Study On The Mechanism Of High Temperature And High Humidity Disaster And Risk Assessment During The Inflorescence Development Period Of Greenhouse Gerber

As a bulk commodity in the cut flower industry,gerbera has become one of the mainstays of the facility cultivation industry with its advantages of annual production and high economic efficiency,while high temperature and high humidity are the main environmental factors limiting the development of gerbera inflorescences and flower quality.In this study,the’Rionegro’was used as the test material.Different temperatures（34°C/24°C,38°C/28°C,and42°C/32°C;daily maximum temperature/daily minimum temperature）and two humidity levels（70±5%and 90±5%）were set at the Agricultural Experiment Station in Nanjing University of Information Science and Technology from April to July 2021 and from September to November2022,with the duration of 4D,6D,8D,and 10D.The temperature of 28°C/18°C and the relative humidity of 50±5%were set as the control.The photoperiod of the climatic chamber was set to13h/11h（day/night）and the maximum daytime photosynthetic active radiation was set to 1000μmol·m^-2·s^-1.The photosynthetic characteristics,fluorescence characteristics,anti-aging characteristics,growth and development data（dry weight and percentage of each organ）and cut flower growth indexes（inflorescence diameter,stem diameter,stem length and stem bending）and flower intrinsic quality（anthocyanin content,soluble protein and soluble sugar）of gerbera leaves were measured.This study extracted the high temperature and high humidity disasters indicators of gerbera,established high temperature and humidity stress levels,and conducted high temperature and high humidity disasters risk zoning for gerbera in the greenhouse,with a view to applying to the optimal layout of greenhouse cultivation in southern gerbera growing areas.Meanwhile,it provided theoretical support and scientific basis for early warning and monitoring of high temperature and high humidity disasters in the greenhouse of gerbera and improved the comprehensive environmental control capacity of the greenhouse.The results showed that:（1）Maximum photosynthetic rate(P_max),light saturation point（LSP）,stomatal conductance（Gs）,transpiration rate（Tr）,and apparent quantum efficiency（AQE）of gerbera leaves under high temperature and high humidity stress showed a decreasing trend with increasing stress temperature,humidity,and duration,while light compensation point（LCP）and stomatal limitation value（Ls）first increased and then decreased,and intercellular CO₂concentration（Ci）decreased and then increased.The reason for the decrease in photosynthesis changed from a stomatal limiting factor to a non-stomatal limiting factor as the stress level increased.The combined performance index(PI_total),photosystem II（PSII）maximum quantum efficiency（F_v/F_m）,photo productivity index(PI_abs),light energy absorbed per unit area（ABS/RS）,light energy captured per unit area（TRo/RC）,the quantum yield of quantum transfer per unit area（ET_o/RC）and heat dissipation per unit area（DI_o/RC）of gerbera leaves decreased under high temperature and high humidity stress.The relative activity of PSⅠand PSⅡin the leaf blade showed a decreasing trend.The relative activity and reaction center efficiency of PSⅠand PSⅡof the leaves were inhibited to different degrees,with the effect on PSⅡbeing greater than that on PSⅠ.The malondialdehyde content（MDA）and electrolyte leakage rate（Drate）tended to increase with the increasing duration of stress,and the antioxidant enzymes catalase（CAT）,superoxide dismutase（SOD）,and peroxidase（POD）tended to increase under each high temperature and humidity treatment.（2）The dry matter distribution of gerbera under high temperature and high humidity stress decreased with increasing stress intensity and duration of stress.In combination with the effects on cut flower growth indicators,it was found that increasing intensity and duration of high temperature and humidity had a negative effect on inflorescence diameter(D_flower),stem diameter(D_stem),stem length(L_stem),and increased stem curvature(B_stem).High temperature and humidity stress also reduced the petal anthocyanin（OPC）content and soluble sugar（SS）content of gerbera,but its soluble protein（SP）content increased with increasing stress levels.（3）Pmax,MDA,PI_abs,D_flower,and OPC were extracted as key indicators by correlation analysis and principal component analysis to construct the high temperature and humidity stress index（SI）for gerbera in the greenhouse,which was classified into three classes:mild（0.15<SI≤0.30）,moderate（0.30<SI≤0.45）and severe（SI>0.45）,and used to determine its meteorological indicators of high temperature and humidity stress.（4）Mild areas in the southern gerbera growing region in 1990-2019 were mostly in southern Yunnan,northern Jiangsu,and coastal areas of Guangdong,Guangxi,and Zhejiang.Moderate high temperature and high humidity disasters mainly occurred in Guangxi,Guangdong,and southern Fujian.Severe high temperature and humidity disasters occurred more frequently than mild ones,mainly in southern Guangxi,Guangdong,and western Fujian.The comprehensive risk index of high temperature and high humidity hazards in the southern region of China showed a general trend of high in the southeast and low in the northwest.The comprehensive intensity index（CI）for the whole southern region of China under different recurrence periods（0.5a,1a,5a,10a,15a,and 20a）ranged from 0.84 to 1.06,and the SI ranged from 0.53 to 0.57,indicating that the intensity risk of high temperature and high humidity disasters was high throughout the southern region.In contrast,the topography of the Sichuan region was complex,with lower average temperatures and less sunshine,and both CI and SI are small in most of its areas except for 5a.In this study,the physiological characteristics and key inflorescence development processes of Gerbera were analysed in response to high temperature and humidity by simulating the high temperature and humidity conditions during the inflorescence development of gerbera,and key physiological and biochemical indicators were extracted by correlation analysis and principal component analysis.Based on the dynamic information such as intensity and duration of high temperature and humidity stress,the levels of high temperature and humidity stress were determined and the risk zones were classified.The results of the study can provide a scientific basis for the defence against high temperature and humidity disasters and the temperature management of production environment in the planting area of gerbera.