PHOTOSYNTHETIC ACTIVITY OF LEAVES AND TOMATO FRUIT YIELD IN GROWING ON SUBSTRATES OF CEREAL STRAW AND ITS MIXTURES WITH OTHER ORGANIC SUBSTANCES

Edward Borowski¹, Józef Nurzyński^2
1 Department of Plant Physiology, Agricultural University in Lublin, Poland
² Department of Horticultural Plant Cultivation and Fertilization, Agricultural University in Lublin, Poland

ABSTRACT

In 2004-2004 studies were conducted with the use of fertigation in a greenhouse concerning the photosynthetic activity of the leaves, water potential and the yielding of tomato cv. ‘Cunero F₁’ cultivated on different substrates. The plants grew in rockwool mats with the volume of 15 dm³ and on mats of analogous dimensions prepared from the chaff of rye straw, rye straw + peat (3:1), wheat straw + bark (3:1). Two plants were grown in each mat in the period between February and October, and they were grown for 22-23 clusters. The obtained results pointed out that the value of the analyzed indexes of chlorophyll fluorescence (Fo, Fm, Fv/Fm) and the gas exchange of the leaves (gs, E, P, Ci) in plants on rockwool and on substrates prepared on the basis of rye and wheat straw did not differ in a statistically significant way. Water potential in the leaves and the fruit yield from plants cultivated on the used substrates were also similar. The authors are of the opinion that in the conditions of the application of fertigation, the cultivation substrates obtained from rye or wheat straw chaff and their mixtures with other organic materials make it possible to obtain the yield of tomato fruits on the level equal to that on rockwool.

Key words: greenhouse tomato, substrates, chlorophyll fluorescence, gas exchange, water potential, yield.

INTRODUCTION

Modern technologies of greenhouse tomato production are based on the cultivation of plants in synthetic or natural substrates. The substrate is supposed to ensure the proper amounts of water, mineral elements and air to the plant roots throughout the period of growth. An insufficient state of any of the enumerated factors can be a reason for stress, which – in turn – causes first of all changes of chlorophyll fluorescence rates [2, 4, 6, 8, 11], water potential in the leaves [4, 5] and the rate of gas exchange [3, 4].

In Poland nearly 70% of the area of greenhouse tomato is cultivated on rockwool [13]. It is considered to be the standard substrate in reference to which the usefulness of other substrates ids estimated [7, 9]. However, because rockwool is difficult to utilize after the production cycle [1], studies are conducted on the possibility of using it again [12] as well as replacing it with other mineral and synthetic substrates. A solution to this problem might be the use of cereal straw and its mixtures with other organic materials for the preparation of horticultural substrates. It is an easily accessible material in Poland, and in some regions of the country there are even problems with managing it. Straw, as an independent cultivation substrate, has not been used on a bigger scale so far [7] since it is an undurable substrate (it gets decomposed quickly) as well as having small water and sorption capacity [10]. It seems, however, that these properties of straw as a substrate are of no greater importance in cultivations under covers with the use of fertigation and that they can be improved a little through cutting the straw for chaff, densifying it and using in mixtures with other components.

The purpose of the present studies was to determine the photosynthetic activity and water potential in the leaves as well as tomato yielding with the use of fertigation on rockwool as well as on substrates prepared of rye or wheat straw or on mixtures of this straw with peat or bark.

MATERIAL AND METHODS

The studies were conducted in a greenhouse in 2004-2006. The tomato cv. ‘Cunero F₁’ cultivated between February and October in the density of 2.3 plants per 1m² was grown for 22-23 clusters. The plants grew in the following substrates: rockwool, rye straw, rye straw + peat (3:1), rye straw + bark (3:1), wheat straw, wheat straw + peat (3:1), wheat straw + bark (3:1). Straw chaff (the length of the pieces about 2 cm) and a mixture of cut straw with peat or coniferous trees bark in the volume ratio 3:1 was placed in boxed of 15 dm³ padded with a white foil of the shape and volume like a mat of rockwool. Two plants were grown in each box filled with the substrate and a mat; hence, 1 plant had a substrate of 7.5 m³. The experiment was conducted in each year according to an analogous scheme in 8 replications, with one plot made by a box or a mat with 2 plants.

The nutrient solution was provided to each plant by a drop irrygation system without recirculation. The frequency of fertigation was established by a soltimer, which set in motion the device providing the medium depending on the light intensity. The medium was supplied with approximately 20% excess, of nutrient solution which was collected in a special container and next used to fertilize plants cultivated in the field.

The measurements of chlorophyll fluorescence and the rate of gas exchange were performed in each year at anthesis of 10-11 clusters in the first or second lateral leaf under the 8^th or 9^th fruit cluster. The analysis was made of the minimum fluorescence (Fo), maximum fluorescence (Fm) and the optimum quantum efficiency (Fv/Fm). The marking was made by means of a fluorometer Handy PEA by Hansatech Instruments, on fragments of leaf blades earlier darkened for 30 minutes by means of special clips.

The measurements of gas exchange of leaves including the marking of stomatal conductance, transpiration, photosynthesis and stomatal concentration of CO₂ were made by means of a portable gas analyzer LCA-4 in the afternoon hours in the range FAR 1500-1700 µmol·m^-2·s^-1 with the temperature in the measurement chamber of 30-32°C. The index of the efficiency of water utilization (WUE) was calculated on the basis of the data concerning photosynthesis and transpiration.

Water potential was established in the petiole lying under the 9^th fruit cluster in the afternoon hours with the radiation of 1500-1700 µmol·m^-2·s^-1. The markings were performed in the pressure chamber of PMS. The fruit were picked every three days, determining the number and weight of fruits from each plant and on the basis of these data the total yield from 1 m² of the cultivation on was calculated on particular substrates. In view of a very similar effect of the used substrates on the analyzed parameters of photosynthetic activity of the leaves and tomato yielding in the successive years of studies, the data in tables 1-3 are the mean values from the year 2004-2006.

RESULTS AND DISCUSSION

Results presented in table 1 indicate a high activity of the leaves of tomato growing in all of the used substrates. The minimum fluorescence (Fo) was low and its value for the used substrates was 376, on average. The lowest Fo value was shown by the leaves of plants growing on the substrate only from wheat (353) and rye (357) straw. An addition of peat and bark slightly increased the value of minimum fluorescence. The maximum fluorescence (Fm) was on average 5.7 times higher than the minimum fluorescence; also Björkman and Demming [2] confirm that the relation Fm/Fo in the plants adopted to darkness should be 5-6. An insignificantly higher value of Fm was shown by the leaves of plants cultivated on rockwool (2196) and on rye straw with an addition of peat (2151) as well as bark (2114). The maximum fluorescence in the leaves of tomato growing on the other substrates ranged between 2094 (wheat straw + bark) and 1971 (wheat straw).

The maximum efficiency PS II is characteristic of the relation between variable fluorescence and maximum Fv/Fm. This parameter reflects the quantum efficiency of chlorophyll and its value, according to numerous authors [4, 6, 11], should range from 0.80 to 0.83. In the present studies the lowest value Fv/Fm was found for the leaves of tomato growing on the substrate prepared from what straw (0.81), while the highest – for the substrate of rockwool and rye straw (0.83). The statistical analysis of the results concerning the minimum, maximum fluorescence and the maximum efficiency PS II showed a lack of significant differences in the effect of the used substrates on the analyzed parameters of chlorophyll fluorescence (tab. 1).

Water potential in leaf petioles of tomatoes cultivated on all the substrates was high and in the afternoon hours it was, on average, 1.0 MPa (tab. 3). Cleary et al. [5] include tomato within the group of plants of low resistance to water stress. In their opinion, water potential in the plant leaves in the range from -0.5 to -0.1 MPa testifies to a good supply of water to plants. This is also confirmed by the results presented in table 2, especially stomatal conductance and transpiration of tomato leaves. Conductivity of stomata for water vapour independent of the kind of substratum was high and it ranged between 0.21 mol H₂O·m^-2·s^-1 for the wheat straw substrate and 0.26 mol H₂O·m^-2·s^-1 for the mixture of rye straw with peat and rockwool. Such a state of opening of stomata in the leaves with intensive light clearly ensured both high water transpiration from the leaves and CO₂ assimilation in them. Photosynthesis in tomato plants using a mixture of rye straw and peat was 15.63 µmol H₂O·m^-2·s^-1, while in the plants on rockwool it was 16.69 µmol H₂O·m^-2·s^-1, while transpiration was 4.54 and 4.53 mmol H₂O·m^-2·s^-1, respectively. On the other hand, CO₂ assimilation intensity in plants cultivated on the substrate of wheat straw dropped to 14.37 µmol H₂O·m^-2·s^-1, while transpiration dropped to 4.07 mmol H₂O·m^-2·s^-1. Borowski et al. [3], Cechin [4] and Flexas et al. [8] in their studies on tomatoes, sorghum and grapevine also found out a relation between stomatal conductance of the leaves, photosynthesis and transpiration. The level of CO₂ assimilation in the leaves of experimental plants is also determined by the inner concentration of this gas in the spaces of the assimilation parenchyma of the leaves, which does not have any greater influence on the state of opening of the stomata (4). Hence, the lowest stomatal concentration of CO₂ was observed in the leaves of plants cultivated in rockwool and rye straw with an addition of peat (mean 232.9 µmol·mol^-1), while the highest in the plants on the substrate of wheat straw (247.7 µmol·mol^-1). The statistical analysis did not show any significant effect of the substrates used in the experiment on any of the analyzed parameters of gas exchange in plants. The studies also found no significant differences in the value of WUE index, which range of changes was between 3.44 and 3.73 µmol·CO₂·mmol H₂O^-1.

The mean values of tomato yield obtained on the used substrates during the 3 years of studies were similar and they did not differ in a significant way. The difference between the highest yield obtained in the mixture of rye straw with bark (15.9 kg·m^-2), and the lowest obtained on rye straw with an addition of peat and on wheat straw (15.3 kg·m^-2) was only 0.6 kg. Dyœko and Stępowska [7] and Nurzyński [9] found out no significant differences in the yielding of tomato cultivated on the substrate from rye straw chaff and rockwool. There are no studies in literature concerning the usefulness of substrates of wheat straw chaff.

CONCLUSIONS

1. Photosynthetic activity of tomato plants (chlorophyll fluorescence, gas exchange) cultivated on rockwool and on the substrates prepared on rye or wheat straw chaff did not differ in a statistically significant way.

2. Tomato plants cultivated on the substrate of rockwool and rye or wheat straw chaff and their mixture with peat or pine bark showed very similar water potential in the leaves.

3. An addition of other organic substances (peat, pine bark) to the substrates prepared of rye or wheat straw chaff did not significantly influence the change of the usefulness of those substrates.

4. Cultivation substrates obtained from rye or wheat straw chaff and their mixtures with peat or bark make it possible to obtain the yield of tomato fruit on the level equal to that on rockwool.

REFERENCES

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Accepted for print: 12.03.2007

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