One Sentence Summary: Empirical evidence from grasslands around the world demonstrates a humped-back relationship between plant species richness and biomass at the 1 m 2 plot scale.Abstract: One of the central problems of ecology is the prediction of species diversity. The humped-back model (HBM) suggests that plant diversity is highest at intermediate levels of productivity; at low productivity few species can tolerate the environmental stresses and at high productivity a small number of highly competitive species dominate. A recent study claims to have comprehensively refuted the HBM. Here we show, using the largest, most geographically diverse dataset ever compiled and specifically built for testing this model that if the conditions are met, namely a wide range in biomass at the 1 m 2 plot level and the inclusion of plant litter, the relationship between plant biomass and species richness is hump shaped, supporting the HBM. Our findings shed new light on the prediction of plant diversity in grasslands, which is crucial for supporting management practices for effective conservation of biodiversity. 4Main Text: The relationship between plant diversity and productivity is a topic of intense debate (1-6). The HBM states that plant species richness peaks at intermediate productivity, taking above-ground biomass as a proxy for annual net primary productivity (ANPP) (7-9). This diversity peak is driven by two opposing processes; in unproductive and disturbed ecosystems where there is low plant biomass, species richness is limited by either stress, such as insufficient water and mineral nutrients, or high levels of disturbance-induced removal of biomass, which few species are able to tolerate. In contrast, in the low disturbance and productive conditions that generate high plant biomass it is competitive exclusion by a small number of highly competitive species that is hypothesized to constrain species richness (7-9). Other mechanisms proposed to explain the unimodal relationship between species richness and productivity include disturbance (10), evolutionary history and dispersal limitation (11,12), and density limitation affected by plant size (13).Different case studies have supported or rejected the HBM, and three separate meta-analyses reached different conclusions (14). This inconsistency may indicate a lack of generality of the HBM, or it may reflect a sensitivity to study characteristics including the type(s) of plant communities considered, the taxonomic scope, the length of the gradient sampled, the spatial grain and extent of analyses (14,15), and the particular measure of net primary productivity (16). Although others would argue (6), we maintain that the question remains whether the HBM serves as a useful and general model for grassland ecosystem theory and management. 5 We quantified the form and strength of the richness-productivity relationship using novel data from a globally-coordinated (17), distributed, scale-standardized and consistently designed survey, in which plant richness and biomass were m...

Aim: Plant species continue to be moved outside of their native range by human activities. Here, we aim to determine whether, once introduced, plants assimilate into native communities or whether they aggregate, thus forming mosaics of native-and alien-rich communities. Alien species might aggregate in their non-native range owing to shared habitat preferences, such as their tendency to establish in high-biomass, species-poor areas.Location: Twenty-two herbaceous grasslands in 14 countries, mainly in the temperate zone.Time period: 2012-2016. Major taxa studied: Plants.Methods: We used a globally coordinated survey. Within this survey, we found 46 plant species, predominantly from Eurasia, for which we had co-occurrence data in their native and non-native ranges. We tested for differences in co-occurrence patterns of 46 species between their native (home) and non-native (away) range. We also tested whether species had similar habitat preferences, by testing for differences in total biomass and species richness of the patches that species occupy in their native and non-native ranges. Results:We found the same species to show different patterns of association depending on whether they were in their native or non-native range. Alien species were negatively associated with native species; instead, they aggregated with other alien species in species-poor, high-biomass communities in their non-native range compared with their native range. Main conclusions:The strong differences between the native (home) and non-native (away) range in species co-occurrence patterns are evidence that the way in which species associate with resident communities in their non-native range is not species dependent, but is instead a property of being away from their native range. These results thus highlight that species might undergo important ecological changes when introduced away from their native range. Overall, we show origin-dependent associations that result in novel communities, in which alien-rich patches exist within a mosaic of native-dominated communities. K E Y W O R D Salien species, biodiversity threats, biological invasions, grassland ecology, native range, novel ecosystems

No abstract

Medicinal plant are grown and produced in different ecosystems and sites under the influence of different potential factors, including the altitude as one of the vital determinants in the quantity and quality of the plants. One of the species that grows in the highlands is Tanacetum polycephalum, an aromatic perennial of the Asteraceae. This species is characterized to be antiseptic, analgesic, anesthetic, disinfective, expectorant, anti-cancer, anti-allergic, and conducive to low blood pressure. The purpose of this study is to investigate the essential compositions in the aerial parts of T. polycephalum at the time of flowering, and in three different altitudes of the Baladeh region of Nour. Thus, the essential oil was extracted from the aerial parts in the flowering stage of the plant at three altitudes of 1 600, 2 400 and 3 200 m using a water distillation method, and the essential oil compositions were identified using GC and GC/MS instruments. One-way ANOVA method was conducted to analyze the obtained data using SPSS, and a Duncan test was administered to compare the means. The results indicated that the essential output obtained from the altitudes of 1 600, 2 400 and 3 200 m was (0.74 ± 0.01)%, (1.09 ± 0.02)%, and (1.32 ± 1.2)%, respectively, so that the altitude of 3 200 m revealed the greatest quantity, and the altitude of 1 600 m represented the smallest quantity. Moreover, the essential oil compositions showed the highest percentage in the altitude of 3 200 m and the lowest percentage at the altitude of 1 600 m. The results showed that as the altitude increases, the essential oil compositions revealed the greater quantity and percentage in the aerial parts of T. polycephalum.

No abstract