Nutritional constraints in terrestrial and freshwater food webs.

Biological and environmental contrasts between aquatic and terrestrial systems have hindered analyses of community and ecosystem structure across Earth's diverse habitats. Ecological stoichiometry provides an integrative approach for such analyses, as all organisms are composed of the same major elements (C, N, P) whose balance affects production, nutrient cycling, and food-web dynamics. Here we show both similarities and differences in the C:N:P ratios of primary producers (autotrophs) and invertebrate primary consumers (herbivores) across habitats. Terrestrial food webs are built on an extremely nutrient-poor autotroph base with C:P and C:N ratios higher than in lake particulate matter, although the N:P ratios are nearly identical. Terrestrial herbivores (insects) and their freshwater counterparts (zooplankton) are nutrient-rich and indistinguishable in C:N:P stoichiometry. In both lakes and terrestrial systems, herbivores should have low growth efficiencies (10-30%) when consuming autotrophs with typical carbon-to-nutrient ratios. These stoichiometric constraints on herbivore growth appear to be qualitatively similar and widespread in both environments.

[Hemorheological changes during exercise]. / Modificazioni emoreologiche nello sforzo.

It is now necessary to study the macro- and microcirculatory modifications of the organism following the stress. We have devoted our attention to the hemorheological parameters, which have been evaluated in a group of ten sedentary subjects, of fourteen athletes under twenty years of age, and of ten subjects whose age was over thirty, who carry on physical unbroken performance. We have evaluated the modifications of total blood viscosity and of red blood cell deformability after an ergometric test. Our results show that the hemorheological pattern gets worse after strenuous muscular exercise; moreover, the advancing age gets worse the hyperviscosity response. The pathophysiological mechanism which causes the hemorheological disorder is yet unknown, so it is clear the importance of studying the hemorheological balance in order to clarify the pathophysiology of stressed muscular function.