Relationship of 2 100-2 300 nm Spectral Characteristics of Wheat Canopy to Leaf Area Index and Leaf N as Affected by Leaf Water Content

The effects of leaf water status in a wheat canopy on the accuracy of estimating leaf area index (LAI) and N were determined in this study using extracted spectral characteristics in the 2 000-2 300 nm region of the short wave infrared (SWI) band. A newly defined spectral index, relative adsorptive index in the 2000-2300 nm region (RAI2000-2300), which can be calculated by RAI2000-2300 = (R2224 - R2054) (R2224 + R2054)-1 with R being the reflectance at 2224 or 2054 nm, was utilized. This spectral index, RAI2000-2300, was significantly correlated (P < 0.01) with green LAI and leaf N concentration and proved to be potentially valuable for monitoring plant green LAI and leaf N at the field canopy scale. Moreover, plant LAI could be monitored more easily and more successfully than plant leaf N. The study also showed that leaf water had a strong masking effect on the 2 000-2 300 nm spectral characteristics and both the coefficient between RAI2000-2300 and green LAI and that between RAI2000-2300 and leaf N content decreased as leaf water content increased.

Impedance analysis of Labisia pumila plant water status

Labisia pumila(Kacip fatimah)is a popular medicinal plant in Malaysia.The constituents of this plant have been reported to possess anticancer,antioxidant and anti-inflammatory properties.The growth and production of L.pumila is greatly influenced by the plant water status.Current techniques to measure plant water status are generally based on the plant soil moisture,which apparently did not indicate the real water content inside the plant.There are other techniques to measure directly on the plant such as based on leaf water potential(LWP)and relative water content(RWC).However,these techniques are destructive and time consuming.In this study,four levels of evapotranspiration replacement(ER)treatment which were 100%ER,75%ER,50%ER and 25%ER was applied to 30 polybags of L.pumila plants.The plant water status was measured using an impedance spectroscopy technique.A pair of electrocardiogram(ECG)electrode connected to an impedance analyzer board was used to measure the impedance value of the leaf samples noninvasively.Plant water status parameters such as LWP,RWC,volumetric moisture content(VMC),and leaf thickness were measured using standard methods.The results show that after 20 weeks of treatment,25%ER had the highest impedance value ranged from 0.10 MX to 0.15 MX at the frequency of 70–100 kHz.The resistance of 100%ER at 20 weeks of treatment increased from 0.70 kX to 1.23 kX as the reactance decreased from 0.51 kX to 0.28 kX.Comparatively,the resistance of 25%ER increased from 1 kX to 1.10 kX as the reactance decreased from 0.88 kX to 0.83 kX.The polynomial regression of impedance measurements with plant water status parameters(VMC,leaf thickness,LWP and RWC)shows that LWP and RWC had the highest R2(0.78,0.73).The results show that impedance measurement technique is auspicious to evaluate plant water status.