water in the rhizosphere especially in the drier weather. In the high rainfall condition, the 2:1 drain to prevent water saturation in the oil palm rhizosphere by moving some water into the drain. Meanwhile, the disturbed soil horizon (big hole area) was drier than un disturbance immediately due to water removal to deeper layers. We concluded that both big hole and 2:1 drain are a suitable technology for Spodosol soil land especially in preparing palms planting to minimize the negative effect of the hardpan layer for oil palm growth.


The authors' methodic for assessing the role of chemical and physic-chemical factors during the structure formation of gypsum stone is presented in the article. The methodic is also makes it possible to reveal the synergistic effect and to determine the ranges of variation of controls factors that ensure maximum values of such effect. The effect of a micro-sized modifier based on zinc hydro-silicates on the structure formation of building gypsum is analyzed and corresponding dependencies are found. It is shown that effects of influence of modifier on the properties of gypsum compositions are determined by chemical properties of modifier. Among the mentioned properties are sorption characteristics (which depend on the amount of silicic acid and its state) and physicochemical properties - the ability to act as a substrate during crystal formation. The proposed method can also be extended to other binding substances and materials. This article contributes to the understanding of the processes that occur during the structure formation of composites, which will make it possible to control the structure formation in the future, obtaining materials with a given set of properties.


The article presents the study of processes of structure formation of cement stone and products of hardening of organic-mineral compositions with fibrous filler (shavings) by the electronic scanning microscopy method. It is established that the additive-free cement stone at the age of 28 days has a dense and homogeneous structure, consists of calcium hydro-silicates, Portlandite and calcite - newgrowths characteristic for cement systems. Cellulose fibers, which make up the bulk of the substance of shavings, are sufficiently active, which determines the high adhesion of the hydration products of the cement binder to their surface. It is shown that the introduction of shavings into the organo-mineral composition leads to inhibition of cement hydration processes. Organo-mineral compositions with different shavings content (two compositions) were analyzed. The first composition is characterized by a fairly dense structure, the cement stone consists of globular nanoscale nuclei of hydrosilicates, Portlandite and calcite. The second composition has a loose porous structure, cement stone consists of non-hydrated cement grains, newgrowths are represented by calcite and vaterite. The structure of the contact zone "osprey fiber-cement stone" in the organo-mineral composition of the first composition indicates a good adhesion of the filler surface with the phases of hydrated cement. The use of shavings as a fibrous filler (the first composition) increases the tensile and bending strength, as well as the wear resistance of organo-mineral compositions. The data obtained by scanning electron microscopy are confirmed by the results of studying the processes of structure formation of cement stone by quantitative x-ray phase analysis.


2013 ◽  
Vol 0 (1) ◽  
pp. 122
Author(s):  
K. Toshtay ◽  
Kuanyshbek Mussabekov ◽  
S. Kumargaliyeva ◽  
С. Turganbay ◽  
Inal Bakhytkyzy

2005 ◽  
Vol 17 (4) ◽  
pp. 343-371 ◽  
Author(s):  
S. Konovalova ◽  
I. S. Akhatov

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