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31901. 题目: Influence of wind erosion on dry aggregate size distribution and nutrients in three steppe soils in northern China
文章编号: N18062544
期刊: CATENA
作者: Yuchun Yan, Xu Wang, Zhenjie Guo, Jinqaing Chen, Xiaoping Xin, Dawei Xu, Ruirui Yan, Baorui Chen, Lijun Xu
更新时间: 2018-06-25
摘要: Wind erosion is a key process that causes soil degradation in the semiarid steppe regions of northern China. However, few studies have quantitatively measured the changes in dry aggregate distribution and nutrients in steppe soils under continuously varying wind erosion intensity. The objectives of this study were as follows: (1) to explore the different responses of three steppe soils to natural windblown treatments and (2) to quantify the changes in soil dry aggregate distribution, particle size distribution and soil nutrient contents under various wind erosion intensities for three steppe soils. We obtained samples of the following soils subjected to varying wind intensity via a natural windblown treatment: meadow steppe (MS), typical steppe (TS) and desert steppe (DS). Then, the physical and chemical properties of all soil samples were measured. The results showed that dry aggregate fractions <0.2 mm were selectively depleted by wind erosion and exhibited an exponential decrease in the residual soils with increasing wind erosion intensity. The organic carbon (OC), total nitrogen and available nitrogen in the three soils and the total phosphorous and available potassium in the TS and DS soils showed exponential decreases with increasing wind erosion intensity. The higher amounts of OC and nutrients were associated with fine dry aggregates (<0.2 mm), and fine dry aggregates were preferentially depleted by wind erosion, providing a mechanism for nutrient depletion caused by wind erosion. Finally, we established a comprehensive conceptual model of fine soil aggregate/particle depletion by wind erosion and subsequent nutrient depletion due to anthropogenic disturbances in temperate steppe areas.

31902. 题目: Integrating multi-source data to improve water erosion mapping in Tibet, China
文章编号: N18062543
期刊: CATENA
作者: Yuanyuan Yang, Ruiying Zhao, Zhou Shi, Raphael A. Viscarra Rossel, Dan Wan, Zongzheng Liang
更新时间: 2018-06-25
摘要: Quantitative estimation for soil erosion is necessary for protection of the environment, and to improve agricultural productivity. However, due to the large area, sparse and limited data in Tibet, soil erosion there is still poorly quantified. Here, we improved the factors of the Revised Universal Soil Loss Equation (RUSLE) and calculated water erosion in Tibet. Rainfall erosivity (R) was calculated with the 0.25°CPC Morphing technique (CMORPH) data and subsequently downscaled to 1-km spatial resolution using artificial neural network (ANN) based on environmental covariates; slope length and steepness (LS) was estimated using the 3 arc sec Shuttle Rader Topography Mission (SRTM) digital elevation model (DEM); cover management (C) and control practice (P) were assigned based on land cover and protection measurements; and soil erodibility (K) was calculated using the Environmental Policy Integrated Climate model (EPIC) with inputs of the contents of sand, silt, clay and organic carbon in soil samples from Tibet. We used the data-mining algorithm to model the K factor and the spatially referenced variables to generate a K factor map. The obtained factors were then used to calculate soil loss in Tibet at1-km resolution. Our study estimated the annual water erosion at5.43 t ha 1 y 1in Tibet, about5.44 × 108 t of soil lost yearly. The erosion rate increased from northwest to southeast, with most serious erosion occurring in the humid rain forest area in the southeast of Tibet. Our estimates of erosion area were generally consistent with previous national estimates. The largest differences were in the humid zone, Hengduan Mountain, and Yarlung Zangbo River basin, which are characterized by complex terrain and climate. Because of the applications of the best available data, we supply better, quantitative, finer spatial resolution estimates than previous studies. Our study is valuable for assessment of soil erosion in other data-scarce area suffering from soil loss by water erosion.

31903. 题目: Pedology of archaeological soils in tells of the Judean foothills, Israel
文章编号: N18062542
期刊: CATENA
作者: Danny Itkin, Onn Crouvi, H. Curtis Monger, Uri Shaanan, Haim Goldfus
更新时间: 2018-06-25
摘要: Tells (archaeological mounds) predominantly consist of poorly consolidated to unconsolidated sediments, and soils that are highly anthropogenic. This study examines pedogenic processes related to carbonate mobilization in tells in comparison with their peripheral soils (reference soil profiles). The key objective of this study is to test the hypothesis that tell deposits evolve through concurrent processes of sedimentation and pedogenesis (synlithogenic pedogenesis), and further explain it. Case studies are presented from three tells in semi-arid and Mediterranean climatic zones of the Levant. The methods applied included field survey, analyses of particle size distribution, pH, %CaCO3 and organic carbon content, and soil micromorphology. Soils of the tells contain miscellaneous cultural materials that derive mainly from degraded mud bricks, pottery and burnt wood. Chemical data show basic pH values, high CaCO3 content, and minor amounts of organic carbon. Field observations and lab analyses both indicate high similarity amongst the tells and their reference soil profiles. Buried tell soils show same characteristics as near-surface soils. However, the reference soil profiles show incipient horizonation, slightly darker colours, and more developed structure. Micromorphology of both the tells and the reference profiles show cohesively welded peds in a vughy microstructure, groundmass with an open porphyric c/f-related distribution, and discontinuous carbonate recrystallization. Relative rates of soil formation in the tells can be estimated when archaeological records are established. Contrary to the tells, the reference soil profiles show lower porosity and only minor remnants related to earth construction materials. We classify the soils of the studied tells as archaeological Calcareous Anthraltic Xerorthents. The correlative WRB classification would be Calcic Urbic Technosols (Archaic). The anthropogenic materials are as calcareous as the natural soils, but due to human action, carbonates in the tells are distributed differently. Based on these observations, ancient human actions and the dry climate have led to very little mobilization and accumulation of carbonates. The information provided in this study adds to the pedological understanding of archaeological environments. Specifically, it can be useful for the study of site formation processes of tells.

31904. 题目: The effectiveness of two contrasting mulch application rates to reduce post-fire erosion in a Portuguese eucalypt plantation
文章编号: N18062541
期刊: CATENA
作者: J.J. Keizer, F.C. Silva, D.C.S. Vieira, O. González-Pelayo, I. Campos, A.M.D. Vieira, S. Valente, S.A. Prats
更新时间: 2018-06-25
摘要: Wildfires are well-known to increase runoff and erosion during the initial stages of the window-of-disturbance, and mulching has been widely documented to effectively minimize this impact. However, the relationship between the rate of mulch application and erosion reduction is poorly studied, in spite of its potential importance for optimizing mulching costs and efforts per ha. Therefore, a field experiment was carried out in a recently burnt eucalypt plantation in Central Portugal that had been burnt by a moderate severity fire during August 2015, comparing sediment as well as organic matter losses from three untreated 2 m × 8 m erosion plots with losses from six plots mulched with eucalypt logging residues at two contrasting rates of either 2.6 or 8.0 Mg ha–1. The two mulching treatments resulted in the targeted litter covers of 50 and 79%, and these covers hardly changed over the ensuing year. Over this first post-fire year, the mulched plots produced significantly less mineral soil as well as organic matter losses than the untreated plots. At the same time, the plots with the high mulching rate lost consistently less sediments and organic matter than the plots with the low mulching rate but the differences were not statistically significant over all measurement periods. Total sediment losses over the first post-fire year were, on average, 86 and 96% lower following mulching at 2.6 and 8.0 Mg ha–1, respectively, than without mulching. In absolute values, total losses dropped from 8.0 to 1.1 and 0.3 Mg ha–1 y–1, respectively, or, in other words, similar to and well-below the widely-accepted threshold of tolerable soil loss of 1 Mg ha–1 y– 1. If this threshold value is acceptable to land managers, they could treat a three times larger area with the same amount of mulch.

31905. 题目: Water table drawdown reshapes soil physicochemical characteristics in Zoige peatlands
文章编号: N18062540
期刊: CATENA
作者: Liangfeng Liu, Huai Chen, Lin Jiang, Ji Hu, Wei Zhan, Yixin He, Dan Zhu, Qiuping Zhong, Gang Yang
更新时间: 2018-06-25
摘要: Warming and human activities have caused peatland degradation and water table drawdown, which greatly influence the physicochemical characteristics of soil at different depths. How water table drawdown affects soil physicochemical characteristics is not well understood for the Tibetan Plateau, especially the Zoige peatlands. This study measured variations in C/N ratio, ash content, δ13C, and humification index (HI) as a function of water table drawdown and depth by sampling 100-cm soil columns from three sites with different water tables in the Zoige peatlands. C/N ratio decreased while ash content and HI increased with water table drawdown, suggesting greater decomposition of soil organic matter at sites with a lower water table. The response of soil physicochemical characteristics to water table drawdown varied with depth: in the layer above the water table, C/N ratio did not vary, ash content decreased and HI increased; in the layer below the water table, C/N ratio and HI decreased, while ash content increased. The physicochemical characteristics above the water table were influenced mainly by new carbon input, while the characteristics below the water table were influenced mainly by decomposition. The depth profile of C/N ratio, ash content and HI aligned well with peat formation and decomposition and may be indicators of peat degradation. δ13C did not vary with water table drawdown, depth, or decomposition process. These insights into the variation of soil physicochemical characteristics with depths and water table may help elucidate the processes behind peatland degradation.

31906. 题目: Contrasting effects of organic and mineral nitrogen challenge the N-Mining Hypothesis for soil organic matter priming
文章编号: N18062539
期刊: Soil Biology and Biochemistry
作者: Kyle Mason-Jones, Niklas Schmücker, Yakov Kuzyakov
更新时间: 2018-06-25
摘要: Addition of easily available organic substances to soil often increases the CO2 efflux from pre-existing soil carbon (C). This phenomenon is often explained in terms of the Nitrogen (N)-Mining Hypothesis. According to this proposed – but never conclusively proven – mechanism, increased C availability induces N limitation in microbes, which then access N by degrading soil organic matter (SOM) – a priming effect. This is supported by some experiments demonstrating reduced CO2 efflux after mineral N addition. However, amino acids cause priming, despite their very low C:N ratios and rapid deamination to mineral N. To explore this contradiction, we applied 14C- and 15N-labelled C and N sources (glucose, alanine and ammonium sulfate) to rigorously test two key predictions of the N-Mining Hypothesis: (i) an amino acid should stimulate much less priming than glucose, and (ii) priming should be similarly suppressed for an amino acid or a stoichiometrically equivalent addition of glucose plus mineral N. Both of these key predictions of the N-Mining Hypothesis failed. Efflux of CO2 from native C was essentially determined by the type and amount of C added, with alanine stimulating more priming than glucose (16–50% cumulative increase relative to control, versus 0–25%, respectively). Higher C additions caused more priming than low additions. Mineral N reduced native-C-derived CO2 efflux when added alone or with organic substrates, but this effect was independent of the organic C additions and did not influence C-induced priming. These results were inconsistent with the hypothesized role of N mining in priming. We conclude that the N-Mining Hypothesis, at least in its current form, is not a universal explanation for observed priming phenomena. Instead, we observed a strong correlation between the rates of priming and the mineralization of the added substrates, especially during the first 8 days. This indicated that priming was best explained by energy-induced synthesis of SOM-degrading exoenzymes, possibly in combination with apparent priming from accelerated turnover of microbial biomass.

31907. 题目: Conversion of Tibetan grasslands to croplands decreases accumulation of microbially synthesized compounds in soil
文章编号: N18062538
期刊: Soil Biology and Biochemistry
作者: Zhen-Huan Guan, Xiao Gang Li, Lin Wang, Xiao Ming Mou, Yakov Kuzyakov
更新时间: 2018-06-25
摘要: Conversion of grassland to cropland affects microbial transformation of plant derived organic substances and the accumulation of microbially synthesized products in soil. We investigated long-term effects of agricultural use [more than 50 years' rotation with barley (Hordeum vulgare) and rapeseed (Brassica rapa)] after conversion from grasslands (grazed in the winter season) on the contents and composition of non-cellulose sugars and amino sugars in a broad range of soils on the Tibetan Plateau. Soils from two types of croplands (barley or rapeseed) were compared to a reference grassland soil by detailed analysis of plant vs. microbial and bacterial vs. fungal biomarkers. Long-term cultivation decreased total soil organic matter (SOM), light SOM and total non-cellulose sugar contents in the 0–20 cm soil by 27%, 47–72% and 57%, respectively, reflecting decreased root biomass compared to grassland. The ratios of (galactose + mannose)/(arabinose + xylose) and (rhamnose + fucose)/(arabinose + xylose) were both 26% smaller in cropland than in grassland soils, while the ratios of hemicelluloses in shoots or roots were similar between native and cultivated plants. Consequently, net transformation of plant substances to microbially synthesized polysaccharides decreased in cultivated soils. The total amino sugars (muramic acid, glucosamine, mannosamine, galactosamine) in cropland soils decreased by 42% as did their contribution to the SOM pool by 22%, compared to grassland soils, but the ratio of glucosamine/muramic acid in cropland soils doubled when compared to the grassland soil. This shows a strong decrease in microbial residue under cultivation, with the magnitude of the decrease greater in the bacterial than in the fungal components. All the above results from the intensively sampled site were confirmed in seven other sites featuring lower sampling intensity. We concluded that the conversion of grassland to cropland strongly decreases microbial transformation of plant residues and accumulation of the resulting microbial compounds – necromass – in soil (i.e., reduction of microbial input to stable SOM). The conversion also leads to a shift in the composition of microbial compounds towards a decreasing contribution of bacterial compared to fungal necromass.

31908. 题目: Depth-dependent response of soil aggregates and soil organic carbon content to long-term elevated CO2 in a temperate grassland soil
文章编号: N18062537
期刊: Soil Biology and Biochemistry
作者: L. Keidel, K. Lenhart, G. Moser, C. Müller
更新时间: 2018-06-25
摘要: Facing rising atmospheric CO2 concentrations, subsoils may play an important role in the global carbon (C) cycle due to the presence of unsaturated mineral surfaces. Further, macroaggregation is considered a crucial process influencing C sequestration. However, analyses on subsoil aggregation and C retention processes under long-term elevated CO2 (eCO2) are lacking. In this study we investigated the long-term effect of +20% above ambient CO2 concentration (corresponds to conditions reached 2035–2045) in a temperate grassland ecosystem at the Giessen Free Air CO2 Enrichment (Gi-FACE), Germany. A depth-dependent response of macroaggregation to eCO2 was observed: While in subsoil (15–45 cm depth) macroaggregation increased under eCO2, no CO2 induced change in macroaggregation was detected in topsoil (0–15 cm). Increased macroaggregation in subsoil coincided with higher SOC content of large macroaggregates (LM). Mean residence time (MRT) of SOC in aggregate-size classes were not different among each other under eCO2. However, macroaggregates and bulk soil differed in their MRT between soil depths. Despite increased macroaggregation and an estimated high SOC sequestration potential in subsoil we could not observe an increase in SOC content of bulk soil.

31909. 题目: Drying and rewetting conditions differentially affect the mineralization of fresh plant litter and extant soil organic matter
文章编号: N18062536
期刊: Soil Biology and Biochemistry
作者: Luis Lopez-Sangil, Iain P. Hartley, Pere Rovira, Pere Casals, Emma J. Sayer
更新时间: 2018-06-25
摘要: Drought is becoming more common globally and has the potential to alter patterns of soil carbon (C) storage in terrestrial ecosystems. After an extended dry period, a pulse of soil CO2 release is commonly observed upon rewetting (the so-called ‘Birch effect’), the magnitude of which depends on soil rewetting frequency. But the source and implications of this CO2 efflux are unclear. We used a mesocosm field experiment to subject agricultural topsoil to two distinct drying and rewetting frequencies, measuring Birch effects (as 3-day cumulative CO2 efflux upon rewetting) and the overall CO2 efflux over the entire drying-rewetting cycle. We used 14C-labelled wheat straw to determine the contribution of fresh (recently incorporated) plant litter or extant soil organic matter (SOM) to these fluxes, and assessed the extent to which the amount of soil microbial biomass + K2SO4-extractable organic C (fumigated-extracted C, FEC) before rewetting determined the magnitude of Birch effect CO2 pulses. Our results showed a gradual increase in SOM-derived organic solutes within the FEC fraction, and a decrease in soil microbial biomass, under more extreme drying and rewetting conditions. But, contrary to our hypothesis, pre-wetting levels of FEC were not related to the magnitude of the Birch effects. In the longer term, rewetting frequency and temperature influenced the overall (31-day cumulative) amount of CO2–C released from SOM upon rewetting, but the overall 14CO2–C respired from fresh straw was only influenced by the rewetting frequency, with no effect of seasonal temperature differences of 15 °C. We conclude that the mineralization of fresh plant litter in soils is more sensitive to water limitations than extant SOM in soils under drying-rewetting conditions. Moreover, we found little evidence to support the hypothesis that the availability of microbial and soluble organic C before rewetting determined the magnitude of the Birch effects, and suggest that future work should investigate whether these short-term CO2 pulses are predominantly derived from substrate-supply mechanisms resulting from the disruption of the soil organo-mineral matrix.

31910. 题目: Effects of artificial warming on different soil organic carbon and nitrogen pools in a subtropical plantation
文章编号: N18062535
期刊: Soil Biology and Biochemistry
作者: Yiqing Li, Yanxia Qing, Maokui Lyu, Shidong Chen, Zhijie Yang, Chengfang Lin, Yusheng Yang
更新时间: 2018-06-25
摘要: Uncertainty about the effects of climate warming on belowground processes of tropical and subtropical forests limits our ability to predict the response and feedback of such ecosystems to future climate change. Few field experiments in the tropics and subtropics have been conducted on the effects of manipulating warming on microbial community, enzyme activities and soil organic carbon (C) decomposition of forest ecosystems. Here, using buried cable techniques, we conducted a microcosm warming experiment to investigate extractable and acid resistant C and nitrogen (N) pools, microbial community composition, and enzyme activity after about 1.5 years of soil warming (+5 °C) in a subtropical plantation in southeastern China. The microbial community structure was quantified with phospholipid fatty acid (PLFA) analysis. Soil extractable and acid resistant C and N fractions were determined using a two-step sulfuric acid hydrolysis. We found that warming increased soil extractable C by 28% and acid resistant N decomposition by 20%. Soil warming decreased soil microbial N use efficiency by 31% but did not alter microbial C use efficiency. Warming differentially affected bacteria, fungi and enzymes activities. Our results suggest that climate warming can alter microbial community structure and enzyme activity and consequently lead to a serious imbalance between soil N and C decomposition in subtropical tree plantations.

31911. 题目: Experimentally testing the species-habitat size relationship on soil bacteria: A proof of concept
文章编号: N18062534
期刊: Soil Biology and Biochemistry
作者: Manuel Delgado-Baquerizo, David J. Eldridge, Kelly Hamonts, Peter B. Reich, Brajesh K. Singh
更新时间: 2018-06-25
摘要: The species-area relationship is one of the most widely reported ecological theories accounting for biodiversity of plants and animals. However, we lack solid experimental data demonstrating whether this key ecological theorem also applies in the microbial world. Here, we conducted a microcosm study to evaluate the role of habitat area in driving the diversity, abundance, composition and functioning (i.e., four enzyme activities linked to organic matter decomposition) of soil bacterial communities. Thus, we aim to evaluate whether the principle of species-area relationship is potentially applicable to soil microbes. We established a fully factorial experimental design of three island sizes ( 9, 50 and 150 cm2) by two sterile soils (low, high resources). After six months of glasshouse incubation, habitat-area was positively related to bacterial richness, relative abundance of Chloroflexi, Verrucomicrobia and δ-proteobacteria, and soil functions in both soils. Soil with higher resources always had the greatest bacterial richness and functions. Our findings provide a proof of concept by demonstrating the potential importance of both habitat-area and resource availability in driving soil bacterial biodiversity and functioning.

31912. 题目: High carbon use efficiency and low priming effect promote soil C stabilization under reduced tillage
文章编号: N18062533
期刊: Soil Biology and Biochemistry
作者: Marie Sauvadet, Gwena?lle Lashermes, Gonzague Alavoine, Sylvie Recous, Matthieu Chauvat, Pierre-Alain Maron, Isabelle Bertrand
更新时间: 2018-06-25
摘要: Increasing the accumulation of organic carbon (C) in soils is a crucial challenge both for soil fertility and for climate change mitigation. Heterotrophic microbial communities are key drivers of C cycling in the soil and are influenced by cultural practices, among other factors. However, whether changes in microbial communities in turn affect their C degradation functions is not well understood. Here, we studied the effects of prior soil management on the microbial taxonomic composition and activity of soils amended with wheat litter. Prior soil management was either conventional (CONV) (i.e., full inversion ploughing) or reduced tillage (RT) during a 5-year period in the same loamy soil in northern France. Soil samples taken from the top 5 cm of field plots were incubated with 13C-labelled litter of either flowering wheat or mature wheat for 29 days at 15 °C. We measured the C-CO2 and 13C-CO2, microbial biomass C (MBC) and 13C, and hydrolytic enzyme activities during decomposition. The initial bacterial and fungal community diversity was studied via high-throughput sequencing of ribosomal genes. The results showed that the MBC in the RT soil was initially 1.5-fold greater than that in the CONV soil; contrasting taxonomic compositions were also recorded. The soil biotic legacy impacted the degradation functions when the soils were amended with wheat litter. Compared with that in the CONV soil, the enzymatic efficiency of microorganisms in the RT soil increased by 49% and 61% in the presence of mature and flowering wheat litter, respectively. Enzyme efficiency was positively correlated with microbial litter C use efficiency (CUE) (r = 0.92, P-Value < 0.001) but negatively associated with the priming effect (PE) (r = 0.85, P-value < 0.001) across all soils and litter treatments. These findings demonstrated that the RT soil benefited both from an increase in litter C incorporated in the microbial biomass and from a reduction in soil C loss due to the PE, regardless of the quality of the decomposed litter. Our study indicated that agricultural practices such as RT, which enriches the amount of soil organic C (SOC) in the topsoil layer, can lead to positive feedback against C stabilization functions.

31913. 题目: Interactions of soil bacteria and fungi with plants during long-term grazing exclusion in semiarid grasslands
文章编号: N18062532
期刊: Soil Biology and Biochemistry
作者: Chao Zhang, Guobin Liu, Zilin Song, Jie Wang, Liang Guo
更新时间: 2018-06-25
摘要: Microbial succession has been extensively investigated during the restoration of degraded environments, but the interactions of microbes with plants and soils have not been well documented. We examined changes in the plant communities, soil variables, and microbial communities of grasslands after different periods of grazing exclusion (0, 10, 25, and 35 y) on the Loess Plateau in China. The microbial communities were characterized based on their biomass, enzymatic activities, quantity of functional microbes, and composition using high-throughput sequencing. Grazing exclusion increased the plant diversity, above- and belowground biomass, organic carbon content, total nitrogen content, microbial biomass, enzymatic activities, abundance of ammonia-oxidizing microbes, and diversities of the bacterial and fungal communities; however, the highest values of these variables occurred at the 25-y exclusion site and subsequently declined, indicating that long-term exclusion could have a negative effect on this grassland. Decreases in the abundances of Alphaproteobacteria and Leotiomycetes and increases in Acidobacteria and Sordariomycetes along the chronosequence indicated different successional patterns in the microbial communities. The patterns of change in the composition and diversity of the plant, bacterial, and fungal communities suggest that plant and bacterial succession occurred in parallel and proceeded faster than fungal succession. Indicators of the bacterial and fungal communities, including their biomass, enzymatic activities, and community composition and diversity, were affected by the plant diversity and organic carbon, total nitrogen, and nitrate nitrogen contents. Fungal succession was also susceptible to changes in the soil moisture content. These results suggest that plant diversity plays an important role in shaping the microbial communities, likely by altering the levels of soil nutrients and moisture.

31914. 题目: Interactive effects of initial pH and nitrogen status on soil organic carbon priming by glucose and lignocellulose
文章编号: N18062531
期刊: Soil Biology and Biochemistry
作者: Nang Seng Aye, Clayton R. Butterly, Peter W.G. Sale, Caixian Tang
更新时间: 2018-06-25
摘要: Soil pH and the availability of carbon (C) substrate and nutrients to microorganisms are well recognized to influence C priming. However, the mechanisms underpinning such interplay so far remain elusive. Given that liming acid soils, residue retention and fertilization are common agricultural practices, small changes in SOC content by these practices could have a big impact on the global C budget. This study aimed to gain insight into the impact of initial pH and mineral N availability on the priming effect of two C substrates with contrasting biodegradability. Stable 13C-labelled substrates, glucose and lignocellulose, were applied at the rate of 0.5 mg C g 1 soil with or without NH4NO3 to the same soil matrix with three different initial pH levels; pH 4.1 (strongly acidic), 4.7 (moderately acidic) and 6.6 (slightly acidic). The N treatment was based on a C:N of 10 of the added substrate (0.05 mg N g 1 soil) to ensure N was non-limiting. Interestingly, the priming effect was not linearly related to soil pH; greatest at pH 4.1, followed by pH 6.6 and lowest at pH 4.7. The greater net increase in microbial biomass upon C supply in strongly acidic soils compared to the moderately and slightly acidic soils would have enhanced co-metabolic decomposition of native soil organic C (SOC). The cumulative amount of primed SOC during the 30-day incubation period was greater in glucose- (21 μg C g 1) than lignocellulose-amended soils (13 μg C g 1). Nitrogen application reduced the C priming effect of both C substrates at all pH levels. This reduction was more prominent with lignocellulose and in the moderately acidic soils. The results suggest that maintaining optimal soil pH for nutrient availability and N application that exceeds the microbial N requirements in agricultural fields may minimize SOC loss via the priming effect in the short term.

31915. 题目: Liming does not counteract the influence of long-term fertilization on soil bacterial community structure and its co-occurrence pattern
文章编号: N18062530
期刊: Soil Biology and Biochemistry
作者: Bin Ma, Xiaofei Lv, Yanjiang Cai, Scott X. Chang, Miles F. Dyck
更新时间: 2018-06-25
摘要: Chemical fertilizer application is a common agronomic practice to improve crop productivity and liming is often used to counteract the soil acidification caused by long-term fertilization; however, it is unclear whether liming will counteract the effect of long-term fertilization on soil bacterial community structure and its co-occurrence pattern. Here, we examined the influence of long-term fertilization (NPKS) and liming (L) on soil bacterial community structure and its co-occurrence networks by sequencing 16S rRNA gene amplicons. Our results showed that liming counteracted the influence of long-term fertilization on soil pH, but not on soluble organic carbon (SOC) and electrical conductivity (EC). Long-term fertilization affected the abundance of Acidobacteriia, Deltaproteobacteria and Gammaproteobacteria in the 0–10 cm soil, and that of Deltaproteobacteria, Gammaproteobacteria and Gemmatimonadetes in the 10–20 cm soil; whereas liming affected the abundance of Acidobacteriia, Gammaproteobacteria, and Chloracidobacteria in the 0–10 cm soil and that of Deltaproteobacteria in the 10–20 cm soil. The bacterial community structure in soils with the NPKS-L treatment was different from that with other treatments, and was mainly affected by SOC, EC, and NO3 concentration. The link numbers in bacterial co-occurrence networks were decreased by long-term fertilization or liming alone, but were increased by the NPKS-L treatment. Notwithstanding the fact that liming alleviates fertilization-induced soil acidification, this study indicates that liming did not counteract the effect of long-term fertilization on soil bacterial community structure and its co-occurrence pattern, hence cannot recuperate the soil microbial functionality that is changed by long-term fertilization.

31916. 题目: Litter chemistry influences earthworm effects on soil carbon loss and microbial carbon acquisition
文章编号: N18062529
期刊: Soil Biology and Biochemistry
作者: Yong Zheng, Shuai Wang, Michael Bonkowski, Xiaoyun Chen, Bryan Griffiths, Feng Hu, Manqiang Liu
更新时间: 2018-06-25
摘要: Earthworms could affect soil C and N cycling process to balance their energy and nutrients requirements, and they could also regulate soil microbial community structure and microbial acquisition for C and N. However, the connection between faunal and microbial stoichiometry in the coupling soil C and N cycling remains poorly understood. In a controlled laboratory experiment, we amended soil with five litters differing in litter chemistry (clover, maize stover, wheat straw, Rumex and bagasse fiber) including a no litter control and treated them without or with earthworms (Metaphire guillelmi). After 90 d incubation, we examined changes in earthworm tissue and microbial stoichiometry and different soil C and N fractions. Earthworm tissue C content was rather stable compared with the fluctuation in tissue N, implying that C is under stronger control and associated with higher demand than N. The presence of earthworm significantly enhanced CO2 emissions and decreased particulate organic carbon (POC) and soil organic carbon (SOC) contents in the low lignin litter species clover, maize stover and wheat straw. Meanwhile, earthworm presence increased N2O cumulative emissions but exerted negligible effects on particulate organic nitrogen (PON) and soil total nitrogen (TN) contents irrespective of litter species. Correspondingly, earthworm regulated microbial C and N acquisition as C to N-degrading enzyme activity ratio were nearly doubled in the low lignin litter species clover, maize stover and wheat straw, while it was decreased in the high lignin litter species Rumex and bagasse fiber. However, the structural equation modeling indicated C loss induced by earthworms was mainly attributed to their effects on soil fungi and bacteria abundance, while much less related to C-degrading enzyme activities. In conclusion, litter species controlled earthworm effects on soil C and N loss and associated microbial acquisition for C and N, highlighting the pivotal role of resource chemistry in the regulation of soil fauna impact on soil functioning and ecosystem services.

31917. 题目: Microbial communities in soil profile are more responsive to legacy effects of wheat-cover crop rotations than tillage systems
文章编号: N18062528
期刊: Soil Biology and Biochemistry
作者: Anil Somenahally, Jesse I. DuPont, Jeffrey Brady, Javid McLawrence, Brian Northup, Prasanna Gowda
更新时间: 2018-06-25
摘要: Declining trends in soil health under continuous monoculture systems of winter wheat are a concern for sustainable production in the Southern Great Plains of the US. This study was conducted to evaluate the long-term implementation of conservation tillage in combination with nitrogen treatments and summer cover crop (cowpeas) rotations with winter wheat, for their legacy effects on soil health attributes of microbial communities and soil organic carbon (SOC). Microbial biomass and composition were estimated, along with soil physico-chemical parameters in the soil profile during the annual rotation cycle of wheat and cover crops. Positive legacy effects of cover crop rotations were evident, as arbuscular mycorrhizal fungi (AMF) biomass during the wheat-growing season was significantly higher in cover crop treatments (by around 30-70%) compared to summer fallow treatment. Some dominant taxons such as Acidobacteria, Actinobacteria, Proteobacteria (>70% of prokaryotic relative abundance) and Ascomycota (>50% of fungal relative abundance) were detected in all experimental treatments. Microbial composition did not significantly change at phylum level, although some reorganization at OTU level was evident throughout the soil profile, mostly because of nitrogen treatments. Several Glomeromycota OTUs were significantly altered by soil depth and by nitrogen fertilization suggest distinct mycorhizosphere interactions in subsurface soil than the surface soil. Tillage treatment did not significantly alter the microbial abundance and their diversity. Differences in microbial biomass-C concentration among experimental treatments did not result in a change in SOC concentrations within the soil profile. Results of this study demonstrated that summer cowpea appeared to be an effective cover crop for enhancing beneficial microbial biomass and expansion of the mycorrhizosphere to deeper soil layers. Cover crop rotations appeared to be a suitable option for rapidly enhancing soil health in winter wheat production systems.

31918. 题目: Organic amendments increase crop yields by improving microbe-mediated soil functioning of agroecosystems: A meta-analysis
文章编号: N18062527
期刊: Soil Biology and Biochemistry
作者: Gongwen Luo, Ling Li, Ville-Petri Friman, Junjie Guo, Shiwei Guo, Qirong Shen, Ning Ling
更新时间: 2018-06-25
摘要: Although numerous studies suggest that organic amendments are better at maintaining soil fertility and crop production than mineral-only fertilization, it is unclear if this occurs in different agricultural systems on a global scale. Here we report a comprehensive meta-analysis of 690 independent experiments comparing the performance of organic amendments and mineral-only fertilization on crop yields, the soil organic carbon (SOC) and total nitrogen (TN) contents, soil nutrient dynamics and biological properties. Our analysis shows that organic amendments increased crop yields on average of 27% than mineral-only fertilization. Farmyard manure (FYM) had the highest effect (49% increase) and this was especially clear in wheat croplands (40% increase). Organic amendment increased the amount of SOC (38%), TN (20%), microbial biomass carbon (MBC; 51%) and microbial biomass nitrogen (MBN; 24%) than mineral-only fertilization. Organic amendments also increased the soil microbiome enzyme activity in terms of soil hydrolytic C acquisition (C-acq; 39%), N acquisition (N-acq; 22%), P acquisition (P-acq; 48%) and oxidative decomposition (OX; 58%). Increased nutrient acquisition and oxidative decomposition could explain the positive effects of organic amendment on crop yields. These observed patterns were consistent for most organic amendments and cropping systems in diverse regions of the world. In summary, our analysis suggests that organic amendments can improve microbe-mediated soil ecosystem functioning, long-term soil fertility and crop productivity, relative to mineral fertilization, on a global scale.

31919. 题目: Physical and microbial mechanisms of decomposition vary in importance among root orders and tree species with differing chemical and morphological traits
文章编号: N18062526
期刊: Soil Biology and Biochemistry
作者: Anthony J. Minerovic, Oscar J. Valverde-Barrantes, Christopher B. Blackwood
更新时间: 2018-06-25
摘要: Decaying roots are the major source of carbon that is stabilized in soil, but our understanding of plant decomposition is primarily based on decay patterns observed in leaf tissues. Chemical traits that impact microbial activity are the primary intrinsic control over leaf decomposition, and it is usually assumed that similar mechanisms control root decay. We hypothesized that root morphological traits may be an alternative control over root decay because root tissue is embedded in soil and is similar in size to soil minerals and aggregates. We compared decomposition of roots from two coexisting tree species with contrasting traits: tulip poplar (Liriodendron tulipifera) and American elm (Ulmus americana). If morphological traits are a stronger control over decomposition than chemical traits, Ulmus roots should decompose faster due to their thinner structure and increased surface area. Alternatively, if chemical traits are more important, then Liriodendron roots should decompose faster because of greater nutrient and energy availability. Unlike previous studies, the experiment was conducted in the field using root litterbags that also included mineral soil to simulate realistic physical processes and root-soil mineral interactions. Our results indicate that controls over decomposition depend on root order. For 3–4th order roots, mass loss in Liriodendron roots was double that in Ulmus roots, reflecting chemical control, but the pattern was reversed for 1–2nd order roots, consistent with morphological control. In addition, tissue chemistry shifted dramatically during decomposition for all Liriodendron root orders, but not for Ulmus. In contrast, root morphology shifted for Ulmus, with large reductions in specific root length and tip abundance, but not for Liriodendron. These results indicate that Liriodendron decomposition occurs evenly across root orders through microbial activity, which is regulated by traditional chemical measures of recalcitrance. Ulmus roots are more chemically recalcitrant, but the finer 1–2nd order Ulmus roots still lost mass very rapidly through physical fragmentation. These differing mechanisms of decomposition have implications for how root carbon is deposited into differing pools of soil organic matter. Thick, labile roots may contribute more C to soil microbial biomass and clay-associated simple organic molecules, whereas thin, recalcitrant roots would be expected to contribute to particulate organic matter.

31920. 题目: Prokaryotic assemblages within permafrost active layer at Edmonson Point (Northern Victoria Land, Antarctica)
文章编号: N18062525
期刊: Soil Biology and Biochemistry
作者: Maria Papale, Antonella Conte, Anu Mikkonen, Luigi Michaud, Rosabruna La Ferla, Maurizio Azzaro, Gabriella Caruso, Rodolfo Paranhos, S. Cabral Anderson, Giovanna Maimone, Alessandro Ciro Rappazzo, Carmen Rizzo, Nunziacarla Spanò, Angelina Lo Giudice, Mauro Guglielmin
更新时间: 2018-06-25
摘要: This study was aimed at gaining insights on the prokaryotic community (in terms of both taxonomic composition and activities) inhabiting the active layer at Edmonson Point, an ice-free area on the eastern slope at the foot of Mount Melbourne (Northern Victoria Land, Antarctica). Samples were collected during the thawing period, when microbial physiological activities are restored to utilize previously frozen organic substrates. Despite the very small cell sizes (<0.1 μm3), indicating the occurrence of stressed, dormant and/or starved cells, the prokaryotic communities appeared to be metabolically active in the decomposition of high molecular weight (>600 Da) substrates, as indicated also by the obtained rates of enzymatic hydrolytic activities over proteolytic, glycolitic and phosphoric compounds. Taxonomical composition showed that Proteobacteria, Actinobacteria and Firmicutes dominated the prokaryotic community, with most of their members playing crucial roles in organic matter turnover, as well as nitrogen cycling, or entering a viable but not cultivable state to cope with continuously changing environmental conditions, such as in the case of the active layer. Finally, non-autochthonous bacteria (mainly of marine origin) were detected and they probably contribute to the organic matter turnover within such cold terrestrial habitat. This research provides the first comprehensive account of the prokaryotic communities inhabiting the Antarctic permafrost and contributes to existing information on the response of their abundance and metabolism in a permafrost area that undergoes to seasonal changes (e.g. in terms of temperature, water availability and ice presence).