ABSTRACT

Experiments have been done in open-top chambers with oilseed rape. Plants have been fumigated with air form outside either as its been composed or enriched with ozon and/or carbon dioxide. In general plant dry matter and seed yield was improved due to CO₂ , whereas ozone had a negative effect. This negative effect was not completely compensated by carbon dioxide. Seeds from plants grown in high CO₂ atmosphere showed highest oil content.

INTRODUCTION

Plants react to changes of their environment and vice versa. This is true also for the composition of the atmosphere. It is known that there will be higher levels of several gaseous components within the biosphere in the near future. Two components of the atmosphere which are known to increase to about the double double concentration of today within the next hundred years are carbon dioxide CO₂ and ozone O₃. These will cause changes of chemical as well as of physical nature (greenhouse effect) (Crane, 1985; Esser, 1989; Woodwell, 1989; Rogers, and Dahlman, 1993).

Ozone is one of the most toxic gaseous components within the biosphere. Although ozone is a rather short living chemical substance, it is envolved in several chemical processes for instances modification of SO₂ or NO_x into acids and decomposition of CH_4. Plant damages due to ozon have been reported already since the 1940s in the USA. Most discussed in this respect have been the damages to forest trees in the 1980s in Europe and the USA. Experiments have been started within the USA in so called open-top chambers (Heagle, et al., 1973) investigating the effects of different concentrations of ozone as well as of other harmfull gasses like for instance SO₂ (Heagel, et al.,1993). Plants of prefered interest have been mostly cereals, grassland plants, trees and different bean species.

Carbon dioxide in some respect agitates as antagonist to ozone as it is promoting plant growth. At present concentrations CO₂ is one of the minimum factors for plant growth but during the last 100 years there has been increasing concentrations of CO₂ with a slight temperature increase going along. Both factors from which it is not quite clear at the moment which one is cause and which one is the consequence will increase in the future (Schnug, 1998).

Because of the well known increase of CO₂ concentration within the atmosphere experimental work changed in the mid 1980s from investigation of effects of harmfull gases on plant growth to investigations of effects of higher CO₂ concentrations on plant growth.

Since it is quite clear that concentrations of both harmfull and promoting gaseous components will increase in the biosphere investigations have been done with higher levels of CO₂ and ozon not only singel but in combination too (Mulchi, et al., 1992; Heagle, et al., 1993; Polle, et al., 1993).

Because changes in the atmosphere will influence all kind of crops and so far not much attention has been paid to oil crops, experiments in open-top chambers have been done with oilseed rape one of the most important oilseed crops all over the world. The purpose of these investigations was to test the reaction of these of plants to elevated levels of CO₂ and ozon single and in combination.

MATERIALS AND METHODS

Experiments have been done in 1996 and 1997 in open-top chambers. Air from outside either as it has been composed (between 360 and 380 ppm CO₂ and about 30 ppb O₃ seasonal mean) or enriched with CO₂ and / or ozon has been blown into the chambers during growth period of oilseed rape (Brassica napus L.) (table 1).

Table 1 Treatments of oilseed rape during growth period

Grotwth conditions	variant
outside (natural conditions)	a (control for b)
within a chamber with air from outside	b (control for c,d,e,f,g,h)
within a chamber with outside air enriched with 1.5x O3 outside conc.	c
within a chamber with outside air enriched with 2 x O3 outside conc.	d
within a chamber with outside air plus 160 ppm CO2	e
within a chamber with outside air plus combination of d and e	f
within a chamber with outside air plus 320 ppm CO2	g
within a chamber with outside air plus combination of d and g	h

Plants have been cultivated in loamy sand in large voulme soil containers with a diameter of 1 m and a depth of 0.5 m. Nutrition of plants was adapted to field conditions and plant protection and water supply was done when necessary.

There have been two to four repetitions per treatment and from each chamber five plants have been analysed for plant hight, root length, number of stalks, number of pods and number of seeds per pod. Material was dried in an oven at 85° C till constant weight. TSW and total number of seeds have been done using a balance in combination with a seed counting instrument.

Chemical analysises have been done for nitrogen using the Kjeldahl method for calculation of protein content, total ash analysis has been done by wet digestion with nitric acid at 450° C. Oil content has been measured with a NMR analyser using rape seed oil as reference.

Statistical analysis was done using the Duncan test.

RESULTS AND DISCUSSION

The two control treatments were necessary because of the different microclimate within the open-top chambers , higher temperatures but lower light intensities than ambient (see Adaros, et al., 1989). As it can be seen there are differences between these two variants in respect to dry matter of the different plant organs, except root dry matter, but TSW, ash and oil content in the seeds has not been influenced.

Dry matter formation showed to be coupled to growth conditions; highest stems developed under higher CO₂ concentrations with the greatest hight in treatment g. Ozone had a negativ influence on stem hight, which had not been completely compensated by the higher CO₂ concentrations. On the contrary treatments with higher ozone concentration showed longer roots (variant c) but there is no explanation to the small root length in treatment d, (see table 2 to this).

Similar unclear growth reactions have been reported by Cardoso-Vilhena, et al. (1998) for wheat varieties and several other plant species. Whereas Utrainen, and Holopainen, (1998) found good correlations between fumigation of pine trees with either ozone and / or CO₂ and shoot and root dry mass as its been shown in the experiments reported here. See also Donnelly, et al. (1998), who found increases of photosynthetic rates due to elevated CO₂ but no significant interactive effect on the photosynthetic rate by higher levels of both CO₂ and ozone in combination.

Number of stalks and number of pods per plant did not show any clear correlation with growth conditions of the plants.

Thousend seed weight showed to be highest after growth of plants in highest ozone concentrations (table 3), but also after growth of the plants in higher CO2 concentrations which also resutled in highest seed weights per plant (table2).

Highest oil content had been measured for seeds of plants grown in highest CO₂ concentrations as has been found for seeds of linseed plants by Sator, (1996). This also fits to the results of Williams, et al. (1995) who found lower lipid contents in wheat grains after growth of plants in higher than ambient temperatures but higher contents after growth in higher CO₂ atmosphere.

Table 2 Influence of different gaseous environment on yield of rape

Variant	plant hight in cm	root length in cm	nr. of stalks per plant	nr. of pods per plant	seed weight per plant in g	stem dm in g	root dm in g
a	136.00 e	15.00 c	6.80 c	85.35 c	10.71 b	13.06 abc	2.71 bc
b	152.00 bc	19.33 abc	12.03 a	194.83 ab	11.34 ab	10.16 bc	1.93 bc
c	149.07 cd	22.17 a	5.53 c	171.00 b	9.96 b	9.20 c	1.69 c
d	139.10 de	18.10 abc	10.10 ab	202.80 ab	13.54 ab	9.75 c	2.52 bc
e	160.50 ab	17.10 bc	9.70 ab	240.80 ab	10.10 b	14.07 abc	2.94 b
f	162.00 ab	20.70 ab	10.20 ab	269.20 a	12.31 ab	15.19 ab	2.89 b
g	168.20 a	20.45 ab	7.85 bc	249.45 ab	14.62 ab	13.77 abc	2.69 bc
h	159.50 abc	19.70 ab	10.10 ab	285.10 a	16.92 a	15.58 a	4.21 a

Table3

Economic relevant data of rape seed after growth of plants in different gaseous environment

Variant	TSW in g	oil content in %	protein content in %	total ash in %
a	3.32 ab	44.58 bc	22.09 ab	4.77 ab
b	3.36 ab	43.89 bc	19.44 c	4.78 ab
c	2.92 b	44.43 bc	22.54 a	5.03 a
d	3.89 a	42.12 c	18.08 c	4.40 c
e	3.45 ab	44.25 bc	22.22 ab	4.47 bc
f	3.92 a	45.80 ab	19.31 c	4.34 c
g	3.57 a	47.15 a	19.76 bc	4.61 bc
h	3.86 a	45.08 ab	20.23 abc	4.32 c

Acknowledgement:

Thanks to D.D. Strauss, FAL, Braunschweig, for doing the statistical calculations.

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