Chlorophyll Fluorescence Based Water Stress Diagnosis For Cut Lilium Grown In Greenhouse

Water is one of the most important factors affect the plant growth. Crop yield and quality are based on the photosynthesis which affects by both stomatal and non-stomatal limitation under water stress. The treats of greenhouse crops and various greenhouse structures and materials restrict the application of the diagnosis methods such as leaf water potential or remote sensing technique which are conveniently used for field crops. As the probe of photosynthesis, chlorophyll fluorescence technique uses artificial light to supervise the photosystem operation rapidly and non-invasively in vitro. In order to explore the possibility of water stress diagnosis based on chlorophyll fluorescence, experiments of cut Lilium spp.’Sorbonne’with different planting dates and water treatments (CK:-4--10kPa、T1:-10～-15kPa、T2:-15～-20kPa、T3:-20～-30kPa、T4:-30～-40kPa) were conducted in a PC multi-span greenhouse in Naijing from March2009to January2011. The correction function of environmental photo-thermal background on chlorophyll fluorescence parameters was development. Through the compare and analysis of photosynthetic rate and chlorophyll fluorescence parameters before and after re-watering, the diagnosis hypothesis had been proposed, the chlorophyll fluorescence diagnosis indices had been determined. By using extended FvCB model, the relationship between photosynthetic rate under light-limited condition (Aj) and quantum use efficiency (Φ2) was preliminary discussed, so did the diagnosis method. The main research results are as follows:(1) Determination of the correction functions of environmental photo-thermal background on chlorophylly fluorescence. By using the experimental data from no-stress plant under different planting dates, we systemtically analyzed the effect of environmental photo-thermal background on chlorophyll fluorescence. The result showed that in the optimum temperature range of photosynthesis, all the chlorophyll fluorescence parameters measured under rated photosynthetically active rate (PAR) remained constant;Φ2decreased exponentially while ΦNPQ increased linearly accompanied the increased PAR. When the temperature was out of the optimum range, O2and photochemical quenching based on the lake model (qL) decreased while ΦNPQ increased sinusoidal accompanied the increase or decrease of the temperature.Non-light induced energy dissipation (ΦNO) and maximum quantum efficiency of PSII photochemistry (Fv/Fm) measured predawn was insensitive to photo-thermal background. Independent experimental data were used to validate the revision function with the results that the coefficient of determination (R2) and the relative root mean square error (rRMSE) between the simulated and the measured values of Φ2, qL, ONO based on the1:1line were0.96,0.87,0.96and3.19%,6.12%,10.9%, respectively.(2) Determination of chlorophyll fluorescence diagnosis indices. By using the experimental data measured before and after re-watering, we analyzed the effect of water stress on photosynthesis and chlorophyll fluorescence parameters. The result showed that except Fv/Fm, other chlorophyll fluorescence parameters could recover more or less after re-watering, thus, Fv/Fm can be used to measure the permanent damage of PSII. ΦNO was more sensitive to water stress than Fv/Fm, and could slightly recover, can be used to prevent the occurrence of water stress. The calculation of qL and ΦNPQ needs both light adapt state and dark adapt state measurement, meanwhile were sensitive to photo-thermal background, which would bring more error and operation difficulty, are not suitable for being diagnosis index. Φ2had the closest tendency with leaf photosynthetic rate, can be used to supervise photosynthesis. The chlorophyll fluorescence diagnosis indices were determined as Φ2,ΦNO and Fv/Fm.(3) Preliminarily discuss the relationship between Aj and Φ2, and the water stress diagnosis method based on the chlorophyll fluorescence indices. By using the extended FvCB model and experimental data before and after re-watering, a linear regression can be performed for Aj against (IincΦ2/4) before and after re-watering, in which the slope of the regression is parameter s and the intercept give an estimate of Rd. Both s and Rd decreased accompanied the aggravation of water stress. Result from the fact that Aj was sensitive to stomatal limitation while chlorophyll fluorescence diagnosis indices were not, only the relationship between Aj and Φ2after re-watering and chlorophyll fluorescence indices before re-watering can be used to estimate whether the stress occur or to what degree it is. The relationship among external quality indices, plant dry weight, photosynthetic rate, Φ2and Fv/Fm were positive, which were negative to that of ΦNO. Through the systematic re-watering experiments, these relationship can be used to diagnosis the water stress, hance, estimate the loss in disasters.