Photosynthetic and biochemical characteristics of invasive species ...

ISSN 10674136, Russian Journal of Ecology, 2010, Vol. 41, No. 6, pp. 498–505. © Pleiades Publishing, Ltd., 2010.

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Photosynthetic and Biochemical Characteristics of Invasive Species (Ambrosia artemisiifolia L., Ambrosia trifida L. and Iva xanthifolia Nutt.) Depending on Soil Humidity and Phenological Phase1 ›

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S. Pajevic a , M. Borisev a, D. Orc ic b , P. Bo z a a, and N. Nikolic a ›

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Department of Biology and Ecology, Faculty of Sciences, University of Novi Sad, Serbia b Department of Chemistry, Faculty of Sciences, University of Novi Sad, Serbia email: [email protected] Received February 19, 2009

Abstract—Environmental factors like temperature and soil humidity are recognized as influencing factors on photosynthetic response and organic productivity, distribution and biochemical characteristics of plants. Here we present measurements of gas exchange parameters, wateruse efficiency (WUE) and nitrogenuse efficiency (NUE) of fieldgrown invasive species Ambrosia artemisiifolia L., Ambrosia trifida L. and Iva xanthifolia Nutt., in order to define their potentials as colonizers. Biogenic volatile organic compounds (BVOC) in leaves and flowers depending on soil humidity were also investigated. Results indicated species A. artemisiifolia as the colonizer with the highest physiological potential because of its high WUE in its vegetative phase and also the highest NUE and the highest photosynthesis/dark respira tion ratio in its flowering phenological phase. It was found that the volatile compounds of Ambrosia species and Iva xanthifolia consist mainly of terpenic compounds. There was a significant difference among the spe cies regarding qualitative composition of monoterpens and sesquiterpens and specific qualitative and quanti tative ratio of monoterpens in flowers and leaves of A. artemisiifolia. Keywords: Ambrosia artemisiifolia, Ambrosia trifida, Iva xanthifolia, photosynthesis, WUE, drought, volatile compounds. Abbreviations: WUE—wateruse efficiensy; NUE—nitrogenuse efficiency; BVOC—Biogenic volatile organic compounds. DOI: 10.1134/S1067413610060068 1

INTRODUCTION

Ambrosia species are American in origin and are known as invaders with high potential of colonization. Ambrosia spp. along with some other adventive species from Asteraceae family, are dangerous adventive spe cies spreding to great parts of Europe and Asisan con tinent (Antipina, 2003; Soyundukova et al., 2007). It is of great importance to determine influence of the eco logical factors on basic physiological parameters for the control of spreading and prediction of bioproduc tion of the potentially invasive species, like Ambrosia for the Serbian territory, because success of invasive species is habitatdependent. Plant invaders spread prolifically following introduction to new regions because they have achieved higher photosynthetic rates at lower resource investments than the noninva sive species (McDowell, 2002). The potential of their 1 The article is published in the original.

overlapping distribution is related to high photosyn thetic nitrogenuse efficiency (NUE), and greater wateruse efficiency (WUE) (Hirose and Bazzaz, 1998). Higher draught adaptability, in other words reducing the negative effects of the lack of water, the invasive species are accomplishing through high rate of photosynthesis per unit water loss (high WUE). Generally, photosynthetic capacity, growth rate resource acquisition, allocation, and phenotypic plas ticity are higher in invasive and introduced, than in native species (Nilsen et al., 1993; Pattison et al., 1998). According to Brodersen et al. (2008) enhanced photosynthetic rates do not indicate successful inva sive genotypes. Morphological traits and defensive secondary compound metabolism instead may play a more important role in the success. Likewise, by inves tigating the role of physiological traits in evolutionary adaptation Arntz and Delph (2001) found that adapta

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tion and selection for favorable photosynthetic traits may often operate indirectly via correlations with other traits as morphology. Volatile oils of some Ambrosia species are alle lochemicals and act against other crop plants and accordingly, allelopathy has a very important role in invasive potential (Wang et al., 2005). Soil humidity determines plant dispersion and abundance, but also chemical composition of pollen what is of significant importance since that species are well known by its damaging influence on the human health causing con tact dermatitis and pollencaused allergies. Allergic contact dermatitis caused by Ambrosia species, mainly by the sesquiterpene lactones from pollen, is the sub ject of an extensive literature (Möller et al., 2002). In order to take action in controlling abundance of invasive plants, the aim of this research has been the understanding of the biology (biochemistry and phys iology) and ecology of Ambrosia artemisiifolia L., Ambrosia trifida L. and Iva xanthifolia Nutt., species that are invasive in our regions, so that their prolifera tion can be controlled. The influence of draught and plant phenological phase on the production and qual itative distribution of volatile biogenic compounds, especially terpens, and their distribution through plant organs were analyzed as well for the effects these mol ecules synthesized in plant tissue and especially pollen have on human health and contents of the atmosphere because they anticipate changes in air composition and climate. MATERIALS AND METHODS Intact plants were collected in the field and brought to the laboratory using plastic bags and immediately processed. The photosynthetic responses of the youngest leaves of three investigated allochtone spe cies Ambrosia artemisiifolia L., Ambrosia trifida L. and Iva xanthifolia Nutt. at saturating light and CO2, were measured with an oxygen electrode (LD2, Hansatech Ltd., Kings Lynn, UK) as described by Walker (1989). Oxygen electrode system allows the measurement of oxygen evolution and uptake within a sealed sample chamber. For determination of maximal photosyn thetic activity, the leaves were exposed to photo syn thetically active radiation (PAR) and the light source was calibrated in order to determine the amount of photon flux density within the reaction chamber at approximately 1000 μmol m–2 s–1, and for the deter mination of respiration, leaves were subjected to dark ness. The sample chamber was maintained at 25°C with a circulating water bath. The photosynthetic oxygen evolution and dark res piration uptake were expressed per leaf mass unit dur ing one hour (μmol O2 g–1 · h–1). Parameter WUE (water use efficiency) was calcu lated as ratio of photosynthesis to transpiration and expressed in unit mMO2 · g–1 · h–1/mMH2O · g–1 · h–1. RUSSIAN JOURNAL OF ECOLOGY

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Parameter NUE (nitrogen use efficiency) was calculated as ratio of photosynthesis to nitrogen concentration in dry matter and expressed in unit mMO2 · g–1 · h–1/% N. Samples of plant species Ambrosia artemisiifolia were taken from three different habitats according soil humidity: dry soil (90%). Soilmoisture based classification was done according to Kamara and Jackson [12]. Although under similar soilvegetation properties and topographical condi tions, soil moisture climatology depends largely on precipitation and the atmospheres evaporative demand (Wang, 2005), in the period when we took samples of plant material, the soil moisture of every locality was precisely defined and classified according to water content. Phenological phase is a significant factor regarding photosynthetic activity and biochemical composition of plant, so we sampled plant Ambrosia artemisiifolia on four stages during its annual vegetation period: (1) vegetative—before flowering; (2) bud formation and early flowering; (3) late flowering; (4) fruiting. Qualitative and quantitative compositions of bio genic volatile organic compounds (BVOC) in leaves and flowers (before opening and pollen ejection) were analyzed using gas chromatographymass spectrome try (Agilent Technologies series 6890N/5975B) with headspace auto sampler (Agilent Technologies 7694E). Approximately 1 g of chopped plant material was placed in 20 ml headspace vials. Headspace parame ters were as follows: vial temperature 90°C, equilibra tion time 5 min, pressurization time 0.15 min, loop temperature 105°C, loop fill time 0.15 min, loop equilibration time 0 min, transfer line temperature 115°C, injection time 1.00 min, inlet temperature 250°C. Helium was used as a carrier, with constant flow of 1.1 ml/min. Components were separated on HP5MS column 30 m × 0.25 mm × 0.25 μm (Agilent Technologies) in temperature programmed mode: start temperature 50°C, 8°C/min to 120°C, and finally 15°C/min to 230°C (total run time 16.08 min). Eluted components were detected by means of mass spec trometer with electronimpact ion source (electron energy 70 eV). Transfer line temperature was set to 280°C, ion source to 230°C, and quadrupole to 150°C. Acquired data were analyzed by Agilent Technolo gies MSD ChemStation software in conjunction with AMDIS and NIST MS Search software. AMDIS was used for mass spectra deconvolution, while NIST pro vided library search algorithm complementary to ChemStation’s PBM algorithm. Four different mass spectra libraries were used for mass spectra identifica tion: Wiley Registry of Mass Spectral Data 7th Edi tion, NIST/EPA/NIH Mass Spectral Library 05, Agi lent Technologies Flavor2 RTL library and Adams ter pene library. Identity is confirmed by Kovats retention indices comparison. 2010

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Table 1. Gas exchange parameters of leaves, wateruse efficiency and nitrogenuse efficiency of three investigated species at the flowering phenological phase under optimal soil humidity conditions Dark respiration

Photosynthesis

Photosynth./dark respiration

Transpiration

Species μM O2 g–1 h–1 μM O2 g–1 h–1 Ambrosia artemisii folia Ambrosia trifida Iva xan thifolia

mM H2O g–1 h–1

Wateruse effi ciency (WUE)

Nuse efficiency (NUE)

mM O2 g–1 h–1/mM μM O2 g–1 h–1/%N H2O g–1 h–1

410.31 b

1488.64 a

3.63 a

56.2 b

0.026 a

330.59 a

527.17 a

702.90 c

1.33 b

60.5 b

0.012 b

152.80 c

220.83 c

1033.88 b

4.68 a

68.6 a

0.015 b

243.15 b

Note: Data with the same letter represent statistically identical values in vertical columns (p < 0.05).

Derived results are represented as area% (normal ized to total area of 100%) and they refer to qualitative and quantitative estimation of biogenic (volatile) organic compounds in the tissue itself and its sur rounding environment (atmosphere). Statistical analyses was conducted on plant samples using Duncan’s Multiple Range Test, at the level of significance p < 0.05, using 1way factor analyses. RESULTS To test genotype specificity and maximal photo synthetic potential in the optimal soil humidity condi tions, specimens of the youngest group of leaves of three examined species were taken in the period of the highest organic production (bud formation and early flowering phenological phase) from the soil classified as optimally humid. Gained results showed that there was a significant genotype difference in oxygen exchange of leaves. The highest net photosynthetic rate of oxygen evolution was recorded in A. artemisii folia leaves (Table 1). This species had also relatively high rate of dark respiration, which indicates that this species had high metabolic (carbon) costs, but ratio of photosynthesis/dark respiration was relatively high (3.63). Species A. trifida had significantly lower level of photosynthetic activity, and significantly higher level of respiratory oxygen adoption, which indicates small neto photosynthetic gaining, as for ratio of photosyn thesis/dark respiration was 1.33. Opposite of this spe cies, I. xanthifolia according to gained data showed the highest potential of organic production, because it had low respiration intensity with relatively high photo synthesis (Table 1). The highest transpiration rate was registered in the optimal conditions in species I. xanthifolia (68.6 mMH2O · g–1 · h–1). The amount of the tran spired water was measured during 48 hours period, and expressed per hour average value. The highest WUE value that directly implicates level of economy in water spending, was noted within the species A. artemisiifolia

which indicates its highest potential in drycondition adaptation and its significant advantage in coloniza tion. The significant NUE value measured at A. artemisi ifolia species implies its highest invader potential (Table 1). This species had the highest nitrogen con tent in its leaves (5.41%), but it also had the highest photosynthetic activity, so its high NUE implies high level of N use regarding organic production. A. artemisiifolia species was chosen for examining the phenological phase and humidity on physiological parameters important for colonization, because the results showed it as a plant species with the highest invasive potential. In the period from sprouting to fruiting the dynamics of the physiological parameters was analyzed to define its bioproduction efficiency. The rate of photosynthetic oxygen evolution of the youngest leaves in optimal soil moisture conditions, sig nificantly relied on the phenological phase, ranging from 276.62 μmol O2 · g–1 · h–1 during fruiting (Octo ber) to 1 488.64 μmol O2 · g–1 · h–1 during bud formation and early flowering period (July–August) (Table 2). The highest respiration rate was registered in the same period, but that increase was not statistically signifi cant comparing to other phases (except the last one), so it can be determined that during flowering period organic matter spent for energetic needs of plant metabolism is high, but it still implicates high ratio of photosynthesis/dark respiration (3.63), in other words high bioproduction efficiency. A high transpiration rate was recorded in the sec ond half of the vegetation period, which is expected and related to higher environmental temperatures (Table 2). In juvenile phases of A. artemisiifolia development the highest levels of WUE and NUE were determined, what clearly implicates that higher colonizing poten tial is in positive corelation with better metabolic use of water and nitrogen during vegetative and at the beginning of generative phase of its life cycle. Statisti

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Table 2. Gas exchange parameters of leaves, wateruse efficiency and nitrogenuse efficiency of Ambrosia artemisiifolia depending of phenological phase under optimal soil humidity conditions Species Dark Photosyn Photosynth./dark Wateruse effi Nuse efficiency Transpiration Ambrosia respiration thesis respiration ciency (WUE) (NUE) artemisii folia mM O2 g–1 h–1/mM mM H2O g–1 h–1 μM O2 g–1 h–1/%N Phenologi μM O2 g–1 h–1 μM O2 g–1 h–1 H2O g–1 h–1 cal phase Vegetative– before flowering Bud for mation and early flowering Late flowering Fruiting

374.71 a

952.45 b

2.54 b

24.9 c

0.038 a

177.30 b

410.31 a

1488.64 a

3.63 a

56.2 b

0.026 b

330.59 a

364.14 a

762.87 b

2.09 b

53.8 b

0.014 c

166.68 b

218.91 b

276.62 c

1.26 b

154.5 a

0.002 d

74.24 c


Table 3. Gas exchange parameters of leaves and nitrogenuse efficiency of Ambrosia artemisiifolia at flowering phenological phase depending of soil humidity conditions Species: Ambrosia artemisiifolia Soil humidity Dry soil Optimally wet soil Wet soil

Dark respiration

Photosynthesis

μM O2 g–1 h–1

μM O2 g–1 h–1

375.00 b 410.31 b 562.50 a

900.00 b 1488.64 a 1125.00 ab

Photosynth./dark res piration

Nuse efficiency (NUE) μM O2 g–1 h–1/%N

2.40 b 3.63 a 2.00 b

216.87 b 330.59 a 249.44 b


cally sinificant decrease of these parameters values is determined at the end of vegetation period. At normal surrounding CO2 concentrations and light saturation, soil and consequently, leaf water defi cit resulted in reduction of photosynthetic O2 evolu tion. This reduction was almost 40% comparing to photosynthesis of plants grown at the optimally humid soil (Table 3). Plants sampled at the wet soil (>90% of humidity) showed decrease of photosynthetic activity for about 25% comparing to photosynthesis of plants grown at the optimally wet soil. The nitrogen content in A. artemisiifolia leaves was about 4% (4.15% dry soil, 4.50% optimally wet soil and 4.51 wet soil), the least was in the plant leaves taken from the dry habitat, but according to statistical analyses, these differences were not significant, so NUE was proportional to photosytheses, in other words it was the highest in optimal moisture soilcon ditions. Gas chromatographymass spectrometry identified 20 volatile organic compounds from leaves and flowers of Ambrosia artemisiifolia (Table 4). Since this plant species its colonization advantage accomplishes by the RUSSIAN JOURNAL OF ECOLOGY

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good physiological response to arid conditions, it was significant to examine does it and in what amount the lack of water influences qualitative and quantitative composition of its volatile organic compounds. Based on gained chromatograms, it can be noted that the soil humidity has a significant influence on the amount of these compounds, as well as their distribution between the flower and leaf. The dominant aldehyde was trans 2hexanal which was registered in higher amount in leaf than in flower, and soil humidity significantly influenced its amount, because the amount registered in leaves was three times higher in plants from wet soil localities. Monoterpene content normalized to total area of 100% depended on plant organ as well as on humidity of the soil from which the plants were taken. The aver age presence of all registered monoterpens was some what higher in the flowers comparing to the leaves, but this significance was the most distinctively expressed in the humid soil conditions (Table 4). The most com monly found monoterpens were βmyrcene, transβ ocimene, limonene, βpinene and camphene. The influence of draught stress was the most expressed in 2010

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Table 4. Biogenic volatile organic compounds from leaves of Ambrosia artemisiifolia at flowering phenological phase depending of soil humidity conditions Species: Ambrosia artemisiifolia Biogenic volatile organic compounds (BVOC) Aldehydes Hexanal trans2hexanal Monoterpens Santolina triene αThujene αPinene Camphene Sabinene Octen3ol 2βPinene βMyrcene Limonene Eucalyptol Ocimene transβOcimene Borneol Bornyl acetate Sesquiterpenes Caryophyllene Germacrene D Bicyclogermacrene βBisabolene

Dry soil

Optimally wet soil

Wet soil

Area, %1 Leaf

Flower

Leaf

Flower

Leaf

Flower

0.705 3.191

1.948 1.250

1.034 4.099

2.414 1.862

7.710 11.283

2.627 1.062

2.068 tr 11.703 8.761 1.149 tr 3.756 17.915 11.150 tr 0.223 11.742 2.574 2.969

1.315 tr 3.231 1.603 0.601 tr 1.686 43.224 5.320 tr 0.293 15.688 0.318 0.674

1.845 tr 2.959 2.012 tr 0.752 1.206 29.312 2.853 tr tr 17.430 tr 1.880

2.602 tr 1.439 1.048 tr tr 0.334 26.355 2.200 tr 0.566 32.515 tr 0.453

tr tr 0.799 1.544 tr tr 1.058 37.593 1.317 0.827 tr 12.580 0.926 1.885

0.152 tr 0.796 0.648 tr tr 2.763 49.400 0.298 tr 0.250 17.467 0.187 0.492

1.077 12.249 0.311 tr

1.275 15.282 1.376 0.451

1.819 19.567 0.978 tr

1.615 20.973 0.967 0.563

1.130 11.064 1.380 tr

1.355 17.233 2.454 tr

Note: 1 Normalized to total area of 100%.

content and distribution of βmyrcene and transβ ocimene. Higher concentrations of transβocimene were registered in flowers, and the lack of water as well as water surplus induced two times decrease of this monoterpene content in flowers. The changes of transβocimene in leaves induced by soil humidity were not that much expressed. Stress provoked by the lack or surplus of water influenced significant increase of βmyrcene amount in flowers (Table 4). The drought induced syntheses of monoterpene limonene in flowers and more obvious in leaves. Similar ten dency of the more intense monoterpene synthesis influenced by drought was detected for βpinene and camphene as well. Dominant sesquiterpenes in the leaves were germa crene D and caryophyllene. Their highest concentra tions were registered in the optimal conditions.

Draught and increased soil humidity influenced leaf flower distribution of these volatile compounds. Species Ambrosia trifida was distinctive by extremely high aldehyde contents in its leaves comparing to A. artemisiifolia and I. xanthifolia. The amount of alde hyde hexanal was 20 times bigger in A. trifida leaves comparing to A. artemisiifolia (Table 5). The monoter pene contents in the A. trifida leaves and flowers were as well specific. While in A. artemisiifolia βmyrcene and transβocimene had the highest presence, in A. trifida they were registered only in flowers and also in very small amounts. The most commonly found monoter pene in A. trifida leaves was camphene, and the most commonly registered terpens in its flowers were limonene and αpinene. The other mono and ses quiterpenes of A. trifida leaves and flowers were regis tered in smaller amounts. Specificity of the invasive species Iva xanthifolia according qualitative and quan


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Table 5. Biogenic volatile organic compounds from leaves of Ambrosia trifida and Iva xanthifolia at flowering phenological phase under optimal soil humidity conditions Species Biogenic volatile organic compounds (BVOC) Aldehydes Hexanal trans2hexanal Monoterpens Santolina triene αThujene αPinene Camphene Sabinene 2βPinene βMyrcene Phellandrene Limonene Eucalyptol Ocimene transβOcimene Camphor Borneol Bornyl acetate Sesquiterpenes Caryophyllene Germacrene D Bicyclogermacrene

Ambrosia trifida

Iva xanthifolia Area, %

1

Leaf

Flower

Leaf

Flower

21.653 10.421

0.907 0.330

tr 1.104

0.948 0.453

tr tr 9.233 20.428 0.744 2.665 tr tr 1.787 1.551 tr tr 4.427 3.445 5.676

0.218 0.215 31.382 0.271 2.594 0.302 1.133 0.777 58.677 tr tr 0.265 tr tr tr

tr tr 11.256 20.906 1.754 24.359 4.156 tr tr tr tr 4.465 tr 6.462 2.410

tr 0.390 7.005 4.530 20.187 4.840 38.901 tr 0.288 tr tr 1.586 tr 0.652 0.688

tr 2.506 tr

tr 0.301 tr

0.745 6.599 tr

0.296 7.555 0.180

Note: 1 Normalized to total area of 100%.

titative BVOC composition is in the highest registered concentration of monoterpenes camphene, αpinene and 2βpinene in the leaves. The higher contents of βmyrcene in the flowers can be noted as the bio chemical specificity (Table 5). The sesquiterpene con tents of I. xanthifolia was a little bit higher comparing to A. trifida, but significantly less comparing to A. arte misiifolia. Therefore the A. artemisiifolia species can be isolated as a specific one comparing to other two, by the significant contents of sesquiterpens. DISCUSSION Ambrosia artemisiifolia (ragweed) and two other allochtone species in Serbia, Ambrosia trifida and Iva xanthifolia, are identified as biotic invaders because they have very high growth potential and spread very fast during the last decade. This invasive species can survive well in the habitats of different disturbance as elevated atmospheric carbon dioxide concentration, RUSSIAN JOURNAL OF ECOLOGY

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soil pollution and drought (Ziska and Caulfield, 2000). Plant invaders can completely alter the biotic and abiotic characteristics in a native ecosystem and can greatly diminish the abundance of native species. Identifying future invaders and taking effective steps to prevent their proliferation are associated with recog nizing factors that affect their growth potential (Baruch and Goldstein, 1999). Because of that, it is of great interest to concern weather the photosynthetic features of the invasive plant species benefit their sur vival and invasive potential at unfavorable ecological conditions. The results gained for the maximal photosynthetic potential of the three examined species in the middle of the vegetation period and in optimal humidity con ditions, indicate that there were significant genotype differences. The highest photosynthetic potential was registered in A. artemisiifolia species, what gives it sig nificant advantage in colonization to new localities. According to Feng et al. (2007), at the same intercel 2010

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lular CO2 concentration, invaders exhibit greater lightsaturated photosynthetic efficiency, higher irra diance plasticity and higher efficiency in photosyn thetic N partitioning than the natives. Photosynthetic parameters are in positive correlation with N content in leaves which confirmed the importance of the higher nitrogen allocation to photosynthesis, because of the higher N investment in Rubisco and electron transport in thylakoid carriers (McDowell, 2002). The highest level of photosynthesis relative to nitrogen (NUE, or photosynthetic nitrogen use efficiency— PNUE), which is favourable for invasive potential is detected for A. artemisiifolia. The increased nitrogen (and phosphorus) content in the photosynthetic machinery resulted in a higher resource capture ability and utilization efficiency in the invader, is the precon dition for the successful and productive colonization. Maximizing photosynthesis, relative to nitrogen and also, water costs, is mechanism of invasive plant suc cess. WUE of the plants with the higher N concentra tion in tissue decreases by a larger value than that of the plants with the low N concentration, due to a larger decrease in photosynthetic rate than in transpi ration rate (Shangguan et al., 2000). Plant populations which suffer strong selection pressure of the arid con ditions, perform lower WUE and higher N, suggesting that plants may be “wasting water” to increase N delivery for photosynthetic apparatuses via the tran spiration stream (Donovan et al., 2007). Good draught adaptation potential is in plant capability to keep high WUE and good distribution of nitrogen in photosynthesis during the draught, in other words good resource investment in bioproduc tion. Ecological advantages afforded by these physio logical features are the base of successful colonization of invasive species. Our results are in accordance with that, indicating species A. artemisiifolia as the colonizer with the high est physiological potential. It is assumed that this spe cies gains the advantage in new habitat invasion com paring to other species, because of its high WUE in the vegetative phase, and also the highest NUE and the photosynthesis/dark respiration rate in flowering phase. High WUE in that period of high temperatures and high light intensities reduced risk of photoinhibi tion under water stress conditions. Based on these results the conclusion is that for the successful coloni zation the time dynamics is also connected by which the certain physiological processes have its maximum: the highest WUE in the vegetative phase, and the high est photosynthesis and best assimilate use in the flow ering phase, and it is important that dark respiration is relatively low and to reflect the economical use of the assimilate. For the high organic production and quick and successful colonization, NUE should be the high est in the flowering phase. Taking the samples of A. artemisiifolia from differ ent soils of different humidity were wanted to identify level of change in the photosynthesis, as well as nitro

gen capture per unit investment assuming that the invader keeps relatively high NUE value in arid condi tions. Although that gained results indicate the signif icant decrease of these parameters in draught condi tions, the examined species can be characterized as physiologically adapted on optimizing water regimen which gives it the advantage in spreading to new local ities with unfavourable ecological characteristics. Ambrosia artemisiifolia has very strong influence on human health, because it is a classical cause of rag weed dermatitis in a large part of the world. Several sesquiterpene lactones, including ambrosin, corono pilin, damsin, isabelin, and psilostachyin have been reported from this species (Wang et al., 2006). Inayama et al. (1974), reported the isolation of ambrosic acid, a sesquiterpenoid “irritant” compound from the pollen and Watanabe et al. (1981) described ambrosic acid as an inhibitory substance for plant growth. Sesquiterpene lactones from Compositae family and genus Ambrosia are identified as the main cause of contact allergy (Möller et al., 2002). Accord ing to results of Geron et al. (2006) the dominant emitted (volatile) compounds of Ambrosia deltoidea were myrcene, dlimonene, and camphene, while lesser amounts of βpinene were also emitted. Also, they observed no increase in monoterpene emission with the increased humidity. Our results on contrary favourize the fact that the habitat humidity, beside its influence on rate and level of colonization of the examined invaders, also determines the qualitative and especially quantitative biogenic potentially irri tant compounds. Our results suggest that soil moisture influences the contents of these substances in the examined species tissue, as well as their nearby envi ronment. Plant speciesspecific variation of VOC was also detected. Although they belong to the same genus, species A. artemisiifolia and A. trifida were dis tinguished by very specific BVOC in their leaves and flowers. A. artemisiifoliia had distinctly greater pres ence of sesquiterpens, as well as specific qualitative and quantitative monoterpene ratio in leaves and flow ers, with the dominant presence of βMyrcene and transβOcimene was registered in flowers. Soil mois ture induced significant increase in βMyrcene from leaves and flowers. Species A. trifida had a specific dis tribution of monoterpens and the most abundant were βpinene and limonene in flowers. Dominant monot erpens in I. xanthifolia flowers were βmyrcene and sabinene, while the dominant presence of camphene and 2βpinene was observed in leaves of this plant spe cies. Soil humidity conditions generally caused leaf flower distribution of volatile compounds in A. artemisii folia. This was more evident in the wet soil conditions, when the amount of these substances increased in flowers compared to the leaves.


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