Browsing by Subject "light"

Now showing 1 - 3 of 3
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    Culvert Length and Interior Lighting Impacts to Topeka Shiner Passage
    (Minnesota Department of Transportation, 2017-11) Kozarek, Jessica; Hatch, Jay; Mosey, Britney
    Culverts can act as barriers to fish passage for a number of reasons including insufficient water depth or excess velocity. In addition, concern is being raised over behavioral barriers where culvert conditions elicit an avoidance response that deters or slows fish movement. Long culverts can block sunlight creating a potential behavioral barrier as fish approach a long, dark culvert. Scant information exists on low light as a potential barrier to fish passage, particularly with warm water species, such as the federally endangered Topeka Shiner. As some older culverts are being replaced with longer total lengths to improve safety by extending the culvert through reengineered road embankments, information is needed to 1) determine when and if light mitigation strategies are necessary, and 2) to design appropriate light mitigation strategies if necessary. Based on literature review, field monitoring, and laboratory experiments, the effect of light on fish passage for Topeka Shiner and other small prairie stream fish was indiscernible. Therefore, no light mitigation for large box culverts (up to 150 feet in length) can be recommended for similar fish communities. Culverts that are very long or have very small openings may benefit from additional light.
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    Effects of the Interaction of Varying Temperatures and Light Intensities on the Response of Flax to 2, 4-D
    (Minnesota Agricultural Experiment Station, 1960-09) Jordan, L. S.; Dunham, R. S.; Linck, A. J.
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    Photosynthesis and leaf nitrogen in five Amazonian tree species during early secondary succession
    (1996) Ellsworth, D S; Reich, Peter B
    Field measurements of maximum net photosynthesis (Pmax), leaf nitrogen (N) content (leaf N per area and percent N), and specific leaf area (SLA) were made for Amazonian tree species within and across early successional sites of known ages after abandonment from slash-and-burn agriculture. We examined five species across a successional sere near San Carlos de Rio Negro, Venezuela, to test whether plasticity was associated with successional status and to determine whether changes in foliar properties during secondary succession can be attributed to shifts in species composition, in resource availability, or both. Average leaf N concentration was high (nearly 3%) for a pioneer species (Cecropiaficifolia) early in succession (1-3 yr after abandonment) but was always lower for the other early and mid- to-late succession species, especially later in succession (1-2% at 5-10 yr after abandonment). Net photosynthetic capacity (P /area and P I mass) varied as much as sixfold, being higher in pioneer species such as Cecropia and Vismia on recently abandoned sites and lower in late successional species such as Miconia and Licania on 10-yr abandoned agricultural sites. Total daily light availability also varied widely (14-fold) from its peak 1 yr after farm abandonment to low levels 9 yr into succession. During the first 5 yr of secondary succession, there were significant (P < 0.05) differences in Pmax and leaf N concentration among species in any given year. In most species, Pmax values declined with increasing time since abandonment within any given site. There were important differences in photosynthetic plasticity among species: Pmax tended to be much greater in earlier than later successional species soon after abandonment. Also, the difference in Pmax among species narrowed (or reversed) over time since abandonment, largely because of decreasing Pmax in pioneer species. The results suggest that changes in both species composition and in resource availability combine to produce the common pattern of decreasing leaf N concentration and photosynthetic rates during early rain forest succession after agriculture. Early successional species showed strong (r2 - 0.57, P = 0.0001) mass-based photosynthesis-N relationships but weak (r2 = 0.40 or lower, P = 0.000 1) area-based relationships both across the secondary successional sere after agriculture and across sites varying in types of disturbance. Both mass- and area-based photosynthesis-N relationships were poorer or not significant (P > 0.05) for mid- to late-successional species. Higher instantaneous Pmax/N and greater slopes of the photosynthesis-N relationships in early than late successional species suggest that pioneer species may show greater carbon assimilation capacity with elevated leaf N concentration on early successional sites than co-occurring species. The data suggest that early and late successional species may differ in the mode and degree of leaf-level physiological plasticity across succession.