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1、HORTSCIENCEhttps:/doi.org/10.21273/HORTSCI15241-20Effects of Diffuse Light onMicroclimate of Solar Greenhouse,and Photosynthesis and Yield ofGreenhouse-grown TomatoesLiang ZhengCollege of Water Resources and Civil Engineering,China AgriculturalUniversity,Beijing 100083,China;and Key Laboratory of Ag
2、riculturalEngineering in Structure and Environment,Ministry of Agriculture andRural Affairs,Beijing 100083,ChinaQi Zhang and Kexin ZhengCollege of Water Resources and Civil Engineering,China AgriculturalUniversity,Beijing 100083,ChinaShumei Zhao,Pingzhi Wang,and Jieyu ChengCollege of Water Resources
3、 and Civil Engineering,China AgriculturalUniversity,Beijing 100083,China;and Key Laboratory of AgriculturalEngineering in Structure and Environment,Ministry of Agriculture andRural Affairs,Beijing 100083,ChinaXuesong Zhang and Xiaowen ChenBeijing Zhongnong Futong Horticulture Co.,Ltd.,Beijing 100083
4、,ChinaAdditional index words.Chinese solar greenhouse,diffuse light,light environment,tomatoAbstract.The application of diffuse light can potentially improve the homogeneity of lightdistribution and other microclimatic factors such as temperature inside greenhouses.In thisstudy,diffuse light plastic
5、 films with different degrees of light diffuseness(20%and 29%)were used as the south roof cover of Chinese solar greenhouses to investigate the spatialdistribution of microclimatic factors and their impacts on the growth and yield of tomato.The horizontal and vertical photosynthetic photon flux dens
6、ity(PPFD)distributions,airtemperature distribution,and leaf temperature distribution inside the canopy,tomato leafnetphotosynthesis(Pn),andfruitproductionduringthegrowthperiodweredetermined.Theresults showed that diffuse light plastic film continuously improved the light distribution inthe vertical
7、and horizontal spaces of the crop canopy in terms of light interception anduniformity.A more diffuse light fraction also decreased the air and leaf temperatures of themiddlecanopyand upper canopyduringthesummer,therebypromoting thephotosynthesisof the tomato plants.Pnof the middle and lower canopies
8、 with higher haze film weresignificantly greater than those with lower haze film(19.0%and 27.2%,respectively).Theyields of higher stem density and lower stem density planted tomatoes in the 29%hazecompartment were increased by 5.5%and 12.9%compared with 20%in the haze group,respectively.Diffuse ligh
9、t plastic films can improve the homogeneity of the canopy lightdistribution and increase crop production in Chinese solar greenhouses.With the development of the greenhouseindustry,vegetables can be grown locallyyear-round despite the restrictions of naturalconditions.In northern China,the typicalCh
10、inese-style solar greenhouses(CSGs)are eastwest-oriented and constructed witha transparent south roof,opaque and insu-lated north wall,and north roof and side-walls;these are passive solar greenhouseswithout auxiliary heating(Tong et al.,2013).Therefore,solar radiation conditionsinside CSGs comprise
11、 the most importantdetermining factors of the creation of thegreenhouse microclimate,which further in-fluences the growth and yield of greenhouse-grown crops.Generally,solar radiation inside a CSG isnot evenly distributed due to its unique struc-ture and the shading of the crop canopy(Zhang et al.,2
12、020).The upper canopyintercepts more direct light,and leaves inthe lower canopy receive limited incident lightas a result of canopy shading.Some of theupper leaves exposed to direct light mayeven experience excess light,eventuallyleading to photoinhibition,whereas theleaves beneath the greenhouse fr
13、ameworksand upper canopy could suffer from a lightenergy deficit,which causes a dramaticdecrease in the photosynthetic rate(Trouwborstet al.,2010).Optimization of the greenhouse cover-ing material provides a practical optionfor improving greenhouse meteorology,in-cluding light and thermal characteri
14、stics(Al-Mahdouri et al.,2013;Baeza et al.,2020;Lamnatou and Chemisana,2013a),thereby achieving improvements in cropgrowthandquality(Hemmingetal.,2008b).Diffuse light covering material wasrecently introduced mainly for conventionalglass greenhouses(Hemming et al.,2008b;Li et al.,2016).Compared with
15、regulargreenhouse cover,light-diffusing cover scat-ters a certain fraction of the transmitted directlight into diffuse light,thus potentially im-proving the uniformityofspatial and temporallight distributions and increasing the radiationefficiency of the crops(Hemming et al.,2008a;Li and Yang,2015).
16、In the verticaldirection of the canopy,diffuse light couldpenetrate deeper inside the canopy,therebyreducing the extinction coefficient and shad-ing of the upper canopy(Lamnatou andChemisana,2013b).In the horizontal canopy,diffuselightalsoimprovesthehomogeneityoflight distribution by reducing the sh
17、adow ofthe greenhouse framework and local peaks inlight intensity(Li and Yang,2015).Many previous researchers have investi-gated the impact of diffuse light on plantgrowth and physiology.It is considered thatplants could use diffuse light more efficientlythan direct light,such as apple trees(Laksoan
18、d Musselman,1976),spruce(Urban et al.,2012),and grass(Sheehy and Chapas,1976).Such studies of diffuse light have beenperformed by comparing plant responses onclear days and cloudy days in natural condi-tions(Gu et al.,2002,2003;Urban et al.,2007).Applying diffuse light in the green-house decreased t
19、he leaf temperature of to-mato and resulted in a higher leaf area indexand lower specific leaf area,which helpregulate photosynthetic activities(Li et al.,2014a)and further benefit the yield at harvest(Adams et al.,2000).In recent years,our research group hasconducted a series of investigations of t
20、heeffects of light diffuse plastic films on CSGmicroclimates and crop growth.The resultsshowed that diffuse light improved the seed-ling index and accumulation of chlorophylland increased the total leaf area of tomato,cucumber,and pepper as well as the qualityand yield of tomato(Fan et al.,2016;Song
21、et al.,2017;Sun et al.,2016).However,thesestudies have focused on the effects of diffuselight plastic films on plant growth and yield,but not environmental factors such as lightand temperature distributions.The main objective of the present studywastoprovidemorecomprehensivetheoreticalReceived for p
22、ublication 19 June 2020.Acceptedfor publication 16 July 2020.Published online 26 August 2020.This research was funded by the Earmarked Fund forModern Agro-industry Technology Research System(CARS-23-C02)and Borouge Sales and Marketing(Shanghai)Co.,Ltd(201704810910196).S.Z.isthecorrespondingauthor.E-
23、mail:.This is an open access article distributed under theCC BY-NC-ND license(https:/creativecommons.org/licenses/by-nc-nd/4.0/).HORTSCIENCEhttps:/doi.org/10.21273/HORTSCI15241-201 of 9knowledge regarding the introduction of dif-fuse light plastic films to CSGs by elaboratingon microclimate factors
24、including light andtemperatureofCSGswithdifferenthazeplasticfilms and investigating the effect of the green-houseenvironmentontomatoplantgrowthandyield.Materials and MethodsExperimental setup.This experiment wasconducted in an eastwest-oriented Chinesesolar greenhouse located in Beijing,China(lat.39
25、?48#N,long.116?56#E).The green-house was divided into two equal compart-ments(328 m2and 41 m 8 m for eachcompartment)with heat insulation board(Fig.1).The greenhouse compartments werecoveredwithtwotypesofdiffuselightplasticfilms(Borouge Co.Ltd.,Shanghai,China)that are regularly used by local growers
26、.The transmittance and haze factor of theplastic films were measured with a lighttransmittance and haze meter(WGT-2S;INESA Physico-Optical Instrument,Shang-hai,China)according to the ASTM Commit-tee(2013).Transmission was measured withthe build-in light source with a wavelengthrange of 200 to 2500 n
27、m.Haze is defined asthe percentage of diffuse light from transmit-ted light that deviates more than 2.5 degreesfrom the direction of the incident light.Hazevalues of the two types of plastic filmsethylene-vinyl acetate(EVA)were 20%and 29%,respectively,whereas the transmis-sion of the plastic films w
28、as 89%.The ex-periment wasconducted for year-roundproduction of tomato(cv.Zhongshu 4)from1Oct.2016.Tomatoplantswerecultivatedinthe greenhouse with peat-based substrate.Irrigation and fertilization were performedaccording to good horticultural practices.Plant rows were southnorth-orientated witha row
29、 distance of 70 cm.Two stem densitieswere set in each row;these were initially 6and 5 stems/m2,but they were reduced to 4.3and 3.6 stems/m2at 66 d after planting.Measurement of PPFD distribution withinthe canopy.The distribution of PPFD wasmeasured with the S-LIA-M003 sensor(OnsetInc.,Bourne,MA)in e
30、ach compartment asshowninFig.2.TheverticalPPFDdistributionwas recorded from Oct.2016 to June 2017.Itwas measured at the top of the canopy,10 cmbelow the top of the crop,the middle of thecanopy,and the bottom of the canopy;mea-surements were replicated three times at eachheight.The vertical PPFD meas
31、uring heightvariedwiththegrowthofthetomatoplant.Thehorizontal PPFD distribution was measured at1.5,4.5,and 6.5 m to the north wall and 50 cmbelow the top of the canopy;measurementswerereplicatedthreetimesateachpointfrom2Mar.2017 to 27 Apr.2017 at the main fruitstage of tomatoes.Measurements ofairtem
32、peratureand leaftemperature.The air temperature was mea-sured with the 175H1 sensor(Testo Inc.,Lenzkirch Germany)with an accuracy of2%.Leaf temperature was measured withT-type fine-wire thermocouples(Omega En-gineering,Norwalk,CT)at three canopydepths with three replicates.The measure-ment positions
33、 were adjusted with the growthof the plants(Fig.2).The temperature wasmeasured from 5 June 2017 to 10 July 2017.Measurements of leaf photosynthesis andsolar radiation transmittance.The Pnof leafwas determined with the CIRAS-2 portablegas exchange device(PP Systems,Ames-bury,MA)at three canopy depths
34、.Canopydepths were defined as leaf number 5,leafnumber 10,and leaf number 15 according toLi et al.(2014a).From 4 Apr.2017 to 30Apr.2017,instantaneous Pnof three repli-cate leaves of different individual plantswas measured on clear days at each canopydepth.Canopy solar radiation transmittance(Rt)refl
35、ectsthedistributionoftotalsolarradiationin crop communities in relation to the pop-ulation structure:Rt=Qh=Q0100%1where Rtis the total solar radiation transmit-tanceofcropcommunities(%),Qhisthetotalsolar radiation at the height of h from theground(molm2d1),andQ0is thetotal solarradiationatthetopofth
36、epopulation(molm2d1).The measurement positionswere at three canopy depths from Jan.2017to June 2017.Measurements of tomato fruit yield.Dur-ing the harvest stage of the tomato plants,fruits were collected and weighed with anelectronic scale balance(Meifu Electronics,Shenzhen,China)each week.The total
37、 yieldwas the sum of each week from 22 Jan.2017to 17 June 2017.Statisticalanalysis.Thesignificanceanal-ysis of data was evaluated by an analysis ofvariance and t test at P=0.05 with SPSS 20.0(IBM Inc.,Armonk,NY).A linear correla-tion analysis was performed assuming thatreplications in the same green
38、house compart-ment were independent.The daily light inte-gral(DLI)was obtained by integrating thevalue of PPFD with MATLAB(MathWorksInc.,Natick,MA).Sigmaplot 14.0 was usedto perform the linear correlation analysis ofthe data and to plot all figures.ResultsPPFD distribution within the tomatocanopy.Ca
39、nopyPPFDofthetwogreenhousecompartments fluctuated on the example day,which was 19 Apr.2017(Fig.3).The maxi-mum fluctuation amplitude of PPFD in theupper canopy of the 29%haze compartmentwas 105.0 mmolm2s1,with an average of53.5 mmolm2s1(Fig.3A);however,themaximum fluctuation amplitude of the 20%haze
40、 compartment was 233.5 mmolm2s1,withanaverageof101.2mmolm2s1(Fig.3B).In the 29%haze compartment,thelower canopy PPFD was kept above than 200mmolm2s1for 4.7 h,which was longer thanthat of the 20%haze compartment,where thatPPFD was kept for 2.0 h.PPFD above 600mmolm2s1in the middle canopy of the 29%ha
41、ze greenhouse lasted for 2.0 h,whereas thatof the 20%haze compartment was kept foronly 0.4 h.PPFD above 800 mmolm2s1inthe upper canopy lasted for 1.3 h in the 29%haze compartment and 0.5 h in the 20%hazecompartment.The DLI values of the middle and lowercanopies of the 29%haze compartment weresignifi
42、cantly greater than those of the 20%haze compartment(Table 1).The DLI valuesof the upper,middle,and lower canopiesfrom January 2017 to June 2017 in the 29%Fig.1.The structureofthe experimentalChinese solar greenhouse(CSG)consistingof a transparent southroof covered with plastic film,a north wall,and
43、 an opaque and insulated north roof and sidewalls.Thenorth wall is constructed with clay bricks(200+200 mm)insulated with polystyrene boards(70 mm)in the middle.The experimental greenhouse was divided into two compartments with heat insulationboard.(A)Outside view of the CSG.(B)Inside view of the gr
44、eenhouse(when seedlings weretransplanted).(C)Schematic structure of the greenhouse.2 of 9HORTSCIENCEhttps:/doi.org/10.21273/HORTSCI15241-20haze compartment were 0.7 to 1.6%,5.7%to23.6%,4.5%to 16.9%greater than those inthe greenhouse with 20%haze,respectively(data not shown).The DLI values at 2 mabov
45、eground(above the canopy)in the 29%haze compartment were significantly lowerthan those in the 20%haze compartment.The PPFD experienced three severe fluctu-ationsinthehorizontalcanopyinthe20%hazegreenhouse compartment between 900 and1200HRon 20 Mar.2017(Fig.4).The max-imum fluctuations were 512.3 mmo
46、lm2s1atthesouth,197.0mmolm2s1atthecentral,and120.7 mmolm2s1at the north areas of thegreenhouse(Fig.4B).However,the fluctuationfrequency of the horizontal canopy in the 29%haze compartment was lower,and the fluctua-tion value was lower than that of a differenthorizontalcanopy(103.9mmolm2s1)(Fig.4A).I
47、n the 29%haze compartment,PPFD in the north canopy was maintainedabove 400 mmolm2s1for 3.3 h(Fig.4A),which was 2.3 h longer than that of the 20%haze compartment.PPFD in the central can-opy was maintained above 600 mmolm2s1for 4.0 h(Fig.4A),which was 1.7 h longerthan that of the 20%haze compartment.P
48、PFD in the south canopy was maintainedabove 800 mmolm2s1for 2.7 h(Fig.4A),but only 1.1 h was recorded for the 20%haze compartment(Fig.4B).The DLI ofthe central and north areas of the 29%haze compartment significantly increased(P 0.05).Under ventilation conditions,the leaftemperature in the upper can
49、opy of the 20%haze compartment was higher than that withhigher haze film(Fig.6).From 1000 to 1500HR,the average leaf temperature in the uppercanopy in the 29%haze compartment was35.1?C,which was 4.9?C lower than that inthe 20%haze compartment(40.0?C).Leaftemperature reached the highest value at1400H
50、R;in the 29%haze compartment itwas 37.3?C and in the 20%haze compart-ment it was 42.6?C.Leaf temperature above40?Cinthe20%hazecompartmentlastedfor4.6 h.After 1200HR,except for a slightincrease in leaf temperature in the uppercanopy,the leaf temperatures in the middleand lower canopies were stable.Fr