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Janka E.,Telemark University College | Korner O.,Institute for Agri Technology and Food innovation | Rosenqvist E.,Copenhagen University | Ottosen C.-O.,University of Aarhus
Plant Physiology and Biochemistry

Under a dynamic greenhouse climate control regime, temperature is adjusted to optimise plant physiological responses to prevailing irradiance levels; thus, both temperature and irradiance are used by the plant to maximise the rate of photosynthesis, assuming other factors are not limiting. The control regime may be optimised by monitoring plant responses, and may be promptly adjusted when plant performance is affected by extreme microclimatic conditions, such as high irradiance or temperature. To determine the stress indicators of plants based on their physiological responses, net photosynthesis (Pn) and four chlorophyll-a fluorescence parameters: maximum photochemical efficiency of PSII [Fv/Fm], electron transport rate [ETR], PSII operating efficiency [F'q/F'm], and non-photochemical quenching [NPQ] were assessed for potted chrysanthemum (Dendranthema grandiflora Tzvelev) 'Coral Charm' under different temperature (20, 24, 28, 32, 36°C) and daily light integrals (DLI; 11, 20, 31, and 43molm-2 created by a PAR of 171, 311, 485 and 667μmolm-2s-1 for 16h). High irradiance (667μmolm-2s-1) combined with high temperature (>32°C) significantly (p<0.05) decreased Fv/Fm. Under high irradiance, the maximum Pn and ETR were reached at 24°C. Increased irradiance decreased the PSII operating efficiency and increased NPQ, while both high irradiance and temperature had a significant effect on the PSII operating efficiency at temperatures >28°C. Under high irradiance and temperature, changes in the NPQ determined the PSII operating efficiency, with no major change in the fraction of open PSII centres (qL) (indicating a QA redox state). We conclude that 1) chrysanthemum plants cope with excess irradiance by non-radiative dissipation or a reversible stress response, with the effect on the Pn and quantum yield of PSII remaining low until the temperature reaches 28°C and 2) the integration of online measurements to monitor photosynthesis and PSII operating efficiency may be used to optimise dynamic greenhouse control regimes by detecting plant stress caused by extreme microclimatic conditions. © 2015 Elsevier Masson SAS. Source

Janka E.,University of Aarhus | Korner O.,Institute for Agri Technology and Food innovation | Rosenqvist E.,Copenhagen University | Ottosen C.-O.,University of Aarhus
Plant Physiology and Biochemistry

Modern highly insulated greenhouses are more energy efficient than conventional types. Furthermore applying dynamic greenhouse climate control regimes will increase energy efficiency relatively more in modern structures. However, this combination may result in higher air and crop temperatures. Too high temperature affects the plant photosynthetic responses, resulting in a lower rate of photosynthesis. To predict and analyse physiological responses as stress indicators, two independent experiments were conducted, to detect the effect of high temperature on photosynthesis: analysing photosystem II (PSII) and stomatal conductance (gs). A combination of chlorophyll a fluorescence, gas exchange measurements and infrared thermography was applied using Chrysanthemum (Dendranthema grandiflora Tzvelev) 'Coral Charm' as a model species. Increasing temperature had a highly significant effect on PSII when the temperature exceeded 38°C for a period of 7 (±1.8) days. High temperature decreased the maximum photochemical efficiency of PSII (Fv/Fm), the conformation term for primary photochemistry (Fv/Fo) and performance index (PI), as well as increased minimal fluorescence (Fo). However, at elevated CO2 of 1000μmolmol-1 and with a photosynthetic photon flux density (PPFD) of 800μmolm-2s-1, net photosynthesis (Pn) reached its maximum at 35°C. The thermal index (IG), calculated from the leaf temperature and the temperature of a dry and wet reference leaf, showed a strong correlation with gs. We conclude that 1) chlorophyll a fluorescence and a combination of fluorescence parameters can be used as early stress indicators as well as to detect the temperature limit of PSII damage, and 2) the strong relation between gs and IG enables gs to be estimated non-invasively, which is an important first step in modelling leaf temperature to predict unfavourable growing conditions in a (dynamic) semi closed greenhouse. © 2013 Elsevier Masson SAS. Source

Schjonning P.,University of Aarhus | Lamande M.,University of Aarhus | Keller T.,ART Agroscope Reckenholz Tanikon | Keller T.,Swedish University of Agricultural Sciences | And 2 more authors.
Soil Use and Management

Subsoil compaction is persistent and can affect important soil functions including soil productivity. The aim of this study was to develop recommendations on how to avoid subsoil compaction for soils exposed to traffic by machinery at field capacity. We measured the vertical stress in the tyre-soil contact area for two traction tyres at ca. 30- and 60-kN wheel loads on a loamy sand at field capacity. Data on resulting stress distributions were combined with those from the literature for five implement tyres tested at a range of inflation pressures and wheel loads. The vertical stress in the soil profile was then predicted using the Söhne model for all tests in the combined data set. The predicted stress at 20cm depth correlated with the maximum stress in the contact area, tyre inflation pressure, tyre-soil contact area and mean ground pressure. At 100cm depth, the predicted vertical stress was primarily determined by wheel load, but an effect of the other factors was also detected. Based on published recommendations for allowable stresses in the soil profile, we propose the '50-50 rule': At water contents around field capacity, traffic on agricultural soil should not exert vertical stresses in excess of 50kPa at depths >50cm. Our combined data provide the basis for the '8-8 rule': The depth of the 50-kPa stress isobar increases by 8cm for each additional tonne increase in wheel load and by 8cm for each doubling of the tyre inflation pressure. We suggest that farmers use this simple rule for evaluating the sustainability of any planned traffic over moist soil. © 2012 The Authors. Journal compilation © 2012 British Society of Soil Science. Source

Dela Cruz M.,Copenhagen University | Christensen J.H.,Copenhagen University | Thomsen J.D.,Institute for Agri Technology and Food innovation | Muller R.,Copenhagen University
Environmental Science and Pollution Research

Volatile organic compounds (VOCs) are found in indoor air, and many of these can affect human health (e.g. formaldehyde and benzene are carcinogenic). Plants affect the levels of VOCs in indoor environments, thus they represent a potential green solution for improving indoor air quality that at the same time can improve human health. This article reviews scientific studies of plants’ ability to remove VOCs from indoor air. The focus of the review is on pathways of VOC removal by the plants and factors affecting the efficiency and rate of VOC removal by plants. Laboratory based studies indicate that plant induced removal of VOCs is a combination of direct (e.g. absorption) and indirect (e.g. biotransformation by microorganisms) mechanisms. They also demonstrate that plants’ rate of reducing the level of VOCs is influenced by a number of factors such as plant species, light intensity and VOC concentration. For instance, an increase in light intensity has in some studies been shown to lead to an increase in removal of a pollutant. Studies conducted in real-life settings such as offices and homes are few and show mixed results. © 2014, Springer-Verlag Berlin Heidelberg. Source

Petersen M.B.,Institute for Agri Technology and Food innovation | Soegaard K.,University of Aarhus | Jensen S.K.,University of Aarhus
Livestock Science

Most work dealing with the impact of species-rich herbage on milk fatty acid content has hitherto been carried out in alpine areas or semi-natural grasslands. The main objective of the present study was to examine the effect of herbs sown and intensively managed in a lowland sward on the concentration of n-3 and n-6 fatty acids and vitamins in cows' milk compared to clover grass and total mixed ration (TMR) feeding. Twelve cows were housed in tie-stall and randomly allocated to three diets fed ad libitum for 14. days: HERBS (mixture of fresh herbs); CLOVER (mixture of fresh white clover and ryegrass); or TMR (total mixed ration based on silage and concentrate). n-3 fatty acid (FA) content was similar between the three diets, while n-6 FA content was highest in the TMR diet. A twofold increase in n-3 FA concentration in milk was observed when feeding HERBS compared to CLOVER and TMR (0.8, 0.4 and 0.3. g/kg milk, respectively). n-6 FA concentration increased as well when feeding HERBS (1.4, 0.9 and 1.0. g/kg milk for HERBS, CLOVER and TMR, respectively). Transfer efficiency from feed to milk was doubled for n-3 FA when feeding HERBS and for transfer efficiency of n-6 FA from feed to milk an increase of 28% was observed for HERBS compared to CLOVER. Retinol content was highest in HERBS milk, while there was no difference in α-tocopherol and ß-carotene milk content between the three diets. The results thus support previous findings on the effect of herbs on the milk fatty acid profile, but it will require further research to understand the effect of herbs on n-3 and n-6 FA concentration in milk. In conclusion, milk content of polyunsaturated fatty acids (PUFA), like n-3 and n-6 FA, was significantly increased when herbs constituted the major part of the herbage, despite lower or similar dietary content of n-3 and n-6 FA in herbs compared to clover grass- and TMR diets. © 2011 Elsevier B.V. Source

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