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The Svalbard reindeer is the only mammalian herbivore in Adventdalen (78°N), Svalbard, where it has no natural predators. To test if herbivores in the absence of predators regulate standing crop to a level independent of productivity, which is one of the predictions of the "exploitation ecosystems" model, herbivore exclosures were set up in 1992 in Salix heath, Luzula heath, Cassiope heath, and Alopecurus meadow in Adventdalen. Standing crop of vascular plants was harvested and measured inside and outside the exclosures in 1994, when the reindeer population was at peak density (ca 5.4 animals km), and in 1996, when the reindeer density was about 30% lower (ca 3.7 animals km). Standing dead material was reduced by grazing in the Luzula heath in 1994. However, we found no effect of grazing, year, or interactions between grazing and year on live standing crop. Also contrary to the predictions from the model, differences in standing crop between vegetation types were highly significant. Mean biomass of plant material was lowest in the Alopecurus meadow (36 g m), two fold higher in the Luzula heath, and about threefold higher in the Salix heath and Cassiope heath, indicating that reindeer do not regulate standing crop to the same level on a local scale. The predictive power of the "exploitation ecosystems" model is low due to lack of recognition of the importance of plant chemistry, plant compensation ability, variation in forage availability during the year, parasites functioning as predators, and adverse weather conditions, which may cause density-independent variations in fecundity and mortality of reindeer.

Potatoes are regarded as a significant antioxidant source in human nutrition. However, different types of environmental stress may affect the level of antioxidants in their tuber tissue. In this study, two purple breeding clones and the yellow fleshed cultivar (cv.) Agave were grown in the glasshouse under control with drought stress conditions for two consecutive years. After harvest, the tubers were analysed for concentrations of antioxidants measured as ascorbic acid equivalent (ACE) and trolox equivalent (TXE) in fresh tissue and after wounding. In addition, the peroxidase enzyme (POD) activities and total amounts of anthocyanins (Ac) were assayed. Drought stress caused a significant decrease in tuber yield but had no significant effect on Ac, POD, ACE and TXE. Wounding stress significantly induced the POD activity in control and drought stressed tubers of all genotypes. Also the ACE and TXE were notably increased by wounding in cv. Agave. This was less pronounced in the purple clones which in general displayed a higher level of antioxidants. The results revealed significant differences between genotypes and that the effect of drought stress on the level of antioxidants is smaller than that of wounding stress

Arabinoxylans are considered as the major limiting factor for use of rye in animal feeding. In this study, four selected winter rye cultivars were grown at nine locations and tested for arabinoxylans including total (TAX), soluble (SAX) and insoluble fractions (IAX), extract viscosity, falling numbers and crude protein contents. Amounts of TAX ranged on average between 89 and 103 g/kg wholemeal flour, and the extract viscosity between 2.6 and 5.1 cSt. The extract viscosity was significantly correlated with falling numbers and all three arabinoxylan fractions. Arabinoxylan contents and extract viscosity were influenced by the rye genotype. The anthocyanin free hybrid cultivar Helltop combined reduced TAX, SAX and IAX levels with low extract viscosity and high crude protein contents and seems to be more suitable for use in animal feeding than the other three cultivars tested in this respect.

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