Native SOC Research Articles

Soil priming effect in the organic and mineral layers regulated by nitrogen mining mechanism in a temperate forest

AbstractSoil organic carbon (SOC) in temperate forests is a crucial part of the global C cycle. The C and nitrogen (N) inputs may greatly increase in forest ecosystems affected by atmospheric CO2 concentration, N deposition, and other climate change, which may further affect SOC dynamics in temperate forests. Nevertheless, how C and N inputs interact to influence the soil priming effect (PE) in the organic and mineral layers of temperate forests remains unclear. Here, we used easily available C and N sources, such as 13C‐glucose with 2% SOC contents and ammonium nitrate (input C:N ratio = 10), to examine the effects and mechanisms of exogenous C and N inputs on soil CO2 production and PE in both soil layers of a temperate forest. Our research revealed that exogenous C input caused a positive PE in both soil layers, with the mineral layer showing a larger PE per unit of SOC than the organic layer (OL). Although C input increased C loss from native SOC, soil net C accumulation still increased. The C and N inputs decreased the soil PE in both soil layers, suggesting that N input alleviates substrate N limitation and weakens microbial N mining in both soil layers. Meanwhile, the C and N inputs increased the exogenous C remaining in the organic layer, which was beneficial for soil C sequestration. Compared to the organic layer, the response of the mineral layer to C and N inputs was weaker. This study suggests that C and N interact to affect PE on SOC decomposition and this interaction should be considered in modeling and prediction of soil C cycling.

Biochar aided priming of carbon and nutrient availability in three soil orders of India

In recent years biochar (BC) has gained importance for its huge carbon (C) sequestration potential and positive effects on various soil functions. However, there is a paucity of information on the long-term impact of BC on the priming effect and nutrient availability in soil with different properties. This study investigates the effects of BC prepared from rice husk (RBC4, RBC6), sugarcane bagasse (SBC4, SBC6) and mustard stalk (MBC4, MBC6) at 400 and 600 °C on soil C priming and nitrogen (N), phosphorus (P), and potassium (K) availability in an Alfisol, Inceptisol, and Mollisol. BC properties were analyzed, and its decomposition in three soil orders was studied for 290 days in an incubation experiment. Post-incubation, available N, P, and K in soil were estimated. CO2 evolution from BC and soil alone was also studied to determine the direction of priming effect on native soil C. Increasing pyrolysis temperature enhanced pH and EC of most of the BC. The pyrolysis temperature did not show clear trend with respect to priming effect and nutrient availability across feedstock and soil type. MBC6 increased C mineralization in all the soil orders while RBC6 in Alfisol and SBC6 in both Inceptisol and Mollisol demonstrated high negative priming, making them potential amendments for preserving native soil C. Most of the BC showed negative priming of native SOC in long run (290 days) but all these BC enhanced the available N, P, and K in soil. SBC4 enhanced N availability in Alfisol and Inceptisol, RBC4 improved N and P availability in Mollisol and P in Alfisol and MBC6 increased K availability in all the soils. Thus, based on management goals, tailored BC or blending different BC can efficiently improve C sequestration and boost soil fertility.

The native SOC increase in woodland and lawn soil amended with biochar surpassed greenhouse — A seven-year field trial

The effects of applying biochar with the same characteristics and at the same dose on the storage, composition, and underlying mechanisms of native organic carbon (n-SOC) dynamics in different ecosystems are still unclear. This study aimed to explore the effects of biochar amendment (7 years) on carbon sequestration and the n-SOC pools of woodland, lawn, and greenhouse soils. The ‘water floating method’ and improved ‘combustion loss method’ were used in this study to quantify residual biochar in soil. The results showed that after 7 years, the amount of biochar left in woodland, lawn, and greenhouse soils was 67.12 %, 87.50 %, and 88.13 % of the initial applied amount, respectively. And the n-SOC content increased approximately 2.07, 3.07, and 0.22 times, respectively, mainly due to increases in the native soil humin (n-HM) content of the soil. Biochar also increased the proportion of large aggregates in woodland and lawn soil and increased the t-SOC content of aggregates in each particle size fraction. Additionally, biochar increased the t-SOC of greenhouse soil aggregates but had no significant effect on the distribution of aggregates. The presence of biochar increased native soil easily oxidizable carbon (n-EOC) and microbial biomass carbon (n-MBC) in all three ecosystems. And increases in n-MBC in woodland and lawn soils occurred, which promoted the depletion of native soil hot water dissolvable organic carbon (n-HWOC) and increased CO2 emissions. Furthermore, the microbial respiration quotient (qCO2) of woodland and greenhouse soils was reduced by biochar, and that of lawn soil was unchanged. The carbon use efficiency (CUE) of lawn soils were reduced, possibly because biochar reduced the abundance of soil fungi/bacteria (F/B). In summary, the 7-year application of biochar significantly enhanced the n-SOC content in woodland and lawn soils, mainly due to an increase in humin, while a weaker enhancement was observed in greenhouse soil.

Biochar application significantly increases soil organic carbon under conservation tillage: an 11-year field experiment

Biochar application and conservation tillage are significant for long-term organic carbon (OC) sequestration in soil and enhancing crop yields, however, their effects on native soil organic carbon (native SOC) without biochar carbon sequestration in situ remain largely unknown. Here, an 11-year field experiment was carried out to examine different biochar application rates (0, 30, 60, and 90 Mg ha−1) on native SOC pools (native labile SOC pool I and II, and native recalcitrant SOC) and microbial activities in calcareous soil across an entire winter wheat–maize rotation. The proportions of C3 and C4-derived native SOC mineralization were quantified using soil basal respiration (SBR) combined with 13C natural isotope abundance measurements. The results showed that 39–51% of the biochar remained in the top 30 cm after 11 years. Biochar application rates significantly increased native SOC and native recalcitrant SOC contents but decreased the proportion of native labile SOC [native labile SOC pool I and II, dissolved organic carbon (DOC), and microbial biomass carbon (MBC)]. Biochar application tended to increase the indicators of microbial activities associated with SOC degradation, such as SBR, fluorescein diacetate hydrolysis activity, and metabolic quotient (qCO2). Meanwhile, higher biochar application rates (B60 and B90) significantly increased the C4-derived CO2 proportion of the SBR and enhanced C4-derived native SOC mineralization. The effect of the biochar application rate on the content and proportion of native SOC fractions occurred in the 0–15 cm layer, however, there were no significant differences at 15–30 cm. Soil depth also significantly increased native labile SOC pool I and II contents and decreased qCO2. In conclusion, the biochar application rate significantly increased native SOC accumulation in calcareous soil by enhancing the proportion of native recalcitrant SOC, and biochar application and soil depth collectively influenced the seasonal turnover of native SOC fractions, which has important implications for long-term agricultural soil organic carbon sequestration.Graphical

Plant litter chemistry controls coarse‐textured soil carbon dynamics

Abstract As soils store more carbon (C) than the Earth's atmosphere and terrestrial biomass together, the balance between soil C uptake in the form of soil organic matter (SOC) and release as CO2 upon its decomposition is a critical determinant in the global C cycle regulating our planet's climate. Although plant litter is the predominant source of C fuelling both soil C build‐up and losses, the issue of how litter chemistry influences this balance remains unresolved. As a contribution to solving that issue, we traced the fate of C during near‐complete decomposition of 13C‐labelled leaf and root litters from 12 plant species in a coarse‐textured soil. We separated the soil organic carbon into mineral‐associated organic matter (MAOM) and particulate organic matter (POM) pools, and investigated how 14 litter chemical traits affected novel SOC formation and native SOC mineralization (i.e. the priming effect) in these soil fractions. We observed an overall net increase in SOC due to the addition of litter, which was stronger for root than for leaf litters. The presumed stable MAOM‐C pool underwent both substantial stabilization and mineralization, whereas the presumably less stable POM‐C pool showed substantial stabilization and reduced mineralization. Overall, the initial increase in soil C mineralization was fully counterbalanced by a later decrease in native soil C mineralization. POM‐C formation as well as MAOM‐C formation and mineralization were positively related to the initial litter lignin concentration and negatively to that of the nitrogen leachates, whereas the opposite was observed for POM‐C mineralization. Synthesis. Our results highlight the importance of litter chemical traits for SOC formation, and stabilization, destabilization and mineralization. In our coarse‐textured soil, the amount of MAOM‐C did not change despite large C fluxes through this pool. The litter chemical traits that drove these processes differed from those frequently reported for fine‐textured soils far from mineral‐associated C saturation. To account for these discrepancies, we propose an integrative perspective in which litter quality and soil texture interactively control soil C fluxes by modulating several SOC stabilization and destabilization mechanisms. Irrespective, our results open new critical perspectives for managing soil C pools globally.

Disentangling carbon stabilization in a Calcisol subsoil amended with iron oxyhydroxides: A dual-13C isotope approach

Calcisols pose some unique challenges, particularly relating to their low organic carbon (C) content and low C storage ceiling. To address this, we investigated the role of iron (Fe) oxyhydroxides – goethite and ferrihydrite (0.36, 0.72, 3.6, and 7.2 g kg−1 soil) in the presence of a labile C substrate (glucose) to simulate rhizodeposition, on C-cycling. As there were three potential C sources: (i) glucose-C, (ii) native SOC, and (iii) soil inorganic C (SIC), a novel dual-13C isotope approach (δ13C-enriched glucose of 29 and 81‰) was implemented to accurately differentiate these three C sources from a Calcisol subsoil (δ13SOC, −23‰; δ13SIC, −3.6‰). Over 28 days, across the glucose and Fe oxyhydroxide treatments, 34.8–41.7% of the supplied glucose-C (1.0 g C kg−1 soil), 7.5–9.6% of the native SOC (3.7 g kg−1 soil), and 0.11–0.19% of the SIC (48 g kg−1 soil) were lost as CO2. Goethite and ferrihydrite generally stabilized organic C (including glucose-C and native SOC) which occurred primarily within the first 10 days following amendment with Fe oxyhydroxide, and the stabilization effect generally increased with increasing Fe oxyhydroxide dose. This is likely due to rapid Fe-OC adsorption that protected the OC from microbial decomposition. Ferrihydrite (cf. goethite) had a smaller effect on suppressing positive priming of SOC mineralization induced by glucose, possibly resulting from the lower C use efficiency and less stable Fe-OC associations due to the higher dissolution rate of ferrihydrite. The SIC loss increased after glucose addition, which was further enhanced by Fe oxyhydroxides. We conclude that Fe oxyhydroxides may be useful amendments for increasing SOC in highly alkaline Calcisols.

Dynamic changes in bacterial community structure are associated with distinct priming effect patterns

The addition of residues (maize straw) to soil stimulates microbial activity and significantly changes the decomposition rates of soil organic matter (SOM), which is referred to as priming effects (PEs). PE patterns are influenced by microorganisms utilising various substrates. However, the varied functional traits of keystone taxa and structure traits of the bacterial community associated with the PEs patterns remain elusive. Therefore, we established a microcosm by adding C4 maize residue (C4 plants have a different 13C signature than C3 plants) to C3 soil amended for 120 d to observe the dynamics of PEs. High-throughput sequencing techniques were used to detect the succession of bacteria; keystone taxa were identified using network analysis. Negative PE (early stage) and positive PE (late stage) were observed during residue decomposition. At the end of the incubation, residue with N resulted in a positive PE, while residue alone had a minimal effect on the decomposition of native SOC. Furthermore, the bacterial community structure displayed distinct successions during residue decomposition. Correspondingly, network analysis revealed differences in the keystone taxa between the early and late stages. Bacillus, Streptomyces, Arthrobacter, and Agromyces were the keystone taxa during the early stage, whereas BD2-11 terrestrial, Bacteroidales, Sphingomonadaceae, and Xanthomonadales were the keystone taxa at the late stage. These putative keystone taxa have different functional traits as drivers of community function, thus linking them to either negative or positive PE. In addition, network modules of bacterial communities differed in the early versus late stages and showed different module-trait relationships during PE. Therefore, the different modules are aggregated in response to distinct PE patterns. This study provides deeper insights into the network structure of bacterial community corresponding to PE patterns and highlights the importance of keystone taxa in PE.

Pyrolysis temperature and soil depth interactions determine PyC turnover and induced soil organic carbon priming

Pyrogenic organic carbon (PyC) is a complex, heterogeneous class of thermally altered organic substrates, but its dynamics and how its behavior changes with soil depth remain poorly understood. We conducted a laboratory incubation study to investigate the interactive effects of pyrolysis temperature and soil depth on the turnover of PyC compared to its precursor wood and native SOC (NSOC). We incubated dual-labeled (13C and 15N) jack pine pyrogenic organic matter produced at 300 °C (PyC300), 450 °C (PyC450), and their precursor pine wood in a fine-loamy, mixed-conifer forest soil for 745 days. A mixture of surface (0–10 cm) and subsurface (50–70 cm) forest soils, with and without labeled biomass were incubated in the dark at 55% soil water field capacity and 25 °C. Total 13C from PyC and wood mineralized as 13C-CO2 (as % of C added to soil) declined with an increase in pyrolysis temperature as follows: 54 ± 7.7% for wood, 3.1 ± 0.2% for PyC300, and 0.94 ± 0.08% for PyC450. After 2 years, soil depth interacted with pyrolysis temperature to affect C turnover, with total wood C losses significantly declining from 70.6% in surface soils to 37.5% in subsurface soil, while total losses of PyC300 and PyC450 were unaffected by differences between surface and subsurface soils. Wood induced negative priming (i.e., decreased mineralization rates) in surface soil at days 3 and 60, while PyC300 induced positive priming (i.e., increased mineralization rates) in subsurface soil at day 60. After 2 years, unlabeled NSOC losses increased from 9.2 ± 0.8% of NSOC in unamended treatments to 16.5 ± 2.6% of NSOC with PyC450 additions. Our results suggest that PyC pyrolyzed at a given temperature can mineralize at similar rates between soil depths, and high amounts of PyC450 in subsurface soils can stimulate NSOC losses. These findings indicate that soil depth imposes critical controls on PyC dynamics belowground.

Biochar altered native soil organic carbon by changing soil aggregate size distribution and native SOC in aggregates based on an 8-year field experiment

Soil aggregates play an important function in soil carbon sequestration because larger aggregates have higher soil organic carbon contents. A field experiment was set up in 2009 that included four treatments, i.e., B0, B30, B60, and B90 representing biochar application rates of 0, 30, 60, and 90 t ha−1, respectively. In 2017, we investigated the soil aggregate distribution, biochar and n-SOC contents in soil and different aggregate sizes using the ignition method, as well as the contribution of wheat and maize residues to n-SOC content in each aggregate by isotopic analysis. The results showed that, relative to B0, the n-SOC content presented an 14.0% decrease in B30, compared with an 18.8% and 8.2% increase in B60 and B90 (p < 0.05), respectively. Furthermore, the decreased n-SOC content in B30 was due to the decreased proportions of < 53 μm and 1000–250 μm aggregates. The increased n-SOC content in B60 was due to the significantly enhanced proportion of 2000–1000 μm and 1000–250 μm aggregates because the n-SOC contents of these two aggregates size classes were not changed by biochar. However, in B90, the increased n-SOC content was ascribed to the enhanced proportions of 2000–1000 μm and < 53 μm aggregates, although the n-SOC content in 2000–1000 μm aggregate was significantly decreased by biochar. Further analysis showed that the decreased n-SOC content in 2000–1000 μm aggregates was associated with decreased wheat-derived n-SOC content. In synthesis, our study showed a long-term effect of biochar on the n-SOC content by mainly changing soil aggregation and native organic carbon derived from wheat residue, and this effect was dependent on the applied amount. The biochar rate of 60 t ha−1 is recommended for carbon sequestration in terms of the more pronounced negative priming of native SOC, while the feasible combination between other biochars and soils needs further clarification.

Effects of inorganic nitrogen and litters of Masson Pine on soil organic carbon decomposition.

Soil organic matter (SOM) mineralization represents one of the largest fluxes in the global carbon cycle. Numerous studies have shown that soil organic carbon decomposition was largely changed owing to the addition of litter, however very few studies have focused on the role of plant organs in the priming effects (PEs). Here, we studied the effects of different Pinus massoniana organs (fresh leaf, leaf litter, twigs, absorptive fine roots, and transport fine roots) on C4 soil respiration by applying the 13C isotopic natural abundance method. Results showed that the effects of plant organs on PEs were significantly different at the end of 210 days incubation, which can be ascribed to contrasting organs traits especially non-structural carbohydrates and water-soluble compounds. Transport fine roots and fresh leaf induced positive PE, whereas absorptive fine roots induced negative PE. Leaf litter did not change the native SOC decomposition. Plant organ addition can change the microbial community and result in the reduction of bacteria-to-fungi ratio. Our results suggest that with regard to determining the PE of the entire ecosystem, using fresh leaf to represent leaf litter and aboveground to represent underground is implausible.

A multi-technique approach to assess the fate of biochar in soil and to quantify its effect on soil organic matter composition

Differentiation of biochar and native soil organic matter (SOM) is required to assess the effect of biochar amendment on in-situ changes of SOM. Therefore, we used C4 biochar produced at high temperature (1200°C) by gasification (BCGS) and measured the 13C abundance of density and particle size fractions. We quantified the BCGS effects on distinct native C3-SOM pools of a grassland topsoil one year after BCGS amendment. The chemical composition was analyzed with solid-state 13C CPMAS NMR, whereas information on the nanostructure of BCGS were obtained by Raman microspectroscopy measurements. Our aim was to assess BCGS induced chemical changes of SOM and physical fractions and to validate the accuracy of BCGS detection by 13C NMR spectroscopy. Quantification by isotopic measurements and 13C NMR spectroscopy for aromatic C yielded similar estimates of BC in soils. Of the total BCGS, 52% were recovered as free particulate organic matter (POM) and 33% were located in aggregated soil structures isolated as occluded POM particles. Around 4% of the total BCGS was detected in the clay fraction. After one year of field exposure, the surface of the BCGS particles decreased in unordered graphitic-like structures. The higher ordered BC residue is supposed to be more recalcitrant. The native SOC stock increase (p=0.06, n=4) in the clay fraction indicated increased sequestration of organic matter as mineral-bound SOM due to BCGS amendment. With respect to soil functionality, the BCGS amendment induced a tremendous shift from a soil system dominated by organo-mineral associations to POM−dominated OC storage, resulting in increased soil air capacity.

Aggregate size distribution in a biochar-amended tropical Ultisol under conventional hand-hoe tillage

Biochar (or pyrogenic organic matter) is increasingly proposed as a soil amendment for improving fertility, carbon sequestration and reduction of greenhouse gas emissions. However, little is known about its effects on aggregation, an important indicator of soil quality and functioning. The aim of this study was to assess the effect of Eucalyptus wood biochar (B, pyrolyzed at 550°C, at 0 or 2.5tha−1), green manure (T, from Tithonia diversifolia at 0, 2.5 or 5.0tha−1) and mineral nitrogen (U, urea, at 0, or 120kgNha−1) on soil respiration, aggregate size distribution and SOC in these aggregate size fractions in a 2-year field experiment on a low-fertility Ultisol in western Kenya under conventional hand-hoe tillage. Air-dry 2-mm sieved soils were divided into four fractions by wet sieving: Large Macro-aggregates (LM; >1000μm); Small Macro-aggregates (SM, 250–1000μm); Micro-aggregates (M, 250–53μm) and Silt+Clay (S+C, <53μm). We found that biochar alone did not affect a mean weight diameter (MWD) but combined application with either T. diversifolia (BT) or urea (BU) increased MWD by 34±5.2μm (8%) and 55±5.4μm (13%), respectively, compared to the control (P=0.023; n=36). The B+T+U combination increased the proportion of the LM and SM by 7.0±0.8%, but reduced the S+C fraction by 5.2±0.23%. SOC was 30%, 25% and 23% in S+C,M and LM/SM fractions, and increased by 9.6±1.0, 5.7±0.8, 6.3±1.1 and 4.2±0.9gkg−1 for LM, SM, M and S+C, respectively. MWD was not related to either soil respiration or soil moisture but decreased with higher SOC (R2=0.37, P=0.014, n=26) and increased with greater biomass production (R2=0.11, P=0.045, n=33). Our data suggest that within the timeframe of the study, biochar is stored predominantly as free particulate OC in the silt and clay fraction and promoted a movement of native SOC from larger-size aggregates to the smaller-sized fraction in the short-term (2 years).

Biochar persistence, priming and microbial responses to pyrolysis temperature series

Biochar and its properties can be significantly altered according to how it is produced, and this has ramifications towards how biochar behaves once added to soil. We produced biochars from corncob and miscanthus straw via different methods (slow pyrolysis, hydrothermal and flash carbonization) and temperatures to assess how carbon cycling and soil microbial communities were affected. Mineralization of biochar, its parent feedstock, and native soil organic matter were monitored using 13C natural abundance during a 1-year lab incubation. Bacterial and fungal community compositions were studied using T-RFLP and ARISA, respectively. We found that persistent biochar-C with a half-life 60 times higher than the parent feedstock can be achieved at pyrolysis temperatures of as low as 370 °C, with no further gains to be made at higher temperatures. Biochar re-applied to soil previously incubated with our highest temperature biochar mineralized faster than when applied to unamended soil. Positive priming of native SOC was observed for all amendments but subsided by the end of the incubation. Fungal and bacterial community composition of the soil-biochar mixture changed increasingly with the application of biochars produced at higher temperatures as compared to unamended soil. Those changes were significantly (P < 0.005) related to biochar properties (mainly pH and O/C) and thus were correlated to pyrolysis temperature. In conclusion, our results suggest that biochar produced at temperatures as low as 370 °C can be utilized to sequester C in soil for more than 100 years while having less impact on soil microbial activities than high-temperature biochars.

The stability of low- and high-ash biochars in acidic soils of contrasting mineralogy

The potential of biochar as a tool for long-term soil carbon (C) storage has led to an increasing interest in its use as a soil amendment. While much research has been conducted on the stability of high C and low ash biochars, the stability of low C (with relatively high inorganic C) and high ash biochars has been largely neglected. In light of this, an incubation experiment was conducted to compare and assess the stability of a high ash and low C biochar produced from tomato green waste and low ash and high C biochar produced from blue mallee biomass. The two biochars were applied at 2% and 4% (w/w) to two acidic soils of contrasting mineralogy, a Ferralsol and a Solonetz. The soil–biochar mixtures were incubated at 20 °C for 120 days. The CO2–C mineralised was captured in NaOH traps and the source of C mineralisation determined by isotope analysis. The tomato biochar was mineralised (1.4–3.7%) to a greater extent than the blue mallee biochar (0.28–0.77%), possibly due to dissolution of the large quantity of inorganic C. In biochar amended soils, with the exception of the Solonetz applied with 2% blue mallee biochar, greater cumulative mineralisation (positive priming) of native SOC occurred as compared to their respective controls. Mean residence time for the two biochars suggests much greater potential of the blue mallee biochar for long-term soil C storage than the tomato biochar. However, the tomato biochar may have greater agronomic value, in particular a high liming potential, although field studies are required to confirm these results.

Chemical composition of organic matter in a deep soil changed with a positive priming effect due to glucose addition as investigated by 13C NMR spectroscopy

Fresh organic carbon becomes more accessible to deep soil following losses of surface soil and deep intentional incorporation of crop residues, which can cause the priming effect and influence the quality and quantity of SOC in deep soil. This study determined the priming effect due to addition of water-dissolved 13C-labeled glucose (0.4 g C kg−1 soil) to a soil taken from 1.00 to 1.20 m depth. The changes in chemical compositions of SOC in soils without (G0) and with (G0.4) glucose addition during a 31-d incubation were investigated with solid-state 13C cross polarization/total sideband suppression (13C-CP/TOSS) and CP/TOSS with dipolar dephasing nuclear magnetic resonance (NMR) techniques. No glucose remained in the soil after 21 days of incubation, with 48% being completely mineralized into CO2 emission and 52% being incorporated into SOC. The native SOC was decomposed by 0.23% more in G0.4 than in G0. The NMR spectra demonstrated that both labile and recalcitrant organic compounds in SOC changed during the incubation, but in different manners in G0 and G0.4. During the incubation, the -(CH2)n-abundance in G0 did not change over time, but in G0.4 it decreased from Day 0 to Day 21 and then increased from Day 21 to Day 31, suggesting shifts of soil microbial communities only in G0.4. After the incubation, in G0 the abundances of ketones/aldehydes and nonpolar alkyl C increased, but those of aromatic C–C and protonated O-alkyl C (OCH) decreased; In G0.4, the abundances of NCH and protonated O-alkyl C (OCH) increased, but those of nonpolar alkyl C and nonprotonated aromatic C–O and ketones/aldehydes decreased. Such inconsistent changes in recalcitrant compounds between G0 and G0.4 indicated that glucose addition likely primed the decomposition of aromatic C–O and suppressed the formation of ketones/aldehydes. We have demonstrated for the first time that the priming effect of SOC decomposition in the deep soil was involved with larger notable changes in both labile and recalcitrant structures of native SOC due to glucose addition compared with that without glucose addition.

Effects of biochar, earthworms, and litter addition on soil microbial activity and abundance in a temperate agricultural soil

Biochar application to arable soils could be effective for soil C sequestration and mitigation of greenhouse gas (GHG) emissions. Soil microorganisms and fauna are the major contributors to GHG emissions from soil, but their interactions with biochar are poorly understood. We investigated the effects of biochar and its interaction with earthworms on soil microbial activity, abundance, and community composition in an incubation experiment with an arable soil with and without N-rich litter addition. After 37 days of incubation, biochar significantly reduced CO2 (up to 43 %) and N2O (up to 42 %), as well as NH4 +-N and NO3 −-N concentrations, compared to the control soils. Concurrently, in the treatments with litter, biochar increased microbial biomass and the soil microbial community composition shifted to higher fungal-to-bacterial ratios. Without litter, all microbial groups were positively affected by biochar × earthworm interactions suggesting better living conditions for soil microorganisms in biochar-containing cast aggregates after the earthworm gut passage. However, assimilation of biochar-C by earthworms was negligible, indicating no direct benefit for the earthworms from biochar uptake. Biochar strongly reduced the metabolic quotient qCO2 and suppressed the degradation of native SOC, resulting in large negative priming effects (up to 68 %). We conclude that the biochar amendment altered microbial activity, abundance, and community composition, inducing a more efficient microbial community with reduced emissions of CO2 and N2O. Earthworms affected soil microorganisms only in the presence of biochar, highlighting the need for further research on the interactions of biochar with soil fauna.

Temperature sensitivity of biochar and native carbon mineralisation in biochar-amended soils

Temperature sensitivity of biochar-C in soils is not well understood. To acquire this information, we incubated two δ13C-depleted (−36.3 or −36.5‰) wood biochars produced at 450 and 550°C, under controlled laboratory conditions at 20, 40 and 60°C in four contrasting soils (Inceptisol, Entisol, Oxisol and Vertisol). The respired CO2 and associated δ13C were analysed periodically (12–22 times) over two years. The temperature sensitivity of biochar-C and native SOC mineralisation was computed as: (i) averaged Q10 (Q10a) for the whole (2-year) time series using a temperature-incorporated mineralisation model to estimate a temperature scaling function for the exponential Q10 model; (ii) instantaneous Q10 (Q10i) by using a time series of C mineralisation rates for a simple Q10 model; and (iii) cumulative Q10 (Q10c) by using cumulative C mineralised over certain incubation periods for a simple Q10 model.The mineralisation rates of biochar-C and native SOC increased with increasing temperature and their temperature sensitivities were significantly (p<0.001) affected by soil type. For example, biochar-C Q10a was the greatest (also for native SOC) in the Vertisol (2.74–2.77), followed by Inceptisol (2.47–2.66) and Entisol (2.39–2.45), and the smallest in the Oxisol (1.93–2.20) for the 20–40°C range. Biochar and native SOC Q10a were the smallest in the Vertisol for the 40–60°C range. Biochar-C Q10a was not influenced by biochar type (450 or 550°C). The presence of biochar decreased Q10a of the native SOC in the Entisol, Vertisol and Inceptisol, but this influence did not occur in the Oxisol, especially at 20–40°C. The temperature sensitivity of biochar-C (Q10a and Q10c) and SOC (Q10a and Q10i) decreased with increasing incubation temperature range. The Q10i values of biochar-C and SOC increased with time in the 20–40°C range. Even though biochar-C was found to be more stable than native SOC (based on their mineralisation rate constants), the Q10a, Q10c and Q10i values for biochar-C were either smaller or similar to that of native SOC. In conclusion, the findings of this study which was conducted in the absence of plant suggest that soil characteristics can alter the temperature sensitivity of biochar-C. Furthermore, biochar can decrease the temperature sensitivity of native SOC mineralisation and consequently enhance C sequestration in soil under climate warming.

Peptidyl-Prolyl Isomerase FKBP52 Controls Chemotropic Guidance of Neuronal Growth Cones via Regulation of TRPC1 Channel Opening

Immunophilins, including FK506-binding proteins (FKBPs), are protein chaperones with peptidyl-prolyl isomerase (PPIase) activity. Initially identified as pharmacological receptors for immunosuppressants to regulate immune responses via isomerase-independent mechanisms, FKBPs are most highly expressed in the nervous system, where their physiological function as isomerases remains unknown. We demonstrate that FKBP12 and FKBP52 catalyze cis/trans isomerization of regions of TRPC1 implicated in controlling channel opening. FKBP52 mediates stimulus-dependent TRPC1 gating through isomerization, which is required for chemotropic turning of neuronal growth cones to netrin-1 and myelin-associated glycoprotein and for netrin-1/DCC-dependent midline axon guidance of commissural interneurons in the developing spinal cord. By contrast, FKBP12 mediates spontaneous opening of TRPC1 through isomerization and is not required for growth cone responses to netrin-1. Our study demonstrates a novel physiological function of proline isomerases in chemotropic nerve guidance through TRPC1 gating and may have significant implication in clinical applications of immunophilin-related therapeutic drugs.

Long-term impact of fertilizers on soil organic carbon pools and sequestration rates in maize–wheat–cowpea cropping system

We assessed the impact of long-term manuring and fertilization on changes in different SOC fractions over ten years period (1994–2003) in a Typic Haplustept under intensive cropping with maize ( Zea mays L.) — wheat ( Triticum aestivum L.) — cowpea ( Vigna unguiculata) in semi-arid, sub-tropical India. The application of graded doses of NPK from 50% (130 kg N, 35 kg P and 41.5 kg K ha − 1 ) to 150% (390 kg N, 105 kg P and 124 kg K ha − 1 ) in the cropping system significantly enhanced SOC, particulate organic C (POC) and KMnO 4 oxidizable C (KMnO 4–C) fractions in soil. The increase in these C fractions was greater when farmyard manure (FYM) was applied conjointly with 100% NPK (260 kg N, 70 kg P and 83 kg K ha − 1 ). This treatment showed highest amount of SOC (58.3 Mg C ha − 1 in 1994 and 72.1 Mg C ha − 1 in 2003), POC (5.30 Mg C ha − 1 in 1994 and 6.33 Mg C ha − 1 in 2003) and KMnO 4-C (10.05 Mg C ha − 1 in 1994 and 11.2 Mg C ha − 1 in 2003) in 0–45 cm soil depth. The C sequestration rate in SOC calculated over ten year period (1994–2003) was highest with 100% NPK + FYM (997 kg C ha − 1 yr − 1 ) followed by the 150% NPK (553 kg C ha − 1 yr − 1 ). It was estimated that 17.1 to 34.0% of the gross C input over ten year period contributed towards the increase in SOC content, while C sequestration efficiency (CSE) in POC (varied between 1.28 and 2.58%) was lower than KMnO 4-C (varied between 1.42 and 3.72%). The CSE was highest in 150% NPK treatment, while 100% NPK + FYM showed the lowest CSE. By applying the values of humification constant ( h) and decay constant ( k) in Jenkinson's equation, it is possible to predict SOC level in the year 2003 and the C inputs required to maintain the SOC level in the year 1994 ( A E) were calculated from Jenkinson's equation. The low k value in native SOC was responsible for lower requirements of C input required to maintain SOC in equilibrium. Thus increase in SOC concentration under long-term maize–wheat–cowpea cropping was due to the fact that annual C input by the system was higher than A E. In semi-arid sub-tropical India, continuous adoption of 100% NPK + FYM treatment in maize–wheat–cowpea cropping system might sequester 1.83 Tg C yr − 1 which corresponds to about 1% of the fossil fuel emissions by India.

STIM1 carboxyl-terminus activates native SOC, Icrac and TRPC1 channels

Receptor-evoked Ca2+ signalling involves Ca2+ release from the endoplasmic reticulum, followed by Ca2+ influx across the plasma membrane. Ca2+ influx is essential for many cellular functions, from secretion to transcription, and is mediated by Ca2+-release activated Ca2+ (I(crac)) channels and store-operated calcium entry (SOC) channels. Although the molecular identity and regulation of I(crac) and SOC channels have not been precisely determined, notable recent findings are the identification of STIM1, which has been indicated to regulate SOC and I(crac) channels by functioning as an endoplasmic reticulum Ca2+ sensor, and ORAI1 (ref. 7) or CRACM1 (ref. 8)--both of which may function as I(crac) channels or as an I(crac) subunit. How STIM1 activates the Ca2+ influx channels and whether STIM1 contributes to the channel pore remains unknown. Here, we identify the structural features that are essential for STIM1-dependent activation of SOC and I(crac) channels, and demonstrate that they are identical to those involved in the binding and activation of TRPC1. Notably, the cytosolic carboxyl terminus of STIM1 is sufficient to activate SOC, I(crac) and TRPC1 channels even when native STIM1 is depleted by small interfering RNA. Activity of STIM1 requires an ERM domain, which mediates the selective binding of STIM1 to TRPC1, 2 and 4, but not to TRPC3, 6 or 7, and a cationic lysine-rich region, which is essential for gating of TRPC1. Deletion of either region in the constitutively active STIM1(D76A) yields dominant-negative mutants that block native SOC channels, expressed TRPC1 in HEK293 cells and I(crac) in Jurkat cells. These observations implicate STIM1 as a key regulator of activity rather than a channel component, and reveal similar regulation of SOC, I(crac) and TRPC channel activation by STIM1.