The project team has been selected after an international competition: Adina Bodescu Ph. D. (half position), Andreea Pag Ph. D. student (half position), Eng. Daniel Tomescu (full position).
Various plant species, which were necessary to carry measurements, have been selected as following: Quercus genus: Q. rubra, Q. cerris, Q. frainetto, Q. petrea, Q. robur; Betulacea family, Betula genus: B. pendula, B. verrucosa; Fagacea family, genus Alnus: A. glutinosa, A. cordata.
The measurement chambers where the plants have been sampled have been designed and build.
The methods for determination of volatile organic compounds (VOC) have been optimized. Our determination used two different methods: a method based on preconcentration on solid adsorbent followed by thermodesorbtion and gas-chromatographic mass spectrometry analysis and a method based on adsorption of VOC on a SPME fiber followed by normal desorbtion and gas-chromatographic mass spectrometry analysis. Both methods have been used for measurements of VOC emission from plants under different abiotic and biotic stresses.
The photosynthetic parameters have been determined using a commercial gas-exchange system GFS-3000 (Heinz Walz Company, Effeltrich, Germany) which have been bought in this project.
It has been studied how plants of the genus Quercus respond to temperature stress. It has been followed the emission of volatile organic compounds from the following plant species: Q. robur, Q. petrea, Q. cerris and Q. rubra. It have been shown that in all cases the emission of green leaves volatile reveal a “breaking point” at around 48-49 oC. The isoprene emission followed the Guenther model.
For the same plant species (except Q. rubra) has been studying how infestation with Erysiphe alphitoides influences the emission of volatile organic compounds and photosynthetic parameters. This study provides important evidence of strong effects of pathogenic infections on constitutive and induced volatile emissions in Quercus robur. These results provide encouraging evidence that the severity of pathogenic stress can be assessed by monitoring the emissions of stress-elicited volatiles.
To study the response of the drought stress of Betula verrucosa plants, the SPME technique has been used. The results have been show that drought induced a high emission of lipoxygenase pathway products while the monoterpenes emissions have been moderated increased.
To study how biotic and abiotic stress combination affect the emission of volatile organic compounds have been started two extensive studies. In both cases measurements were made on plants of A. glutionsa and abiotic factor has been used drought. We used in one study: Monsoma pulveratum larvae (Hymenoptera: Tenthredinidae) and in the other study Orthosia gothica larvae (Lepidoptera: Noctuidae), both being one the major defoliation of the alder. The data have been shown that the emission of secondary metabolites (α-pinene, β-pinene, camphene, limonene, 3-carene, para-cymene, beta-phelandrene and (E)-beta- ocimene) have been increasing. The measurements have been repeated next year for confirmation and to have measurements only with drought stress.
It has been studied how plants of the familia Betulaceae family respond to temperature stress. It has been followed the emission of volatile organic compounds from the following plant species: A. glutinosa, A. cordata, B. verrucosa. It have been shown that in all cases the emission of green leaves volatile reveal a “breaking point” at around 46-47 oC which have been compared with isoprene emitters.
Can be noticed that net assimilation rate and stomatal conductance shows higher peak in respect of plants which emit isoprene (Quercus) from those that do not have emission constitutive (A. glutinosa and B. verrucosa). This observation supports the theory that specific thermo-protective role of isoprene.
The long temperature stress has been used for Quercus rubra plants which have been kept at 45 deg for 6 hours. The emissions of different secondary metabolites are increased until a plateau.
For the same plants species, it has been study the drought stress. It can be noticed in this case an increase in the concentration of total GLV very first day of stress (soil relative water content around 85%) and in terms of terpenes, their concentration increases since day two and achieve a maximum after which the emission is diminishes.
The SPME method has been used to study the influence of flooding on B. verrucosa plants. The plants have been kept for 14 days in water and VOC concentration had been measured daily. GLV emission is increased from first day of stress while monoterpene emission is significantly different from control plants only in day two.
Have been finished the measurements about influence of Erysiphe alphitoides on Q. robur. Some measurements have been repeated and as well we have been seen how different inhibitors influence the emission of isoprene and monoterpenes.
Another study on the influence of biotic factors on the emission of volatile organic compounds from plants includes a phytopathogenic attack Phylloxera quercus on Q. robur plants. Plants have been infested with spores gradually and thus were obtained infested leaf surfaces at different stages. It has been shown an increased of GLV with the degree of infection while isoprene emission is decreasing.
It have been studied the effect of Epirrita autumnata (Borkhausen) (Lepidoptera: Geometridae) larvae feeding on Betula pubescens plants. It can be noticed that it is no significant influence of larvae on photosynthetic parameters, but the emission of volatile compounds: GLV, monoterpenes and sesquiterpenes have been increased.
The influence of temperature on European ash (Fraxinus excelsior) has been studied. It has been show that net assimilation rate and stomatal conductance decreases with temperature increasing until a breaking point. It have been demonstrated that volatile organic compounds emission increase with temperature especially methyljasmonate (a specific compound used in plant defence).
The influence of flooding on Red oak (Quercus rubra) plants has been studied. It has been showing that f photosynthesis parameters are drastically influenced by presence of large amounts of water. Green leaf volatiles (GLV) have been increased during 21 days of flooding while monoterpenes emission increased slowly.
After the stress has been removed, the emission of GLV decreased until a plateau.
In order to demonstrate the cumulative effect of the stresses on the plants Red oak (Quercus rubra) plants subject to water stress has been thermal stress at the same time for 5 minutes. The results revealed that the emission of volatile organic compounds is increased but there was not a real cumulative effect.
The studies were extended to show the effect of Arctia caja larva (Fam. Arctiinae, Order: Lepidoptera) on Quercus rubra plants. Arctia caja larvae generally attack plants from Rosaceae family but tests showed that they feed on oak leaves as well. Larvae have been brought from Estonian University of Life Sciences and determinations of volatile compounds were carried out in the laboratories of Arad. We used our own conception measure chambers after the system described in (Toome et al., 2010) with improved temperature sensors on each camera and illuminated with cool light. The volatiles were adsorbed in carbotrap tubes and then analyzed by GC-MS. The results show that the rate of emission of green leaf volatiles (GLV) increases with the number of days in which the larvae have been eaten.
Another study refers to how plants oak (Quercus robur) respond to attacks Lymantria dispar larvae. This type of larvae is the main defoliator of oak, causing generally significant damage to forests in the south of Europe, and in Romania in particular. Laboratory study showed that there may be a correlation between the amount of leaf eaten by larvae (stress strength) and the amount of volatile organic compounds emitted by the plant. To confirm these studies were conducted measurements of volatile organic compounds, carotenoids pigments and photosynthetic parameters in leaves of trees affected by massive attack Lymantria dispar from the Forest District Lipova.
To determine if the larvae of Lymantria dispar dispar affects not only Quercus robur plants but also Quercus rubra (red oak) it has been conducted an experiment with different numbers of larvae. There is an increase in net assimilation rate and stomatal conductance after 3 days of infection followed by a decrease due to total defoliation. The relative rates of emission of volatile organic compounds increase over time with the amount of leaf eaten.