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Leaf gas exchange characteristics,biomass partitioning,and water use efficiencies of two C4 African grasses under simulated drought

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Grassland Research 2023年第1期2卷 37-45页

作者： kevin z.mganga Jana Kuhla Andrea Carminati Johanna Pausch Mutez A.Ahmed Copernicus Institute of Sustainable Development Utrecht UniversityUtrechtthe Netherlands Department of Agricultural Sciences South Eastern Kenya UniversityKituiKenya Bayreuth Center of Ecology and Environmental Research(BayCEER) University of BayreuthBayreuthGermany Department of Environmental Systems Science ETH ZurichZürichSwitzerland Department of Land Air and Water ResourcesUniversity of California DavisDavisCaliforniaUSA

Background:Few studies have evaluated the effect of drought on the morphophysiological characteristics of African C_(4) grasses.We investigated how drought affects leaf gas exchange characteristics,biomass partitioning,and water use efficiencies of Enteropogon macrostachyus and Cenchrus ciliaris.Methods:The grasses were grown in a controlled environment under optimum conditions,that is,70%of the maximum water‐holding capacity(WHC)for the first 40 days.Thereafter,half of the columns were maintained under optimum or drought conditions(30%of maximum WHC)for another 20 days.Results:Under optimum conditions,C.ciliaris showed a significantly higher photosynthetic rate,stomatal conductance,and transpiration rate than E.macrostachyus.Drought decreased the photosynthetic rate,stomatal conductance and transpiration rate only in C.ciliaris.The net photosynthetic rate,stomatal conductance,and leaf transpiration of E.macrostachyus did not differ significantly under optimum and drought conditions.E.macrostachyus showed an increase in its water use efficiencies under drought to a greater extent than C.ciliaris.Conclusions:Our results demonstrate that C.ciliaris is more sensitive to drought than E.macrostachyus.The decrease in the intercellular CO_(2) concentration and the increase in stomatal limitation with drought in C.ciliaris and E.macrostachyus suggest that stomatal limitation plays the dominant role in photosynthesis of the studied African C_(4) grasses.

关键词： biomass fractions C_(4)grasses drought photosynthesis stomatal conductance transpiration

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Phenological Stage, Plant Biomass, and Drought Stress Affect Microbial Biomass and Enzyme Activities in the Rhizosphere of Enteropogon macrostachyus

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Pedosphere 2019年第2期29卷 259-265页

作者： kevin z.mganga Bahar S.RAzAVI Muhammad SANAULLAH Yakov KUzYAKOV Department of Soil Science of Temperate Ecosystems Institute of Soil Science University of G?ttingen Department of Range and Wildlife Sciences South Eastern Kenya University Department of Agricultural Soil Science Institute of Soil Science University of G?ttingen Institute of Soil and Environmental Sciences University of AgricultureFaisalabad Institute of Environmental Sciences Kazan Federal University

Indigenous grasses have been effectively used to rehabilitate degraded African drylands. Despite their success, studies examining their effects on soil bioindicators such as microbial biomass carbon(C) and enzyme activities are scarce. This study elucidates the effects of drought stress and phenological stages of a typical indigenous African grass, Enteropogon macrostachyus, on microbial biomass and enzyme activities(β-glucosidase, cellobiohydrolase, and chitinase) in the rhizosphere soil. Enteropogon macrostachyus was grown under controlled conditions. Drought stress(partial watering) was simulated during the last 10 d of plant growth, and data were compared with those from optimum moisture conditions. The rhizosphere soil was sampled after 40 d(seedling stage), 70 d(elongation stage), and 80 d(simulated drought stress). A high root:shoot ratio at seedling stage compared with elongation and reproduction stages demonstrated that E. macrostachyus invested more on root biomass in early development, to maximise the uptake of nutrients and water. Microbial biomass and enzyme activities increased with root biomass during plant growth. Ten-day drought at reproduction stage increased the microbial biomass and enzyme activities, accompanying a decrease in binding affinity and catalytic efficiency. In conclusion, drought stress controls soil organic matter decomposition and nutrient mobilization, as well as the competition between plant and microorganisms for nutrient uptake.

关键词： African grass catalytic efficiency cellobiohydrolase chitinase β-glucosidase nutrient uptake optimum moisture soil bioindicators

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Determinants and rates of land degradation： Application of stationary time-series model to data from a semi-arid environment in Kenya

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Journal of Arid Land 2018年第1期10卷 1-11页

作者： kevin z.mganga dickson m nyariki nashon k r musimba dorothy a amwata department of range and wildlife sciences south eastern kenya university170-90200 KituiKenya department of agricultural economics and agribusiness south eastern kenya university170-90200 KituiKenya school of business and economics murangáuniversity of technology75-10200 MurangaKenya

The causes of land degradation in the African drylands have been shown to vary. Some researchers consider climate to be the major contributor to degradation, with anthropogenic factors playing a minor role. Others reverse the significance of these two factors. A third group attributes land degradation to climate and anthropogenic factors equally. This study was undertaken to establish the factors influencing land degradation in a semi-arid environment in southeastern Kenya and the rate of change in vegetation types for a period of 35 years （1973-2007）. The reduction in grassland cover was used as an indicator of land degradation. Causes of land degradation were determined by a multiple regression analysis. A log-linear regression analysis was used to establish the rate of vegetation change. The multiple and log-linear regression analyses showed：（1） woody vegetation, livestock population and cultivated area to be the main contributors of reduction in grassland cover in the area, and （2） an increase in undesirable woody species, livestock population and cultivated area had a significant （P〈0.05） negative effect on grassland vegetation. Increased human population, low amounts of rainfall and drought showed no significant negative effect on grassland vegetation cover. In conclusion, human and livestock population growth and increased agricultural land have contributed to intensive crop cultivation and overgrazing in the semi-arid lands. This overuse of the semi-arid rangelands has worsened the deterioration of the natural grassland vegetation.

关键词： regression analysis land degradation grassland cover semi-arid Kenya Sub-Saharan Africa

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Injury and protection of spiral ganglion neurons

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Chinese Medical Journal 2024年第6期137卷 651-656页

作者： Beilei Duan kevin A.Peng Line Wang Department of Otorhinolaryngology Head and Neck SurgeryBeijing Friendship HospitalCapital Medical UniversityBeijing 100050China Department of Neurotology House ClinicLos AngelesCA 90017USA

Cochlear spiral ganglion neurons(SGNs)are bipolar ganglion cells and are the first neurons in the auditory transduction pathway.They transmit complex acoustic information from hair cells to second-order sensory neurons in the cochlear nucleus for sound processing.Injury to SGNs causes largely irreversible hearing impairment because these neurons are highly differentiated cells and cannot regenerate,making treatment of sensorineural hearing loss(SNHL)arising from SGN injury difficult.When exposed to ototoxic drugs or damaging levels of noise or when there is loss of neurotrophic factors(NTFs),aging,and presence of other factors,SGNs can be irreversibly damaged,resulting in SNHL.It has been found that NTFs and stem cells can induce regeneration among dead spiral ganglion cells.In this paper,we summarized the present knowledge regarding injury,protection,and regeneration of SGNs.

关键词： Spiral ganglion Injury Protection Auditory hair cell Ototoxic drugs Aminoglycosides Presbycusis

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Potential transformation of organic matter by microbes in cryoconite,Tibetan Plateau

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Science China Earth Sciences 2024年第6期67卷 1978-1989页

作者： Bixi GUO Yongqin LIU kevin Xu zHONG Quan SHI Chen HE Qiang zHENG Ruanhong CAI State Key Laboratory of Tibetan Plateau Earth System Environment and Resources(TPESER)Institute of Tibetan Plateau ResearchChinese Academy of SciencesBeijing 100101China Center for the Pan-Third Pole Environment Lanzhou UniversityLanzhou 730000China Department of Earth Oceanand Atmospheric SciencesUniversity of British ColumbiaVancouverBC V6T 1Z4Canada State Key Laboratory of Heavy Oil Processing Petroleum Molecules Engineering Center(PMEC)China University of PetroleumBeijing 102249China State Key Laboratory for Marine Environmental Science Collage of Ocean and Earth SciencesXiamen UniversityXiamen 361102China Fujian Key Laboratory of Marine Carbon Sequestration Xiamen UniversityXiamen 361005China

Microorganisms play an essential role in the glacier carbon cycle;how they transform organic matter in mountain glacial cryoconite remains to be studied.Here,we applied ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry(FT-ICR MS)and deep sequencing of 16S rRNA gene,to investigate the temporal microbial transformation of dissolved organic matter(DOM)of the Tibetan Plateau cryoconite.During the 60-day incubation,we found that DOM in cryoconite underwent a three-stage transformation,with decreasing bioavailability over time.The microbial community did not change much in the first week while degrading DOM molecules that were associated with higher H/C_(wa)and lower O/C_(wa).During days 15-30,DOM composition remained stable while microbial diversity increased.By day 60,the DOM was microbially converted into a higher state of recalcitrance,with higher values of aromatic index,O/C_(wa),and lower H/C_(wa),which contained molecules containing more heteroatoms.Cooperation among various microbial taxa,like Cyanobacteria,Bacteroidota,Gammaproteobacteria,Firmicutes,and Actinobacteriota,drove the DOM transformation in cryoconite.This study sheds light on the in-situ transformation of DOM composition meditated by microbial populations in cryoconite at a temporal scale,providing new insights into understanding the microbial roles in the glacier organic carbon transformation.

关键词： Cryoconite Dissolved organic matter Biodegradation Microbial community Temporal variation

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The valuation of barrier options under a threshold rough Heston model

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Journal of Management Science and Engineering 2023年第1期8卷 15-31页

作者： kevin z.Tong Allen Liu Department of Mathematics and Statistics University of Ottawa585 King EdwardOttawaOntarioK1N 6N5Canada Enterprise Risk and Portfolio Management Bank of MontrealFirst Canadian PlaceTorontoOntarioM5X 1A3Canada

In this paper,we propose a novel model for pricing double barrier options,where the asset price is modeled as a threshold geometric Brownian motion time changed by an integrated activity rate process,which is driven by the convolution of a fractional kernel with the CIR process.The new model both captures the leverage effect and produces rough paths for the volatility process.The model also nests the threshold diffusion,Heston and rough Heston models.We can derive analytical formulas for the double barrier option prices based on the eigenfunction expansion method.We also implement the model and numerically investigate the sensitivities of option prices with respect to the parameters of the model.

关键词： Rough stochastic volatility Threshold diffusion Barrier options Eigenfunction expansion Stochastic time change

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BUILDING CLIMATE-RESILIENT FOOD SYSTEMS IN EAST AND SOUTHEAST ASIA:VULNERABILITIES,RESPONSES AND FINANCING

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Frontiers of Agricultural Science and Engineering 2023年第1期10卷 16-30页

作者： Yunyi zHOU ziqi CHEN kevin z.CHEN China Academy for Rural Development and School of Public Affairs Zhejiang UniversityHangzhou 310058China International Food Policy Research Institute Washington DC 20005USA

Food system resilience to climate change is uniquely imperative for bringing Sustainable Development Goals within reach and leaving no one behind.Food systems in East and Southeast Asia are interacting with planetary boundaries and are adversely affected by extreme weather-related events.A practical question for East and Southeast Asian stakeholders is how to foster climate-resilient food systems in the face of lingering food system vulnerabilities and policy gaps.This paper reviews food system vulnerabilities and policy responses to climate change.In the policy-based review,this paper compares the economy-wide and agriculture-specific targets of low-carbon development across East and Southeast Asia.With China and member states of the Association of Southeast Asia Nations as case studies,multilevel policies in building and financing climate-resilient food systems are further synthesized.The findings confirm significant differences in agriculture-specific emission goals and public financing supports across East and Southeast Asian nations.With an objective to break practical barriers and finance climate-resilient food systems for the future,this paper recommends defining agriculture-specific greenhouse gas emission goals,reorienting the public finance scheme and enhancing mechanisms for the synergy of public and private resources.

关键词： food systems climate change East policy resilience and Southeast Asia

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Surgical outcomes and quality of life following exercise-based prehabilitation for hepato-pancreatico-biliary surgery:A systematic review and meta-analysis

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Hepatobiliary & Pancreatic Diseases International 2022年第3期21卷 207-217页

作者： Andy Deprato kevin Verhoeff Kieran Purich Janice Y Kung David L Bigam Khaled z Dajani University of Alberta 116 St&85 AveEdmontonAlberta T6G 2R3Canada Department of Surgery University of Alberta Hospital8440112 Street NWEdmontonAlberta T6G 2B7Canada John W.Scott Health Sciences Library University of Alberta Hospital8440112 Street NWEdmontonAlberta T6G 2B7Canada Department of Surgery Division of General SurgeryHPB Transplant and OncologyUniversity of Alberta Hospital8440112 Street NWEdmontonAlberta T6G 2B7Canada

Background:Hepato-pancreatico-biliary(HPB)patients experience significant risk of preoperative frailty.Studies assessing preventative prehabilitation in HPB populations are limited.This systematic review and meta-analysis evaluates outcomes for HPB patients treated with exercise prehabilitation.Data sources:A comprehensive search of MEDLINE(via Ovid),Embase(Ovid),Scopus,Web of Science Core Collection,Cochrane Library(Wiley),Pro Quest Dissertations,Theses Global,and Google Scholar was conducted with review and extraction following PRISMA guidelines.Included studies evaluated more than 5 adult HPB patients undergoing≥7-day exercise prehabilitation.The primary outcome was postoperative length of stay(LOS);secondary outcomes included complications,mortality,physical performance,and quality of life.Results:We evaluated 1778 titles and abstracts and selected 6(randomized controlled trial,n=3;prospective cohort,n=1;retrospective cohort,n=2)that included 957 patients.Of those,536 patients(56.0%)underwent exercise prehabilitation and 421(44.0%)received standard care.Patients in both groups were similar with regards to important demographic factors.Prehabilitation was associated with a 5.20-day LOS reduction(P=0.03);when outliers were removed,LOS reduction decreased to 1.85 days and was non-statistically significant(P=0.34).Postoperative complications(OR=0.70;95%CI:0.39 to 1.26;P=0.23),major complications(OR=0.83;95%CI:0.60 to 1.14;P=0.24),and mortality(OR=0.67;95%CI:0.17 to 2.70;P=0.57)were similar.Prehabilitation was associated with improved strength,cardiopulmonary function,quality of life,and alleviated sarcopenia.Conclusions:Exercise prehabilitation may reduce LOS and morbidity following HPB surgery.Studies with well-defined exercise regimens are needed to optimize exercise prehabilitation outcomes.

关键词： Exercise-based prehabilitation Preoperative exercise Hepatobiliary Pancreaticoduodenectomy Hepatic resection Pancreatectomy

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Managing Climate Change Risk in China's Agricultural Sector: The Potential for an Integrated Risk Management Framework

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Journal of Integrative Agriculture 2014年第7期13卷 1418-1431页

作者： kevin z.Chen Claire Hsu International Food Policy Research Institute-Beijing Office

Climate change poses a serious threat to the future food security of China, which is among the most disaster-prone countries in the world. This paper discusses the implications of climate change for China＇s agricultural sector. Its main objectives are to identify the agricultural risks associated with climate change, to introduce a conceptual framework for agricultural climate risk management and to enumerate key adaptation strategies, challenges, and recommendations.

关键词： climate change food security risk management agricultural development

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Elite capture,the“follow-up checks”policy,and the targeted poverty alleviation program:Evidence from rural western China

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Journal of Integrative Agriculture 2021年第4期20卷 880-890页

作者： CHENG Xiao-yu WANG Jian-ying kevin z.CHEN Institute of Agricultural Economics and Development Chinese Academy of Agricultural SciencesBeijing 100081P.R.China School of Economics Zhejiang University of Finance&EconomicsHangzhou 310018P.R.China China Academy for Rural Development Zhejiang UniversityHangzhou 310058P.R.China International Food Policy Research Institute WashingtonD.C.20005USA

Decentralized methods for targeting poverty are widely adopted in developing countries to improve the performance of various poverty alleviation programs.A common challenge for implementing successful decentralized targeting is the existence of elite capture.China has recently implemented a nationwide decentralized poverty targeting program,the targeted poverty alleviation(TPA)policy,to achieve the national goal of eliminating absolute poverty by the end of 2020.As the largest decentralized poverty targeting program in the world,TPA's successful implementation was believed to be threatened by elite capture in some earlier reports.Since 2015,a targeting correction mechanism,called"follow-up checks"policy,has been introduced.With the"follow-up checks"policy,the elites and other ineligible households who receive benefits under TPA were removed from the program.This paper investigates the elite capture phenomenon in TPA using village census data from a poverty-stricken county in 2017-two years after implementing the"follow-up checks"policy.We find no evidence of elite capture in TPA.The elites are unlikely to become beneficiaries or receive more benefits than non-elites.Our results contradict earlier findings that reported elite capture in TPA.We argue that the reason is the accountability emphasized by the central government in the"follow-up checks"policy.Our findings imply that having proper accountability is critical for improving targeting performance by global antipoverty initiatives.

关键词： elite capture decentralized poverty targeting targeted poverty alleviation the"follow-up checks"policy accountability

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