The Functional Importance of Forbs in Grassland Ecosystems

Herbaceous vegetation in grassland ecosystems is characterised by grass dominance in a species-rich forb-grass mixture. Forbs (i.e. the non-graminoid herbaceous component) represent the largest proportion of total species- and functional richness, which secure important ecosystem functions. Although grasses remain the most important forage source, certain forb species provide nutritious food sources for herbivores. Moreover, forbs provide food- and habitat sources to enhance invertebrate diversity and hence, agricultural food security through the maintenance of healthy pollinator communities. Important food and medicinal sources for human livelihoods in developing countries are also largely contributed by forbs. However, the dynamics and ecology of forb species are poorly understood in rangeland systems. Increasing global pressures are threatening the hyper-diverse grassland ecosystems (including African savannas) and in particular the diversity of the forb flora. The sub-ordinate role of forbs in savanna and grassland rangeland management practices led us to accumulate evidence of important ecosystem functions and services provided by this diverse life form. In this study, we present results that were obtained from several independent studies in which forb data were collected and analysed as an equally important herbaceous life form, to contribute to our current understanding of the ecology of grassland ecosystems. Our results revealed evidence of forbs as important forage for large African mammalian herbivores, including domestic cattle, during periods when other forage resources are severely limited. However, sustained overgrazing can severely deplete forb populations and diversity. Forbs as grazing indicators have been identified as the basis of a proposed forb-condition scoring method for mesic grasslands. Furthermore, the importance of intermediate disturbances, such as moderate grazing and/or the maintenance of crop field margins were identified for invertebrate community conservation. Studies on useful indigenous plants exposed forbs as an important life form to provide food- and medicinal resources to human livelihoods in African grassland ecosystems

Hypoxia-induced regulation of nitric oxide synthase in cardiac endothelial cells and myocytes and the role of the PI3-K/PKB pathway

The roles of endothelial nitric oxide synthase (eNOS), and its putative association with protein kinase B (PKB), and inducible nitric oxide synthase (iNOS) are not well characterized in hypoxic cardiac cells and there is a lack of studies that measure nitric oxide (NO) directly. Objective: To measure NO production in cardiomyocytes and cardiac microvascular endothelial cells (CMECs) under baseline and hypoxic conditions and to evaluate the expression, regulation and activation of eNOS, iNOS and PKB. The effect of PI3-K/PKB inhibition on NO production and eNOS expression/activation was also investigated. Methods: Adult rat cardiomyocytes and rat CMECs were made hypoxic by cell pelleting and low PO2 incubation. Intracellular NO was measured by FACS analysis of DAF-2/DA fluorescence, and eNOS, iNOS and PKB were evaluated by Western blotting or flow cytometry. Upstream PKB inhibition was achieved with wortmannin. Results: (1) NO levels increased in both cell types after exposure to hypoxia. (2) In hypoxic CMECs, eNOS was upregulated and activated, no iNOS expression was observed and PKB was activated. (3) In myocytes, hypoxia did not affect eNOS expression, but increased its activation. Activated PKB also increased during hypoxia. FACS analysis showed increased iNOS in hypoxic myocytes. (4) Wortmannin resulted in decreased hypoxia-induced NO production and reduced activated eNOS levels. Conclusions: Cardiomyocytes and CMECs show increased NO production during hypoxia. eNOS seems to be the main NOS isoform involved as source of the increased NO generation, although there may be a role for iNOS and other non-eNOS sources of NO in the hypoxic myocytes. Hypoxia-induced PKB and eNOS activation occurred simultaneously in both cell types, and the PI3-K/PKB pathway was associated with hypoxia-induced NO production via eNOS activation. © Springer Science+Business Media, LLC. 2008.Articl