Search

Despite the fact that, on average, approximately 5-6 metric tons/ha of Bt maize stubble enter the soil on more than 170 million of hectares worldwide, the environmental impact of genetically modified maize plants on the arbuscular mycorrhizal fungi (AMF) is poorly known. In this study, the mycorrhizal colonisation on the roots of Bt maize (DAS-59122-7) and its near isogenic line was examined during the whole vegetation period. Cry3 toxin-producing Bt maize and its near isogenic line were grown in an experimental field in Julianna-major, Nagykovacsi, Hungary. DAS-59122-7 maize produces Cry34Ab1 , Cry35Ab1 toxins and pat proteins for herbicide tolerance. The study assessed whether similar arbuscular mycorrhizal colonisation can be observed on the root of the Bt and near isogenic maize line and whether there are any differences in the temporal dynamics of AMF development. The arbuscular, hyphal and the arbuscular mycorrhizal fungi colonisation were higher in the near isogenic line as compared to its Bt counterpart, but no significant effect of the maize line was found as regards vesicle colonisation. The intensity of the arbuscular infection increased over time during plant maturation. DAS-59122-7 Bt maize had a negative effect on the initial development of AMF under field conditions, but no difference was seen in the case of the last two sampling dates (day 82 and 135). The reason of the latter is still not known.

Nematodes are key agents in important soil processes, such as decomposition, mineralization and nutrient cycling. Therefore, alterations of the nematode community structure induced by global change may have a considerable influence on ecosystem functioning. However, it is not clear whether minor changes in soil temperature and/or moisture have any significant effect on nematode community structure. A field experiment was performed in a mosaic of open sand grassland and Juniper–Poplar woodland (VULCAN Project). Soil temperature and moisture were modified to the extent expected for the near future due to global changes. Community diversity and multivariate structure of the nematode community proved to be more sensitive to minute changes in soil temperature and moisture than different indices, such as specific richness (SR), maturity index (MI), plant parasite index (PPI), enrichment index (EI), channel index (CI), fungal feeder to bacterial feeder ratio (F/B) and nematode channel ratio (NCR). Nematode genera with high densities (>0.1 individual g−1 soil) were better indicators of the temperature and moisture changes than those of low density (

Collembolas are important members of belowground food webs. There is little information available on the effects of the plant residues of transgenic maize expressing Bacillus thuringiensis (Bt) toxin on soil animals, including collembola. This is why two questions were addressed in laboratory feeding experiments with three collembolan species: (i) Are collembola equally distributed on residues of isogenic and Bt-maize? and (ii) Do collembola show feeding preference to either of the maize types? Bt-maize (producing Cry1Ab toxin) proved to be a less preferred food source for Folsomia candida than the isogenic one. No similar phenomenon was found in the case of Heteromurus nitidus and Sinella coeca . F. candida reacted to as low as 3.45 (± 0.8 mg g −1 ) Bt-toxin content of the maize. Our results show that the effect of the Bt-toxin producing maize on the collembolan is species specific.

Zn uptake by maize plants may be affected by the presence of arbuscular mycorrhizal fungi (AMF). Collembola often play an important controlling role in the inter-relationship between AMF and host plants. The objective of this experiment was to examine whether the presence of Collembola at different densities (0.4 and 1 individuals g−1 dry soil) and their activity have any effect on Zn uptake by maize through the plant–AMF system. The presence of the AMF (Glomus intraradices) and of the Collembola species Folsomia candida was studied in a laboratory microcosm experiment, applying a Zn exposure level of 250 mg kg−1 dry soil. Biomass and water content of the plants were no different when only AMF or when both AMF and Collembola were present. In the presence of AMF the Zn content of the plant shoots and roots was significantly higher than without AMF. This effect was reduced by Collembola at both low and high density. High densities of Collembola reduced the extent of AMF colonization of the plant roots and hyphal length in the soil, but low densities had no effect on either. The results of this experiment reveal that the F. candida–G. intraradices interaction affects Zn uptake by maize, but the mechanisms are still unknown.

In a field microcosm experiment, we tested the hypothesis that adult collembola, depending on their density, may enhance or decrease mycorrhizal development and growth of maize ( Zea mays L.) or red fescue ( Festuca rubra L.). Collembola decreased mycorrhizal spore number in the soil. A significant decrease in the spore number, compared to the treatment without collembola, was recorded and ranged from 0.2 to 1.6 individuals g −1 soil in both experiments. Highest AM fungi colonization was found at 0.2 and 0.4 collembola g −1 soil density in the maize and red fescue treatments, respectively. This finding may explain why about 0.1 individuals g −1 soil was reported as optimum for plant growth by some authors.

Summary A field experiment was established to examine the effects of temperature and moisture modifications on the nematode fauna of a semiarid grassland. Several combinations of drying, wetting, warming and cooling were applied to plots and compared with untreated control plots. The experiment was performed from July to October 1996. A significant shift was observed in the structure of the nematode fauna between late summer and early autumn. This shift was manifested in the disappearance of four rare genera; Ecumenicus, Eucephalobus, Paraphelenchus and Pungentus. A significant decrease was found in the density of Acrobeles, Aphelenchoides, Ditylenchus and Prismatolaimus; in addition there was a significant increase in the density of Cephalobus, Helicotylenchus, Paratylenchus and Tylenchorhynchus. Community structural change was represented by an initial decrease in nematode generic richness of 30–50%, and in a statistically significant decrease of nematode diversity in the control and all treated plots. Thereafter, emergence of a new community was demonstrated. Data show that temperature manipulation was the main factor to influence nematode diversity, Maturity Index, and Plant Parasite Index. However, nematode population density was influenced predominantly by the soil moisture content. Coenological analysis of soil nematode fauna appears to be a useful tool for the biological monitoring of the effects of global change on semiarid grasslands.

The effect of the nematofauna on the microbiology and soil nitrogen status was studied in 6 major European grassland types (Northern tundra (Abisko, Sweden), Atlantic heath (Otterburn, UK), wet grassland (Wageningen, Netherlands), semi-natural temperate grassland (Linden, Germany), East European steppe (Pusztaszer, Hungary) and Mediterranean garigue (Mt. Vermion, Greece). To extend the range of temperature and humidity experienced locally during the investigation period, soil microclimates were manipulated, and at each site 14 plots were established representing selected combinations of 6 temperature and 6 moisture levels. The investigated soils divided into two groups: mineral grassland soils that were precipitation fed (garigue, wet grassland, seminatural grassland, steppe), and wet organic soils that were groundwater fed (heath, tundra). Effects of the nematofauna on the microflora were found in the mineral soils, where correlations among nematode metabolic activity as calculated from a metabolic model, and microbial activity parameters as indicated by Biolog and ergosterol measurements, were significantly positive. Correlations with bacterial activity were stronger and more consistent. Microbial parameters, in turn, were significantly correlated with the size of the soil nitrogen pools NH4, NO3, and Norganic. Furthermore, model results suggested that there were remarkable direct effects of nematodes on soil nitrogen status. Calculated monthly nematode excretion contributed temporarily up to 27% of soluble soil nitrogen, depending on the site and the microclimate. No significant correlation among nematodes and microbial parameters, or nitrogen pools, were found in the wet organic soils. The data show that the nematofauna can under favourable conditions affect soil nitrogen status in mineral grassland soils both directly by excretion of N, and indirectly by regulating microbial activity. This suggests that the differences in nitrogen availability observed in such natural grasslands partly reflect differences in the activity of their indigenous nematofauna.