SOC Quality Research Articles

Zero-field splitting in tetracoordinate Co(II) complexes containing heterocyclic aromatic ligands

A series of tetracoordinate mononuclear Co(II) complexes [Co(L1)2(X)2] (1-3) and [Co(L2)2(X)2] (4-6) {where L1 = 2-amino-1-methyl-benzimidazole; L2 = 4-methylquinoline; X = Cl, Br, I} have been synthesized and studied in detail. Compounds were characterized by spectroscopic methods along with their molecule structure determined by the single-crystal X-ray diffraction. All complexes have been investigated in the static magnetic field Bdc = 0.1 T using SQUID magnetometry. DC magnetic data were fitted by a spin Hamiltonian model appropriate to a zero-field splitting system. The axial zero-field splitting parameters D ranged as -14.44 (1), -13.05 (2), -7.50 (3), -6.76 (4), +7.19 (5), -5.58 (6) cm−1. The experimental zero-field splitting parameters are compared with those obtained by ab initio calculations of the CASSCF + NEVPT2 + SOC quality.

Dark CO2 fixation in temperate beech and pine forest soils

Soils are the largest terrestrial organic carbon pool and the largest terrestrial source of atmospheric CO2. Non-phototrophic CO2 fixation by microbes re-fixes and recycles CO2 respired in soils. Our previous study showed that in temperate deciduous forest soil profiles, rates of dark CO2 fixation were proportional to microbial biomass, irrespective of soil depth. However, the amount and quality of organic matter entering different soil depths vary for different temperate forest types and these influence microbial communities with unknown consequences for CO2 fixation rates. To test whether differences in the amount and quality of SOC caused by tree species affect dark CO2 fixation rates with depth, we conducted a study using acidic soils from two forest plots from the Schorfheide-Chorin Exploratory, Germany. These soils, dominated by either beech (deciduous) or pine (coniferous) tree stands differ in their SOC content and quality. We traced the incorporation of 2% (v:v) 13C–CO2 label into microbial biomass and estimated the CO2 fixation rates relative to microbial biomass carbon content (in μg C g MBC−1 d−1) across the soil profiles. The rates of dark CO2 fixation per g MBC were similar across the beech soil profiles, but significantly lower in the pine soils at the B2 and BC horizons, suggesting that while dark CO2 fixation rates are linked to MBC in deciduous forest soils, other factors influence dark CO2 fixation rates in coniferous forest soils. The pine subsoils had low SOC content and quality, with a microbial community enriched with heterotrophic fermenters like Chloroflexi that are predicted to have a lower potential for heterotrophic CO2 fixation compared to the other dominant bacteria phyla. In contrast, the beech soil profiles, characterized by higher SOC inputs, featured higher fractions of copiotrophs like Proteobacteria, Acidobacteria, and Actinobacteria predicted to have high heterotrophic CO2 fixation potential. We thus speculate that in contrast to the beech soils, lower SOC inputs in the pine subsoils affected the community composition, leading to lower CO2 fixation rates. We further made comparisons to soils dominated by mixed deciduous trees and featuring a higher MBC and SOC content. Over this range of temperate forest soils, CO2 fixation rates were highest in the mixed deciduous forest soils, with MBC and Shannon index (used as a proxy parameter for community composition) showing the strongest correlations with the varying CO2 fixation rates. Our study suggests that predictions of dark CO2 fixation rates need to consider tree-species specific or site-specific conditions, as these may alter root carbon inputs and affect microbial community composition and their metabolic CO2 fixation potentials in soil.

Sensitivity of soil aggregation to soil organic carbon fractions under land-use conversion from rice to organic vegetable cultivation

Conversion of rice-wheat rotation (RWR) to conventional vegetable cultivation, especially vegetable cultivation in plastic sheds, readily causes soil structure degradation, and organic manure is commonly applied to mitigate such degradation. Although many studies have focused on changes in SOC properties or structural soil parameters, additional details about the changes, such as the relationships between SOC fractions and soil aggregates during unique land-use changes, are unknown. Here, we studied the changes in soil aggregation, and SOC parameters in 14-year-old plastic-shed vegetable fields (PVFs) and open-air vegetable fields (OVFs) covered with organic manure, with adjacent RWR fields serving as a control. The vegetable fields were converted from RWR fields. SOC fractions were analyzed by using 13C solid-state NMR spectroscopy, and the aggregate classes were divided as follows: large macro-aggregates (>2 mm), small macro-aggregates (2–0.25 mm), micro-aggregates (0.25–0.053 mm), and silt and clay particles (<0.053 mm). PVFs had higher SOC and MBC than OVFs and RWR fields. In terms of the SOC fractions, the proportion of O-alkyl C decreased as RWR (53.90%) > PVF (43.21%) > OVF (35.37%), in contrast to the trends in the carbonyl C and aromatic C fractions. The aggregate-associated C, especially that associated with large macro-aggregates and micro-aggregates, in the PVFs was highest among the treatments. The O-alkyl C fraction in large macro-aggregates decreased in the order RWR (44.67%) > OVF (35.76%) > PVF (32.40%), consistent with the results for micro-aggregates. Furthermore, there was a significant (P ≤ 0.05) positive relationship between macro-aggregates (>0.25 mm) and the active C fractions, in contrast to the relationships with stable fractions. It suggested that plastic-shed cultivation might have a more positive effect than open-air cultivation on soil structure and the carbon stock when large amounts of organic manure are applied; moreover, the SOC quantity and quality affect soil aggregation differently.

Insights Gained in the Aftermath of the COVID-19 Pandemic: A Follow-Up Survey of a Recreational Training Program, Focusing on Sense of Coherence and Sleep Quality.

The original aim of this study was a follow-up assessment of a recreational program running for six months (September 2019–February 2020) within controlled conditions. Following the arrival of the COVID-19 pandemic, the survey acquired a new goal: how do the subjects of the follow-up sampling experience this severe stress situation, and in this experience, what role does physical activity and a salutogenetic sense of coherence play. Austrian women (N = 53) took part in the training program, whose physical condition was assessed before the start of the program, then reassessed after three months and after six months; the organizers also had them fill out the sense of coherence questionnaire (SOC) as well as the Regensburger insomnia scale. After the lifting of the lockdown introduced due to the pandemic, participants completed an online survey relating to their changed life conditions, physical activities, sense of coherence and sleep quality. Results: After the first three months of the training, no significant changes were detected. After six months, the participants SOC and sleep quality improved (Friedman test: p = 0.005 and p < 0.001). During the lockdown, sleep quality generally deteriorated (W-rank test: p = 0.001), while SOC did not change. The women in possession of a relatively stronger SOC continued the training (OR = 3.6, CI 95% = 1.2–12.2), and their sleep quality deteriorated to a lesser degree. (OR = 1.7, CI 95% = 1.1–2.8). Conclusion: The data reinforce the interdependency between physical exercise (PE) and SOC; furthermore, the personal training that the authors formulated for middle-aged women proved to be successful in strengthening their sense of coherence, and it also reduced the deterioration in sleep quality due to stress.

Parent material modulates land use effects on soil selenium bioavailability in a selenium-enriched region of southwest China

Land use effects on the biogeochemical cycling of the essential trace element selenium (Se) and underlying mechanisms are not well understood yet. Here, total Se (Setotal) and its potential bioavailability, as represented by phosphate extractability (Sephosphate), were evaluated in top soils (0–15 cm) of cropland and woodland over two contrasting geological parent materials (i.e. limestone versus clasolite) in a Se-enriched region of southwest China. After about twenty years of conversion of land use from cropland to woodland, Setotal in soils significantly (P < 0.05) and marginally significantly (P < 0.1) increased over limestone and clasolite, respectively. In terms of Sephosphate, it was not significantly changed after land use change from cropland to woodland in soil over limestone, whereas remarkably increased in soil over clasolite (P < 0.01). Furthermore, a significant positive relationship between Sephosphate and Setotal was found in soil over clasolite, but not in soil over limestone. Land use conversion from cropland to woodland caused a decrease in the proportion of Sephosphate in Setotal over limestone, while the opposite was found over clasolite. In comparison, the proportion of Sephosphate in Setotal was greater in cropland over limestone than that in cropland over clasolite, indicating that limestone derived soils may have an advantage of producing Se-rich food over clasolite derived soils. SOC content and quality (i.e. C:N ratio) crucially determined Se accumulation and bioavailability in soil over limestone, while pH played a vital role in soil over clasolite. Taken together, our results provide strong evidence that land use effects on Se biogeochemistry can be substantially modulated by the underlying geology, and have important practical implications for effective utilization and management of Se-enriched soil resources in other parts of the world.

Soil extracellular enzyme activity and stoichiometry in China's forests

Abstract Ecoenzymatic stoichiometry links microbial decomposition with nutrient mineralization and improves our understanding of nutrient cycling in terrestrial ecosystems. Microbial C:N:P acquisition in the topsoil converged at a ratio of 1:1:1 in global ecosystems. However, whether the ratio of microbial acquisition is stable in forest soils, and is applicable among different soil depths remain unknown. Based on large‐scale soil sampling in China's forests, we examined the patterns and environmental drivers of the eight most‐widely measured enzyme activities and the relevant stoichiometry. We found that the ratio of C:N:P acquisition significantly deviated from 1:1:1. The specific enzyme activities (normalized by SOC) did not change significantly with latitude except those for xylosidase and acid phosphatase. Similarly, only the C:P acquisition ratio increased with latitude. Vertically, the specific activities of C‐acquiring enzymes mainly increased, N‐acquiring enzymes decreased and P‐acquiring enzymes did not change with soil depth. Moreover, all ratios of microbial acquisition decreased, and the percentage of recalcitrant C increased significantly with increasing depth. Our study also showed that temperature and soil C:N ratio were the important factors in explaining the variations in specific enzyme activities and microbial nutrient acquisition, respectively. Our results indicated that no constant microbial C:N:P acquisition ratio can be widely recognized, and that SOC quality changed from labile to recalcitrant with depth. We highlight that depth‐dependent enzymatic processes should be considered in future SOC dynamic models. A free Plain Language Summary can be found within the Supporting Information of this article.

Dynamics of Soil Carbon Concentrations and Quality Induced by Agricultural Land Use in Central South Africa

Core Ideas Converting grasslands to cropland deprives soils of C regardless of lability or recalcitrant nature. Reversion into secondary grasslands can reverse soil C losses in semiarid agro‐ecosystems. Secondary grassland management improves SOC quality to resemble primary grasslands. Relative losses and gains of soil C fractions are modulated by climatic and soil conditions. Prolonged soil cultivation has been identified as a major cause of land degradation and a threat to soil quality in drought‐prone environments. This study evaluated land use effects on soil carbon (C) fractions and organic C (SOC) quality across three semiarid agro‐ecosystems (Harrismith, Tweespruit, and Kroonstad) in central South Africa. Soil samples were collected from croplands, primary and secondary grasslands at the 0‐ to 200‐mm layer in each agro‐ecosystem and analyzed for various soil C fractions. The SOC structure was characterized with 13C nuclear magnetic resonance (NMR) spectroscopy. All analyses were done on bulk soil samples. Conversion of primary grasslands into croplands decreased C fractions by 27 to 90% across the three agro‐ecosystems, with highest losses recorded in Harrismith and Tweespruit and lowest in Kroonstad, suggesting site‐specific conditions acted together with cultivation to effect C losses. The 13C NMR spectra revealed a slight change in SOC structural composition when O‐alkyl C decreased with concomitant increase in aromatic and alkyl C due to cultivation, with differences in the range of 1 to 11%. O‐alkyl C remained almost the same in Harrismith, suggesting that lignin‐derived methoxy groups were probably more dominant than easily decomposable carbohydrates as opposed to O‐alkyl C in Tweespruit and Kroonstad. Meanwhile, reversion of cultivated soils into perennial pastures restored and even increased some soil C fractions (by 3–129%) to represent primary grasslands, especially in Kroonstad. Organic C decomposition was lower in the cultivated soils relative to virgin and restored soils. This underscores the importance of determining plant biomass composition because these unusual responses were probably related to vegetation differences. Overall, this study demonstrates the potential of secondary grassland management to rehabilitate degraded cultivated soils with implications for restoration of agro‐ecosystem functions and services.

Revegetation affects soil denitrifying communities in a riparian ecotone

Denitrification is one of the most important processes in the nitrogen (N) cycle due to its permanently removing excess N from ecosystems into the atmosphere. In practice, revegetation has employed to facilitate the process for preventing nitrogen from terrestrial into aquatic ecosystems, in particular in the terrestrial-aquatic ecotone (i.e., riparian zone). However, how revegetation drives the shift in the denitrifying bacterial community and consequently alters denitrification is still unclear. In this study, we investigated soil denitrifiers in three vegetation types with respective dominant species of trees, shrubs and herbs in the water-level-fluctuate-zone in the Three Gorges Reservoir, China. We hypothesized that revegetation affected the composition of denitrifiers. Results revealed that the functional gene composition in herb samples was well separated from that in tree samples, which was dependent on the interactions between plant traits (i.e., species number and diversity, root C:N ratio) and environmental factors (i.e., soil temperature and pH). Herb soils has more abundance of nirS and nirK genes and nirS gene diversity due to their higher species number, soil pH, soil organic C, TN, soil C:N ratio and root C:N ratio compared with the shrub and tree soils. Vegetation types did not significantly affect soil denitrification rate, which could be largely explained by the combined effects of plant attributes (species number, root organic C and root N), and soil pH. Our results have demonstrated that herb plantations could increase the abundance of soil denitrifiers through altering both the quantity and quality of SOC and soil pH.

Effects of Biochar Pyrolyzed at Varying Temperatures on Soil Organic Carbon and Its Components:Influence on the Soil Active Organic Carbon

Soil active organic carbon is the most important carbon pool and a good indicator in ecosystem management due to its great significance in soil carbon cycling and soil quality.In order to investigate the effect of biochar (BC) addition on soil organic matter fractions,apple tree twigs were used to produce BC at 300,400,500 and 600℃,respectively.Elemental analysis and Fourier transform infrared (FTIR) spectroscopy were used to determine the characteristics of BC.Four kinds of BC were added into soils at five application rates (0,0.5%,1%,2% and 3%) and incubated at 25℃ in lab for over 360 days.Soil organic carbon (SOC),microbial biomass carbon (MBC),water soluble organic carbon (WSOC) and readily oxidized organic carbon (ROC) were measured during the incubation.The mass fraction of carbon (C) in the generated BC ranged from 62.20%-80.01%,while hydrogen (H) ranged from 2.72%-5.18% and Oxygen (O) ranged from 15.98%-30.92%.The increasing temperature increased the mass fraction of C,while decreased the O and H mass content,as well as the ratio of H/C and O/C.The addition of BC significantly increased SOC,and the treatments amended with BC500 had the highest increments.Compared with the control treatment (CK),the addition of BC produced at temperatures below 400℃ increased the contents of MBC,WSOC and ROC during the incubation,at the end of the incubation,BC300 treatments significantly increased the contents by 38.25%,82.09% and 63.53%(P<0.05),respectively;BC400 treatments significantly increased the contents by 26.07%,65.61% and 48.09%(P<0.05),respectively;while lower contents of MBC,WSOC and ROC were found in the treatments amended with BC produced at temperatures above 400℃ after 40-60 d incubation.After 360 d of incubation,the contents of MBC,WSOC and ROC were significantly decreased by 0.27%,13.48% and 14.67% in BC500 treatments and 7.80%,14.66% and 15.79% in BC600 treatments (except for the MBC in BC500 treatment)(P<0.05).The relative contents of ROC ranged from 3.39% to 15.65%,BC application decreased the relative content of ROC,suggesting that the increase was in proportion to the stability of organic carbon in the soil.Considering the content and quality of SOC,when the BC products were applied to the Loutu soil,500℃ was the optimal temperature for preparing apple-derived BC due to its significant increase of the soil organic carbon and a slight decrease of the relative content of soil active organic carbon.

Patient-Reported Outcomes from a Global Phase 3 Randomized Controlled Trial of Inotuzumab Ozogamicin Versus Standard of Care Chemotherapy for Relapsed/Refractory Acute Lymphoblastic Leukemia

Background: Inotuzumab Ozogamicin (InO), an anti-CD22 antibody-calicheamicin conjugate, has demonstrated superior clinical activity versus standard of care (SOC; intensive chemotherapy) for relapsed/refractory (R/R) acute lymphoblastic leukemia (ALL) in the phase 3 INO-VATE trial (Kantarjian. N Engl J Med. June 12, 2016 [E-pub]). A previous intent-to-treat (ITT) analysis of patient-reported outcomes (PROs) in 279 randomized patients demonstrated that InO is associated with generally better quality of life (QoL), functioning, and symptoms versus SOC (Kantarjian. J Clin Oncol 34, 2016 [abstract 7027]; data cutoff date, October 2, 2014). Herein, updated PROs results from 326 randomized patients are presented (data cutoff date, March 8, 2016; median follow-up, 6.6 [range, 0.03-39.75] months; long-term safety follow-up is ongoing).Methods: Patients were randomized to InO (max 1.8 mg/m2/cycle [≤6 cycles]) or SOC (fludarabine/cytarabine [ara-C]/granulocyte colony-stimulating factor, ara-C + mitoxantrone, or high-dose ara-C [≤4 cycles]) and completed the European Organization for Research and Treatment of Cancer Quality of Life Core Questionnaire (EORTC QLQ-C30) and the EuroQoL 5 Dimensions questionnaire (EQ-5D) Index and EQ visual analogue scale (EQ-VAS) at baseline, day 1 of each cycle, and end of treatment. Treatment differences in PRO measures over time were assessed in the ITT populationusing longitudinal mixed-effects models with random intercepts and slopes with treatment, time, treatment-by-time interaction, and baseline scores as covariates. Analyses were supportive and no multiplicity adjustments were made.Results: EORTC QLQ-C30 completion rates in patients receiving InO and SOC who completed ≥1 question were 85% and 65%, respectively; EQ-5D completion rates were similar. Baseline PRO scores were in general comparable for InO (n=164) and SOC (n=162) arms (eg, mean [SE] EORTC QLQ-C30 Global Health Status/QoL, 56.51 [2.06] vs 55.24 [2.18]; Physical, 73.69 [1.78] vs 73.48 [2.08], Role, 57.17 [2.67] vs 62.36 [2.97], Social functioning, 62.03 [2.52] vs 55.16 [3.17]; Appetite loss, 20.97 [2.31] vs 21.84 [2.62]; Dyspnea, 20.53 [2.34] vs 22.13 [2.55]; Fatigue, 40.84 [2.08] vs 40.23 [2.46]; EQ-5D Index, 0.77 [0.01] vs 0.76 [0.02]; EQ-VAS, 59.79 [2.12] vs 62.27 [2.03]). Compared with SOC, patients receiving InO reported numerically better QoL, functioning, and symptom scores (except for Constipation and Emotional functioning). After adjusting for baseline scores, as well as treatment, time, and treatment-by-time interaction, least squares mean [95% CI] differences in Physical, Role, Social functioning, and Appetite loss were statistically significant (6.9 [1.4-12.3], 11.4 [3.2-19.5], 8.4 [0.7-16.1], -8.7 [-16.0, -1.4], respectively; P<0.05); and exceeded 5 (generally considered the minimally important difference [MID] to be clinically meaningful) (Figure). Mean treatment differences in favor of InO inEQ-VAS and Global Health Status/QoL, dyspnea, and fatigue reached or were close to the MID of 5, although without statistical significance. There was no dimension that was clinically significantly worse in patients receiving InO compared with those receiving SOC.Conclusion: This updated analysis of PROs from the phase 3 INO-VATE trial with the full ITT population (n=326) adds to earlier findings based on a smaller ITT population that the superior clinical activity of InO versus SOC in patients with relapsed/refractory ALL is accompanied by generally better patient-reported QoL, functioning, and symptoms. Patients receiving InO were observed to have significantly better appetite, are significantly more ambulatory, and experience significantly less impact on family and social life. They were also observed to be significantly more able to perform strenuous activities, basic living needs, work, other daily activities, hobbies, and other leisure activities. These data support the favorable qualitative benefit risk ratio of InO for R/R ALL treatment, with superior clinical efficacy that does not compromise patients' QoL. [Display omitted] DisclosuresSu:Pfizer: Employment, Equity Ownership; Bristol Myers Squibb: Equity Ownership. Jabbour:ARIAD: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding; Novartis: Research Funding; BMS: Consultancy. Bhattacharyya:Pfizer Inc: Employment, Equity Ownership. Yan:Pfizer Inc: Employment, Equity Ownership. Shapiro:Pfizer Inc: Employment, Equity Ownership. Cappelleri:Pfizer Inc: Employment, Equity Ownership. Marks:Pfizer Inc: Consultancy, Membership on an entity's Board of Directors or advisory committees.

Microbial crop residue decomposition dynamics in organic and conventionally managed soils

Agricultural practices can influence soil microbial communities, which are the primary regulators of soil carbon and nutrient cycling processes. Differences in microbial community composition have the potential to affect the fate of carbon and nutrients during decomposition and may therefore influence the retention of C and provisioning of crop nutrients in agroecosystems. Long term management-induced shifts in microbial communities and resource availability may interact to affect the microbial utilization of fresh inputs of crop residues in the short term, with lasting impacts on soil C accrual and fertility. The objective of this study was to investigate whether long-term organic and conventional management resulted in differences in microbial residue decomposition. Soils under conventional and organic management planted with annual crops or with a mix of annual crops and three years of perennial alfalfa were collected from a long-term (19 y) field study in Saskatchewan, Canada and were incubated in the laboratory with and without 13C-labelled barley residues for 98d. We measured extracellular enzyme activities (EEAs) and the incorporation of crop residue-derived C within major microbial groups (fungi, actinobacteria, and Gram positive and negative bacteria) during decomposition. Total PLFA biomass and EEAs were highest in soils from the conventional-annual system, similar between the conventional and organic perennial systems, and similar or lowest in the organic-annual system. Crop residue additions alleviated these differences; that is, in residue-amended soils total PLFA biomass, EEAs, and the abundance of the fungal biomarker increased in the organic systems compared to the unamended soils to become similar to the conventional systems. In contrast, residue additions induced small or no changes in biomass and EEAs in the conventional-annual soils. Using 13C-PLFA-SIP we showed that the general pattern of microbial succession during decomposition was similar among soils, but that fungi and especially actinobacteria were relatively more dominant in organic compared to conventionally managed soils during early and later stages of decomposition, respectively. Thus, shifts in the decomposer community composition were greater in soils originating from organic management, possibly as a result of larger changes in resource availability during the incubation that advanced the rate of microbial succession. This may reinforce long term differences in SOC quality and nutrient availability between management regimes. Organically-managed cropping systems are particularly reliant on biological cycling of organic nutrients to support crop growth. This work reinforces the importance of adequate crop residue returns for maintaining soil function, particularly where external organic amendments are not applied to balance nutrients exported as crop products.

Disentangling the effects of conservation agriculture practices on the vertical distribution of soil organic carbon. Evidence of poor carbon sequestration in North- Eastern Italy

Conservation agriculture is one of the agro-environment measures promoted by the Veneto Region (North-eastern Italy) to regulate and support many ecosystem services. This study compared conventional and conservation agriculture management systems in order to evaluate their effects on both SOC stocks and quality i.e. humic C and its molecular weight fractions, microbial C and N. The experiment was set up in 2010 on three farms in Veneto Region. In order to improve the monitoring procedures, a massive soil sampling programme was conducted in 2011 and 2014 in ca. 150 positions, considering the SOC stratification within a 0–50cm profile.Results suggested that conservation agriculture practices affected SOC distribution rather than its total amount. The retention of crop residues on the soil surface and the absence of tillage operations drove SOC dynamics in the top layer (0–5cm) of the conservation system, while residues incorporation with ploughing was responsible for SOC accumulation at the 30–50cm depth in the conventional one. SOC stock variation in the conservation treatment was also influenced by root C input, which was identified as a major factor able to promote SOC accumulation in the 0–30cm profile. The role of clay on SOC dynamics was not uniform in the three farms since it depended both on the clay amount and its mineral composition. The strong interactions existing between management systems and local soil conditions were also confirmed by the C quality analyses.This research did not demonstrate the benefits of conservation practices on SOC sequestration during the transition period. However, SOC sequestration is only one of the numerous ecosystem services provided by conservation practices. Some of these depend on the C content and quality in the top layers that, as demonstrated in our work, were strongly affected by the C stratification processes triggered by conservation agriculture.

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.

Lasting influence of biochemically contrasting organic inputs on abundance and community structure of total and proteolytic bacteria in tropical soils

The SOM field experiments in Kenya, which have been initiated in 2002 on two contrasting soils (clayey Humic Nitisol (sand: 17%; silt: 18%; clay: 65%) at Embu, sandy Ferric Alisol (sand: 66%; silt: 11%; clay: 22%) at Machanga), were used for exploring the effect of nine year annual application of biochemically contrasting organic inputs (i.e., Zea mays (ZM; C/N ratio: 59; (lignin + polyphenols)-to-N ratio: 9.8); Tithonia diversifolia (TD; 13; 3.5); Calliandra calothyrsus (CC; 13; 6.7)) on the soil bacterial decomposer community. Soil samples were taken at the onset of the rainy season before application of fresh organic inputs in March 2011. We studied the abundance (quantitative PCR) and community structure (T-RFLP analysis) of the total (i.e., 16S rRNA gene) and specifically proteolytic (i.e., npr gene encoding neutral metalloproteases) bacteria. Alterations of the soil microbial decomposer community were related to differences of quantity (i.e., soil carbon (TC)) and particularly composition of SOC, where mid-infrared spectroscopic (DRIFTS) information, and contents of extractable soil polyphenol (PP) and the newly introduced PP-to-TC ratio served as SOC quality indicators. For total bacteria, effect of organic input quality was minor in comparison to the predominant influence of soil texture. Elevated soil PP content, driven by polypheneol rich organic inputs, was not suppressive for overall bacterial proliferation, unless additional decomposable C substrates were available as indicated by PP-to-TC ratios. In contrast to the total bacterial community, biochemical quality of organic inputs exposed a stronger effect on functionally specialized bacterial decomposers, i.e., proteolytic bacteria. The npr gene abundance was depressed in the TD treated soils as opposed to soils receiving CC, and showed a positive correlation with soil PP. It was suggested that the high presence of lignin and polyphenol relative to the N content in organic inputs was increasing the npr gene abundance to counteract most likely the existence of polyphenol–protein complexes aggravating protein degradation. We concluded from our study that integration of spectroscopic, geochemical (i.e., soil PP) and molecular soil data provides a novel pathway to enhance our understanding of the lasting effect of organic input quality induced SOC quality changes on bacterial decomposers and particularly proteolytic bacteria driving soil organic N cycling.

Aggregation and soil organic carbon fractions under different land uses on the tableland of the Loess Plateau of China

Land uses and cultivation are important factors controlling SOC storage on the Loess Plateau. These factors may also affect the relative importance of different mechanisms for the stabilization of organic matter in the soil. Easily oxidizable organic carbon (EOC), aggregation and aggregate C fractions in the soil were measured under different land uses. Aggregates were fractionated using a wet-sieving procedure to obtain the distribution of water-stable aggregates. The fractions of aggregates, aggregate SOC and aggregate EOC in grassland and forestland were generally higher than those in farmland. Furthermore, because conventional cultivation destroyed aggregates, the dominant aggregate size fractions were <0.5mm for farmland and >0.5mm for other land uses. Compared to the corresponding values in farmland, the mean weight diameter (MWD) in forestland and grassland increased by 808%–417%, and the stability ratio of water-stable aggregate (WSAR) increased by 920%–553%. Aggregate formation and its dominant size fraction were associated closely with its carbon fractions. SOC and EOC in farmland tended to be concentrated in smaller-sized aggregates, whereas SOC and EOC under other land uses tended to concentrate in larger-sized aggregates. EOC tended to concentrate in larger aggregates than SOC. The small fractions of the aggregates formed large fractions by combining with fresh organic matter. So converting slope farmland to forestland and grassland could improve the storage and quality of SOC, and the tendency of SOC transfer.

Effect of wildfires on soil respiration in three typical Mediterranean forest ecosystems in Madrid, Spain

Mediterranean forests are vulnerable to numerous threats including wildfires due to a combination of climatic factors and increased urbanization. In addition, increased temperatures and summer drought lead to increased risk of forest fires as a result of climate change. This may have important consequences for C dynamics and balance in these ecosystems. Soil respiration was measured over 2 successive years in Holm oak (Quercus ilex subsp. ballota; Qi); Pyrenean Oak (Quercus pyrenaica Willd; Qp); and Scots pine (Pinus sylvestris L.; Ps) forest stands located in the area surrounding Madrid (Spain), to assess the long term effects of wildfires on C efflux from the soil, soil properties, and the role of soil temperature and soil moisture in the variation of soil respiration. Soil respiration, soil temperature, soil moisture, fine root mass, microbial biomass, biological and chemical soil parameters were compared between non burned (NB) and burned sites (B). The annual C losses through soil respiration from NB sites in Qi, Qp and Ps were 790, 1010, 1380 gCm−2 yr−1, respectively, with the B sites emitting 43 %, 22 % and 11 % less in Qi, Qp and Ps respectively. Soil microclimate changed with higher soil temperature and lower soil moisture in B sites after fire. Exchangeable cations and the pH also decreased. The total SOC stocks were not significantly altered, but 6–8 years after wildfires, there was still measurably lower fine root and microbial biomass, while SOC quality changed, indicated by lower the C/N ratio and the labile carbon and a relative increase in refractory SOC forms, which resulted in lower Q10 values. We found long term effects of wildfires on the physical, chemical and biological soil characteristics, which in turn affected soil respiration. The response of soil respiration to temperature was controlled by moisture and changed with ecosystem type, season, and between B and NB sites. Lower post-burn Q10 integrated the loss of roots and microbial biomass, change in SOC quality and a decrease in soil moisture.