Note sur la présence de Hardya helgae Nickel, Holzinger & Remane 2017 en Belgique (Hemiptera, Cicadellidae)

La cicadelle Hardya helgae Nickel, Holzinger & Remane 2017 est signalée pour la première fois de Belgique où elle a été récoltée entre Rochefort et Eprave (province de Namur) les 14.vii.2014, 21.iii.2019 et 14.vi.2019. Cette espèce décrite récemment du sud-ouest de l’Allemagne, puis signalée de l’est de la France et du Grand-Duché de Luxembourg, était auparavant confondue avec Hardya tenuis (Germar 1821). H. helgae est confiné aux pelouses calcaires et se développe sur la graminée Bromus erectus Huds. L'occurrence de H. tenuis en Belgique est remise en question du fait qu'elle repose seulement sur deux spécimens du 19ème siècle dont la révision montre qu'ils correspondent plutôt à H. helgae.

Soil Respiration Dynamics in Bromus erectus-Dominated Grasslands under Different Management Intensities

Reduction of soil greenhouse gas emissions is crucial to control increases in atmospheric CO2 concentrations. Permanent grasslands are of considerable importance in climate change mitigation strategies as they cover about 13% of the global agricultural area. However, uncertainties remain for the effects of management practices on soil respiration, especially over the short term. This study investigated the influence of different mowing intensities on soil respiration over the short term for Bromus erectus-dominated grasslands in the central Apennines. From 2016 to 2018, soil respiration, temperature, and moisture were measured under three different management systems: customary management, intensive use, and abandonment. Both soil water content and temperature changed over time, however mowing did not affect soil water content while occasionally altered soil temperature. The intensive use promoted higher seasonal mean soil respiration compared to the abandonment only during the 2016 growing season. Soil temperature was the main driver of soil respiration above a soil water content threshold that varied little among treatments (18.23–22.71%). Below the thresholds, soil moisture was the main driver of soil respiration. These data suggest that different mowing regimes have little influence on soil respiration over the short term in Bromus erectus-dominated grasslands. Thus, more intensive use would not have significative impacts on soil respiration, at least over the short term. Future studies need to clarify the role of root mycorrhizal and microbial respiration in the light of climate change, considering the seasonal redistribution of the rainfall.

The Festuco-Brometea Grasslands on Sandstone and Marl-Clay-Sandstone Substrata in Tuscany (Northern-Central Italy)

The grasslands dominated by Bromus erectus and/or Brachypodium rupestre cover large areas on sandstone and marl-clay-sandstone substrata (limestone is excluded), of the Apennines and pre-Apennines between Pistoia and Arezzo provinces (Tuscany, Central Italy). Our investigation was focused on to 71 unpublished releves and 45 literature releves from Tuscany and surrounding areas, reporting the original releves of Astragalo monspessulani-Brometum erecti, Centaureo bracteatae-Brometum erecti and Ononido masquillerii-Brometum erecti. The releves were submitted to exploratory multivariate analysis, allowing to detect nine distinct groups. Their consistence was verified by mean of NMDS against Ellenberg/Pignatti indicator values, and CCA constrained against chorotypes and growth forms. Diagnostic species of the definitive groups resulting from the analysis were chosen according to species fidelity, based on the φ coefficient of association. The analysis splits the data set in two main subclusters; the first one (A) includes few releves of low altitude, thermophilous conenoses, interpreted as a transition between the submediterranean aspects of Festuco-Brometea class and other Mediterranean herbaceous and shrubby classes; the second subcluster (B) includes most of the data set and can be clearly subdivided in pioneering, mesoxerophilous communities (B1 and B2a groups) and mesophilous communities (B2b group). The releves of clusters B1 and B2a are referred to Coronillo minimae-Astragaletum monspessulanii association and to three other groups: Plantago argentea-Carex caryophyllea communities, Tragopogon samaritani-Bromus erectus communities, Festuco trachyphyllae-Brometum erecti ass. nova. The mesophilous group (B2b) includes the original Centaureo bracteatae-Brometum erecti and Ononido masquillerii-Brometum erecti releves, together with a slightly differentiated community; due to the non-relevant differences between these grassland types from floristic, ecological and chorological perspectives, we propose herewith to treat them as three subassociations of Centaureo bracteatae-Brometum erecti (typicum, ononidetosum masquillerii and linetosum cathartici). Post-cultural grasslands in human-disturbed areas were also detected. All these communities can be attributed to Polygalo mediterraneae-Bromenion erecti suballiance (Bromion alliance), even if a clear subdivision between the mesoxerophilous pioneer aspects and the more mesophilous and evolved ones can be noted.

A Comparative Analysis of the Mechanical Role of Leaf Sheaths of Poaceae, Juncaceae, and Cyperaceae

Similarities in structural organization of the culm in Poaceae, Juncaceae, and Cyperaceae such as leaf sheaths and the presence of intercalary meristems at every node suggest the same mechanical properties and, accordingly, the same functionality. Meristems are zones of tissue formation, which constitute areas of weakness along the entire culm and provide the basis for rapid shoot elongation. Leaf sheaths clasp the culm preventing the shoot from breaking, ensuring the rigidity to grow erectly and to avoid damage of the meristematic tissue. The mechanical influence of leaf sheaths was investigated in members of Poaceae, Juncaceae, and Cyperaceae in the flowering stage. Mechanical properties of Poa araratica, Bromus erectus, Arrhenatherum elatius (Poaceae), Luzula nivea (Juncaceae), and Carex arctata (Cyperaceae) were determined in three-point bending before and after the removal of leaf sheaths. The presence of leaf sheaths results in smoothing the distribution of flexural rigidity and therefore avoids stress peaks. The achieved maxima of relative contribution of leaf sheaths to entire flexural rigidity ranged from 55% up to 81% for Poaceae, 72% for C. arctata, and 40% for L. nivea. Across the investigated families, the mechanical role of leaf sheaths could be verified as essential for culm stability during development and beyond.

Classification of mesic and wet grasslands in northwest Croatia

In this paper, 450 relevés of grassland vegetation of the Molinio-Arrhenatheretea class in northwest Croatia have been classified using the agglomerative Ward’s Method in the PC-ORD program. In the process of classification, the following seven groups were obtained: 1. Bromus erectus-Arrhenatherum elatius, 2. Arrhenatherum elatius, 3. Crepis biennis-Arrhenatherum elatius, 4. Luzula campestris-Holcus lanatus, 5. Deschampsia cespitosa-Betonica officinalis, 6. Equisetum palustre, 7. Oenanthe silaifolia-Alopecurus pratensis. The results of the classification for the most part correspond to the traditional syntaxonomic system. The plant communities with the largest number of relevés in the data set are the association Arrhenatheretum elatioris “typicum” (group 2) and the association Holcetum lanati (group 4). They represent the most anthropogenically influenced grasslands of the study area. In the analysis of the ecological factors by PCA in the CANOCO program it is established that separation of the relevés is influenced most greatly by moisture, followed by humus, temperature, light and soil reaction. From the standpoint of nature conservation, the wet meadows of the Molinietalia order are the most valuable, because of the notable diversity of species and communities, as well as a considerable number of threatened plant species.