Arable weeds are one of the most endangered species groups in Central Europe. Modern agriculture and intensive land use management with the application of herbicides and fertilizers, enhanced seed treatments, simplified crop rotation, and abandonment of marginal arable sites caused a dramatically decline of arable weeds and a shift in the spectrum of the wild arable plant species. Besides changing land use, global climate change may present a further challenge to the adaptability of arable weeds. Differing climate scenarios predict a general increase of annual mean temperatures and an increased frequency of extreme meteorological conditions. As a consequence, plants may be more often subjected to high temperatures and low soil moisture during the growing season in spring and summer. Germination is a crucial stage especially for annual species. As temperature and water availability control germination of seeds, changes in these factors may have major impacts on the establishment and survival of plant populations. For the development of successful conservation programs it is essential to understand the response of endangered species to future changes in environmental conditions.In this context, the presented studies investigated the response patterns of arable weeds to changes in temperature and water availability during germination. The results revealed a distinct germination response of endangered and common arable weeds. At optimal water supply endangered species tended to germinate to a higher percentage than common arable weeds, however, this trend was reversed when water availability decreased. Thus, endangered arable weeds showed a stronger negative response to water stress during germination than common arable weeds. In addition, endangered arable species germinated in a narrower time window, e.g. shorter mean germination time and higher synchrony of germination. The endangered species place everything on one card, while the more common species spread their germination over a longer time period. Therefore they are less sensitive towards short-term unfavourable site conditions and disturbances. Based on comprehensive collection of data over a broad range of temperatures (3 - 35 °C) combined with several water potentials (0.0 - 1.2 MPa) germination response of endangered and common arable weeds could be modelled for differing climate scenarios. Less flexibility to decreasing water availability of the endangered species and a significant lower mean germination temperature (15.8 °C ± 0.4) compared to the common species (18.4 °C ± 0.2) suggests that the endangered arable weed species will be more negatively affected by global warming than common species.The results of the study about the impact of the mean germination time on plant fitness show that the common weed species are following a bet-hedging strategy. They are sacrificing fitness of individual plants in order to decrease the risk of a failure of the whole seed batch. Timing of germination has a significant influence on plant fitness across the life-cycle. At delayed germination of seven days individuals of the target species Agrostemma githago had 54 % less shoots, 23 % less height, 57 % less biomass, 52 % less flowers, 37 % less seeds per capsule and 36 % lighter seeds. To set-up a conservation strategy for endangered species in the agricultural landscapes of Central Europe it has to be considered that climate change will further enhance the decline of several arable weeds initiated through land use changes. As the consequences of climate change are not avoidable, the conservation efforts have to focus on measures to compensate negative effects. To increase biodiversity of agricultural landscapes and to stop the further decline of arable weed species, conservation measures for arable weeds should be explicitly intensified. It is necessary to move away from local release of endangered species to a denser grid of weed conservation sites, which enables migration of arable weed species. Conservation measures on landscape-scale would give arable weed species greater scope to face future climatic changes.
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