Climatic factors, such as air temperature, CO2 concentration and precipitation, play a crucial role in host tree-insect/pathogen interactions by influencing the regulating factors in host plant-insect/pathogen interactions in many ways, such as nutritional quality of host trees and their defense mechanism, the synchronization in the phenology of the involved organisms as well as their reproduction rate.
Global climate change-related abiotic and biotic stresses and their influence on types of plant secondary compounds (PSCs) in forest trees; VOCs: Volatile PSCs.
Source: Holopainen J. et al 2018: Climate Change Effects on Secondary Compounds of Forest Trees in the Northern Hemisphere. Frontiers in Plant Science. 9. 10.3389/fpls.2018.01445.
The aim of the study is to evaluate changes in the nutritional quality, the plant secondary compounds (PSCs) as indicators of host treey’s defense mechanisms and the synchronization in the phenology of the involved organisms (host tree, defoliating insects, fungal pathogens) under several varying and combined environmental conditions (temperature, humidity, CO2).
Current Research Topics:
Combined and single effects of elevated CO2 concentration, temperature and fertilization on interactions among host trees and defoliating insects
We simulate atmospheric scenarios with elevated CO2, increased temperature, or soil nutrient availability in glass dome facilities for climate change research and growth chambers to study single and combined effects on the nutrient content and defense reaction of spruce trees needles and oak leaves on the development and fecundity of sawfly larvae (Pristiphora abietina), nun moth (Lymantria monacha) and gypsy moth (Lymantria dispar).
A glass dome allowing tree growth under manipulated environmental conditions (CO2, precipitations, fertilisation). Norway spruces were used for nutritional experiment with spruce sawflies. The sawflies were kept individually in nylon bags.
Growth chambers allow independently programming of light-, temperature-, humidity-, and CO2- conditions for studies on insect-plant interaction.
Different nutritional suitability of three European elm species under drought stressed and non-stressed conditions for the development of two invasive elm insects: the elm zigzag sawfly, Aproceros leucopoda, and the Japanese elm aphid, Tinocallis takachihoensis
The recently introduced elm insects, the zigzag sawfly Aproceros leucopoda, and the Japanese elm aphid Tinocallis takachihoensis, may become important pests for the European elm species (Ulmus spp.), which already suffer mainly under the fungal infection by the Dutch elm disease and may additionally be stressed by drought under climate change conditions. In order to study the nutritional quality of three Elm species, Ulmus laevis, U. glabra, U. minor, for both introduced insect species under ambient and water stressed conditions, we assess in a first step the total nitrogen and carbohydrate content as well as the protein precipitation capacity by tannins of the host trees under different categories of water supply. In a second step we record the survival rate, the total development time and the weight gain of the sawfly larvae feeding separately or together with the aphid colony on the tested trees.
Rearing of elm zigzag sawfly larvae in bags on three different elm species.
Influence of elevated temperatures and drought on diapause development of selected defoliating insects
Climatic factors are among the most important drivers of plant and insect phenology. Thus, changes in temperature and humidity conditions might affect the metabolism and energy reserves of arrested, non-feeding stages in insects, especially through overwintering and aestivation. This again might have a crucial impact on the length of the arrested period and lead to desynchronizing effects with the phenology of their host plants.
The proportion of the important pine defoliating moth, Panolis flammea, emerging from the overwintering pupae is known to be markedly affected by pupation substrate, temperature and relative humidity. In our study we examine the combined effect of elevated temperature and drought on the respiration rate and frost resistance of diapausing pupae to assess the diapause intensityand its termination.
From the pupal aestivation period of the winter moth Operophtera brumata it is known that it has a synchronizing effect for the development of adult eclosion. When larval development is accelerated by high temperatures resulting in an early date of pupation, the subsequent aestivation period is prolonged. Whether this effect is due to a simple nonlinear temperature-dependence with developmental thresholds to both low and high temperatures and an unusually low optimum temperature of 9°-10°C (Peterson & NIllsen, 1998) or is regulated by variability in a pupal diapause development (Topp & Kirsten, 1991) is controversial. Therefore, we check the metabolism rate of pupae during their aestivation period depending on various temperature conditions by means of their O2 consumption.
Influence of mycorrhizas and pathogens on woody tree species morphology, physiology and defence against biotic and abiotic factors
In the roots of coniferous trees, the increased concentration of trehalose is an indicator of successful colonization of the roots by a mycorrhizal fungus and tree vitality. Thus, the absence of mycorrhiza means not only a reduced availability of water and minerals that the fungus provides to the plant, but also a lower concentration of some oligosaccharides, which are the metabolic product of fungi. As part of the SP3, we analyze the content of water-soluble carbohydrates (e.g. trehalose and mannitol) produced by the mycorrhizal fungus in the roots and verify whether their increased content is also reflected in the assimilation apparatus. Previous measurements have focused only on the content of trehalose in roots, which show a significantly lower concentration in spruce when infested by the fungus Gemmamyces piceae, the cause of the Gemmamyces bud blight of Picea spp. Thus, reduced concentrations of oligosaccharides in the assimilation apparatus may result from lower or missing mycorrhiza colonization, which again might cause the reduced resistance of Norway spruce to pathogen attack.
We have expanded the issue of mycorrhizae and the successful survival of seedlings with the application of a hydrogel, which protects against drying out and enables the survival of seedlings during long drought spell. In addition to the physiological and biochemical parameters of trees infested with fungal pathogens, we focus our research on the species composition of mycorrhizal fungi by means of molecular analyzes using PCR.
Myccorhizal roots of healthy Norway spruce from Ore Mountains in autumn 2020
Oomycetes of the genus Phytophthora are known as pathogens of many cultural plants and tree species. Especially newly introduced Phytophthora species, like Phytophthora x alni are a particular problem for our native tree species which are often highly susceptible to these pathogens due to the lack of coevolution In the SP3, we analyze diversity and distribution of Phytophthora species in alder stands in the field. First results show that altitude matters in terms of the infection level of alder trees. We also found out that there is a difference in ecophysiology in the infected alders compared to the asymptomatic trees. The laboratory experiments will further explain pathogenicity of Phytophthora species on alders in elevated CO2 concentrations.
Cooperation with Institutions
- Czech Academy of Sciences (CzechGlobe)
- Phytophthora Research Centre, Mendel University in Brno
- University of Eastern Finland
- Forest Research Institute, Krakow, Poland
- Institute of Biodiversity and Ecosystem research, Bulgarian Academy of Sciences, Sofia, Bulgaria
- Institute of Forest Entomology, Forest Pathology and Forest Protection, University of Natural Resources and Life Sciences, Vienna, (BOKU) Austria