Spectral reflectance as an indicator of foliar concentrations of arsenic in common sunflower (Helianthus annuus)

Studies were conducted to investigate the use of spectral reflectance by foliage of common sunflower as a potential indicator of arsenic contamination of soil. Germination method was developed for sunflower seeds, and cohorts of sunflower seedlings in hydroponic tanks were established. The cohorts were exposed to 0 ppm, 5 ppm, 7.5 ppm, and 10 ppm treatments of As (V) and reflectance measurements of foliage were collected using a spectroradiometer during two experiments.Results demonstrated the feasibility of using spectral reflectance by foliage of common sunflower as a potential indicator of arsenic contamination. In both experiments, arsenic concentrations in leaf tissues were directly proportional to arsenic concentrations in hydroponic solutions in which such plants were grown. Although the effect(s) of arsenic accumulation had minimal impact on reflectance of visible wavelengths, the effects on NIR reflectance were substantial and resulted in a progressive decrease in reflectance as arsenic concentrations in foliage increased

An Acid-Bath Technique to Break Seed Dormancy in Common Sunflower, Helianthus L. annuus (Asteraceae)

The phenomenon of seed dormancy is widespread in plants and serves to prevent all or most of a given population from germinating at the “wrong” time, e.g., during an unusually mild fall in an area subject to typically harsh winters. Seed dormancy is an effective survival strategy in many plant populations, but may greatly complicate efforts to establish large cohorts of seedlings (groups of similar age or developmental stage) needed for re-search and other purposes. In an effort to break seed dormancy in common sunflower, Helianthus annuus L. (Asteraceae), we conducted experiments designed to compare germination times and overall germination success among groups of field-collected H. annuus seeds subjected to several treatments. Overall germination success during a 14-d period posttreatment was lowest among untreated controls and groups soaked in a disinfecting solution for 15-h (1.2% and 2.6% germination, respectively;

Effects of Leaf Excision and Sample Storage Methods on Spectral Reflectance by Foliage of Giant Reed, Arundo donax

Research was conducted to evaluate the effects of leaf excision and sample storage methods on spectral reflectance by foliage of giant reed, Arundo donax, an invasive weed which has caused extensive damage in many areas of the Rio Grande Basin in Texas and Mexico. Within 24 hours of excision, A. donax leaves exposed to ambient laboratory conditions (room temperature under natural lighting conditions) exhibited two trends indicative of physiological stress: 1) small but significant increases in reflectance of blue and red wavelengths (400-500 nm and 600-700 nm, respectively) and 2) a substantial reduction in reflectance of near-infrared (NIR) wavelengths (700-1,100 nm). A similar but less pronounced trend was evident among leaf samples held within conventional paper sacks. Leaf samples held within sealed plastic bags (Glad-Bags) under two types of lighting conditions (natural light and artificial darkness) and temperature regimes (room temperature vs artificially cooled) exhibited slight but significant increases in both visible and NIR wavelengths (a trend that was also evident in attached foliage), al-though no evidence of physiological stress was detected during a 96-hour observation period. These trends indicate that accurate spectral measurements may be obtained from samples of A. donax foliage under for periods up to 72 - 96 hours following excision if such samples are transported and maintained in suitable containers designed to minimize effects of desiccation

Techniques to Facilitate the Acquisition of Accurate Spectral Measurements and Multispectral Imagery of Plant Foliage Under Artificial Lighting Conditions

Spectral measurements obtained in the laboratory under artificial lighting sources have been used for many years to develop spectral ‘libraries’ for various soil types, rocks and minerals, and other inanimate features occurring on or near the earth’s surface. Quartz halogen lamps have been shown to emit all of the electromagnetic (EMR) wavelengths required for the acquisition of quality multispectral imagery, and various techniques have been developed to facilitate the acquisition of accurate spectral measurements using such artificial lighting sources. Our objectives in this study were to evaluate the several factors of critical importance in obtaining accurate spectral measurements for plant foliage in the laboratory, including the effects of leaf orientation, excision, and background reflectance on reflectance of visible and NIR wavelengths. Results demonstrated that accurate spectral measurements and imagery of various types of foliage may be obtained using quartz halogen lighting provided that excised leaf samples are placed on an NIR-absorbent background and samples are maintained in containers designed to minimize desiccation