School of Agriculture, Food and Ecosystem Sciences - Research Publications
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ItemDifferential root responses in two cultivars of winter wheat (Triticum aestivum L.) to elevated ozone concentration under fully open-air field conditions(WILEY, 2018-06)Abstract The effect of elevated tropospheric ozone concentration [O3] on root processes in wheat systems of different O3 sensitivity is not well understood. Two wheat cultivars (cv. Y15 and YN19) with contrasting O3 tolerance were grown in a fully open‐air O3 enrichment platform for one season. We found that elevated O3 (EO3) (50% above the ambient O3) significantly decreased the total biomass at all key growth stages and the yield of the O3‐sensitive cultivar YN19 but did not affect those of the O3‐tolerant cultivar Y15. EO3 significantly decreased the root biomass of two wheat cultivars at the jointing and grain‐filling stages. EO3 significantly decreased the root length, length density, surface area and volume of the two cultivars at the jointing stage but increased those of YN19 at the grain‐filling stage. EO3 significantly increased the root activities (specific root respiration rates) of Y15 and YN19 at the jointing, heading and grain‐filling stages. EO3 significantly decreased the contribution of fresh root respiration to soil respiration (CRS) of YN19 at the jointing stage but increased it at the heading stage; however, it did not change the CRS of Y15 at any growth stages. This study indicates that the effects of EO3 on root morphology and activity varied among wheat cultivars, and suggest that we can breed O3‐tolerant cultivars to maintain crop yield under higher [O3] scenarios.
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ItemNitrifier-induced denitrification is an important source of soil nitrous oxide and can be inhibited by a nitrification inhibitor 3,4-dimethylpyrazole phosphate(WILEY, 2017-12)Soil ecosystem represents the largest contributor to global nitrous oxide (N2 O) production, which is regulated by a wide variety of microbial communities in multiple biological pathways. A mechanistic understanding of these N2 O production biological pathways in complex soil environment is essential for improving model performance and developing innovative mitigation strategies. Here, combined approaches of the 15 N-18 O labelling technique, transcriptome analysis, and Illumina MiSeq sequencing were used to identify the relative contributions of four N2 O pathways including nitrification, nitrifier-induced denitrification (nitrifier denitrification and nitrification-coupled denitrification) and heterotrophic denitrification in six soils (alkaline vs. acid soils). In alkaline soils, nitrification and nitrifier-induced denitrification were the dominant pathways of N2 O production, and application of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) significantly reduced the N2 O production from these pathways; this is probably due to the observed reduction in the expression of the amoA gene in ammonia-oxidizing bacteria (AOB) in the DMPP-amended treatments. In acid soils, however, heterotrophic denitrification was the main source for N2 O production, and was not impacted by the application of DMPP. Our results provide robust evidence that the nitrification inhibitor DMPP can inhibit the N2 O production from nitrifier-induced denitrification, a potential significant source of N2 O production in agricultural soils.
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ItemUsing nitrification inhibitors to mitigate agricultural N2O emission: a double-edged sword?(WILEY, 2017-02)Nitrification inhibitors show promise in decreasing nitrous oxide (N2 O) emission from agricultural systems worldwide, but they may be much less effective than previously thought when both direct and indirect emissions are taken into account. Whilst nitrification inhibitors are effective at decreasing direct N2 O emission and nitrate (NO3- ) leaching, limited studies suggest that they may increase ammonia (NH3 ) volatilization and, subsequently, indirect N2 O emission. These dual effects are typically not considered when evaluating the inhibitors as a climate change mitigation tool. Here, we collate results from the literature that simultaneously examined the effects of nitrification inhibitors on N2 O and NH3 emissions. We found that nitrification inhibitors decreased direct N2 O emission by 0.2-4.5 kg N2 O-N ha-1 (8-57%), but generally increased NH3 emission by 0.2-18.7 kg NH3 -N ha-1 (3-65%). Taking into account the estimated indirect N2 O emission from deposited NH3 , the overall impact of nitrification inhibitors ranged from -4.5 (reduction) to +0.5 (increase) kg N2 O-N ha-1 . Our results suggest that the beneficial effect of nitrification inhibitors in decreasing direct N2 O emission can be undermined or even outweighed by an increase in NH3 volatilization.
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ItemCan knowledge-based N management produce more staple grain with lower greenhouse gas emission and reactive nitrogen pollution? A meta-analysis(WILEY, 2017-05)Knowledge-based nitrogen (N) management, which is designed for a better synchronization of crop N demand with N supply, is critical for global food security and environmental sustainability. Yet, a comprehensive assessment on how these N management practices affect food production, greenhouse gas emission (GHG), and N pollution in China is lacking. We compiled the results of 376 studies (1166 observations) to evaluate the overall effects of seven knowledge-based N management practices on crop productivity, nitrous oxide (N2 O) emission, and major reactive N (Nr) losses (ammonia, NH3 ; N leaching and runoff), for staple grain (rice, wheat, and corn) production in China. These practices included the application of controlled-release N fertilizer, nitrification inhibitor (NI) and urease inhibitor (UI), higher splitting frequency of fertilizer N application, lower basal N fertilizer (BF) proportion, deep placement of N fertilizer, and optimal N rate based on soil N test. Our results showed that, compared to traditional N management, these knowledge-based N practices significantly increased grain yields by 1.3-10.0%, which is attributed to the higher aboveground N uptake (5.1-12.1%) and N use efficiency in grain (8.0-48.2%). Moreover, these N management practices overall reduced GHG emission and Nr losses, by 5.4-39.8% for N2 O emission, 30.7-61.5% for NH3 emission (except for the NI application), 13.6-37.3% for N leaching, and 15.5-45.0% for N runoff. The use of NI increased NH3 emission by 27.5% (9.0-56.0%), which deserves extra-attention. The cost and benefit analysis indicated that the yield profit of these N management practices exceeded the corresponding input cost, which resulted in a significant increase of the net economic benefit by 2.9-12.6%. These results suggest that knowledge-based N management practice can be considered an effective way to ensure food security and improve environmental sustainability, while increasing economic return.
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ItemNo Preview AvailableLong-Term Nickel Contamination Increases the Occurrence of Antibiotic Resistance Genes in Agricultural Soils(AMER CHEMICAL SOC, 2017-01-17)Heavy metal contamination is assumed to be a selection pressure on antibiotic resistance, but to our knowledge, evidence of the heavy metal-induced changes of antibiotic resistance is lacking on a long-term basis. Using quantitative PCR array and Illumina sequencing, we investigated the changes of a wide spectrum of soil antibiotic resistance genes (ARGs) following 4-5 year nickel exposure (0-800 mg kg-1) in two long-term experimental sites. A total of 149 unique ARGs were detected, with multidrug and β-lactam resistance as the most prevailing ARG types. The frequencies and abundance of ARGs tended to increase along the gradient of increasing nickel concentrations, with the highest values recorded in the treatments amended with 400 mg nickel kg-1 soil. The abundance of mobile genetic elements (MGEs) was significantly associated with ARGs, suggesting that nickel exposure might enhance the potential for horizontal transfer of ARGs. Network analysis demonstrated significant associations between ARGs and MGEs, with the integrase intI1 gene having the most frequent interactions with other co-occurring ARGs. The changes of ARGs were mainly driven by nickel bioavailability and MGEs as revealed by structural equation models. Taken together, long-term nickel exposure significantly increased the diversity, abundance, and horizontal transfer potential of soil ARGs.
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ItemTrade-offs between soil carbon sequestration and reactive nitrogen losses under straw return in global agroecosystems(Wiley, 2018-12-01)It is widely recommended that crop straw be returned to croplands to maintain or increase soil carbon (C) storage in arable soils. However, because C and nitrogen (N) biogeochemical cycles are closely coupled, straw return may also affect soil reactive N (Nr) losses, but these effects remain uncertain, especially in terms of the interactions between soil C sequestration and Nr losses under straw addition. Here, we conducted a global meta‐analysis using 363 publications to assess the overall effects of straw return on soil Nr losses, C sequestration and crop productivity in agroecosystems. Our results show that on average, compared to mineral N fertilization, straw return with same amount of mineral N fertilizer significantly increased soil organic C (SOC) content (14.9%), crop yield (5.1%), and crop N uptake (10.9%). Moreover, Nr losses in the form of nitrous oxide (N2O) emissions from rice paddies (17.3%), N leaching (8.7%), and runoff (25.6%) were significantly reduced, mainly due to enhanced microbial N immobilization. However, N2O emissions from upland fields (21.5%) and ammonia (NH3) emissions (17.0%) significantly increased following straw return, mainly due to the stimulation of nitrification/denitrification and soil urease activity. The increase in NH3 and N2O emissions was significantly and negatively correlated with straw C/N ratio and soil clay content. Regarding the interactions between C sequestration and Nr losses, the increase in SOC content following straw return was significantly and positively correlated with the decrease in N leaching and runoff. However, at a global scale, straw return increased net Nr losses from both rice and upland fields due to a greater stimulation of NH3 emissions than the reduction in N leaching and runoff. The trade‐offs between increased net Nr losses and soil C sequestration highlight the importance of reasonably managing straw return to soils to limit NH3 emissions without decreasing associated C sequestration potential.
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ItemSoil urease and catalase responses to ozone pollution are affected by the ozone sensitivity of wheat cultivars(WILEY, 2018-08)Abstract Understanding the effects of elevated O3 (EO3) on belowground process such as soil enzyme activities is essential to evaluate plant physiological reaction and soil processes (e.g. carbon and nitrogen turnover) under predicted increases in atmospheric O3. In this study, O3‐induced changes in soil urease (UA) and catalase activities (CTA) under two contrasting wheat cultivars (O3‐sensitive versus O3‐tolerant) were investigated using a free‐air O3 enrichment (O3FACE) facility in China. EO3 (60 ppb compared with 40 ppb in ambient O3) generally increased UA under the O3‐tolerant cultivar but reduced it under the O3‐sensitive cultivar for different soil depths and growth stages. In contrast, the effects of EO3 on CTA were not consistent and varied with soil depths and growth stages. These results suggest that the O3 sensitivity of wheat cultivars plays an important role in determining the effects of EO3 on soil enzyme activities. The contrasting responses of soil UA and CTA to EO3 may alter the effect of projected increase in tropospheric O3 on soil carbon and nitrogen turnover.
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ItemA review of precision fertilization research(SPRINGER, 2014-05)
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