[Show abstract][Hide abstract] ABSTRACT: The relationship between degradation speed of soil-buried biodegradable polyester film in a farmland and the characteristics of the predominant polyester-degrading soil microorganisms and enzymes were investigated to determine the BP-degrading ability of cultivated soils through characterization of the basal microbial activities and their transition in soils during BP film degradation. Degradation of poly(butylene succinate-co-adipate) (PBSA) film was evaluated in soil samples from different cultivated fields in Japan for 4 weeks. Both the degradation speed of the PBSA film and the esterase activity were found to be correlated with the ratio of colonies that produced clear zone on fungal minimum medium-agarose plate with emulsified PBSA to the total number colonies counted. Time-dependent change in viable counts of the PBSA-degrading fungi and esterase activities were monitored in soils where buried films showed the most and the least degree of degradation. During the degradation of PBSA film, the viable counts of the PBSA-degrading fungi and the esterase activities in soils, which adhered to the PBSA film, increased with time. The soil, where the film was degraded the fastest, recorded large PBSA-degrading fungal population and showed high esterase activity compared with the other soil samples throughout the incubation period. Meanwhile, esterase activity and viable counts of PBSA-degrading fungi were found to be stable in soils without PBSA film. These results suggest that the higher the distribution ratio of native PBSA-degrading fungi in the soil, the faster the film degradation is. This could be due to the rapid accumulation of secreted esterases in these soils.
AMB Express 12/2015; 5(1). DOI:10.1186/s13568-014-0088-x
[Show abstract][Hide abstract] ABSTRACT: Pyrolysis of waste biomass is a promising technology to produce sterile and renewable organic phosphorus fertilizers. Systematic studies are necessary to understand how different pyrolysis platforms influence the chemical speciation of dissolved (bioavailable) phosphorus. This study employed solution-phase 31P NMR analyses on slow pyrolysis, fast pyrolysis, and flash carbonization charcoals. Dissolved P speciation of ash-rich (15-62 wt%) biochars produced from manures, sewage sludge, and corn stover were compared with low ash (2-5 wt%) pecan shell biochars. Each biochar was sequentially extracted to investigate the strongly complexed (by NaOH-EDTA; 250 mM NaOH+5 mM EDTA for 16 h) and acid-extractable (by acidic oxalate; 200 mM oxalate at pH 3.5 for 4 h) P fractions. In NaOH-EDTA extracts, P concentration correlated (p < 0.0005) with Zn (r = 0.89), Mn (r = 0.90), and Mg (r = 0.98) concentrations. A strong correlation between orthophosphate and Mg (r = 0.98, p < 0.0005; n = 13) indicated the presence of Mg orthophosphate (and struvite or whitlockite) in all biochars. Only in acidic oxalate extracts, P concentration correlated (p < 0.0005) with Al (r = 0.87) and Fe (r = 0.92) concentrations. Pyrophosphate (P2O74-) persisted (23-52% of total P in NaOH-EDTA extracts) in low-ash pecan shell 300-700 °C slow pyrolysis biochars. In contrast, ash-rich biochars were primarily (≥90%) composed of inorganic orthophosphate (PO43-), except 350 °C slow pyrolysis swine manure biochar (26% pyrophosphate) and sewage sludge-derived flash carbonization charcoal (14% pyrophosphate). Solid-state 13C cross polarization and magic angle spinning NMR analyses of bulk aromaticity indicated partially carbonized (aliphatic) nature of 350 °C swine manure biochar. Surface functional groups of swine manure and sewage sludge biochars could stabilize pyrophosphate by (i) utilizing bridging cations (Al3+, Fe3+, and Mg2+) to form stable six-membered ring complexes, and (ii) direct hydrogen bonding.
[Show abstract][Hide abstract] ABSTRACT: To evaluate organic carbon (OC) accumulation processes in peat deposits in tropical mangrove ecosystems, solid-state 13C cross-polarization and magic angle spinning nuclear magnetic resonance signals were measured to determine the OC compositions of decomposed leaves and roots. These account for a large majority of mangrove litters and mangrove peat in a coral reef-type Rhizophora forest on Pohnpei Island, Federated States of Micronesia. Radiocarbon dating was also used to understand the sources of peat deposits at each depth. The mass loss rate of mangrove leaves during 1-year litterbag incubation was much higher than that of roots. These mass loss rates are expected to be affected by the varying chemical characteristics of leaves and roots and the different aerobic/hydrological conditions present in the two litter types during decomposition. The decomposability of individual OC components also varied markedly between leaf and root litters. Significant increases in aryl-C/O-alkyl-C and aliphatic-C/O-alkyl-C ratios and minor increases in the aryl-C/aliphatic-C ratio during leaf decomposition implied that O-alkyl-C was more labile than aryl- and aliphatic-C and that aliphatic-C was also slightly more decomposable than aryl-C, but not significantly so, in leaf litters on the forest floor. Regarding roots, a stable aryl-C/O-alkyl-C ratio during decomposition suggested that aryl- and O-alkyl-C components did not differ greatly in decomposability in the peat deposit, while the minor increase in the aliphatic-/O-alkyl-C ratio and the substantial decrease in the aryl-/aliphatic-C ratio with decomposition implied that aliphatic-C was more recalcitrant than aryl- and O-alkyl-C in the peat. The OC compositional properties were quite homogenous throughout the peat profile, and 14C dating mostly indicated modern, which suggest that large amounts of mangrove roots penetrate to at least 80 cm depth. These findings provide quantitative and qualitative insights into the potential importance of very high production of mangrove fine roots for OC accumulation in peat in tropical mangrove ecosystems.
[Show abstract][Hide abstract] ABSTRACT: To conserve indigenous natural ecosystem and help in the recovery of natural vegetation on Nakoudojima Island, which is a subtropical oceanic island in Ogasawara Islands in Japan, we clarified the mechanisms of the changes in soil chemical properties as affected by soil erosion and seabird activities on the island. Under grassland vegetation where influence of feral goat (exotic species) had been severe, the chemical properties of surface soils with a thickness of 5 cm were variable even in a small area of 0.375 km2; pH(H2O) value range between 4.6 and 6.9, total C content range between 0.36 and 5.62%, total N content range between 0.03 and 0.45%, exchangeable acidity range between 0.5 and 50 mmolc kg− 1, and plant-available phosphate (Bray II P) range between 0.4 and 170 mg P2O5 100 g− 1. By clarifying soil profile characteristics under natural and disturbed vegetation and distribution patterns of these soils on the island, the changes in the soil chemical properties were reasonably assigned to the effect of soil erosion caused by feral goats for increased soil exchangeable acidity and decreased soil pH (mainly found in inland area) and to the effect of seabird activities for increased Bray II P and soil exchangeable acidity and decreased soil pH (mainly found in outer rim area with high altitude). It was also clarified that the high soil exchangeable acidity was significantly related to the low productivity of plant biomass for these plots (P < 0.01). Soil erosion would have removed surface soils having weak acidity and exposed subsoils having strong acidity to the ground surface, resulting in inhibition of plant growth and delay of vegetation recovery. Based on the findings obtained in the present study, several options were proposed to stop soil erosion and to recover the vegetation, although careful preliminary examination would be necessary for applying them.
[Show abstract][Hide abstract] ABSTRACT: Dissolved organic carbon (DOC) components of soil amendments such as biochar will influence the fundamental soil chemistry including the metal speciation, nutrient availability, and microbial activity. Quantitative correlation is necessary between (i) pyrogenic DOC components of varying aromaticity and ionizable (carboxyl, hydroxyl) substituents and (ii) bulk and solution properties of biochars. This study employed fluorescence excitation-emission (EEM) spectrophotometry with parallel factor analysis (PARAFAC) to understand the influence of pyrolysis platform (flash and high-yield carbonization, slow pyrolysis, and fast pyrolysis) and solution pH on the DOC structure of carbonaceous materials. The PARAFAC fingerprint representative of conjugated, polyaromatic DOC correlated (Pearson’s r ≥ 0.6, p < 0.005) with (i) volatile matter content and (ii) total organic carbon and nitrogen concentrations in water and base (50-100 mM NaOH) extracts. Electric conductivity of the extracts correlated with S (indicative of labile sulfate species) and Na+K concentrations (r > 0.9, p < 0.0005). The pH-dependent changes in fluorescence peak position and intensity suggested (i) protonation of carboxylate/phenolic functionalities and (ii) acid-induced aggregation of colloidal particles for ≤350 °C slow pyrolysis biochars; DOC of high-yield/flash carbonization charcoals and ≥500 °C slow pyrolysis biochars were less sensitive to pH. Solid state 13C cross polarization and magic angle spinning NMR analysis of bulk aromaticity (-C=C- peak at 110-160 ppm) suggested that both recalcitrant and labile fluorescence DOC fingerprints are composed of polyaromatic structures that begin to form near 350 °C. These biochar-borne DOC of varying aromaticity and carboxyl substituents will participate in hydrophobic and H-bonding interactions with soil components that will ultimately impact the biogeochemical cycles.
Energy & Fuels 04/2015; 29(4):2503-2513. DOI:10.1021/acs.energyfuels.5b00146 · 2.79 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Organic matter (OM) bound to soil mineral particles (higher-density particles) tends to be more stabilized, enriched in 13C and 15N, and has a lower C:N ratio. Yet how these variations in OM chemistry are linked to the nature of organo-mineral assemblage remains poorly understood, especially in allophanic soils where high amounts of OM are stabilized by interactions with reactive inorganic phases such as short-range-order (SRO) minerals. We thus assessed the extent to which the degree of aggregation and its disruption during fractionation control the distribution and chemistry of the soil organo-mineral particles across six density fractions using a volcanic soil (allophanic Andisol) based on selective dissolution, microscopy (SEM), solid-state 13C NMR spectroscopy and δ13C and δ15N analyses. Intermediate-density fractions (2.0-2.5 g cm− 3) accounted for 63-86% of organic C and N, 73-93% of pyrophosphate-extractable iron and aluminum (Fep, Alp), and 78-95% of oxalate-extractable metals (Feo, Alo) in the bulk soil sample. While air-drying pretreatment had little effect, sonication during fractionation led to (i) fragmentation of both plant detritus and some of the aggregates of 30-100 mm sizes, (ii) release of occluded low-density fraction (< 1.6 g cm− 3) which largely originated from the aggregates of 1.6-2.0 g cm− 3 density range, and (iii) redistribution of organo-mineral particles (15-16% of total OM and 7-19% of the extractable metals) within the intermediate density fractions. Positive correlation of Alp with C:N ratio and negative correlation of Alp with δ15N among the fractions suggest preferential binding of Alp phase (e.g., organo-Al complexes) to decaying plant detritus. Positive correlation of Alo and Feo with δ15N, together with theoretical density calculations of idealistic organo-mineral association modes, suggests that 15N enrichment may be coupled with OM binding to SRO minerals and with the formation of physically-stable aggregates of micron/submicron sizes in accord with our conceptual model (Asano and Wagai, 2014). The general pattern of 13C and 15N enrichment and C:N decline with increasing particle density remained largely unchanged despite the sonication effects detected, indicating that sonication-resistant organo-mineral assemblages largely control the observed patterns. The similarity in the density-dependent changes of OM chemistry between the studied Andisol and the soils with crystalline clay and metal oxide mineralogies in previous studies strongly suggests a common biogeochemical control which deserves further investigation.
[Show abstract][Hide abstract] ABSTRACT: This study examined the recovery, via biotic and abiotic pathways, of a grassland ecosystem after eradication of introduced exotic goats. We used path analyses to evaluate the relative strength of relationships among aboveground biomass, soil chemical properties (carbon, nitrogen, and phosphorus content; soil acidity), presence of nesting seabirds after goat eradication, extent of vegetation degraded by goats before their eradication, plant species composition after removal of goats, and topography. Models including the same variables with different paths were constructed using the Bayesian estimation method, and the best-fit models were constructed by comparing deviance information criterion values. Results of the path analyses demonstrated that vegetation degradation and soil erosion prior to goat eradication increased soil exchangeable acidity, which resulted in limitation of aboveground biomass. Seabird nesting after goat eradication increased the quantity of soil nutrients, possibly through inputs of feces, eggshells, and dead chicks or adults. The increase in nutrients was affected indirectly, via seabird nesting, by topography and vegetation type after goat eradication. The direct and indirect relationships demonstrated by our results suggest the existence of complex interrelationships during recovery of ecosystem function after eradication of exotic mammals.
[Show abstract][Hide abstract] ABSTRACT: Aluminum (Al) accumulators are widely distributed in the plant kingdom but phylogenetic implications of internal Al detoxification mechanisms are not well understood. We investigated differences in the characteristics of Al accumulation (i.e., accumulation potential, chemical form, and localization) in three woody Al accumulators, Symplocos chinensis (Symplocaceae, Ericales), Melastoma malabathricum, and Tibouchina urvilleana (both Melastomataceae, Myrtales). The order of Al accumulation potential under hydroponic conditions was S. chinensis ≈ M. malabathricum > T. urvilleana. Oxalate was at least partly involved in the internal Al detoxification mechanisms in leaves of all three Al accumulators, based on a correlation analysis between Al and organic acid in water and 0.02 M HCl extracts and the 27Al nuclear magnetic resonance spectra of intact leaves. However, the Al forms in the leaves were not simple Al-ligand complexes in a specific cell structure. Al localization in leaf sections differed among the three species. Extremely high levels of Al were found in trichomes of the lower epidermis in leaves of T. urvilleana. These data illustrate that woody Al accumulating angiosperms have independently developed various internal Al tolerance mechanisms in which oxalate plays a significant role.
[Show abstract][Hide abstract] ABSTRACT: Okayama and Tochigi, all sites are under forest. New Zealand sites were Ngahinapouri, Waihora and Whatawhata. They are under pasture. Soil samples were collected from different soil depths (Fig. 1 & Table 1). The degree of SWR was measured as the soil-water contact angle using the SDM and the MED test. The persistence of SWR was determined with the WDPT. MED: Measures the molarity of an ethanol (M) droplet requires for a droplet to infiltrate in 5 s. Contact angle (α i) was measured using following equations. íµí»¾ íµí± = 61.05 − 14.75 ln(íµí± + 0.5) cos α i = (γ c / γ L) 1/2 -1 (Carillo et al., SDM Microphotograph of a water droplet placed on an adhesive tape was taken using digital microscope. The soil-water contact angle was directly measured. ~100 o 100 µm The relationships between SWR parameters and SOC were agreed well with recently published work of Kawamoto et al. (2007) and Karunarathna et al. (2010). While the Japanese soils had high SOC contents below 10 cm depths, these horizons were not water repellent. Therefore, further studies are scheduled to analyze quality of SOC utilizing a C-solid NMR technique, targeting to characterize surface functional groups of soil organic materials.
[Show abstract][Hide abstract] ABSTRACT: Soil water repellency (SWR) is known to lead to preferential flow and to degrade the soil's filtering efficiency. However, no method is available to quantify directly how SWR affects the transport of reactive solutes. We propose a new method for conducting solute transport experiments in water-repellent soils. It involves sequentially applying two liquids, one water, the other a reference fully wetting liquid, namely aqueous ethanol, to the same intact soil core with air-drying between liquids. We applied this approach to quantify the impact of SWR on the filtering of the herbicide 2,4-Dichlorophenoxyacetic acid (2,4-D) in two Andosols. In batch experiments conducted prior to the transport experiments, 2,4-D sorption was not influenced by aqueous ethanol for one soil. However, sorption in the second soil followed the co-solvency theory, which predicts decreasing sorption with increasing solvent fractions. Thus, sorption experiments are necessary to complement our new method. Breakthrough curves were characterized by preferential flow with large initial concentrations, tailing and a long prevalence of solutes remaining in the soil. In the soil in which 2,4-D sorption was unaffected by aqueous ethanol, SWR increased 2,4-D losses by four and 50 times in the first 5-mm outflow compared with the 2,4-D losses with water. After 50-mm outflow, the 2,4-D losses were similar for one core, but in the other core they were still about four times greater with water than with aqueous ethanol. This method to quantify the reduction of the soil's filtering efficiency by SWR is needed for assessing the increased risk of groundwater contamination by solutes exogenously applied to water-repellent soils.
European Journal of Soil Science 03/2014; 65(3). DOI:10.1111/ejss.12136 · 2.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Pyrolysis of plant and animal wastes produces a complex mixture of phosphorus species in amorphous, semi-crystalline, and crystalline inorganic phases, organic (char) components, and within organo-mineral complexes. In order to understand the solubility of different phosphorus species, plant (cottonseed hull) and manure (broiler litter) wastes were pyrolyzed at 350, 500, 650, and 800 °C, and exposed to increasingly more rigorous extraction procedures: water (16 h), Mehlich 3 (1 mM EDTA at pH 2.5 for 5 min), oxalate (200 mM oxalate at pH 3.5 for 4 h), NaOH-EDTA (250 mM NaOH+5 mM EDTA for 16 h), and total by microwave digestion (conc. HNO3/HCl + 30% H2O2). Relative to the total (microwave digestible) P, % extractable P increased in the following order: M3 < oxalate ≈ water < NaOH-EDTA for plant biochars; water < M3 < NaOH-EDTA < oxalate for manure biochars. Solution phase 31P NMR analysis of NaOH-EDTA extracts showed the conversion of phytate to inorganic P by pyrolysis of manure and plant wastes at 350 °C. Inorganic orthophosphate (PO43-) became the sole species of ≥500 °C manure biochars, whereas pyrophosphate (P2O74-) persisted in plant biochars up to 650 °C. These observations suggested the predominance of (i) amorphous (rather than crystalline) calcium phosphate in manure biochars especially at ≥650 °C, and (ii) strongly complexed pyrophosphate in plant biochars (especially at 350-500 °C). Correlation (Pearson's) was observed between (i) electric conductivity and ash content of biochars with the amount of inorganic P species, and (ii) total organic carbon and volatile matter contents with the organic P species.
Journal of Agricultural and Food Chemistry 02/2014; 62(8). DOI:10.1021/jf4053385 · 2.91 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: At 12,900 a BP, the eruption of the Laacher See volcano generated a new parent material forHolocene soil formation in parts of Western Germany. Weathering of these ashes commonly includes the formation of poorly crystalline minerals such as allophane, imogolite and ferrihydrite. Detection of these minerals in soil is difficult, yet an important task, because they may govern soil functions and processes, e.g., stabilisation of organic matter and
nutrient availability. Therefore, we characterised three forested Andosols by a combination of wet-chemical
and spectroscopic techniques including infrared and (27Al, 29Si) nuclear magnetic resonance (NMR) spectroscopy together with X-ray diffractometry. Deconvoluting the 29Si-NMR spectra revealed that 1.6 to 10.4% of total Si was present as allophanic compounds, which coincided with the amounts of oxalate-extractable Si. Since extraction methods are not completely selective,we observed a slight overestimation of allophanic Si estimated from oxalate extraction. Although the sites under study are located close to each other in similar relief positions and with similar vegetation, the combination of our results revealed varying amounts of loess in the parent materials and varying weathering intensity. High weathering intensities correlate with the amounts of allophane.
Chemical Geology 01/2014; 363:13-21. DOI:10.1016/j.chemgeo.2013.10.029 · 3.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To establish a rapid high-throughput evaluation system for the enhanced plant growth-inhibitory activity caused by modifications of cis-cinnamic acid's (cis-CA's) chemical structure, a DNA microarray assay was used to analyze the changes in early gene responses of Arabidopsis thaliana seedlings. After a 6-hr exposure to (Z)-3-(3-iodophenyl)acrylic acid, we observed an upregulation in three classes of early auxin-responsive genes, which was similar to the transcriptional response to indole-3-acetic acid (IAA), together with an upregulation of the genes related to environmental stress and toxin detoxification responses. Gene responses to 2-(3,4-dihydronaphthalen-1-yl)acetic acid were similar to those to IAA. In contrast, fewer genes were upregulated in response to its double-bond isomer, (Z)-2-[3,4-dihydronaphthalen-1(2H)-ylidene]acetic acid, than to cis-CA. DNA microarray data suggest that the structurally different cis-CA analogues trigger diverse gene responses. (C) Pesticide Science Society of Japan
[Show abstract][Hide abstract] ABSTRACT: 1-O-cis-Cinnamoyl-β-d-glucopyranose is known to be one of the most potent allelochemical candidates and was isolated from Spiraea thunbergii Sieb by Hiradate et al. (2004), who suggested that it derived its strong inhibitory activity from cis-cinnamic acid, which is crucial for phytotoxicity. In this study, key structural features and substituent effects of cis-cinnamic acid (cis-CA) on lettuce root growth inhibition was investigated. These structure-activity relationship studies indicated the importance of the spatial relationship of the aromatic ring and carboxylic acid moieties. In this context, conformationally constrained cis-CA analogues, in which the aromatic ring and cis-olefin were connected by a carbon bridge, were designed, synthesized, and evaluated as plant growth inhibitors. The results of the present study demonstrated that the inhibitory activities of the five-membered and six-membered bridged compounds were enhanced, up to 0.27μM, and were ten times higher than cis-CA, while the potency of the other compounds was reduced.
[Show abstract][Hide abstract] ABSTRACT: 1-O-cis-Cinnamoyl-β-d-glucopyranose is one of the most potent allelochemicals that has been isolated from Spiraea thunbergii Sieb by Hiradate et al. It derives its strong inhibitory activity from cis-cinnamic acid (cis-CA), which is crucial for phytotoxicity. By preparing and assaying a series of cis-CA analogues, it was previously found that the key features of cis-CA for lettuce root growth inhibition are a phenyl ring, cis-configuration of the alkene moiety, and carboxylic acid. On the basis of a structure-activity relationship study, the substituent effects on the aromatic ring of cis-CA were examined by systematic synthesis and the lettuce root growth inhibition assay of a series of cis-CA analogues having substituents on the aromatic ring. While ortho- and para-substituted analogues exhibited low potency in most cases, meta-substitution was not critical for potency, and analogues having a hydrophobic and sterically small substituent were more likely to be potent. Finally, several cis-CA analogues were found to be more potent root growth inhibitors than cis-CA.
[Show abstract][Hide abstract] ABSTRACT: In addition to the 17 essential elements needed for plants to complete their life cycle, the soil contains various non-essential elements, which plants may absorb. Interestingly, some plant species accumulate very high concentrations of non-essential element in their shoots. These species are often called “(hyper) accumulators”. It has been suggested that the distribution of accumulators is phylogenetically determined. Whereas many studies focused on accumulation of various elements in angiosperms, little information about is available for pteridophytes (ferns). Therefore, we performed a comprehensive element analysis in leaves of pteridophytes, and examined their aluminium (Al) accumulation in more detail.
17th International Plant Nutrition Colloquium, Istanbul, Turkey; 08/2013
[Show abstract][Hide abstract] ABSTRACT: Eucalyptus (Eucalyptus camaldulensis) has relatively high resistance to aluminum (Al) toxicity than the various herbaceous plants and model plant species. To investigate Al-tolerance mechanism, the metabolism of organic acids and the chemical forms of Al in the target site (root tips) in Eucalyptus was investigated. To do this, 2-year old rooted cuttings of E. camaldulensis were cultivated in half-strength Hoagland solution (pH 4.0) containing Al (0, 0.25, 0.5, 1.0, 2.5 and 5.0mM) salts for 5weeks; growth was not affected at concentrations up to 2.5mM even with Al concentration reaching 6000μgg(-1) DW. In roots, the citrate content also increased with increasing Al application. Concurrently, the activities of aconitase and NADP(+)-isocitrate dehydrogenase, which catalyze the decomposition of citrate, decreased. On the other hand, the activity of citrate synthase was not affected at concentrations up to 2.5mM Al. (27)Al-NMR spectroscopic analyses were carried out where it was found that Al-citrate complexes were a major chemical form present in cell sap of root tips. These findings suggested that E. camaldulensis detoxifies Al by forming Al-citrate complexes, and that this is achieved through Al-induced citrate accumulation in root tips via suppression of the citrate decomposition pathway.
[Show abstract][Hide abstract] ABSTRACT: Temperature sensitivity of soil organic matter (SOM) decomposition may have a significant impact on global warming. Enzyme-kinetic hypothesis suggests that decomposition of low-quality substrate (recalcitrant molecular structure) requires higher activation energy and thus has greater temperature sensitivity than that of high-quality, labile substrate. Supporting evidence, however, relies largely on indirect indices of substrate quality. Furthermore, the enzyme-substrate reactions that drive decomposition may be regulated by microbial physiology and/or constrained by protective effects of soil mineral matrix. We thus tested the kinetic hypothesis by directly assessing the carbon molecular structure of low-density fraction (LF) which represents readily accessible, mineral-free SOM pool. Using five mineral soil samples of contrasting SOM concentrations, we conducted 30-days incubations (15, 25, and 35 °C) to measure microbial respiration and quantified easily soluble C as well as microbial biomass C pools before and after the incubations. Carbon structure of LFs (<1.6 and 1.6-1.8 g cm(-3) ) and bulk soil was measured by solid-state (13) C-NMR. Decomposition Q10 was significantly correlated with the abundance of aromatic plus alkyl-C relative to O-alkyl-C groups in LFs but not in bulk soil fraction or with the indirect C quality indices based on microbial respiration or biomass. The warming did not significantly change the concentration of biomass C or the three types of soluble C despite two- to three-fold increase in respiration. Thus, enhanced microbial maintenance respiration (reduced C-use efficiency) especially in the soils rich in recalcitrant LF might lead to the apparent equilibrium between SOM solubilization and microbial C uptake. Our results showed physical fractionation coupled with direct assessment of molecular structure as an effective approach and supported the enzyme-kinetic interpretation of widely observed C quality-temperature relationship for short-term decomposition. Factors controlling long-term decomposition Q10 are more complex due to protective effect of mineral matrix and thus remain as a central question.
Global Change Biology 04/2013; 19(4):1114-25. DOI:10.1111/gcb.12112 · 8.04 Impact Factor