A novel method to estimate the response of habitat types to nitrogen deposition.

Increasing nitrogen depositions adversely affect European landscapes, including habitats within the Natura2000 network. Critical loads for nitrogen deposition have been established to quantify the loss of habitat quality. When the nitrogen deposition rises above a habitat-specific critical load, the quality of the focal habitat is expected to be negatively influenced. Here, we investigate how the quality of habitat types is affected beyond the critical load. We calculated response curves for 60 terrestrial habitat types in the Netherlands to the estimated nitrogen deposition (EMEP-data). The curves for habitat types are based on the occurrence of their characteristic plant species in North-Western Europe (plot data from the European Vegetation Archive). The estimated response curves were corrected for soil type, mean annual temperature and annual precipitation. Evaluation was carried out by expert judgement, and by comparison with gradient deposition field studies. For 39 habitats the response to nitrogen deposition was judged to be reliable by five experts, while out of the 41 habitat types for which field studies were available, 25 showed a good agreement. Some of the curves showed a steep decline in quality and some a more gradual decline with increasing nitrogen deposition. We compared the response curves with both the empirical and modelled critical loads. For 41 curves, we found a decline already starting below the critical load.

Threshold effects of air pollution and climate change on understory plant communities at forested sites in the eastern United States.

Forest understory plant communities in the eastern United States are often diverse and are potentially sensitive to changes in climate and atmospheric inputs of nitrogen caused by air pollution. In recent years, empirical and processed-based mathematical models have been developed to investigate such changes in plant communities. In the study reported here, a robust set of understory vegetation response functions (expressed as version 2 of the Probability of Occurrence of Plant Species model for the United States [US-PROPS v2]) was developed based on observations of forest understory and grassland plant species presence/absence and associated abiotic characteristics derived from spatial datasets. Improvements to the US-PROPS model, relative to version 1, were mostly focused on inclusion of additional input data, development of custom species-level input datasets, and implementation of methods to address uncertainty. We investigated the application of US-PROPS v2 to evaluate the potential impacts of atmospheric nitrogen (N) and sulfur (S) deposition, and climate change on forest ecosystems at three forested sites located in New Hampshire, Virginia, and Tennessee in the eastern United States. Species-level N and S critical loads (CLs) were determined under ambient deposition at all three modeled sites. The lowest species-level CLs of N deposition at each site were between 2 and 11 kg N/ha/yr. Similarly, the lowest CLs of S deposition, based on the predicted soil pH response, were less than 2 kg S/ha/yr among the three sites. Critical load exceedance was found at all three model sites. The New Hampshire site included the largest percentage of species in exceedance. Simulated warming air temperature typically resulted in lower maximum occurrence probability, which contributed to lower CLs of N and S deposition. The US-PROPS v2 model, together with the PROPS-CLF model to derive CL functions, can be used to develop site-specific CLs for understory plants within broad regions of the United States. This study demonstrates that species-level CLs of N and S deposition are spatially variable according to the climate, light availability, and soil characteristics at a given location. Although the species niche models generally performed well in predicting occurrence probability, there remains uncertainty with respect to the accuracy of reported CLs. As such, the specific CLs reported here should be considered as preliminary estimates.

Methods for the Quantification of Resistance of Apple Genotypes to European Fruit Tree Canker Caused by Neonectria ditissima.

European fruit tree canker, caused by Neonectria ditissima, is an important disease of pome fruit worldwide. Apple cultivars differ in their levels of susceptibility to N. ditissima. In order to design an effective plant resistance test, we examined the effectiveness of two resistance parameters: infection frequency and lesion growth. Both parameters were evaluated in parallel tests using 10 apple cultivars in three experimental years, applying seminatural infection of leaf scars (infection frequency) or inoculation of artificial wounds (lesion growth). We compared six parameters for lesion growth, of which a new parameter, lesion growth rate (LGR), appeared to be the best with respect to reproducibility and statistical significance. LGR is defined as the slope of the regression of lesion size versus time. The slope was estimated for each lesion, employing a common start date and a lesion-specific end date determined by the girdling of the lesion. The two parameters (infection frequency and LGR) were examined in separate experiments and in three successive years, and provided complementary information and resulted in reproducible conclusions on the relative resistance levels to N. ditissima of the tested cultivars. The presented methods can be used to develop strategies for the control of European fruit tree canker (e.g., in the breeding of new apple cultivars with high levels of resistance to N. ditissima).

Climate change increases deoxynivalenol contamination of wheat in north-western Europe.

Climate change will affect the development of cereal crops and the occurrence of mycotoxins in these crops, but so far little research has been done on quantifying the expected effects. The aim of this study was to assess climate change impacts on the occurrence of deoxynivalenol in wheat grown in north-western Europe by 2040, considering the combined effects of shifts in wheat phenology and climate. The study used climate model data for the future period of 2031-2050 relative to the baseline period of 1975-1994. A weather generator was used for generating synthetic series of daily weather data for both the baseline and the future periods. Available models for wheat phenology and prediction of deoxynivalenol concentrations in north-western Europe were used. Both models were run for winter wheat and spring wheat, separately. The results showed that both flowering and full maturation of wheat will be earlier in the season because of climate change effects, about 1 to 2 weeks. Deoxynivalenol contamination was found to increase in most of the study region, with an increase of the original concentrations by up to 3 times. The study results may inform governmental and industrial risk managers to underpin decision-making and planning processes in north-western Europe. On the local level, deoxynivalenol contamination should be closely monitored to pick out wheat batches with excess levels at the right time. Using predictive models on a more local scale could be helpful to assist other monitoring measures to safeguard food safety in the wheat supply chain.

Modeling deoxynivalenol contamination of wheat in northwestern Europe for climate change assessments.

Climate change will affect mycotoxin contamination of feed and food. Mathematical models for predicting mycotoxin concentrations in cereal grains are useful for estimating the impact of climate change on these toxins. The objective of the current study was to construct a descriptive model to estimate climate change impacts on deoxynivalenol (DON) contamination of mature wheat grown in northwestern Europe. Observational data from 717 wheat fields in Norway, Sweden, Finland, and The Netherlands were analyzed, including the DON concentrations in mature wheat, agronomical practices, and local weather. Multiple regression analyses were conducted, and the best set of explanatory variables, mainly including weather factors, was selected. The final model included the following variables: flowering date, length of time between flowering and harvest, wheat resistance to Fusarium infection, and several climatic variables related to relative humidity, temperature, and rainfall during critical stages of wheat cultivation. The model accounted for 50 % of the variance, which was sufficient to make this model useful for estimating the trends of climate change on DON contamination of wheat in northwestern Europe. Application of the model in possible climate change scenarios is illustrated.

Occurrence of Fusarium Head Blight species and Fusarium mycotoxins in winter wheat in the Netherlands in 2009.

Most recent information on the occurrence of Fusarium Head Blight species and related mycotoxins in wheat grown in the Netherlands dates from 2001. This aim of this study was to investigate the incidence and levels of Fusarium Head Blight species and Fusarium mycotoxins, as well as their possible relationships, in winter wheat cultivated in the Netherlands in 2009. Samples were collected from individual fields of 88 commercial wheat growers. Samples were collected at harvest from 86 fields, and 2 weeks before the expected harvest date from 21 fields. In all, 128 samples, the levels of each of seven Fusarium Head Blight species and of 12 related mycotoxins were quantified. The results showed that F. graminearum was the most frequently observed species at harvest, followed by F. avenaceum and M. nivale. In the pre-harvest samples, only F. graminearum and M. nivale were relevant. The highest incidence and concentrations of mycotoxins were found for deoxynivalenol, followed by zearalenone and beauvericin, both pre-harvest and at harvest. Other toxins frequently found--for the first time in the Netherlands--included T-2 toxin, HT-2 toxin, and moniliformin. The levels of deoxynivalenol were positively related to F. graminearum levels, as well as to zearalenone levels. Other relationships could not be established. The current approach taken in collecting wheat samples and quantifying the presence of Fusarium Head Blight species and related mycotoxins is an efficient method to obtain insight into the occurrence of these species and toxins in wheat grown under natural environmental conditions. It is recommended that this survey be repeated for several years to establish inter-annual variability in both species composition and mycotoxin occurrence.

Monitoring phytoplankton and marine biotoxins in production waters of the Netherlands: results after one decade.

Shellfish products may be contaminated with marine biotoxins which, after consumption, may lead to human illness. The Netherlands has a regular monitoring programme for marine biotoxins and the possible toxic phytoplankton in shellfish production waters. The aim of the current study was to evaluate the presence of potential toxic phytoplankton species and marine biotoxins in Dutch production waters over the last decade, and to analyse the relationship between toxin levels and abundance of possible causative phytoplankton species. The results of the monitoring programme of the period 1999-2009 were used. The presence of Alexandrium spp. were negligible, but Pseudo-nitzschia spp. and phytoplankton causing diarrhetic shellfish poisoning (DSP toxin-producing phytoplankton) were present in nearly all three main production areas and years. The main DSP toxin-producing species was Dinophysis acuminata followed by D. rotundata and Prorocentrum lima. Toxins causing paralytic shellfish poisoning (PSP) and amnesic shellfish poisoning (ASP) were present in only a few individual shellfish samples, all at low levels. At the end of 2002, an episode of DSP toxicity was recorded, based on the rat bioassay results. Of the samples that were chemically analysed for DSP toxins in 2007 and 2008, about half of the samples in 2007 contained these toxins, although levels were low and no positive results were obtained using the rat bioassay. There was a slight positive correlation between concentrations of DSP toxin-producing phytoplankton and levels of DSP toxins in 2007. Increased DSP toxin levels were found up to 5 weeks after the peak in DSP toxin-producing phytoplankton. This positive, but weak, relationship needs to be confirmed in future research using more samples and chemical methods to quantify the presence of DSP toxins. If this relationship is further substantiated and quantified, it could be used within the current monitoring programme in the Netherlands to predict the risk areas regarding DSP toxicity in shellfish.

Genetic similarity as a measure for connectivity between fragmented populations of the moor frog (Rana arvalis).

Genetic differentiation among populations of the moor frog (Rana arvalis) was tested on a spatial scale where some dispersal between populations is expected to occur, in a landscape in The Netherlands that has become fragmented fairly recently, in the 1930s. Five microsatellite loci were used, with 2-8 alleles per locus. FIS was 0.049 across loci, and most populations were in HW equilibrium. The degree of population subdivision was low (FST=0.052). A significant positive correlation between genetic distance and geographical distance was found, indicating a limitation in dispersal among populations due to distance. To test the impact of the landscape mosaic on the connectivity between patches, distance measures were corrected for relative amounts of habitat types with known positive or negative influence on moor frog dispersal. Notably, the resistance variable for the fraction of negative linear elements (roads and railways) gave a higher explanatory value than geographical distance itself. Therefore, it is particularly the number of barriers (roads and railways) between populations that emerges as a factor that reduces exchange between populations. It is concluded that genetic techniques show promise in determining the influence of landscape connectivity on animal dispersal.

Transfer of Cs-137 from grass and wilted grass silage to milk of dairy cows.

Deposition of radiocaesium from the Chernobyl reactor accident on the Netherlands made it possible to collect contaminated fresh grass and first cut wilted grass silage. These contaminated roughages were used in transfer experiments with lactating dairy cows to determine transfer coefficients and half-lives for Cs-137 in milk. The experimental design was based on three consecutive periods: a preliminary period to determine the background concentration of the isotope in milk, a contamination period to determine the magnitude of accumulation and finally a depletion period to measure the rate at which the activity concentration of Cs-137 in milk declined after continuous feeding. The average transfer coefficient (Fmilk) for cows fed on contaminated dried grass under steady-state conditions was 0.002 d/kg and for cows fed on slightly contaminated second cut fresh grass 0.006 d/kg. The highest transfer coefficients were obtained for cows fed on contaminated grass silage for 119 days, which also included the dry period of about two months. For the first five days after calving the Fmilk values varied from 0.0066 to 0.0091 d/kg. There were no significant differences in transfer coefficients between cows in early lactation (third month of lactation), cows in late lactation (the last month of the lactation period) and cows fed on both contaminated grass silage and uncontaminated maize silage simultaneously. Half-life values for the rate of decline of the isotope in milk during the depletion period were estimated on the basis of a mathematical model with two exponential components. These components were characterized by half-lives of 0.5 to 3.5 days and 10 to 46 days.