Contrasting patterns of photosynthetic acclimation and photoinhibition in two evergreen herbs from a winter deciduous forest

Abstract

The relationship between the microclimate within an Oak-Hickory forest and photosynthetic characters of two resident evergreen herbs with contrasting leaf phenologies was investigated on a monthly basis for 1 full year. Heuchera americana has leaf flushes in the spring and fall, with average leaf life spans of 6-7 months. Hexastylis arifolia produces a single cohort of leaves each spring with a leaf life span of 12-13 months. We predicted that among evergreen plants inhabiting a seasonal habitat, a species for which the frequency of leaf turnover is greater than the frequency of seasonal extremes would have a greater annual range in photosynthetic capacity than a species that only produced a single flush of leaves during the year. Photosynthetic parameters, including apparent quantum yield, maximum photosynthetic capacity (P), temperature of maximum photosynthesis, photochemical efficiency of PSII and leaf nitrogen (N) and chlorophyll concentrations, were periodically measured under laboratory conditions in leaves sampled from natural populations of both species. Mature leaves of both species acclimated to changing understory conditions with the mean seasonal differences being significantly greater for Heuchera than for Hexastylis. Area based maximum photosynthetic rates at 25°C were approximately 250% and 100% greater in winter leaves than summer leaves for Heuchera and Hexastylis respectively. Nitrogen concentrations were highest in winter leaves. Chlorophyll concentrations were highest in summer leaves. Low P/N values for these species suggest preferential allocation of leaf nitrogen into non-photosynthetic pools and/or light-harvesting function at the expense of photosynthetic enzymes and electron transport components. Despite the increase in photosynthetic capacity, there was evidence of chronic winter photoinhibition in Hexastylis, but not in Heuchera. Among these ecologically similar species, there appears to be a trade-off between the frequency of leaf production and the balance of photosynthetic acclimation and photoinhibition.

Interspecific variation in leaf pigments and nutrients of five tree species from a subtropical forest in southern Brazil

“…In general, chlorophyll content decreases with increased irradiance, because when there is greater availability of photosynthetic active radiation, photosystems can operate at satisfactory levels for metabolism with less chlorophyll. On the other hand, low irradiance causes chlorophyll content and accessory pigments to increase so as to absorb more light energy and transfer it to reaction centers (Taiz and Zeiger 2013, Zhang et al 2009). Skillman et al (1996 observed that leaf chlorophyll content was considerably higher in summer for herbaceous species of deciduous forests.…”

Shape of leaf photosynthetic electron transport versus temperature response curve is not constant along canopy light gradients in temperate deciduous trees

“…Yet, daily average air and leaf temperatures change across the season, and this may also bring about alterations in the shape of J max versus T response curve. Seasonal variability in the temperature optima of net assimilation and J max has been demonstrated in a number of investigations (Mooney et al 1978;Mooney 1980;Skillman, Strain & Osmond 1996) and further studies are necessary to identify the kinetic constants of temperature acclimation.…”

Our Eclectic Adventures in the Slower Eras of Photosynthesis: From New England Down Under to Biosphere 2 and Beyond

“…Blessed with a diversity of opportunities for support, and augmented by the North Carolina Biotechnology Center gift of the mass spectrometer that attracted a decade of funding from the DOE, research at Duke was just as exciting and as productive of papers as RSBS. To some extent, the weight shifted from postdocs to students; 25% of all students I have cosupervised obtained Duke PhDs from projects that commenced during our three and a half years in Durham (10,55,57,154,182). The failure of three attempts to win funding from multidisciplinary tri-agency programs to support the phytotron research was most disappointing.…”