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Scientia Horticulturae 195(2015)188194Contents lists available at ScienceDirectScientia Horticulturaejournal homepage: and evaluation of strawberry growth,photosyntheticcharacteristics,biomass yield and quality in an artificial closedecosystemJuan Yua,b,c,1,Minjuan Wanga,b,c,1,Chen Donga,b,c,1,Beizhen Xiea,b,c,Guanghui Liua,b,c,Yuming Fua,b,c,Hong Liua,b,c,aSchool of Biological Science and Medical Engineering,Beihang University,Beijing 100191,ChinabInstitution of Environmental Biology and Life Support Technology,Beihang University,Beijing 100191,ChinacInternational Joint Research Center of Aerospace Biotechnology&Medical Engineering,Beihang University,Beijing 100191,Chinaa r t i c l e i n f oArticle history:Received 21 April 2015Received in revised form 31 August 2015Accepted 2 September 2015Keywords:StrawberrySpace life supportFruit qualityBiomass productiona b s t r a c tPlant cultivation plays an important part in deep space manned mission,and the techniques could beused in ground facility agriculture.The screening of strawberry cultivars and a complete cultivationtechnique for strawberry are necessary in space life support system.In this work,two strawberry cultivarsBenihoppe and Frandy were cultivated under high CO2concentration in a closed ecosystem to establishkey techniques for strawberry planting for space life support.The main objective of the study is to analyzeand evaluate of growth,photosynthetic characteristics,biomass yield and quality of strawberry in a closedecosystem.Our result showed that the two strawberry cultivars grew well during the 105-day-closedexperiment,providing 37.4 g fresh berries every day for the crew in the closed system.The yield,harvestindex and sugar content of Frandy were comparatively higher than those of Benihoppe,among whichthe daily dietary allowance of trace elements and amino acids(18 kinds)in the fruits stood out.Thisstudy provided experimental support for the cultivation techniques of berry plants both for life supportsystem and ground facility agriculture,and afforded a new perspective and sufficient information aboutstrawberry cultivation and selection under the special condition of closed ecosystem.2015 Elsevier B.V.All rights reserved.1.IntroductionBioregenerative Life Support System(BLSS)is an artificialecosystem consisting of complex symbiotic relationships amonghigher plants,animals,and microorganisms.Biotechnology andengineering control technologies perfectly integrated build theBLSS according to the principles of ecological system(Dong et al.,2014;Gitelson and Lisovsky,2003).Similar to in the Earths bio-sphere,higher plants in BLSS can provide human beings with freshair,clean drinking water,nutrient-rich food and spiritual conso-lation necessary,essential to long-term manned space missions(Lasseur et al.,1996;Levine and Par,2009).At present,food crops and vegetable cultivars are the main focusin the study of plant unit in BLSS.Some plant species suitable forCorresponding authors at:School of Biological Science and Medical Engineering,Beihang University,Beijing,100191,China.Fax:+86 10 82339283.E-mail addresses:(Y.Fu),LH(H.Liu).1These authors contributed equally to this work.the space cultivation have been screened,environmental factors forplant cultivation under controlled conditions(Xu and Liu,2008;Huet al.,2011)partially optimized,and meanwhile,the vegetable cul-tivation system for spacecraft studied(Fu et al.,2013;Hu et al.,2014).As a berry with high nutrition,strawberry is full of vita-mins and nutrition elements,and has been widely cultivated underplant factory systems in China and other Asian countries.Besides,strawberry possesses such characteristics as long harvest time andshorter plant height,which meet the criteria of species selec-tion for BLSS(Xu and Liu,2008).Currently,strawberry has beenchosen as candidate crop worldwide in experimental life supportsystem to provide vitamins,mineral elements and improve diettastes.Although studies for strawberry have been done by NASAand MELISSA in their life-support experiments(Gros et al.,2003;Wheeler and Sager,2006),strawberry cultivation as a life supportsystem research is still in its infancy with little experimental results.Compared with other food crops,the horticultural operation anddaily management of strawberry cultivation are more complex,requiring stringent temperature and humidity control,and straw-berry is vulnerable to pathogen infection.Therefore,in life supporthttp:/dx.doi.org/10.1016/j.scienta.2015.09.0090304-4238/2015 Elsevier B.V.All rights reserved.J.Yu et al./Scientia Horticulturae 195(2015)188194 189Table 1The yield per square meter of two strawberry cultivars.Data were calculated from the yield data at each harvest per cultivar.Fresh weight(g)Dry weight(g)Daily fresh weight(g)Daily dry weight(g)Harvest indexFrandy 1701.5 178.41 24.3 2.55 0.32Benihoppe 916.2 57.33 13.1 0.82 0.18Total 2617.7 235.72 37.4 3.37system a complete cultivation technique for strawberry is needed,where there is relatively high CO2concentration and tempera-ture.Some studies done in controlled environments have foundthat high CO2concentration,temperature,and nitrogen conditionswould reduce strawberry yield and fruit quality(Konsin et al.,2001;Ledesma et al.,2008),making the screening of strawberry cultivarsnecessary.Although previous studies have screened some straw-berry cultivars for life support system based on the yield and qualityin conventional environment(Gros et al.,2003;Wheeler and Sager,2006),few studies have been done to study the planting and qualitycharacteristics under special environment of an actual life supportsystem.Lunar Palace 1 is a ground experimental test-bed of bioregen-erative life-support system,composed of a comprehensive cabinand one plant cultivation cabins(Fig.S1).As an artificial closedecosystem,Lunar Palace 1 could provide human with basic livingrequirements.Oxygen,water and food regenerate through biotech-nology,making it possible for human to live for long periods.LunarPalace 1 is air-tight and composed of a comprehensive cabin anda plant cultivation cabin.The plant cultivation cabin includes tworooms;the environmental conditions within these two rooms werecontrolled separately according to the growth demands of differentplants.In order to screen out a suitable strawberry cultivar and estab-lish a complete cultivation technique for strawberry for space lifesupport system,two strawberry cultivars Benihoppe and Frandywere cultivated in the plant cabin of Lunar Palace 1,when threevolunteers lived in this closed system for a 105-day period.Thecultivation technologies for strawberry with inorganic matrix asgrowing media and water supplied by the negative pressure ofporous tubes were established.The main objective of this study isto analyze and evaluate of growth,photosynthetic characteristics,biomass yield and quality of strawberry for screening out suit-able strawberry cultivar for life support system by actual plantingin simulated life support system environment.This study pro-vided experimental support for the cultivation techniques of berryplants both for life support system and ground facility agriculture,and afforded a new perspective and information about strawberrycultivation and selection under the condition of artificial closedecosystem.2.Materials and methods2.1.Plant material and cultivation conditionsIn Lunar Palace 1,plants were grown in plant cultivation racksdesigned by our team.Plant racks were divided into three lay-ers,each having a separate light board and cultivation tank.Theso-called“Soil”was a kind of inorganic matrix“vermiculite”deter-mined by a special screening,and nutrient solution supplied by thenegative pressure of the porous tubes.This cultivation method inlow gravity of the lunar-base is still feasible,as well as the micro-gravity conditions in space station.Seedlings were cultivated firstin plastic pots with nutrient solution for one week in an artificialclimate chamber,and then transplanted into the plant compart-ment in Lunar Palace 1.The cultivation condition in artificial climatechamber and Lunar Palace 1,such as light intensity,photoperiod,temperature,relative humidity and nutrient solution were similar,while the CO2level in the artificial climate chamber was atmo-spheric level.The strawberry cultivars were Benihoppe and Frandy,twowidely cultivated cultivars in China with high yield and good dis-ease resistance.The planting acreage was 0.5 m2for each seedlingand planting density was 10 seedlings.The planting matrix wasmedium-grained vermiculite supplied with Hoagland nutrientsolution.LED lights with full spectrum were used as light source,and the light intensity was 500?moL m2s1with a photoperiodof 12/12 h light/dark.The CO2level was in a dynamic range of5005000 ppm in the closed ecosystem.The relative humidity(RH)was maintained at 55 4.6%,with a temperature of 21 1.3C dur-ing daytime and night.The Hoagland nutrient solution(Hoagland and Arnon,1950)included:Ca(NO3)24H2O,945 mg/L;KNO3,607 mg/L;NH4H2PO4,115 mg/L;MgSO47H2O,493 mg/L;Fe-EDTA,30 mg/L;MnSO4H2O,2.13 mg/L;CuSO45H2O,0.08 mg/L;ZnSO47H2O,0.22 mg/L;(NH4)6Mo7O244H2O,0.02 mg/L;H2BO3,2.86 mg/L,and the pHwas 6.0.Seedlings needed regularly pruning of old yellow leaves afterplanting,and thinning the flowers timely after the inflorescenceappeared.Generally 35 flowers were reserved per inflorescence.The weight of all these wastes was recorded and added into theweight of inedible weight.After flowering,the flowers were polli-nated artificially.2.2.Yield and physiological analyses2.2.1.Photosynthesis related indicatorsNet photosynthesis rate(Pn)of leaves of two cultivars was mea-sured using the LI-COR portable infrared CO2gas analyzer(LI-6400XRT portable photosynthesis system,LI-COR Biosciences,Lincoln,NE,USA).Block temperature was kept at 22C during all mea-surements(registered leaf temperatures ranging 2122C)vaporpressure deficit(VPD)at around 1.5 kPa(Peng et al.,2009;Yanget al.,2008),and each plant were determined with fully expand-ing leaves in the same position.As the CO2concentration changeddynamically,the Pn is measured only when the CO2concentrationwas relatively stable.The concentration was:500 ppm,1500 ppm,2000 ppm.Other experimental conditions such as PPFD,air temper-ature,and relative humidity(RH)were set as 500?moL m2s1,21C,and 55%respectively.After each determination of Pn,Pho-tosynthetic pigment content was extracted by acetone from theleaves(fully expanded,exposed)of 10 plants at a similar positionfor each treatment.The optical density was measured with a UV-1200 spectrophotometer(SP-75,Shanghai spectrum instrumentsco.,LTD,China)at 663 nm(OD663)for chlorophyll a(Chl.a),and645 nm(OD645)for chlorophyll b(Chl.b)(Hartmut,1983).2.2.2.Biomass yield and quality analysesStrawberry seedlings flowered on the 10th day after planting(DAP)into the closed system,and strawberry were harvested at a7-day interval per cv.,starting from 30 DAP,when fruit turned tored.Harvest was staggered in order to simulate the typical situa-tion in BLSS where fruit storing space is limited and a sustainablework load for astronauts is needed.At each harvest,yield data(freshweight and dry weight of fruits)were determined per cultivar(edi-ble biomass).At the end of the harvest,plants were collected to190 J.Yu et al./Scientia Horticulturae 195(2015)188194determine fresh(FW)and dry weight(DW)of different organs(inedible biomass).Then,the yield,moisture content of both fruitsand inedible parts,and harvest index were calculated.The content of sugar,protein,ascorbic acid(vitamin C),aminoacids of 18 kinds,and mineral element of fresh fruits were deter-mined respectively under different conditions(Junfeng,2000).Thecontent of neutral detergent fiber(NDF),acid detergent fiber(ADF),acid detergent lignin(ADL)and acid-insoluble ash(Ash)in the ined-ible parts of plants were determined according to Van Soest method(Van Soest et al.,1991)by using FIWE six raw fiber extractor(Velp-Scientifica,Italy).The contents of hemicellulose,cellulose and rawlignin were given by the differences between NDF and ADF,ADFand ADL,and ADL and Ash respectively(Li et al.,2013;Van Soestet al.,1991).3.Results and discussion3.1.yield and harvest indexThe two strawberry cultivars grew well in In Lunar Palace 1,theirleaves being luxuriant and inflorescences massive.Fruit harvestedin In Lunar Palace 1 was similar to that in field conditions,bright redin the color,and round in the shape and delicious tasted.The pro-duction data of the two cultivars during the experiment is shownin Table 1,with a total of 70 days of harvest.The average supplyof fresh berries for the experimental volunteers was 37.4 g daily.The plant of Frandy cultivars grew better than Benihoppe andbetter adapted to a closed system.Meanwhile,the yield of Frandywas significantly higher(nearly twice)than Benihoppe,and theharvest index of Frandy was 0.32,also much higher than that ofBenihoppe(0.18).The low harvest index of Benihoppe may bedue to inappropriate environment which had certain influence onblossoming,fruit bearing,and the growth of stolon which led to anincrease in inedible biomass.High yield and high ratio of edible partare important principles of plant screening for life support system(Krauss,1962;Wheeler et al.,1996).The harvest index of Frandywas similar to that of strawberry in Advanced Life Support exper-iment by NASA(0.30.4)(Wheeler and Sager,2006).Consideringthe above mentioned,Frandy is better to be cultivated in a closedlife support system.3.2.Difference in photosynthesis and photosynthetic pigmentDue to the harvesting and planting of crops,as well as thedaily activity of crew,the carbon dioxide concentration in theclosed ecosystem was dynamic changing,ranging from 500 ppmto 2000 ppm with the highest at 5000 ppm.We did photosynthesisrate test only when the CO2concentration was relatively stable,andthe CO2concentration gradient was 500 ppm,1500 ppm,2000 ppm.From the results shown in Fig.1,it can be seen that net pho-tosynthetic rate of Frandy were higher than that of Benihoppeunder all different CO2levels,which may account for the higheryield of Frandy.The results of stomatal conductance and transpi-ration rate were consistent with net photosynthetic rate.Results ofchlorophyll content(Fig.2)showed that there was no significantdifference between the two cultivars.Net photosynthetic rate ofthe two cultivars showed a decreasing trend after the first rise withthe increasing CO2concentration,and the top was at 1500 ppm.Theatmospheric concentration of CO2is about 350 ppm,and the satura-tion point of CO2of plant is generally around 1500 ppm.Therefore,an appropriate increase in CO2concentration(3501500 ppm)hasa positive effect on plant growth,such as increasing the photo-synthetic rate,reducing moisture loss and increasing crop yields(Smith et al.,2000).However,an excessive CO2concentration(oversaturation point)can also inhibit plant growth,or even result inFig.1.The net photosynthetic rate(A),st