Phenoseasonal subcanopy light dynamics and the effects of light on the physiological ecology of a common understory shrub, Lindera benzoin

Abstract

The purpose of this work was to quantify the variation of subcanopy spatiotemporal light dynamics over the course of a year and to link it to the physiological ecology of the understory shrub, Lindera benzoin L. Blume (northern spicebush). Covering all seven phenoseasons of a deciduous forest, this work utilized a line quantum sensor to measure the variation in subcanopy light levels under all sky conditions at different times of the day. A total of 4,592 individual subcanopy measurements of photosynthetic photon flux density (PPFD, μmol m-2 s-1) were taken as 15-second spatially-integrated one-meter linear averages to better understand the dynamism of light exposure to L. benzoin. Both open (n = 2, one continuous and one instantaneous) and subcanopy location (n = 25) measurements of PPFD were taken on each sampling date in and near the forested plot (Maryland, USA). In addition, we explored the effect of four photointensity-photoperiod combinations on the growth of L. benzoin under controlled conditions to compare to field conditions. On average, understory PPFD was less than 2% of open PPFD during the leafed months and an average of 38.8% of open PPFD during leafless winter months, indicating that: (1) often overlooked woody surfaces intercept large amounts of light; and (2) spicebush within the plot receive limited light even in early spring before canopy leaf-out. Statistical results suggested phenoseason accounted for nearly three-quarters of the variation in incident radiation between the three plant canopy heights. Spicebush under controlled conditions exhibited the highest fitness levels at an intensity of 164.5 μmol m-2 s-1 for 12-hour duration. Similarly, spicebush growth in the field occurred at subcanopy locations receiving higher incidence of PPFD (i.e., >128 μmol m-2 s-1). Results suggest that the ecological niche for these plants is very specific in terms of light intensity.

Phenotypic and transcriptomic responses of the sun- and shade-loving plants to sunlight and dim-light conditions

“…Plants are autotrophic species that convert solar energy into a chemical form stored in organic compounds (Freudenthal et al ., 2020). In natural habitats, however, both the intensity and composition of light are highly dynamic on temporal and spatial scales (Hudson et al ., 2017). Plant species have thus evolved shade-avoidance and shade-tolerance strategies to cope with variable light conditions.…”

Citizen science across two centuries reveals phenological change among plant species and functional groups in the Northeastern US

“…The differences we found in phenological change among functional groups (seasonality and growth form) and phenophases between time periods suggest that interactions between different canopy levels may change, possibly affecting species that compete for light to support early-season growth and photosynthesis, and those that rely on light in the understory during flowering (Heberling et al, 2019;Hudson et al, 2017;Kudo et al, 2008;Sercu et al, 2017). We found that first leaf date for many of the common tree species in New York's contemporary second growth forests have advanced by about 2-4 weeks.…”

Direct and Indirect Effects of Overstory Canopy and Sex-Biased Density Dependence on Reproduction in the Dioecious Shrub Shepherdia canadensis (Elaeagnaceae)

“…In cases where low or moderate light availability increases plant abundance, the niche may include other conditions that reduce fitness of competing plants [66]. Likewise, biomass and photosynthetic rate may not simply increase with greater light, but rather peak at an intermediate irradiance level as a result of a specific niche adapted to low or moderate light availability [67]. Light availability can also interact with temperature, with some shrubs demonstrating significant differences in photosynthetic plasticity in response to light conditions at certain temperature ranges [68].…”