No abstract

The sea urchin, Lytechinus variegatus, has been estimated to consume between 50 and 90% of annual net aboveground production in selected turtlegrass (Thalassia testudinum) meadows in the eastern Gulf of Mexico. Nevertheless, turtlegrass persists where sea urchin grazing is intense. We hypothesized that turtlegrass productivity is stimulated by grazing, as has been reported from terrestrial grassland systems, and that this best explains the persistence of heavily grazed turtlegrass in St. Joseph Bay, Fla. This hypothesis was tested by manipulating sea urchin densities (0, 10, and 20 individuals/m) in 1-m enclosures. These densities encompass the range of average densities at the study site and those reported in the literature. Changes in turtlegrass abundance (e.g., short shoot density and biomass), production by short shoots, and leaf width were monitored in these enclosures during the summer. Repeated-measures ANOVA showed that production by short shoots, leaf density/shoot, and leaf width decreased over time in all treatments. Leaf density/shoot and leaf width were not significantly impacted by grazing, nor did grazing significantly reduce seagrass biomass, but it did lead to significantly higher densities of short shoots than found in control cages. Our results indicate that turtlegrass compensates for the effects of sea urchin herbivory by increasing the recruitment of short shoots during the growing season. We estimate that this increased shoot density led to a 40% increase in net aboveground primary production (g dry weight/m) in grazing treatments, which helps to explain the lack of significant reductions of sea grass biomass during the growing season.

This paper presents the results of two cognitive load studies comparing three augmented reality display technologies: spatial augmented reality, the optical see-through Microsoft HoloLens, and the video see-through Samsung Gear VR. In particular, the two experiments focused on isolating the cognitive load cost of receiving instructions for a button-pressing procedural task. The studies employed a self-assessment cognitive load methodology, as well as an additional dual-task cognitive load methodology. The results showed that spatial augmented reality led to increased performance and reduced cognitive load. Additionally, it was discovered that a limited field of view can introduce increased cognitive load requirements. The findings suggest that some of the inherent restrictions of head-mounted displays materialize as increased user cognitive load.

-Picea mariana (Mill.) B.S.P. seedlings were hardened for overwintering under four regimes. In three regimes, seedlings were kept inside a heated greenhouse for 11 weeks during and after dormancy induction (August to mid-November), with either 1. Natural daylengths (46°31' N) and warm temperatures of 20 °C or more (NDW), 2. As 1, but fertilized (NDWF) or 3. As 1, but with shortened daylengths (SD). In the fourth regime (OD), seedlings were hardened outside at naturally declining temperatures and daylengths without fertilizer. Seedlings hardened in any warm temperature treatment had buds with more needle primordia and shoots more resistant to desiccation than OD seedlings. Initially, cold hardiness tended to be greatest in SD seedlings. As hardening progressed OD seedlings became equally cold hardy to SD. In late November when all trees were outside, NDW seedlings were usually least cold hardy. Spring root growth potential was least in OD seedlings.cold hardiness / desiccation / needle primordia / transpiration / water potential Résumé -Effets de la longueur du jour, de la température et de la fertilisation sur la résistance à la dessiccation et au froid, et au potentiel de croissance de plants de Picea mariana. On a soumis des semis de Picea mariana (Mill.) à quatre traitements pour les endurcir au froid en vue de la période hivernale. Pour trois traitements les plants ont été installés sous serre chauffée pendant 11 semaines, pendant et après l'induction de la dormance, avec les 3 modalités suivantes : (1) longueur naturelle du jour (latitude 46° 31' N) et chauffage à une température égale ou supérieure à 20 °C (NDW); (2) comme le traitement 1, mais avec fertilisation (NDWF); (3) comme le traitement 1 mais en jours courts (SD). Pour le quatrième traitement (OD) les plants ont été endurcis à l'extérieur avec la baisse de température et la diminution de la longueur des jours des conditions naturelles, sans faire appel à une fertilisation. Les plants issus des traitements comportant une phase sous serre chaude présentaient des bourgeons ayant davantage d'ébauches foliaires et des pousses plus résistantes à la dessication que les plants du traitement OD. Dans un premier stade, l'endurcissement au froid des plants SD tendait à être plus élevé. Ultérieurement celui des plants OD est devenu équivalent à celui des SD. Fin novembre, tous les plants étaient à l'extérieur, les plants NDW étaient moins résistants au froid. Le potentiel de croissance racinaire au printemps était moins élevé pour les plants OD. endurcissement pour la résistance au froid / dessication / ébauche racinaire / transpiration / potentiel hydrique