Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    De noordse woelmuis in het herinrichtingsgebied polder Zeevang, Noord-Holland
    Bierhuizen, B.R. ; Bergers, P.J.M. - \ 1995
    Wageningen : Instituut voor Bos- en Natuuronderzoek (IBN-rapport 196) - 50 p.
    The effect of light and CO2 on photosynthesis of various pot plants
    Bierhuizen, J.F. ; Bierhuizen, J.M. ; Martakis, G.F.P. - \ 1984
    Gartenbauwissenschaft 49 (1984). - ISSN 0016-478X - p. 251 - 257.
    potplanten - fotosynthese - sierplanten - licht - fotoperiode - fotoperiodiciteit - schaduw - milieufactoren - kooldioxide - binnen kweken (van planten) - pot plants - photosynthesis - ornamental plants - light - photoperiod - photoperiodism - shade - environmental factors - carbon dioxide - indoor culture
    Onderzoek naar de netto fotosynthese van 13 potplantesoorten. Hiertoe zijn metingen verricht bij 180 graden Celsius, 600 mg CO2 per m3, 7 lichtintensiteiten en twee O2-concentraties (21% en 1%). Tevens is de reactie van de nettofotosynthese op kunstmatig toegevoegde CO2 gemeten, uitgaande van 7 CO2-concentraties van 100-2000 mg per m3 en 21% O2, 18 graden Celcius en 150 W per m2
    Light responses of photosynthesis and transpiration of two tomato cultivars under ambient and altered CO2 and O2
    Lakso, A.N. ; Bierhuizen, J.F. ; Martakis, G.F.P. - \ 1984
    Scientia Horticulturae 23 (1984). - ISSN 0304-4238 - p. 119 - 128.
    Growth, photosynthesis and yield of some snapbean (Phaseolus vulgaris L.) cultivars. I. Gas exchange measurements
    Magid, A.H.A. ; Bierhuizen, J.F. - \ 1984
    Gartenbauwissenschaft 49 (1984). - ISSN 0016-478X - p. 1 - 6.
    The influence of irradiance and external CO2 concentration on photosynthesis of different tomato genotypes
    Nilwik, H.J.M. ; Gosiewski, W. ; Bierhuizen, J.F. - \ 1982
    Scientia Horticulturae 16 (1982). - ISSN 0304-4238 - p. 117 - 123.
    With 4 genotypes of tomato, irradiance and CO2-response curves of net photosynthesis were analysed by means of curve fitting. Estimated values of the light compensation point Ic showed small but significant differences between the genotypes, the overall value being in the order of 8 W m−2. The photochemical efficiency (αn) and the maximum net photosynthesis per unit leaf area basis (Pnm) reached the highest values for ‘F6 IVT’ (13.3 μg CO2 J−1 resp. 0.549 mg CO2 m−2 s−1), the lowest value of αn with ‘Bonabel’ (9.9 μg CO2 J−1), and the lowest value of Pnm with ‘PI 114969’ (0.424 mg CO2 m−2 s−1). The CO2-compensation point (Cc) was relatively high (177–245 mg m−3). ‘F6 IVT’ demonstrated the highest value of Cc, the lowest carboxylation efficiency and the highest maximum rate of net photosynthesis. The results clearly demonstrate that the latter genotype requires a much higher external CO2-concentration than the other genotypes in order to exhibit the highest rate of net photosynthesis.
    The influence of temperature on photosynthesis of different tomato genotypes
    Gosiewski, W. ; Nilwik, H.J.M. ; Bierhuizen, J.F. - \ 1982
    Scientia Horticulturae 16 (1982)2. - ISSN 0304-4238 - p. 109 - 115.
    Net photosynthesis and dark respiration from whole plants of various tomato genotypes were measured in a closed system. At low irradiance (27 W m−2) and low external CO2 concentration (550 mg m−3), net photosynthesis of 10 genotypes was found to vary between 0.122 and 0.209 mg CO2 m−2 s−1. Correlation was observed between net photosynthesis, net uptake on a daily basis (8 h photoperiod at 20°C and 16 h nyctoperiod at 10°C), specific leaf weight and leaf area ratio. At high irradiance (243 W m−2), high external CO2 concentration (1480 mg m−3) and ambient temperatures of 10, 18, 20 and 26°C, four genotypes were analysed. ‘F6 I.V.T.’ had the highest rate of photosynthesis at 10°C, while ‘Sonatine’ ranked high at 26°C. Dark respiration increased with temperature, except in the case of ‘Bonabel’ where the effect of temperature was slight.
    Plant-water relationships
    Bierhuizen, J.F. - \ 1981
    Acta Horticulturae 119 (1981). - ISSN 0567-7572 - p. 59 - 66.
    Optimum temperature range for germination of vegetable seeds
    Wagenvoort, W.A. ; Boot, A. ; Bierhuizen, J.F. - \ 1981
    Gartenbauwissenschaft 46 (1981). - ISSN 0016-478X - p. 97 - 101.
    Growth and photosynthesis of lettuce
    Holsteijn, H.M.C. van - \ 1981
    Landbouwhogeschool Wageningen. Promotor(en): J.F. Bierhuizen. - Wageningen : Holsteijn - 132
    lactuca sativa - slasoorten - fotosynthese - groei - lactuca sativa - lettuces - photosynthesis - growth

    Butterhead lettuce is an important glass-house crop in the poor light period in The Netherlands. Fundamental data about the influence of temperature, light and CO 2 on growth and photosynthesis are important e.g. to facilitate selection criteria for new cultivars. In this study on lettuce emphasis has been given to light interception in the poor light period, the relationship of growth rate and relative growth rate with time, dry weight and soil cover, and to photosynthesis properties of the cultivar 'Amanda Plus' and other cultivars.

    The soil area which is covered by a lettuce plant determines to a certain extent the light interception and growth of a plant. Therefore, the process of soil covering was studied in two experiments, the first one in spring with 8 cultivars and the second one in autumn with 5 lettuce cultivars and one endive cultivar ( chapter 2 ). The cultivar 'Amanda Plus' was used in both experiments. Three plant densities (20 cm x 20 cm; 25 cm x 25 cm; 35 cm x 35 cm) and 3 day/night temperatures were applied. The soil cover was determined according to the dot counting method. The process of soil covering related with time was described by a four parameter sigmoid curve with the parameters t (time in days from planting), S (amount of soil cover at time t), S max (maximal covered area) and p (the position of the inflexion point (t i , S i ). of the curve). Derived parameters are r (the initial soil cover rate), L i (S i /S max ) and R i (the soil cover rate in the inflexion point). W max is the fresh weight of the head at t max (time from transplanting until no visible increase in soil cover occurred), and W end is the fresh weight at the end of the experiment.
    Sigmoid curves fitted from the obtained data were all asymmetrical. Problems with curve-fitting occurred for the data of the treatments with long growing periods (low temperatures, 35 cm x 35 cm spacing). The data of the endive cultivar also could be fitted according to the similar sigmoid curve. The standard errors for the parameters r and p were high and these parameters were less useful for further analysis. At higher temperatures t max is lower. Mutual shading shortens the period until t i . At lower temperatures t i became higher. Wider spacings resulted in higher t i - and S i -values. The soil covering process of 'Amanda Plus' is more rapid in autumn than in spring. For the 35 cm x 35 cm plant density S max tended to decrease at lower temperatures. For the other two densities the maximum available soil cover was reached in almost all treatments. When t max is low and the growth period is short or the plant density high, L i becomes high. Differences between the parameters of the S-curves of the cultivars existed in spring as well as in autumn.
    A favourable combination between some parameters e.g. low t i with high S i , or high r with high L i , is present for some treatments and cultivars, but no cultivar showed the optimal combination of all parameters (high r, high L i , low t i combined with a high S i , high R i and low t max ). for a fast soil covering process. The correlations of some max of the soil cover parameters (t i , L i or W max ). with W end were low, especially of L i with W end , and of t i with W end for a number of cultivars in spring. The low correlation was partly due to the late harvest dates in the experiments. High correlations, however, are not to be expected and indirect selection of a high W end based on parameters of the soil cover curve is doubtful.

    In chapter 3 a quantitative growth analysis for the butterhead-- cultivar 'Noran' grown in spring and 'Deciso' in autumn has been described. The plants were cultivated at similar day/night temperatures and plant densities as those described in chapter 2. For the quantitative analysis a good fit of the growth curves is essential. Polynomials between the third and ninth degree were needed for an adequate description of dry weight (W) and leaf area (A) versus time (t). The long growth period and the partly controlled conditions of the glasshouse complicated a good fit of some data.
    The growth rate (GR = dW/dt), being the derivative of the polynomial of dry weight with time, was also used for the calculation of other parameters. The relative growth rate (RGR = dW/dt.1/W) decreases with time as well as with an increase in dry weight for all treatments presented. Plants grown at wider spacings have a higher RGR than plants at narrow spacings.
    Attention was paid to the relationship of GR with soil cover. These GR-S curves indicate the growth stage during wich mutual and self shading occur and heading becomes visible. When head formation occurs (between 2 and 5 gram dry weight) GR reaches a maximum value and starts to decrease. Plants at 35 cm x 35 cm have higher maximal growth rates, whereas the decrease of GR starts at a higher dry weight. The relationship between GR and S for the growth period until 80% of S max is almost linear. After this period the rise of GR is larger and than followed by a decline of GR at maximal or increasing S. Except one situation, the linear relation of GR with S gave higher correlation coefficients than those with A and W. Multilinear regression showed that mainly S is related to the increase of GR over that period until 80% of S max .
    The plants grown at lower temperatures in spring had a lower GR and reached a certain soil cover at a later date in this season than plants grown at higher temperatures, which resulted in a higher interception of irradiance and/or better use of the intercepted irradiance. In the autumn experiment the plants grown at higher temperatures intercepted more irradiance than those grown at lower temperatures, because a high S was reached earlier during that period with a high level of irradiance and a longer day-length (Fig. 6). The growth rates of the plants of the narrow spacings were lower than those of the plants of the wider spacings. The relationship between accumulated dry weight and total irradiance, intercepted per plant after correction for the covered area, is almost linear.
    The relationship between leaf area ratio (LAR A/W) and heading has also been studied. When LAR is lower than 550 cm 2 g -1 resp. 710 cm 2 g -1 for 'Noran' and 'Deciso' the quality of the head is good.

    Since equipment for photosynthesis measurements and determination of CO 2 compensation concentrations was not available at the Department of Horticulture of the Agricultural University of Wageningen, a closed system was built suitable for whole plants of lettuce and of other crops (sweet pepper, tomato). The system is described in chapter 4. The internal gaseous volume of the closed circuit as used for the lettuce measurements is 180 litres. The circuit consists of a cylindrical perspex plant chamber, a copper duct with a built-in fan, cooling coil, air-heating elements and connecting flexible tubes. The internal diameter of the chamber is 441 nun and the height is 340 mm, which can be enlarged to 690 mm. A cylindrical perspex pot chamber which has an internal diameter of 190 mm and a height of 190 mm is placed in the plant chamber.
    The equipment is placed on a metal trolley in a room, in which the temperature can be regulated between 10 and 34°C + 1° C. The temperature in the plant chamber can be kept constant between 5 and 32°C + 0.5°C and in the pot chamber between 15 and 35°C + 0.5°C. Temperatures are measured by thermocouples. The light equipment consists of 5 Philips high mercury vapour lamps (400 W) arranged above a waterbath with running water, which is constructed above the plant chamber. The maximum irradiance on plant level is 215 Wm -2 . Irradiance is measured by selenium photocells and the air humidity with thin film humidity sensors. Windspeed in the centre of the plant chamber is about 0.8 ms -1 . An infra-red gas-analyser determines the rate of CO 2 exchange. Injection of pure CO 2 or a mixture of air with CO 2 admits continuous monitoring of this exchange. During the relatively short periods of measurements leakage can be neglected. All measurements are recorded by a 24 channel mV-recorder or a data logger.

    Photosynthesis rates of whole lettuce shoots of butterhead cultivar 'Amanda Plus' were measured with this closed system ( chapter 5 ). In a first experiment the response of photosynthesis (P) to irradiance (I) was measured for plants of 3 different ages at 14°C and 26°C and in the second experiment the response to CO 2 -concentration (C) was measured at 15°C and 25°C, and the CO 2 compensation concentration was determined. In both experiments plants were cultivated at 2 different levels of irradiance and 2 different day/night temperatures.
    The photosynthesis data per plant were fitted with the use of a rectangular hyperbola, which related photosynthesis to both irradiance (I) and CO 2 -concentration (C), in which a represents the initial slope of the P-I-curve, i.e. the photochemical efficiency, and τthe initial slope of the P-C-curve, i.e. the plant conductance for CO 2 transfer. The carboxylation efficiency is included in this conductance. In the light series τdetermines to a great extent the gross maximal photosynthesis (P m,g = τ g C).
    Attention was paid to the basis of expression for the photosynthetic rates, obtained per plant. Since those rates expressed per unit leaf area, weight (or soil cover) were not adequate for comparison with other results, another basis, the effective leaf area (EL) was introduced. EL = α g-1g,con (m 2 Pl -1 ), with α g as the gross photochemical efficiency per plant and α g,con as the constant value of α g when all light quanta should be absorbed. For the calculations of the photosynthesis rates on EL-basis only α g -values have been used.
    A multilinear regression model of α g with S, A and W (in this order) gave high correlation coefficients, while addition of the
    height of the plant, as included in the profile area, did not improve the model significantly. The linear relation of α g with the covered area by the plant gave higher correlation coefficients than of a with leaf area or weight, except for the group of younger plants.
    In experiment 1 the gross photochemical efficiency per plant (α g ). and per unit leaf area (α g1 ). the maximal gross photosynthesis per plant (P m,g ) and per unit leaf area (P 1m,g ), the dark respiration per unit dry weight (R d ) and the light compensation point (I c ) were calculated and listed. The values of α g and α g1 the net photosynthetic rates at 35 and 100 Wm -2 and at saturated level of irradiance, expressed on the basis of α g , the P 1m,g , I c and the corrected light compensation point (I cαg ) were used in a 3 way analysis of variance.
    The values of α g1 and P 1m,g decreased with ageing, but α g1 was almost not affected by the temperatures of the treatment and of the measurement. The net photosynthetic rates on α g -basis gave lower values for the group of young plants and similar values for the other age-groups. At a low irradiance level (35 Wm -2 ). the effect of the various cultivation treatments on net photosynthesis diminished, but at 100 Wm -2 the influence of the treatments on net photosynthesis increased, and this influence
    became much more distinct on the maximal net photosynthetic rates. At 35 Wm -2 the net photosynthesis on α g -basis is higher at 14°C than at 26°C. At saturated level of irradiance the opposite situation occurred, while at 100 Wm -2 this difference is absent. The light compensation point is strongly influenced by temperature during measurements and much less by treatment and age. The corrected I c was affected by age and measurement temperature and not by cultivation. The correlation coefficients (r) between specific leaf weight (SLW = W/A), as an average of the leaf area and leaf weight of the plant, and P m,n on α g -basis at 14°C is 0.73 and at 26°C 0.55.
    In experiment 2 the net conductance for CO 2 transfer per plant (τ n ) and per unit leaf area (τ n1 ), the maximal net photosynthesis per plant and per unit leaf area (P m,n and P 1m,n ) and the CO 2 compensation concentration (C c ) were calculated. The values of τ n and τ n1 decreased and the Pm,n increased with a rise in measurement temperature. C c is strongly influenced by temperature during measurement but not by temperature during cultivation.

    The use of the rectangular hyperbola and of αand τwas discussed in relation with the light interception and CO 2 transport of whole lettuce shoots. It was suggested that the boundery air layer resistance for CO 2 transport of the whole plant, which is considered to be low for most plants or crops in optimal conditions, can play a more important role for plants with a dense leaf orientation, such as lettuce. The use of α g as basis of expression did not completely solve the interpretation problems of photosynthesis data obtained per plant.

    In chapter 6 six experiments have been described in which the response of photosynthesis to irradiance of whole lettuce shoots of various cultivars was measured in an open system at 22°C. The butterhead lettuce cultivars 'Amanda Plus', 'Ostinata' and 'Hilde' were cultivated in 3 experiments (nrs. 2, 3, 5) in the glass-house, one in the phytotron (nr. 1) and one outdoor (nr. 6). Besides those 3 cultivars 4 other butterhead cultivars were used in the first spring experiment (nr. 3). Five butterhead, 2 cos- and 2 iceberg cultivars were used in the second spring experiment (nr. 4).
    According to a similar procedure as described in chapter 5 the gross photochemical efficiency per plant (α g ) and per unit leaf area (α g1 ), the maximal 1 net photosynthetic rates per plant (P m,n ) and per unit leaf area (P 1m,n ), the dark respiration per unit dry weight (R d ) and the light compensation point (I c ) were calculated. The SLW, stomatal (r s ) and residual (r m ) resistances were also calculated. The α g -values were used as basis of expression for photosynthetic rates according to the theory outlined in chapter 5. A multilinear regression of α g with S, A and W was carried out and the best fit of α g was obtained with S.
    In a two way analysis of variance α g , α g1 , the net photosynthetic rates at 30, 50, 100 and 150 Wm -2 and at saturated level of irradiance (all on basis of α g ), the P m,n per unit S, the I c and corrected (I c (I cαg ) were analysed for the 3 cultivars in the 5 experiments. For the plants of experiments 3 and 4 a one way analysis of variance for the same parameters except the net photosynthetic rates at 30, 100 and 150 Wm -2 was carried out. For 'Amanda Plus', 'Ostinata' and 'Hilde' α g1 is more influenced by treatment (thus experiments 1, 2, 3, 5 and 6) than by cultivar. The α g1 of 'Hilde' differs from those of 'Amanda Plus' and 'Ostinata'. A lower irradiance during growth resulted in a high α g and α g1 . In experiments 3 and 4 varietal differences for α g1 appeared to be higher. P m,n increased after a higher irradiance during growth. Differences between the values of P n (and also other parameters involved in photosynthesis) increased when differences between the cultivars regarding habitus, growth and genetical background were more pronounced (exp. 4). Results of the analysis of variance of P m,n per
    unit soil cover were identical to those of P m,n per unit α g for 'Amanda Plus', 'Ostinata' and 'Hilde'. When the photosynthesis measurements are carried out at a level of irradiance close to that during growth, no significant differences between the photosynthetic rates of the cultivars on α g -basis occur (exp. 3 and 4).
    For butterhead lettuce the influence of cultivar on the light compensation point is less pronounced than that of treatment. In two experiments the r m of 'Hilde' was larger than those of 'Amanda Plus' and 'Ostinata'. In the two spring experiments different r m -values between the cultivars were also present. A period of low irradiance resulted in a high r m for the plant. Differences between the r s -values existed only in experiments 3 and 4. The correlation coefficient (r) between the total plant resistance for CO 2 transfer (1/ τ n1 ) and r s +  r m for all data is 0.81.
    For butterhead cultivars the specific leaf weight is more influenced by cultivation conditions than by genetic differences. However, significant differences between cultivars existed. A high negative correlation existed between SLW and r m when the differences were m caused by the various cultivation conditions. The two cos-lettuce cultivars, one selected for glass-house cultivation and one for outdoor growing, gave different results, while the two iceberg genotypes, both selected as glass-house crops, always gave similar results. The used cos- and iceberg lettuce cultivars were less adapted for growth during the winter season in The Netherlands.
    No clear criteria for indirect selection on higher yield have been found between the parameters, which describe the photosynthetic process. Success with indirect selection on higher yield based on parameters of the soil cover curve was also expected to be doubtful. When photosynthesis will be measured at irradiance and temperature conditions close to that during growth, no differences between the photosynthetic rates on α g -basis of the various genotypes can be expected. It is felt desirable that more research is carried out on the morphology of the lettuce plant in relation to growth, light interception and CO 2 transport and diffusion from the external air to the carboxylation sites. The introduction and use of non-heading cultivars would make the study of lettuce easier and facilitate cultivation of lettuce during the poor light period.


    Water relations and keeping-quality of cut Gerbera flowers
    Meeteren, U. van - \ 1980
    Landbouwhogeschool Wageningen. Promotor(en): J.F. Bierhuizen. - Wageningen : van Meeteren - 78
    sierplanten - asteraceae - ornamental plants - asteraceae
    The aim of the present investigation is to study the internal water relations,of ageing Gerbera inflorescences and their consequence on keepingquality of cut inflorescences. As in all parts of this paper, the term "flower" will be used to describe an inflorescence with its supporting stem.
    A great problem during vase-life of cut Gerbera flowers is ',stem break", a sudden bending of the stem. As described in part 1, this phenomenon was caused by a water shortage in the flower. The water-stress was a result of a decline of the absorption rate, due to an increase of the resistance to the water flow between the vase and the petals. In roses (which show a similar phenomenon) a water deficit in the flower-neck occurs because of competition between the various organs when the water supply is limiting (Zieslin et al., 1978). Also in the Gerbera flower there seems to be a competition for the available water, between flower head and stem.
    The increase in flow resistance causing stem break, was a result of microbial activity in the vase water. "Stem-plugging" by bacteria can be considerable already after 2 days for many flower species (Aarts, 1957). Silver-ions can extend keeping-quality of cut carnation flowers by their anti-ethylene effect (Halevy and Kofranek, 1977; Veen and Van de Geijn, 1978). However, the prevention of stem break by silver nitrate in the vase water is related to its bactericidal effect, as the mobility of silver supplemented as silver nitrate, is very low in flower stew (Veen and Van de Geijn, 1978; Nowak, 1979). Moreover, a pretreatment (1-24 h) of Gerbera stems with silver nitrate does not counteract the detrimental effect of etephon (Nowak, 1979). Mayak et al. (1977) demonstrated, that a pretreatment of the carnation stem with silver nitrate reduced the microbial population of the vase solution by the release of silver from the impregnated stem. They found that another important beneficial effect of such a pretreatment of the stem base is to decrease the toxic effect of metabolites produced by bacteria. So, the use of silver nitrate as a short pretreatment immediately after cutting will have advantages above other bactericides.
    There are 2 different pathways for water uptake by a Gerbera stem: a direct one through the xylem vessels at the cut surface and an indirect one through the cavity in the stem. Only the direct water uptake is strongly inhibited by bacterial activity in the vase water. Stem break can be prevented therefore without the use of chemicals by cutting the stem through the cavity in its center. The beneficial effect of this treatment could be improved by making a small hole in the stem as an air outlet from the
    cavity, together with a high water level in the vase in order to promote the rise of water inside the cavity.
    Stem stiffness consists of the strength from turgor of the cells and that of the structural elements. Gerbera cultivars with structurally strong stew do not show the phenomenon of stem break when a water deficit develops (De Jong, 1978). Breeding for flowers with structurally strong stems only will prevent stem break, however, not the water stress caused by microbial activity in the vase water. It is worthwhile therefore to select flowers not only with a structural strong stem, but also with a hollow one all the year round from an early stage of development.
    When Gerbera flowers were placed in water with silver nitrate, there was. still a gradual increase in the resistance for water flow through the stem ("physiological plugging") causing a decrease of water potential of the petals (part II). This decrease of petal water potential, however, was not accompanied by stem break. Possible explanations for this apparent discrepancy are discussed in detail in part II. The calculated resistance of the flower stem was obtained without induced pressure differences between 2 sides of a cut stem piece, so the results could not be due to artifacts caused by artificial pressures as suggested by Carpenter and Rasmussen (1973) for roses. The physiological plugging could be prevented by a constant low pH of the vase water.
    Even when the stem resistance for water flow remained constant at a low pH, water absorption of the cv.'Wageningen Rood' became lower than transpiration after 5 days, resulting in a decrease of flower fresh weight and petal water content (as a percentage of dry weight and as relative water content). The water potential of the petals, however,' remained steady, which seems a rather conflicting result. It should be realised, that the pressure chamber method used for estimating petal water potential, actually measures the non-osmotic component of the xylem water potential. As there ate no semi-permeable membranes between petal xylem elements and vase water, it is an accurate value for calculating stem flow resistance, but not for the actual water potential of the petal cells. This problem is discussed in more detail later on.
    Ageing petals of cut Gerbera flowers without stem plugging (part Ill) showed that the water content (W.C.) as a percentage of dry weight was correlated with ion leakage (I.L.) and with petal dry weight (D.W.) as given by the formula: W.C. = a + b(I.L.) - c(I.L.) 2 - d(D.W.). The increase in W.C. during the first days of vase life of cut flowers was due to a decrease of dry weight, while the sudden decrease in W.C. after some days of vase life was correlated with an increase in I.L., indicating a change in the semi- permeability of the membranes. Flowers ageing on the plant did not show the sharp decrease of W.C., whereas also the increase of I.L. was absent. The date at which I.L. of cut flowers increased depended on the cultivar and was affected by temperature and cytokinin treatments. The influence of temperature on the onset of the decrease of W.C. and increase of I.L. showed the importance for keeping-quality of a low temperature during storage and transport of the flowers.
    In part IV is demonstrated that the internal water relations of ageing petal-tissue were influenced to a large extent when flowers were separated from the plant. Sap osmotic potential (ψ osm ) of petals of cut flowers cv. 'Wageningen Rood' increased the first 6 days of vase life, followed by a decrease. Pressure potential (ψ press ) decreased during the entire vase period. When flowers were left on the plant, ψ osm was steady during the first 6 days and increased thereafter, whereas ψ press was steady until day 6 and then decreased. This different behaviour of the various components of water potential was due to the increase of ion leakage of petal cells of ageing cut flowers, whereas ion leakage remained constant when flowers were ageing on the plant. An increase of ion leakage of petal cells will decrease the osmotic potential of the xylem fluid of the petals. This change in xylem osmotic potential will not influence the potential difference between vase water and petal cells and thus absorption rate of vase water. However, it will decrease the water potential of the petal cells and therefore water content, osmotic potential and pressure Potential. The increase of ion concentration of the xylem fluid of the petals will cause a water shortage in the petal cells, even when these cells still act as good osmometers.
    Comparison of the results with literature data are difficult because of different measuring techniques and experimental circumstances. Mayak et al. (1974) using an isopiestic method, found a decline of petal water potential after 6 days with roses. However, they demonstrated an increase in stem water flow resistance when the flowers aged. Osmotic values of ageing carnation petals as given by Mayak et al. (1978) are conflicting with that given by Acock and Nichols (1979).
    Changes in ion leakage from the petal cells dominate the petal water relations of cut Gerbera flowers as discussed already previously. To obtain a better understanding of factors involved in keeping-quality of cut flowers, it will be important to know more about the triggering processes inducing the changes in ion leakage. Some experiments in this aspect are described in parts V and VI.
    It is known for many plant 'species that root-synthesized cytokinins are transported to the shoots, while ageing of leaves is hastend by excising and retarded by exogenous cytokinins. Moreover, ageing of cut flowers can be retarded by application of cytokinins. Therefore, experiments were done to investigate if differences in ion leakage between Gerbera petals of flowers ageing in a vase and on the plant could be ascribed to differences in cytokinin activities (part V). Cytokinin activities in petal-extracts of 3 cultivars, differing in their keeping-quality, were also compared. Activities decreased when the flowers aged (except on day 8 of the experiment). However, there were no differences between flowers ageing in a vase or on the plant. With the 3 cultivars used, there was no correlation between cytokinin content of petals at day of harvest and their keeping-quality. The results suggest strongly that no correlation exists between cytokinin activities of Gerbera petal cells and changes in their ion leakage.
    From the data given in part VI, it is concluded that changes in pressure potential of Gerbera petal cells can induce changes in the leakage of ions from the cells. The positive results of "pulsing" flowers, either with sugar (Kohl and Rundle, 1972; Mayak et al., 1973; Nichols, 1974; Sacalis and Chin, 1976) or mineral salts (Halevy, 1976), could also be a result of enhancing the pressure potential of the petal cells. Carnation flowers grown under dry conditions kept longer than those grown under moist irrigation regime (Hanan and Jasper, 1969; Mayak and Kofranek, 1976). It is likely, that the "dry grown" flowers have a higher pressure potential at the same water potential, than the "moist grown" flowers, as was found with leaves of plants grown in culture solutions with different osmotic potential (Jarvis and Jarvis, 1963).
    For the 3 Gerbera cultivars used, there was a correlation between their keeping-quality and their pressure potential at day of harvest.
    When a decrease of pressure potential initiates an increase of ion leakage, and subsequently causes a decrease of water content, the process of ageing will accelerate itself, once it has began.
    There seems to be a discrepancy between the conclusion that pressure potential of petal cells influences ion leakage of the cells and the data in Fig. 4 of part III where induced changes of water content did not influence ion leakage. The changes in water content in part III, however, were induced within 24 h, while the results in part VI were obtained when pressure potential was influenced during some days.
    The dominant influence of ion leakage on water relations, as demonstrated in parts III and IV, and the results of part VI suggest strongly that keeping pressure potential of flower petals above a certain level will be very important for a good keeping-quality of cut flowers. It might be possible that pressure potential at day of harvest, can be a selection criterion for potential keeping-quality of cut flowers.

    Root temperature and growth of young tomato plants
    Harssema, H. - \ 1978
    Landbouwhogeschool Wageningen. Promotor(en): J.F. Bierhuizen. - Wageningen : Veenman - 86
    plantkunde - solanum lycopersicum - tomaten - botany - solanum lycopersicum - tomatoes

    During recent years sophisticated techniques are applied in the glasshouse industry for the control of the glasshouse climate. Along with that development, extensive research programs were carried out to establish optimum conditions for growth. Air temperature, radiation, CO 2 -concentration and humidity of the air were the most important factors studied. Relatively little is known about optimum conditions in the root environment. Although some reports are available on the effect of root temperature on growth of tomato plants, the results have only limited applicability and were often contradictory. Therefore, the effect of root temperature on growth of young tomato plants was studied, with two objectives:
    a. to quantify the effect of root temperature on growth of young tomato plants in order to establish the profitability of root temperature control techniques in practice, and
    b. to understand the physiological background of the observed effects.

    Tomato plants were raised at root temperatures of 12, 15, 20, 25, 30 and 35°C in a glasshouse under natural radiation conditions throughout the year. Air temperature ranged from 17°C in winter to 30°C in summer by day and from 15°C in winter to 20°C in summer by night. Data on plant height, number of leaves, fresh and dry weight of leaves, petioles and stems and on leaf area were recorded periodically during each experiment.

    The effect of season on growth was much larger than the effect of root temperature. At root temperatures below 20°C growth was reduced irrespective of the season; above 30°C growth was-reduced during the summer only. An apparent interaction between season and low root temperature could be ascribed to the fact that plants, although of the same age, were at different stages of growth after some time of treatment.

    Growth analysis showed, that the reduced growth rate at low root temperature was mainly caused by a decrease of the Specific Leaf Area (SLA). Net Assimilation Rate (NAR) was not affected by root temperature. Daily measurements of leaf length revealed, that especially leaf expansion rate was reduced by low root temperatures, this reduction was not correlated with incoming radiation or evaporation in the glasshouse.

    The after-effect of root temperature during raising on subsequent growth, development and yield was studied in three experiments in which plants were raised at either 12, 25 or 35°C root temperature until flowering. After transplanting the plants into a glasshouse normal cultural practices were applied. The first experiment started in very early winter (sowing in September), the second one was a normal early crop (sowing in November) while the third one was a rather late crop (sowing in January). Besides the after-effect of root temperature, the influence of the leaf area per plant was studied by partial defoliation.

    The first experiment was too early for normal fruit set and almost no fruits were produced in any of the treatments. Raising the plants at a low root temperature did not adversely affect the yield in the second experiment, but reduced total yield by approximately 10% in the third one. This reduction of yield was caused by a decrease in the number of fruits. Halving the leaf area at transplanting reduced fruit set in January but was without effect later on in the season. Continuous removal of every second leaf accelerated the development during the first weeks but later on weak plants with a much smaller yield were obtained.

    The relative effect on air and root temperature was studied under controlled conditions. Leaf growth rate by day and night was measured separately with various combinations of air and root temperatures by day or by night. After 7 days of treatment, Leaf Weight Ratio (LWR) and SLA were determined as well. Air temperature by day was by far the most important factor, followed by air temperature during the night. Leaf growth rate was slightly reduced when root temperature was low during part of the day only. No difference between the effect of root temperature by day and that by night was observed. Growth was reduced more than additional at continuously low root temperatures.

    Since the effect of root temperature on growth was independant of season and of time-of-day, the most common hypothesis, that the growth reduction at low root temperatures is due to a reduced rate of water uptake, was doubted. Therefore, some experiments were done in which the relation between water balance, root temperature and leaf growth were studied. One of the results was, that both water stress and a low root temperature decreased leaf growth rate, but this decrease was not accompanied by a decrease in SLA at drought, whereas it was reduced at a low root temperature. These doubts on the primary rôle of the water balance in the root. temperature response of tomato plants was a reason for an investigation into the possible involvement of phytohormones.

    Application of phytohormones in foliar sprays on plants at low or optimum root temperatures showed, that complicated interactions exist between these factors. In some cases the growth reduction due to a low root temperature could be partly compensated by addition of gibberellines and cytokinins, but the results were too variable for definite conclusions.

    Finally, it may be concluded, that root temperature is not an important factor in the practice of glasshouse tomato growing in the Netherlands. A detailed study into the hormonal balance of tomato plants will be useful for a better understanding of the growth process.

    Analysis of the relationship between temperature and germination of sweet pepper
    Bierhuizen, J.F. ; Wagenvoort, W.A. ; Nilwik, H. - \ 1978
    Acta Horticulturae 83 (1978). - ISSN 0567-7572 - p. 1955 - 200.
    Water relations of cucumber, tomato, and sweet pepper
    Behboudian, M.H. - \ 1977
    Landbouwhogeschool Wageningen. Promotor(en): J.F. Bierhuizen. - Wageningen : Veenman - 85
    plantkunde - capsicum annuum - komkommers - cucumis sativus - solanum lycopersicum - tomaten - paprika's - botany - capsicum annuum - cucumbers - cucumis sativus - solanum lycopersicum - tomatoes - sweet peppers

    The ever increasing importance of water as a critical resource for agricultural production has encouraged more research on water relations in recent years. Most attention has been paid to field crops and less information is available for horticultural crops, especially vegetables. The results of studies on water relations of cucumber, tomato, and pepper are reported and discussed in this thesis.
    Drying cycle experiments were carried out with tomato, cucumber, and sweet pepper at two temperatures and three light intensities in order to: (1) examine suitability of some plant parameters as criteria for expression of plant water status; (2) investigate which parameter is most suitable as a basis for timing of irrigation; and (3) observe the change of various parameters during a drying cycle as affected by environment. Measurements were carried out on transpiration rate, stomatal diffusive resistance ( rs ), leaf temperature, plant and soil water potentials, and relative water content. The transpiration rate at 25°C was in general higher than that at 21°C due to the higher vapour pressure deficit (vpd) at the former temperature. For all the three species, a more pronounced stomatal closure was demonstrated at 25°C as compared to that at 21°C when drought was imposed on the plants. This result could be due to the fact that at 25°C the vpd and/or the internal CO 2 concentration was higher. Various levels of irradiance did not invoke different responses of stomata or transpiration rates throughout the drying cycles. The difference among the three light intensities used are thought to have been too small to show distinct responses. Moreover, relatively low intensities were used in this series of experiments. The measured rs , values did not always correlate significantly with soil water potentials because rs , measurements were carried out on single leaves at only one point in the photoperiod and the measurements were also affected by other environmental factors, such as humidity, prevailing during the measurements. Calculated rs , values showed better correlations with soil water potential, presumably because transpiration rates of the whole plants over the entire photoperiod were used for their calculation. Relative water content and leaf water potential correlated significantly with soil water potential. Among the plant parameters studied, the plant water potential as measured with the pressure chamber, was judged as the most suitable parameter expressing plant water status.
    Some physical aspects of the internal plant water relations were considered for the three species. The measured parameters were relative water content, sap electrical conductivity, and leaf water potential and its components (osmotic, pressure, and matric potentials). The contribution of matric potential to the total plant water potential was considerable. Neglecting the matric component would result in unrealistically low levels of pressure potential for the three species. Tomato was considered to have the best osmotic and matric adjustments, followed by cucumber and pepper. Sap osmotic potential and electrical conductivity were found to be significantly correlated with leaf water potential. Electrical conductivity was considered as an easy and accurate method to determine the osmotic potential indirectly. From the regression of relative water content on leaf water potential, cucumber, tomato, and pepper showed, in this order, decreasing drought resistance. Examination of some other parameters, however, such as osmotic and matric adjustments and reduction of photosynthesis in stress conditions, confirmed a better drought resistance property to tomato, followed by cucumber and pepper. Relative position of cucumber and tomato in drought resistance was discussed. For all the criteria examined, pepper was considered to be the least drought resistant. It was concluded that a better understanding of the drought resistance mechanisms in plants is required.
    Carbon dioxide exchange and transpiration rates were measured in a gas exchange assembly in two series of experiments. In the first series, measurements were carried out on cucumber and pepper at light saturation and in darkness. In the second series, photosynthesis-light curves for cucumber, tomato, and pepper were obtained. For both series, well-watered as well as stressed plants were used. Both photosynthesis and transpiration were reduced as stress set in. It was shown that both stomatal and nonstomatal mechanisms were involved in the reduction of photosynthesis. For all the three species, an increase in mesophyll resistance was observed as a result of water stress. In experiments with different levels of irradiance, it was observed that the stressinduced reduction of photosynthesis was more pronounced at light saturation compared to low light. After showing some initial opening reaction to light, the stomata of stressed plants showed a closing pattern, especially for cucumber and pepper, regardless of irradiance levels. It was proposed that the closing effect of drought overrode the opening effect of light. Severely stressed plants of cucumber and pepper were rewatered to study their recovery. Photosynthesis did not reach the pre-stress level one day after rewatering, this was due to an aftereffect of drought on stomata in cucumber and pepper and a damage to the photosynthetic system in pepper.
    Diurnal changes in water relations parameters were measured in a glasshouse for tomato and pepper. In a constant environmental condition, gas exchange rates were monitored throughout the photoperiod for cucumber, pepper, and two cultivars of tomato. Both well-watered and stressed plants were used for the above measurements. In the glasshouse, transpiration, leaf water potential, stomatal diffusive resistance, as well as the diurnal changes in environmental factors such as radiation, temperature, vpd, and evaporation were measured. It was observed that the diurnal variation in leaf water potential followed that of transpiration. Changes in the whole plant transpiration were not necessarily accounted for by the rs values measured on single leaves. Multiple regression relationships were obtained for plant water potentials on radiation and temperature and suggestions were made to their use in timing of irrigation. In a constant environmental condition, all species showed maximum rates of transpiration and photosynthesis during the first hour of the photoperiod. The rates steadily declined thereafter, and the decline was more pronounced in stressed plants. A decrease in leaf water potential could not account for these diurnal phenomena, and other internal control mechanisms were thought to be involved. It has been suggested that photorespiration increased under the high irradiance employed. Internal CO 2 levels then increased, causing stomatal closure, leading to a decline in transpiration. Photosynthesis also decreased through both stomatal closure and a decrease in the CO 2 gradient. Increases in mesophyll. resistance in the case of cucumber and pepper also occurred.

    Some aspects of seed germination in vegetables. II. Effect of temp. fluct., depth of sowing, seed size and cultivar, on heat sum and min. temp. for germination
    Wagenvoort, W.A. ; Bierhuizen, J.F. - \ 1977
    Scientia Horticulturae 6 (1977)4. - ISSN 0304-4238 - p. 259 - 270.
    Water quality and crop production
    Bierhuizen, J.F. - \ 1976
    In: Series Philosophical Society Khartoum
    Irrigation and water use efficiency
    Bierhuizen, J.F. - \ 1976
    In: Ecological studies, Analysis and Synthesis, Water and plant life / Lange, O.L., Kappen, L., Schulze, E.D., - p. 421 - 431.
    Effects of temperature and radiation on lettuce growing.
    Bierhuizen, J.F. ; Ebbens, J.L. ; Koomen, N.C.A. - \ 1973
    Netherlands Journal of Agricultural Science 21 (1973)2. - ISSN 0028-2928 - p. 110 - 116.
    Use temperature and short wave radiation to predict the rate of seedling emergence and the harvest date
    Bierhuizen, J.F. ; Feddes, R.A. - \ 1973
    Wageningen : I.C.W. (Verspreide overdrukken / Instituut voor Cultuurtechniek en Waterhuishouding no. 144) - 9
    zaadkieming - oogsttijdstip - luchttemperatuur - kiemkracht - seed germination - harvesting date - air temperature - germinability
    Zouttolerantie van komkommer
    Ploegman, C. ; Bierhuizen, J.F. - \ 1970
    Wageningen : I.C.W. (Mededeling / Instituut voor cultuurtechniek en waterhuishouding no. 126) - 8
    cucumis sativus - komkommers - irrigatiewater - zout water - waterkwaliteit - vloeistoffen (liquids) - absorptie - wortels - toxische stoffen - toxinen - planten - cucumbers - irrigation water - saline water - water quality - liquids - absorption - roots - toxic substances - toxins - plants
    Studies on productivity of coffee
    Nunes, M.A. ; Bierhuizen, J.F. ; Ploegman, C. - \ 1969
    Wageningen : [s.n.] (Technical bulletin / Institute for land and water management research no. 65)
    coffea - koffie - plantkunde - coffee - botany
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