Soil organic carbon and labile and recalcitrant carbon fractions attributed by contrasting tillage and cropping systems in old and recent alluvial soils of subtropical eastern India

Conservation agriculture-based sustainable intensification (CASI) technologies comprising zero-tillage with crop residue retention (>30%) on the soil surface, diversified cropping systems, and balanced nutrient management are recognized as operative and efficacious strategies to ensure food security in the parts of South Asia. The present investigation was a component of CASI technologies undertaken in the farmers’ field of Malda (old alluvial Inceptisol) Coochbehar (recent alluvial Entisol) district, West Bengal (subtropical eastern India). This study was conducted to evaluate the short-term impact of contrasting tillage (zero and conventional) and cropping systems (rice–wheat and rice–maize) on total organic carbon (TOC) and its fractions, viz., labile pool-1 (LP1), labile pool-2 (LP2) and recalcitrant carbon (RC) fractions after 4-year trial of conservation agriculture (CA) in the old and recent alluvial soils. Soil samples were collected from three depths (0–5, 5–10, and 10–20 cm), and thus, our study was focused on two factors, viz., cropping system and tillage. Results pointed that TOC along with LP1, LP2, and RC fractions under rice–maize (RM) cropping system were significantly (p<0.05) greater (15–35%) over rice–wheat (RW) system as a result of higher residue biomass addition. Zero-tillage (ZT) improved the C fractions by 10–20% over conventional tillage (CT) in all aspects. TOC and its fractions were observed to be greater under the ZT system in the topmost soil depths (0–5 and 5–10 cm), but the same system failed to improve these at 10–20 cm. Interestingly, the CT increased all the fractions at 10–20 cm depth due to the incorporation of crop residues. The concentration of TOC along with its fractions decreased with increasing soil depth was evident. Comparatively, all the C fractions, including TOC were maximum in soils from Malda sites as compared to Coochbehar sites because of a higher amount of residue biomass application, higher clay content, and greater background content of C in these soils. All the studied C fractions showed a significant correlation (r = >0.635; p<0.01) with TOC among all the soil depths in both the districts but the relationship with soil texture showed some interesting results. TOC fractions were significantly correlated (p<0.01) with clay particles indicating that its higher stabilization with clay in old alluvial Inceptisol (Malda); while in recent alluvial Entisol (Coochbehar), sand particle showed its strong relation with TOC fractions. Higher stratification ratio (SR) in the ZT system suggested that the concentration of TOC and its fractions are confined to the upper soil layers whereas in the case of CT, by and large, the distribution of these was comparatively high in subsequent soil depths due to residue incorporation effect. The concentration of C fractions in soils followed the order: TOC > RC > LP2 > LP1. The present investigation concluded that ZT under the RM system increases the turnover rates of C in both soil types but the amount of clay influences the stabilization/storage of C.

Chemical Composition of Labile Carbon Fractions in Forest Soils as Affected by Soil Parameters

Understanding how the chemical composition of dissolved and particulate organic matter (DOM and POM) is affected by environment factors is critical because these labile pools of carbon are involved in an array of biological, chemical and physical processes. In this study, the chemical composition of DOM and POM was measured in 13 forest soils using UV-Vis spectroscopy, fluorescence spectroscopy with PARAFAC modelling and FT-IR spectroscopy.There were significant differences between the soils for the SUVA indexes, PARAFAC components and relative intensities of different IR bands. Redundancy analysis (RDA) revealed that soil parameters had a great influence on the chemical composition of DOM and POM with high constrained variability (77.9 and 77.1 %, respectively). The pH of the soils proved to be an important controlling factor for both DOM and POM, regulating the concentration of the C3 PARAFAC component (low-molecular-weight compounds associated with biological activity) and the aromatic compounds of POM (aromaticity, rA1630 and rA1515). The silt content was the other main regulating factor controlling the chemical characteristics of the labile pool, having a strong negative correlation with the SUVA values of DOM due to the preferential adsorption of hydrophobic moieties. RDA analysis also revealed that, despite their different origins, there is a strong correlation between the chemical composition of POM and DOM.

Is the thermal stability of soil organic matter related to its biogeochemical stability in cultivated Arenosols of the groundnut basin of Senegal?

&lt;p&gt;Soil carbon (C), now more than ever, attracts the interest of the scientific community for its importance in combating climate change and achieving food security. As a result, its key role in agricultural soil fertility and in anthropogenic greenhouse gas emissions mitigation is high on international agendas. A key issue regarding the linkage between food security and carbon storage concerns the mineralization or the stability of soil organic matter (SOM). Rock-Eval&lt;sup&gt;&amp;#174;&lt;/sup&gt; analysis was used to examine the thermal stability of SOM and these results were presented in details at the EGU General Assembly in 2020 (EGU2020-11229). Several indicators are used to further appreciate the quantity and quality of SOM: particle size fractionation (POM-C), determination of permanganate oxidizable carbon (POX-C) and carbon mineralization kinetics (Min-C). The results of both approaches are crossed and presented here. Soils were sampled from two soil layers (0-10 et 10-30 cm) in agricultural plots representative organic inputs practices in local agricultural systems (No input, +Millet residues, +Manure and +Organic wastes). Total soil organic carbon (SOC) concentrations ranged from 1.8 to 18.5 g C.kg&lt;sup&gt;-1&lt;/sup&gt; soil (mean &amp;#177; standard deviation: 5.6 &amp;#177; 0.4 g C.kg&lt;sup&gt;-1&lt;/sup&gt; soil) in the surface layer (0-10 cm) and from 1.5 to 11.3 g C.kg&lt;sup&gt;-1&lt;/sup&gt; soil (mean &amp;#177; standard deviation: 3.3 &amp;#177; 0.2 g C.kg&lt;sup&gt;-1&lt;/sup&gt; soil) in 10-30 cm deep layer. The soil organic matter in these Arenosols while positively affected by organic inputs is dominated by thermally labile forms. The POM-C fractions represent respectively 45 % and 24 % of the COS in the 0-10 cm and 10-30 cm soil layers respectively. Permanganate oxidizable carbon (POX-C) and mineralizable C (Min-C) averaged 254 &amp;#177; 14 mg C.kg&lt;sup&gt;-1&lt;/sup&gt; soil and 10.7 &amp;#177; 1.2 mg C-CO&lt;sub&gt;2&lt;/sub&gt; kg&lt;sup&gt;-1&lt;/sup&gt; soil in the 0-10 cm layer. Our results show that in different situations, the labile pools POM-C, POX-C and Min-C are linked to the active thermal pools A1 (highly labile pool), A2 (labile pool), A3 (resistant pool) and even A4 (refractory pool). The A3 and A4 pools, which are known to be relatively stable in more clayey soils, are in fact quickly mineralized in the sandy soils of this region. This intense mineralization of SOM promotes the recycling of nutrients which is excellent for productivity of these agrosystems, but not for mitigation of climate change in the long term.&lt;/p&gt;&lt;p&gt;keywords: Sahel ; Arenosols ; Thermal stability ; Biogeochemical stability ; Rock-Eval analysis, POM-C ; POX-C ; Min-C.&lt;/p&gt;

Bacterial iron detoxification at the molecular level

Iron is an essential micronutrient, and, in the case of bacteria, its availability is commonly a growth-limiting factor. However, correct functioning of cells requires that the labile pool of chelatable “free” iron be tightly regulated. Correct metalation of proteins requiring iron as a cofactor demands that such a readily accessible source of iron exist, but overaccumulation results in an oxidative burden that, if unchecked, would lead to cell death. The toxicity of iron stems from its potential to catalyze formation of reactive oxygen species that, in addition to causing damage to biological molecules, can also lead to the formation of reactive nitrogen species. To avoid iron-mediated oxidative stress, bacteria utilize iron-dependent global regulators to sense the iron status of the cell and regulate the expression of proteins involved in the acquisition, storage, and efflux of iron accordingly. Here, we survey the current understanding of the structure and mechanism of the important members of each of these classes of protein. Diversity in the details of iron homeostasis mechanisms reflect the differing nutritional stresses resulting from the wide variety of ecological niches that bacteria inhabit. However, in this review, we seek to highlight the similarities of iron homeostasis between different bacteria, while acknowledging important variations. In this way, we hope to illustrate how bacteria have evolved common approaches to overcome the dual problems of the insolubility and potential toxicity of iron.

A laboratory assay of in situ stabilization of toxic metals in contaminated boreal forest soil using organic and inorganic amendments

Metal-contaminated soils present a great threat to natural ecosystems and human health. Remediation studies focusing on metal-polluted soils with high organic matter (OM > 20%) are limited. This study evaluated the effectiveness of biochar, compost, diammonium phosphate (DAP), and iron oxides (Fe-O), in immobilizing metals from an OM-rich boreal forest soil contaminated with arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn). A laboratory incubation study was conducted with soil amended with biochar (5% w w−1), compost (5% w w−1), DAP (0.2% w w−1), or Fe-O (0.2% w w−1), and a control (without amendment) for 6 months at field capacity moisture content. Metal concentrations were determined in pore water collected at 0, 2, 4, and 6 months after incubation. Soil was extracted sequentially for metals after the incubation period. Metal concentrations in pore water were significantly reduced by different amendments as follows: As by biochar and Fe-O, Cd by biochar, compost, and DAP, Cu by biochar, Pb by compost and DAP, and Zn by biochar and compost. Sequential extractions revealed biochar and (or) compost transferred Cd, Cu, Pb, and Zn from the labile pool to the non-labile pool confirming their effectiveness as amendments for remediation of metal-contaminated OM-rich boreal forest soil.

Water-extractable organic matter in the profile of mineral and organic soils of Upper Dniester alluvial plane

Content of cold water extracted organic matter (CWEOM) in organic and mineral soils of Upperdniester alluvial plane was estimated. The largest CWEOM content (mg∙100 g-1) in the upper (10 cm) soil layers was found in peat soils – 105-135, and the smallest – 20-30– in arable sod and meadow soils. The highest CWEOM content was found in the lower horizons of peat soil, where it reaches 290 mg∙100 g-1. Strong correlation (r=0.81 -0.99; P<0.05) between CWEOM and TOC was found. It indicates the presence of dynamic equilibrium in the SOM system that supports certain level of labile pool compounds – the main source of bioavailable materials and energy.

Interaction between distinct actin pools controls activity-dependent actin dynamics in the dendritic spine

Actin cytoskeleton is composed of functionally distinct pools of filamentous (F)-actin defined by their regulatory machinery and dynamics. Although these networks may compete for actin monomers and regulatory factors1–4, the interaction between them remains poorly understood. Here, we show that disruption of the labile F-actin pool in neurons by limited actin depolymerization5,6 unexpectedly triggers rapid enhancement of the F-actin content at the dendritic spine. Long-term blockade of NMDA-type receptors decreases spine actin polymerization, which is specifically restored by the labile pool ablation. Increase in the spine actin is triggered by blockade of formin-induced actin polymerization in a manner dependent on Arp2/3 complex activity. Finally, limited actin depolymerization increases F-actin levels in a cultured cell line, suggesting the generality of the two-tiered actin dynamics. Based on these findings, we propose a model whereby the labile pool of F-actin controlled by formin restricts the polymerization state of the Arp2/3-regulated stable spine actin, suggesting a feedback principle at the core of cytoskeletal organization in neurons.HighlightsDisruption of labile F-actin by limited depolymerization rapidly increases the synaptic F-actin content;The depolymerization-induced F-actin boost reverses decrease in synaptic F-actin induced by long-term NMDA receptor blockade;Blockade of formin-dependent actin polymerization boosts synaptic F-actin in an Arp2/3-dependent manner;Limited actin depolymerization enhances overall F-actin content in a mammalian cell line.