Phosphorus efficiency of ornamental plants in peat substrates

Abstract

A pot experiment was conducted to investigate factors contributing to phosphorous (P) efficiency of ornamental plants. Marigold (Tagetes patula) and poinsettia (Euphorbia pulcherima) were cultivated in a peat substrate (black peat 80% + mineral component 20% on a volume basis), treated with P rates of 0, 10, 35, 100, and 170 mg (L substrate)–1. During the cultivation period, plants were fertigated with a complete nutrient solution (including 18 mg P L–1) every 2 d. Both poinsettia and marigold attained their optimum yield at the rate of 35 mg P (L substrate)–1 and the critical level of P in shoot dry matter of both crops was 5–6 mg g–1. After planting, plant‐available P increased at lower P rates to a higher level for poinsettia than for marigold, but no significant change was observed at higher P rates. Balance sheet calculations indicated that at lower P rates more P was fertigated than was taken up by the plants. Root‐length density, root‐to‐shoot ratio, and root‐hair length of marigold were doubled compared to that of poinsettia. Root‐length density increased with crop growth, and 10 d after planting the mean half distance between roots exceeded the P‐depletion zone around roots by a factor of 3 and 1.5 for poinsettia and marigold, respectively. Thus, at this early stage poinsettia exploited only 10% of the substrate volume whereas marigold utilized 43%. Later in the cultivation period, the depletion zones around roots overlapped for both crops. Taking into account P uptake via root hairs, the simulation revealed that this was more important for marigold compared to poinsettia especially at low P‐supply levels. However, increase of P uptake due to root hairs was only 10%–20% at optimum P supply. For the two lower P levels, the P‐depletion profile around roots calculated for 10 d after planting showed that after 2 d of depletion the concentration at the root surface was below the assumed Km value (5 μM) and the concentration gradient was insufficient to fit the demand. A higher content of plant‐available P in the substrate was observed for poinsettia compared to marigold in the treatment with P application adequate for optimum growth, because more fertigated P was accumulated during early stages of cultivation due to lower root‐length density of poinsettia. The observed difference of root morphological parameters did not contribute significantly to P‐uptake efficiency, since P mobility in the peat substrate was high.

Phosphorus buffering capacity of substrate clays and its significance for plant cultivation

“…The plant P concentrations necessary for optimum growth were in the same range as reported by Khandan‐Mirkohi and Schenk (2009) for poinsettia and marigold plants and were achieved with a 17 mg P L −1 fertigation solution (Figs. 4b and 5a).…”

“…Buffer power ( b ) was calculated as the ratio of P CAT : P sol ( Khandan‐Mirkohi and Schenk , 2009).…”

“…Furthermore, the RLD is a magnitude higher than under field conditions. This leads to an exploitation of the whole substrate volume, since P depletion zones around roots overlap ( Khandan‐Mirkohi and Schenk , 2009), which contrasts completely to field conditions, in which plants only use about 20% of the soil volume around roots for P acquisition ( Jungk and Claassen , 1997; Claassen and Steingrobe , 1999). The P utilization per unit substrate volume is increased for pot plants compared to field conditions, since the substrate volume is limited and the growth rates of plants are often enhanced under greenhouse conditions.…”

High resolution imaging to assess oilseed species’ root hair responses to soil water stress

“…Conventional methods of root hair characterization involve root excavation from soil-or hydroponicallygrown plants, followed by image capture with light or electron microscopy (Guo et al 2009;Hofer 1996;Khandan-Mirkohi and Schenk 2009). Excavation of roots can damage root hairs, resulting in erroneous measurement of lengths and density.…”

“…Due to the minimal expense of supplies and capability of analyzing large soil volume, the technique we introduce allows larger sample sizes that may answer questions regarding root hairs in field conditions. Understanding crop root hair morphology will enable better understanding of nutrient uptake efficiency (Dechassa et al 2003;Khandan-Mirkohi and Schenk 2009) and ultimately improve crop management. Early digital scanners were adapted to capture root images for quantitative measurement of washed roots (Pan and Bolton 1991) as well as field grown plants , but did not have adequate resolution to image root hairs.…”