Mycorrhizae are ubiquitous symbiotic associations between arbuscular mycorrhizal fungi (AMF) and terrestrial plants, in which AMF receive photosynthates from and acquire soil nutrients for their host plants. Plant uptake of soil nitrogen (N) reduces N substrate for microbial processes that generate nitrous oxide (N2O), a potent greenhouse gas. However, the underlying microbial mechanisms remain poorly understood, particularly in agroecosystems with high reactive N inputs. We examined how plant roots and AMF affect N2O emissions, N2O-producing (nirK and nirS) and N2O-consuming (nosZ) microbes under normal and high N inputs in conventional (CONV) and organically managed (OM) soils. Here, we show that high N input increased soil N2O emissions and the ratio of nirK to nirS microbes. Roots and AMF did not affect the (nirK + nirS)/nosZ ratio but significantly reduced N2O emissions and the nirK/nirS ratio. They reduced the nirK/nirS ratio by reducing nirK-Rhodobacterales but increasing nirS-Rhodocyclales in the CONV soil while decreasing nirK-Burkholderiales but increasing nirS-Rhizobiales in the OM soil. Our results indicate that plant roots and AMF reduced N2O emission directly by reducing soil N and indirectly through shifting the community composition of N2O-producing microbes in N-enriched agroecosystems, suggesting that harnessing the rhizosphere microbiome through agricultural management might offer additional potential for N2O emission mitigation.

Reactive N inputs (Nr) may alleviate N-limitation of plant growth and are assumed to help sustain plant responses to the rising atmospheric CO2 (eCO2). However, Nr and eCO2 may elicit a cascade reaction that alters soil chemistry and nutrient availability, shifting the limiting factors of plant growth, particularly in acidic tropical and subtropical croplands with low organic matter and low nutrient cations. Yet, few have so far examined the interactive effects of Nr and eCO2 on the dynamics of soil cation nutrients and soil acidity. We investigated the cation dynamics in the plant-soil system with exposure to eCO2 and different N sources in a subtropical, acidic agricultural soil. eCO2 and Nr, alone and interactively, increased Ca2+ and Mg2+ in soil solutions or leachates in aerobic agroecosystems. eCO2 significantly reduced soil pH, and NH4+-N inputs amplified this effect, suggesting that eCO2-induced plant preference of NH4+-N and plant growth may facilitate soil acidification. This is, to our knowledge, the first direct demonstration of eCO2 enhancement of soil acidity, although other studies have previously shown that eCO2 can increase cation release into soil solutions. Together, these findings provide new insights into the dynamics of cation nutrients and soil acidity under future climatic scenarios, highlighting the urgency for more studies on plant-soil responses to climate change in acidic tropical and subtropical ecosystems.

Orchard management practices such as weed control and irrigation are primarily aimed at maximizing fruit yields and economic profits. However, the impact of these practices on soil fertility and soil microbiology is often overlooked. We conducted a two-factor experimental manipulation of weed control by herbicide and trickle irrigation in a nutrient-poor peach (Prunus persica L. cv. Contender) orchard near Jackson Springs, North Carolina. After three and eight years of treatments, an array of soil fertility parameters were examined, including soil pH, soil N, P and cation nutrients, microbial biomass and respiration, N mineralization, and presence of arbuscular mycorrhizal fungi (AMF). Three general trends emerged: 1) irrigation significantly increased soil microbial biomass and activity, 2) infection rate of mycorrhizal fungi within roots were significantly higher under irrigation than non-irrigation treatments, but no significant difference in the AMF community composition was detected among treatments, 3) weed control through herbicides reduced soil organic matter, microbial biomass and activity, and mineral nutrients, but had no significant impacts on root mycorrhizal infection and AMF communities. Weed-control treatments directly decreased availability of soil nutrients in year 8, especially soil extractable inorganic N. Weed control also appears to have altered the soil nutrients via changes in soil microbes and altered net N mineralization via changes in soil microbial biomass and activity. These results indicate that long-term weed control using herbicides reduces soil fertility through reducing organic C inputs, nutrient retention and soil microbes. Together, these findings highlight the need for alternative practices such as winter legume cover cropping that maintain and/or enhance organic inputs to sustain the soil fertility.

Intensive tillage and high inputs of chemicals are frequently used in conventional agriculture management, which critically depresses soil properties and causes soil erosion and nonpoint source pollution. Conservation practices, such as no-tillage and organic farming, have potential to enhance soil health. However, the long-term impact of no-tillage and organic practices on soil microbial diversity and community structure has not been fully understood, particularly in humid, warm climate regions such as the southeast USA. We hypothesized that organic inputs will lead to greater microbial diversity and a more stable microbial community, and that the combination of no-tillage and organic inputs will maximize soil microbial diversity. We conducted a long-term experiment in the southern Appalachian mountains of North Carolina, USA to test these hypotheses. The results showed that soil microbial diversity and community structure diverged under different management regimes after long term continuous treatments. Organic input dominated the effect of management practices on soil microbial properties, although no-tillage practice also exerted significant impacts. Both no-tillage and organic inputs significantly promoted soil microbial diversity and community stability. The combination of no-tillage and organic management increased soil microbial diversity over the conventional tillage and led to a microbial community structure more similar to the one in an adjacent grassland. These results indicate that effective management through reducing tillage and increasing organic C inputs can enhance soil microbial diversity and community stability.

Chuju, a cultivar of Chrysanthemum morifolium, has been growing for both drink and medicinal uses for hundreds of years in China. In recent years, however, continuous monoculture of Chuju has caused declines in growth and yields. In this study, we investigated the plant growth and yields, soil microbial community composition dynamics, and the improvements of bio-organic fertilizer on plant growth and yield in Chuju continuous cropping systems. Results showed that the yield of Chuju flowers was decreased by 11-37%, but Fusarium oxysporum and total fungus populations were respectively increased by 34-79% and 53-107% in soils continuously monocultured with Chuju for two to four years, as compared to those for one year. Bio-organic fertilizer significantly reduced F. oxysporum population and the ratio of F. oxysporum to total fungus population, but enhanced shoot biomass, flower diameter, and flower yields, in comparison with synthetic fertilizer. These results indicate that bio-organic fertilizer could be used to alleviate soil problems and to sustain crop production in continuous cropping systems of Chuju. (C) 2017 Friends Science Publishers

A near infrared spectroscopy (NIRS) method was used for rapid quality evaluation of ferulic acid content in chrysanthemum morifolium cv. (Chuju) continuous cropping soil. Standard leverage, studentized residual and Mahalanobis distance were calculated to eliminate abnormal samples. After the initial near infrared spectrum was treated by two second derivative and Norris smoothing filter noise, 6000–4000 cm−1 wave number range and 7 factors were chosen for partial least squares (PLS) calibration model. The results showed that good correlations were presented between the calibration set/validation set and the HPLC values, and the calibration correlation coefficient (Rc) and validation correlation coefficient (Rcv) were 0.9914 and 0.9935. Root mean square error of calibration (RMSEC), root mean square error of prediction (RMSEP) and root mean square error of cross prediction (RMSECV) were 0.484, 0.539 and 0.615, respectively. This method was accurate, simple, rapid, nondestructive, and suitable for analysis of ferulic acid in continuous cropping soil.

Atmospheric carbon dioxide enrichment (eCO2) often increases soil nitrous oxide (N2O) emissions, which has been largely attributed to increased denitrification induced by CO2-enhancement of soil labile C and moisture. However, the origin of the N remains unexplained. Emerging evidence suggests that eCO2 alters plant N preference in favor of ammonium (NH4+-N) over nitrate (NO3−-N). Yet, whether and how this attributes to the enhancement of N2O emissions has not been investigated. We conducted a microcosm experiment with wheat (Triticum aestivum L.) and tall fescue (Schedonorus arundinaceus (Schreb.) Dumort.) to examine the effects of eCO2 on soil N2O emissions in the presence of two N forms (NH4+-N or NO3−-N). Results obtained showed that N forms dominated eCO2 effects on plant and microbial N utilization, and thus soil N2O emissions. Elevated CO2 significantly increased the rate and the sum of N2O emissions by three to four folds when NO3−-N, but not NH4+-N, was supplied under both wheat and tall fescue. While enhanced N2O emission was more related to the reduced plant NO3−-N uptake under wheat, it concurred with increased labile C under tall fescue. In the presence of NO3−-N, significantly lower shoot biomass N and 15N, but higher plant biomass C:N ratio, microbial biomass C and N, and/or soil extractable C indicated that eCO2 constrained plant NO3−-N utilization and likely stimulated root exudation. We propose a new conceptual model in which eCO2-inhibition of plant NO3−-N uptake and/or CO2-enhancement of soil labile C enhances the N and/or C availability for denitrifiers and increases the intensity and/or the duration of N2O emissions. Together, these findings indicate that CO2-enhancement of soil N and labile C favors denitrification, suggesting that management of N fertilizers in intensive systems will likely become more challenging under future CO2 scenarios.

To remove salicylic acid from aqueous solutions, Biochars (BC300, BC400 and BC500) as a low-cost adsorbent derived from wheat straw was pyrolyzed under different temperatures, characterized by surface area determination, CHN elemental analysis, FUR spectroscopy, scanning electron microscopy and X-ray diffraction. Batch sorption studies were carried and the adsorption kinetics, isotherm and thermodynamic were investigated. The results showed that pseudo second-order kinetics were the best model (R-2>0.99) for describing the adsorption of salicylic acid onto biochars. Equilibrium data were well fitted to the Langmuir (R-2>0.9779) and Freundlich (R-2>0.9264) isotherm models. The maximum monolayer coverage capacity (Q(m)) was calculated according to the linear form of the Langmuir equation was 60.24 mg.g(-1) for BC300, 50.25 mg.g(-1) ;for BC400, 30.67 mg.g(-1) for BC500 and 21.83 mg.g(-1) for BC600. The values of Q(m) increased with operating temperatures among four adsorbents. Various thermodynamic parameters such as Gibbs free energy (Delta G(0)), enthalpy (Delta H-0), and entropy (Delta S-0) changes were computed, and the data showed that the sorption process of salicylic acid solution onto BC300, BC400 and BC500 were spontaneous and endothermic but that they were spontaneous and exothermic for BC600.

Most plants prefer nitrate (NO3 (-)-N) to ammonium (NH4 (+)-N). However, high NO3 (-)-N in soil and water systems is a cause of concern for human health and the environment. Replacing NO3 (-)-N in plant nutrition regimes with an appropriate amount of NH4 (+)-N may alleviate these concerns. The purpose of this study was to evaluate the effects of different NH4 (+)-N/NO3 (-)-N ratios on chlorophyll content, stomatal conductance, Rubisco activity, net photosynthetic rate, dry matter yield and NO3 (-)-N accumulation in spinach grown hydroponically. The NH4 (+)-N/NO3 (-)-N percentage ratios were 0:100 (control), 25:75, 50:50, 75:25 and 100:0. Chlorophyll a and b, total chlorophyll, stomatal conductance, initial activity and activation state of Rubisco and net photosynthetic rate in spinach leaves were all reduced by increased NH4 (+)-N/NO3 (-)-N ratios. Significant correlation existed between these measurements. However, no statistical differences in dry matter yield were revealed between the 0:100 and 25:75 treatments. Leaf nitrate concentrations were reduced by 38% at the 25:75 treatment relative to the 0:100 treatment. These findings suggest that lowering the relative proportion of NO3 (-)-N in fertilizer could effectively reduce NO3 (-)-N contents in leafy vegetables without decreasing their yields.

在IGCC基础上发展起来的煤基甲醇动力多联产系统作为一种高效清洁的能源系统在中国具有广泛的应用前景.该文基于相对节能率,单位能量生产成本研究了联产系统热力性能和经济性能间的关联关系.研究表明,对甲醇动力多联产系统而言,不仅存在使相对节能率最高的最佳循环倍率,而且还存在使单位成本最低的最佳循环倍率.当化工岛的未反应气循环倍率位于2.17～4.44时,可以使相对节能率和单位成本二者都达到比较优化的状态.

Climate change factors such as elevated atmospheric carbon dioxide (CO2) and ozone (O3) can exert significant impacts on soil microbes and the ecosystem level processes they mediate. However, the underlying mechanisms by which soil microbes respond to these environmental changes remain poorly understood. The prevailing hypothesis, which states that CO2- or O3-induced changes in carbon (C) availability dominate microbial responses, is primarily based on results from nitrogen (N)-limiting forests and grasslands. It remains largely unexplored how soil microbes respond to elevated CO2 and O3 in N-rich or N-aggrading systems, which severely hinders our ability to predict the long-term soil C dynamics in agroecosystems. Using a long-term field study conducted in a no-till wheat-soybean rotation system with open-top chambers, we showed that elevated CO2 but not O3 had a potent influence on soil microbes. Elevated CO2 (1.5×ambient) significantly increased, while O3 (1.4×ambient) reduced, aboveground (and presumably belowground) plant residue C and N inputs to soil. However, only elevated CO2 significantly affected soil microbial biomass, activities (namely heterotrophic respiration) and community composition. The enhancement of microbial biomass and activities by elevated CO2 largely occurred in the third and fourth years of the experiment and coincided with increased soil N availability, likely due to CO2-stimulation of symbiotic N2 fixation in soybean. Fungal biomass and the fungi∶bacteria ratio decreased under both ambient and elevated CO2 by the third year and also coincided with increased soil N availability; but they were significantly higher under elevated than ambient CO2. These results suggest that more attention should be directed towards assessing the impact of N availability on microbial activities and decomposition in projections of soil organic C balance in N-rich systems under future CO2 scenarios.

Management intensity critically influences the productivity and sustainability of pasture systems through modifying soil microbes, and soil carbon (C) and nutrient dynamics; however, such effects are not well understood yet in the southeastern USA. We examined the effects of grazing intensity and grass planting system on soil C and nitrogen (N) dynamics, and microbial biomass and respiration in a long-term field experiment in Goldsboro, North Carolina, USA. A split-plot experiment was initiated in 2003 on a highly sandy soil under treatments of two grass planting systems (ryegrass rotation with sorghum-sudangrass hybrid and ryegrass seeding into a perennial bermudagrass stand) at low and high grazing densities. After 4 years of continuous treatments, soil total C and N contents across the 0–30 cm soil profile were 24.7% and 17.5% higher at the high than at the low grazing intensity, likely through promoting plant productivity and C allocation belowground as well as fecal and urinary inputs. Grass planting system effects were significant only at the low grazing intensity, with soil C, N, and microbial biomass and respiration in the top 10 cm being higher under the ryegrass/bermudagrass than under the ryegrass/sorghum-sudangrass hybrid planting systems. These results suggest that effective management could mitigate potential adverse effects of high grazing intensities on soil properties and facilitate sustainability of pastureland.

Turfgrass systems represent one major group of intensively managed ecosystems and a potential carbon (C) sink. Turfgrass management practices critically influence C inputs to soil, soil microbial dynamics, and in turn soil C and nitrogen (N) balance. However, how management practices influence soil organic C and microbial dynamics in turfgrass systems is not well understood. We investigated the effect of management duration and intensities on soil microbial biomass, microbial activities and soil organic C contents in two golf courses dominated by Bermuda grass near Raleigh, NC, USA. In Hope Valley, two fairways were studied under the same management scheme but for a huge difference in duration (10 vs. 80 years). Whereas, in Treyburn, rough, fairway, and tee areas that were constructed in the same year but received different N and water inputs, and with different cutting frequencies were examined. Results showed conversion of a pine forest to turfgrass course reduced soil microbial biomass, microbial activities and soil organic C. Long term turfgrass planting accumulated soil organic C and N at rates of 71.9 and 10.6 g m(-2) y(-1) over 80 years. Moderate management intensity resulted in highest soil organic C and microbial biomass C. High N and water inputs stimulated decomposition and reduced the C accumulation in highly managed areas such as the tee area. These results suggest that management practices may critically affect organic C sequestration in turfgrass management systems. (C) 2014 Friends Science Publishers

Invasive plant species can interact with native soil microbes in ways that change how they use nutrients and allocate biomass. To examine whether Microstegium vimineum form symbiotic associations with arbuscular mycorrhizal fungi (AMF) and whether AMF mediate nutrient acquisition and growth of the plant, we conducted a field survey in Raleigh, NC and Hangzhou, China and two experiments in growth chambers. This is the first report that M. vimineum is mycorrhizal, with colonization rates of 47 and 21 % in its native and invaded range, respectively. In the growth chamber, addition of an AMF inoculum mixture significantly promoted M. vimineum biomass accumulation in both field and sterilized soils, particularly after 64 days of growth. Arbuscular mycorrhizal fungi also increased plant phosphorous (P) uptake but did not consistently affect total plant nitrogen (N) acquisition, leading to decreases in plant N:P ratios. More interestingly, AMF significantly altered plant morphology, increasing the number of stolons and aerial roots per individual (59 and 723 %), aerial roots per gram aboveground biomass (374 %) and aerial roots per stolon (404 %). Our results suggest that mycorrhizal enhancement of plant growth by stimulating tillering may serve as another mechanism by which M. vimineum can quickly take over new territory. Future studies on invasive plant-microbial interactions are needed to understand the mechanisms through which microbes contribute to the competitive ability of invasive plants.

Two field microcosm experiments and 15N labeling techniques were used to investigate the effects of biochar addition on rice N nutrition and GHG emissions in an Inceptisol and an Ultisol.

AimsWhy invasive plants are more competitive in their introduced range than native range is still an unanswered question in plant invasion ecology. Here, we used the model invasive plant Solidago canadensis to test a hypothesis that enhanced production of allelopathic compounds results in greater competitive ability of invasive plants in the invaded range rather than in the native range. We also examined the degree to which the allelopathy contributes increased competitive ability of S. canadensis in the invaded range.MethodsWe compared allelochemical production by S. canadensis growing in its native area (the USA) and invaded area (China) and also by populations that were collected from the two countries and grown together in a 'common garden' greenhouse experiment. We also tested the allelopathic effects of S. canadensis collected from either the USA or China on the germination of Kummerowia striata (a native plant in China). Finally, we conducted a common garden, greenhouse experiment in which K. striata was grown in monoculture or with S. canadensis from the USA or China to test the effects of allelopathy on plant plant competition with suitable controls such as adding activated carbon to the soil to absorb the allelochemicals and thereby eliminating any corresponding allopathic effects.Important findingsAllelochemical contents (total phenolics, total flavones and total saponins) and allelopathic effects were greater in S. canadensis sampled from China than those from the USA as demonstrated in a field survey and a common garden experiment. Inhibition of K. striata germination using S. canadensis extracts or previously grown in soil was greater using samples from China than from the USA. The competitive ability of S. canadensis against K. striata was also greater for plants originating from China than those from the USA. Allelopathy could explain about 46% of the difference. These findings demonstrated that S. canadensis has evolved to be more allelopathic and competitive in the introduced range and that allelopathy significantly contributes to increased competitiveness for this invasive species.

The extent to which terrestrial ecosystems can sequester carbon to mitigate climate change is a matter of debate. The stimulation of arbuscular mycorrhizal fungi (AMF) by elevated atmospheric carbon dioxide (CO2) has been assumed to be a major mechanism facilitating soil carbon sequestration by increasing carbon inputs to soil and by protecting organic carbon from decomposition via aggregation. We present evidence from four independent microcosm and field experiments demonstrating that CO2 enhancement of AMF results in considerable soil carbon losses. Our findings challenge the assumption that AMF protect against degradation of organic carbon in soil and raise questions about the current prediction of terrestrial ecosystem carbon balance under future climate-change scenarios.

Climate change factors such as elevated atmospheric carbon dioxide (CO₂) and ozone (O₃) can exert significant impacts on soil microbes and the ecosystem level processes they mediate. However, the underlying mechanisms by which soil microbes respond to these environmental changes remain poorly understood. The prevailing hypothesis, which states that CO₂- or O₃-induced changes in carbon (C) availability dominate microbial responses, is primarily based on results from nitrogen (N)-limiting forests and grasslands. It remains largely unexplored how soil microbes respond to elevated CO₂ and O₃ in N-rich or N-aggrading systems, which severely hinders our ability to predict the long-term soil C dynamics in agroecosystems. Using a long-term field study conducted in a no-till wheat-soybean rotation system with open-top chambers, we showed that elevated CO₂ but not O₃ had a potent influence on soil microbes. Elevated CO₂(1.5×ambient) significantly increased, while O₃ (1.4×ambient) reduced, aboveground (and presumably belowground) plant residue C and N inputs to soil. However, only elevated CO₂ significantly affected soil microbial biomass, activities (namely heterotrophic respiration) and community composition. The enhancement of microbial biomass and activities by elevated CO₂ largely occurred in the third and fourth years of the experiment and coincided with increased soil N availability, likely due to CO₂-stimulation of symbiotic N₂ fixation in soybean. Fungal biomass and the fungi∶bacteria ratio decreased under both ambient and elevated CO₂ by the third year and also coincided with increased soil N availability; but they were significantly higher under elevated than ambient CO₂. These results suggest that more attention should be directed towards assessing the impact of N availability on microbial activities and decomposition in projections of soil organic C balance in N-rich systems under future CO₂ scenarios.

Conventional agriculture with intensive tillage and high inputs of synthetic chemicals has critically depleted the soil C pools. Alternative practices such as no-tillage and organic inputs have been shown to increase soil C content. However, the long-term impact of these practices on soil C pools was not fully understood under humid and warm climate conditions such as the southeast USA. We hypothesized that a combination of sustainable production practices will result in greater microbial biomass and activity and soil organic C than any individual practice. To test this hypothesis, we conducted a long-term experiment examining how different farming practices affect soil C and N pools and microbial biomass and activities in a fine-sandy loam (FAO: Acrisol) in the southern Appalachian mountains of North Carolina, USA. The experiment was a randomized complete design with four replications. Six management treatments, i.e., tillage with no chemical or organic inputs (Control, TN), tillage with chemical inputs (TC), tillage with organic inputs (TO), no-tillage with chemical inputs (NC), no-tillage with organic inputs (NO), and fescue grasses (FG), were designed. Organic C and N pools and microbial properties in 0-15 cm soils were markedly different after 15 years of continuous treatments. Both no tillage and organic inputs significantly promoted soil microbial biomass by 63-139% and 54-126%; also microbial activity increased by 88-158% and 52-117%, respectively. Corresponding increases of soil organic C by 83-104% and 19-32%, and soil organic N by 77-94% and 20-32% were measured. The combination of no tillage and organic management increased soil organic C by 140% over the conventional tillage control, leading to a soil C content comparable to an un-disturbed grassland control. No tillage reduced the proportion of organic C in the light fraction with d < 1.0 g cm(-3) (from 1.53-3.39% to 0.80-1.09%), and increased the very heavy fraction with d > 1.6 g cm(-3) (from 95% to 98%). Organic inputs, however, had little impact on C distribution among different density fractions of the soil except light fraction in tillage treatment. Over all, no-tillage practices exerted greater influence on microbial biomass levels and activity and soil organic C levels and fractionations than organic inputs. Our results support the hypothesis and indicate that management decisions including reducing tillage and increasing organic C inputs can enhance transformation of soil organic C from the labile into stable pools, promote soil C accumulation, improve soil fertility and while mitigate atmospheric CO(2) rise. (C) 2011 Elsevier B.V. All rights reserved.

Earthworms play important roles in sustaining turfgrass systems through enhancing soil aeration, water filtration, and thatch mixing and decomposition. However, high surface activities of earthworms can lead to uneven playing surfaces, soil erosion and new niches favorable to weed invasion in the playing area of a golf course. Shifts from highly toxic and persistent to less toxic and easily degradable pesticides have been suggested to be largely responsible for high earthworm activities observed in turf systems worldwide. In this study, we examined the impact of fungicides and insecticides on earthworm behavior in controlled environments and on the dynamics of earthworm community in the field. Single application of insecticides Sevin (carbaryl) and Merit (imidacloprid) at the manufactures' suggested doses significantly inhibited earthworm feeding activity for at least three weeks without leading to any earthworm death. Fungicides did not show significant toxicity to earthworms when applied only once, but their toxicities increased as application frequency increased. Consecutive weekly applications of Sevin, Merit and T-methyl for four times led to earthworm mortality of 35, 45 and 80%, respectively. In the field, six consecutive weekly applications of T-methyl and Sevin significantly reduced the abundance and biomass of earthworms with suppressive effects lasting for at least 6 weeks after the chemical application was terminated. Taken together, these findings suggest that the surface activities of earthworms in turfgrass systems may be managed through moderate application of pesticides at peak periods of earthworm activities. (c) 2010 Elsevier B.V. All rights reserved.