Applying Non-destructive Techniques to Evaluate the Nitrogen Status, Irrigation Index, and Seedling Vigor for Star Cluster (Pentas lanceolata)
Date Issued
2015
Date
2015
Author(s)
Wu, Chun-Wei
Abstract
This project is using ornamental herbaceous star cluster (Pentas lanceolata) as the experimental plant materials. The chlorophyll fluorescence (ChlF, e.g., the effective photochemical quantum yield of PSII, ∆F/Fm’; photochemical quenching, qP), reflectance spectra and vegetation indices used to build up a realtime evaluation system for leaf nitrogen (N) concentration, N demand timing for fertilizer, leaf water potential (WP), irrigation timing and seedling vigor (SV). The system will provide suitable sugestions for plant material selection and cultivation management model and could improve landscaping qualities and functions. The objective of nitrogen (N) study was to predict the N demand timing for fertilizer application through ChlF, soil-plant analysis development (SPAD), and normalized difference vegetation index (NDVI). The tested plants were grown in potting soil by weekly irrigation with five concentrations (0, 4, 8, 16, and 24 mM) of N for 30 d. These five N application levels corresponding to the N concentration in leaves of tested plants were 2.62%, 3.48%, 4.00%, 4.23%, and 4.69%, respectively. The trends and rates of increase from 0 to 8 mM N treatments to its peak in Dickson’s quality index (DQI), above ground dry weight (DW), total DW, flowering rate, ∆F/Fm’, and qP were all similar to SPAD, NDVI, and the maximum photochemical quantum yield (Fv/Fm) indices. Consistent and strongly high correlations (R2 = 0.60 to 0.85) were observed among leaf N concentration (%) and SPAD, NDVI, ∆F/Fm’, and above-ground DW. With validation of these vegetation indices, leaf SPAD, NDVI, and ∆F/Fm’ are shown to be accurate and non-destructive predictors of leaf N concentration and can be used to accurately estimate N-solution irrigation timing for P. lanceolata. Therefore, the saturation point of plant N irrigation is recommended when leaf N concentration, SPAD, NVDI, and ∆F/Fm’ ratio are 4.00%, 50.68, 0.64, or 0.137, respectively. The objective of moisture study was to use non-destructive measurements as the precise irrigation indices. Drought stress was imposed on plants for 0, 3, 5, 7, 12, and 16 days by withholding water. Measurements were conducted on the third leaf counted from the apex (upper-leaves) and the third leaf from the bottom. Within the range of soil water content (WC) from 10 to 45%, leaf WP, soil WC, soil matric potential (MP), ChlF, photochemical reflectance index (PRI), adjusted normalized difference vegetation index (aNDVI) and the reflectance (R) at 1950 nm (R1950) were measured. Results show that the plants reached the temporary wilting point exhibited –3.87 MPa for leaf WP, and the maximal fluorescence yield of the light adapted state (Fm’) ratio of upper-to-lower leaves was 1.7. When the Fm’ ratio was 1.3, which corresponded to lower leaf WP < –2.27 MPa, soil WC < 21%, MP < –20 kPa, PRI < 0.0443, aNDVI < 0.0301, and R1950 > 8.904, it was time to irrigate. In conclusion, the Fm’ ratio of upper-to-lower-leaves is shown to be a non-destructive predictor of leaf WP and can be used to estimate irrigation timing. The objective of quality study was to use the non-destructive measurement of ChlF (such as ∆F/Fm’ and qP) and leaf area index (LAI) as SV indices. Plants were grown in potting soil under nature sunlight for 120 d. Plants were separated into 5 root growth potential (RGP) groups based on the number of new roots, and morphological and physiological parameters were also separated into those same levels. The trends and rates of increase from levels 1 to 5 in DQI, LAI, total dry weight, ∆F/ Fm’, and qP were all similar to the RGP index. Although RGP and DQI are frequently used as indices for SV, these measurements are time-consuming and require sample destruction. Consistent and strongly high correlations (R2 =0.59 to 0.93) were observed among DQI and LAI, ∆F/Fm’, and LAI × (∆F/Fm’), demonstrating the applicability of these indices for measuring SV in star cluster. In particular, LAI × (∆F/Fm’) was predicted using multiple variables from validation datasets, predictions were compared to actual DQI and RGP values for star cluster, and SV indices were predicted. Therefore, LAI × (∆F/Fm’) can replace DQI and RGP in the non-destructive estimation of SV.
Subjects
reflectance spectra
normalized differentiation vegetative index
photosystem II
non-destructive
drought
leaf water potential
soil water content
chlorophyll fluorescence
photochemical reflectance
seedling vigor
Dickson’s quality index
leaf area index
root growth potential
Type
thesis
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