Dennis Dannehl

The potential of a confined closed greenhouse in terms of sustainable production, crop growth, yield and valuable plant compounds of tomatoes

A confined closed greenhouse (CGH) was applied to save energy and to investigate how tomatoes respond to specific microclimatic conditions. As such, new dynamic set-points for precise climate control were used in the CGH compared to those applied in a conventional greenhouse. Based on the reduced ventilation frequency in the CGH, the results showed that higher levels of mean temperature, CO 2 concentration and relative humidity were achieved. Although the light interception was increased in the CGH, these changing microclimatic conditions resulted in higher rates of photosynthesis and an associated faster crop growth. This means that the mean plant height was increased by 1.5 m, which was the decisive factor to increase the total yield by 21.4% in relation to that produced in the conventional greenhouse. The new microclimatic environment caused by the CGH promoted the accumulation of primary and secondary plant compounds in tomatoes such as soluble solids (by 9%), lycopene (by 22%), s-carotene (by 21%), phenolics (by 8%) and L-ascorbic acid (by 26%) compared to conventional produced tomatoes. Compared to existing greenhouse systems, the results suggested that a CGH can be used to produce tomatoes in a sustainable way, where the water use and the energy use efficiency can be improved by 71% and 43%, respectively.

Comparison of Different Greenhouse Systems and Their Impacts on Plant Responses of Tomatoes

A semi-closed greenhouse was used for sustainable tomato production and to investigate the effects of the prevailing climate conditions within this greenhouse on different plant parameters of tomatoes. Compared to conventionally cultivated tomato plants, the leaf area index, the number of trusses and the yield of marketable fruit of tomato plants exposed to the microclimatic conditions in the semi-closed greenhouse were significantly increased by 21, 11 and 31.9 %, respectively. Furthermore, the application of this new technology led to a significant increase in contents of lycopene (by 30 %), ß-carotene (by 40 %), phenolic compounds (25 %), titratable acids (by 8 %) and soluble solids (by 15 %) in tomatoes during the summer period. These results were attributed to higher photosynthetic activities, which predominantly occurred in the greenhouse with the semi-closed operation mode. Furthermore, the new technology can be seen as new horticultural approach to reduce the yield of blossom-end rot fruit by 75.2 %. This quality improvement was caused by higher levels of relative humidity, where this humidity states were also responsible for a reduction in the annual plant transpiration rate by 10 %.ZusammenfassungTomaten wurden in einem semi-geschlossenen Gewächshaus im Vergleich zu einem konventionellen Gewächshaus produziert und die Auswirkungen der vorherrschenden Klimabedingungen in den Gewächshäusern auf verschiedene Pflanzenparameter untersucht. Im Vergleich zu konventionell kultivierten Tomatenpflanzen waren der Blattflächenindex (um 21 %), die Anzahl der Rispen (um 11 %) und der Ertrag der vermarktungsfähigen Früchte (um 31.9 %) der Tomatenpflanzen, die den mikroklimatischen Bedingungen im semi-geschlossenen Gewächshaus ausgesetzt waren, signifikant erhöht. Darüber hinaus führte die Applikation dieser neuen Technologie in den Sommermonaten zu einer signifikanten Erhöhung der Gehalte von Lykopin (um 30 %), ß-Carotin (um 40 %), phenolischen Verbindungen (um 25 %), titrierbaren Säuren (um 8 %) und löslicher Trockensubstanz (um 15 %) in Tomaten. Diese Ergebnisse wurden auf höhere photosynthetische Aktivitäten zurückgeführt, die überwiegend im Gewächshaus mit semi-geschlossenem Betriebsmodus auftraten. Weiterhin kann die neue Technologie als gartenbaulicher Ansatz gesehen werden, um den Ertrag der mit Blütenendfäule befallenden Früchte um 75,2 % zu reduzieren. Diese Qualitätsverbesserung wurde durch das höhere Niveau der relativen Luftfeuchtigkeit hervorgerufen, wobei diese Feuchtezustände auch für die Reduzierung der jährlichen Transpirationsrate um 10 % verantwortlich war.

Evaluation of substitutes for rock wool as growing substrate for hydroponic tomato production

To reduce the rock wool waste, the present study is focused on the evaluation of sheep wool, Sphagnum and hemp slabs, which may be used as replacement for rock wool as growing substrate for hydroponic tomato production. As such, physical and chemical properties of substrates, the plant growth, yield, fruit characteristics, as well as primary and secondary metabolites of tomatoes were considered. The marketable fruit yield of plants grown in Sphagnum slabs (12.8 kg plant -1 ) was reduced to only a small extent compared to the yield produced by rock wool slabs (13.8 kg plant -1 ). Sheep wool (12.3 kg plant -1 ) and hemp (10.4 kg plant -1 ), however, showed higher deviations. The lowest yield of blossom end rot (BER) fruit was produced by Sphagnum . Compared to this result, the BER-yield was nearly 2-fold higher caused by sheep wool. The soluble solid content in fruit ripened by the hemp material was decreased compared to those caused by the remaining substrates. Furthermore, it was found that the volume of easy available water (EAW) was mainly responsible for changes in plant development. As such, a high correlation was found between EAW and: leaf area (r = 0.851); flowers (r = 0.785); lycopene (r = -0.918); s-carotene (r = -0.997); penolics (r = -0.918); LAA (r = -0.848). The findings suggested that Sphagnum slabs can be used as replacement for rock wool slabs, whereas the usage of slabs consisting of hemp and sheep wool is not suitable as growing substrate for hydroponic tomato production.

Cultivar and Production Effects on Bioactive Polyphenols

To increase the intake of secondary plant compounds, the consumer can either increase consumption of fruit and vegetables or choose species that contain a high content of health-promoting plant compounds. Even within one species the content of phenolics can vary considerably. This effect is due to differences among cultivars or can be caused by several technical and crop production methods. Regarding the latter option, the research of the horticultural sector is focused on the enhancement of the content of phenolic compounds in plants during the last decade. These methods include breeding and the application of different intensities or concentrations of light quantity and quality, temperatures, carbon dioxide, mineral nutrients, water supply, as well as electricity to various plant species during the production cycle. To represent the different effects of such methods, this chapter will give an overview of the main results.

Impact of direct-electric-current on growth and bioactive compounds of African nightshade (Solanum scabrum Mill.) plants

Production of indigenous African leafy vegetables such as African nightshade ( Solanum scabrum Mill.), whose high nutritional and medicinal value is well documented is still limited due to insufficient preharvest techniques. Electric current is known to improve quality in food crops. Therefore, in the present study, the effects of direct-electric-current (DC) on growth and characteristic bioactive and health promoting compounds were evaluated in different morphological sections, i.e., leaves and stems of African nightshade cv. Olevolosi. Six weeks old plants were exposed to different DC applied with a voltage of 8 and 16 V, 10 h/day for 12 days. Non-treated plants served as control. Plant growth, primary and secondary plant compounds were evaluated. Applying DC increased leaf fresh (11.5-14.4%) and dry (12.1-24.2%) weight as well as marketable leaves (29.1-55.3%). Biosynthesis of chlorophylls and carotenoids was enhanced by increased DC. Furthermore, dietary fibre fractions such as hemicellulose was promoted (23.3-45.3%) by DC applications, while cellulose and lignin remained unaffected. Minerals accumulated with increasing DC. Alteration of cell membrane permeability due to DC may enhance physiological processes leading to the improved growth and acceleration of bioactive compounds in African nightshade leaves.

Reuse of Organomineral Substrate Waste from Hydroponic Systems as Fertilizer in Open-Field Production Increases Yields, Flavonoid Glycosides, and Caffeic Acid Derivatives of Red Oak Leaf Lettuce (Lactuca sativa L.) Much More than Synthetic Fertilizer

Effects of organic waste from a hydroponic system added with minerals (organomineral fertilizer) and synthetic fertilizer on major polyphenols of red oak leaf lettuce using HPLC-DAD-ESI-MS(3) were investigated. Interestingly, contents of the main flavonoid glycosides and caffeic acid derivatives of lettuce treated with organomineral fertilizer were equal to those synthesized without soil additives. This was found although soil nutrient concentrations, including that of nitrogen, were much lower without additives. However, lettuce treated with synthetic fertilizer showed a significant decrease in contents of caffeic acid derivatives and flavonoid glycosides up to 78.3 and 54.2%, respectively. It is assumed that a negative effect of a high yield on polyphenols as described in the growth-differentiation balance hypothesis can be counteracted by (i) a higher concentration of Mg or (ii) optimal physical properties of the soil structure. Finally, the organomineral substrate waste reused as fertilizer and soil improver resulted in the highest yield (+78.7%), a total fertilizer saving of 322 kg ha(-1) and waste reduction in greenhouses.