Dr. Johann G. Zaller

Institute of Zoology
University of Natural Resources and
Applied Life Sciences
Gregor Mendel Strasse 33
A-1180 Vienna
Austria

Phone: +43 1 47654 3205
Fax: +43 1 47654 3203
E-mail: johann.zaller(at)boku.ac.at

Forschung -  BOKU Forschungsdokumentation

Research topic
Landscape structure and its influence on insect pest abundance, insect damage and interactions between insect pests and beneficial organisms

Many ecological processes and interactions depend on scales larger than a single habitat. Here we investigated how the structure and complexity of the surrounding landscape can affect pest-predator-crop interactions in winter oilseed rape (Brassica napus). We studied this in 29 landscape sectors ranging from structurally poor to complex and considered the spatial relationships at 8 radii (250-2000 m centered in the studied oilseed rape fields). We found that abundances of pollen beetles (Meligethes aeneus) and stem weevils (Ceutorrhynchus pallidactylus and C. napi) were significantly positively correlated with soil quality and negatively related to oilseed rape area in the surroundings. Generally, abundances of all groups were positively related to woody areas, but not related to grassy fallow area. Pod midges (Dasineura brassicae) and stem weevils tended to respond primarily to landscape variables at small (250-500 m) and medium (1000-1250 m) scales, while pollen beetles responded at medium to large (1000-2000 m) scales. We make differences in overwintering strategies and mobility of pest insects responsible for these relationships. Within these landscapes we also investigated how damage on winter oilseed rape caused by pollen beetle, cabbage and rape stem weevil and pod midge is related to within-field and oilseed rape-specific landscape factors in the surroundings (radius 2000 m). The results showed that pollen beetle and pod midge damage was mainly influenced by the amount of oilseed rape the landscape while stem weevil damage seemed to be more affected by within-field characteristics that might have altered the nutritional quality of the oilseed rape crop and/or the stand microclimate. Results on beneficial organisms will be reported soon.

This project is led by Prof. Thomas Frank, University of Natural Resources and Applied Life Sciences Vienna, Austria.

Selected publications on this topic (several other publications are in preparation/review):

Zaller JG, Moser D, Drapela T, Schmöger C, Frank T (2008): Effect of within-field and landscape factors on insect damage in winter oilseed rape. Agriculture Ecosystems and Environment 123, 233-238.
Zaller JG, Moser D, Drapela T, Schmöger C, Frank T (2008): Insect pests in winter oilseed rape affected by field and landscape characteristics. Basic and Applied Ecology, in press.

Research topic
Global environmental changes and its impact on organismic interactions in terrestrial ecosystems: atmospheric CO2, ultraviolet-B radiation, decline of plant species diversity

As part of a long-term study on the interactive effects of plant species diversity and elevated CO2 on grassland communities we studied its impact on earthworms. The density and biomass of earthworm communities declined linearly when the number of plant species in the community was reduced from 31 to 5 species due mainly to a decline in an endogeic earthworm species. The responses of earthworm communities to a decline in plant species diversity appear to reflect changes in community fine root biomass in the topsoil (e.g. declining worm biomass with declining fine root biomass). We also tested the hypothesis that the spatial proximity of a plant species to nutrient-rich earthworm casts (e.g., 100% more ammonium and 30% more phosphate than in adjacent soil) is an important determinant of a plant’s responsiveness to elevated atmospheric CO2. We observed a positive relationship between the response of grass species to elevated CO2 and their degree of association (%) with surface casts at ambient CO2. Thus, grass species that were more often associated with casts produced more ramets at elevated CO2 than those less often associated with and may respond more strongly to rising CO2 than those less highly associated with casts. Results of another study showed that earthworms under elevated CO2 (610 µL CO2 /L air) produced 35% more casts on the soil surface than under ambient CO2. The CO2 -induced increase in earthworm surface casting activity also corresponded to a 30% increase of the amount of total nitrogen and organic carbon egested by the worms in one year. Thus, our results demonstrate an important indirect stimulatory effect of elevated atmospheric CO2 on earthworm activity which may have profound effects on ecosystem function and plant community structure in the long term. We also tested whether elevated CO2 can affect interactions between plants and insect herbivores. Therefore we introduced equivalent populations of fourth instar Spodoptera eridania, a lepidopteran generalist, to complex model ecosystems containing seven species of moist tropical plants. Our results indicated that leaf tissue quality is not necessarily affected by elevated CO2 under relatively low nutrient conditions. Hence, the potential importance of CO2 -induced shifts in leaf nutritional quality, as determinants of herbivory, may be overestimated for many plant communities growing on nutrient-poor sites if estimates are based on traditional laboratory feeding studies.

Effects of solar ultraviolet-B radiation (UV-B, 280–315 nm) on ecosystem processes were studied in a serious of experiments conducted in Tierra del Fuego on the southernmost tip of South America, a region that is subjected to the influence of ozone depletion and to increased levels of UV-B. Results showed that even moderate changes in UV-B radiation (e.g., corresponding to those expected with current stratospheric ozone depletion) may species-specifically influence growth, morphology and biomass allocation of dominant sedges (Carex spp.) in a fen ecosystem. This can affect competitive relationships of these species in the field. Solar UV-B radiation has also been shown to affect herbivory of native plant species by the slug Deroceras reticulatum. For the tree species, Nothofagus, slugs had consumed only one-third as much foliage grown under near-ambient UV-B as of foliage grown under reduced UV-B. In contrast, leaves of the sedge C. decidua that had been grown under near-ambient UV-B were consumed twice as much as leaves grown under reduced UV-B radiation. Most effects of UV-B might be expected to occur aboveground since sunlight does not penetrate effectively belowground. Interestingly, we could also demonstrate that UV-B radiation is causing large changes of belowground processes in a fen ecosystem. We found that when the ambient solar UV-B radiation was substantially reduced, there was a 30% increase in root length production and as much as a threefold decrease in already low symbiotic mycorrhizal colonisation frequency of the roots compared with plots receiving near-ambient solar UV-B. Such large changes in root system behaviour may have decided effects on competition and other ecological interactions in this ecosystem.

The project on atmospheric CO2 and biodiversity was led by Prof. Christian Körner (University of Basel, Switzerland), Prof. Bernhard Schmid (University of Zurich, Switzerland) and Prof. Jay Arnone (Desert Research Institute, Reno, USA). The project on ultraviolet-B radiation was led by Prof. Martyn Caldwell and Steve Flint (Utah State University, USA), Prof. Osvaldo Sala (Brown University, USA), Prof. Ana Scopel and Prof. Carlos Ballaré (University of Buenos Aires, Argentina).

Selected publications:

Zaller JG, Searles PS, Caldwell MM, Flint SD, Scopel AL, Sala OE (2004): Growth responses to ultraviolet-B radiation of two Carex species dominating a fen in Tierra del Fuego, Argentina. Basic and Applied Ecology 5: 153-162. [download pdf]
Zaller JG, Searles PS, Rousseaux MC, Flint SD, Caldwell MM, Ballaré CL, Scopel AL, Sala OE (2003): Ultraviolet-B radiation can affect slug herbivory of plant species native in a fen ecosystem in Tierra del Fuego, Argentina. Plant Ecology 169: 43-51. [download pdf]
Zaller JG, Caldwell MM, Flint SD, Scopel AL, Sala OE, Ballaré CL (2002): Solar UV-B radiation affects belowground parameters in a fen ecosystem in Tierra del Fuego, Argentina: implications of stratospheric ozone depletion. Global Change Biology 8: 867-871. [download pdf]
Ballaré CL, Rousseaux MC, Zaller JG, Giordano CV, Robson TM, Caldwell MM, Sala OE, Scopel AL (2001): Impacts of solar ultraviolet-B radiation on terrestrial ecosystems of Tierra del Fuego (southern Argentina). An overview of recent progress. Journal of Photochemistry and Photobiology B 62: 67-77. [download pdf]
Arnone JA III, Zaller JG, Spehn E, Niklaus PA, Wells CA, Körner C (2000): Dynamics of fine root systems in intact native grasslands: effects of elevated atmospheric CO2. New Phytologist 147: 73-85. [download pdf]
Zaller JG, Arnone JA III (1999): Earthworm and soil moisture effects on the productivity and structure of grassland communities. Soil Biology and Biochemistry 31: 517-523. [download pdf]
Zaller JG, Arnone JA III (1999): Earthworm responses to plant species' loss and elevated CO2 in calcareous grassland. Plant and Soil 208: 1-8. [download pdf]
Zaller JG, Arnone JA III (1999): Interactions between earthworm casts and plant species in a calcareous grassland under elevated CO2. Ecology 80: 873-881. [download pdf]
Zaller JG, Arnone JA III (1997): Activity of surface-casting earthworms in a calcareous grassland under elevated atmospheric CO2. Oecologia 111: 249-254. [download pdf]
Arnone JA III, Zaller JG, Ziegler C, Zandt H, Körner C (1995): Leaf quality and insect herbivory in model tropical plant communities after long-term exposure to elevated atmospheric CO2. Oecologia 104: 72-78. [download pdf]