5 research outputs found
Sugar accumulation stage in sugar beets is a key stage in response to continuous cropping soil microbial community assembly
No full textAimsContinuous cropping effects are a major constraint to the sugar beet industry. Although the microbial community of continuously cropped sugar beets has been studied, the effect of continuous cropping on microbial symbiotic networks and their function during plant development is unclear.MethodsWe analyzed bulk soil and rhizosphere from continuously cropped sugar beet at four growth stages using amplicon and metagenome sequencing and explored the microbial composition, co-occurrence networks, and potential functions of the microbiome at each plant developmental stage. Soil metrics were correlated with microbial communities, and sugar beet from fields with a maize-beet crop rotation acted as a control group.ResultsContinuous cropping and the plant developmental stage had far-reaching effects on plant compartment microbial diversity, composition, and cross-kingdom networks, with the strongest effects observed in the rhizosphere of plants at the sugar accumulation stage. Metagenomic analyses further showed that continuous cropping profoundly affects the assembly and function of the soil microbiome at the host developmental stage. Significant changes in the compositions of the fungal and bacterial communities were observed as the plants developed especially during the sugar accumulation stage, as disease-associated pathogens increased and became the core microbial population in the continuously cropped group.ConclusionsContinuous cropping alters the structure of the microbial core population and resulting in very strong selective regulation of the composition and potential function of the soil microbiome during plant development
Environmental issues related to bioenergy
No full textExtensive efforts have been made in the conversion of biomass into renewable energy using thermochemical and biochemical approaches. During biomass thermochemical conversion, nitrogen oxides (NOx), particulate matter (PM), and tar are the major environmental emissions generated. NOx and PM generated in thermochemical conversion processes can be effectively removed by existing technologies, and tar can be reduced through end treatment and in situ process control. In bioconversion of biomass, the major environmental emissions are volatile organic compounds (VOCs), sulfur-containing gases (e.g., H2S), wastewater, and biogas slurry. Biogas slurry can be utilized as a value-added resource, and wastewater and VOCs can be treated via physical-chemical or biological methods. From a green engineering perspective, the most effective approach is the source reduction of pollution, which can be achieved through process improvement/control or the development of new conversion processes. Employing emission treatment and source-reduction approaches, bioenergy-related environmental issues can be minimized. Developing new industrial technologies or processes that use biomass as a source of energy or chemicals is the future direction of clean production.BioFuelNet CanadaNSER
Three essays on family economics with applications to China
No full textPh.D.This thesis contains three papers on family economics with applications to the Chinese economy.In Chapter 1, Rationed Fertility: Theory and Evidence, we analyze the effect of exogenous changes in fertility on child quality both at and off the unrestricted optimal fertility level in a general model with rationed fertility. Besides the price and substitution effects analyzed in the literature, we show that a desired fertility change, representing a shift towards the optimal level, induces a positive income effect, while a forced fertility change, representing a shift away from the optimal level, induces a negative incomeeffect. To empirically test the theory, we combine a natural experiment, i.e., twins, with a policy change, i.e., One-child Policy and find results that are consistent with the theoretical implications of our model. Our paper provides a theory of rationed fertility that reconciles recent empirical literature on the heterogeneous fertility effects on child quality, and advances our understanding of how population control policy affects human capital investment and economic development.Chapter 2, Filial Piety, Old-Age Support, and Children’s Gender Composition, we use a unique data set of Chinese twins to examine if parents cultivate children’s preference for old-age support. Sibling gender composition provides variations in the supply of old-age support from children because sons are perceived as better providers of old-age support than daughters. However, sibling gender composition is endogenous if parents select a family size based on the gender composition of existing children. We combine the natural experiment of twins with China’s One-Child Policy to eliminate the endogeneity of sibling gender composition. Consistent with the theoretically analysis, we find that having a brother rather than a sister reduces parents’ expectation of old-age support from and parents’instilling of filial piety in daughters but not sons. We provide the first set of evidence that parents forge children’s preference for old-age support. Our findings imply that public provisions of old-age support crowd out private provision by weakening the forging of filial piety.In Chapter 3, Housing Prices and Son Preference: Evidence from China’s Housing Reform, we study whether high housing prices reduce the demand for sons. As Chinese parents need to acquire houses for their sons’ marriage, high housing prices increase the cost of sons relative to daughters. We exploit China’s housing reform in the 1990s as a natural experiment to identify the effect of housing prices on the demand for sons. We find that housing prices have no effect on the probability of having a son at the first birth. High housing prices reduce the probability of having a son at the second birth, especially when the first-born is a daughter. A ten percent increase in housing prices reduces the probability of having a son at the second birth by roughly one percentage point.本文包括三篇應用於中國經濟的家庭經濟學的論文。第一篇論文是“配額生育：理論與證據”。本文構建了一個配額生育的一般模型，分析了外生的小孩數量變動在無配額均衡點上和無配額均衡點以外對小孩質量的影響。除了文獻中的價格效應與替代效應以外，本文發現一個新的收入效應。當生育率變動趨向於無配額均衡點時，引起正的收入效應，而當生育率變動遠離無配額均衡點時，引起負的收入效應。為了檢驗這一理論，我們結合一個自然實驗（雙胞胎）與一個政策變動（一孩政策），發現了支持理論的經驗結果。本文提供了配額生育的一般化理論，解釋了近期文獻中的差異化效應，讓我們更好的理解生育政策對人力資本積累和經濟發展的影響。第二篇論文是“孝道，養老與小孩性別組成”。本文使用一套獨特的雙胞胎數據檢驗了家長是否培育小孩的偏好以尋求養老支持。由於傳統上兒子比女兒被作為更好的養老支持的來源，小孩性別組成提供了養老支持的供給側變動。但由於家長的生育決策會基於已有小孩的性別組成，使得小孩性別組成有內生性。我們結合雙胞胎自然實驗與中國的一孩政策，消除了這一內生性。與理論分析一致，我們發現對於一個小孩而言，有一個兄弟而不是姐妹會減少家長對女孩的養老需求量，但是不影響家長對男孩的養老需求量。本文首次提供了家長培育小孩偏好以尋求養老支持的經驗證據。政府提供的公共養老會弱化孝道，擠出私人的養老供應。第三篇論文是“住房價格與男孩偏好”。我們研究了高房價是否降低家長對男孩的需求。中國的家長常常為男孩提供婚房，房價變動會改變男孩和女孩的相對價格。本文利用中國九十年代的住房改革這一自然實驗，識別了房價對男孩偏好的影響。本文發現高房價對一胎生男孩的比例沒有影響。高房價會降低二胎生男孩的比例，尤其當一胎為女孩時。房價增加百分之十，二胎生男孩的比例降低大約一個百分點。Guo, Rufei.Thesis Ph.D. Chinese University of Hong Kong 2017.Includes bibliographical references (leaves 169-176).Abstracts also in Chinese.Title from PDF title page (viewed on 15, October, 2019)
Table_1_The response of sugar beet rhizosphere micro-ecological environment to continuous cropping.DOCX
No full textContinuous cropping can lead to increased soil-borne diseases of sugar beet (Beta vulgaris L.), resulting in a reduction in its yield quality. However, our understanding of the influence of continuous cropping on sugar beet-associated microbial community is limited and their interactions remain unclear. Here, we described and analyzed microbial diversity (N = 30) from three sugar beet belowground compartments (bulk soil, rhizosphere soil, and beetroot) using 16S rRNA and ITS sequencing. The continuous cropping showed lower bacterial alpha diversity in three belowground compartments and higher fungal alpha diversity in roots compared to the non-continuous cropping. There were significant differences in fungal community composition between the two groups. Compared with non-continuous cropping, continuous cropping increased the relative abundance of potentially pathogenic fungi such as Tausonia, Gilbellulopsis, and Fusarium, but decreased the relative abundance of Olpidium. The fungal flora in the three compartments displayed different keystone taxa. Fungi were more closely related to environmental factors than bacteria. Overall, changes in microbial diversity and composition under continuous cropping were more pronounced in the fungal communities, and the results of the study could guide development strategies to mitigate continuous crop adversity.</p
