Search

The mechanism by which temperature sensitivity (TS) of soil N 2 O emissions is increased by agricultural management with application of nitrogen fertilizer (AMN) is unclear. We hypothesized that a higher TS of N 2 O emission induced by AMN is the result of the faster growth of specific microorganisms in response to faster nitrogen (N) mineralization at higher temperatures. To test this hypothesis, we used reciprocal transplants to separate the contributions of abiotic and microbial components to the TS of N 2 O emissions in an arable soil receiving organic and inorganic fertilizers and its neighboring natural grassland soil treated with two levels of N. N 2 O sources were separated with acetylene, and the abundances of N 2 O-producing microbes were assessed by quantifying the copy numbers of the associated functional genes. Compared with natural soil, only changes in abiotic properties increased the Q 10 (the factor by which the rate increases with a 10 °C rise in temperature) by 105.7%, while changes in both abiotic and the microbiome increased the Q 10 by 225.2%. Higher TS of N 2 O emission in the arable soil induced by a microbiome shift was associated with faster N mineralization, increased proportion of nitrification-N 2 O emission, and faster growth of ammonia-oxidizing bacteria at higher temperatures. Addition of ammonium nitrate further enhanced the TS of N 2 O emissions, the proportion of nitrification-N 2 O emission, and the increased extent of the growth of ammonia-oxidizing bacteria in the soil with AMN compared to the natural grassland soil. Substrate-driven growth of ammonia-oxidizing bacteria with higher substrate preference contributes significantly to the higher TS of N 2 O emission caused by AMN. [ABSTRACT FROM AUTHOR]

A spatial system dynamic (SSD) model for simulating desertification was developed by integrating climate, soil water, population, economy, pasturage, and land use. Net Primary Production (NPP) was selected as an intermediate variable to measure the impacts of driving forces and desertification grades. Ordos in China was selected to test the model. Ten scenarios were designed to simulate desertification dynamics in Ordos from 2011 to 2030. The results showed that the SSD model was reliable, and the overall accuracy of desertification degree was approximately 83%. Climate factors had relatively higher sensitivities than other parameters. Although humid climate and sustainable development strategy would reduce desertified land area and desertification degree before 2025, the rapid increase in pasturage pressure would offset this trend. Arid climate and unsustainable development strategy would accelerate desertification expansion. For local government, it is necessary to persist in the present desertification prevention policy and completely banned grazing after 2025. [ABSTRACT FROM AUTHOR]

Nitrogen (N) is an essential element for plant growth and development. N levels in soil may also impact plant disease occurrence. However, the physiological and microbial mechanisms between N levels in soil and plant disease occurrence are not quite clear at present. In this study, we examined the impact of seven urea levels (0 to 800 mg kg−1 soil) on the physiology of tomato (Lycopersicon esculentum) and fungal disease occurrence. Our results showed that the disease incidence and index caused by a tomato early blight pathogen (Alternaria alternata) increased with increasing N levels. The disease index and percentage of disease incidence were positively correlated with N content, indole-3-acetic acid (IAA) and salicylic acid (SA) in plants, but negatively correlated with fungal community diversity. In addition to pathogens (A. alternata) that cause known early blight, 39 other fungal taxa were also identified as plant pathogens in tomato roots, leaves, and soil, the dominant putative pathogens included Ceratobasidiaceae sp., Fusarium oxysporum , Macrophomina phaseolina , Nectriaceae sp., Podosphaera fusca and Trichoderma viride. N levels affected the distribution and dynamics of the fungal pathogen community, such as the abundance of Fusarium oxysporum increased by 33% on roots from days 25 to 35. Our results demonstrated that plants undergo complex disease risk from different pathogens under different N levels, highlighting a need for proper N management, and integration of nutrient management as a disease control approach for sustainable agricultural production. [Display omitted] • The disease incidence and index of tomato early blight increased with increasing nitrogen levels. • Disease occurrence was positively correlated with plant N nutrition. • Disease occurrence was negatively correlated with connectance and average degree of fungal co-occurrence network. • 39 fungal taxa were identified as potential plant pathogens in tomato-soil system. • The pathogens abundance varied with pathogen types, time, and plant tissue under different nitrogen levels. [ABSTRACT FROM AUTHOR]

Temperature is an important factor governing the community traits of N 2 O-emission related functional guilds (mainly autotrophic ammonia oxidizers and heterotrophic denitrifiers) and their activities. However, there have been few attempts to explore the broad response patterns of these guilds to temperature changes across arable soils. For this, a temperature-controlled (15, 25 and 35 °C) microcosm experiment was conducted using three arable soils (Fujian, Gansu, and Jiangsu) in China under two different fertilizations (no fertilization control (CK) and inorganic fertilization (NPK)). In conjunction with the measurement of N 2 O emission, the community structure and abundance of ammonia oxidizing archaea (AOA) and bacteria (AOB), as well as nirS - and nirK -denitrifiers were assessed using T-RFLP and quantitative PCR, respectively. The analysis of community traits indicated a consistent response pattern of AOAs to temperature in terms of guild abundance, and a consistent effect of inorganic fertilization on the abundance of AOBs, but soil-dependent response patterns to fertilization and temperature were found for nirS - and nirK -denitrifiers in terms of abundance and community structure. The correlation analysis suggested that AOAs possibly assumed a role in N 2 O emission in all the tested soils, and nirS -denitrifiers probably participated in N 2 O emission in both the Fujian and Gansu soil, while a considerable amount of N 2 O emission in the Jiangsu soil might have been derived from heterotrophic nitrification. [ABSTRACT FROM AUTHOR]

Belowground biodiversity is essential for soil functioning, but the effect of belowground biodiversity loss on food safety is unknown. We investigated the loss of soil microbial diversity on insecticides accumulation in Brassica. We manipulated soil biodiversity using the dilution-to-extinction approach in a Brassica-soil-insecticide system, monitored microbial communities via high-throughput sequencing, and identified potential functional microbes. Compared with unsterilized soil, the richness of functional bacteria was reduced by 14.1%, 36.2%, 51.6% and 73.2%, respectively, in the corresponding sterilized soil inoculated with 1-, 10 −2 -, 10 −4 - and 10 −6 -fold diluted soil suspension. The acetamiprid and imidacloprid concentrations increased significantly in Brassica tissues grown in sterilized soil inoculated with 10 −6 -fold diluted suspension. A bacterial group predominated in functional microbes of soils inoculated with 1-, 10 −2 - or 10 −4 -fold diluted suspension, but the relative abundance declined in soil inoculated with a 10 −6 -fold diluted suspension. Our findings revealed that undesirable impacts by the loss of soil biodiversity at an intermediate level on the accumulation of soil contaminant in plants could be alleviated by microbial functional redundancy through disproportionally complementary growth of specific functional microbial taxa, but severe loss of soil biodiversity would threaten food safety. [ABSTRACT FROM AUTHOR]

The impacts of long-term application of inorganic and organic fertilizers on the activity, community composition, and abundance of denitrifying bacteria in an aquic soil of Northeast China were analyzed in this study. Denitrifying taxa were characterized for their nitrite reductase genes, nirS and nirK . The results showed that addition of inorganic fertilizer to soil decreased potential denitrification enzyme activity (DEA) by 41.1%, and this effect was mirrored by a reduction (39.0%) in the nirS -, but not nirK -denitrifiers' abundance. Addition of organic fertilizer increased DEA by 41.3% but had no impact on the abundance of either nirS - or nirK -denitrifiers. Inorganic fertilization strongly altered the community structure of nirK but only marginally impacted the community structure of nirS -denitrifiers; organic fertilizer had no influence on the community structures of these two guilds. DEA was significantly correlated with community structure of nirK -denitrifiers, but not with community structure of nirS -denitrifiers and abundances of both nirK - and nirS -denitrifiers. Moreover, community structure of nirK -denitrifiers was significantly correlated with pH, while nirS -denitrifiers were impacted by soil pH, total phosphorus (TP), and Olsen phosphorus (Olsen P) status. Our results suggest that different influences of inorganic and organic fertilization on DP are linked to a distinct structural change of nirS - and nirK -denitrifying bacterial communities in this aquic brown soil. [ABSTRACT FROM AUTHOR]

We integrated chemical, enzymatic, isotopic and molecular approaches to investigate both straw decomposition and its priming effect (PE) on native soil organic carbon (SOC) decomposition in soils with 23 years of application of chemical fertilizer (NPK) and partial substitution of chemical fertilizer by organic manure (NPKM). We found that NPK and NPKM past application significantly increased decomposition of straw. The increases in straw decomposition were not correlated with the abundances of microbiome assimilating straw carbon, but were significantly correlated with abundances of total bacteria, fungi and activities of cellulose-degrading enzymes. In addition, application of NPK did not change straw-induced PE while application of NPKM markedly reduced PE. The variation of PE with different past fertilization was correlated with the abundance of residue-stimulated fungi. The unchanged PE with NPK application in the presence of enriched nutrients and reduced pH was probably due to residue-promoted growth of acid-tolerant SOC-decomposing taxa (unclassified bacteria families belong to Acidobacteria GP3, Gamaproteobacteria and WPS-2 and unclassified fungal families belong to Chaetothyriales and Agaricomycetes). Our research sheds light on the complex processes of carbon transformation in the soils undergoing different long-term nutrient management. • NPK and NPK-manure application increased straw decomposition. • NPK application did not change residue-induced priming effect. • NPK-manure application reduced residue-induced priming effect. • Straw decompositions were mainly related to cellulose depolymerizing ability. • Priming effects were mainly related to abundance of stimulated fungi. [ABSTRACT FROM AUTHOR]

Sand-stabilization, the most important ecological service provided by desert and desertified lands, can alleviate severe wind erosion of soil and is induced by both climate change and human activities. However, with a lack of related data, few studies have focused on the spatial differences in driving factors of sand-stabilization services at a large scale. The present study, based on climatic and socioeconomic data, employed Inner Mongolia as a study area and assessed different climatic and human factors affecting changes of the sand-stabilization services from 1981 to 2010. The results showed that the sand-stabilization service of Inner Mongolia has changed significantly over the past 30 years over an area of 563,584 km 2 , and the spatial distribution of the regions affected exhibited considerable heterogeneity. With respect to regions experiencing a significant increase of sand-stabilization service, climate change, human activities, and the coupled effect of the two accounted for 68.49%, 61.25%, and 60.72%, respectively, of the total area experiencing a significant increase in area. Temperature and afforestation projects were the most important drivers of change in these areas. With respect to regions with a significant decrease of sand-stabilization service, climate change, human activities, and the coupled effect of the two accounted for 51.87%, 68.35%, and 42.64%, respectively, of the total area experiencing a significant decrease in area, which was mainly attributed to the increase of livestock stocking rates and crop area. [ABSTRACT FROM AUTHOR]

Emissions of the greenhouse gas nitrous oxide (N 2 O) from soil are sensitive to many factors including temperature, nutrient status, pH and bulk-density. Interactions among these are complex, particularly in agricultural systems where fertilizer-addition has interactive influences across many soil properties. Under laboratory conditions, the temperature sensitivity of N 2 O emissions, as measured by Q 10 values (fractional change in rate with a 10 °C increase in temperature), was higher in soils receiving long-term fertilizer addition compared with control. Different fertilization regimes significantly influenced the emission pathways. Application of manure increased the proportion of potential N 2 O derived from denitrification although the incubation condition used in the present study might not be favorable for anaerobic denitrification. The abundance of archaeal amoA gene copies increased under all fertilizer treatments, but that of bacterial amoA only increased under mineral (NPK) fertilization. Meanwhile, abundance of nirS , nirK and nosZ only increased under OM and MNPK fertilization. T-RFLP analyses showed that both ammonia oxidizing and denitrifier community structures were altered by fertilization, but only the nirS community structure was sensitive to temperature change. Furthermore, a strong correlation was observed between nirS gene abundance and potential N 2 O emissions. Relationships between AOA, nirK gene abundances and potential N 2 O emission were significant but relatively weak. PLS path model revealed that besides direct effect, potential N 2 O emission was also indirectly influenced by temperature through mediation of NH 4 + concentration and nirS -type denitrifier. Our work suggests that warming-induced elevation of potential N 2 O emission could be strengthened by long-term application of fertilizers, especially organic manure, via shifting community abundance and structure of nirS -type denitrifier. [ABSTRACT FROM AUTHOR]

Abstract: It is unclear how inhibition of nitrous oxide (N2O) emissions by nitrification inhibitor (NI) is regulated through the ammonia oxidizing bacteria (AOB) or archaea (AOA) in arable soils. In this study, we investigated effects of 2-chloro-6-(trichloromethyl)-pyridine (Nitrapyrin, NP) on N2O emissions, and characterized the ammonia oxidizing microbial community in three arable soils typical of northern China. In alluvial, black, and paddy soils, average N2O emission rates were increased by addition of urea by 3.5, 0.7 and 2.1 pM N2O g−1 soil h−1, respectively, but were reduced by 2.9, 0.4 and 2.2 pM N2O g−1 soil h−1 when urea was applied with NP. The stimulation and suppression of N2O emission by urea and NP occurred alongside fluctuation in the growth of AOB in alluvial and paddy soils (P < 0.01). Weak stimulation and suppression of N2O emissions by urea and NP corresponded with weak effects on AOB abundances in the black soil. Changes in N2O emissions were not significantly correlated with AOA abundances in any of the three soils. The results showed that differential responses of N2O emission to urea and NP application in arable soils can be mainly explained by differences in growth of ammonia oxidizing bacteria. [Copyright &y& Elsevier]