Experiments were conducted to examine whether leaf adaptation to light in Fragaria virginiana (Rosaceae) was determined by peak photon‐flux density or by total quanta received during the day. Leaf structure and apparent photosynthesis rates were similar under environments where total energy received was the same even though peak photon‐flux density was different. When peak photon‐flux density was held constant and total quanta varied, significant differences were noted in apparent photosynthesis, leaf thickness, specific leaf weight, mesophyll cell volume, and Ames/A ratio. High total quanta produced high‐light or sun‐type leaves even at relatively low peak intensities. Thus, total light energy received during the day has a greater influence on leaf adaptation to light than does peak photon‐flux density.

Temporal and spatial patterns of specific leaf weight (SLW, g/m2) were determined for deciduous hardwood tree species in natural habitats in northern lower Michigan to evaluate the utility of SLW as an index of leaf photosynthetic capacity. No significant diurnal changes in SLW were found. Specific leaf weight decreased and then increased during leaf expansion in the spring. Most species, especially those located in the understory, then had relatively constant SLW for most of the growing season, followed by a decline in SLW during autumn. Specific leaf weight decreased exponentially down through the canopy with increasing cumulative leaf area index. Red oak (Quercus rubra), paper birch (Betula papyrifera), bigtooth aspen (Populus grandidentata), red maple (Acer rubrum), sugar maple (A. saccharum), and beech (Fagus grandifolia) generally had successively lower SLW, for leaves at any one level in the canopy. On a given site, comparisons between years and comparisons of leaves growing within 35 cm of each other showed that differences in SLW among species were not due solely to microenvironmental effects on SLW. Bigtooth aspen, red oak, and red maple on lower‐fertility sites had lower SLW than the same species on higher‐fertility sites. Maximum CO2 exchange rate, measured at light‐saturation in ambient CO2 and leaf temperatures of 20 to 25 C, increased with SLW. Photosynthetic capacities of species ranked by SLW in a shaded habitat suggest that red oak, red maple, sugar maple, and beech are successively better adapted to shady conditions.

Apparent photosynthesis and dark respiration were followed during development in four light environments of leaves of Fragari igniaa Duchesne. Leaf expansion was completed more rapidly the higher the growth photon flux density and leaves senesced more quickly in high light. Maximum photosynthetic capacity coincided with the completion of blade expansion and declined quickly thereafter. Leaves were transferred from high to low and low to high photon flux densities at several stages during expansion. Leaf Experimental Treatments. Two sets of experiments were performed. In the first, the effects of irradiance and leaf age on photosynthetic performance were studied. Leaves were individually tagged as they appeared in each of the four light treatments. Length and width of leaflets were measured to the nearest 0.5 mm at 1-to 3-day intervals until expansion was essentially complete and at longer intervals thereafter. Longevity was estimated by allowing some leaves to die naturally. Apparent photosynthesis and dark respiration were measured on leaves of different ages.A second experiment examined adaptive capacity as a function of leaf age at the highest and lowest growth chamber light levels. Leaves which appeared after the plants had been in the high or low light levels for at least I week were individually tagged. A plant was transferred to the contrasting light level when its tagged leaf was at one of three stages of development (Fig.

Abstract:We examined the effects of sediment depth on emergence of seedlings from wetland seed banks, with the goal of understanding potential effects on wetlands of sediment runoff from agricultural fields. Seed germination was studied in the greenhouse using seed bank samples taken from natural wetlands in central Iowa, U.S.A. Sediment loads as low as 0.25 cm significantly reduced the number of species and total number of individuals recruited from seed bank samples. Addition of sediment decreased the number of individuals appearing for most, but not all, species. The change in number of seedlings that occurred in treatments with 1 cm of sediment cover was related to seed mass, with larger-seeded species showing the least effect of burial by sediment.

Plants of a single geDotype of wild strawberry, Fragaria virgnuiana Duchesne, were grown with or without fertilizer in high (406 microeinsteins per square meter per second) and low (80 microeinsteins per square meter per second) light. High-light leaves were thicker than low-Ht leaves and had greater development of the mesophyll. Within a ight level, highnutrient leaves were thicker, but the proportions of leaf tissues did not change with nutrient level. Maximum net CO2 exchange rate and leaf size were greatest in high-light, high-nutrient leaves and lowest in high-Ught, low-nutrient leaves. Changes in mesophyli cell volume largely accounted for differences in CO2 exchange rate in low-Ught leaves, but not in highlight leaves.Leaf size in these experiments was apparently determined by nutrient and carbon supply. This may explain the observation that the largest leaves produced by wild strawberries in the field occur in high-light, mesic habitats, rather than in shady habitats.