Robert H. Stamps

Correlation of Visual Quality Grading and SPAD Reading of Green-Leaved Foliage Plants

Abstract Green-leaved foliage plants are valued for their leaf forms and sizes but mainly for their foliar greenness. Evaluation of the quality of these plants has been based primarily on visual grading, which often brings biases, depending on the appraisers. The objective of this study was to evaluate the possibility of using the SPAD-502 as an instrument for estimating plant quality. Ten green-leaved foliage plant species were grown in shaded greenhouses and treated with either a water-soluble fertilizer or a controlled-release fertilizer, each at four nitrogen (N) rates. Six months later, mature leaf thickness was measured and visual quality graded. After the greenness of the mature leaves was measured with the SPAD-502 meter, leaf chlorophyll was extracted using dimethyl sulphoxide, and chlorophyll content was determined. Results showed that leaf thickness ranged from 0.19–0.66 mm among the 10 species but had no apparent effect on either SPAD readings or chlorophyll content. Visual-quality grades of the plants were closely correlated with the SPAD readings (r ≥ 0.84). Highly significant linear relationships (r 2 ≥ 0.87) were found between SPAD readings and chlorophyll a, b, or total chlorophyll content. Thus, the SPAD-502 could be used as an instrument to provide quick, nondestructive, and objective estimation of quality for green-leaved foliage plants.

Phytoremediation of arsenic-contaminated groundwater using arsenic hyperaccumulator Pteris vittata L.: Effects of frond harvesting regimes and arsenic levels in refill water

A large-scale hydroponic system to phytoremediate arsenic-contaminated groundwater using Pteris vittata (Chinese brake fern) was successfully tested in a field. In this 30-wk study, three frond-harvesting regimes (all, mature, and senescing fronds) and two water-refilling schemes to compensate for evapotranspiration (high-As water of 140-180 μg/L and low-As water of <7 μg/L) were investigated. Two experiments (Cycle 1 and Cycle 2) were conducted using the same plants in 24 tanks with each containing 600 L of arsenic-contaminated groundwater and 32 ferns. During Cycle 1 and with initial As of 140 μg/L, As in tanks refilled with low-As water was reduced to <10 μg/L in 8 wks compared to <10 μg/L in 17 wks in tanks refilled with high-As water. During Cycle 2 and with initial As of 180 μg/L, the remediation time was reduced by 2-5 wks, indicating that more established ferns were more efficient. In areas where clean water is limiting, refilling high-As water coupled with harvesting senescing fronds is recommended for more effective As phytoremediation.

PHYTOFILTRATION OF ARSENIC-CONTAMINATED GROUNDWATER USING PTERIS VITTATA L.: EFFECT OF PLANT DENSITY AND NITROGEN AND PHOSPHORUS LEVELS

This field-scale hydroponic experiment investigated the effects of plant density and nutrient levels on arsenic (As) removal by the As-hyperaccumulator Pteris vittata L. (Chinese brake fern). All ferns were grown in plastic tanks containing 30 L of As-contaminated groundwater (130 μg·L−1 As) collected from South Florida. The treatments consisted of four plant densities (zero, one, two, or four plants per 30 L), two nitrogen (N) concentrations (50% or 100% of 0.25-strength Hoagland solution [HS]), and two phosphorous (P) concentrations (15% and 30% of 0.25 strength HS). While low P was more effective than high P for plant As removal initially, N levels showed little effect. At 15% P, it took 3 wk for the ferns at a plant density of four to reduce As to less than 10 μg L−1 (USEPA and WHO standard), whereas it took 4–6 wk at plant densities of one or two. For reused ferns, established plants with more extensive roots than “first-time” ferns, a low plant density of one plant/30 L was more effective, reducing As in water to less than 10 μg L−1 in 8 h. This translates to an As removal rate of 400 μg h−1plant−1, which is the highest rate reported to date. Arsenic-concentration in tanks with no plants as a control remained high throughout the experiment. Using more established ferns supplemented with dilute nutrients (0.25 HS with 25% N and 15% P) with optimized plant density (one plant per 30 L) reduced interplant competition and secondary contamination from nutrients, and can be recommended for phytofiltration of As-contaminated groundwater. This study demonstrated that P. vittata is effective in remediating As-contaminated groundwater to meet recommended standards.

EFFECTS OF NITROGEN AND PHOSPHORUS LEVELS, AND FROND-HARVESTING ON ABSORPTION, TRANSLOCATION AND ACCUMULATION OF ARSENIC BY CHINESE BRAKE FERN (PTERIS VITTATA L.)

This hydroponic experiment was conducted to determine the effects of nitrogen (N) and phosphorus (P) levels and frond-harvesting on the effectiveness of arsenic (As)-hyperaccumulator Chinese brake fern (Pteris vittata L.) to remove As from contaminated groundwater collected from south Florida. Three-month old ferns were grown in 38-L plastic tanks (two ferns per tank) containing 30-L of As-contaminated water (130 μg·L−1 As), which was amended with modified 0.25 strength Hoaglands solution #2. Two N (26 or 52 mg·L−1) and two P levels (1.2 and 2.4 mg·L−1) were tested in one experiment, whereas the effect of frond-harvesting was tested in a separate experiment. Initially, N had little effect on plant As removal whereas low P treatment was more effective than high P and As was reduced to <5 μg·L−1 in 28 d compared to 35 d. For well-established ferns, N and P levels had little effect. Reused fern, with or without harvesting the As-rich fronds, took up arsenic more rapidly so the As concentration in the groundwater declined faster (130 to ∼10 μg·L−1 in 8 h). Regardless of the treatments, most As (85–93%) was located in the aboveground tissue (rhizomes and fronds). Frond As concentrations were higher for non-harvested ferns than for ferns where fronds were partially harvested prior to treatment. Conversely, rhizomes accumulated more arsenic in ferns where fronds had been partially harvested. Low-P treatment coupled with reuse of more established ferns with or without harvesting fronds can be used to effectively remove arsenic from contaminated water using P. vittata