Study On The Response Model Of Spectra And Sap Flow Under Drought Stress Of Citrus

As a main component of the organism,water plays an irreplaceable role in the control of plant metabolism including photosynthesis and growth.However,drought is one of the world's major natural disasters,and drought had a very important influence on citrus yield and quality caused by a biotic stresses.So how to acquire the real-time,non-destructive citrus information about leaf water status of citrus and make a decision before drought stress occurring is not only an important theoretical value for drought-resistant but also an important guiding for the citrus production.Where as there are many kinds of diagnostic methods on plant water status now.physiological and biochemical analysis obviously does not meet the demand of scientific research and production needs for drought stress monitoring.It is necessary to establish a more real-time,dynamic,precision and non-destructive system of drought monitoring technology than before.In recent years,the diagnostic technology of plant drought stress developed rapidly in the world.And the relevant researches about assessing and monitoring crop water status by spectrometry have been involved in wheat,rice,cotton,grapes and other crops.However,there is still a wide gap between the production and the development of technology,such as character wavelength riddling and quantitative analysis,as a result of few reports relate to citrus.Whilst,monitoring sap flow is another new monitor technology for plant water status recently.However the further development and practicality applications is limited by lacking in the understanding to the stem-flow patterns and influencing factors roundly.In order to lay a foundation to develop the real-time,non-invasive monitoring techniques for citrus drought stress,we conducted the research on the response of citrus leaves spectrum,tree canopy spectrum and sap flow to drought stress.The results were presented as following:1.The dynamic changes in leaves relative water content(RWC) and reflectance spectrum of Fukumoto navel orange(Citrus sinensis(L) cv.Fukomoto navel orang) were analyzed in a simulated drought stress environment. It was fund that the citrus leaves have an ability of keeping a low water loss rate to resist drought stress.There is a higher relationship between the 1195-1442nm spectrum reflectance and the RWC than the other spectra ranges. And the leaf RWC linear regression model between 1400nm spectrum reflectance was established y=-0.5965x+82.3833with R²=0.842,the linear regression model between RWC(y) and the depth(xd) and area(xa) of the reflectance spectrum absorption peak at 1400 nm was firstly established,y= 0.3879xd - 53.2324 with R²=0.894 and y=0.00269xa-54,2000 with R²=0.902 by the spectrum normalization technology,respectively. The results showed that the reflectance spectrum around 1400 nm was a good indicator of citrus leaves RWC and could be used to assess RWC of citrus leaves. 2.The impact of limited irrigation on the chlorophyll content(SPAD value),leaf RWC of 'Trovita' orange, soil RWC and Canopy Spectra were investigate.The results showed that RWC of leaf and soil RWC decreased significantly with drought stress time increasing,and leaf water loss rate is greater than that of the soil.And,the drought stress did not have a significant influence on canopy spectrum,however,the spectral reflectivity at 460-950 nm increased significantly,especially at 550 nm(chlorophyll spectral absorption peak).Partial least square(PLS) techniques were used to data prediction model,and the correlativity of prediction value and true value indicated that a reasonable to bad prediction performance for leaf water content although R2reached to 0.884 the model.Whilst,the prediction model between R_515,520 and leaf SPAD value with R2=0.802,and R_915,920 and leaf RWC value with R2=0.862,In all,the regression model for leaf RWC by a portable field spectrometer to collect spectra data of citrus plants for drought detection and diagnosis provides a basis for field real-time drought monitoring technology.3.8-year-old healthy field cultivation Fukumoto navel orange(Citrus sinensis(L) cv.Fukomoto navel orang) plants on Citrange(Carrizo citrage hybrid) in Citrus Research Institute,Chinese Academy of Agricultural Sciences were selected to install TDP and automatic meteorological observation instrument for acquisition data about sap flow and meteorological parameters.The results showed that there were better relevance and synchronization between solar radiation and stem flow,and rate of stem flow increased after 1-1.5 h of solar radiation increscent,and reached to maximum around 14:00,then stem-flow stopped around 19:00 to 9:00 next day.However,there was a significant negative correlation between rate of sap flow and air relative humidity,rate of sap flow decline significantly with air relative humidity increasing.And the cubic equation prediction model between solar radiation and sap flow rate with R2=0.92.The preliminary research proved that the solar radiation and air humidity with citrus sap flow showed a good correlation and established a higher performance of regression model,which help to real-time diagnosis and early warning systems of drought based on the detection of stem-flow data.