Christian Storm

Are low-productive plant communities responsive to nutrient addition Evidence from sand pioneer grassland

Abstract Question: What is the effect of nutrient addition on primary production, phytodiversity and succession of a very unproductive plant community (ca. 100 g.m−2.a−1)? Location: A nutrient-poor, calcareous inland sand ecosystem in the northern upper Rhine valley, Germany. Methods: Within a five-fold replicated randomized block design, 10-m2 plots were given six single or combined applications of nitrogen, phosphorus, potassium and other essential nutrients for four years. An organic carbon treatment was included as a measure to immobilize soil nitrogen. Data were analysed by mixed linear models. Results: Productivity of above-ground vascular plant species doubled after nitrogen addition. Additional nutrient elements did not increase productivity further. The cover of ten species and the height of 15 (out of 19 examined) species were significantly enhanced by nutrient addition. Centaurea stoebe is nitrogen-limited and exhibits a decisive impact on total above-ground vascular species productivity. Nutrients did not affect phytodiversity. Low-dosage nitrogen addition (25 kg.ha−1a−1) and organic carbon treatment had no significant impact. However, long-term effects cannot be excluded. Conclusions: The productivity of the examined plant community is responsive to nutrient addition. Although the response is actually more pronounced than in plant communities with higher initial productivity, productivity remained at a low level. Nutrient limitation (mostly phosphorus + nitrogen co-limitation) of many individual species across all life forms is shown. Total above-ground vascular plant productivity is nitrogen-limited. No species were suppressed completely, nor has there yet been an encroachment of new species. However, high-dosage nitrogen addition resulted in accelerated succession. Nomenclature: Wisskirchen & Haeupler (1998) for vascular plants; Koperski et al. (2000) for bryophytes.

MeCP2 Dependent Heterochromatin Reorganization during Neural Differentiation of a Novel Mecp2-Deficient Embryonic Stem Cell Reporter Line

The X-linked Mecp2 is a known interpreter of epigenetic information and mutated in Rett syndrome, a complex neurological disease. MeCP2 recruits HDAC complexes to chromatin thereby modulating gene expression and, importantly regulates higher order heterochromatin structure. To address the effects of MeCP2 deficiency on heterochromatin organization during neural differentiation, we developed a versatile model for stem cell in vitro differentiation. Therefore, we modified murine Mecp2 deficient (Mecp2 −/y) embryonic stem cells to generate cells exhibiting green fluorescent protein expression upon neural differentiation. Subsequently, we quantitatively analyzed heterochromatin organization during neural differentiation in wild type and in Mecp2 deficient cells. We found that MeCP2 protein levels increase significantly during neural differentiation and accumulate at constitutive heterochromatin. Statistical analysis of Mecp2 wild type neurons revealed a significant clustering of heterochromatin per nuclei with progressing differentiation. In contrast we found Mecp2 deficient neurons and astroglia cells to be significantly impaired in heterochromatin reorganization. Our results (i) introduce a new and manageable cellular model to study the molecular effects of Mecp2 deficiency, and (ii) support the view of MeCP2 as a central protein in heterochromatin architecture in maturating cells, possibly involved in stabilizing their differentiated state.

Inland Sand Ecosystems: Dynamics and restitution as a consequence of the use of different grazing systems

In Germany, sand ecosystems are among the endangered habitats, particularly the open and the ecotone-rich forms including open oak and pine woodland. A practicable nature conservation concept has to take into account the often anthropo-zoogenically caused dynamics of sand ecosystems. The conservation of these ecosystems is problematic, as they form dynamic systems which lose relevance for species and habitat conservation if they are not used or if they are intensively used or fertilized.

Binding of MBD proteins to DNA blocks Tet1 function thereby modulating transcriptional noise

Abstract Aberrant DNA methylation is a hallmark of various human disorders, indicating that the spatial and temporal regulation of methylation readers and modifiers is imperative for development and differentiation. In particular, the cross-regulation between 5-methylcytosine binders (MBD) and modifiers (Tet) has not been investigated. Here, we show that binding of Mecp2 and Mbd2 to DNA protects 5-methylcytosine from Tet1-mediated oxidation. The mechanism is not based on competition for 5-methylcytosine binding but on Mecp2 and Mbd2 directly restricting Tet1 access to DNA. We demonstrate that the efficiency of this process depends on the number of bound MBDs per DNA molecule. Accordingly, we find 5-hydroxymethylcytosine enriched at heterochromatin of Mecp2-deficient neurons of a mouse model for Rett syndrome and Tet1-induced reexpression of silenced major satellite repeats. These data unveil fundamental regulatory mechanisms of Tet enzymes and their potential pathophysiological role in Rett syndrome. Importantly, it suggests that Mecp2 and Mbd2 have an essential physiological role as guardians of the epigenome.

Community structure and diversity of vegetation and flower-visiting wild bees (Hymenoptera: Apoidea) in sandy dry grassland: are there congruent characteristics?

We studied community structures of mainly threatened types of sandy dry grassland, and those of flower-visiting wild bees, in successional, non-ruderal or ruderal gradients in the Upper Rhine Valley (Germany). We searched for congruent characteristics in the floristic/faunistic structure of plant and bee species, and for differences between two study years. We also asked which vegetation type or complex plays the most important role as a pollen or nectar resource for wild bees, and what conclusions can be drawn for nature conservation. The vegetation types or complexes range from basiphytic pioneer stages to consolidated basiphytic to slightly acidophytic grasslands (classes Koelerio-Corynephoretea and Festuco-Brom- etea): Koelerion glaucae complex (1), Armerio-Festucetum trachyphyllae (2a, typical; 2b, ruderalized), ruderalized ex-arable field (3), and Allio-Stipetum capillatae (4). We used a plot-based approach for recording vegetation data and flower-visiting wild bees. Releves were sampled and flower- visiting bees netted on defined flower resources (2004, 2005). Data were analyzed by ordination, mixed linear models and regres- sion analysis. Phytosociological table and DCA show clear floristic differentiations between the vegetation types and complexes. For the bee data there were weaker species-based differentiations. In the year 2004 there were two bee assemblages, in the year 2005 this dif- ferentiation was not detectable. The most species- and individual-rich wild-bee populations were detected in the vegetation types 2b, 3 and 4. These types were characterized by a high diversity of entomophilous plant species in combination with high flower density. Although ruderalized sandy grasslands have only moderate conservation value based on vegetation characteristics, they offer remarkable resources for species-rich populations of wild bees. Important flower resources for endangered wild-bee species are, among others, Centaurea stoebe s.l., Berteroa incana and Carduus nutans. The diversity characteristics of the studied vegetation types or complexes do not always correspond to those of the flower-visit- ing bees, which should be taken into account in developing conservation strategies.