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In this study, we aimed to investigate lignin accumulation and its relationship with the composition of bacterial laccase-like genes in three arable lands (i.e., upland limestone soil (UL), upland red soil (UR), and upland-paddy rotation red soil (UPR)), which are subjected to long-term straw incorporation. After 9-13 years of straw incorporation, the lignin content significantly increased from 337.1, 414.5, and 201.6 mg/kg soil to 2096.5, 2092.4, and 1972.2 mg/kg soil in UL, UR, and UPR, respectively. The dominant lignin monomer changed from vanillyl (V)-type to cinnamyl (C)-type in UR. Both V- and C-types were the dominant monomers in UPR, and V-type monomer remained the dominant monomer in UL. Compared with the treatment without straw, straw incorporation significantly promoted the activity of laccase enzyme and the abundance of bacterial laccase-like genes in all soils. The redundancy analysis showed that the main influencing factors on lignin accumulation patterns with straw incorporation were the laccase enzyme activity, nitrogen availability, and some specific bacterial communities possessing the laccase-like genes (e.g., Thermotogae and Acidobacteria). The variation partitioning analysis confirmed that the strongest influencing factor on lignin accumulation was the composition of bacterial laccase-like genes (explained 31.4% of variance). The present study provides novel insights into the importance of bacterial laccase-like genes in shaping lignin monomer accumulation with straw incorporation in arable soils. [ABSTRACT FROM AUTHOR]

Laccase enzymes produced by both soil bacteria and fungi play important roles in refractory organic matter turnover in terrestrial ecosystems. We investigated the abundance and diversity of fungal laccase genes and bacterial laccase-like genes in soil from subtropical arable lands, and identified which microbial group was associated with laccase activity. Compared with fungal laccase genes, the bacterial laccase-like genes had greater abundance, richness and Shannon-Wiener diversity. More importantly, laccase activity can be explained almost exclusively by the bacterial laccase-like genes, and their abundance had significant linear relationship with laccase activity. Thus, bacterial laccase-like gene has great potential to be used as a sensitive indicator of laccase enzyme for refractory organic matter turnover in subtropical arable lands. [ABSTRACT FROM AUTHOR]

Flue-cured tobacco ( Nicotiana tabacum L.) production is important since there are still more than 300 millions of smokers in China. It is essential to allocate tobacco to the most suitable land areas precisely for the best production since arable land area has been decreasing. Therefore, we herein assess land suitability for tobacco production in tobacco zone of Shandong province, China. The assessment used 20 factors as suitability parameters, including climatic condition, soil type and nutrient characters, and topography data. The fuzzy set model, analytic hierarchy process (AHP) method, and GIS technique were integrated to create land suitability map. The results showed that 29.82% of the total area was highly suitable for tobacco production and 17.74% was unsuitable. Land in western part of the region had higher suitability, while the eastern region close to the Yellow Sea, had lower suitability. The most limiting factors included the number of continuous days with daily temperature ⩾20 °C and high soil exchangeable Mg. This study demonstrates that Fuzzy set is an excellent mechanism to transform numerical data with various magnitudes into grades of membership functions, and representing land suitability. AHP is an effective and superior method to determine the weights of multiple factors in a systematic and logical way. The modeling results produced are based on individual land mapping unit, which facilities the land resource allocation and management. This result is significant in that it provides effective approaches to increase land use efficiency and better management for tobacco production. [ABSTRACT FROM AUTHOR]

Aims: This study was undertaken to investigate laccase-containing basidiomycete communities at the cDNA and DNA levels and to assess the influences of vegetation and soil types on the basidiomycete communities in forest soils. Materials and methods: Soil samples were collected from the upper soil layers of two typical subtropical forests (a broad-leaved forest developed in Karst limestone soil and an artificial coniferous forest with Pinus massoniana in red soil) in China. The basidiomycete communities were characterized by cloning and sequencing of the laccase genes at both the cDNA and DNA levels. Compositions of lignin monomers were determined by gas chromatography-mass spectrometry. Results: Most of the laccase genes obtained in this study were new, highlighting the research gap of this functional group. The trends of the basidiomycetous laccase gene diversity among the upper soil layers of the two forests were consistent between the cDNA and DNA levels. The Agaricales had high activity because they dominated all the tested soils. However, the total basidiomycete communities reflected at the cDNA and DNA levels were significantly different due to the presence of some quiescent basidiomycetous groups. Almost all of the lignin components were decomposed from the O to the A layers in the two forests, and laccases produced by Agaricales were likely responsible for the decomposition of guaiacyl monomers. Both vegetation and soil types had great influences on the active laccase-containing basidiomycete communities, primarily via the pH, C/N, and the contents of lignin monomers. Conclusions: The cDNA- and DNA-level approaches presented good consistency of diversities but different compositions of laccase-containing basidiomycete communities, thus emphasizing the importance of focusing on laccase genes at the cDNA level in future studies. It is the quality but not the quantity of SOM to determine the diversity and composition of the active laccase-containing basidiomycete communities. [ABSTRACT FROM AUTHOR]

Soil microorganisms play vital roles in recovering and maintaining the health of ecosystems, particularly in fragile Karst ecosystems that are easily degraded after cultivation. We investigated the composition and diversity of soil bacterial communities, based on RFLP and 16S rDNA sequencing, in a cropland, a naturally revegetated land with former cultivation disturbance and a primeval forest in the subtropical Karst of southwest China. Our results illustrated that Proteobacteria accounted for 44.8% of the 600 tested clones, making it the most dominant phylum observed. This phylum was followed by Acidobacteria and Planctomycetes for the three Karst soils analyzed. Compared with the primeval forest soil, the proportions of Proteobacteria were decreased by 30.2 and 37.9%, while Acidobacteria increased by 93.9 and 87.9%, and the Shannon-Wiener diversity indices and the physicochemical parameters declined in the cropland and the revegetated land, respectively. Among the three soils, the proportion of dominant bacterial phyla and the diversity indices in the revegetated land were similar to the cropland, implying the bacterial community in the cropland was relatively stable, and the after-effects of cultivation were difficult to eliminate. However, similar distributions of the four Proteobacteria subphyla were observed between the revegetated land and the primeval forest soil. Furthermore, the proportion of Rhizobiales belonging to α- Proteobacteria was sharply decreased with cultivation compared to the primeval forest soil, while a small cluster of Rhizobiales recurred with vegetation recovery. These results indicated that although the subphyla of the dominant bacterial phylum had some positive responses to 20 years of vegetation recovery, it is a slow process. Our results suggest that priority should be given to conserve the primeval forest and inoculation of functional microorganisms on the basis of vegetation recovery may be more effective for the restoration of Karst ecosystems after cultivation. [ABSTRACT FROM AUTHOR]

Conventional aerobic methanotrophs oxidize methane (CH4) and covert CH4-derived carbon (C) into biomass at the oxic-anoxic interface of inundated rice paddy fields, playing indispensable role in mitigating greenhouse gas emissions and loss of organic C from methanogenesis. Two phylogenetically distinct groups of methanotrophs, type I (γ-proteobacteria) and type II (α-proteobacteria) methanotrophs, often co-exist in rice paddy soil and compete for CH4 biotransformation. Since these two methanotrophic groups also possess differential kinetics of CH4 oxidation and pathways of C assimilation, the consequence of their niche differentiation and metabolic differences in soil is expected to affect the CH4 oxidation rate and C conversion efficiency. Here, we examined the microbiology, chemistry, and CH4 metabolism in 24 geographically different paddy soils, covering four climate zones of eastern China. High-throughput sequencing of pmoA gene displayed a clear separation of in situ methanotrophic compositions between temperate (warm and mid-temperate) and warmer (subtropics and tropics) climate zones, likely driven by soil pH. Both methanotrophic groups were detected in soils but proportions of type I methanotrophs increased in temperate soils of higher pH (accounting for 76.1 ± 12.4% and 44.1 ± 14.8% in warm temperate and mid-temperate, respectively). Type II methanotrophs prevailed in warmer zones (accounting for 66.2 ± 21.6% and 70.5 ± 12.1% in tropics and subtropics, respectively) where soils were more acidic. Higher incorporation of 13C for synthesis in C14+C16 PLFAs (63.1–93.4% of total production of 13C-PLFAs) was found based on microcosm incubation, reflecting type I methanotrophs dominated the CH4 assimilation in paddy soils. Particularly, temperate soils with increased proportions of type I methanotrophs showed higher CH4 oxidation rate and C conversion efficiency. Collectively, this study depicts a continental-scale disparity of methanotrophic dynamics that tightly associates with consequence of niche differentiation of different types of methanotrophs and highlights the importance of microbiological control to maximize the rate and efficiency of methanotrophy. [ABSTRACT FROM AUTHOR]

Copper‐based halides have emerged as promising scintillator materials for X‐ray imaging due to their favorable photophysical characteristics, such as negligible self‐absorption, high light output, and fast decay. Among these materials, Cs3Cu2I5, a blue emitter, currently delivers the highest scintillation light output under steady‐state X‐rays. However, there is a significant spectral mismatch between its emission band and the spectral responsivity of regular flat‐panel photodiode arrays. In this study, a comprehensive analysis of the physical properties of the CsCu2I3 scintillator is conducted, and its perfect spectral compatibility is discovered, which results in a higher photodiode signal despite its relatively lower light output compared to typical Cs3Cu2I5 scintillators. Furthermore, CsCu2I3 exhibits faster light decay properties, making it especially suitable for Computed Tomography (CT) X‐ray imaging. High‐quality X‐ray cone beam computed tomography (CBCT) imaging is successfully demonstrated using the fast‐decaying CsCu2I3 scintillator screen. Additionally, the flexibility of the scintillator allows for non‐planar imaging, showcasing advantages not available with traditional rigid scintillators. These results not only highlight the significant promise of the CsCu2I3 scintillator but also emphasize the necessity of considering spectral compatibility when designing novel scintillator materials. [ABSTRACT FROM AUTHOR]

Conventional scintillator‐based X‐ray imaging typically captures the full spectral of X‐ray photons without distinguishing their energy. However, the absence of X‐ray spectral information often results in insufficient image contrast, particularly for substances possessing similar atomic numbers and densities. In this study, an innovative multi‐energy X‐ray linear‐array detector is presented that leverages side‐illuminated X‐ray scintillation using the emerging metal halide Cs3Cu2I5. The negligible self‐absorption characteristic not only improves the scintillation output but is also beneficial for improving the energy resolution for the side‐illuminated scintillation scenarios. By exploiting Beer's law, which governs the absorption of X‐ray photons with different energies, the incident X‐ray spectral can be reconstructed by analyzing the distribution of scintillation intensity when the scintillator is illuminated from the side. The relative error between the reconstructed and measured X‐ray spectral is < 5.63%. This method offers an additional energy‐resolving capability for X‐ray linear‐array detectors commonly used in computed tomography (CT) imaging setups, surpassing the capabilities of conventional energy‐integration approaches, all without requiring extra hardware components. A proof‐of‐concept multi‐energy CT imaging system featuring eight energy channels is successfully implemented. This study presents a simple and efficient strategy for achieving multi‐energy X‐ray detection and CT imaging based on emerging metal halides. [ABSTRACT FROM AUTHOR]

The first funding No. should be 41671298 instead of 41301298. [ABSTRACT FROM AUTHOR]

Particulate organic matter (POM) chemistry and microbial degraders are important determinants of soil carbon (C) mineralization, but the effects of their interactions on C mineralization are largely unknown. Two contrasting soils with different POM chemical composition from karst ecosystems were sampled, sterilized, and cross-inoculated with microorganisms for 124 days to explore the relationships between POM chemical composition, microbial community composition, and soil organic C (SOC) mineralization. Pyrolysis-gas chromatography/mass spectrometry analysis was used to determine POM chemistry, and phospholipid fatty acid (PLFA) analysis was used to characterize the soil microbial community. Microbial cross-inoculation showed that the microbial community composition did not change in response to changes in soil C and that the relatively labile POM components, e.g. , fatty acids and n -alkenes, explained 61.2% of the variation in microbial community composition. Microbial community composition, such as PLFAs cy19:0, i17:0, 10Me16:0, and 18:2ω6,9c, strongly influenced POM chemical composition, explained 94.5% of the variation in POM chemical composition. These results indicated that soil microbial communities could adapt to changes in POM and served as main drivers of POM chemistry alterations. In addition, mineralized soil C (% of SOC) was significantly influenced by microbial community composition, soil source, and their interactions. Redundancy analysis and Mantel tests further revealed that SOC mineralization was strongly affected by POM chemical composition ( e.g. , the content of ketones and p -hydroxyphenyl) and microbial community composition ( e.g. , the content of PLFAs 16:1ω7c and 10Me16:0), and that the influence of microbial community composition on SOC mineralization was highly dependent on POM chemical composition, suggesting that the interactions of POM chemistry and microbial community composition mediate SOC mineralization. These analyses indicate a tight relationship between POM chemistry and microbial community composition, and highlight the importance of their interactions in mediating the persistence of organic matter in karst soils. [ABSTRACT FROM AUTHOR]

Perovskite light‐emitting diodes (PeLEDs) have attracted much attentions due to the superior optoelectronic properties such as pure spectrum, high photoluminescence quantum yield, tunable emission, and ease of fabrication. Though lots of progresses have been made on PeLEDs and optically pumped lasers, microcavity perovskite lasing device under electrical pumping remains extremely challenging. Microcavity perovskite LEDs can be considered as a step toward laser diode due to the common structure of resonant cavity. In this study, a new type of metal‐dielectric microcavity PeLED is designed and fabricated by using 2.5 pairs of TiO2/SiO2 distributed bragg reflector (DBR) and Al as cavity coplanar mirrors. A microcavity device with forward spectral full‐width at half‐maximum of 11.8 and 9.5 nm, under electrical and optical excitations, respectively, the directional forward emission within 30° is enhanced by 3 times compared to the control device without cavity is realized. To the best of the knowledge, this study demonstrates the narrowest spectrum for three‐demisional PeLEDs so far, it helps to expand the color space in display applications and may also serve as a reference device for solution processed perovskite exciton–polariton electroluminescent devices and electrically driven vertical cavity surface emitting lasers due to the similar device structure and processing. [ABSTRACT FROM AUTHOR]

[Display omitted] • We quantified microbial anabolism (growth and necromass formation) in agricultural soils. • Stronger microbial 13C incorporation and necromass formation in upland than paddy soil. • Microbial growth and necromass formation in warm temperate were the lowest in upland. • Weaker growth but stronger necromass formation in warmer than cooler climates in paddy. • Consistent pattern of necromass formation between short-term and long-term periods. Well-drained upland soils generally have stronger microbial catabolism during organic C transformation than water-logged paddy soils. However, the intensity of microbial anabolism and necromass formation processes in these contrasting agricultural soils is unclear. To quantify these processes, 40 pairs of adjacent upland and paddy soils collected from four climates (mid-temperate, warm temperate, subtropics, and tropics) across eastern China were incubated with 13C-labeled root exudates under simulated field water conditions for 50 days. Upland soil collected from warm temperate exhibited a higher 13C incorporation into living microbial biomass than other climates. In contrast, the lowest newly formed necromass was detected due to the inhibition of fungal anabolism under the high pH condition. Paddy soils collected from cooler climates (mid-temperate and warm temperate) exhibited faster microbial biomass growth than those from warmer climates (subtropics and tropics). Still an opposite trend was observed for microbial necromass accumulation, possibly because of the faster turnover rate of microbial biomass induced by the high N availability in warmer climates. Regardless of climates, 13C incorporated into living microbial biomass (phospholipid fatty acids) was 1.4–2.6 times higher in upland than paddy soils, resulting in 1.8–3.9 times greater accumulation of newly-formed microbial necromass in the former. This was mainly caused by the stronger fungal anabolism (2.5–5.6 times higher) due to the oxygen-sufficient condition of upland soil. Our findings highlighted the weaker accumulation but stronger stability of organic C stored in upland soils because of the greater microbial catabolism and anabolism during organic C transformation. [ABSTRACT FROM AUTHOR]

Low-molecular-weight organic carbon (LMWOC) from root exudate influences soil organic carbon cycling via priming of microbial activity. However, the mechanisms underlying the uptake and utilization of specific exudates by microorganisms in soils remain unclear. To address this gap in knowledge, a one-month 13C (0.1 mg C﹒g soil) tracer incubation study was conducted to investigate the fate of the most abundant root exudate groups (using 13C-labeled glucose, acetic acid, and oxalic acid) in paddy vs. upland soil. After 2 days of incubation, the microbial substrate use efficiency (SUE) was >80% in paddy soil, which was approximately 1.9, 2.9, and 1.3 times that in uplands with glucose, acetic acid, and oxalic acid addition, respectively. The SUE in paddy soil with glucose or acetic acid addition was always higher than that in uplands over time (P < 0.05). In both soils, the SUE of glucose was 1–4 times that of carboxylic acids (P < 0.05). The recovery of 13C-labeled total phospholipid fatty acids (PLFAs) in paddy soils was 1.5–2 times that in uplands (P < 0.05). In both soils, bacteria preferred to utilize glucose and acetic acid to synthesize cellular components. Throughout the incubation period, bacteria dominated over fungi in terms of LMWOC consumption. Gram-positive and -negative bacteria were dominant in upland and paddy soils, respectively. From days 11–30, the contribution of fungi and actinomycetes to LMWOC utilization began to appear. Temperature positively regulated 13C distribution in microbial groups (P < 0.05), and increased dissolved organic carbon in upland soil accelerated microbial SUE. The results of this study clarify microbial effects on the high soil carbon sequestration capacity of paddy soil as compared with upland in subtropical areas. [ABSTRACT FROM AUTHOR]

This document is a correction notice for an article titled "Type I methanotrophs dominated methane oxidation and assimilation in rice paddy fields by the consequence of niche differentiation" published in the journal Biology & Fertility of Soils. The correction states that the title of the article was incorrectly given and should have been "Type I methanotrophs dominated methane oxidation and assimilation in rice paddy fields by the consequence of niche differentiation." The original article has been corrected. The correction notice also includes the names of the authors of the article. Springer Nature, the publisher, remains neutral regarding jurisdictional claims and institutional affiliations. [Extracted from the article]

Regularly flooded rice paddies usually show greater soil organic C and microbial-derived C contents than adjacent upland counterparts, but the soil microbial physiological traits under these two different land uses spanning regions remain unclear. Here, we collected 40 pairs of adjacent paddy and upland soils from four different climates (mid temperate, warm temperate, subtropics, and tropics) across eastern China to determine the microbial growth, respiration, and C use efficiency using the 18O-H 2 O incubation method. Upland soils from warmer climates exhibited lower microbial growth but higher respiration normalized to microbial biomass C (q Growth and q Respiration , respectively) than those from cooler climates, since the lower soil pH and higher clay content in warmer climates induced a shift from microbial growth to respiration. Whereas, paddy soils from warmer climates had consistently lower q Growth and q Respiration than cooler climates , probably due to the long term water-logged condition decreased the sensitivity of microbial metabolism in response to lower pH. Paddy soils had higher q Growth , but lower q Respiration than upland soils, resulting in a greater C use efficiency regardless of climate zones. The difference in microbial C use efficiency between paddy and upland soils was positively correlated to their difference in soil organic C content. From the perspective of microbial C metabolism, the greater organic C accumulation in paddy than that in upland soils is attributed to the weaker microbial uptake of organic C and stronger microbial anabolism under the water-logged condition. • Paddy soils in warmer climates had lower q Growth and q Respiration than cooler climates. • Upland soils in warmer climates had lower q Growth but higher q Respiration than in cooler climates. • Paddy soils had higher C use efficiency than upland soils regardless of climate zone. [ABSTRACT FROM AUTHOR]

Flooding and straw returning are effective agricultural practices in promoting phosphorus (P) availability in paddy soils. However, little is known about the effects of these practices and their interaction on the soil P pools and functional microbes responsible for soil P mobilization. Our 4-year paddy field experiment aimed to analyze the responses of soil P fractions and phoD-harboring bacterial communities in a double-rice cropping system to intermittent flooding (IF) and continuous flooding (CF), in plots with (+ S) and without (-S) straw return. Compared to IF, CF significantly increased soil citrate-P and marginally decreased the HCl-P fractions, suggesting that the stable inorganic P pools are transferred to labile inorganic P at lower redox potentials. Compared to the -S treatments, + S treatments significantly increased the labile organic fractions (enzyme-P). Correspondingly, a decreased soil total organic P concentration was observed in + S treatment. Additionally, + S treatment significantly increased the activity of acid phosphomonoesterase and alkaline phosphomonoesterase and the abundance of phoD-harboring bacteria. These results indicated that straw promoted organic P minimization to release orthophosphate. The diversity of the phoD-harboring bacteria and complexity of the co-occurrence network decreased under the CF + S treatment; however, all keystone species of the phoD-harboring bacteria were retained in this oxygen-deficient environment. This study highlights that irrigation regimes mediate the processes of inorganic P mobilization, while straw returns regulate the processes of organic P mineralization. Additionally, flooding could be a more effective agricultural practice than straw returning to promote soil P availability in paddy soils. Key points: •Soil P pools and phoD-harboring bacteria communities were assessed. •Straw return mainly affects the mineralization of organic P. •Continuous flooding mainly affects the mobilization of inorganic P. [ABSTRACT FROM AUTHOR]

The fate of hydrophilic, hydrophobic, and insoluble fractions extracted from 13C-labelled maize straw and their use for the formation of bacterial and fungal-derived amino sugars (AS) were monitored during a 40-day incubation of upland and paddy soils. The highest sequestration of C in the AS pool was present in the hydrophilic fraction in both soils (1.1–1.4% of input C). Bacterial community in upland soil utilized the hydrophilic fraction the most for the formation of AS, whereas fungi used the hydrophobic fraction, suggesting that bacteria and fungi have different substrate preference. In contrast, fungi used similar portions of all fractions for AS formation in the paddy soil, which could be a substrate utilization strategy under anoxic conditions. Sequestration of microbial-derived C, formed from the added fractions, was lower in paddy than in upland soils (0.7–1.1% vs. 1.2–1.4%), while total AS content showed the opposite trend (493–509 mg kg−1 in paddy vs. 387–405 mg kg−1 in upland soils). This was attributed to the 1.5 times lower microbial activity in paddy than in upland soils based on the relative incorporation of 13C into total MBC. Thus, sequestration of microbial-derived C from various organic C sources is closely related to substrate quality, but soil management and its properties modulate the microbial utilization of substances with various hydrophobicity. [ABSTRACT FROM AUTHOR]

All‐inorganic perovskite quantum dots (QDs) CsPbX3 (X = Cl, Br, and I) have recently emerged as a new promising class of X‐ray scintillators. However, the instability of perovskite QDs and the strong optical scattering of the thick opaque QD scintillator film imped it to realize high‐quality and robust X‐ray image. Herein, the europium (Eu) doped CsPbBr3 QDs are in situ grown inside transparent amorphous matrix to form glass‐ceramic (GC) scintillator with glass phase serving as both matrix and encapsulation for the perovskite QD scintillators. The small amount of Eu dopant optimizes the crystallization of CsPbBr3 QDs and makes their distribution more uniform in the glass matrix, which can significantly reduce the light scattering and also enhance the photoluminescence emission of CsPbBr3 QDs. As a result, a remarkably high spatial resolution of 15.0 lp mm−1 is realized thanks to the reduced light scattering, which is so far a record resolution for perovskite scintillator based X‐ray imaging, and the scintillation stability is also significantly improved compared to the bare perovskite QD scintillators. Those results provide an effective platform particularly for the emerging perovskite nanocrystal scintillators to reduce light scattering and improve radiation hardness. [ABSTRACT FROM AUTHOR]

Paddy soils make up the largest anthropogenic wetlands on earth, and are characterized by a prominent potential for organic carbon (C) sequestration. By quantifying the plant‐ and microbial‐derived C in soils across four climate zones, we identified that organic C accrual is achieved via contrasting pathways in paddy and upland soils. Paddies are 39%–127% more efficient in soil organic C (SOC) sequestration than their adjacent upland counterparts, with greater differences in warmer than cooler climates. Upland soils are more replenished by microbial‐derived C, whereas paddy soils are enriched with a greater proportion of plant‐derived C, because of the retarded microbial decomposition under anaerobic conditions induced by the flooding of paddies. Under both land‐use types, the maximal contribution of plant residues to SOC is at intermediate mean annual temperature (15–20°C), neutral soil (pH~7.3), and low clay/sand ratio. By contrast, high temperature (~24°C), low soil pH (~5), and large clay/sand ratio are favorable for strengthening the contribution of microbial necromass. The greater contribution of microbial necromass to SOC in waterlogged paddies in warmer climates is likely due to the fast anabolism from bacteria, whereas fungi are unlikely to be involved as they are aerobic. In the scenario of land‐use conversion from paddy to upland, a total of 504 Tg C may be lost as CO2 from paddy soils (0–15 cm) solely in eastern China, with 90% released from the less protected plant‐derived C. Hence, preserving paddy systems and other anthropogenic wetlands and increasing their C storage through sustainable management are critical for maintaining global soil C stock and mitigating climate change. [ABSTRACT FROM AUTHOR]

Biological nitrogen (N2) fixation as a source of new N input into the soil by free-living diazotrophs is important for achieving sustainable rice agriculture. However, the dominant environmental drivers or factors influencing N2 fixation and the functional significance of the diazotroph community structure in paddy soil across a climatic gradient are not yet well understood. Thus, we characterized the diazotroph community and identified the ecological predictors of N2 fixation potential in four different climate zones (mid-temperate, warm-temperate, subtropical, and tropical paddy soils) in eastern China. Comprehensive nifH gene sequencing, functional activity detection, and correlation analysis with environmental factors were estimated. The potential nitrogenase activity (PNA) was highest in warm-temperate regions, where it was 6.2-, 2.9-, and 2.2-fold greater than in the tropical, subtropical, and mid-temperate regions, respectively; nifH gene abundance was significantly higher in warm-temperate and subtropical zones than in the tropical or mid-temperate zones. Diazotroph diversity was significantly higher in the tropical climate zone and significantly lower in the mid-temperate zone. Non-metric multidimensional scaling and canonical correlation analysis indicated that paddy soil diazotroph populations differed significantly among the four climate zones, mainly owing to differences in climate and soil pH. Structural equation models and automatic linear models revealed that climate and nutrients indirectly affected PNA by affecting soil pH and diazotroph community, respectively, while diazotroph community, C/P, and nifH gene abundance directly affected PNA. And C/P ratio, pH, and the diazotroph community structure were the main predictors of PNA in paddy soils. Collectively, the differences in diazotroph community structure have ecological significance, with important implications for the prediction of soil N2-fixing functions under climate change scenarios. [ABSTRACT FROM AUTHOR]

Hydrophilic and hydrophobic organic compounds extracted from 13C-labelled maize residues were incubated with soils to evaluate their mineralization and priming effect (PE) caused by their utilization by microbial groups. Two soils with contrasting soil properties were collected from well-drained upland and water-logged paddy. Mineralization of the 13C-labelled fractions and their PE were quantified by monitoring the CO2 efflux and 13C enrichment during a 40-day incubation. The composition of main microbial groups (bacteria and fungi) involved in the utilization of 13C-labelled fractions was determined based on phospholipid fatty acids (PLFAs) analysis. At the initial stage (6–24 h), hydrophilic fraction had faster mineralization rate (3.6–70 times) and induced 1.5–10 times stronger PE (positive in upland soil and negative in paddy soil) than those of hydrophobic fraction. The 13C-PLFAs data showed that the incorporation of hydrophilic fraction into bacteria was 11.4–16.4 times greater than that into fungi, whereas the hydrophobic fraction incorporated into fungi was 1.0–1.5 times larger than that into bacteria at day 2. This indicated greater contributions of r-strategists (fast-growing bacteria) for the uptake of hydrophilic fraction versus K-strategists (slow-growing fungi) for hydrophobic fraction. Compared with K-strategists, the r-strategists possessed a much faster metabolism and thus triggered stronger apparent PE by accelerating microbial biomass turnover, resulting in higher mineralization and stronger PE for the hydrophilic than hydrophobic fraction. The slower and less mineralization of both fractions in paddy than in upland soils is due to the suppression of microbial activity and substrate utilization under flooding. At the end of 40-day incubation, the cumulative mineralization of hydrophilic and hydrophobic fractions was similar. Consequnently, microbial mechanisms underlying the utilization of organic compounds with contrasting solubility (hydrophilic or hydrophobic) are crucial for evaluating the stabilization and destabilization (e.g., priming) processes of soil organic matter. [ABSTRACT FROM AUTHOR]

Aims: Although nitrogen (N) fertilization is widely used to increase rice yield, its impact on the distribution, transformation, and fates of photosynthetic carbon (C) in rice–soil systems is poorly understood. To address this, we quantified the C flows into various pools in a rice–soil system. Methods: Rice (Oryza sativa L.) was pulse-labeled with 13CO2 at the tillering stage. Samples were collected six times during the 26 days following labeling. We quantified the partitioned photosynthesized C into various pools using stable isotopic techniques and estimated C flows. Results: Although the net distribution of assimilated C to belowground pools did not change, N fertilization promoted C assimilation in aboveground biomass. C allocation into soil was enhanced by N fertilization during early growth, but decreased during late growth. N fertilization induced higher mass-specific rhizodeposition (per unit root dry weight) and its turnover rate compared with the unfertilized system. However, with higher microbial turnover, the daily C allocation from roots to soil was similar at both fertilization levels. Conclusions: Although total C input into soil is enhanced by N fertilization, its further fate is N fertilization independent, thus leading to a net accumulation of C input in rice paddy soil similar to that observed unfertilized soil. [ABSTRACT FROM AUTHOR]

Microbial residues are key components of stable soil organic C (SOC). However, the accumulation patterns of fungal and bacterial residues across climate regions are largely unknown, especially in paddy soils. In this study, the amounts of microbial-derived amino sugars (AS) with their constituents, glucosamine (GlcN), galactosamine (GalN), and muramic acid (MurN, a biomarker of bacterial residues) were quantified in paddy soils, which were collected from mid-temperate, warm-temperate, subtropical, and tropical climate regions across eastern China. The contents of total AS and fungal-derived GlcN (F-GlcN, a biomarker of fungal residues) were lowest in the warm-temperate region, but not significantly different among the other three climate regions. The MurN content and its contribution to SOC accumulation were higher in the warmer and wetter regions (subtropic and tropic) than in the cooler and drier ones (mid-temperate and warm-temperate). Consequently, the ratio of F-GlcN to MurN was lower in the warmer and wetter regions (8.5–15.4) than in the cooler and drier ones (12.8–28.8). These results illustrate that the bacteria participating in SOC transformation and stabilization in paddy soils exerted more prominent activities in the warmer and wetter regions than in the cooler and drier regions. Structure equation models emphasize that the contrasting patterns of fungal and bacterial residues' contribution to SOC accumulation in paddy ecosystems along the latitudinal gradient were mainly attributed to their different responses to the climate factors of temperature and precipitation. [ABSTRACT FROM AUTHOR]

• The 13C recovery was affected by soil management and the types of exogenous carbon. • More carbon was distributed in the mineral grains of paddy soil than upland soil. • In paddy, protection of organic carbon was proportional to the increase of fractions < 2.65 g.cm−3. Low molecular weight organic carbon (LMWOC) can be physiochemically protected by soil particles via sorption and enfolding. Soil management usually changed the soil particle distribution (e.g. upland vs paddy soil). Higher organic carbon stocks in paddy soil than upland soil could partially be because of the greater immobilization and inaccessibility of LMWOC in paddy soil. To assess the effects of soil management and types of LMWOC on its carbon stabilization in soil density fractions, a simulated study was conducted to investigate the distribution of LMWOC (i.e., glucose, acetic acid, and oxalic acid) in soil density fractions based on 13C-labeling experiments in both soils. The results showed that the total 13C recovery was determined by LMWOC types, following the order of glucose> acetic acid > oxalic acid (p < 0.05). Both soil management and types of LMWOC significantly affect carbon distribution in soil density fractions. The 13C from LMWOC was predominant in the 1.85–2.4 g.cm−3 fraction of upland soil, while the highest concentration of LMWOC 13C was found in mineral grains (2.4–2.65 g.cm−3) in paddy soil, suggesting that more LMWOC was preserved in high density fractions in paddy soil than in upland soil. Our results highlighted that the LMWOC was mainly associated with aggregates in upland soil while subjected to mineral adsorption in paddy soil. [ABSTRACT FROM AUTHOR]

The photosynthate carbon (C) released in the rhizosphere plays a crucial role in C sequestration, microbial activities and nutrient availability in soil. Nitrogen (N) fertilization modifies the allocation and dynamics of photosynthates in paddy rice systems, but these effects depend on plant growth stages. Rice (Oryza sativa L.) plants were pulse labelled with 13CO2 at the tillering, elongation, heading and grain‐filling stages with 0 and 225 kg N ha−1 fertilizer. The plants and soil were sampled shortly after each pulse labelling and at harvest. Relative 13C (as % of assimilated C) in the roots and rhizosphere soil was largest at the early growth stage (tillering) and subsequently decreased. At harvest, 68% of the rhizodeposited C remained in bulk soil without N fertilizer, which corresponded to 6.2% of the net assimilated 13C. The absolute amount of net belowground C input (root + rhizodeposition) by rice was 268 and 468 kg C ha−1 under 0 and 225 kg N ha−1 fertilizer, of which rhizodeposition accounted for 60 and 40%, respectively. We concluded that N fertilization raised the belowground C input by rice mainly by increasing root biomass rather than by rhizodeposition. Highlights: Rice photosynthesis‐derived carbon (C) was quantified in soil by multiple pulse labelling with 13CO2Young rice plants allocated more assimilates into the soil compared to mature plantsNitrogen deficiency led to greater C retention in bulk soil than in the rhizosphereNitrogen fertilization increased the net belowground C input mainly with larger root biomass [ABSTRACT FROM AUTHOR]

Abstract The diversity patterns of plants at large scale are broadly documented, but that of soil fungi remains elusive. Limited reports on soil fungal biogeography mainly are based on species richness. We carried out a large-scale field investigation on soil fungi originating from 365 forest plots covering five climate zones in China. We tested whether and to what degree a range of different fungal diversity estimates are subject to latitudinal constraints and compared co-occurrence patterns of plants and soil fungi. We found that alpha diversity of plants increased towards lower latitude, while that of soil fungi only tended to increase. Abiotic but not biotic factors controlled fungal alpha diversity. Multiple-site and pairwise beta diversity of soil fungi were closely linked to plant communities. Null model revealed an increasing interaction strength between plant species, while there was a hump-shaped pattern of interaction strength between fungal species from high-latitude towards low-latitude. Our results allow a deeper insight into the multidimensional distribution of soil fungal diversity and reveal contrasting co-occurrence patterns between soil fungi and plants along a latitude gradient, highlighting the need for more inclusive theories to explain these disparities between micro- and macroorganism communities. Highlights • A large-scale investigation on soil fungal diversity was carried out in forest ecosystems in China. • Abiotic factors, but not biotic factors, controlled fungal alpha diversity. • Fungal beta diversity was highly related to plant communities. • Fungal species interaction strength followed a hump-shaped pattern towards lower latitude. • There were contrasting co-occurrence patterns between soil fungi and plants along latitude. [ABSTRACT FROM AUTHOR]

Crop straw retention is believed to effectively promote soil phosphorus (P) availability. However, little is known about how specific components of crop straw, such as cellulose and lignin, regulate soil P availability, which depends on several processes, including the reactions catalyzed by phosphomonoesterase activities. Of the genes encoding alkaline phosphomonoesterase, phoD are ubiquitous in soil. Here, we studied the effects of cellulose and lignin on soil P fractions and phoD-harboring bacterial community in P-deficient upland and paddy soils. In the upland soil, cellulose amendment significantly increased microbial P assimilation and decreased soil citrate-P and HCl-P fractions, suggesting that cellulose mediated the conversion of soil P fractions from the non-labile to the labile P pool (e.g., microbial P) via microbial enrichment. Lignin significantly increased soil Olsen-P content, but scarcely influenced P-related microbial parameters after incubation for 60 days. Therefore, lignin directly increased soil available P via competitive P adsorption by lignin functional groups, rather than by altering soil microbial processes. Compared to upland soil, a smaller effect of both cellulose and lignin on phoD gene abundance, alkaline phosphomonoesterase activity, and phoD-harboring bacterial community was observed in paddy soil, suggesting that the carbon inputs may be unable to promote organic P availability under oxygen-deficient conditions. Our results highlight the contrasting mechanisms of soil P availability regulation via cellulose or lignin in P-deficient soils. [ABSTRACT FROM AUTHOR]

Highlights • SOC recovers to levels of primary forest within a shorter period than soil N. • Recuperation time of SOC and soil N had opposite patterns in topsoil and subsoil. • Soil N is capable of sustaining SOC accumulation in the long term in karst regions. Abstract Vegetation restoration following agricultural abandonment is an effective method for soil organic carbon (SOC) sequestration. However, SOC dynamics during post-agriculture succession in different soil layers, and its regulation by soil nitrogen (N), are not well understood. We investigated SOC and soil N dynamics during post-agriculture succession at soil depths of 0–10, 10–20, 20–30, and 30–50 cm in a subtropical karst area in southwest China. The succession sequence included grassland (∼9 years), shrubland (∼25 years), secondary forest (∼52 years), and primary forest, with cropland as a reference. In the 0–50 cm soil profile, the SOC and soil N stocks will recover to the primary forest level in ∼74 years at a rate of 112.35 g C m−2 yr−1 and in ∼100 years at a rate of 12.07 g N m−2 yr−1, respectively. The accumulation rate of SOC and soil N was higher in the topsoil (0–20 cm) than in the subsoil (20–50 cm). The estimated time for SOC stock to recover to the primary forest level in topsoil and subsoil was similar (72 and 76 years, respectively), whereas that for soil N stock require more time in topsoil than in subsoil (106 and 89 years, respectively). The higher rate of relative N stock change than that of SOC suggests that progressive N limitation does not occur in the long term following agricultural abandonment. Our results highlight the importance of soil depth and soil N in determining SOC change for secondary succession. Furthermore, the results suggest that, compared to that of previous studies, which considered only surface soil in the karst regions of southwest China, the recovery period of C and N in soil profile may be longer than that assumed previously. [ABSTRACT FROM AUTHOR]

Phosphorus (P) acquisition by plants from soil organic P mainly relies on microorganisms. Examining the community of functional microbes that encode phosphatases (e.g. PhoD) under different fertilization managements may provide valuable information for promoting soil organic P availability. Here, we investigated how the abundance and community diversity of phoD -harboring bacteria responded to long-term fertilization in Karst soils. Six fertilization treatments were designed as follows: non-fertilized control (CK), inorganic fertilization only (NPK), and inorganic fertilization combined with low- and high amounts of straw (LSNPK and HSNPK), or cattle manure (LMNPK and HMNPK). We found that soil available phosphorus (AP) content and the activity of alkaline phosphatase (ALP) were significantly higher in all combined inorganic/organic fertilization treatments, while the abundance of the phoD gene was only higher in the HMPNK treatment, compared to NPK. The combination of inorganic/organic fertilizations had no effect on the diversity of phoD genes compared to NPK alone, but the phoD gene richness was greater in these treatments as compared to the control. Only organic fertilization combinations with high amounts of organic matter (both HSNPK and HMNPK) significantly affected the phoD community structure. A structure equation model demonstrated that soil organic carbon (SOC), rather than P, greatly affected the phoD community structure, suggesting that organic P mineralization in soils is decoupled from C mineralization. Our results suggested that optimized combinations of inorganic/organic fertilizations could promote P availability via regulating soil phoD -harboring bacteria community diversity and ALP activity. [ABSTRACT FROM AUTHOR]

A 100-day incubation experiment was conducted to (i) trace the fate of rice residue-derived 13C in the amino sugar (AS) pool in 0-1-cm (oxic) and 1-5-cm (anoxic) layers of paddy soil and (ii) evaluate the effects of inorganic N ((NH4)2SO4) fertilization on the formation of AS at early and late incubation times (5 and 100 days, respectively). The accumulation of rice residue-derived AS occurred at 5 and 100 days in both soil layers as a result of AS stabilization. Inorganic N addition increased the contents of rice residue-derived muramic acid, glucosamine, and galactosamine in the 0-1-cm soil layer for both incubation times by average on 14.7-20.8%, 23.7-31.8%, and 11.6-23.3%, respectively. In contrast, no effects of N fertilization on AS content in the 1-5-cm soil layer were found. The amount of rice residue-derived AS was higher in the 1-5-cm than in the 0-1-cm soil layer at early incubation time, probably due to the higher contents of ammonium here compared to the upmost oxic layer where nitrate was the dominated N form. Thus, the preferential uptake of ammonium but not nitrate by microorganisms led to the higher formation of rice residue-derived AS in the anoxic soil layer. The ratio of fungal to bacterial residues (fungal glucosamine/muramic acid) ranged between 1.0 and 1.7 for rice residue-derived AS and was 12.5-14.6 for total AS, indicating that fungi and bacteria have similar contributions to the decomposition of fresh rice residue whereas native soil organic matter (SOM) is a fungi-predominated process. This study emphasized that coupling of C and N cycles in paddy soils is different in oxic and anoxic layers, resulting in variation of plant residue decomposition and formation of SOM. [ABSTRACT FROM AUTHOR]

Soil organic matter (SOM) mineralization is affected by various abiotic and biotic factors, as well as the input of exogenous organic substances. Our previous studies have shown that SOM mineralization in flooded rice paddies is lower than that in adjacent upland soils in subtropical agro-ecosystems. However, the main factors contributing to the differences in SOM mineralization remain unclear. To compare the effects of biotic and abiotic factors on SOM mineralization between upland and paddy soils, we incubated upland and paddy (flooded) soils with three low molecular weight organic substances (LMWOS, i.e., glucose, acetic acid, or oxalic acid) for 30 days under field conditions. Generally, the average CO 2 efflux from upland soil was higher than that in paddy soil with the same LMWOS addition. The total content of phospholipid fatty acids (PLFAs) in paddy soil was 2–5 times higher than that of upland soil, irrespective of the LMWOS added. Redundancy analyses indicated that microbial community composition was influenced mainly by the low redox potential (Eh) and dissolved organic carbon in paddy soil. Structural equation modeling revealed that, among abiotic factors, temperature exerted indirect effects on SOM mineralization by influencing biotic factors in both soils; Eh has a positive and direct effect on SOM mineralization in paddy soil. In terms of biotic factors, SOM mineralization in upland soil was mainly regulated by the quantity of bacteria. In paddy soil, SOM mineralization was largely influenced by the ratio of fungal to bacterial PLFAs and peroxidase activity. [ABSTRACT FROM AUTHOR]

Although soil organic matter (SOM) and microbial biomass pools in flooded paddy soils are generally larger than they are in upland soils, the processes (i.e., slower mineralisation, other types of C stabilization, and a negative priming effect) underlying higher SOM stocks in paddy soil are unclear. To elucidate these processes, three 13 C labelled low molecular weight organic substances ( 13 C-LMWOS) (i.e., glucose, acetic acid, and oxalic acid) were incubated in upland and paddy soils under simulated field conditions. Within 30 days of incubation, acetic acid exhibited the highest mineralisation in both soils. The amount of mineralisation of glucose in upland soil was higher than that of oxalic acid ( p < 0.05), whereas the opposite was observed for paddy soil. Mineralisation of all three LMWOS was lower in paddy soil than that in upland soil ( p < 0.05), illustrating that the molecular structure of the LMWOS as well as soil management determined the mineralisation rate. The priming effect evoked by oxalic acid and glucose was lower in paddy than in upland soil ( p < 0.05). Therefore, the generally weaker mineralisation and priming effect of LMWOS observed in paddy soil contributed to higher carbon accumulation than they did in upland soil. Priming effect was positively correlated with fungal abundance, which was lower in paddy soil than in upland soil. Thus, slow organic C turnover in paddy soil is partly attributed to the suppression of fungal activity by flooding. [ABSTRACT FROM AUTHOR]

Background and aims: The turnover of plant- and microbial- derived carbon (C) plays a significant role in the soil organic C (SOC) cycle. However, there is limited information about the turnover of the recently photosynthesized plant- and soil microbe-derived C in paddy soil. Methods: We conducted an incubation study with four different C-labeled substrates: rice shoots (Shoot-C), rice roots (Root-C), rice rhizodeposits (Rhizo-C), and microbe-assimilated C (Micro-C). Results: Shoot- and Root-C were initially rapidly transformed into the dissolved organic C (DOC) pool, while their recovery in microbial biomass C (MBC) and SOC increased with incubation time. There were 0.05%, 9.8% and 10.0% of shoot-C, and 0.06%, 15.9% and 16.5% of root-C recovered in DOC, MBC and SOC pools, respectively at the end of incubation. The percentages of Rhizo- and Micro-C recovered in DOC, MBC, and SOC pools slowly decreased over time. Less than 0.1% of the Rhizo- and Micro-C recovered in DOC pools at the end of experiment; while 45.2% and 33.8% of Rhizo- and Micro-C recovered in SOC pools. Shoot- and Root-C greatly increased the amount of C-PLFA in the initial 50 d incubation, which concerned PLFA being indicative for fungi and actinomycetes while those assigning gram-positive bacteria decreased. The dynamic of soil microbes utilizing Rhizo- and Micro-C showed an inverse pattern than those using Shoot- and Root-C. Principal component analysis of C-PLFA showed that microbial community composition shifted obviously in the Shoot-C and Root-C treatments over time, but that composition changed little in the Rhizo-C and Micro-C treatments. Conclusions: The input C substrates drive soil microbial community structure and function with respect to carbon stabilization. Rhizodeposited and microbial assimilated C have lower input rates, however, they are better stabilized than shoot- and root-derived C, and thus are preferentially involved in the formation of stable SOC in paddy soils. [ABSTRACT FROM AUTHOR]

The addition of exogenous inorganic carbon (CaCO 3 ) and organic carbon has an important influence on soil organic carbon (SOC) mineralization in karst soil, but the microbial mechanisms underlying the SOC priming effect are poorly understood. We conducted a 100-day incubation experiment involving four treatments of the calcareous soil in southwestern China's karst region: control, 14 C-labeled rice straw addition, 14 C-labeled CaCO 3 addition, and a combination of 14 C-labeled rice straw and CaCO 3 . Changes in soil microbial communities were characterized using denaturing gradient gel electrophoresis with polymerase chain reaction (PCR-DGGE) and real-time quantitative PCR (q-PCR). Both 14 C-rice straw and Ca 14 CO 3 addition stimulated SOC mineralization, suggesting that organic and inorganic C affected SOC stability. Addition of straw alone had no significant effect on bacterial diversity; however, when the straw was added in combination with calcium carbonate, it had an inhibitory effect on bacterial and fungal diversity. At the beginning of the experimental period, exogenous additives increased bacterial abundance, although at the end of the 100-day incubation bacterial community abundance had gradually declined. Incubation time, exogenous input, and their interaction significantly affected SOC mineralization (in terms of priming and the cumulative amount of mineralization), microbial biomass carbon (MBC), and microbial community abundance and diversity. Moreover, the key factors influencing SOC mineralization were MBC, bacterial diversity, and soil pH. Overall, these findings support the view that inorganic C is involved in soil C turnover with the participation of soil microbial communities, promoting soil C cycling in the karst region. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal (AM) fungi are crucial for vegetation regeneration because they play an important role in plant establishment and growth. We investigated the relationships among AM fungal diversity, plant diversity, and soil properties during vegetation restoration in degraded karst ecosystems. Pyrosequencing approach was used to determine the genetic diversity and composition of AM fungal communities in four typical ecosystems of vegetation restoration (tussock (TK), shrub (SB), secondary forest (SF), and primary forest (PF)) in a karst region of southwest China. The diversity, richness, and evenness of plant species were evaluated through field surveys. Basic soil properties were measured. Plant species diversity and soil nutrient contents increased with vegetation restoration from tussock to primary forest, but the diversity of AM fungi followed the order of shrub ≈ secondary forest ≈ primary forest < tussock. The composition of AM fungi and plant communities differed significantly between ecosystems ( p < 0.05). The richness of AM fungi was negatively correlated with both the plant diversity (the indices of plant Shannon–Wiener, evenness and richness) and soil properties (soil available phosphorus (AP), soil organic carbon (SOC) and pH) ( p < 0.05). Redundancy analysis showed that the AM fungal communities closely linked to plant richness, soil organic carbon, soil available phosphorus and pH. These results suggest that the diversity and composition of AM fungi in karst region are influenced by plant communities and soil nutrient conditions. [ABSTRACT FROM AUTHOR]

Understanding the effects of straw return and N fertilization on soil organic matter (SOM) transformations will help maintain crop production and soil function, which can ultimately contribute to mitigating climate change. In this study, we conducted a 100-day soil incubation experiment with the addition of 13C-labeled maize straw and/or N fertilization. Soils that were used in the study included soil without fertilizers (Control), with mineral fertilizer alone (NPK), and with mineral fertilizer and straw (NPK+Straw). Compared with the control, the NPK- and NPK+Straw-treated soils showed higher straw decomposition by 59% and 55%, and SOM mineralization by 27% and 37%, respectively, although the priming effect was decreased by 59% and 39%, respectively. The priming effect (PE) was higher with increased N content and lower with decreased N additions because of an improved C/N ratio for microorganisms. Straw additions compared to without straw increased the bacterial and fungal abundance by 1.4- and 4.9-fold, respectively. N fertilization lowered C/N ratios resulting in decreased fungal diversity. Although the bacterial abundance decreased, the diversity increased with the duration of incubation as the bacteria preferred to utilize the labile organic compounds that were abundant in the initial stages of incubation. In addition to the depletion of labile organic compounds, the fungal abundance increased. Bacteria (Firmicutes, Actinobacteria, and Proteobacteria phyla) and fungi (Ascomycota, Basidiomycota, and Mucoromycota phyla) dominated straw and SOM decomposition. Firmicutes were mostly involved in straw and SOM mineralization during the first day after straw addition. The edge number and ratio for pairwise correlations between environmental factors and fungal taxa (22.1–24.6%) were greater than those with bacterial taxa (1.0–2.9%) in the microbial correlation network. Overall, straw combined with a low level of added N benefited soil C sequestration by decreasing the PE. Compared to bacteria, the functional role of fungi in SOM mineralization is more prominent and should be considered during agricultural management. • Straw with low nitrogen addition increased carbon sequestration by a low priming effect. • Firmicutes are mainly involved in the initial stage of organic matter mineralization. • Firmicutes, Actinobacteria, and Proteobacteria of bacteria aid organic matter mineralization. • Fungal phyla Ascomycota, Basidiomycota, and Mucoromycota dominate organic matter decomposition. • Fungal taxa correlate closer with organic matter mineralization than bacterial groups. [ABSTRACT FROM AUTHOR]

• Increased C mineralization in soil caused by frequent glucose additions. • Increasing frequency of glucose additions decreased soil Eh and improved rice straw mineralization. • Frequent glucose additions decreased fungi/bacteria ratio and accelerated rice straw mineralization. Crop straw amendment is a farm management approach for enhancing soil carbon sequestration. Moreover, crop straw residue decomposition rates are affected by irregular exogenous organic carbon secretion or metabolism such as that from root exudates or microbial metabolites. To quantify the mineralization rate of straw residue affected by exogenous organic carbon addition and elucidate the underlying mechanisms, in this study, a total of 0.5 g 13C- labeled dry rice straw was added into pre-incubated soil (equivalent to 200 g dry soil) and incubated for 20 days. Then,1mL of a solution with 50 mg glucose was added only once into the soil on day 21 (G(1a)) or day 35 (G(1b)), twice with 25 mg glucose every 14 days (G(2)) or four times with 12.5 mg glucose every 7 days (G(4)). Soil without glucose addition served as a control. The frequent addition of glucose induced higher soil respiration than that induced by only one addition, and stimulated the mineralization of rice straw carbon compared to that in the control in the following order: G(4) (14.6%) > G(1a) (12.7%) > G(2) (12.3%) > G(1b) (11.2%) = control (11.2%). In general, frequent addition of glucose decreased the soil redox potential (Eh) and fungi to bacteria ratio. Structural equation modeling analysis showed that the rice straw carbon mineralization rate was positively correlated with the 13C-dissolved organic carbon (13C-DOC) content and negatively regulated by Eh. Microbial bioactivity exerted indirect positive effects on rice straw carbon mineralization by influencing the 13C-DOC content. A decrease in the fungi to bacteria ratio induced by frequent addition of glucose improved the microbial bioactivity and enhanced rice straw carbon mineralization. Our results suggested that single exogenous organic carbon additions may underestimate residue or soil organic matter decomposition rates in the field. [ABSTRACT FROM AUTHOR]

The impacts of biochar amendment on the net greenhouse gas emission (NGHGE) and greenhouse gas intensity (GHGI) of double rice cropping systems are not well examined. In this study, a field experiment was carried out to investigate the effects of biochar amendment on NGHGE and GHGI emissions in a subtropical double rice cropping system managed with intermittent flooding during two rice-growing seasons and drainage during a fallow season from April 2012 to April 2013. Three biochar treatments were studied, with application rates of 0, 24 and 48 t ha −1 (named CK, LC and HC, respectively). In each treatment, the fluxes of methane (CH 4 ), nitrous oxide (N 2 O) and soil heterotrophic respiration (Rh) were measured using a static chamber/gas chromatography method. Key soil properties related to greenhouse gas (GHG) emissions were also determined throughout an entire double rice cycle. The results showed that biochar amendment significantly reduced annual CH 4 emissions by up to 40% compared with the CK treatment, possibly due to the soil pH increase after biochar amendment other than increased soil aeration. In contrast, annual N 2 O emissions significantly increased by 150% and 190% in the two biochar treatments, compared with the CK treatment, which may be related to the increase of soil dissolvable organic C or NH 4 + in the biochar treatments. The cumulative Rh significantly increased by 19% in the HC treatment possibly due to the additional carbon dioxide (CO 2 ) emissions from decomposition of the labile C within biochar, but showed no increase and even a decrease in the LC treatment throughout the study period. Annually, the global warming potential for CH 4 and N 2 O emissions, NGHGEs, and GHGIs in the biochar amendment treatments were reduced by 31–36%, 1551–2936% and 1452–2894%, respectively ( p < 0.05). Our collective data may suggest that as the rice grain yield was improved by the biochar amendment found in this study, the biochar application in paddy fields may be an effective measure for GHG emission mitigation in the subtropics. [ABSTRACT FROM AUTHOR]

Abstract: Soil organic matter (SOM) content in paddy soils is higher than that in upland soils in tropical and subtropical China. The dissolved organic matter (DOM) concentration, however, is lower in paddy soils. We hypothesize that soil moisture strongly controls the fate of DOM, and thereby leads to differences between the two agricultural soils under contrasting management regimens. A 100-day incubation experiment was conducted to trace the fate and biodegradability of DOM in paddy and upland soils under three moisture levels: 45%, 75%, and 105% of the water holding capacity (WHC). 14C labeled DOM, extracted from the 14C labeled rice plant material, was incubated in paddy and upland soils, and the mineralization to 14CO2 and incorporation into microbial biomass were analyzed. Labile and refractory components of the initial 14C labeled DOM and their respective half-lives were calculated by a double exponential model. During incubation, the mineralization of the initial 14C labeled DOM in the paddy soils was more affected by moisture than in the upland soils. The amount of 14C incorporated into the microbial biomass (2.4–11.0% of the initial DOM-14C activity) was less affected by moisture in the paddy soils than in the upland soils. At any of the moisture levels, 1) the mineralization of DOM to 14CO2 within 100days was 1.2–2.1-fold higher in the paddy soils (41.9–60.0% of the initial DOM-14C activity) than in the upland soils (28.7–35.7%), 2) 14C activity remaining in solution was significantly lower in the paddy soils than in the upland soils, and 3) 14C activity remaining in the same agricultural soil solution was not significantly different among the three moisture levels after 20days. Therefore, moisture strongly controls DOM fate, but moisture was not the key factor in determining the lower DOM in the paddy soils than in the upland soils. The UV absorbance of DOM at 280nm indicates less aromaticity of DOM from the paddy soils than from the upland soils. At any of the moisture levels, much more labile DOM was found in paddy soils (34.3–49.2% of the initial 14C labeled DOM) compared with that in upland soils (19.4–23.9%). This demonstrates that the lower DOM content in the paddy soil compared with that in the upland soil is probably determined by the less complex components and structure of the DOM. [Copyright &y& Elsevier]

In light of the limited resources of phosphorus (P) fertilizer, investigating the response of organic P (Po)-mineralizing microbial communities on the resource supply can be an avenue to optimize P recycling in agricultural systems. The alkaline phosphomonoesterase (alkaline PAse)-encoding gene PhoD is universally occurring in soil microorganisms. Here we collected 102 soil samples from Chinese agricultural fields to explore the effect of resource supply on the community of phoD -harboring bacteria. The relationships between the community diversity and soil organic carbon (SOC), total nitrogen (TN) and available Po concentration were fitted to the linear and quadric models suggested by the resource competition theory as well as the Michaelis-Menten model suggested by the metabolic theory of ecology. The results revealed that the response of phoD -harboring bacterial diversity to SOC and TN was likely related to the resource competition theory, with highest diversity at moderate SOC and TN concentration. In contrast, the phoD diversity increased with increasing available Po until the stationary value, which was consistent with the metabolic theory of ecology. Random forest models and multiple regression tree analyses identified the Po availability as the most important predictor on the variation of the phoD -harboring bacterial diversity and network topological features prior to the climate, soil texture, pH and all tested soil nutrient variables. This study highlights the critical role that Po plays in structuring phoD -harboring bacterial communities. Furthermore, for the first time, we correlated functional gene diversity to the corresponding enzymatic substrate availability from a metabolic theory perspective, confirming that the relationship follows the Michaelis-Menten model which was well known to predict the substrate regulation on the rate of enzymatic reactions. • PhoD diversity related to SOC and TN following the unimodal model. • PhoD diversity related to available organic P following the Michaelis-Menten model. • Available organic P shaped the phoD -harboring bacterial co-occurrence. [ABSTRACT FROM AUTHOR]

Microbial processes involving in nitrogen (N) assimilation mediate the continuous supply of mineral N for crop growth and the reactive N loss in intensively managed agriculture soils. This study aimed to reveal the microbial assimilation role in N accumulation in paddy soils under partial substitution of mineral fertilizer with organic materials (straw or manure), by quantifying the microbial N derived from living biomass and necromass. Rice rhizosphere and bulk soils were collected at a 31-year field trial including five fertilization treatments: no fertilizer (Control), mineral fertilizer alone (NPK), 20% mineral fertilizer substituted by rice straw (NPKS), and 30% and 60% mineral fertilizer substituted by manure (NPKLM and NPKHM, respectively). Incorporation of organic materials increased the total soil N by 22–76% compared to NPK, with a greater increase under manure- than rice straw-treated soils. Both organic inputs enhanced the amounts of living biomass and necromass N by 1.1–1.5 times via stimulating the activity of N cycling genes (chiA , AOA, narG , nirK , nirS , nosZ , nifH) in bulk soils. Although the pools of living biomass and necromass N in soils with manure amendments were 12–34% and 13–22% higher, than those with rice straw incorporation, their corresponding contributions to total N were 7.2–7.4% and 6.2–15% lower, respectively, suggesting a weaker relative microbial contribution in soil N accrual with manure amendments. Rice rhizosphere processes strengthened the role of microbial participation in soil N accumulation, particularly with organic inputs. The relative contribution of fungal necromass N to total N as well as the ratios of fungi to bacteria in both living biomass and necromass were lower under manure amendments than rice straw incorporation. As a whole, as compared with the incorporation of rice straw, the greater N accumulation in paddy soil with manure amendments is associated with the relatively weaker accumulation of fungal necromass and stronger retention of organic debris without microbial processing. • Organic inputs increase microbial derived-N relative to mineral fertilization. • Manure induces lower relative contribution of microbial necromass to soil N than rice straw. • Rhizosphere process strengthens the microbial participation in soil N accumulation. [ABSTRACT FROM AUTHOR]

Denitrification is important for nitrogen balance in agricultural ecosystems. It is well established that the abundance and structure of denitrifier are strongly influenced by environmental factors. However, knowledge of how nirS - and nirK -harboring microbial communities vary in paddy soils of different climatic regions is lacking, along with how these microbes are associated with denitrification potential. In this study, forty paddy soils from tropical, sub-tropical, warm-temperate, and mid-temperate climate zones were collected. The results showed that soils from the sub-tropical zone had the highest denitrification rates. The abundances of nirS and nirK had a strong negative association with C/N ratio and clearly varied among the four climate zones. Variation in nirS- and nirK- containing communities existed across sampling sites from each climate zone in terms of α- and β-diversity. Soil pH and climate factors significantly affected community diversity. Network analysis revealed that different climate regions had similar keystone taxa like Azospira , and Achromobacter , which were significantly related to denitrification rates. Structural equation modeling indicated that the differences in denitrifying enzyme activity among the four climate zones were mostly explained by climate factors, soil pH, and nirS biodiversity. Specifically, the biodiversity of nirS was more important than that of nirK in regulating potential denitrification activity in paddy soil, suggesting that nirS- type denitrifiers may have high activity under anaerobic conditions. Our results allow a deeper insight into the relative contribution of nirS- and nirK- containing communities to the soil denitrification activity in paddy soils across climate zones. This study highlighted the need of manipulation experiment to explain how denitrifier biodiversity affect potential denitrification activity in the future. • Soils from the sub-tropical zone have the highest denitrification rates. • nirS and nirK gene abundances show clear variations among the four climate zones. • nirS and nirK gene abundances have strong negative associations with C/N ratio. • The pH, C/N and climate factor significantly affected the community structure. • nirS gene biodiversity is important to regulate denitrification rates in paddy soil. [ABSTRACT FROM AUTHOR]

Abstract: Interactions among vegetation, soil physical and chemical conditions, and soil microbial communities determine the functions, resilience and stability of ecosystems. However, these interactions are largely unclear in the fragile Karst ecosystems. This study therefore investigated the bulk soils from five vegetation stages representing the dominant vegetation succession of subtropical Karst ecosystems. The results of this study indicated that, along the vegetation succession steps from arable farming, tussock, shrub, to secondary and primary forest, the contents of organic carbon (OC) and total nitrogen (TN), cation exchange capacity (CEC), water stability index (WSI), the amounts of microbial biomass carbon (Cmb) and biomass nitrogen (Nmb), Nmb:TN ratio, and Shannon indexes of fungal phylogenetic diversity (H′pf) and bacterial phylogenetic and catabolic diversities (referred as H′pb and H′cb, respectively) increased significantly (p < 0.05), whilst soil bulk density (BD) and metabolic quotient (qCO2) decreased (p < 0.05). Soil microbial properties (Cmb, Nmb, qCO2, H′pb, H′pf and H′cb) were correlated (p < 0.05) with the contents of soil OC, TN, CEC and BD. There were also correlations (p < 0.05) between the OC and the TN, CEC and BD of soils, and between the H′cb and the qCO2 of soil microbial communities. In conclusion, the accumulation of OC with vegetation succession drives improvements of soil physico-chemical properties, and the phylogenetic diversities as indicated by their partial 16S/18S rRNA genes and catabolic capability as indicated by utilization patterns of different carbon sources of microbial communities, which in turn may accelerate the restoration of the degraded ecosystems in the subtropical Karst region. [Copyright &y& Elsevier]

• Upland decreased soil C, but increased soil P. • Paddy increased soil C, N and P, but N and P increases exceeded that of C. • Both paddy and upland decreased the soil C:N:P stoichiometric ratios. • Responses of soil C:N:P stoichiometry across all climatic zones were similar in direction. • Effects of agricultural use on C:N:P stoichiometry were greater in warmer and wetter zones. Agricultural land use profoundly alters soil carbon (C), nitrogen (N), and phosphorus (P) contents, impacting crop productivity, environmental quality, and soil C sequestration. However, how the soil C:N:P stoichiometry is affected by upland and paddy cropping over broad geographical scale remains largely unknown. The objective of this study is to examine the soil C:N:P stoichiometry in woodland (as control), agricultural upland and paddy from four climate zones (tropics, subtropics, warm temperate, and mid-temperate) across eastern China. 720 surface soil samples were collected from 240 sites with adjacent woodland, upland, and paddy at a depth of 0–15 cm. Total C, N, and P contents and their ratios were determined. Among climate zones, C and N contents and C:N ratios decreased in the order of mid-temperate > tropics > subtropics > warm temperate, whereas C:P and N:P ratios followed the order of subtropics > mid-temperate and tropics > warm-temperate. Compared to woodland, upland agriculture decreased the C content by 4.0–6.4 g kg−1, but increased P content by 0.2–0.5 g kg−1, resulting in the decreases of C:N, C:P, and N:P ratios by 1.4–5.1, 3.4–91.5, and 1.6–4.1, respectively. Hence, uplands are relatively limited by C and N but enriched with P, particularly in warm temperate zone. By contrast, the C, N, and P contents in paddy soils were all increased compared to woodland soils, but larger N and P increase leads to the decreases in C:N and C:P ratios. The higher P content, and consequently lower C:N:P ratios in both agricultural soils are the consequences of intensive fertilization. As a whole, the direction of soil C, N, and P contents and their stoichiometric ratios in response to agricultural use was similar in the four climate zones: P increased, but C:N:P ratios decreased. The more intensive agricultural practices and stronger biological and geochemical processes with higher temperature and precipitation in warmer and wetter zones lead to more pronounced differences of soil C, N, and P contents and their stoichiometric ratios among land-use types than those in cooler and drier climates. [ABSTRACT FROM AUTHOR]

This study aimed to trace the incorporation of 13C-labeled hydrophilic and hydrophobic compounds extracted from maize straw into bacterial and fungal phospholipid fatty acids (PLFAs) in upland and paddy soils. In both soils, the amounts of bacterial 13C-PLFAs recovered from hydrophilic C were 1.2–2.8 times higher than those from hydrophobic C. By contrast, the amounts of fungal 13C-PLFAs recovered from hydrophobic C were 3.8–12.8 times greater than those from hydrophilic C. These results indicate that bacteria have a preference for the uptake of hydrophilic compounds, whereas fungi prefer hydrophobic compounds in both soils. The fungal preference for hydrophobic compounds is stronger than bacterial preference for hydrophilic compounds. This is partly owing to the efficient incorporation of hydrophobic compounds into actinomycete PLFA of 10Me18:0 in upland soil and bacterial PLFA of 18:1ω7c in paddy soil. Consequently, the specific uptake of hydrophilic and hydrophobic compounds from plant residues by bacteria and fungi will lead to divergent C pathways in soil. • Bacteria prefer to take up hydrophilic C. • Fungi prefer to take up hydrophobic C. • Fungal preference for hydrophobic C is stronger than bacterial preference for hydrophilic C. [ABSTRACT FROM AUTHOR]

• We describe microbial biomass role in C sequestration in fertilized paddy soil. • Organic inputs increase microbial growth and necromass accumulation. • Organic inputs do not alter microbial CUE in bulk soil, but reduce CUE in rhizosphere soil. • Microbial CUE is lower in rhizosphere soil than in bulk soil. Microbial anabolism relative to catabolism, reflected by the C use efficiency (CUE), determines the fate of C transformation in soil. Understanding how the microbial CUE and microbial necromass respond to fertilization is crucial for the evaluation of the C sequestration potential in intensively managed paddy soils. We examined the microbial CUE, microbial biomass turnover, and necromass accumulation in rice rhizosphere and bulk soils subjected to long-term (31 years) fertilizations: no fertilizers (control), mineral fertilizers alone (NPK), mineral fertilizers plus rice straw incorporation (NPK-Straw), and mineral fertilizers combined with a low or a high amount of organic manure (NPK-lowM or NPK-highM). The microbial CUE was determined by 18O incorporation into DNA. Microbial necromass accumulation was quantified by the biomarker analysis of amino sugars. Rice straw and manure incorporation reduced the microbial CUE in the rhizosphere soil, whereas the CUE remained constant in the bulk soil. CUE was lower in the rhizosphere soil than in the bulk soil due to nutrients uptake and root exudate release by rice plants, leading to a higher C/nutrient ratio in the rhizosphere. Organic inputs strengthened these rhizosphere processes and could thus weaken the relative potential of C sequestration. The microbial CUE decreased with the increase of the available C/N ratio in the rhizosphere but not in the bulk soil. The microbial CUE mainly depended on the respiration in the bulk soil and on the microbial growth in the rhizosphere soil, indicating the divergent microbial utilization of organic substrates between rhizosphere and bulk soils. In both rhizosphere and bulk soils, organic inputs promoted the microbial biomass growth rate and further increased the amount of microbial necromass by 27–52 % compared with NPK alone, which was highly correlated with the soil organic C pools. Despite enhancing rhizosphere respiration, our findings highlight that rice straw and manure applications increase C sequestration in paddy soils by enhancing the net flux of microbial biomass formation, and consequently promoting necromass accumulation. [ABSTRACT FROM AUTHOR]

• Microbial resource limitation is useful to identify effective fertilization strategies. • Soil microbes in karst croplands is limited by C and P, rather than by N. • Karst croplands do not need too much N fertilizer. • Combined inorganic and organic fertilization is better for karst croplands. Fertilization is a key management practice for maintaining or improving soil fertility in agro-ecosystems. Nevertheless, how fertilization strategies impact the status of soil microbial resource limitation is poorly understood. Here, we investigated the effects of long-term (11 years) fertilization on microbial resource limitation in a karst cropland under maize–soybean rotation. Soil microbial resource limitation was assessed using enzymatic stoichiometry. Six fertilization strategies were included, i.e., i) no fertilization (control), ii) inorganic fertilizers only (NPK), iii) inorganic fertilizers plus a low amount of straw (LSNPK), iv) inorganic fertilizers plus a low amount of manure (LMNPK), v) inorganic fertilizers plus a high amount of straw (HSNPK), and vi) inorganic fertilizers plus a high amount of manure (HMNPK). Overall, soil microbes were not limited by nitrogen, but co-limited by carbon and phosphorus across the six fertilization strategies. However, the degrees of microbial resource limitations were different between the control and fertilizer treatments. Application with inorganic fertilizers only aggravated microbial carbon limitation, but combined application of inorganic fertilizers and organic matters did not change the status of carbon limitation relative to the control. None of the fertilizer treatments changed the status of microbial nitrogen limitation. The treatments of NPK, LSNPK and LMNPK alleviated microbial phosphorus limitation, but HSNPK and HMNPK had no significant effects on phosphorus limitation relative to the control. By contrast, the crop production had no significant difference among all fertilizer treatments in the current study. Together, our results indicate that fertilizations can change microbial resource limitation status, which might be a more sensitive indicator to identify effective fertilization strategies relative to the crop production. Here we suggest that karst croplands do not need too much nitrogen fertilizer due to the nitrogen-rich characteristic, and that combined inorganic and organic fertilization strategies are better than single fertilization strategy in karst croplands. [ABSTRACT FROM AUTHOR]