Seasonal Alteration of Photosynthetic Unit Sizes in Three Herb Layer Components of a Deciduous Forest Community

Abstract

The pigment content and photosynthetic unit size of three herbs on the floor of a mature yellow oak (Quercus meuhlenbergii) forest were measured during most of the growing season. Two species, dutchman's breeches (Dicentra cucullaria) and Virginia bluebell (Mertensia virginica) are spring ephemerals, while Hepatica acutiloba has a semi‐evergreen habit. Although pigment composition changed in Dicentra, photosynthetic unit size only varied slightly. Mertensia was nearly invariant in pigment composition, but unit size was modified as the growing season progressed. The semi‐evergreen herb, Hepatica, underwent a remarkable alteration in pigment content, photosynthetic unit size, and number following overstory leaf expansion. The results indicate that an alteration of photosynthetic unit size is possible in fully expanded leaves of two forest floor herbs.

Photosynthetic potential of sun and shade Viola species

“…The principal micrometeorological difference between their habitats is in the intensity and quantity of available light, which potentially are the primary factors limiting the species's growth and distribution (Curtis 1979). In forests, reduced light intensity often limits photosynthesis of herbs on the forest floor (Haberlandt 1914;Bohning and Burnside 1956;Taylor and Pearcy 1976;Harvey 1980;Wallace and Dunn 1980;Young and Smith 1980). As a result, forest herbs have been classified as either shade-tolerant (shade species) or shade-intolerant (sun species) on the basis of their photosynthetic responses to light intensity (Grime 1966;Sparling 1967;Taylor and Pearcy 1976 productive phenologies of shade-tolerant and shade-intolerant plants are closely related to canopy development.…”

Early spring warming may hasten leaf emergence in Erythronium americanum

“…These plants spend most of the year underground, producing aboveground leaves after snowmelt that senesce with canopy closure at the end of spring (Muller, ; Tessier, ). The limited photosynthetic period makes the timing of leaf out and senescence critical to productivity in spring ephemerals (Sparling, ; Taylor and Pearcy, ; Harvey, ; Hull, ; Gandin et al., ). Functionally, spring ephemerals are very important to nutrient retention in terrestrial ecosystems at a time when nutrient losses can be high (Muller and Bormann, ; Anderson and Eickmeier, ).…”

Vernal Photosynthesis and Nutrient Retranslocation in Dryopteris intermedia

“…It may be critical to an understory species that usually receives low light levels in the shade of canopy species during the summer season (Anderson, 1964;Federer and Tanner, 1966;Hutchison and Matt, 1977) to take advantage of high light conditions prior to canopy leaf out. Spring ephemerals, species that develop above ground early in spring and senesce with canopy leaf out, are capable of high rates of photosynthesis during spring as compared to summer rates (Harvey 1980) and are adapted to growth and reproduction during this period of higli light prior to canopy leaf out. Also, some disturbance-adapted species can acclimate to periods of high light (Brach et al, 1993) and increase their photosynthetic rate.…”