Descriptive "keys", including definitions and explanatory diagrams, are given for the standardization and simplification of anatomical descriptions of the epidermides of grass leaf blades as seen in surface view. About 340 characters of the epidermis are included with ample room for expansion. Notes on variation and taxonomic importance of the characters are also included.
Grazing lawns are a distinct grassland community type, characterised by short-stature and with their persistence and spread promoted by grazing. In Africa, they reveal a long co-evolutionary history of grasses and large mammal grazers. The attractiveness to grazers of a low-biomass sward lies in the relatively high quality of forage, largely due to the low proportion of stem material in the sward; this encourages repeat grazing that concomitantly suppresses tall-grass growth forms that would otherwise outcompete lawn species for light. Regular grazing that prevents shading and maintains sward quality is thus the cornerstone of grazing lawn dynamics. The strong interplay between abiotic conditions and disturbance factors, which are central to grazing lawn existence, can also cause these systems to be highly dynamic. Here we identify differences in growth form among grazing lawn grass species, and assess how compositional differences among lawn types, as well as environmental variables, influence their maintenance requirements (i.e. grazing frequency) and vulnerability to degradation. We also make a clear distinction between the processes of lawn establishment and lawn maintenance. Rainfall, soil nutrient status, grazer community composition and fire regime have strong and interactive influences on both processes. However, factors that concentrate grazing pressure (e.g. nutrient hotspots and sodic sites) have more bearing on where lawns establish. Similarly, we discuss the relevance of enhanced rates of nitrogen cycling and of sodium levels to lawn maintenance. Grazer community composition and density has considerable significance to grazing lawn dynamics; not all grazers are adapted to foraging on short-grass swards, and differences in body size and relative mouth dimensions determine which species are able to convert tall-grass swards into grazing lawns under different conditions. Hence, we evaluate the roles of different grazers in lawn dynamics, as well as the benefits that grazer populations derive from having access to grazing lawns. The effects of grazing lawns can extend well beyond their borders, due to their influence on grazer densities, behaviour and movements as well as fire spread, intensity and frequency. Variation in the area and proportion of a landscape that is grazing lawn can thus have a profound impact on system dynamics. We provide a conceptual model that summarises grazing lawn dynamics, and identify a rainfall range where we predict grazing lawns to be most prevalent. We also examine the biodiversity associated with grazing lawn systems, and consider their functional contribution to the conservation of this biodiversity. Finally, we assess the utility of grazing lawns as a resource in a rangeland context.
Descriptive "keys", including definitions and diagrams, for standardizing and simplifying the description of grass leaf structure as seen in transverse section are given. Over 500 characters are included with the possibility for expansion to 999. Notes on variation and taxonomic importance of the characters are also included. Resume UN PRO CED EPO U R STAN D ARD ISER L'ANATOM IE COMPAREE DE LA FEUILLE DE POACEAE. I. LE LIM BE VU EN SECTION TRANSVERSALEDes "clefs" descriptives incluant des definitions et des diagrammes pour standardiser et simplifier la descrip tion de la structure des feuilles de graminees vues en section transversale sont donnees. Plus de 500 caracteres sont inclus avec la possibilite d'expansion jusqu a 999. Des notes sur la variation et /'importance taxonomique des caracteres sont egalement fournies.
: This review of starch is concerned with its industrial uses, origins and structure. The current demand for starch is met by a restricted range of crops, the most important of which are potatoes, maize, wheat and tapioca. Improvements in the properties of starches for industrial uses can be achieved through chemical and physical modiÐcation of extracted starch and through the manipulation of starch biosynthesis in the plant itself. We examine starch structure and composition in relation to its use and exploitation by industry. The current understanding of physiological and biochemical mechanisms inÑuencing starch formation in higher plants is described. This information is set in the context of the need to know the physical/chemical speciÐcation for each individual starch and to understand the genetic control of these characteristics in order to identify target genes for manipulation.1998 SCI. ( J Sci Food Agric 77, 289È311 (1998)
The grass flora of Namibia (374 species in 110 genera) shows surprisingly little variation in δC values along a rainfall gradient (50-600 mm) and in different habitat conditions. However, there are significant differences in the δC values between the metabolic types of the C4 photosynthetic pathway. NADP-ME-type C4 species exhibit the highest δC values (-11.7 ‰) and occur mainly in regions with high rainfall. NAD-ME-type C4 species have significantly lower δC values (-13.4 ‰) and dominate in the most arid part of the precipitation regime. PCK-type C4 species play an intermediate role (-12.5 ‰) and reach a maximum abundance in areas of intermediate precipitation. This pattern is also evident in genera containing species of different metabolic types. Within the same genus NAD species reach more negative δC values than PCK species and δC values decreased with rainfall. Also in Aristida, with NADP-ME-type photosynthesis, δC values decreased from -11 ‰ in the inland region (600 mm precipitation) to -15 ‰ near the coast (150 mm precipitation), which is a change in discrimination which is otherwise associated by a change in metabolism. The exceptional C3 species Eragrostis walteri and Panicum heterostachyum are coastal species experiencing 50 mm precipitation only. Many of the rare species and monotypic genera grow in moist habitats rather than in the desert, and they are not different in their carbon isotope ratios from the more common flora. The role of species diversity with respect to habitat occupation and carbon metabolism is discussed.
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